JP4198775B2 - Method for manufacturing polycrystalline silicon thin film transistor - Google Patents

Description

図２に、表１の各条件によって堆積された窒化シリコン薄膜について、加熱温度と含有水素放出量との関係（加熱温度に対する含有水素放出量のプロファイル）を示す。図２に示す様に、条件１では、含有水素放出量のプロファイルのピークが５９０℃に現れる。また、条件２では６２０℃に現れ、条件３では６５０℃に現れ、条件４では６８０℃に現れる。なお、脱水素は、膜中の水素の拡散によって律速されるので、窒化シリコンの膜厚がこれよりも薄いときには、放出速度ピークは低くなる。
【００１９】
次に、ガラス基板上に、表１に示した成膜条件で窒化シリコン薄膜を５０ｎｍ成膜し、さらにその上に、プラズマＣＶＤを用いて厚さ１００ｎｍの酸化シリコン薄膜を堆積し、その上に、厚さ５０ｎｍの非晶質シリコン薄膜を堆積した。次に、非晶質シリコン薄膜中に含まれる水素を除去するため、窒素雰囲気中で温度４５０℃で１時間の加熱処理を行った。なお、この温度４５０℃の加熱処理では、アンダーコート層として使用される窒化シリコン薄膜の含有水素放出量のプロファイルのピークが現れる温度は、ほとんど変化しない。
【００２０】
次に、以上の様にして形成された各種の非晶質シリコン薄膜に、下記に示す各照射エネルギー密度でレーザ照射を施して非晶質シリコン薄膜を多結晶化し、形成された多結晶シリコン薄膜の平均結晶粒径及び水素の放出によるダメージ発生の有無を観察した。なお、非晶質シリコン薄膜に対するレーザ照射には、波長３０８ｎｍのＸｅＣｌエキシマレーザ（パルス発振）を使用し、その照射エネルギー密度を、２００ｍＪ／ｃｍ² から４００ｍＪ／ｃｍ² まで、２０ｍＪ／ｃｍ² 刻みで変化させた（１１水準）。
【００２１】
図３に、窒化シリコン薄膜の堆積の際の条件（表１に示した条件１から条件４）をパラメータとして、エキシマレーザの照射エネルギー密度と、それにより形成された多結晶シリコン薄膜の平均結晶粒径との関係を示す。なお、図３において、白抜きのマークは、顕微鏡観察によって多結晶シリコン薄膜にダメージが認められなかったことを示し、黒塗りのマークはダメージが認められたことを示している。また、多結晶シリコン薄膜の結晶粒径の測定は、下記の方法で行った。即ち、試料をセコエッチング処理し、結晶粒界を選択的にエッチングした後、走査型電子顕微鏡で試料表面を観察して結晶粒径を測定した。
【００２２】
図３に示す様に、窒化シリコン薄膜（アンダーコート層）を条件１あるいは条件２によって形成した場合には、照射エネルギー密度が３８０ｍＪ／ｃｍ² まで多結晶シリコン薄膜に水素の放出によるダメージが発生しない。また、照射エネルギー密度３００ｍＪ／ｃｍ² から３８０ｍＪ／ｃｍ² までの広い範囲で０．３μｍ以上の大きな結晶粒径の多結晶シリコン薄膜が得られる。これに対して、窒化シリコン薄膜（アンダーコート層）を条件３あるいは条件４によって形成した場合には、照射エネルギー密度が２６０ｍＪ／ｃｍ² で多結晶シリコン薄膜にダメージが発生する。なお、この照射エネルギー密度における多結晶シリコン薄膜の結晶粒径は０．１５μｍ以下であった。
【００２３】
以上の実験結果から、次のことが判明した。レーザビーム照射後の多結晶シリコン薄膜に発生する水素の放出によるダメージは、アンダーコート層として使用される窒化シリコン薄膜の特性に大きく影響される。即ち、アンダーコート層として、加熱温度に対する含有水素放出量のプロファイルのピークが６００℃以下の範囲に現れるような特性を備えた窒化シリコン薄膜を使用した場合には、レーザビーム照射後の多結晶シリコン薄膜の結晶粒径を０．３μｍ以上に設定した場合にも、多結晶シリコン薄膜に水素の放出に起因するダメージが発生しない。
【００２４】
次に、本発明に基づく多結晶シリコン薄膜トランジスタの製造方法について説明する。図１に、その製造工程の概要を示す。
先ず、図１（ａ）に示す様に、ガラス基板１の上に前述の条件１に従いプラズマＣＶＤを用いて厚さ５０ｎｍの窒化シリコン薄膜２を堆積する。なお、前述の条件１は次の通りである、ＳｉＨ₄ 流量＝２０ｓｃｃｍ、ＮＨ₃ 流量＝２００ｓｃｃｍ、Ｎ₂ 流量＝１０００ｓｃｃｍ、ＲＦ出力＝３００Ｗ、圧力＝２．５ｔｏｒｒ、電極間距離＝２０ｍｍ、基板温度＝４００℃、加熱温度に対する含有水素放出量のプロファイルのピーク温度＝５９０℃。
【００２５】
