JP2004014876A - Adjustment method, method for measuring spatial image, method for measuring image surface, and exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly perform highly accurate adjustment for a multi-point focal point detection system. <P>SOLUTION: An exposure device 100 is provided with multi-point AF systems (60a, 60b) for irradiating the surface of an object with a plurality of detection beams, individually receiving respective reflected beams from the surface of the object by corresponding sensors and detecting the positions of the object in the optical axis direction of a projecting optical system PL on the irradiation points of respective detection beams; and a pattern plate 90 having a spatial image measuring slit 22 on a part of the multi-point AF system and having high surface flatness. Then the image plane of the projecting optical system is detected by repeating slit scanning type spatial image measurement by using the pattern plate 90 while servo-controlling the optical axis direction and inclination of the pattern plate 90 by using the multi-point AF system. The offsets of detection origins of the plurality of sensors are highly accurately measured in a state that the pattern plate 90 is accurately located on the image plane of the projecting optical system PL by using the multi-point AF system. <P>COPYRIGHT: (C)2004,JPO

Description

【０１３２】
【数２】

【０１３３】
すなわち、観測される強度信号ｍ（ｙ）はスリッ卜ｐ（ｙ）と空間像の強度分布ｉ（ｙ）のコンボリューションになる。
【０１３４】
従って、計測精度の面からは、スリット幅２Ｄは、小さいほど良く、本実施形態のようにＰＭＴを光センサ２４として用いる場合には、スリット幅が非常に小さくなっても走査速度を遅くして計測に時間を掛ければ光量（光強度）の検出は可能である。しかしながら、現実には、スループットの面から空間像計測時の走査速度には、一定の制約があるため、スリット幅２Ｄがあまりにも小さいと、スリット２２を透過する光量が小さくなり過ぎて、計測が困難となってしまう。
【０１３５】
発明者がシミュレーション及び実験等により得た知見によれば、スリット幅２Ｄの最適値は、露光装置の解像限界ピッチ（デューティ比５０％のＬ／Ｓパターンのピッチ）の半分程度となることが確認されたので、本実施形態では、そのように設定したものである。
【０１３６】
なお、前述の如く、スリット板９０上には、第１スリット２２ｙ、第２スリット２２ｘの計測方向が異なる２種類のスリットが設けられているが、これらを用いた空間像計測に際してその計測方向に対応する計測マークが用いられ、計測マークの投影像（空間像）の向きに平行なスリットだけに空間像が重なるようにスリット板９０を空間像に対して走査するようになっている。
【０１３７】
上述した空間像計測装置５９及びそれを用いた空間像計測方法は、ａ．ベストフォーカス位置の検出、ｂ．ＸＹ面内でのパターン像の結像位置の検出、ｃ．アライメント系のベースライン計測等に用いられる。
【０１３８】
本実施形態の露光装置１００におけるｃ．ベースライン計測については既に説明した。また、ｂ．ＸＹ面内でのパターン像の結像位置の検出は、本発明との関連が薄いため、以下、上記ａ．ベストフォーカス位置の検出について、説明する。
【０１３９】
このベストフォーカス位置の検出は、例えば投影光学系ＰＬのベストフォーカス位置の検出及び最良結像面（像面）の検出などの目的に用いられる。
【０１４０】
本実施形態では、一例として次のようにして投影光学系ＰＬのベストフォーカス位置の検出を行う。
【０１４１】
このベストフォーカス位置の検出には、例えば、解像限界付近の１次元方向（ここではＹ軸方向）に所定ピッチで配列された複数本ラインパターンから成るデューティ比５０％の周期パターン、すなわちいわゆるロンキーグレーティング状のパターンが、計測マークＰＭとして形成されたレチクルＲが用いられる。
【０１４２】
まず、不図示のレチクルローダにより、レチクルステージＲＳＴ上にレチクルＲがロードされる。次に、主制御装置２０では、投影光学系ＰＬの視野内でベストフォーカス位置を計測すべき所定点（ここでは投影光学系ＰＬの光軸上）にレチクルＲ上の計測マークＰＭが位置決めされるように、レチクルステージＲＳＴを移動する。
【０１４３】
次に、主制御装置２０では、照明光ＩＬが計測マークＰＭ部分のみに照射されるように可動レチクルブラインド１２を駆動制御して照明領域を規定する。この状態で、主制御装置２０では、照明光ＩＬをレチクルＲに照射して、前述と同様にして、ウエハテーブル５４をＹ軸方向に走査しながら空間像計測装置５９を用いて、計測マークＰＭの空間像計測を前述と同様にスリットスキャン方式により行う。この際、主制御装置２０では、スリット板９０のＺ軸方向の位置（すなわち、ウエハテーブル５４のＺ位置）を例えば０．１μｍピッチで１５ステップ程度）変化させつつ、複数回繰り返し、各回の光強度信号（光電変換信号）を内部メモリに記憶する。ステップ範囲は、例えば設計上のベストフォーカス位置をほぼ中心とする範囲で行われる。
【０１４４】
主制御装置２０は、上述のようにして内部メモリに記憶された光強度信号をそれぞれフーリエ変換し、それぞれの１次周波数成分と０次周波数成分の振幅比であるコントラストを評価量としてを求める。このコントラストはフォーカス位置によって敏感に変化するので強度信号からベストフォーカス位置を決定するのに便利である。そして、主制御装置２０では、一例として、横軸をフォーカス位置（Ｚ位置）とし、縦軸をコントラストする座標系上に得られたコントラスト値のデータをプロットし、そのプロットデータを適当な関数（２次以上、例えば４〜６次関数）でフィッティングしてその関数曲線（以下、「コントラストカーブ」と呼ぶ）がピーク値を示すＺ位置を算出することでベストフォーカス位置を求める。
【０１４５】
次に、本実施形態の露光装置１００で行われる多点ＡＦ系の調整方法について詳述する。この多点ＡＦ系の調整は、以下のａ．〜ｃ．の３つのステップに分けられる。
ａ．多点ＡＦ系の光学調整（粗調整）
ｂ．センサ間オフセットの調整（多点ＡＦ系のファイン調整）
ｃ．フォーカスセンサ面キャリブレーション（フォーカスセンサ面の経時変化の管理）
【０１４６】
本実施形態のような多点ＡＦ系（６０ａ，６０ｂ）では、検出点（スリット像）Ｓ_１１〜Ｓ_７７それぞれに対応するフォーカスセンサＤ_１１〜Ｄ_７７の検出原点の投影光学系ＰＬのベストフォーカス面（最良結像面）からの相対距離（Ｚ軸方向の位置ずれ量）を正確に計測する必要がある。
【０１４７】
多点ＡＦ系（６０ａ，６０ｂ）では、前述の如く回転方向振動板７６を変調器として用い、スリット像Ｓ_１１〜Ｓ_７７の反射スリット像の受光用スリット板７８上の各スリットに対する位置ずれ量をウエハＷ表面のＺ位置に読み替えてフォーカス計測を行うようになっている。そのため、機械的な原点に対して反射スリット像の位置ずれ誤差分のオフセットが生じる。これは複数のフォーカスセンサで光学系を共用する多点ＡＦ系では必ず生じる現象で、全てのフォーカスセンサのオフセットを機械的にゼロとするのは困難である。
【０１４８】
また、多点ＡＦ系を構成する複数のフォーカスセンサの検出原点の集合によって形成される面の近似平面（以下、「フォーカスセンサ面」と呼ぶ）を完全に投影光学系の像面の近似平面に一致させることが理想的であるが現実的にはある程度機械的な誤差が生じる。
【０１４９】
以上のような種々の原点ずれの成分は記録可能なデータとして管理する必要がある。本実施形態の多点ＡＦ系のような光電式フォーカスセンサは被検面の原点からの光軸方向に関する距離に略比例した電圧値の信号を出力する。これは、前述の如くＳカーブ信号と呼ばれており、Ｚ位置と電圧との関係を予め計測しておけば電圧値から正確な被検面のＺ位置を測定することが出来る。Ｚ位置の原点ずれ、すなわち各フォーカスセンサＤの検出原点の機械的な原点からのずれ量は残留オフセットとしてデジタルデータ等の記憶可能なデータに変換して、主制御装置２０に接続された記憶装置５１あるいは内部メモリなどに記憶しておけば各フォーカスセンサの正確な原点（検出オフセット）を管理することが可能になる。
【０１５０】
多点ＡＦ系の各フォーカスセンサの最終的な検出オフセットを計測する前に、多点ＡＦ系のキャプチャーレンジ内（例えば原点を中心とする±１０μｍ程度の範囲内）に投影光学系ＰＬの像面を位置させる必要がある。光学調整の初期の段階では必ずしも多点ＡＦ系の各フォーカスセンサのキャプチャーレンジ内に像面が位置するとは限らない。
【０１５１】
そのため、本実施形態では、主制御装置２０は、多点ＡＦ系（６０ａ，６０ｂ）の中央１点の検出点Ｓ_４４のみを用いて、投影光学系ＰＬの像面（この場合検出点Ｓ_４４のベストフォーカス位置）を計測することとしている。これは、多点ＡＦ系であっても、中央１点の検出点のみを用いて計測する場合には、前述の平行平板ガラス７４の角度を変化させることにより、キャプチャーレンジを中立点（真の原点）を中心とする±５０μｍ程度の範囲まで拡大可能であるので光学調整が精密になされていなくても、投影光学系ＰＬの像面にフォーカスの原点を設定することが可能だからである。
【０１５２】
本実施形態では、この多点ＡＦ系の光学調整に際し、投影光学系ＰＬの視野内の一部領域（固定レチクルブラインドの開口で設定可能な矩形領域（前述の照明領域ＩＡＲに対応））内の複数の評価点（光軸上の評価点を含む）に対応して計測マークＰＭが形成されたレチクル（便宜上、「レチクルＲ１」と呼ぶ）が用いられる。
【０１５３】
そして、主制御装置２０では、平行平板ガラス７４が任意の傾斜角度に設定された初期状態で、空間像計測装置５９を用いて投影光学系ＰＬの光軸上の評価点におけるベストフォーカス位置の計測を次のようにして試みる。
【０１５４】
まず、不図示のレチクルローダにより、レチクルステージＲＳＴ上にレチクルＲ１がロードされる。次に、主制御装置２０では、レチクルＲ１上の中心に位置する計測マークＰＭ（以下、識別のため「ＰＭ_１」と記述する）が、投影光学系ＰＬの光軸上に一致するように、レチクルステージＲＳＴを位置決めする。
【０１５５】
次いで、投影光学系ＰＬの光軸上の第１検出点に対応する計測マークＰＭ_１部分にのみ照明光ＩＬが照射されるように、可動レチクルブラインド１２を駆動制御して照明領域を規定する。
【０１５６】
この状態で、主制御装置２０では、照明光ＩＬをレチクルＲに照射して、前述と同様にして、スリットスキャン方式により空間像計測装置５９を用いて計測マークＰＭの空間像計測を、スリット板９０のＺ軸方向位置を所定ステップピッチで変化させながら繰り返し行う。その際に、主制御装置２０では、検出点Ｓ_４４に対応するフォーカスセンサＤ_４４のみを選択装置７５を介して選択し、そのフォーカスセンサＤ_４４の検出値のみに基づいて基準平面部材５８のスリット板９０のＺ軸方向の位置を制御する。また、スリット板９０の傾き、すなわちウエハテーブル５４の投影光学系ＰＬの光軸に直交するＸＹ平面に対する傾斜は、前述したウエハ干渉計３１、より正確には、ウエハテーブル５４のピッチング、ローリングをそれぞれ検出する測長軸を有する一対のＹ干渉計（ピッチング干渉計として機能する）、Ｘ干渉計（ローリング干渉計として機能する）の計測値に基づいて、所望の一定角度となるように（例えばピッチング、ローリングがともに零となるように）制御することとしても良い。
【０１５７】
そして、主制御装置２０では、その空間像の計測結果に基づいて前述と同様にして得られたコントラストカーブがピーク値を示すＺ位置があるか否かを判断し、その判断が否定された場合には、駆動部８１に適当なオフセット指令値（ＯＦＳ）を駆動信号として与えて、平行平板ガラス７４を所定量回転駆動して、再度、上記のベストフォーカス位置の計測を行う。このようにして、主制御装置２０では、平行平板ガラス７４を所定量づつ回転しながら、ベストフォーカス位置の計測、コントラストカーブの算出を繰り返し、コントラストカーブにピーク値があらわれた段階で、そのピーク値に対応する光軸方向に関する位置Ｚ_１を算出し、その位置Ｚ_１を検出点Ｓ_４４にほぼ一致する投影光学系ＰＬの光軸上の評価点におけるベストフォーカス位置として内部メモリに記憶する。
【０１５８】
次に、投影光学系ＰＬの視野内の一部領域、すなわち前述の矩形領域（前述の照明領域ＩＡＲに対応）内の複数の評価点におけるベストフォーカス位置の計測、すなわち投影光学系ＰＬの像面の計測を、空間像計測装置５９を用いて行うが、この方法としては、次の２つの方法を採用することが可能である。
【０１５９】
＜第１の像面計測方法＞
主制御装置２０では、投影光学系ＰＬの視野内の第２評価点に対応するレチクルＲ１上の計測マークＰＭ（以下、識別のため「ＰＭ_２」と記述する）部分にのみ照明光ＩＬが計測マークＰＭ部分のみに照射されるように可動レチクルブラインド１２を駆動制御して照明領域を規定する。この状態で、上記と同様に、フォーカスセンサＤ_４４あるいは第２評価点の近傍の１つの検出点に対応するフォーカスセンサＤの検出値のみに基づいて基準平面部材５８のスリット板９０のＺ軸方向の位置を制御するとともに、スリット板９０の傾きをウエハテーブル５４のピッチング、ローリングをそれぞれ検出する一対のＹ干渉計（ピッチング干渉計として機能する）、Ｘ干渉計（ローリング干渉計として機能する）の計測値に基づいて制御して、スリットスキャン方式で計測マークＰＭ_２の空間像計測及び第２評価点におけるベストフォーカス位置Ｚ_２の検出を行って、その結果を内部メモリに記憶する。
【０１６０】
以後、主制御装置２０では、上記と同様に、投影光学系ＰＬの視野内の評価点を変更しつつ、計測マークＰＭについて空間像の計測及び投影光学系ＰＬのベストフォーカス位置の検出を繰り返し行う。なお、主制御装置２０は、第２評価点以降のベストフォーカス位置の計測に際しては、先に求めた位置Ｚ_１を中心とする＋Ｚ側、−Ｚ側の所定幅の範囲で、所定ステップピッチでスリット板９０のＺ位置を変更しながら、空間像計測を行う。
【０１６１】
そして、主制御装置２０は、上述のようにして得られた各ベストフォーカス位置Ｚ_１、Ｚ_２、……、Ｚ_ｎに基づいて、所定の統計的処理を行うことにより、投影光学系ＰＬの像面の近似平面（及び像面形状）を算出する。このとき、像面形状とは別に像面湾曲を算出することも可能である。
【０１６２】
投影光学系ＰＬの像面、すなわち、最良結像面は、光軸からの距離が異なる無数の点（すなわち、いわゆる像の高さが異なる無数の点）におけるベストフォーカス点の集合から成る面であるから、このような手法により、像面形状及びその近似平面を容易にかつ正確に求めることができる。
【０１６３】
この第１の像面計測方法は、基準平面部材５８（スリット板９０）のスリット２２の近傍で平面度が悪化している場合に、その位置を避けてフォーカス計測、管理などを行う必要がある場合にメリットがある。例えば図４（Ｂ）の遮光膜（クロム膜）９１の部分と反射膜（アルミニウム膜）８３部分の境界はプロセス上レジストが残留しがちであるが、そのような場合にその境界部分に掛からない中央１点の検出点のみを用いてフォーカス計測を行うことができる。この一方、後述するように、スリット板９０を基準平面板として使用する場合には、クロム膜部分に多点ＡＦ系の検出点（スリット像）が掛からないようにすることが肝要である。従って、上述の場合においても、仮に検出点Ｓ_４４が上記の境界に掛かるような場合には、その近傍の検出点で境界に掛からない検出点に対応するフォーカスセンサ（フォーカスセンサ）Ｄを用いて、前述のフォーカス計測及び像面計測を行う必要がある。
【０１６４】
なお、この第１の像面計測方法において、主制御装置２０では、ウエハテーブル５４を駆動する駆動装置内の前述の３つ（一組）のエンコーダ２８の出力に基づいて前述のスリット板９０の傾斜を制御することとしても良い。
【０１６５】
＜第２の像面計測方法＞
この第２の像面計測方法は、投影光学系ＰＬの視野内の複数の評価点のそれぞれでその近傍に位置する検出点Ｓに対応するフォーカスセンサＤ、例えば露光領域ＩＡの４隅及び中央に位置する合計５点の検出点Ｓ_３１、Ｓ_５１、Ｓ_４４、Ｓ_３７、Ｓ_５７に個別に対応するフォーカスセンサＤ_３１、Ｄ_５１、Ｄ_４４、Ｄ_３７、Ｄ_５７を選択し、それらのフォーカスセンサＤの計測値に基づいて前述した像面計測の際のスリット板９０のＺ軸方向の位置及び傾斜を制御する点が前述の第１の像面計測方法と異なり、その他の点は、前述の第１の像面計測方法と同様である。
【０１６６】
そして、主制御装置２０は、この場合にも得られた各ベストフォーカス位置Ｚ_１、Ｚ_２、……、Ｚ_ｎに基づいて、所定の統計的処理を行うことにより、投影光学系ＰＬの像面の近似平面（及び像面形状）を算出する。また、必要であれば、像面湾曲を算出しても良い。なお、この第２の像面計測方法の利点については、後述する。
【０１６７】
次に、主制御装置２０では、上述のようにして求められた投影光学系ＰＬの像面の近似平面に、基準平面板の機能を有するスリット板９０表面がなるべく平行になるように、その時点の調整状態の多点ＡＦ系（６０ａ、６０ｂ）を用いて、ウエハテーブル５４の傾斜をステージ駆動系を介して制御する。次いで、主制御装置２０では、この状態でウエハテーブル５４のＺ位置及び傾斜が維持されるように、前述のエンコーダ２８を用いたサーボ制御を行いつつ、多点ＡＦ系（６０ａ、６０ｂ）の光学調整を行う。この光学調整は、スリット板９０の表面が多点ＡＦ系（６０ａ、６０ｂ）の複数（この場合最大１２個）のフォーカスセンサＤの検出原点の近似平面から成る面（フォーカスセンサ面）が平行になるように、すなわち、選択された１２個のフォーカスセンサの検出オフセットがなるべく平均化されるように、駆動部８１を介して平行平板ガラス７４の傾斜角を調整することにより行われる。
【０１６８】
なお、本実施形態では、レチクルＲ１に複数の計測マークＰＭを形成しておき、可動レチクルブラインド１２によって各計測マークＰＭに照明光ＩＬを順次照射して、それぞれの計測マークに対応する投影光学系ＰＬの評価領域においてベストフォーカス位置を検出することとしたが、これに限らず、レチクルを移動してベストフォーカス位置を計測すべき複数点にそれぞれ計測マークＰＭを配置することとしても良い。この場合には、計測マークＰＭが１つだけのレチクルを用いることができる。また、レチクルステージＲＳＴ上に基準板を設け、この基準板上に複数の計測マークＰＭを形成しても良い。
【０１６９】
ｂ．センサ間オフセットの調整（多点ＡＦ系のファイン調整）
この多点ＡＦ系のファイン調整は、フォーカスセンサＤ_１１〜Ｄ_７７個々の個体差及び調整誤差などに起因する相対的な計測誤差を極限まで小さく抑えるために必要な工程である。
【０１７０】
この多点ＡＦ系のファイン調整では、平坦度の良好な平面板、例えば前述のスリット板９０、スーパーフラットウエハあるいはウエハなどを、投影光学系ＰＬの像面の近似平面に平行な状態に設定し、その平面板の傾きを維持しつつ、多点ＡＦ系の複数のフォーカスセンサ間の計測値の相対的なオフセットを計測する。この多点ＡＦ系のファイン調整では、スリット板９０などの平面板が搭載されたウエハテーブル５４の静止性が上述のセンサ間オフセット計測にとって重要である。このため、本実施形態では、多点ＡＦ系のファイン調整中は、ウエハテーブル５４を多点ＡＦ系（６０ａ、６０ｂ）の計測値に基づくサーボモード（フォーカスサーボモード）で制御する。すなわち、このフォーカスサーボモードでは、多点ＡＦ系（６０ａ、６０ｂ）の複数のフォーカスセンサの中から選択された複数のフォーカスセンサの計測値を目標値（与えられた検出オフセット）と比較しながらサーボ制御が行われるため、前述したピッチング干渉計やローリング干渉計だけでウエハテーブル５４を静止させる（姿勢を一定状態に維持する）よりも投影光学系ＰＬに対して安定してスリット板９０の姿勢を制御できる。
【０１７１】
主制御装置２０は、例えば投影光学系ＰＬの視野内の５点の検出点、例えば検出点Ｓ_３１、Ｓ_５１、Ｓ_４４、Ｓ_３７、Ｓ_５７に個別に対応するフォーカスセンサＤ_３１、Ｄ_５１、Ｄ_４４、Ｄ_３７、Ｄ_５７それぞれに、スリット板９０を投影光学系ＰＬの像面の近似平面に平行な状態にするのに必要な検出オフセットを目標値として与え、それらのフォーカスセンサＤ_３１、Ｄ_５１、Ｄ_４４、Ｄ_３７、Ｄ_５７を用いてスリット板９０の姿勢をサーボ制御しつつ、そのサーボ制御に使用されていない残り４４個のフォーカスセンサＤの検出オフセット（計測値）を取り込み、それらの値を内部メモリに記憶する。このとき、サーボ制御に使用するフォーカスセンサＤ_３１、Ｄ_５１、Ｄ_４４、Ｄ_３７、Ｄ_５７の目標値としてそれぞれ与えるべき検出オフセットは、上記の多点ＡＦ系（６０ａ、６０ｂ）の光学調整後に前述の第１、第２の像面計測方法と同様の計測を再度行うことにより計測することが可能である。
【０１７２】
但し、例えば前述の第２の像面計測方法により像面計測を行った場合には、その際に得られた選択されたフォーカスセンサの近傍の評価点におけるベストフォーカス位置に対するその選択されたフォーカスセンサＤ_３１、Ｄ_５１、Ｄ_４４、Ｄ_３７、Ｄ_５７の検出オフセット値を、そのまま用いることが可能である。換言すれば、前述の多点ＡＦ系の光学調整の工程では、すなわち、前述した第２の像面計測方法では、その像面計測の際に、その後に続いて行われるセンサ間オフセットの調整の際にフォーカスサーボ時に各フォーカスセンサに与えるべきフォーカスオフセット値をその段階で入手できるという大きなメリットを有している。この意味からすると、多点ＡＦ系の光学調整の工程では、前述の第２の像面計測方法を採用した方が、調整時間の短縮を図るという点では望ましいと言える。
【０１７３】
上述の４４点の検出点に個別に対応する４４個のフォーカスセンサＤの検出オフセットの計測が終了すると、主制御装置２０では、それら４４個のフォーカスセンサＤの中から、その検出点がなるべく周辺部に位置する複数点、例えば６点の検出点Ｓに個別に対応するフォーカスセンサＤを選択し、それらのフォーカスセンサＤの計測値を目標値（上記で検出した検出オフセット）と比較しながらフォーカスサーボモードでスリット板９０を制御し、最初にフォーカスサーボモードに用いた５つのフォーカスセンサの検出オフセットを再度計測して、その結果を内部メモリに記憶する。これにより、多点ＡＦ系（６０ａ、６０ｂ）のファイン調整が終了する。
【０１７４】
ここで、本実施形態の露光装置１００で行われる、上記のフォーカスサーボによる、センサ間オフセットの計測、調整方法は、ウエハテーブル５４の制御性だけではなく、空気揺らぎの影響の排除の観点からも非常に有効である。その理由は、複数のフォーカスセンサＤは、それぞれの検出点Ｓが高々２０ｍｍ程度しか離れていないとともに、これに対応してフォーカスセンサ同士も互いに近接した位置に配置されているので、空気揺らぎが各フォーカスセンサＤに与える影響は、センサ間ではほぼ均一であることから、空気揺らぎはフォーカスサーボにより計測値からはキャンセルされているからである。
【０１７５】
本実施形態の露光装置１００では、以上のような手順で調整が行われた多点ＡＦ系（６０ａ、６０ｂ）を用いて、例えば前述の走査露光中などに前述のオートフォーカス・オートレベリングが行われるので、デフォーカスに起因する色むらなどのない、高精度なレチクルパターンの転写像のウエハ上での形成が可能となる。
【０１７６】
また、前述した手法により空間像計測装置５９を用いて計測された投影光学系ＰＬの像面形状や像面湾曲などが正確に計測され、この計測結果に基づいて、主制御装置２０により投影光学系ＰＬの光学特性が不図示の調整装置を介して精度良く調整される。そして、この光学特性が調整された投影光学系ＰＬを用いて前述の走査露光が行われるので、レチクルパターンとウエハＷ上のショット領域に既に形成されたパターンとを正確に重ね合わることが可能となる。
【０１７７】
ｃ．フォーカスセンサ面キャリプレーション（フォーカスセンサ面の経時変化の管理）