窒化シリコン薄膜２の上に、プラズマＣＶＤを用いて厚さ１００ｎｍの酸化シリコン薄膜３を堆積した後、その上に、厚さ５０ｎｍの非晶質シリコン薄膜４を堆積する。次に、非晶質シリコン薄膜４の中に含まれる水素を除去するため、窒化雰囲気中で温度４５０℃で１時間の加熱処理を行う。
【００２６】
次に、図１（ｂ）に示す様に、非晶質シリコン薄膜４の表面に波長３０８ｎｍのＸｅＣｌエキシマレーザ（パルス発振）を、エネルギー密度３００ｍＪ／ｃｍ² で照射して非晶質シリコン薄膜４を一時的に溶融して多結晶化する。なお、この結果形成される多結晶シリコン薄膜５の平均結晶粒径は０．３μｍである。
【００２７】
次に、以上の様にして形成された多結晶シリコン薄膜５をフォトリソグラフィによりパターニングして、図１（ｃ）に示す様に、島状の多結晶シリコン薄膜６を形成する。次に、図１（ｄ）に示す様に、島状の多結晶シリコン薄膜６の上にプラズマＣＶＤを用いて厚さ１００ｎｍの酸化シリコン薄膜７を堆積してゲート絶縁膜を形成する。次に、酸化シリコン薄膜７の上にスパッタリングにより厚さ３００ｎｍのモリブデンタンタル合金層を堆積し、これをフォトリソグラフィによりパターニングして、図１（ｅ）に示す様に、ゲート電極８を形成する。
【００２８】
次に、図１（ｆ）に示す様に、ゲート電極８をマスクとして用いて、質量分離型のイオン注入装置により酸化シリコン薄膜７を介して多結晶シリコン薄膜５に不純物としてＰ（燐）を注入し、ソース領域９及びドレイン領域１０を形成する。なお、Ｐを注入する際、質量分離型のイオン注入装置に限らず、非晶量分離型のものを使用することもできる。
【００２９】
次に、図１（ｇ）に示す様に、プラズマＣＶＤを用いて厚さ４００ｎｍの酸化シリコン薄膜を堆積して層間絶縁膜１１を形成した後、エキシマレーザを照射して、先に注入したＰを活性化させ、次いで、フォトリソグラフィにより層間絶縁膜１１をパターニングしてコンタクトホールを形成する。
【００３０】
次に、図１（ｈ）に示す様に、スパッタリングにより厚さ４００ｎｍモリブデンタンタル合金層を堆積し、これをフォトリソグラフィによりパターニングしてソース電極１２及びドレイン電極１３を形成する。
以上の工程によって、多結晶シリコン薄膜トランジスタが完成する。
【００３１】
【発明の効果】
本発明の多結晶シリコン薄膜トランジスタの製造方法によれば、ガラス基板の上に設けられるアンダーコート層としてプラズマＣＶＤによる窒化シリコン薄膜（あるいは酸窒化シリコン薄膜）を使用し、且つ、このアンダーコート層を、加熱温度に対する含有水素放出量のプロファイルのピークが６００℃以下に現れる様な条件及び膜厚で形成する。これによって、レーザビーム照射による非晶質シリコン薄膜の多結晶化の際に、アンダーコート層からの水素放出に起因する多結晶シリコン薄膜へのダメージを防ぐとともに、ガラス基板からの多結晶シリコン薄膜への不純物の拡散を防ぐことができる。
【００３２】
なお、窒化シリコン（あるいは酸窒化シリコン）からなるアンダーコート層の上に、更に酸化シリコン薄膜を設けて、その上に多結晶シリコン薄膜を形成すれば、多結晶シリコン薄膜と酸化シリコン薄膜との間に欠陥の少ない界面を形成することができるので、優れた特性を備えた薄膜トランジスタを形成することができる。
【図面の簡単な説明】
【図１】本発明に基づく多結晶シリコン薄膜トランジスタの製造工程を示す図、（ａ）〜（ｈ）は、各工程における断面図を表す。
【図２】ＣＶＤの条件を変えて形成された各種窒化シリコン薄膜について、加熱温度と含有水素放出量との関係、即ち含有水素放出量のプロファイルを示す図。
【図３】エキシマレーザの照射エネルギー密度と、それにより形成される多結晶シリコン薄膜の結晶粒径及び多結晶シリコン薄膜に生ずるダメージの有無との関係を示す図。
【符号の説明】
１・・・ガラス基板、
２・・・窒化シリコン薄膜、
３・・・酸化シリコン薄膜、
４・・・非晶質シリコン薄膜、
５・・・多結晶シリコン薄膜、
６・・・島状の多結晶シリコン薄膜、
７・・・酸化シリコン薄膜（ゲート絶縁膜）、
８・・・ゲート電極、
９・・・ソース領域、
１０・・・ドレイン領域、
１１・・・層間絶縁膜、
１２・・・ソース電極、
１３・・・ドレイン電極。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a polycrystalline silicon thin film transistor using a polycrystalline silicon thin film as a semiconductor active layer.
[0002]