露光装置１００などの投影露光装置では、その使用中の投影光学系に照射される照明光を吸収することや、設置環境の大気圧の変化、その他の変動要因により、投影光学系の光学特性、例えば像面形状や像面傾斜などが経時的に変化することが知られている。このような場合には、そのような像面形状や像面傾斜などの変化をモニタするとともに、それに応じて多点ＡＦ系（６０ａ、６０ｂ）の調整、すなわちフォーカスセンサ面キャリブレーションを行う必要がある。
【０１７８】
また、像面傾斜やフォーカスセンサ面のキャリブレーションは、本実施形態の露光装置１００のように、空間像計測装置５９を備える場合には、空間像計測を用いた各種計測のためにも、像面傾斜などの経時変化に起因するフォーカスセンサ面のキャリブレーションが重要である。その理由は次の通りである。
【０１７９】
空間像位置計測などの空間像計測に際しては、像面の近似平面内あるいは像面と平行で光軸方向に所定距離隔てた面（目標走査面）内でスリット２２を空間像に対してスキャンする。この場合に、像面とスリットとの光軸方向の相対距離が変わると収差の影響が変化し、その結果空間像の計測結果が異なることとなるため、かかる事態の発生を防止するためにも、スリット２２（スリット板９０）を上記の目標走査面内で正確に走査する必要があるからである。
【０１８０】
投影光学系ＰＬの視野内の複数の評価点について、前述した方法により、空間像計測装置５９を用いたベストフォーカス位置の計測を実行すれば、その計測結果に基づいて像面の近似面が求まり、その結果、その近似面とフォーカスセンサ面との相対的な傾きが求まる。
【０１８１】
投影光学系ＰＬの光学特性が何らかの原因により経時変化した場合も、上述の空間像計測を利用した像面形状、あるいは像面の近似平面の計測により、その経時変化をモニタすることが可能である。そして、経時変化が検出された場合には多点ＡＦ系（６０ａ、６０ｂ）の複数のフォーカスセンサの検出オフセットを再度計測して、以前に計測されていたオフセット値を更新する必要がある。
【０１８２】
多点ＡＦ系（６０ａ、６０ｂ）の全検出点について空間像計測装置５９を用いた計測マークのベストフォーカス位置の計測を利用したフォーカスセンサの検出オフセット計測を実行しても良いが、本実施形態の露光装置１００では、次のようにして、フォーカスセンサ面のキャリブレーションを、定期的にあるいは必要に応じて行うようになっている。
【０１８３】
すなわち、主制御装置２０では、投影光学系ＰＬの視野内の３箇所以上の同一の評価点（各評価点は多点ＡＦ系の検出点の近傍に存在する）において、前述の空間像計測装置５９を用いたベストフォーカス位置の計測を行う、前述の第２の像面計測方法を実行することにより、フォーカスセンサ面と投影光学系ＰＬの像面（あるいはその近似平面）との相対的な角度変化をモニタしている。
【０１８４】
図８には、一例として、視野内の５箇所の検出点Ｓ_３１、Ｓ_５１、Ｓ_４４、Ｓ_３７、Ｓ_５７に個別に対応するフォーカスセンサＤ_３１、Ｄ_５１、Ｄ_４４、Ｄ_３７、Ｄ_５７の検出原点によって構成されるフォーカスセンサ面ＦＰ、上記５箇所の検出点Ｓ_３１、Ｓ_５１、Ｓ_４４、Ｓ_３７、Ｓ_５７それぞれの近傍の空間像コントラストカーブＡＣに基づいて求められた投影光学系ＰＬの像面の近似平面ＩＰと、前記同様にして求められた投影光学系ＰＬの像面の近似平面ＩＰ’との関係が、模式的に示されている。
【０１８５】
そして、このようにして、図８に模式的に示されるように、フォーカスセンサ面ＦＰからの投影光学系ＰＬの像面ＩＰの角度変化が計測された場合に、主制御装置２０は、図９に模式的に示されるように、角度の変化から各フォーカスセンサの検出オフセットの補正値（図９中の黒矢印ＣＶ_ｐ，ｑ参照）を演算にて求め、その補正値をもとの検出オフセット（図９中の白矢印ＯＦ_ｐ，ｑ）に加算して新たな検出オフセットとする。このようにすることにより、投影光学系ＰＬの視野内の最低３点の評価点における空間像計測により、多点ＡＦ系（６０ａ、６０ｂ）の全ての検出点に個別に対応するフォーカスセンサＤ_１１〜Ｄ_７７の全てについて、検出オフセット（フォーカスオフセット）を更新することが可能となり、多点ＡＦ系（６０ａ、６０ｂ）の全検出点について空間像計測装置５９を用いた計測マークのベストフォーカス位置の計測を利用したフォーカスセンサの検出オフセット計測を行う場合に比べて、短時間で、かつ同等の精度でフォーカスセンサ面のキャリブレーションを行うことが可能となる。
【０１８６】
ところで、投影光学系ＰＬの像面形状を正確に計測するためには、投影光学系ＰＬの視野内の任意の評価点で空間像計測、及びその計測時のスリット板９０の光軸方向に関する位置の計測が正確に行われる必要がある。このためには、スリット板９０は、その表面の平坦度が極力高いことが望ましく、スリット板９０のスキャン中は常時フォーカスサーボによりその姿勢が制御されるべきである。
【０１８７】
しかるに、スリット板９０の中心には前述のクロム膜から成る遮光膜９１が存在し、特にその遮光膜９１と周囲の反射膜８３との境界で平坦度が悪化している。
【０１８８】
そこで、本実施形態では、像面形状そのものを計測するに際しては、主制御装置２０が、上記の境界にその検出点がかかるフォーカスセンサを選択装置を介して選択し、フォーカスサーボモードでスリット板９０をスキャンするアルゴリズムが採用されている。
【０１８９】
このように、本実施形態では、多点ＡＦ系（６０ａ、６０ｂ）と基準平面板を兼ねたスリット板９０を備えた空間像計測装置５９との組み合わせ採用して、前述の像面計測などを行うことにより、正確に投影光学系ＰＬの像面とスリット２２との相対位置を管理できるようになっている。
【０１９０】
なお、このような計測は多点ＡＦ系（６０ａ、６０ｂ）の光学調整前には困難であるが、いったん調整された後は、あらゆる計測に際して、前述のフォーカスサーボモードによるウエハテーブル５４の制御を行うことが望ましい。
【０１９１】
これまでの説明から明らかなように、本実施形態では、主制御装置２０によって制御装置、検出装置、演算装置が構成され、空間像計測装置５９と主制御装置２０とによって計測装置が構成され、ウエハ干渉計３１と主制御装置２０とによって傾斜検出系が構成されている。但し、これに限らず、例えば主制御装置２０によって構成される、制御装置、検出装置、演算装置などの構成各部の全てあるいは一部を、複数のハードウェアによって構成しても良い。
【０１９２】
以上詳細に説明したように、本実施形態の露光装置１００によると、多点ＡＦ系（６０ａ、６０ｂ）の調整、例えば複数のフォーカスセンサの検出原点のオフセット調整などのため、各フォーカスセンサの検出原点と投影光学系ＰＬの像面との位置関係を計測する際に、多点ＡＦ系の照射系６０ａからの複数の検出光束が照射される物体として、その一部に空間像計測が可能なスリット２２を有し、その表面の平坦度が高く設定された基準平面部材５８が用いられている。このため、その基準平面部材５８を用いた空間像計測により、前述の如く、投影光学系ＰＬの像面の計測が可能となる。また、複数のフォーカスセンサの検出原点のオフセット計測の際に、多点ＡＦ系を用いて基準平面部材５８（より正確には、スリット板９０）を投影光学系ＰＬの像面に位置させることにより、そのオフセット計測を精度良く行うことが可能となる。従って、レジスト塗布、露光及び現像等を経ることなく、多点ＡＦ系（６０ａ、６０ｂ）高精度な調整を、短時間で行うことが可能となる。
【０１９３】
これを更に詳述すると、本実施形態の露光装置１００によると、多点ＡＦ系（６０ａ、６０ｂ）の調整、特に前述のファイン調整に際して、主制御装置２０が、多点ＡＦ系の複数の検出点Ｓ_１１〜Ｓ_７７のうちの一部の検出点に対応するフォーカスセンサＤを用いて常時その一部の検出点（例えば検出点Ｓ_３１、Ｓ_３７、Ｓ_４４、Ｓ_５１、Ｓ_５７）におけるその検出対象の物体である基準平面部材５８（スリット板９０）表面の投影光学系ＰＬの光軸方向に関する位置を検出しながら、その基準平面部材５８表面が予め、例えば前述の光学系調整工程で計測された既知の投影光学系ＰＬの像面に一致するように基準平面部材５８が搭載されたウエハテーブル５４の位置を制御するとともに、一部の検出点を除く残りの検出点に個別に対応する各フォーカスセンサの検出原点の基準平面部材５８表面、すなわち投影光学系ＰＬの像面（の近似平面）からの光軸方向に関する位置ずれ量を対応するフォーカスセンサの検出オフセットとして検出する。このため、投影光学系ＰＬの像面に対して安定して基準平面部材５８（スリット板９０）を一致させた状態で、その位置制御に使用されていない残りのフォーカスセンサの検出オフセットを精度良く求めることが可能となる。
【０１９４】
また、主制御装置２０は、前記検出オフセットの検出後、前記残りの検出点に個別に対応するフォーカスセンサの少なくとも一部を用いて対応する検出点における基準平面部材５８表面の光軸方向に関する位置を検出しながら、基準平面部材５８表面が既知の投影光学系ＰＬの像面に一致するようにウエハテーブル５４の位置を制御するとともに、前記一部の検出点に個別に対応する各フォーカスセンサの検出原点の基準平面部材５８表面、すなわち投影光学系ＰＬの像面（の近似平面）からの光軸方向に関する位置ずれ量を対応するフォーカスセンサの検出オフセットとして検出する。これにより、多点ＡＦ系（６０ａ、６０ｂ）の全てのフォーカスセンサの検出オフセットを精度良く求めることができる。
【０１９５】
この場合において、基準平面部材５８に代えて、スーパーフラットウエハや、スリット２２の存在しない基準平面板、あるいはデバイス製造用のウエハなどを、多点ＡＦ系の検出対象の物体として用いることは可能である。
【０１９６】
また、本実施形態の露光装置１００によると、多点ＡＦ系の調整、特にフォーカスセンサ面のキャリブレーションに際して、主制御装置２０は、多点ＡＦ系（６０ａ、６０ｂ）の複数のセンサの検出原点の集合から形成される近似平面（フォーカスセンサ面）と投影光学系ＰＬの像面の近似平面との成す角度の変化を検出する。次いで、主制御装置２０は、その検出された角度の変化に基づいて前記各フォーカスセンサの検出オフセットの補正値を算出するとともに、その算出した補正値を予め検出された対応するフォーカスセンサの検出オフセットに加算して新たな検出オフセットとする。このため、投影光学系ＰＬの像面が経時的に変化した場合などにその像面の経時変化に対応してフォーカスセンサの検出オフセットの補正を簡易かつ正確に行うことが可能となる。この場合において、フォーカスセンサ面と像面との成す角度の変化は、主制御装置２０により、空間像計測装置５９を用いて、投影光学系の視野内の少なくとも３つの評価点について、空間像計測の手法を利用してベストフォーカス位置の検出を行うことによって検出される。従って、全ての検出点におけるベストフォーカス位置の計測を行うことなく、全てのフォーカスセンサの検出オフセットの調整が可能となる。従って、多点ＡＦ系の高精度な調整を短時間に行うことが可能となる。
【０１９７】
また、本実施形態の露光装置１００によると、例えば前述の像面計測やベストフォーカス位置の検出のために空間像計測装置５９を用いて空間像を計測する際に、主制御装置２０が、多点ＡＦ系（６０ａ、６０ｂ）の複数のフォーカスセンサの内の少なくとも一部の複数の特定フォーカスセンサの検出結果に基づいてウエハテーブル５４上に一体的に設けられたスリット板９０表面と投影光学系ＰＬの像面の近似平面との間隔と相対角度とが所望の値となるようにスリット板９０の位置・姿勢を制御しながら、ウエハテーブル５４と一体的にスリット板９０を投影光学系の光軸方向に直交する面上で移動する。この場合、多点ＡＦ系（６０ａ、６０ｂ）の複数の特定フォーカスセンサの検出結果に基づくサーボ制御（フォーカスサーボ制御）によりスリット板９０の投影光学系ＰＬとの間隔を一定に保ち、かつスリット板９０と投影光学系ＰＬの像面とを平行に保った状態で、スリット板９０を空間像に対して相対走査できるので、高精度な空間像計測が可能となる。
【０１９８】
この場合において、主制御装置２０では、前記特定フォーカスセンサとして、前記複数の検出点のうちスリット板９０表面の平坦度の良好な位置に位置する検出点に対応するフォーカスセンサを選択装置を介して選択することができる。このため、上記のフォーカスサーボ制御に際して、スリット板９０を投影光学系ＰＬの像面とを正確に平行に保つことが可能となる。
【０１９９】
また、本実施形態の露光装置１００では、例えば前述した第２の像面計測方法の実行に際して、主制御装置２０が、投影光学系ＰＬの視野内の複数の評価点毎に選択された該評価点の近傍の検出点にそれぞれ対応する複数の特定フォーカスセンサの検出結果に基づいてスリット板９０の投影光学系ＰＬの光軸方向の位置及び姿勢を管理しつつ、スリット板９０の光軸方向に関する位置を変化させて、スリット板９０を光軸に直交する面内で移動して、複数の評価点それぞれに対応する計測マークＰＭの空間像を繰り返し計測する。この場合、主制御装置２０は、上記のフォーカスサーボ制御によりスリット板９０の投影光学系ＰＬとの間隔、傾斜を一定に保った状態で、スリット板９０を計測マークの空間像に対して相対走査できるので、高精度な空間像計測が、各評価点毎にかつ光軸方向に関する複数の位置で行われることとなる。そして、その計測結果、すなわち評価点毎の光軸方向の複数の位置における空間像の計測結果に基づいて、主制御装置２０が、各評価点におけるベストフォーカス位置を検出するとともに、その検出結果に基づいて所定の演算により投影光学系ＰＬの像面を算出する。従って、短時間でかつ投影光学系の像面を精度良く検出することができる。
【０２００】
また、本実施形態の露光装置１００によると、例えば前述した第１の像面計測方法の実行に際して、主制御装置２０が、多点焦点位置検出系（６０ａ、６０ｂ）を用いてスリット板９０の投影光学系の光軸方向の位置を任意の１点の検出点（パターン板の平坦度が良好な領域内の検出点、例えば光軸上の検出点）で管理するとともに、傾斜検出系、例えばピッチング干渉計、ローリング干渉計を用いてスリット板９０の光軸に直交する面に対する傾斜を管理しつつ、スリット板９０の光軸方向に関する位置を変化させてスリット板９０をウエハテーブル５４と一体で光軸に直交する面内で移動して投影光学系ＰＬの視野内の複数の評価点それぞれに対応する計測マークの空間像を繰り返し計測する。この場合、主制御装置２０は、多点焦点位置検出系の１つのフォーカスセンサの検出結果に基づくサーボ制御によりスリット板９０の投影光学系ＰＬとの間隔を一定に保ち、かつ傾斜検出系の検出結果に基づいてスリット板９０と投影光学系ＰＬの像面とを平行に保った状態で、スリット板９０を計測マークの空間像に対して相対走査できるので、高精度な空間像計測が、各評価点毎にかつ光軸方向に関する複数の位置で行われることとなる。そして、主制御装置２０は、その計測結果、すなわち評価点毎の光軸方向の複数の位置における空間像の計測結果に基づいて各評価点におけるベストフォーカス位置を検出するとともに、その検出結果に基づいて所定の演算により投影光学系の像面を算出する。従って、短時間でかつ投影光学系ＰＬの像面を精度良く検出することができる。第１の像面計測方法では、焦点位置検出系は、必ずしも多点ＡＦ系でなくとも良い。
【０２０１】
更に、本実施形態の露光装置１００では、以上のような手順で調整が行われた多点ＡＦ系（６０ａ、６０ｂ）を用いて、例えば前述の走査露光中などに前述のオートフォーカス・オートレベリングが行われるので、デフォーカスに起因する色むらなどのない、高精度なレチクルパターンの転写像のウエハ上での形成が可能となる。また、前述した手法により空間像計測装置５９を用いて計測された投影光学系ＰＬの像面形状や像面湾曲などの計測結果に基づいて、主制御装置２０により投影光学系ＰＬの光学特性が不図示の調整装置を介して精度良く調整され、この調整後の投影光学系ＰＬを用いて走査露光が行われるので、レチクルパターンとウエハＷ上のショット領域に既に形成されたパターンとを正確に重ね合わせることが可能となる。
【０２０２】
なお、上記実施形態では、本発明がステップ・アンド・スキャン方式の投影露光装置に適用された場合について説明したが、これに限らず、マスクと基板とを静止した状態でマスクのパターンを基板に転写するとともに、基板を順次ステップ移動させるステップ・アンド・リピート型の露光装置にも本発明は適用することができる。
【０２０３】
また、上記実施形態では、本発明が半導体製造用の露光装置に適用された場合について説明したが、これに限らず、例えば、角型のガラスプレート上に液晶表示素子パターンを転写する液晶用の露光装置や、プラズマディスプレイや有機ＥＬなどの表示装置、薄膜磁気ヘッドの製造に用いられるデバイスパターンをセラミックウエハ上に転写する露光装置、及び撮像素子（ＣＣＤなど）、マイクロマシン、ＤＮＡチップなどの製造に用いられる露光装置などにも適用することができる。また、半導体素子などのマイクロデバイスだけでなく、光露光装置、ＥＵＶ露光装置、Ｘ線露光装置、及び電子線露光装置などで使用されるレチクル又はマスクを製造するために、ガラス基板又はシリコンウエハなどに回路パターンを転写する露光装置にも本発明を適用できる。ここで、ＤＵＶ（遠紫外）光やＶＵＶ（真空紫外）光などを用いる露光装置では一般的に透過型レチクルが用いられ、レチクル基板としては石英ガラス、フッ素がドープされた石英ガラス、螢石、フッ化マグネシウム、又は水晶などが用いられる。また、プロキシミティ方式のＸ線露光装置、又は電子線露光装置などでは透過型マスク（ステンシルマスク、メンブレンマスク）が用いられ、マスク基板としてはシリコンウエハなどが用いられる。
【０２０４】
また、上記実施形態では、光源としてＫｒＦエキシマレーザ光源などの紫外光源、Ｆ_２レーザ、ＡｒＦエキシマレーザ等の真空紫外域のパルスレーザ光源を用いるものとしたが、これに限らずＡｒ_２レーザ光源（出力波長１２６ｎｍ）などの他の真空紫外光源を用いても良い。また、例えば、真空紫外光として上記各光源から出力されるレーザ光に限らず、ＤＦＢ半導体レーザ又はファイバーレーザから発振される赤外域、又は可視域の単一波長レーザ光を、例えばエルビウム（Ｅｒ）（又はエルビウムとイッテルビウム（Ｙｂ）の両方）がドープされたファイバーアンプで増幅し、非線形光学結晶を用いて紫外光に波長変換した高調波を用いても良い。
【０２０５】
また、上記実施形態では、投影光学系として縮小系かつ屈折系を用いる場合について説明したが、これに限らず、投影光学系として等倍あるいは拡大系を用いても良いし、屈折系、反射屈折系、あるいは反射系のいずれを用いても良い。
【０２０６】
なお、複数のレンズから構成される照明光学系、投影光学系ＰＬを露光装置本体に組み込み光学調整をするとともに、多数の機械部品からなるレチクルステージＲＳＴやウエハステージＷＳＴを露光装置本体に取り付けて配線や配管を接続し、更に総合調整（電気調整、動作確認等）をすることにより本実施形態の露光装置１００を製造することができる。なお、露光装置の製造は温度及びクリーン度等が管理されたクリーンルームで行うことが望ましい。
【０２０７】
また、半導体デバイスは、デバイスの機能・性能設計を行うステップ、この設計ステップに基づいたレチクルを製作するステップ、シリコン材料からウエハを製作するステップ、前述した実施形態の露光装置１００によりレチクルのパターンをウエハに転写するステップ、デバイス組み立てステップ（ダイシング工程、ボンディング工程、パッケージ工程を含む）、検査ステップ等を経て製造される。
【０２０８】
【発明の効果】
以上説明したように、請求項１〜６に記載の各調整方法によると、多点焦点位置検出系の高精度な調整を、短時間で行うことができるという効果がある。
【０２０９】
また、請求項７〜９に記載の各空間像計測方法によると、高精度な空間像の計測が可能になるという効果がある。
【０２１０】
また、請求項１０〜１３に記載の各像面計測方法によると、投影光学系の像面を短時間でかつ精度良く検出することができるという効果がある。
【０２１１】
また、請求項１４〜１８に記載の各露光装置によると、多点焦点位置検出系の高精度な調整を、短時間で行うことができるという効果がある。
【０２１２】
請求項１９〜２１に記載の各露光装置によると、高精度な空間像の計測が可能になるという効果がある。
【０２１３】
また、請求項２２〜２５に記載の各露光装置によると、投影光学系の像面を短時間でかつ精度良く検出することができるという効果がある。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る露光装置の構成を概略的に示す図である。
【図２】図１の空間像計測器の内部構成を示す図である。
【図３】空間像計測器を用いてレチクル上の計測マークＰＭの空間像を計測しているときの様子を示す図である。
【図４】図４（Ａ）は、基準平面部材を示す斜視図、図４（Ｂ）は基準平面部材の平面図である。
【図５】焦点位置検出系、及び該焦点位置検出系の出力信号を処理するとともに、プレーンパラレルを駆動する処理駆動部の構成を概略的に示す図である。
【図６】多点ＡＦ系の検出点であるスリット像の配置と露光領域との位置関係を示す図である。
【図７】図７（Ａ）は、空間像の計測に際してスリット板上に空間像ＰＭ’が形成された状態の空間像計測器を示す平面図、図７（Ｂ）はその空間像計測の際に得られる光電変換信号（光強度信号）Ｐの一例を示す線図である。
【図８】視野内の５箇所の検出点に個別に対応するフォーカスセンサの検出原点によって構成されるフォーカスセンサ面ＦＰ、上記５箇所の検出点それぞれの近傍の評価点についての空間像コントラストカーブＡＣに基づいて求められた投影光学系ＰＬの像面の近似平面ＩＰと、前回の像面の近似平面ＩＰ’との関係を、模式的に示す図である。
【図９】フォーカスセンサ面ＦＰからの投影光学系ＰＬの像面ＩＰの角度変化から各フォーカスセンサの検出オフセットの補正値ＣＶ_ｐ，ｑと、もとの検出オフセットＯＦ_ｐ，ｑとを加算して新たな検出オフセットを算出する様子を模式的示す図である。
【符号の説明】
２０…主制御装置（制御装置、検出装置、演算装置、計測装置の一部、傾斜検出系の一部）、３１…ウエハ干渉計（傾斜検出系の一部）、５４…ウエハテーブル（テーブル）、５８…基準平面部材（基準平面板）、５９…空間像計測装置（計測装置の一部）、６０ａ…照射系（多点焦点位置検出系の一部）、６０ｂ…受光系（多点焦点位置検出系の一部）、９０…スリット板（パターン板）、１００…露光装置、ＰＬ…投影光学系、Ｗ…ウエハ（感光物体）。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an adjustment method, an aerial image measurement method and an image plane measurement method, and an exposure apparatus. More specifically, the present invention irradiates a plurality of detection points set on an object with detection light fluxes, A multi-point focal position detection system (hereinafter, referred to as a “multi-point AF system”) that receives reflected light beams by sensors individually corresponding to a plurality of detection points and detects position information of the object at each detection point in the optical axis direction of the projection optical system. ), An aerial image measurement method using the multi-point AF system, an image plane measurement method using the aerial image measurement, and an exposure apparatus suitable for performing these methods.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, when a semiconductor element or a liquid crystal display element or the like is manufactured by a photolithography process, a pattern of a photomask or a reticle (hereinafter, collectively referred to as a “reticle”) is formed on a surface through a projection optical system. A projection exposure apparatus that transfers onto a substrate such as a wafer or a glass plate coated with a photosensitive agent, for example, a step-and-repeat type reduction projection exposure apparatus (so-called stepper), or a step-and-scan type scanning projection exposure An apparatus (a so-called scanning stepper) or the like is used.