[Prior art]
In an active matrix liquid crystal display device, conventionally, an amorphous silicon thin film transistor (a thin film transistor using an amorphous silicon thin film as a semiconductor active layer) has been used as a switching element of a pixel. This is because the semiconductor active layer made of amorphous silicon can be formed on a large-area substrate with good uniformity, and can be formed at a relatively low temperature.
[0003]
On the other hand, recently, in order to realize a compact liquid crystal display device, a so-called drive circuit integrated liquid crystal display device in which a drive circuit is formed on the same substrate in the periphery of a pixel region has been developed. In such a drive circuit integrated liquid crystal display device, a polycrystalline silicon thin film transistor (a thin film transistor using a polycrystalline silicon thin film as a semiconductor active layer) is used for the drive circuit. This is because polycrystalline silicon has a mobility of about 100 higher than that of amorphous silicon. Therefore, the polycrystalline silicon thin film transistor has a much faster response speed than that of the amorphous silicon thin film transistor.
[0004]
High-temperature processes and low-temperature processes are known as methods for forming a polycrystalline silicon thin film that constitutes a semiconductor active layer of a polycrystalline silicon thin film transistor.
In the case of a so-called high temperature process, first, after depositing an amorphous silicon thin film on a quartz substrate having excellent heat resistance, this amorphous silicon thin film is heated at a temperature of 600 ° C. or higher, and based on a solid phase growth method. Convert amorphous silicon thin film to polycrystalline silicon thin film. Such a high-temperature process has a high manufacturing cost because the quartz substrate used is very expensive, and it is not practical to apply it to a large display device.