[0003]
When manufacturing a semiconductor device or the like using this type of exposure apparatus, an exposure area (an area irradiated with illumination light) on a substrate is projected in order to minimize the occurrence of exposure failure due to defocus. It is necessary to make it coincide with the range of the depth of focus of the best imaging plane of the optical system. For this purpose, a best focus plane or best focus position of the projection optical system is accurately measured, and a focus position detection system (focus) for detecting the position of the substrate in the optical axis direction of the projection optical system based on the measurement result. It is important to calibrate the detection system).
[0004]
As a method of measuring the best focus position of the projection optical system, a predetermined measurement mark on the reticle, for example, a line and space mark, is changed while changing the position of the substrate in the optical axis direction of the projection optical system at predetermined step intervals. Are sequentially transferred to different regions on the substrate via a substrate, and the line width of a resist image formed on the substrate after the substrate is developed is measured using an SEM (scanning electron microscope) or the like. Conventionally, a method of setting a position in the optical axis direction of a substrate corresponding to a resist image having a line width as a best focus position (hereinafter, referred to as a “printing method”) has been mainly performed.
[0005]
In addition, a measurement mark formed on the reticle, for example, a line and space mark is illuminated with illumination light, and a spatial image (projection image) of the measurement mark formed by the projection optical system is measured using an aerial image measurement device. A method of calculating the best focus position based on the measurement result (hereinafter, referred to as “aerial image measurement method”) is also known.
[0006]
However, conventionally, in the above-described calibration of the multipoint AF system, which is a kind of focus detection system, the position of the substrate in the optical axis direction of the projection optical system of the substrate is managed by only one point for each detection point of the multipoint AF system. While changing the position of the substrate with respect to the optical axis direction of the projection optical system at predetermined step intervals, the measurement marks described above are sequentially transferred to the positions of the detection points in different regions on the substrate via the projection optical system. I do. Then, based on the measurement result of the line width of the resist image formed on the substrate after developing the substrate, the best focus position at each point is obtained by the same method as described above, and the obtained best focus position at each point is obtained. The detection offset at each detection point has been detected by calculating the amount of deviation of the detection origin of the corresponding sensor from. That is, in this way, the relationship between the detection origin of each sensor of the multipoint AF system and the image plane of the projection optical system is also evaluated and managed based on the result of printing the pattern on the substrate.
[0007]
[Problems to be solved by the invention]
However, in the above-described calibration method of the multipoint AF system based on the printing method, since the focus sensor is adjusted and managed through the resist image on the substrate, only the detection of the best focus position which is a premise of the calibration is performed. In addition, it is necessary to go through a series of procedures of resist coating, exposure, development, and line width measurement, which is troublesome and takes too much time for the measurement, which causes a decrease in throughput. In addition to this, the optical axis of the projection optical system due to the resist process, the flatness of the substrate, the flatness of the substrate holder holding the substrate, and the unevenness of the moving guide surface of the substrate stage on which the substrate holder is mounted, etc. The measurement error in the optical axis direction reached about several tens of nm or more due to various error factors such as backlash in the direction, and the measurement reproducibility was not sufficient.
[0008]
The present invention has been made under such circumstances, and a first object of the present invention is to provide an adjustment method capable of performing highly accurate adjustment of a multipoint focal position detection system in a short time.
[0009]
A second object of the present invention is to provide an aerial image measurement method capable of measuring an aerial image with high accuracy.
[0010]
A third object of the present invention is to provide an image plane measuring method capable of detecting an image plane of a projection optical system in a short time and with high accuracy.
[0011]
A fourth object of the present invention is to provide an exposure apparatus capable of performing high-accuracy adjustment of a multipoint focal position detection system in a short time.
[0012]
A fifth object of the present invention is to provide an exposure apparatus capable of measuring an aerial image with high accuracy.
[0013]
A sixth object of the present invention is to provide an exposure apparatus capable of detecting an image plane of a projection optical system in a short time and with high accuracy.
[0014]
[Means for Solving the Problems]
The invention according to claim 1 irradiates a plurality of detection light beams onto the object, and individually reflects reflected light beams from a plurality of detection points on the object irradiated with the detection light beam to the plurality of detection points. Detecting the position information in the optical axis direction of the projection optical system of the object at each of the detection points by receiving light at the detection points, a method of adjusting a multi-point focal position detection system, wherein the detection origin of each sensor and When measuring the positional relationship with the image plane of the projection optical system, a reference plane plate having a measurement pattern capable of aerial image measurement in a part thereof, the flatness of the surface of which is set high, This is an adjustment method characterized by being used as an object.
[0015]
Here, the detection origin of the sensor refers to the detection standard of the sensor, and corresponds to, for example, the position of the object to be detected in the state where the reflected light beam is incident on the detection center of the sensor in the optical axis direction of the projection optical system. I do. In this specification, the term “detection origin of the sensor” is used in this sense.
[0016]
According to this, when measuring the positional relationship between the detection origin of each sensor and the image plane of the projection optical system, for adjustment of the multi-point focal position detection system, for example, for offset adjustment of the detection origin of a plurality of sensors, etc. An object to which a plurality of detection light beams from a multi-point focal position detection system are irradiated is a reference plane plate having a measurement pattern capable of measuring an aerial image on a part thereof and having a flat surface having a high flatness. Used as That is, while controlling the position and inclination (posture) of the reference plane plate in the optical axis direction using the multi-point focal position detection system, the aerial image measurement can be accurately performed using the reference plane plate. By performing such measurement for a plurality of evaluation points in the field of view of the projection optical system, it is possible to accurately measure the image plane of the projection optical system. In addition, when measuring the offset of the detection origin of multiple sensors, it is possible to accurately measure the offset by positioning the reference plane plate on the image plane of the projection optical system using the multi-point focal position detection system. It becomes. Therefore, highly accurate adjustment of the multipoint focal position detection system can be performed in a short time without using the printing method.
[0017]
The invention according to claim 2 irradiates a plurality of detection light beams onto the object, and individually corresponds reflected light beams from a plurality of detection points on the object irradiated with the detection light beam to the plurality of detection points. Detecting the position information in the optical axis direction of the projection optical system of the object at each of the detection points by receiving light at the detection points, a multi-point focus position detection system adjusting method, wherein the plurality of detection points While always detecting the position of the object surface in the optical axis direction at the some detection points using a sensor corresponding to some of the detection points, the object surface is on a known image plane of the projection optical system. A first step of controlling the position of the object so that they coincide with each other; in parallel with the first step, the object at the detection origin of each sensor individually corresponding to the remaining detection points excluding the part of the detection points With respect to the direction of the optical axis from the surface An adjustment method comprising: second step and detecting a location shift amount as a detection offset of the corresponding sensor.
[0018]
Here, the “detection offset” of the sensor means a deviation of the detection origin from the image plane of the projection optical system in the optical axis direction, and the term “detection offset” is used in this specification in this specification. Further, "matching with the image plane" means that the projection optical system is located within the range of the depth of focus of the image plane, and in this specification, the expression "matching with the image plane" is used in this sense. .
[0019]
According to this, while constantly detecting the position in the optical axis direction of the object surface at the some detection points using a sensor corresponding to some of the plurality of detection points, the object surface is known. In parallel with controlling the position of the object so that it coincides with the image plane of the projection optical system, the object surface at the detection origin of each sensor individually corresponding to the remaining detection points except for some of the detection points, i.e., projection The amount of displacement in the optical axis direction from (the approximate plane of) the image plane of the optical system is detected as the detection offset of the corresponding sensor. For this reason, it is possible to accurately determine the detection offset of the remaining sensor not used for position control in a state where the object surface is stably aligned with the image plane of the projection optical system. Therefore, the multi-point focal position detection system can be adjusted with high throughput and high accuracy without using the printing method. The position of the image plane of the projection optical system is measured in advance by the printing method or the aerial image measurement method described above irrespective of the adjustment method of the multipoint focus position detection system of the present invention, and the information is used. It is good.
[0020]
In this case, a substrate such as a wafer may be used as the object, but as in the adjustment method according to claim 3, a reference flat plate whose surface has a high flatness is used as the object. It can be. For the same purpose, of course, an ultra-flat wafer (super flat wafer) whose surface has a high degree of flatness may be used as the object.
[0021]
In each of the adjustment methods according to claims 2 and 3, as in the adjustment method according to claim 4, the object at a detection point corresponding to the remaining detection point using at least a part of a sensor individually corresponding to the remaining detection point. A third step of controlling the position of the object such that the surface of the object coincides with a known image plane of the projection optical system while detecting the position of the surface in the optical axis direction; A fourth step of detecting, as a detection offset of the corresponding sensor, an amount of displacement of the detection origin of each sensor individually corresponding to the partial detection point from the object surface in the optical axis direction from the object surface. It can be.
[0022]
The invention according to claim 5 irradiates a plurality of detection light beams on the object, and individually corresponds to the plurality of detection light beams reflected from a plurality of detection points on the object irradiated with the detection light beam. Detecting the position information in the optical axis direction of the projection optical system at each of the detection points to receive light at the detection point, a method of adjusting a multi-point focal position detection system, from a set of detection origin of the plurality of sensors A first step of detecting a change in an angle between an approximate plane to be formed and an approximate plane of an image plane of the projection optical system; and correcting a correction value of a detection offset of each of the sensors based on the detected change in the angle. A second step of calculating and adding the calculated correction value to the detection offset of the corresponding sensor detected in advance to make a new detection offset.
[0023]
According to this, a change in an angle between an approximate plane formed from a set of detection origins of a plurality of sensors of the multi-point focal position detection system and an approximate plane of the image plane of the projection optical system is detected, and the result is detected. The correction value of the detection offset of each sensor is calculated based on the change of the angle, and the calculated correction value is added to the detection offset of the corresponding sensor detected in advance to obtain a new detection offset. For this reason, it is possible to simply and accurately correct the detection offset of the sensor corresponding to a case where the image plane of the projection optical system changes with time. That is, the best focus position is measured at all the detection points only by measuring the change in the angle between the approximate plane formed from the set of the detection origins of the plurality of sensors and the approximate plane of the image plane of the projection optical system. Without this, it is possible to adjust the detection offsets of all the sensors. Therefore, highly accurate adjustment of the multipoint focal position detection system can be performed in a short time.
[0024]
In this case, as in the adjusting method according to claim 6, in the first step, an approximate plane of the image plane is detected by using an aerial image measurement method for detecting the change in the angle. can do.
[0025]
The invention according to claim 7 is an aerial image measurement method using a pattern plate having a measurement pattern capable of aerial image measurement on a part thereof, wherein the object is irradiated with a plurality of detection light beams, and the detection is performed. Reflected light beams from a plurality of detection points on the object irradiated with the light beam are received by sensors individually corresponding to the plurality of detection points, and position information regarding the optical axis direction of the projection optical system at each of the detection points is detected. Using a multi-point focal position detection system, the distance between the pattern plate surface and the approximate plane of the image plane of the projection optical system based on the detection results of at least some of the plurality of specific sensors among the plurality of sensors While controlling the position and orientation of the pattern plate so that the relative angle becomes a desired value, the pattern plate is moved on a plane orthogonal to the optical axis direction to measure an aerial image. Aerial image measurement method A.
[0026]
According to this, the distance between the pattern plate surface and the approximate plane of the image plane of the projection optical system based on the detection results of at least some of the plurality of specific sensors among the plurality of sensors of the multipoint focal position detection system. Position (position in the optical axis direction) / posture (inclination with respect to a plane perpendicular to the optical axis, etc.) of a pattern plate having a measurement pattern capable of measuring an aerial image in a part thereof so that the angle and the relative angle have a desired value. A), the pattern plate is moved on a plane orthogonal to the optical axis direction to measure an aerial image. In this case, the pattern plate can be relatively scanned with respect to the aerial image while the distance between the pattern plate and the projection optical system is kept constant by the servo control, and the pattern plate and the image plane of the projection optical system are kept parallel. Therefore, highly accurate aerial image measurement can be performed.
[0027]
In this case, as in the aerial image measurement method according to claim 8, the specific sensor is a sensor corresponding to a detection point located at a position where the flatness of the pattern plate surface is good among the plurality of detection points. It can be. Due to the formation of the pattern for measurement on the pattern plate, the flatness of the nearby part may be worse than other parts, but it corresponds to the detection point located in the area excluding the part with the poor flatness Since the position / posture of the pattern plate is controlled using only the sensor that performs the control, high-precision position / posture control is possible. From this point of view, it is desirable to switch the sensor used for the control according to the position of the evaluation point (point to be measured for the aerial image) in the field of view of the projection optical system.
[0028]
In each of the aerial image measurement methods according to the seventh and eighth aspects, as in the aerial image measurement method according to the ninth aspect, a reference plane plate whose surface is set to have a high flatness is used as the pattern plate. It can be.
[0029]
According to a tenth aspect of the present invention, there is provided an image plane measuring method for measuring an image plane of a projection optical system using a pattern plate having a measurement pattern capable of measuring an aerial image in a part thereof. Irradiating the detection light beams respectively, and receiving the reflected light beams from a plurality of detection points on the object irradiated with the detection light beams by sensors individually corresponding to the plurality of detection points, and projecting the projection light at each of the detection points. A multi-point focal position detection system for detecting position information in the optical axis direction of the system is used, and a plurality of detection points near each of the evaluation points selected for each of the plurality of evaluation points in the field of view of the projection optical system. While managing the position and orientation of the pattern plate surface in the optical axis direction based on the detection result of the specific sensor, changing the position of the pattern plate in the optical axis direction, the pattern plate with the optical axis In an orthogonal plane Aerial image measurement step of moving and repeatedly measuring the aerial image of the measurement mark corresponding to each of the plurality of evaluation points; and detecting a best focus position at each of the evaluation points based on the measurement result, A calculating step of calculating an image plane of the projection optical system by a predetermined calculation based on the calculation.
[0030]
According to this, based on the detection results of the plurality of specific sensors corresponding to the detection points near the evaluation point selected for each of the plurality of evaluation points in the field of view of the projection optical system, a part of the spatial image measurement is performed. While managing the position and orientation of the projection optical system in the optical axis direction of the surface of the pattern plate having the measurement pattern capable of being measured, the position of the pattern plate in the optical axis direction is changed, and the pattern plate is orthogonal to the optical axis. And moves repeatedly in a plane to be measured, and repeatedly measures the aerial image of the measurement mark corresponding to each of the plurality of evaluation points. In this case, the servo control based on the detection results of the plurality of specific sensors described above keeps the interval between the pattern plate and the projection optical system constant, and keeps the pattern plate and the image plane of the projection optical system parallel, Since the pattern plate can be scanned relative to the aerial image of the measurement mark, highly accurate aerial image measurement is performed for each evaluation point and at a plurality of positions in the optical axis direction.
[0031]
The best focus position at each evaluation point is detected based on the measurement result, that is, the measurement result of the aerial image at a plurality of positions in the optical axis direction for each evaluation point, and projection is performed by a predetermined calculation based on the detection result. Calculate the image plane of the optical system. That is, the best focus position at each evaluation point can be detected with high accuracy, and the image plane can be calculated with high accuracy based on the detection result. Therefore, according to the tenth aspect of the present invention, the image plane of the projection optical system can be accurately detected in a short time regardless of the printing method.
[0032]
In this case, as in the image plane measuring method according to claim 11, in the calculating step, the detection origin from the image plane of the detection origin of each of the specific sensors individually corresponding to a detection point near each of the evaluation points. Based on the amount of displacement in the optical axis direction, the detection offset of each of the specific sensors can be calculated together.