[0005]
Therefore, recently, a so-called low temperature process using a glass substrate having low heat resistance but low cost has been developed. In the low temperature process, the following steps are employed in order to form a polycrystalline silicon thin film with high uniformity at a relatively low temperature on a glass substrate. That is, first, an amorphous silicon thin film is deposited on a glass substrate using plasma CVD. Note that plasma CVD makes it possible to deposit an amorphous silicon thin film with high uniformity on a large-area substrate at a relatively low temperature. Next, the amorphous silicon thin film is irradiated with a laser beam (usually, a pulsed excimer laser beam) to melt the amorphous silicon thin film and quickly solidify it into a polycrystalline silicon thin film.
[0006]
By the way, in the case of a low-temperature process, as a result of replacing the substrate from a quartz substrate to a glass substrate, impurities contained in the glass substrate diffuse from the glass substrate into the amorphous silicon thin film (later converted to a polycrystalline silicon thin film). Thus, there is a problem that the quality of the polycrystalline silicon thin film is deteriorated or the transistor characteristics are changed when the thin film transistor is used. For this reason, an undercoat layer is inserted between the glass substrate and the amorphous silicon thin film for the purpose of preventing the diffusion of impurities from the glass substrate into the amorphous silicon thin film. As such an undercoat layer, a silicon nitride thin film having a high impurity diffusion preventing ability is generally employed. It should be noted that plasma CVD is generally used when forming this silicon nitride thin film because it can be deposited on a large area substrate at a relatively low temperature with good uniformity.
[0007]
However, a large amount of hydrogen is usually contained in the silicon nitride thin film formed by plasma CVD. For this reason, in the subsequent step of polycrystallizing the amorphous silicon thin film by laser beam irradiation, hydrogen contained in the silicon nitride layer is suddenly released and damages the polycrystalline silicon thin film overlying it. Newly occurs. In addition to this, when a large amount of hydrogen is contained in the amorphous silicon thin film, there is also a problem that the polycrystalline silicon thin film is damaged by hydrogen release from the amorphous silicon thin film itself.
[0008]
In the case of an amorphous silicon thin film, hydrogen contained therein can be removed by heating at about 400 to 500 ° C., which is lower than the upper limit of the heat resistance temperature of the glass substrate. In this case, hydrogen contained in the glass substrate cannot be removed by heating at about 500 ° C. corresponding to the upper limit of the heat resistant temperature of the glass substrate.
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problems in the manufacturing process of a conventional polycrystalline silicon thin film transistor, and an object of the present invention is to change an amorphous silicon thin film into a polycrystalline silicon thin film by laser beam irradiation. At the same time, an object of the present invention is to provide a method of manufacturing a polycrystalline silicon thin film transistor capable of preventing damage to the polycrystalline silicon thin film due to hydrogen release from the undercoat layer.
[0010]
[Means for Solving the Problems]
The method for producing a polycrystalline silicon thin film transistor of the present invention comprises:
Depositing a silicon nitride thin film on a glass substrate using plasma CVD;
Depositing an amorphous silicon thin film on the silicon nitride thin film;
Forming a semiconductor active layer comprising a polycrystalline silicon thin film by polycrystallizing the amorphous silicon thin film by laser beam irradiation;
In a method for producing a polycrystalline silicon thin film transistor comprising:
As the silicon nitride thin film, a silicon nitride thin film in which the peak of the profile of the amount of released hydrogen with respect to the heating temperature is 600 ° C. or lower is used.
[0011]
Preferably, a silicon oxide thin film is further deposited on the silicon nitride thin film, and an amorphous silicon thin film is deposited on the silicon oxide thin film.
(Function)
According to the method for manufacturing a polycrystalline silicon thin film transistor of the present invention, a silicon nitride thin film having a property that the peak of the profile of the amount of released hydrogen with respect to the heating temperature appears at 600 ° C. or lower is used as an undercoat layer using plasma CVD. The deposition prevents diffusion of impurities from the glass substrate to the polycrystalline silicon thin film, and also prevents damage to the polycrystalline silicon thin film due to hydrogen released from the silicon nitride thin film during laser beam irradiation. it can.
[0012]
Note that a silicon nitride thin film that satisfies the peak conditions of the hydrogen release amount profile with respect to the heating temperature described above can be formed by appropriately setting plasma CVD conditions (for example, pressure, reaction gas flow rate, etc.). it can.