[0033]
According to a twelfth aspect of the present invention, there is provided an image plane measurement method for measuring an image plane of a projection optical system by using a pattern plate having a measurement pattern capable of measuring an aerial image in a part thereof, wherein the detection is performed on an object. A focus position detection system that irradiates a light beam, receives a reflected light beam from a detection point on the object irradiated with the detection light beam by a sensor, and detects position information regarding the optical axis direction of the projection optical system at the detection point. While managing the position of the pattern plate in the optical axis direction using, while managing the inclination of the pattern plate with respect to a plane orthogonal to the optical axis using another detection system different from the focus position detection system, By changing the position of the pattern plate in the direction of the optical axis and moving the pattern plate in a plane perpendicular to the optical axis, the space of the measurement mark corresponding to each of the plurality of evaluation points in the field of view of the projection optical system Statue An aerial image measurement step of returning measurement; a calculation step of detecting a best focus position at each of the evaluation points based on the measurement result and calculating an image plane of the projection optical system by a predetermined calculation based on the detection result And an image plane measurement method.
[0034]
According to this, a projection optical system of a projection optical system of a pattern plate having a measurement pattern capable of measuring an aerial image in a part thereof using a focal position detection system (regardless of whether or not there are multiple points) is used. While managing the position, while controlling the inclination of the pattern plate with respect to a surface orthogonal to the optical axis using another detection system different from the focus position detection system, the position of the pattern plate in the optical axis direction is changed. Then, the pattern plate is moved in a plane orthogonal to the optical axis to repeatedly measure the spatial images of the measurement marks corresponding to each of the plurality of evaluation points in the field of view of the projection optical system. In this case, the distance between the pattern plate and the projection optical system is kept constant by the servo control based on the detection result of one sensor of the above-mentioned focus position detection system, and the pattern plate and the projection plate are projected based on the detection result of the other detection system. Since the pattern plate can be relatively scanned with respect to the aerial image of the measurement mark while keeping the image plane of the optical system in parallel, high-precision aerial image measurement can be performed for each evaluation point and in a plurality of positions in the optical axis direction. Will be done at the location. In this case, the position of the detection point can be set in a region where the flatness of the pattern plate is good, thereby preventing a decrease in aerial image measurement accuracy due to poor flatness of the pattern plate surface. .
[0035]
The best focus position at each evaluation point is detected based on the measurement result, that is, the measurement result of the aerial image at a plurality of positions in the optical axis direction for each evaluation point, and projection is performed by a predetermined calculation based on the detection result. Calculate the image plane of the optical system. That is, the best focus position at each evaluation point can be detected with high accuracy, and the image plane can be calculated with high accuracy based on the detection result. Therefore, according to the twelfth aspect of the present invention, the image plane of the projection optical system can be detected in a short time and with high accuracy without using the printing method.
[0036]
In this case, as the other detection system, various detection systems can be used. For example, as in the image plane position detection method according to claim 13, the pattern plate is provided as the other detection system. A set of interferometers for detecting rotation angles of two members about two axes orthogonal to the optical axis, and a set of encoders for detecting displacements of the plurality of support points supporting the members in the optical axis direction, respectively. Can be used.
[0037]
The invention according to claim 14 is an exposure apparatus that transfers a device pattern onto a photosensitive object (W) via a projection optical system (PL), wherein the object pattern is irradiated with a plurality of detection light beams, and the detection is performed. Reflected light beams from a plurality of detection points on the object irradiated with the light beam are received by sensors individually corresponding to the plurality of detection points, and the light beams are reflected on the optical axis direction of the projection optical system of the object at the respective detection points. A multi-point focal position detection system (60a, 60b) for detecting position information; a table (54) on which the object is mounted; and detection of a part of the plurality of detection points of the multi-point focal position detection system While detecting the position in the optical axis direction of the object surface at the partial detection point using a sensor corresponding to a point, the table so that the object surface coincides with the known image plane of the projection optical system Control position And a control for detecting, as the detection offset of the corresponding sensor, the amount of displacement of the detection origin of each sensor corresponding to the remaining detection points except for some of the detection points from the object surface in the optical axis direction. And (20) an exposure apparatus.
[0038]
According to this, the control device always uses the sensor corresponding to a part of the plurality of detection points of the multi-point focal position detection system to project the projection optical system of the object surface at the part of the detection points. While detecting the position in the optical axis direction, while controlling the position of the table on which the object is mounted so that the surface of the object coincides with the image plane of the known projection optical system, the remaining surface excluding some detection points The amount of displacement in the optical axis direction from the object surface of the detection origin of each sensor individually corresponding to the detection point, that is, from the image plane (approximate plane of) the projection optical system, is detected as the detection offset of the corresponding sensor. For this reason, it is possible to accurately determine the detection offset of the remaining sensor not used for position control in a state where the object surface is stably aligned with the image plane of the projection optical system. Therefore, according to the exposure apparatus of the present invention, highly accurate adjustment of the multipoint focal position detection system can be performed in a short time without performing resist coating, exposure, development, and the like.
[0039]
In this case, as in the exposure apparatus according to the fifteenth aspect, the object can be a reference flat plate whose surface has a high degree of flatness.
[0040]
In each of the exposure apparatuses according to claims 14 and 15, as in the exposure apparatus according to claim 16, after the detection of the detection offset, at least one of the sensors individually corresponding to the remaining detection points. Controlling the position of the table so that the object surface coincides with a known image plane of the projection optical system while detecting the position of the object surface at the corresponding detection point in the optical axis direction at a corresponding detection point. In addition, the amount of displacement of the detection origin of each sensor individually corresponding to the part of the detection points from the object surface in the optical axis direction can be detected as a detection offset of the corresponding sensor.
[0041]
The invention according to claim 17 is an exposure apparatus for transferring a device pattern onto a photosensitive object (W) via a projection optical system (PL), wherein the object pattern is irradiated with a plurality of detection light beams, and the detection is performed. Reflected light beams from a plurality of detection points on the object irradiated with the light beam are received by sensors individually corresponding to the plurality of detection points, and position information regarding the optical axis direction of the projection optical system at each of the detection points is detected. A multipoint focal position detection system (60a, 60b) for detecting a change in an angle between an approximate plane formed from a set of detection origins of the plurality of sensors and an approximate plane of the image plane of the projection optical system A device (20) for calculating a correction value of the detection offset of each of the sensors based on a change in the angle detected by the detection device and detecting the calculated correction value for the detection of the corresponding sensor detected in advance; Arithmetic unit as a new detection offset is added to the set (20) which is an exposure apparatus comprising a.
[0042]
According to this, the detection device detects a change in an angle formed between an approximate plane formed from a set of detection origins of a plurality of sensors of the multipoint focal position detection system and an approximate plane of the image plane of the projection optical system, The arithmetic unit calculates a correction value of the detection offset of each of the sensors based on the detected change in the angle, and adds the calculated correction value to the detection offset of the corresponding sensor detected in advance to generate a new detection offset. This is the detection offset. For this reason, when the image plane of the projection optical system changes over time, it is possible to easily and accurately correct the detection offset of the sensor in accordance with the change. In this case, the detection offsets of all the sensors can be adjusted without measuring the best focus positions at all the detection points. Therefore, highly accurate adjustment of the multipoint focal position detection system can be performed in a short time.
[0043]
In this case, the exposure apparatus according to claim 18, further comprising a measurement device (59, 20) for measuring the image plane of the projection optical system by using an aerial image measurement technique, wherein the detection device comprises: The change in the angle may be detected based on a measurement result of the measurement device.
[0044]
An invention according to claim 19 is an exposure apparatus for transferring a device pattern onto a photosensitive object (W) via a projection optical system (PL), wherein the object pattern is irradiated with a plurality of detection light beams, and the detection is performed. Reflected light beams from a plurality of detection points on the object irradiated with the light beam are received by sensors individually corresponding to the plurality of detection points, and position information regarding the optical axis direction of the projection optical system at each of the detection points is detected. A multi-point focal position detection system (60a, 60b); a table (54) on which the photosensitive object is mounted; and a pattern plate (90) integrally provided on the table. An aerial image measurement device (59) that receives light via the formed measurement pattern to measure an aerial image; and, when measuring an aerial image by the aerial image measurement device, the aerial image measurement device (59). Of the sensors The position of the pattern plate such that the distance and the relative angle between the pattern plate surface and the approximate plane of the image plane of the projection optical system are at desired values based on the detection results of at least some of the specific sensors. A control device (20) for moving the pattern plate on a plane orthogonal to the optical axis direction while controlling the attitude, integrally with the table.
[0045]
According to this, the control device, when measuring the aerial image by the aerial image measurement device, on the table based on the detection results of at least some of the plurality of specific sensors among the plurality of sensors of the multi-point focal position detection system While controlling the position and orientation of the pattern plate so that the distance and the relative angle between the surface of the pattern plate provided integrally and the approximate plane of the image plane of the projection optical system become desired values, the pattern and the table are integrated. Then, the pattern plate is moved on a plane orthogonal to the optical axis direction of the projection optical system. In this case, the distance between the pattern plate and the projection optical system is kept constant by servo control based on the detection results of the plurality of specific sensors of the multipoint focal position detection system, and the pattern plate and the image plane of the projection optical system are set in parallel. Since the pattern plate can be relatively scanned with respect to the aerial image in the state where the aerial image is kept, high-precision aerial image measurement becomes possible.
[0046]
In this case, as in the exposure apparatus according to claim 20, the specific sensor is a sensor corresponding to a detection point located at a position with good flatness on the surface of the pattern plate among the plurality of detection points. It can be.
[0047]
In each of the exposure apparatuses according to claims 19 and 0, as in the exposure apparatus according to claim 21, the pattern plate may be a reference plane plate whose surface flatness is set high. it can.
[0048]
The invention according to claim 22 is an exposure apparatus for transferring a device pattern onto a photosensitive object (W) via a projection optical system (PL), and irradiates the object with a plurality of detection light beams, respectively. Reflected light beams from a plurality of detection points on the object irradiated with the light beam are received by sensors individually corresponding to the plurality of detection points, and position information regarding the optical axis direction of the projection optical system at each of the detection points is detected. A multi-point focal position detection system (60a, 60b); a table (54) on which the photosensitive object is mounted; and a pattern plate (90) integrally provided on the table. An aerial image measurement device (59) for receiving a light via the formed measurement pattern and measuring an aerial image; in the vicinity of the evaluation points selected for each of a plurality of evaluation points in the field of view of the projection optical system Corresponding to the detection points of While managing the position and orientation of the surface of the pattern plate in the optical axis direction based on the detection result of the number of specific sensors, changing the position of the pattern plate in the optical axis direction to move the pattern plate to the optical axis A control device (20) that moves together with the table in a plane perpendicular to the plane and repeatedly measures the aerial image of the measurement mark corresponding to each of the plurality of evaluation points; An arithmetic unit (20) that detects a best focus position and calculates an image plane of the projection optical system by a predetermined calculation based on the detection result.
[0049]
According to this, the control device is configured to perform part of the evaluation based on the detection results of the plurality of specific sensors respectively corresponding to the detection points near each of the evaluation points selected for each of the plurality of evaluation points in the visual field of the projection optical system. While managing the position and orientation in the optical axis direction of the projection optical system on the surface of the pattern plate having a measurement pattern capable of aerial image measurement, by changing the position of the pattern plate in the optical axis direction, the pattern plate Moving in a plane orthogonal to the optical axis, the aerial image of the measurement mark corresponding to each of the plurality of evaluation points is repeatedly measured. In this case, the controller keeps the distance between the pattern plate and the projection optical system constant and maintains the pattern plate and the image plane of the projection optical system parallel by servo control based on the detection results of the plurality of specific sensors. In this state, the pattern plate can be relatively scanned with respect to the aerial image of the measurement mark, so that high-accuracy aerial image measurement is performed for each evaluation point and at a plurality of positions in the optical axis direction.
[0050]
Then, based on the measurement result, that is, the measurement result of the aerial image at a plurality of positions in the optical axis direction for each evaluation point, the arithmetic unit detects the best focus position at each evaluation point, and based on the detection result. The image plane of the projection optical system is calculated by a predetermined calculation. That is, the best focus position at each evaluation point can be detected with high accuracy, and the image plane can be calculated with high accuracy based on the detection result. Therefore, according to the present invention, the image plane of the projection optical system can be detected in a short time and with high accuracy.
[0051]
In this case, as in the exposure apparatus according to claim 23, the arithmetic unit is configured to control each of the specific sensors individually corresponding to a detection point near each of the evaluation points obtained in the process of detecting the best focus position. The detection offset of each of the specific sensors may be calculated together based on the displacement amount of the detection origin from the image plane in the optical axis direction.
[0052]
The invention according to claim 24 is an exposure apparatus for transferring a device pattern onto a photosensitive object (W) via a projection optical system (PL), and irradiates the object with a detection light beam, and the detection light beam is irradiated on the object. A focus position detection system for receiving a reflected light beam from a detection point on the object by a sensor and detecting position information in the optical axis direction of the projection optical system at the detection point; and a table on which the photosensitive object is mounted An aerial image measurement device having a pattern plate integrally provided on the table and receiving light via a measurement pattern formed on the pattern plate to measure an aerial image; An inclination detection system capable of at least detecting an inclination with respect to a plane perpendicular to the optical axis; and a position in the optical axis direction of the pattern plate managed by using the focus position detection system, and the inclination detection system is used by using the inclination detection system. While controlling the inclination of the turn plate with respect to the surface orthogonal to the optical axis, the position of the pattern plate in the optical axis direction is changed to move the pattern plate integrally with the table in a plane orthogonal to the optical axis. And a control device for repeatedly measuring the spatial image of the measurement mark corresponding to each of the plurality of evaluation points in the field of view of the projection optical system; and detecting a best focus position at each of the evaluation points based on the measurement result; And an arithmetic unit for calculating the image plane of the projection optical system by a predetermined calculation based on the detection result.
[0053]
According to this, the control device uses the focus position detection system (regardless of whether or not it is a multi-point) to form a projection optical system of a pattern plate having a measurement pattern capable of measuring an aerial image in a part thereof. While managing the position in the optical axis direction, while controlling the inclination of the pattern plate with respect to a surface orthogonal to the optical axis using an inclination detection system, the position of the pattern plate in the optical axis direction is changed to change the position of the pattern plate. Is moved integrally with the table in a plane orthogonal to the optical axis to repeatedly measure the aerial images of the measurement marks corresponding to each of the plurality of evaluation points in the field of view of the projection optical system. In this case, the control device keeps the distance between the pattern plate and the projection optical system constant by servo control based on the detection result of one of the above-described focus position detection systems, and performs pattern control based on the detection result of the tilt detection system. The pattern plate can be scanned relative to the aerial image of the measurement mark while the plate and the image plane of the projection optical system are kept parallel, so high-precision aerial image measurement can be performed for each evaluation point and in the optical axis direction. Will be performed at multiple locations. In this case, the position of the detection point can be set in a region where the flatness of the pattern plate is good, thereby preventing a decrease in aerial image measurement accuracy due to poor flatness of the pattern plate surface. .
[0054]
The arithmetic unit detects the best focus position at each evaluation point based on the measurement result, that is, the measurement result of the aerial image at a plurality of positions in the optical axis direction for each evaluation point, and determines a predetermined focus position based on the detection result. Is calculated to calculate the image plane of the projection optical system. That is, the best focus position at each evaluation point can be detected with high accuracy, and the image plane can be calculated with high accuracy based on the detection result. Therefore, according to the twenty-fourth aspect, the image plane of the projection optical system can be detected in a short time and with high accuracy.
[0055]
In this case, as in the exposure apparatus according to claim 25, the tilt detection system supports a set of interferometers for detecting rotation angles of the table around two axes orthogonal to the optical axis, and a front table. It is possible to include any of a set of encoders that respectively detect displacements of the plurality of support points in the optical axis direction.
[0056]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of an exposure apparatus 100 according to one embodiment. The exposure apparatus 100 is a step-and-scan type scanning projection exposure apparatus, that is, a so-called scanning stepper.
[0057]
The exposure apparatus 100 holds an illumination system 10 including a light source and an illumination optical system, a reticle stage RST holding a reticle R as a mask, a projection optical system PL, and a wafer W as a photosensitive object to freely move in an XY plane. It has a movable wafer stage WST, a body BD on which a projection optical system PL and the like are mounted, and the like.
[0058]
The illumination system 10 includes a light source (not shown), a beam shaping optical system, an energy rough adjuster, an optical integrator (a fly-eye lens, a rod type (internal reflection type) integrator, a diffractive optical element, or the like), and an illumination system aperture stop plate. , A beam splitter, a relay optical system, a fixed reticle blind (all not shown), an illumination optical system including a movable reticle blind 12 (not shown in FIG. 1, see FIG. 2), and the like. The illumination system 10 uniformly forms a rectangular (for example, rectangular) slit-shaped illumination area IAR (defined by the opening of the fixed reticle blind) extending in the X-axis direction on the reticle R held on the reticle stage RST. Illuminate with illuminance distribution. The configuration of the illumination system similar to that of the present embodiment is disclosed in detail in, for example, JP-A-2000-260682.
[0059]
As the light source, a KrF excimer laser (oscillation wavelength 248 nm), an ArF excimer laser (oscillation wavelength 193 nm) or F ₂ A laser (oscillation wavelength: 157 nm) or the like is used. This light source is actually installed on a floor surface F in a clean room in which the exposure apparatus main body is installed, or on a room (service room) with a low degree of cleanness different from the clean room, and a drawing optical system (not shown) is provided. The illumination optical system is connected to the entrance end of the above-mentioned illumination optical system.
[0060]
2 and 3, for simplicity of explanation, the movable reticle blind 12 is shown as being disposed near the illumination system side with respect to the reticle R.
[0061]
The movable reticle blind 12 is controlled by the main controller 20 at the start and end of the scanning exposure, and further restricts the illumination area IAR to prevent unnecessary portions from being exposed. Further, in the present embodiment, the movable reticle blind 12 is also used for setting an illumination area when measuring an aerial image using an aerial image measurement device described later.
[0062]
The reticle stage RST floats above a reticle base 36 constituting a top plate portion of a second column 34, which will be described later, via an air bearing (not shown) provided on the bottom surface of the reticle base 36 via a clearance of about several μm, for example. Supported. On this reticle stage RST, reticle R is fixed by, for example, vacuum suction (or electrostatic suction). Here, reticle stage RST is two-dimensionally (X-axis direction, Y-axis) in a XY plane perpendicular to an optical axis AX of projection optical system PL described later by a reticle stage drive system (not shown) including a linear motor and the like. In the rotation direction (θz direction) around the Z-axis orthogonal to the direction and the XY plane, it can be driven minutely, and can be driven on the reticle base 36 at a scanning speed designated in the Y-axis direction.
[0063]
The reticle stage RST has a movement stroke in the Y-axis direction that allows the entire surface of the reticle R to cross at least the optical axis AX of the projection optical system PL. In the case of the present embodiment, the movers of the above-described linear motor are attached to one side and the other side (the near side and the near side in FIG. 1) of the reticle stage RST in the X-axis direction, respectively. The corresponding stators are respectively supported by support members (not shown) provided separately from the body BD. For this reason, the reaction force acting on the stator of the linear motor when the reticle stage RST is driven is transmitted (released) to the floor F of the clean room via those support members.
[0064]
A movable mirror 15 that reflects a laser beam from a reticle laser interferometer (hereinafter, referred to as a “reticle interferometer”) 13 fixed to a reticle base 36 is fixed on the reticle stage RST, and the XY of the reticle stage RST is fixed. The position in the plane (including the rotation in the θz direction, which is the rotation direction around the Z axis) is always detected by the reticle interferometer 13 with a resolution of, for example, about 0.5 to 1 nm. Here, a moving mirror having a reflecting surface orthogonal to the Y-axis direction and a moving mirror having a reflecting surface orthogonal to the X-axis direction are provided on the reticle stage RST. Although a reticle Y interferometer and a reticle X interferometer are provided, these are typically shown as a movable mirror 15 and a reticle interferometer 13 in FIG. Note that, for example, the end surface of reticle stage RST may be mirror-finished to form a reflection surface (corresponding to the reflection surface of movable mirror 15). Further, at least one corner cube type mirror may be used instead of the reflecting surface extending in the X-axis direction used for detecting the position of the reticle stage RST in the scanning direction (Y-axis direction in the present embodiment). Here, one of the reticle Y interferometer and the reticle X interferometer, for example, the reticle Y interferometer is a two-axis interferometer having two measurement axes, and the reticle stage RST is controlled based on the measurement value of the reticle Y interferometer. In addition to the Y position, rotation in the θz direction can be measured.
[0065]
The position information of reticle stage RST from reticle interferometer 13 is sent to main controller 20, and main controller 20 controls reticle stage RST via a reticle stage drive system based on the position information of reticle stage RST.
[0066]
The projection optical system PL is held below the reticle stage RST in FIG. 1 in a first column 32 forming a body BD. Here, the configuration of the body BD will be described.
[0067]
The body BD includes a first column 32 installed on a floor F of a clean room, and a second column 34 placed on the upper surface of the first column 32. The first column 32 includes four legs 37A to 37D (however, legs 37C and 37D on the back side of the drawing in FIG. 1 are not shown), and upper end surfaces of these legs 37A to 37D are provided at lower end surfaces thereof. The lens barrel base 38 is connected to each other and constitutes a ceiling of the first column 32.
[0068]
Each of the legs 37 </ b> A to 37 </ b> D includes an anti-vibration unit 39 installed on the floor surface, and a column 40 fixed to an upper portion of the anti-vibration unit 39. Micro vibrations from the floor F are insulated at the micro G level by the respective vibration isolating units 39, and are hardly transmitted to the lens barrel base 38. The lens barrel base 38 has a circular opening (not shown) formed substantially at the center thereof, and the projection optical system PL is inserted into the opening from above with the optical axis AX direction being the Z axis direction.
[0069]
A flange FLG is provided substantially at the center in the height direction of the lens barrel of the projection optical system PL, and the projection optical system PL is supported by the lens barrel base 38 via the flange FLG. On the upper surface of the barrel base 38, the lower ends of, for example, four legs 41A to 41D (however, legs 41C and 41D on the back side of the drawing in FIG. 1 are not shown) are fixed at positions surrounding the projection optical system PL. The above-mentioned reticle base 36 is placed on the upper portions of these legs 41A to 41D, and is horizontally supported. That is, the reticle base 36 and the four legs 41A to 41D supporting the reticle base constitute the second column 34.
[0070]
As the projection optical system PL, a double-sided telecentric reduction system is used here, and a refraction optical system including a plurality of lens elements arranged at predetermined intervals along the optical axis AX direction is used. The projection magnification of the projection optical system PL is, for example, 1/4 or 1/5. Therefore, when the illumination light IL from the illumination system 10 illuminates the slit-shaped illumination area IAR on the reticle R, the illumination light IL that has passed through the reticle R causes the circuit of the reticle R in the slit-shaped illumination area IAR to be illuminated. A reduced image (partially inverted image) of the pattern via the projection optical system PL is formed in an exposure area IA conjugate to the illumination area IAR on the wafer W having a surface coated with a photoresist.
[0071]
The wafer stage WST includes an XY stage 21 that moves within an XY two-dimensional plane, and a wafer table 54 as a table mounted on the XY stage 21.
[0072]
The XY stage 21 is freely driven along the upper surface of the stage base 16 in an XY two-dimensional plane (including θz rotation) by a drive system (not shown) such as a linear motor or a planar motor. The stage base 16 is also called a surface plate, and is installed on the floor F via a plurality of anti-vibration tables 43 in the present embodiment. That is, the stage base 16 has a configuration separated from the body BD that holds the projection optical system PL and the like.
[0073]
The wafer table 54 is supported at three points on the XY stage 21 by three Z position drive units 23 (however, the Z position drive unit on the back side of the paper is not shown). These Z-position drive units 23 are three actuators (for example, voice coil motors) 26 (for example, voice coil motors) that independently drive respective support points on the lower surface of the wafer table 54 in the optical axis direction (Z-axis direction) of the projection optical system PL. However, the actuator 26 on the back side of the paper surface in FIG. 1 is not shown), and three encoders 28 (in which, however, the driving amounts (displacement from the reference position) of the respective support points by the actuators 26 in the Z-axis direction are individually detected. (The encoder on the back side of the paper in FIG. 1 is not shown). Here, as each encoder 28, for example, a linear encoder of an optical type or a capacitance type is used. In the present embodiment, the actuator 26 causes the wafer table 54 to tilt the wafer table 54 with respect to the optical axis AX direction (Z-axis direction) and a plane orthogonal to the optical axis (XY plane), that is, the θx direction, which is a rotation direction about the X axis. A driving device that drives in the θy direction, which is the rotation direction around the Y axis, is configured. The detection signal (output signal) of each encoder 28 is supplied to main controller 20.
[0074]
Therefore, the wafer table 54 will be described as a single stage freely driven in six degrees of freedom of X, Y, and θz by a wafer stage drive system (not shown) controlled by the main controller 20.
[0075]
The wafer holder 25 is placed on the wafer table 54, and the wafer W is held by the wafer holder 25 by vacuum suction (or electrostatic suction).
[0076]
On the wafer table 54, a movable mirror 27 that reflects a laser beam from a wafer laser interferometer (hereinafter, referred to as “wafer interferometer”) 31 is fixed, and the wafer table 54 is fixed by the wafer interferometer 31 fixed to the body BD. The position in the XY plane of (wafer stage WST) is always detected with a resolution of, for example, about 0.5 to 1 nm.
[0077]
Here, actually, on the wafer table 54, there is a movable mirror having a reflecting surface orthogonal to the Y-axis direction, which is the scanning direction during scanning exposure, and a reflecting surface orthogonal to the X-axis direction, which is the non-scanning direction. A movable mirror is provided, and correspondingly, the laser interferometer is provided with an X laser interferometer for measuring the position in the X-axis direction and a Y laser interferometer for measuring the position in the Y-axis direction. These are representatively shown as a movable mirror 27 and a wafer interferometer 31. Note that, for example, the end surface of the wafer table 54 may be mirror-finished to form a reflection surface (corresponding to the reflection surface of the movable mirror 27). Further, the X laser interferometer and the Y laser interferometer are multi-axis interferometers having a plurality of measurement axes, and in addition to the X and Y positions of the wafer table 54, rotation (yaw (θz rotation which is rotation about the Z axis)) , Pitching (θx rotation around the X axis) and rolling (θy rotation around the Y axis) can also be measured. Therefore, in the following description, it is assumed that the wafer interferometer 31 measures the positions of the wafer table 54 in the X, Y, θz, θy, and θx directions of five degrees of freedom. Further, the multi-axis interferometer irradiates a laser beam onto a reflecting surface (not shown) provided on a body BD on which the projection optical system PL is mounted, via a reflecting surface provided on the wafer table 54 at an angle of 45 °. Alternatively, relative position information about the optical axis direction (Z-axis direction) of the projection optical system PL may be detected.
[0078]
The position information (or speed information) of the wafer table 54 is sent to the main controller 20, and based on the position information (or speed information), the stage controller (not shown) drives the XY stage 21 based on the position information (or speed information). The wafer stage WST (the XY stage 21 and the wafer table 54) is controlled via a system and a drive device.
[0079]
Further, inside the wafer table 54, a part of an optical system constituting the aerial image measuring device 59 used for measuring the optical characteristics of the projection optical system PL is arranged.
[0080]
Here, the configuration of the aerial image measurement device 59 will be described in detail. As shown in FIG. 2, the aerial image measurement device 59 includes a stage side component provided on the wafer table 54, that is, a relay including a reference plane member 58 including a slit plate 90 as a pattern plate, and lenses 84 and 86. An optical system, a mirror 88 for bending the optical path, a light guide 85 composed of an optical fiber, and a light transmitting lens 87, and a component outside the stage provided outside the wafer stage WST, that is, a light receiving lens 89 and light composed of a photoelectric conversion element. A sensor 24 and a signal processing circuit 42 (see FIG. 1) for the photoelectric conversion signal from the optical sensor 24 are provided.
[0081]
More specifically, the reference plane member 58 has a disk shape of a predetermined thickness as shown in FIG. 4A, and is a cylindrical member having an open bottom surface.
As shown in FIG. 2 and the like, the reference flat member 58 is in a state of closing a circular opening formed on the upper surface of the wafer table 54, and its upper surface is substantially flush with the wafer W vacuum-adsorbed to the wafer holder 25. Is fixed to the wafer table 54 in such a state as to be located at the position shown in FIG. The reference plane member 58 is made of synthetic quartz or glass made of fluorite or the like, which has high transmittance for ultraviolet pulse light such as KrF excimer laser light or ArF excimer laser light, and its upper wall has a slit plate 90. It has been. As shown in the plan view of FIG. 4B, the slit plate 90 is made of a circular light-receiving glass 82 and a light-shielding film made of an aluminum thin film having a circular opening at the center formed on the upper surface of the light-receiving glass 82. It is configured to include a reflective film 83 also serving as a film, and a light-shielding film 91 made of a chromium thin film formed so as to fill a circular opening at the center of the reflective film. The surface of each of the reflection film 83 and the light-shielding film 91 is set to have a very high flatness.
[0082]
In this case, for example, the reflective film 83 has a substantially rectangular shape with a length in the X-axis direction of 50 mm and a length in the Y-axis direction of 30 mm, and the central light-shielding film 91 has a diameter of, for example, about 4.5 mm. ing. As shown in FIG. 4B, the light-shielding film 91 has a slit-shaped first opening pattern (hereinafter, referred to as a “first slit”) having a predetermined width (2D) as a measurement pattern extending in the X-axis direction. 22y) and a slit-shaped second opening pattern (hereinafter, referred to as a “second slit”) 22x as a measurement pattern having a predetermined width (2D) that is elongated in the Y-axis direction and is formed by patterning. ing. Here, the predetermined width 2D is about the half pitch of a line-and-space pattern (hereinafter abbreviated as “L / S pattern”) with a duty ratio of 50% at the resolution limit, for example, 2D = 0.2 μm. Shall be. The chromium film is used because of the necessity of forming such fine slits. Note that, in the following description, the first slit 22y and the second slit 22x are collectively referred to as a slit 22.
[0083]
As shown in FIGS. 2 and 3, a mirror 88 that horizontally folds the optical path of an illumination light beam (image light beam) incident vertically downward through the slit 22 is interposed inside the wafer table 54 below the slit 22. A relay optical system (84, 86) including lenses 84, 86 is disposed. The incident end 85a is located at a position behind the optical path of the relay optical system (84, 86) where the illumination light beam relayed by a predetermined optical path length is collected, that is, at a position conjugate to the light receiving surface where the slit 22 is formed. The light guide 85 is arranged in the state. A light transmitting lens 87 for transmitting an illumination light beam guided by the light guide 85 to the outside of the wafer table 54 is fixed to an upper wall of the wafer table 54 so as to face the light emitting end 85 b of the light guide 85.
[0084]
A light receiving lens 89 having a larger diameter than the light transmitting lens 87 is disposed on the optical path of the illumination light beam sent out of the wafer table 54 by the light transmitting lens 87. The optical sensor 24 is disposed above the light receiving lens 89 at a position conjugate with the exit end 85b. The light receiving lens 89 and the optical sensor 24 are housed in a case 92 while maintaining a predetermined positional relationship. The case 92 is fixed to a side surface of a barrel of the projection optical system PL via a mounting member 93.
[0085]
As the optical sensor 24, a photoelectric conversion element (light receiving element) capable of detecting weak light with high accuracy, for example, a photomultiplier tube (PMT, photomultiplier) or the like is used. The signal processing circuit 42 (see FIG. 1) for the output signal of the optical sensor 24 is configured to include an amplifier, an A / D converter (a 16-bit resolution is usually used), and the like.
[0086]
As described above, the slits 22 are formed in the light-shielding film 91, but the following description will be made on the assumption that the slits 22 are formed in the slit plate 90 for convenience.
[0087]
According to the aerial image measuring device 59 configured as described above, when measuring a projection image (aerial image) of the measurement mark formed on the reticle R via the projection optical system PL, which will be described later, the projection optics When the slit plate 90 constituting the aerial image measurement device 59 is illuminated by the illumination light IL transmitted through the system PL, the illumination light IL transmitted through the slit 22 on the slit plate 90 is transmitted through the lens 84, the mirror 88, and the lens 86. , A light guide 85, and a light transmitting lens 87, and are led out of the wafer table 54. The light guided to the outside of the wafer table 54 is received by the optical sensor 24 via the light receiving lens 89, and a photoelectric conversion signal (light amount signal) P corresponding to the amount of received light is processed by the optical sensor 24. Output to main controller 20 via circuit 42.
[0088]
In the case of the present embodiment, the measurement of the projected image (spatial image) of the measurement mark is performed by the slit scan method. In this case, the light transmitting lens 87 moves with respect to the light receiving lens 89 and the optical sensor 24. become. Therefore, in the aerial image measurement device 59, the sizes of the light transmitting lens 87 and the light receiving lens 89 are set such that all light passing through the light transmitting lens 87 that moves within a predetermined range enters the light receiving lens 89. I have.
[0089]
As described above, in the aerial image measuring device 59, the slit plate 90, the lenses 84 and 86, the light guide 85, and the light transmitting lens 87 constitute a light deriving unit that guides light passing through the slit 22 to the outside of the wafer table 54. The light receiving lens 89 and the optical sensor 24 constitute a light receiving unit for receiving the light led out of the wafer table 54. In this case, the light guiding section and the light receiving section are mechanically separated. Then, only at the time of aerial image measurement, the light deriving unit and the light receiving unit are optically connected.
[0090]
That is, in the aerial image measurement device 59, since the optical sensor 24 is provided at a predetermined position outside the wafer table 54, the heat generation of the optical sensor 24 adversely affects the measurement accuracy of the laser interferometer 31 or the like. I can't. Further, since the outside and the inside of the wafer table 54 are not connected by a light guide or the like, the driving accuracy of the wafer table 54 is adversely affected as in the case where the outside and the inside of the wafer table 54 are connected by a light guide. Not even.
[0091]
Of course, if the influence of heat can be eliminated, the optical sensor 24 may be provided inside the wafer table 54.
[0092]
Returning to FIG. 1, the exposure apparatus 100 includes a light source whose on / off is controlled by the main controller 20, and forms a plurality of slits (or pinholes) toward the image plane of the projection optical system PL. An irradiation system 60a for irradiating the image forming light beam from the oblique direction with respect to the optical axis AX, and a light receiving system 60b for receiving the reflected light beam of the image forming light beam on the surface of the wafer W. An oblique incidence type multi-point focal position detection system (hereinafter, appropriately referred to as “multi-point AF system”) for detecting a position in the AX direction (Z-axis direction) and an inclination with respect to the XX plane is provided.
[0093]
FIG. 5 shows a processing drive unit that processes output signals of the multipoint AF system (60a, 60b) and the multipoint AF system (60a, 60b) and drives a parallel flat glass (plane parallel) described later. The configuration of 56 (see FIG. 1) is schematically shown. In FIG. 5, it is assumed that the best imaging plane of the projection optical system PL and the surface of the wafer W match.
[0094]
As shown in FIG. 5, the irradiation system 60a includes an optical fiber bundle 62, a condenser lens 64, a pattern forming plate 66, a lens 67, a mirror 68, an irradiation objective lens 70 including a reduction lens, and the like. The light receiving system 60b includes a light receiving objective lens 72 composed of a magnifying lens, a parallel plate glass 74, a rotational direction vibration plate 76, an imaging lens 77, a light receiving slit plate 78, and a light receiving device having a plurality of focus sensors as sensors. Device 80 and the like.
[0095]
Here, the above-mentioned respective parts constituting the irradiation system 60a and the light receiving system 60b will be described together with their operations. Illumination light having a wavelength that does not expose the photoresist on the wafer W, which is different from the exposure light, is guided from an unillustrated illumination light source via an optical fiber bundle 62. The illumination light emitted from the optical fiber bundle 62 illuminates the pattern forming plate 66 via the condenser lens 64.
[0096]
On this pattern forming plate 66, 49 slit-like opening patterns (not shown) are formed in a 7-by-7 matrix arrangement, and illumination light transmitted through each slit-like opening pattern of the pattern forming plate 66 is provided. The (image light flux of the aperture pattern) is projected onto the exposure surface of the wafer W via the lens 67, the mirror 68, and the irradiation objective lens 70, and the exposure surface of the wafer W has a total of 49 × 7 × 7 on the pattern forming plate 66. An image of the slit-shaped opening pattern is projected and formed. Here, actually, the image light flux of the aperture pattern from the irradiation system 60a is in a plane at 45 degrees with respect to the YZ plane and the XZ plane, from the direction inclined at a predetermined angle α with respect to the optical axis AX in the plane of the wafer W ( Alternatively, the light is irradiated onto the slit plate 90 or the reference mark plate surface (not shown).
[0097]
Therefore, in the vicinity of the rectangular exposure region IA having a predetermined area AS (AS is, for example, 25 mm × about 10 mm) on the surface of the wafer W, as shown in FIG. , A total of 49 images of the slit-shaped opening pattern inclined 45 degrees with respect to the X-axis and the Y-axis (hereinafter referred to as “slit images” or “detection points” as appropriate) S ₁₁ ~ S ₇₇ Are formed at intervals of, for example, 3.5 mm along the X-axis direction and at intervals of, for example, 3.5 mm along the Y-axis direction. These slit images S ₁₁ ~ S ₇₇ Reflected light from the surface of the wafer W advances in a direction inclined by a predetermined angle α symmetrically with respect to the optical axis AX with respect to the image light beam from the irradiation system 60a, and the light receiving objective lens 72, the parallel plate glass 74, The image is re-formed on the light receiving slit plate 78 disposed on the front side of the light receiver 80 via the directional diaphragm 76 and the imaging lens 77.
[0098]
More specifically, the slit image S ₁₁ ~ S ₇₇ A focus sensor (hereinafter referred to as “focus sensor D” for convenience) as a sensor including 49 photosensors such as photodiodes in a matrix of 7 rows and 7 columns corresponding to ₁₁ ~ D ₇₇ The light receiving slit plate 78 disposed on the front surface (the lower surface in FIG. 5) of the light receiver 80 has a focus sensor D. ₁₁ ~ D ₇₇ Are respectively formed so as to face each other, and the slit images S shown in FIG. 6 are respectively formed on these slits. ₁₁ ~ S ₇₇ Are re-imaged respectively. In the following description, when a plurality of focus sensors are collectively referred to, or when each focus sensor is described, it will be appropriately described as “focus sensor D”.
[0099]
Here, an oscillator (OSC.) 73 is built in the processing drive unit 56 as shown in FIG. 5, and the vibration in the rotational direction is transmitted through a vibrating device 91 driven by a drive signal from the oscillator 73. When a predetermined vibration is applied to the plate 76, the position of each re-formed image on the light receiving slit plate 78 vibrates in a predetermined direction (a direction orthogonal to the longitudinal direction of each slit of the slit plate 78). Thereby, the focus sensor D ₁₁ ~ D ₇₇ Are synchronously detected by the signal processing device 71 via the selection device 75 with the signal of the rotational vibration frequency. A large number of focus signals FS obtained by synchronous detection by the signal processing device 71 are supplied to the main control device 20. The configurations of the signal processing device 71 and the selection device 75 will be described later.
[0100]
The parallel flat glass 74 is configured to be rotatable within a certain angle range by a driving unit 81. Due to the rotation (tilt) of the parallel flat glass 74, the slit image S formed on the light receiving slit plate 78 is formed. ₁₁ ~ S ₇₇ Of the enlarged image (reflection slit image) is shifted in a direction orthogonal to the longitudinal direction of each slit on the slit plate 78. The shift of the vibration center with respect to each slit is equivalent to shifting the position of the wafer W in the Z-axis direction when the focus signal FS is determined to be in focus (zero point on an S-curve signal waveform described later). .
[0101]
In the present embodiment, the output ENS of a rotary encoder (not shown) provided in the rotation driving mechanism of the parallel flat glass 74 is supplied to the main controller 20. The main controller 20 performs a simple operation based on the output ENS of the rotary encoder. The rotation angle of the parallel plate glass 74 is calculated by performing the calculation. Such details are disclosed, for example, in JP-A-61-183928.
[0102]
The drive unit 81 is provided with an offset command value (OFS) from the main controller 20 as a drive signal. For example, the main controller 20 adjusts the detection offset of each focus sensor D of the multipoint AF system (60a, 60b) at the time of later-described calibration of the multipoint AF system (60a, 60b). Is given as a drive signal to the motor driver in the drive unit 81 to control the tilt amount (rotation angle θ) of the parallel flat glass 74.
[0103]
As is clear from the above description, in the case of the present embodiment, the slit image S which is a detection point on the wafer W ₁₁ ~ S ₇₇ And the focus sensor D on the light receiver 80 ₁₁ ~ D ₇₇ Are in a one-to-one correspondence, and information (focus information) of the Z position on the surface of the wafer W at the position of each slit image is obtained based on a focus signal FS output from each focus sensor D.
[0104]
The selection device 75 here includes a microprocessor, and the selection device 75 has a focus sensor D to which a reverse bias voltage is applied. ₁₁ , D ₁₂ …… D ₇₇ Are connected via a switch circuit (not shown). The signal processing device 71 is connected to the selection device 75 via n output lines. In the following description, a case where n = 12 will be described as an example.
[0105]
Based on a predetermined criterion, the selecting device 75 provides 49 focus sensors D to each of up to 12 output lines via a switch circuit. ₁₁ , D ₁₂ …… D ₇₇ By connecting any one of the above, the photoelectric conversion circuit of the focus sensor including at least a part of the output line is closed, and the output signal of the arbitrary focus sensor (the intensity of light received by the arbitrary focus sensor D The corresponding photocurrent is sent to the signal processing device 71 via a desired output line among the 12 output lines. That is, the selecting device 75 selects the maximum of 12 focus sensors from among the 49 focus sensors as described above, thereby substantially controlling the focus / leveling of the wafer W from the 49 focus sensors. For example, a maximum of 12 focus sensors, that is, detection points to be used, are selected.
[0106]
The signal processing device 71 includes twelve signal processing circuits connected to twelve output lines, respectively, and output circuits connected thereto. Each signal processing circuit has a built-in phase-locked detection circuit (PSD). An alternating-current signal having the same phase as the drive signal from the oscillator 73 is input to the PSD. Then, each signal processing circuit performs synchronous rectification (synchronous detection) on the signal from each output line with reference to the phase of the AC signal, thereby obtaining each slit image S on the wafer W. ₁₁ ~ S ₇₇ A focus signal (focal position detection signal) FS corresponding to the position (focus position) in the Z-axis direction at the location is generated. Then, the focus signal FS from the signal processing circuit is digitally converted by the output circuit, and is output to the main controller 20 as serial data.
[0107]
Incidentally, each focus signal FS is called a so-called S-curve signal, and becomes zero level when the center of each slit of the light receiving slit plate 78 coincides with the center of vibration of the reflected slit image from the wafer W, and the wafer W The signal is a positive level when the wafer W is displaced upward from the state, and is a negative level when the wafer W is displaced downward. Therefore, when no offset is added to each focus signal FS, main controller 20 detects the height position (position in the optical axis direction) of wafer W at which each focus signal FS is at zero level as a focal point. Will be.