[0013]
The inventors of the present application conducted various experiments for the condition of the undercoat layer that does not damage the polycrystalline silicon thin film, and as a result, obtained the following knowledge. That is, a polycrystalline silicon thin film formed when hydrogen is released from the undercoat layer on the lower layer side of the amorphous silicon thin film in a temperature region where the amorphous silicon thin film is partially melted by laser beam irradiation. However, if the hydrogen is released from the undercoat layer in a temperature region where the amorphous silicon thin film does not melt, the formed polycrystalline silicon thin film is hardly damaged. Based on such knowledge, the method for producing a polycrystalline silicon thin film transistor of the present invention is based on the properties of the silicon nitride thin film used as the undercoat layer (specifically, the dependency of the hydrogen release amount on the heating temperature). It is specified.
[0014]
In the method for manufacturing a polycrystalline silicon thin film transistor of the present invention, the amorphous silicon thin film itself contains a large amount of hydrogen, and a heating step for removing hydrogen from the amorphous silicon thin film in advance is provided before laser beam irradiation. It is also effective when the amorphous silicon thin film itself has a small hydrogen content, and such a heating step can be omitted (for example, an amorphous silicon thin film is formed by LPCVD, sputtering, or hydrogen containing). In the case of being formed by plasma CVD using a special condition that the amount is small), since there is no hydrogen release from the amorphous silicon thin film itself, no dehydrogenation process is required, ,It is valid.
[0015]
In addition, even when a silicon oxynitride thin film is used instead of the silicon nitride thin film as the undercoat layer, a silicon oxynitride thin film having a property that the peak of the profile of the hydrogen release amount with respect to the heating temperature appears at 600 ° C. or less By depositing using plasma CVD, a similar effect can be realized. The silicon oxynitride thin film has a lower hydrogen content than the silicon nitride thin film and has a higher impurity diffusion blocking capability than the silicon oxide thin film, which improves the quality of the polycrystalline silicon thin film formed thereon. effective.
[0016]
Further, by inserting a silicon oxide thin film between an undercoat layer made of silicon nitride or silicon oxynitride and an amorphous chamber silicon thin film (later converted to a polycrystalline silicon thin film), the silicon oxide thin film and the polycrystalline silicon Since an interface with few defects is formed between the thin film and the thin film, the quality of the polycrystalline silicon thin film can be improved.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
First, the requirements for the undercoat layer used in the polycrystalline silicon thin film transistor according to the present invention and the formation method thereof will be described.
In order to obtain conditions for forming a silicon nitride thin film used as an undercoat layer, the following experiment was conducted. A silicon nitride thin film having a thickness of 50 nm was deposited on the Si wafer using plasma CVD under the following conditions, and the relationship between the heating temperature and the amount of released hydrogen was measured for each silicon nitride thin film. Table 1 shows the conditions for depositing the silicon nitride thin film.
[0018]

FIG. 2 shows the relationship between the heating temperature and the amount of released hydrogen (profile of the amount of released hydrogen with respect to the heating temperature) of the silicon nitride thin film deposited under the conditions shown in Table 1. As shown in FIG. 2, in the condition 1, the peak of the hydrogen release amount profile appears at 590 ° C. In Condition 2, it appears at 620 ° C., in Condition 3 it appears at 650 ° C., and in Condition 4 it appears at 680 ° C. Note that dehydrogenation is rate-determined by the diffusion of hydrogen in the film, so that when the silicon nitride film is thinner than this, the release rate peak is low.
[0019]
Next, a silicon nitride thin film having a thickness of 50 nm is formed on the glass substrate under the film formation conditions shown in Table 1, and a silicon oxide thin film having a thickness of 100 nm is further deposited thereon using plasma CVD. A 50 nm thick amorphous silicon thin film was deposited. Next, in order to remove hydrogen contained in the amorphous silicon thin film, heat treatment was performed at a temperature of 450 ° C. for 1 hour in a nitrogen atmosphere. In the heat treatment at a temperature of 450 ° C., the temperature at which the peak of the hydrogen release amount profile of the silicon nitride thin film used as the undercoat layer appears hardly changes.