[0108]
In addition, in the main controller 20, in addition to the movement of the wafer table 54 in the Z-axis direction via a wafer stage drive system (not shown) based on the focus signal FS from the light receiving system 60 b at the time of scanning exposure to be described later, etc. By controlling the two-dimensional tilt (ie, rotation in the θx and θy directions), that is, by controlling the movement of the wafer table 54 using the multipoint AF system (60a, 60b), the irradiation area of the illumination light IL is controlled. Autofocus (autofocusing) and autoleveling for substantially matching the image plane of the projection optical system PL and the surface of the wafer W within the (illumination area IAR) are executed.
[0109]
Further, in the exposure apparatus of the present embodiment, although not shown, an alignment mark (alignment mark) on the wafer W, the slit 22 on the reference plane member 58, or a reference mark on a reference mark plate (not shown) An off-axis alignment system for detecting the like is arranged on the side surface of the lens barrel of the projection optical system PL. As the alignment system, for example, a target band is irradiated with a broadband detection light beam that does not expose the resist on the wafer W, and an image of the target mark formed on the light receiving surface by reflected light from the target mark and an index (not shown) An image processing type FIA (Field Image Alignment) sensor that captures an image of the image using an image sensor (CCD or the like) and outputs an image signal of the image is used. In addition to the FIA system, a target mark is irradiated with coherent detection light to detect scattered light or diffracted light generated from the target mark, or two diffracted lights (for example, the same order) generated from the target mark. Of course, it is possible to use an alignment sensor for detecting by causing interference with each other alone or in an appropriate combination.
[0110]
The main controller 20 includes a workstation (or a microcomputer) and the like, and a signal processing circuit 42, a processing driver 56, and the like are connected to the main controller 20 as shown in FIG. As shown in FIG. 1, the main controller 20 includes a storage device 51 such as a hard disk, a pointing device such as a keyboard and a mouse, and an input / output device 30 including a display such as a CRT or a liquid crystal panel. It is attached.
[0111]
Next, the operation of the exposure process in the exposure apparatus 100 of the present embodiment will be briefly described.
[0112]
First, a reticle R is transported by a reticle transport system (not shown), and is held by suction on a reticle stage RST at a loading position. Next, the positions of wafer stage WST and reticle stage RST are controlled by main controller 20, and a projection image (spatial image) of a reticle alignment mark (not shown) formed on reticle R is read using aerial image measuring device 59. The measurement is performed as described later (see FIG. 3), and the projection position of the reticle pattern image is obtained. That is, reticle alignment is performed.
[0113]
Next, main controller 20 moves wafer stage WST such that aerial image measurement device 59 is located immediately below the alignment system, and slit 22 serving as a position reference of aerial image measurement device 59 is detected by the alignment system. You. Main controller 20 adjusts the projection position of the pattern image of reticle R and the alignment system based on the detection signal of the alignment system, the measurement value of wafer interferometer 31 at that time, and the projection position of the reticle pattern image obtained earlier. , Ie, the baseline amount of the alignment system.
[0114]
When the baseline measurement is completed, main controller 20 performs wafer alignment such as EGA (enhanced global alignment) disclosed in detail in, for example, Japanese Patent Application Laid-Open No. 61-44429, and performs wafer alignment on wafer W. The positions of all shot areas are determined. In this wafer alignment, a wafer alignment mark Mw of a predetermined sample shot of a plurality of shot areas on the wafer W is measured as described above using an alignment system (see FIG. 3). ).
[0115]
Next, main controller 20 moves wafer stage WST to the first position while monitoring position information from interferometers 31 and 13 based on the position information of each shot area on wafer W and the baseline amount obtained above. The reticle stage RST is positioned at the scanning start position while the reticle stage RST is positioned at the scanning start position (acceleration start position) for exposure of the shot area, and scanning exposure of the first shot area is performed.
[0116]
In other words, main controller 20 starts relative scanning of reticle stage RST and wafer stage WST in the opposite direction of the Y-axis direction, and when both stages RST and WST reach their respective target scanning speeds, reticle R by illumination light IL. Illuminated, and the scanning exposure is started. Prior to the start of the scanning exposure, the light emission of the light source is started, but the movement of each blade of the movable blind 12 constituting the reticle blind is controlled by the main controller 20 in synchronization with the movement of the reticle stage RST. The prevention of irradiation of the illumination light IL to the outside of the pattern area on the reticle R is the same as in a normal scanning stepper.
[0117]
In main controller 20, particularly during the above-described scanning exposure, moving speed Vr of reticle stage RST in the Y-axis direction and moving speed Vw of wafer stage WST in the X-axis direction are set to a speed ratio corresponding to the projection magnification of projection optical system PL. Reticle stage RST and wafer stage WST are synchronously controlled so as to be maintained.
[0118]
Then, the different areas of the pattern area of the reticle R are sequentially illuminated with the ultraviolet pulse light, and the illumination of the entire pattern area is completed, thereby completing the scanning exposure of the first shot area on the wafer W. Thereby, the circuit pattern of the reticle R is reduced and transferred to the first shot area via the projection optical system PL.
[0119]
When the scanning exposure of the first shot area is completed, a stepping operation between shots for moving wafer stage WST to a scanning start position (acceleration start position) for exposure of the second shot area is performed. Then, the scanning exposure of the second shot area is performed in the same manner as described above. Thereafter, the same operation is performed in the third shot area and thereafter.
[0120]
In this manner, the stepping operation between shots and the scanning exposure operation for shots are repeated, and the pattern of the reticle R is transferred to all shot regions on the wafer W by the step-and-scan method.
[0121]
Here, during the above-mentioned scanning exposure, the above-mentioned autofocus / autoleveling is performed using the above-mentioned focus sensors (60a, 60b).
[0122]
By the way, in order for the pattern of the reticle R and the pattern already formed in the shot area on the wafer W to be accurately overlapped during the above scanning exposure, the optical characteristics and the baseline of the projection optical system PL must be accurately adjusted. It is important that the measurement is performed and that the optical characteristics of the projection optical system PL are adjusted to a desired state. It is also important that the multi-point AF system (60a, 60b) is accurately adjusted in order to prevent the occurrence of exposure failure (for example, so-called color unevenness) due to defocus.
[0123]
In the present embodiment, the aerial image measurement using the aerial image measurement device 59 is performed at the time of measuring the optical characteristics and adjusting the multipoint AF system (60a, 60b). Therefore, hereinafter, the aerial image measurement by the aerial image measurement device 59 will be described in detail.
[0124]
FIG. 3 shows a state where the aerial image of the measurement mark formed on the reticle R is being measured using the aerial image measurement device 59. As the reticle R, a reticle R dedicated to aerial image measurement, a device reticle used for manufacturing a device in which a dedicated measurement mark is formed, or the like is used. Instead of these reticles, a fixed mark plate (also called a reticle fiducial mark plate) made of a glass material of the same material as the reticle is provided on the reticle stage RST, and a mark on which a measurement mark is formed is used. Is also good.
[0125]
Here, it is assumed that a measurement mark PM composed of an L / S pattern having periodicity in the Y-axis direction is formed at a predetermined location on the reticle R as shown in FIG. Further, as shown in FIG. 7A, the slit plate 90 of the aerial image measuring device 59 is formed with a slit 22 having a predetermined width 2D extending in the X-axis direction.
[0126]
In measuring the aerial image, the movable reticle blind 12 is driven by the main controller 20 via the blind driving device, and the illumination area of the illumination light IL of the reticle R is defined only in the measurement mark PM portion (see FIG. 3). . In this state, when illumination light IL is applied to reticle R, light (illumination light IL) diffracted and scattered by measurement mark PM is refracted by projection optical system PL, as shown in FIG. A spatial image (projection image) PM ′ of the measurement mark PM is formed on the image plane of the system PL. At this time, it is assumed that the wafer table 54 is set at a position where the aerial image PM 'is formed on the + Y side (or -Y side) of the slit 22 on the slit plate 90 of the aerial image measuring device 59. FIG. 7A is a plan view of the aerial image measurement device 59 at this time.
[0127]
Then, when main controller 20 drives wafer table 54 in the + Y direction as shown by arrow F in FIG. 7A via wafer stage drive system, slit 22 is moved relative to aerial image PM ′. Scanning along the Y-axis direction. During this scanning, the light (illumination light IL) passing through the slit 22 is received by the optical sensor 24 via the light guiding section in the wafer table 54 and the light receiving lens 89, and the photoelectric conversion signal is transmitted to the signal processing circuit 42. The power is supplied to the main controller 20 via the main controller 20. Main controller 20 measures the light intensity distribution corresponding to aerial image PM ′ based on the photoelectric conversion signal.
[0128]
FIG. 7B shows an example of a photoelectric conversion signal (light intensity signal) P obtained at the time of the aerial image measurement.
[0129]
In this case, the spatial image PM ′ is averaged due to the width (2D) of the slit 22 in the scanning direction (Y-axis direction).
[0130]
Accordingly, if the slit is p (y), the intensity distribution of the aerial image is i (y), and the observed light intensity signal is m (y), the intensity distribution i (y) of the aerial image and the observed intensity signal m The relationship of (y) can be expressed by the following equation (1). In the equation (1), the unit of the intensity distribution i (y) and the intensity signal m (y) is the intensity per unit length.
[0131]
(Equation 1)

[0132]
(Equation 2)

[0133]
That is, the observed intensity signal m (y) is a convolution of the slit p (y) and the intensity distribution i (y) of the aerial image.
[0134]
Therefore, from the viewpoint of measurement accuracy, the smaller the slit width 2D is, the better. When the PMT is used as the optical sensor 24 as in the present embodiment, the scanning speed is reduced even if the slit width is very small. If it takes time for the measurement, the amount of light (light intensity) can be detected. However, in reality, the scanning speed at the time of measuring the aerial image has a certain restriction from the viewpoint of throughput. Therefore, if the slit width 2D is too small, the amount of light transmitted through the slit 22 becomes too small, and the measurement is not performed. It will be difficult.
[0135]
According to the knowledge obtained by the inventor through simulations, experiments, and the like, the optimum value of the slit width 2D is about half the resolution limit pitch of the exposure apparatus (the pitch of the L / S pattern with a duty ratio of 50%). Since it was confirmed, in the present embodiment, it is set as such.
[0136]
As described above, on the slit plate 90, two types of slits having different measurement directions of the first slit 22y and the second slit 22x are provided. A corresponding measurement mark is used, and the slit plate 90 is scanned with respect to the aerial image so that the aerial image overlaps only the slit parallel to the direction of the projection image (aerial image) of the measurement mark.
[0137]
The above-described aerial image measurement device 59 and the aerial image measurement method using the same are described in a. Detection of the best focus position, b. Detection of the imaging position of the pattern image in the XY plane, c. It is used for baseline measurement of an alignment system.
[0138]
C. In exposure apparatus 100 of the present embodiment. Baseline measurement has already been described. B. Since the detection of the image forming position of the pattern image in the XY plane is not closely related to the present invention, the following a. The detection of the best focus position will be described.
[0139]
The detection of the best focus position is used, for example, for the purpose of detecting the best focus position of the projection optical system PL and detecting the best imaging plane (image plane).
[0140]
In the present embodiment, as an example, the best focus position of the projection optical system PL is detected as follows.
[0141]
To detect the best focus position, for example, a periodic pattern having a duty ratio of 50%, which is composed of a plurality of line patterns arranged at a predetermined pitch in a one-dimensional direction (here, the Y-axis direction) near the resolution limit, that is, a so-called Ronkey A reticle R in which a grating-like pattern is formed as a measurement mark PM is used.
[0142]
First, reticle R is loaded on reticle stage RST by a reticle loader (not shown). Next, main controller 20 positions measurement mark PM on reticle R at a predetermined point (here, on the optical axis of projection optical system PL) at which the best focus position is to be measured in the field of view of projection optical system PL. Reticle stage RST is moved as described above.
[0143]
Next, main controller 20 controls the drive of movable reticle blind 12 so as to irradiate illumination light IL only to measurement mark PM to define an illumination area. In this state, the main controller 20 irradiates the reticle R with the illumination light IL, and scans the wafer table 54 in the Y-axis direction using the aerial image measurement device 59 to scan the measurement mark PM Is performed by the slit scan method in the same manner as described above. At this time, the main controller 20 repeats a plurality of times while changing the position of the slit plate 90 in the Z-axis direction (that is, the Z position of the wafer table 54) at, for example, about 15 steps at a pitch of 0.1 μm. The intensity signal (photoelectric conversion signal) is stored in the internal memory. The step range is performed, for example, in a range around the design best focus position.
[0144]
Main controller 20 performs a Fourier transform on the light intensity signals stored in the internal memory as described above, and obtains a contrast, which is an amplitude ratio between the primary frequency component and the zero-order frequency component, as an evaluation amount. Since this contrast changes sensitively depending on the focus position, it is convenient to determine the best focus position from the intensity signal. In the main controller 20, as an example, the horizontal axis is a focus position (Z position), and the vertical axis is a plot of contrast value data obtained on a coordinate system for contrast, and the plot data is converted into an appropriate function ( The best focus position is obtained by fitting with a quadratic or higher order function, for example, a 4th to 6th order function, and calculating a Z position at which the function curve (hereinafter referred to as “contrast curve”) shows a peak value.
[0145]
Next, a method of adjusting the multipoint AF system performed by the exposure apparatus 100 of the present embodiment will be described in detail. The adjustment of the multi-point AF system is performed by the following a. ~ C. Is divided into three steps.
a. Optical adjustment (coarse adjustment) of multi-point AF system
b. Adjustment of offset between sensors (Fine adjustment of multi-point AF system)
c. Focus sensor surface calibration (management of temporal change of focus sensor surface)
[0146]
In the multipoint AF system (60a, 60b) as in the present embodiment, the detection point (slit image) S ₁₁ ~ S ₇₇ Focus sensor D corresponding to each ₁₁ ~ D ₇₇ It is necessary to accurately measure the relative distance (the amount of positional deviation in the Z-axis direction) of the detection origin from the best focus plane (best image plane) of the projection optical system PL.
[0147]
In the multipoint AF system (60a, 60b), the rotation direction diaphragm 76 is used as a modulator as described above, and the slit image S ₁₁ ~ S ₇₇ The amount of positional deviation of the reflected slit image with respect to each slit on the light receiving slit plate 78 is read as the Z position on the surface of the wafer W to perform focus measurement. For this reason, an offset corresponding to the positional deviation error of the reflection slit image is generated with respect to the mechanical origin. This is a phenomenon that always occurs in a multipoint AF system in which an optical system is shared by a plurality of focus sensors, and it is difficult to mechanically set the offsets of all focus sensors to zero.
[0148]
Further, an approximate plane of a plane formed by a set of detection origins of a plurality of focus sensors constituting the multipoint AF system (hereinafter, referred to as a “focus sensor plane”) is completely set as an approximate plane of an image plane of the projection optical system. It is ideal to make them coincide, but in reality there is some mechanical error.
[0149]
It is necessary to manage the various origin deviation components as described above as recordable data. The photoelectric focus sensor such as the multi-point AF system according to the present embodiment outputs a signal having a voltage value substantially proportional to the distance in the optical axis direction from the origin of the test surface. This is called an S-curve signal as described above, and if the relationship between the Z position and the voltage is measured in advance, the accurate Z position of the test surface can be measured from the voltage value. The origin shift of the Z position, that is, the amount of shift of the detection origin of each focus sensor D from the mechanical origin is converted into a storable data such as digital data as a residual offset, and is stored in the storage device connected to the main controller 20. If it is stored in the memory 51 or an internal memory, it is possible to manage the exact origin (detection offset) of each focus sensor.
[0150]
Before measuring the final detection offset of each focus sensor of the multipoint AF system, the image plane of the projection optical system PL is set within the capture range of the multipoint AF system (for example, within a range of about ± 10 μm around the origin). Need to be located. At the initial stage of the optical adjustment, the image plane is not always located within the capture range of each focus sensor of the multipoint AF system.
[0151]
For this reason, in the present embodiment, the main control device 20 determines one detection point S at the center of the multipoint AF system (60a, 60b). ₄₄ Using only the image plane of the projection optical system PL (in this case, the detection point S ₄₄ The best focus position). This is because, even in the case of a multi-point AF system, when the measurement is performed using only one detection point at the center, the capture range is changed to the neutral point (true The reason is that the focus can be set on the image plane of the projection optical system PL even if the optical adjustment is not performed precisely because it can be expanded to a range of about ± 50 μm centered on the origin).
[0152]
In the present embodiment, when performing the optical adjustment of the multipoint AF system, a part of the field of view of the projection optical system PL (a rectangular area (corresponding to the above-described illumination area IAR) that can be set by the opening of the fixed reticle blind) is used. A reticle (for convenience, called "reticle R1") on which measurement marks PM are formed corresponding to a plurality of evaluation points (including evaluation points on the optical axis) is used.
[0153]
Then, main controller 20 measures the best focus position at the evaluation point on the optical axis of projection optical system PL using aerial image measurement device 59 in the initial state where parallel plate glass 74 is set at an arbitrary inclination angle. Is attempted as follows.
[0154]
First, the reticle R1 is loaded on the reticle stage RST by a reticle loader (not shown). Next, in main controller 20, measurement mark PM (hereinafter, referred to as “PM” for identification) positioned at the center on reticle R1. ₁ The reticle stage RST is positioned so that the reticle stage RST coincides with the optical axis of the projection optical system PL.
[0155]
Next, the measurement mark PM corresponding to the first detection point on the optical axis of the projection optical system PL ₁ The drive area of the movable reticle blind 12 is controlled to define an illumination area so that only a portion is irradiated with the illumination light IL.
[0156]
In this state, main controller 20 irradiates reticle R with illumination light IL, and performs a spatial image measurement of measurement mark PM using slit image scanning device 59 with spatial image measuring device 59 in the same manner as described above. This process is repeated while changing the Z-axis position at 90 at a predetermined step pitch. At that time, main controller 20 detects detection point S ₄₄ Focus sensor D corresponding to ₄₄ Only through the selection device 75, and the focus sensor D ₄₄ The position of the slit plate 90 of the reference plane member 58 in the Z-axis direction is controlled based on only the detected value of The inclination of the slit plate 90, that is, the inclination of the wafer table 54 with respect to the XY plane orthogonal to the optical axis of the projection optical system PL is determined by the above-described wafer interferometer 31, more precisely, pitching and rolling of the wafer table 54, respectively. Based on measurement values of a pair of Y interferometers (functioning as a pitching interferometer) and X interferometers (functioning as a rolling interferometer) having a length measurement axis to be detected, a desired angle is set (for example, pitching). , So that the rolling becomes zero).
[0157]
Then, main controller 20 determines whether or not there is a Z position at which the contrast curve obtained in the same manner as described above has a peak value based on the measurement result of the aerial image, and when the determination is negative. Then, an appropriate offset command value (OFS) is given to the drive unit 81 as a drive signal, and the parallel flat glass 74 is driven to rotate by a predetermined amount, and the above-described best focus position is measured again. In this way, the main controller 20 repeats the measurement of the best focus position and the calculation of the contrast curve while rotating the parallel flat glass 74 by a predetermined amount, and when the peak value appears in the contrast curve, the peak value Z corresponding to the optical axis direction corresponding to ₁ And the position Z ₁ At the detection point S ₄₄ Is stored in the internal memory as the best focus position at the evaluation point on the optical axis of the projection optical system PL that substantially matches
[0158]
Next, measurement of the best focus position at a plurality of evaluation points in a partial area in the field of view of the projection optical system PL, that is, the aforementioned rectangular area (corresponding to the aforementioned illumination area IAR), that is, the image plane of the projection optical system PL Is performed using the aerial image measurement device 59, and the following two methods can be adopted as this method.
[0159]
<First image plane measurement method>
In main controller 20, measurement mark PM on reticle R1 corresponding to a second evaluation point in the field of view of projection optical system PL (hereinafter referred to as “PM ₂ The movable reticle blind 12 is drive-controlled so that the illumination light IL is irradiated only to the measurement mark PM portion only to the portion) to define the illumination region. In this state, the focus sensor D ₄₄ Alternatively, the position of the slit plate 90 in the Z-axis direction of the reference plane member 58 is controlled based on only the detection value of the focus sensor D corresponding to one detection point near the second evaluation point, and the inclination of the slit plate 90 is adjusted. Control is performed based on measurement values of a pair of Y interferometers (functioning as a pitching interferometer) and X interferometers (functioning as a rolling interferometer) that respectively detect pitching and rolling of the wafer table 54, and a slit scan method is used. Measurement mark PM ₂ Focus position Z at aerial image measurement and second evaluation point ₂ Is detected, and the result is stored in the internal memory.
[0160]
Thereafter, the main controller 20 repeats the measurement of the aerial image for the measurement mark PM and the detection of the best focus position of the projection optical system PL while changing the evaluation point in the field of view of the projection optical system PL in the same manner as described above. . When measuring the best focus position after the second evaluation point, main controller 20 determines the position Z calculated earlier. ₁ The aerial image measurement is performed while changing the Z position of the slit plate 90 at a predetermined step pitch in a range of a predetermined width on the + Z side and the −Z side around the center.
[0161]
Then, main controller 20 sets each best focus position Z obtained as described above. ₁ , Z ₂ , ..., Z _n , An approximate plane (and image plane shape) of the image plane of the projection optical system PL is calculated by performing predetermined statistical processing. At this time, it is also possible to calculate the field curvature separately from the image plane shape.
[0162]
The image plane of the projection optical system PL, that is, the best image formation plane is a plane composed of a set of best focus points at countless points at different distances from the optical axis (ie, countless points at different image heights). Therefore, the image plane shape and its approximate plane can be easily and accurately obtained by such a method.
[0163]
In the first image plane measuring method, when the flatness is deteriorated in the vicinity of the slit 22 of the reference plane member 58 (slit plate 90), it is necessary to perform focus measurement, management, and the like avoiding the position. There are advantages in the case. For example, resist tends to remain on the boundary between the light-shielding film (chrome film) 91 and the reflective film (aluminum film) 83 in FIG. 4B, but in such a case, the resist does not cover the boundary. Focus measurement can be performed using only one central detection point. On the other hand, as will be described later, when the slit plate 90 is used as a reference plane plate, it is important to prevent detection points (slit images) of the multipoint AF system from being applied to the chrome film portion. Therefore, even in the case described above, the detection point S ₄₄ In such a case, it is necessary to perform the above-described focus measurement and image plane measurement using a focus sensor (focus sensor) D corresponding to a detection point that does not overlap the boundary at a detection point in the vicinity thereof. is there.
[0164]
In the first image plane measurement method, the main controller 20 controls the slit plate 90 based on the outputs of the three (one set) encoders 28 in the driving device for driving the wafer table 54. The inclination may be controlled.
[0165]
<Second image plane measurement method>
The second image plane measuring method includes a focus sensor D corresponding to a detection point S located near each of a plurality of evaluation points in the field of view of the projection optical system PL, for example, at four corners and a center of the exposure area IA. 5 detection points S in total ₃₁ , S ₅₁ , S ₄₄ , S ₃₇ , S ₅₇ Focus sensor D individually corresponding to ₃₁ , D ₅₁ , D ₄₄ , D ₃₇ , D ₅₇ Is different from the above-described first image plane measuring method in that the position and inclination of the slit plate 90 in the Z-axis direction at the time of the above-described image plane measurement are controlled based on the measurement values of the focus sensor D. The other points are the same as those of the first image plane measuring method described above.
[0166]
Then, main controller 20 determines each best focus position Z obtained in this case as well. ₁ , Z ₂ , ..., Z _n , An approximate plane (and image plane shape) of the image plane of the projection optical system PL is calculated by performing predetermined statistical processing. If necessary, the field curvature may be calculated. The advantage of the second image plane measuring method will be described later.
[0167]
Next, main controller 20 adjusts the time so that the surface of slit plate 90 having the function of the reference plane plate is as parallel as possible to the approximate plane of the image plane of projection optical system PL obtained as described above. The tilt of the wafer table 54 is controlled via the stage drive system using the multi-point AF system (60a, 60b) in the adjusted state. Next, main controller 20 performs optical control of multipoint AF system (60a, 60b) while performing servo control using encoder 28 so that the Z position and tilt of wafer table 54 are maintained in this state. Make adjustments. In this optical adjustment, the surface of the slit plate 90 (focus sensor surface) formed by an approximate plane of the detection origin of a plurality of (in this case, up to 12) focus sensors D of the multipoint AF system (60a, 60b) is parallel. This is performed by adjusting the inclination angle of the parallel flat glass 74 via the drive unit 81 so that the detected offsets of the selected 12 focus sensors are averaged as much as possible.
[0168]
In the present embodiment, a plurality of measurement marks PM are formed on the reticle R1, and each measurement mark PM is sequentially irradiated with the illumination light IL by the movable reticle blind 12, and a projection optical system corresponding to each measurement mark is formed. Although the best focus position is detected in the PL evaluation area, the present invention is not limited to this, and the measurement marks PM may be arranged at a plurality of points where the best focus position is to be measured by moving the reticle. In this case, a reticle having only one measurement mark PM can be used. Further, a reference plate may be provided on reticle stage RST, and a plurality of measurement marks PM may be formed on the reference plate.
[0169]
b. Adjustment of offset between sensors (Fine adjustment of multi-point AF system)
The fine adjustment of this multi-point AF system is performed by the focus sensor D ₁₁ ~ D ₇₇ This is a process necessary to minimize relative measurement errors caused by individual differences and adjustment errors.
[0170]
In the fine adjustment of the multipoint AF system, a flat plate having good flatness, for example, the above-described slit plate 90, super flat wafer or wafer is set in a state parallel to an approximate plane of the image plane of the projection optical system PL. The relative offset of the measurement value between the plurality of focus sensors of the multi-point AF system is measured while maintaining the inclination of the flat plate. In the fine adjustment of the multipoint AF system, the staticity of the wafer table 54 on which a flat plate such as the slit plate 90 is mounted is important for the above-described offset measurement between sensors. For this reason, in the present embodiment, during the fine adjustment of the multipoint AF system, the wafer table 54 is controlled in the servo mode (focus servo mode) based on the measurement values of the multipoint AF system (60a, 60b). That is, in this focus servo mode, the servo values are compared while comparing the measurement values of a plurality of focus sensors selected from a plurality of focus sensors of the multipoint AF system (60a, 60b) with a target value (given detection offset). Since the control is performed, the attitude of the slit plate 90 with respect to the projection optical system PL is more stable than the case where the wafer table 54 is kept stationary (the attitude is kept constant) by only the pitching interferometer or the rolling interferometer described above. Can control.
[0171]
The main controller 20 controls, for example, five detection points in the field of view of the projection optical system PL, for example, the detection point S ₃₁ , S ₅₁ , S ₄₄ , S ₃₇ , S ₅₇ Focus sensor D individually corresponding to ₃₁ , D ₅₁ , D ₄₄ , D ₃₇ , D ₅₇ A detection offset required to make the slit plate 90 parallel to the approximate plane of the image plane of the projection optical system PL is given as a target value to each of them, and their focus sensors D ₃₁ , D ₅₁ , D ₄₄ , D ₃₇ , D ₅₇ While the servo of the position of the slit plate 90 is servo-controlled using, the detection offsets (measured values) of the remaining 44 focus sensors D not used for the servo control are fetched, and those values are stored in the internal memory. At this time, the focus sensor D used for servo control ₃₁ , D ₅₁ , D ₄₄ , D ₃₇ , D ₅₇ The detection offset to be given as the target value of the above is measured by performing the same measurement as the above-described first and second image plane measuring methods again after the optical adjustment of the multi-point AF system (60a, 60b). Is possible.
[0172]
However, for example, when the image plane measurement is performed by the above-described second image plane measurement method, the selected focus sensor with respect to the best focus position at the evaluation point near the selected focus sensor obtained at that time. D ₃₁ , D ₅₁ , D ₄₄ , D ₃₇ , D ₅₇ Can be used as it is. In other words, in the above-described step of optical adjustment of the multipoint AF system, that is, in the above-described second image plane measurement method, at the time of the image plane measurement, the adjustment of the inter-sensor offset performed subsequently is performed. In this case, there is a great merit that a focus offset value to be given to each focus sensor at the time of focus servo can be obtained at that stage. In this sense, in the optical adjustment process of the multi-point AF system, it is preferable to employ the above-described second image plane measurement method in terms of shortening the adjustment time.
[0173]
When the measurement of the detection offsets of the 44 focus sensors D individually corresponding to the above-mentioned 44 detection points is completed, the main control device 20 sets the detection points out of the 44 focus sensors D as near as possible. The focus sensors D individually corresponding to a plurality of points, for example, six detection points S located in the section, are selected, and the focus value is measured while comparing the measured values of the focus sensors D with a target value (the detection offset detected above). The slit plate 90 is controlled in the servo mode, the detection offsets of the five focus sensors used in the focus servo mode are measured again, and the results are stored in the internal memory. Thus, the fine adjustment of the multipoint AF system (60a, 60b) is completed.
[0174]
Here, the method of measuring and adjusting the inter-sensor offset by the focus servo performed by the exposure apparatus 100 of the present embodiment is not limited to the controllability of the wafer table 54 but also from the viewpoint of eliminating the influence of air fluctuation. Very effective. The reason is that the plurality of focus sensors D have their detection points S separated by at most about 20 mm at the same time, and the corresponding focus sensors are also arranged at positions close to each other. This is because the influence on the focus sensor D is substantially uniform between the sensors, and the air fluctuation has been canceled from the measured value by the focus servo.
[0175]
In the exposure apparatus 100 of the present embodiment, the multi-point AF system (60a, 60b) adjusted according to the above procedure is used to perform the above-described auto-focusing and auto-leveling during the above-described scanning exposure, for example. Therefore, it is possible to form a high-accuracy reticle pattern transfer image on a wafer without color unevenness due to defocus.
[0176]
In addition, the image plane shape and the field curvature of the projection optical system PL measured by using the aerial image measurement device 59 by the above-described method are accurately measured, and based on the measurement result, the main controller 20 executes the projection optical system. The optical characteristics of the system PL are accurately adjusted via an adjustment device (not shown). Since the above-mentioned scanning exposure is performed using the projection optical system PL whose optical characteristics have been adjusted, it is possible to accurately overlap the reticle pattern with the pattern already formed in the shot area on the wafer W. Become.
[0177]
c. Focus sensor surface calibration (management of changes over time on the focus sensor surface)
The projection exposure apparatus such as the exposure apparatus 100 absorbs illumination light applied to the projection optical system in use, changes the atmospheric pressure of the installation environment, and other fluctuation factors. For example, it is known that the image plane shape and the image plane inclination change with time. In such a case, it is necessary to monitor such changes in the image plane shape and image plane inclination, and to adjust the multipoint AF system (60a, 60b), that is, to perform focus sensor plane calibration accordingly. is there.
[0178]
In addition, when the aerial image measurement device 59 is provided as in the exposure apparatus 100 of the present embodiment, calibration of the image plane tilt and the focus sensor surface is performed for various measurements using the aerial image measurement. It is important to calibrate the focus sensor surface due to a temporal change such as a surface inclination. The reason is as follows.
[0179]
When measuring an aerial image such as aerial image position measurement, the slit 22 is scanned with respect to the aerial image in an approximate plane of the image plane or in a plane parallel to the image plane and separated by a predetermined distance in the optical axis direction (target scanning plane). . In this case, if the relative distance in the optical axis direction between the image plane and the slit changes, the influence of aberration changes, and as a result, the measurement result of the aerial image will be different. This is because it is necessary to accurately scan the slit 22 (slit plate 90) in the target scanning plane.
[0180]
When the measurement of the best focus position using the aerial image measurement device 59 is performed for a plurality of evaluation points in the field of view of the projection optical system PL by the above-described method, an approximate surface of the image plane is obtained based on the measurement result. As a result, the relative inclination between the approximate surface and the focus sensor surface is obtained.
[0181]
Even when the optical characteristics of the projection optical system PL change with time due to some cause, the change with time can be monitored by measuring the image plane shape using the above-described aerial image measurement or an approximate plane of the image plane. . When a change with time is detected, it is necessary to measure again the detection offsets of the plurality of focus sensors of the multipoint AF system (60a, 60b) and update the previously measured offset value.
[0182]
Although the detection offset measurement of the focus sensor using the measurement of the best focus position of the measurement mark using the aerial image measurement device 59 may be executed for all the detection points of the multipoint AF system (60a, 60b), the present embodiment In the exposure apparatus 100, calibration of the focus sensor surface is performed periodically or as needed as follows.
[0183]
That is, the main controller 20 uses the aerial image measurement device described above at three or more identical evaluation points (each evaluation point exists near the detection point of the multipoint AF system) in the field of view of the projection optical system PL. The relative angle between the focus sensor surface and the image plane of the projection optical system PL (or an approximate plane thereof) is obtained by executing the above-described second image plane measurement method in which the best focus position is measured using the 59. Monitoring changes.
[0184]
FIG. 8 shows, as an example, five detection points S in the visual field. ₃₁ , S ₅₁ , S ₄₄ , S ₃₇ , S ₅₇ Focus sensor D individually corresponding to ₃₁ , D ₅₁ , D ₄₄ , D ₃₇ , D ₅₇ Of the focus sensor surface FP constituted by the detection origin of ₃₁ , S ₅₁ , S ₄₄ , S ₃₇ , S ₅₇ Relationship between the approximate plane IP of the image plane of the projection optical system PL obtained based on the respective neighboring spatial image contrast curves AC and the approximate plane IP 'of the image plane of the projection optical system PL obtained in the same manner as described above. Is schematically shown.
[0185]
When the angle change of the image plane IP of the projection optical system PL from the focus sensor plane FP is thus measured, as schematically shown in FIG. As schematically shown in FIG. 9, the correction value of the detection offset of each focus sensor from the change in the angle (the black arrow CV in FIG. 9) _{p, q} 9), and the correction value is used as the original detection offset (white arrow OF in FIG. 9). _{p, q} ) To obtain a new detection offset. By doing so, the focus sensors D individually corresponding to all the detection points of the multi-point AF system (60a, 60b) by aerial image measurement at least three evaluation points in the field of view of the projection optical system PL. ₁₁ ~ D ₇₇ , The detection offset (focus offset) can be updated, and the measurement of the best focus position of the measurement mark using the aerial image measurement device 59 for all the detection points of the multipoint AF system (60a, 60b) is used. Calibration of the focus sensor surface can be performed in a shorter time and with the same accuracy as compared with the case where the detection offset measurement of the focus sensor is performed.
[0186]
By the way, in order to accurately measure the image plane shape of the projection optical system PL, it is necessary to measure the aerial image at an arbitrary evaluation point within the field of view of the projection optical system PL and the position of the slit plate 90 in the optical axis direction at the time of the measurement. Measurement must be performed accurately. For this purpose, it is desirable that the flatness of the surface of the slit plate 90 is as high as possible, and the attitude of the slit plate 90 should always be controlled by the focus servo during scanning of the slit plate 90.
[0187]
However, at the center of the slit plate 90, there is a light-shielding film 91 made of the chromium film described above, and the flatness is particularly deteriorated at the boundary between the light-shielding film 91 and the surrounding reflection film 83.
[0188]
Therefore, in the present embodiment, when measuring the image plane shape itself, the main controller 20 selects a focus sensor having the detection point at the above-described boundary via the selector, and the slit plate 90 in the focus servo mode. A scanning algorithm is employed.
[0189]
As described above, in the present embodiment, the combination of the multi-point AF system (60a, 60b) and the aerial image measurement device 59 having the slit plate 90 also serving as the reference plane plate is employed to perform the above-described image plane measurement and the like. By doing so, the relative position between the image plane of the projection optical system PL and the slit 22 can be accurately managed.
[0190]
Note that such measurement is difficult before the optical adjustment of the multi-point AF system (60a, 60b), but once adjusted, the control of the wafer table 54 in the focus servo mode described above is performed for any measurement. It is desirable to do.
[0191]
As is clear from the above description, in the present embodiment, a control device, a detection device, and a calculation device are configured by the main control device 20, and a measurement device is configured by the aerial image measurement device 59 and the main control device 20, The wafer interferometer 31 and the main controller 20 constitute an inclination detection system. However, the present invention is not limited to this. For example, all or a part of each component of the control device, the detection device, the arithmetic device, and the like configured by the main control device 20 may be configured by a plurality of hardware.
[0192]
As described above in detail, according to the exposure apparatus 100 of the present embodiment, detection of each focus sensor is performed for adjustment of the multipoint AF system (60a, 60b), for example, offset adjustment of the detection origin of a plurality of focus sensors. When measuring the positional relationship between the origin and the image plane of the projection optical system PL, an aerial image measurement can be performed on a part of an object irradiated with a plurality of detection light beams from the irradiation system 60a of the multipoint AF system. A reference plane member 58 having the slit 22 and having a high flatness on the surface is used. Therefore, the aerial image measurement using the reference plane member 58 enables the measurement of the image plane of the projection optical system PL as described above. Further, at the time of offset measurement of the detection origins of the plurality of focus sensors, the reference plane member 58 (more precisely, the slit plate 90) is positioned on the image plane of the projection optical system PL using a multipoint AF system. , The offset measurement can be performed with high accuracy. Therefore, high-precision adjustment of the multipoint AF system (60a, 60b) can be performed in a short time without performing resist coating, exposure, development, and the like.
[0193]
More specifically, according to the exposure apparatus 100 of the present embodiment, in the adjustment of the multi-point AF system (60a, 60b), particularly, in the above-described fine adjustment, the main controller 20 controls the plurality of detections of the multi-point AF system. Point S ₁₁ ~ S ₇₇ Of the detection points (for example, the detection point S ₃₁ , S ₃₇ , S ₄₄ , S ₅₁ , S ₅₇ ), The position of the surface of the reference plane member 58 (slit plate 90), which is the object to be detected, in the optical axis direction of the projection optical system PL is detected, and the surface of the reference plane member 58 is previously adjusted, for example, by the above-described optical system adjustment The position of the wafer table 54 on which the reference plane member 58 is mounted is controlled so as to coincide with the known image plane of the projection optical system PL measured in the process, and is individually set for the remaining detection points excluding some detection points. Is detected as the detection offset of the focus sensor corresponding to the detection origin of each focus sensor from the surface of the reference plane member 58, that is, the image plane of the projection optical system PL (an approximate plane thereof) in the optical axis direction. For this reason, in a state where the reference plane member 58 (slit plate 90) is stably aligned with the image plane of the projection optical system PL, the detection offsets of the remaining focus sensors not used for position control are accurately detected. It is possible to ask.
[0194]
Further, after detecting the detection offset, the main controller 20 uses at least a part of the focus sensor individually corresponding to the remaining detection points to determine the position of the surface of the reference plane member 58 at the corresponding detection point in the optical axis direction. While controlling the position of the wafer table 54 so that the surface of the reference plane member 58 coincides with the known image plane of the projection optical system PL. The amount of positional deviation in the optical axis direction from the surface of the reference plane member 58 at the detection origin, that is, from (the approximate plane of) the image plane of the projection optical system PL, is detected as the corresponding detection offset of the focus sensor. Thereby, the detection offsets of all the focus sensors of the multi-point AF system (60a, 60b) can be obtained with high accuracy.
[0195]
In this case, instead of the reference plane member 58, a super flat wafer, a reference plane plate having no slit 22, or a wafer for manufacturing a device can be used as an object to be detected by the multipoint AF system. is there.
[0196]
Further, according to the exposure apparatus 100 of the present embodiment, when adjusting the multi-point AF system, in particular, when calibrating the focus sensor surface, the main controller 20 determines the detection origin of the plurality of sensors of the multi-point AF system (60a, 60b). The change in the angle between the approximate plane (focus sensor plane) formed from the set of the optical axis and the approximate plane of the image plane of the projection optical system PL is detected. Next, main controller 20 calculates a correction value of the detection offset of each of the focus sensors based on the detected change in the angle, and calculates the correction value of the detection offset of the corresponding focus sensor detected in advance. To obtain a new detection offset. For this reason, when the image plane of the projection optical system PL changes with time, it is possible to simply and accurately correct the detection offset of the focus sensor in accordance with the change with time of the image plane. In this case, the change in the angle formed between the focus sensor surface and the image plane is determined by the main controller 20 using the aerial image measurement device 59 for at least three evaluation points in the field of view of the projection optical system. The best focus position is detected by using the above method. Therefore, it is possible to adjust the detection offsets of all the focus sensors without measuring the best focus positions at all the detection points. Accordingly, highly accurate adjustment of the multipoint AF system can be performed in a short time.
[0197]
In addition, according to the exposure apparatus 100 of the present embodiment, when the aerial image is measured using the aerial image measurement device 59 for the image plane measurement and the detection of the best focus position, for example, the main control device 20 The surface of the slit plate 90 provided integrally on the wafer table 54 and the projection optical system based on the detection results of at least some of the plurality of specific focus sensors among the plurality of focus sensors of the point AF system (60a, 60b). While controlling the position and orientation of the slit plate 90 so that the distance and the relative angle between the approximate plane of the image plane of the PL and the approximate plane become desired values, the slit plate 90 is integrated with the wafer table 54 by the light of the projection optical system. It moves on a plane perpendicular to the axial direction. In this case, the distance between the slit plate 90 and the projection optical system PL is kept constant by servo control (focus servo control) based on the detection results of the plurality of specific focus sensors of the multipoint AF system (60a, 60b), and the slit plate Since the slit plate 90 can be relatively scanned with respect to the aerial image while the image plane of the projection optical system PL and the image plane of the projection optical system PL are kept parallel, the aerial image measurement can be performed with high accuracy.
[0198]
In this case, in the main control device 20, a focus sensor corresponding to a detection point located at a position where the flatness of the surface of the slit plate 90 is good among the plurality of detection points is selected as the specific focus sensor via the selection device. You can choose. For this reason, at the time of the above-described focus servo control, it is possible to keep the slit plate 90 exactly parallel to the image plane of the projection optical system PL.
[0199]
In the exposure apparatus 100 of the present embodiment, for example, when executing the above-described second image plane measurement method, the main controller 20 sets the evaluation selected for each of a plurality of evaluation points in the visual field of the projection optical system PL. The position and orientation of the slit plate 90 in the optical axis direction of the projection optical system PL are controlled based on the detection results of the plurality of specific focus sensors respectively corresponding to the detection points near the point, and the position and orientation of the slit plate 90 in the optical axis direction of the slit plate 90 are controlled. By changing the position, the slit plate 90 is moved in a plane orthogonal to the optical axis, and the aerial image of the measurement mark PM corresponding to each of the plurality of evaluation points is repeatedly measured. In this case, main controller 20 scans slit plate 90 relative to the aerial image of the measurement mark while maintaining the interval and inclination of slit plate 90 with projection optical system PL constant by the focus servo control. Therefore, highly accurate aerial image measurement is performed for each evaluation point and at a plurality of positions in the optical axis direction. Then, based on the measurement result, that is, the measurement result of the aerial image at a plurality of positions in the optical axis direction for each evaluation point, main controller 20 detects the best focus position at each evaluation point, and The image plane of the projection optical system PL is calculated by a predetermined calculation based on the calculation. Therefore, the image plane of the projection optical system can be accurately detected in a short time.
[0200]
Further, according to the exposure apparatus 100 of the present embodiment, for example, when the above-described first image plane measuring method is performed, the main controller 20 uses the multipoint focal position detection system (60a, 60b) to control the slit plate 90. The position of the projection optical system in the optical axis direction is managed by one arbitrary detection point (a detection point in a region where the flatness of the pattern plate is good, for example, a detection point on the optical axis), and an inclination detection system, for example, Using a pitching interferometer and a rolling interferometer, the slit plate 90 is integrated with the wafer table 54 by changing the position of the slit plate 90 in the optical axis direction while controlling the inclination of the slit plate 90 with respect to a plane perpendicular to the optical axis. It moves in a plane perpendicular to the optical axis and repeatedly measures the aerial image of the measurement mark corresponding to each of the plurality of evaluation points in the field of view of the projection optical system PL. In this case, main controller 20 keeps the distance between slit plate 90 and projection optical system PL constant by servo control based on the detection result of one focus sensor of the multipoint focus position detection system, and detects the inclination detection system. The slit plate 90 can be relatively scanned with respect to the aerial image of the measurement mark while the slit plate 90 and the image plane of the projection optical system PL are kept parallel based on the result. This is performed at a plurality of positions in the optical axis direction for each evaluation point. Then, main controller 20 detects the best focus position at each evaluation point based on the measurement result, that is, the measurement result of the aerial image at a plurality of positions in the optical axis direction for each evaluation point, and based on the detection result. The image plane of the projection optical system is calculated by a predetermined calculation. Therefore, the image plane of the projection optical system PL can be accurately detected in a short time. In the first image plane measurement method, the focus position detection system does not necessarily have to be a multipoint AF system.
[0201]
Further, the exposure apparatus 100 of the present embodiment uses the multi-point AF system (60a, 60b) adjusted in the above-described procedure, for example, during the above-described scanning exposure or the like, to perform the above-described autofocus / autoleveling. Is performed, it is possible to form a high-accuracy reticle pattern transfer image on a wafer without color unevenness due to defocus. Further, based on the measurement results such as the image plane shape and the field curvature of the projection optical system PL measured using the aerial image measurement apparatus 59 by the above-described method, the main control device 20 changes the optical characteristics of the projection optical system PL. Since the exposure is adjusted with high precision via an adjustment device (not shown) and the scanning exposure is performed using the adjusted projection optical system PL, the reticle pattern and the pattern already formed in the shot area on the wafer W can be accurately determined. It becomes possible to overlap.
[0202]
In the above-described embodiment, the case where the present invention is applied to the step-and-scan type projection exposure apparatus has been described. However, the present invention is not limited to this. The present invention can also be applied to a step-and-repeat type exposure apparatus that transfers a substrate and sequentially moves a substrate.
[0203]
Further, in the above embodiment, the case where the present invention is applied to an exposure apparatus for manufacturing a semiconductor has been described. However, the present invention is not limited to this. For example, a liquid crystal display element pattern is transferred onto a square glass plate. For manufacturing exposure devices, display devices such as plasma displays and organic ELs, exposure devices that transfer device patterns used in the manufacture of thin-film magnetic heads onto ceramic wafers, and imaging devices (such as CCD), micromachines, and DNA chips. The present invention can also be applied to an exposure apparatus used. In addition to micro devices such as semiconductor elements, glass substrates or silicon wafers for manufacturing reticles or masks used in light exposure equipment, EUV exposure equipment, X-ray exposure equipment, electron beam exposure equipment, etc. The present invention can also be applied to an exposure apparatus that transfers a circuit pattern to a substrate. Here, in an exposure apparatus using DUV (far ultraviolet) light or VUV (vacuum ultraviolet) light, a transmission type reticle is generally used, and as a reticle substrate, quartz glass, fluorine-doped quartz glass, fluorite, Magnesium fluoride, quartz, or the like is used. In a proximity type X-ray exposure apparatus, an electron beam exposure apparatus, or the like, a transmission mask (stencil mask, membrane mask) is used, and a silicon wafer or the like is used as a mask substrate.
[0204]
In the above embodiment, the light source is an ultraviolet light source such as a KrF excimer laser light source. ₂ A pulsed laser light source in the vacuum ultraviolet region such as a laser or an ArF excimer laser is used. ₂ Another vacuum ultraviolet light source such as a laser light source (output wavelength 126 nm) may be used. Further, for example, not only the laser light output from each of the above light sources as vacuum ultraviolet light, but also a single-wavelength laser light in the infrared or visible range oscillated from a DFB semiconductor laser or a fiber laser may be used, for example, erbium (Er). A harmonic wave amplified by a fiber amplifier (or both erbium and ytterbium (Yb)) doped and wavelength-converted to ultraviolet light using a nonlinear optical crystal may be used.
[0205]
Further, in the above embodiment, the case where the reduction system and the refraction system are used as the projection optical system has been described. However, the present invention is not limited to this, and an equal magnification or enlargement system may be used as the projection optical system. Either a system or a reflection system may be used.
[0206]
The illumination optical system composed of a plurality of lenses and the projection optical system PL are incorporated in the main body of the exposure apparatus to perform optical adjustment, and a reticle stage RST and a wafer stage WST including a large number of mechanical parts are attached to the main body of the exposure apparatus and wired. The exposure apparatus 100 of the present embodiment can be manufactured by connecting the pipes and pipes and further performing overall adjustment (electric adjustment, operation confirmation, and the like). It is desirable that the manufacture of the exposure apparatus be performed in a clean room in which the temperature, cleanliness, and the like are controlled.
[0207]
Further, in the semiconductor device, a step of designing the function and performance of the device, a step of manufacturing a reticle based on this design step, a step of manufacturing a wafer from a silicon material, and a step of forming a reticle pattern by the exposure apparatus 100 of the above-described embodiment. It is manufactured through a step of transferring to a wafer, a step of assembling a device (including a dicing step, a bonding step, and a package step), an inspection step, and the like.
[0208]
【The invention's effect】
As described above, according to the respective adjustment methods of the first to sixth aspects, there is an effect that highly accurate adjustment of the multipoint focal position detection system can be performed in a short time.
[0209]
Further, according to each of the aerial image measurement methods described in claims 7 to 9, there is an effect that a highly accurate aerial image measurement can be performed.
[0210]
Further, according to each of the image plane measuring methods according to the tenth to thirteenth aspects, there is an effect that the image plane of the projection optical system can be detected accurately in a short time.
[0211]
According to each of the exposure apparatuses according to the fourteenth to eighteenth aspects, there is an effect that highly accurate adjustment of the multipoint focal position detection system can be performed in a short time.
[0212]
According to each of the exposure apparatuses according to the nineteenth to twenty-first aspects, there is an effect that a highly accurate measurement of an aerial image becomes possible.
[0213]
Further, according to each of the exposure apparatuses according to the twenty-second to twenty-fifth aspects, there is an effect that the image plane of the projection optical system can be accurately detected in a short time.
[Brief description of the drawings]
FIG. 1 is a view schematically showing a configuration of an exposure apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram showing an internal configuration of the aerial image measuring device of FIG.
FIG. 3 is a diagram illustrating a state in which a spatial image of a measurement mark PM on a reticle is measured using a spatial image measuring device.
FIG. 4A is a perspective view showing a reference plane member, and FIG. 4B is a plan view of the reference plane member.
FIG. 5 is a diagram schematically illustrating a configuration of a focus position detection system and a processing drive unit that processes an output signal of the focus position detection system and drives a plane parallel.
FIG. 6 is a diagram illustrating a positional relationship between an arrangement of a slit image, which is a detection point of the multipoint AF system, and an exposure area.
FIG. 7A is a plan view showing an aerial image measuring device in a state where an aerial image PM ′ is formed on a slit plate at the time of aerial image measurement, and FIG. FIG. 7 is a diagram showing an example of a photoelectric conversion signal (light intensity signal) P obtained at this time.
FIG. 8 shows a focus sensor surface FP constituted by detection origins of focus sensors individually corresponding to five detection points in a visual field, and an aerial image contrast curve AC for evaluation points near each of the five detection points. FIG. 4 is a diagram schematically showing a relationship between an approximate plane IP of the image plane of the projection optical system PL calculated based on the above and an approximate plane IP ′ of the previous image plane.
FIG. 9 shows a correction value CV of a detection offset of each focus sensor based on a change in an angle of an image plane IP of the projection optical system PL from the focus sensor plane FP. _{p, q} And the original detection offset OF _{p, q} FIG. 9 is a diagram schematically showing a state in which a new detection offset is calculated by adding.
[Explanation of symbols]
20: Main control unit (control unit, detection unit, arithmetic unit, part of measurement unit, part of tilt detection system), 31: Wafer interferometer (part of tilt detection system), 54: Wafer table (table) Reference numeral 58: Reference plane member (reference plane plate) 59: Aerial image measurement device (part of measurement device) 60a: Irradiation system (part of multipoint focus position detection system) 60b: Light receiving system (multipoint focus) 90: slit plate (pattern plate), 100: exposure apparatus, PL: projection optical system, W: wafer (photosensitive object).

Claims (25)

Each of the plurality of detection light beams is irradiated on the object, and the detection light beams are received by the sensors individually corresponding to the plurality of detection points and the reflected light beams from the plurality of detection points on the object irradiated with the detection light beam are detected. An adjustment method for adjusting a multi-point focal position detection system, which detects position information on the optical axis direction of the projection optical system of the object at a point,
When measuring the positional relationship between the detection origin of each of the sensors and the image plane of the projection optical system, a part thereof has a measurement pattern capable of measuring an aerial image, and the flatness of the surface is set high. Using a reference plane plate as the object. Each of the plurality of detection light beams is irradiated on the object, and the detection light beams are received by the sensors individually corresponding to the plurality of detection points and the reflected light beams from the plurality of detection points on the object irradiated with the detection light beam are detected. An adjustment method for adjusting a multi-point focal position detection system, which detects position information on the optical axis direction of the projection optical system of the object at a point,
While constantly detecting the position in the optical axis direction of the object surface at the part of the detection points using a sensor corresponding to some of the plurality of detection points, the object surface is known A first step of controlling the position of the object so as to coincide with the image plane of the projection optical system;
In parallel with the first step, the displacement of the detection origin of each sensor individually corresponding to the remaining detection points excluding the part of the detection points in the optical axis direction from the object surface of the sensor corresponds to A second step of detecting as a detection offset. The adjustment method according to claim 2, wherein a reference flat plate whose surface has a high degree of flatness is used as the object. An image of the projection optical system in which the object surface is known while detecting the position in the optical axis direction of the object surface at the corresponding detection point using at least a part of the sensor individually corresponding to the remaining detection points. A third step of controlling the position of the object to coincide with a plane;
In parallel with the third step, a displacement amount of the detection origin of each sensor individually corresponding to the partial detection point from the object surface in the optical axis direction is detected as a detection offset of the corresponding sensor. The adjustment method according to claim 2, further comprising: Each of the plurality of detection light beams is irradiated on the object, and the detection light beams are received by the sensors individually corresponding to the plurality of detection points and the reflected light beams from the plurality of detection points on the object irradiated with the detection light beam are detected. Detecting position information in the optical axis direction of the projection optical system at a point, an adjustment method for adjusting a multi-point focal position detection system,
A first step of detecting a change in an angle between an approximate plane formed from a set of detection origins of the plurality of sensors and an approximate plane of an image plane of the projection optical system;
A correction value of the detection offset of each of the sensors is calculated based on the detected change in the angle, and the calculated correction value is added to the detection offset of the corresponding sensor detected in advance to obtain a new detection offset. And a second step. 6. The adjustment method according to claim 5, wherein in the first step, an approximate plane of the image plane is detected by using an aerial image measurement technique to detect the change in the angle. A spatial image measurement method using a pattern plate having a measurement pattern capable of aerial image measurement in a part thereof,
Each of the plurality of detection light beams is irradiated on the object, and the detection light beams are received by the sensors individually corresponding to the plurality of detection points, and the light beams reflected from the plurality of detection points on the object irradiated with the detection light beam are detected. Using a multi-point focal position detection system that detects position information about the optical axis direction of the projection optical system at a point, the pattern plate surface based on the detection results of at least some of the plurality of specific sensors among the plurality of sensors While controlling the position and orientation of the pattern plate so that the distance and the relative angle between the approximate plane of the image plane of the projection optical system and the approximate plane become desired values, the pattern plate is placed on a surface orthogonal to the optical axis direction. An aerial image measurement method characterized by moving an aerial image to measure an aerial image. The aerial image measurement method according to claim 7, wherein the specific sensor is a sensor corresponding to a detection point located at a position where the flatness of the pattern plate surface is good among the plurality of detection points. 9. The aerial image measurement method according to claim 7, wherein a reference flat plate whose surface is set to a high degree of flatness is used as the pattern plate. An image plane measurement method for measuring the image plane of the projection optical system using a pattern plate having a measurement pattern capable of aerial image measurement in a part thereof,
Each of the plurality of detection light beams is irradiated on the object, and the detection light beams are received by the sensors individually corresponding to the plurality of detection points and the reflected light beams from the plurality of detection points on the object irradiated with the detection light beam are detected. Using a multi-point focal position detection system that detects position information about the optical axis direction of the projection optical system at a point, a detection point in the vicinity of the evaluation point selected for each of a plurality of evaluation points in the field of view of the projection optical system While managing the position and orientation of the pattern plate surface in the optical axis direction based on the detection results of the corresponding plurality of specific sensors, changing the position of the pattern plate in the optical axis direction, the pattern plate An aerial image measurement step of moving in a plane orthogonal to the optical axis to repeatedly measure an aerial image of a measurement mark corresponding to each of the plurality of evaluation points;
A calculating step of detecting a best focus position at each of the evaluation points based on the measurement result and calculating an image plane of the projection optical system by a predetermined calculation based on the detection result. In the calculating step, the detection of each of the specific sensors is performed based on the amount of displacement in the optical axis direction from the image plane of the detection origin of each of the specific sensors individually corresponding to the detection points near each of the evaluation points. 11. The image plane measuring method according to claim 10, wherein the offset is also calculated. An image plane measurement method for measuring the image plane of the projection optical system using a pattern plate having a measurement pattern capable of aerial image measurement in a part thereof,
A focus for irradiating a detection light beam on an object, receiving a reflected light beam from a detection point on the object irradiated with the detection light beam with a sensor, and detecting positional information in the optical axis direction of the projection optical system at the detection point. Using a position detection system to manage the position of the pattern plate in the optical axis direction, and using another detection system different from the focus position detection system to tilt the pattern plate with respect to a plane orthogonal to the optical axis. While managing, the position of the pattern plate in the direction of the optical axis is changed to move the pattern plate in a plane orthogonal to the optical axis to correspond to each of a plurality of evaluation points in the field of view of the projection optical system. An aerial image measurement step of repeatedly measuring the aerial image of the measurement mark;
A calculating step of detecting a best focus position at each of the evaluation points based on the measurement result and calculating an image plane of the projection optical system by a predetermined calculation based on the detection result. As the other detection system, a set of interferometers for detecting a rotation angle around two axes orthogonal to the optical axis of the member provided with the pattern plate, and a plurality of support points each supporting the member. 13. The image plane measurement method according to claim 12, wherein a detection system including any one of a set of encoders for detecting a displacement in an optical axis direction is used. An exposure apparatus that transfers a device pattern onto a photosensitive object via a projection optical system,
Each of the plurality of detection light beams is irradiated on the object, and the detection light beams are received by the sensors individually corresponding to the plurality of detection points and the reflected light beams from the plurality of detection points on the object irradiated with the detection light beam are detected. A multi-point focal position detection system for detecting position information of the object at a point in the optical axis direction of the projection optical system;
A table on which the object is mounted;
While detecting the position in the optical axis direction of the object surface at the part of the detection points using a sensor corresponding to a part of the plurality of detection points of the multiple point focus position detection system, While controlling the position of the table so that the object surface coincides with the known image plane of the projection optical system, the detection origin of each sensor individually corresponding to the remaining detection points except for the part of the detection points A control device for detecting the amount of displacement in the optical axis direction from the surface of the object as a detection offset of a corresponding sensor. The exposure apparatus according to claim 14, wherein the object is a reference flat plate whose surface has a high flatness. The control device, after the detection of the detection offset, while detecting the position in the optical axis direction of the object surface at the corresponding detection point using at least a part of the sensor individually corresponding to the remaining detection point, While controlling the position of the table so that the object surface coincides with the known image plane of the projection optical system, the detection origin of each sensor individually corresponding to the partial detection points from the object surface 16. The exposure apparatus according to claim 14, wherein an amount of displacement in an optical axis direction is detected as a detection offset of a corresponding sensor. An exposure apparatus that transfers a device pattern onto a photosensitive object via a projection optical system,
Each of the plurality of detection light beams is irradiated on the object, and the detection light beams are received by the sensors individually corresponding to the plurality of detection points, and the light beams reflected from the plurality of detection points on the object irradiated with the detection light beam are detected. A multipoint focal position detection system for detecting position information of the projection optical system in the optical axis direction at a point;
A detection device that detects a change in an angle between an approximate plane formed from a set of detection origins of the plurality of sensors and an approximate plane of an image plane of the projection optical system;
A correction value of the detection offset of each of the sensors is calculated based on a change in the angle detected by the detection device, and the calculated correction value is added to a detection offset of the corresponding sensor detected in advance to perform a new detection. An exposure device comprising: an arithmetic device for setting an offset. Further comprising a measurement device for measuring the image plane of the projection optical system using a method of aerial image measurement,
18. The exposure apparatus according to claim 17, wherein the detection device detects a change in the angle based on a measurement result of the measurement device. An exposure apparatus that transfers a device pattern onto a photosensitive object via a projection optical system,
Each of the plurality of detection light beams is irradiated on the object, and the detection light beams are received by the sensors individually corresponding to the plurality of detection points and the reflected light beams from the plurality of detection points on the object irradiated with the detection light beam are detected. A multi-point focal position detection system for detecting position information of the projection optical system in the optical axis direction at a point:
A table on which the photosensitive object is mounted;
An aerial image measurement device having a pattern plate integrally provided on the table, receiving light via a measurement pattern formed on the pattern plate, and measuring an aerial image;
When measuring an aerial image by the aerial image measurement device, the pattern plate surface and the projection optical system based on detection results of at least some of a plurality of specific sensors among the plurality of sensors of the multipoint focal position detection system. While controlling the position and orientation of the pattern plate so that the distance and relative angle between the approximate plane of the image plane and the approximate plane become desired values, the pattern plate is orthogonal to the optical axis direction integrally with the table. A control device that moves on a surface. 20. The exposure apparatus according to claim 19, wherein the specific sensor is a sensor corresponding to a detection point located at a position where the flatness of the surface of the pattern plate is good among the plurality of detection points. 21. The exposure apparatus according to claim 19, wherein the pattern plate is a reference flat plate whose surface has a high degree of flatness. An exposure apparatus that transfers a device pattern onto a photosensitive object via a projection optical system,
Each of the plurality of detection light beams is irradiated on the object, and the detection light beams are received by the sensors individually corresponding to the plurality of detection points and the reflected light beams from the plurality of detection points on the object irradiated with the detection light beam are detected. A multi-point focal position detection system for detecting position information of the projection optical system in the optical axis direction at a point:
A table on which the photosensitive object is mounted;
An aerial image measurement device having a pattern plate integrally provided on the table, receiving light via a measurement pattern formed on the pattern plate, and measuring an aerial image;
The position of the pattern plate surface in the optical axis direction based on detection results of a plurality of specific sensors respectively corresponding to detection points near the evaluation points selected for each of the plurality of evaluation points in the field of view of the projection optical system. While managing the posture and changing the position of the pattern plate in the optical axis direction, the pattern plate is moved integrally with the table in a plane orthogonal to the optical axis to each of the plurality of evaluation points. A control device for repeatedly measuring the aerial image of the corresponding measurement mark;
An arithmetic unit that detects a best focus position at each of the evaluation points based on the measurement result and calculates an image plane of the projection optical system by a predetermined calculation based on the detection result. The arithmetic unit is configured to displace the detection origin of each of the specific sensors in the optical axis direction from the image plane, which individually corresponds to a detection point near each of the evaluation points obtained in the process of detecting the best focus position. 23. The exposure apparatus according to claim 22, wherein the detection offset of each of the specific sensors is also calculated based on the amount. An exposure apparatus that transfers a device pattern onto a photosensitive object via a projection optical system,
A focus for irradiating a detection light beam on an object, receiving a reflected light beam from a detection point on the object irradiated with the detection light beam with a sensor, and detecting positional information in the optical axis direction of the projection optical system at the detection point. With position detection system:
A table on which the photosensitive object is mounted;
An aerial image measurement device having a pattern plate integrally provided on the table, receiving light via a measurement pattern formed on the pattern plate, and measuring an aerial image;
An inclination detection system capable of detecting at least an inclination of the pattern plate with respect to a plane orthogonal to the optical axis;
While managing the position of the pattern plate in the optical axis direction using the focus position detection system, while managing the inclination of the pattern plate with respect to a plane orthogonal to the optical axis using the inclination detection system, the pattern The position corresponding to the optical axis direction of the plate is changed, and the pattern plate is moved integrally with the table in a plane orthogonal to the optical axis, and measurement corresponding to each of a plurality of evaluation points in the visual field of the projection optical system is performed. A control device for repeatedly measuring the aerial image of the mark;
An arithmetic unit that detects a best focus position at each of the evaluation points based on the measurement result and calculates an image plane of the projection optical system by a predetermined calculation based on the detection result. The tilt detection system is a set of interferometers for detecting a rotation angle about two axes orthogonal to the optical axis of the table, and the displacement in the optical axis direction of each of a plurality of support points supporting the table. The exposure apparatus according to claim 24, further comprising any one of a set of encoders for detecting.

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