[0020]
Next, various amorphous silicon thin films formed as described above are subjected to laser irradiation at each irradiation energy density shown below to polycrystallize the amorphous silicon thin film, and the formed polycrystalline silicon thin film The average crystal grain size and occurrence of damage due to hydrogen release were observed. Note that the laser irradiation for the amorphous silicon thin film, using a XeCl excimer laser having a wavelength of 308 nm (pulsed), the irradiation energy density from 200 mJ / cm ² to 400 mJ / cm ^2, at 20 mJ / cm ² increments Changed (11 levels).
[0021]
FIG. 3 shows the irradiation energy density of the excimer laser and the average crystal grains of the polycrystalline silicon thin film formed by using the conditions during deposition of the silicon nitride thin film (conditions 1 to 4 shown in Table 1) as parameters. The relationship with the diameter is shown. In FIG. 3, white marks indicate that no damage was observed in the polycrystalline silicon thin film by microscopic observation, and black marks indicate that damage was observed. The crystal grain size of the polycrystalline silicon thin film was measured by the following method. That is, the sample was subjected to a seco-etching process and the crystal grain boundary was selectively etched, and then the surface of the sample was observed with a scanning electron microscope to measure the crystal grain size.
[0022]
As shown in FIG. 3, when the silicon nitride thin film (undercoat layer) is formed under the condition 1 or 2, the polycrystalline silicon thin film is not damaged by the release of hydrogen until the irradiation energy density is 380 mJ / cm ^2. . Also, the polycrystalline silicon thin film of large grain size of more than 0.3μm is obtained in a wide range of irradiation energy density 300 mJ / cm ² to 380 mJ / cm ^2. On the other hand, when the silicon nitride thin film (undercoat layer) is formed under Condition 3 or Condition 4, the polycrystalline silicon thin film is damaged when the irradiation energy density is 260 mJ / cm ² . The crystal grain size of the polycrystalline silicon thin film at this irradiation energy density was 0.15 μm or less.
[0023]
From the above experimental results, the following was found. Damage caused by the release of hydrogen generated in the polycrystalline silicon thin film after laser beam irradiation is greatly influenced by the characteristics of the silicon nitride thin film used as the undercoat layer. That is, when a silicon nitride thin film having such a characteristic that the peak of the hydrogen release amount profile with respect to the heating temperature appears in the range of 600 ° C. or less is used as the undercoat layer, the polycrystalline silicon after laser beam irradiation is used. Even when the crystal grain size of the thin film is set to 0.3 μm or more, the polycrystalline silicon thin film is not damaged due to the release of hydrogen.
[0024]
Next, a method for manufacturing a polycrystalline silicon thin film transistor according to the present invention will be described. FIG. 1 shows an outline of the manufacturing process.
First, as shown in FIG. 1A, a silicon nitride thin film 2 having a thickness of 50 nm is deposited on a glass substrate 1 using plasma CVD according to the above-mentioned condition 1. The above condition 1 is as follows: SiH ₄ flow rate = 20 sccm, NH ₃ flow rate = 200 sccm, N ₂ flow rate = 1000 sccm, RF output = 300 W, pressure = 2.5 torr, interelectrode distance = 20 mm, substrate temperature = 400 ° C, peak temperature of profile of hydrogen release amount with respect to heating temperature = 590 ° C.
[0025]
After depositing a silicon oxide thin film 3 having a thickness of 100 nm on the silicon nitride thin film 2 by using plasma CVD, an amorphous silicon thin film 4 having a thickness of 50 nm is deposited thereon. Next, in order to remove hydrogen contained in the amorphous silicon thin film 4, a heat treatment is performed in a nitriding atmosphere at a temperature of 450 ° C. for 1 hour.
[0026]
Next, as shown in FIG. 1B, the surface of the amorphous silicon thin film 4 is irradiated with a XeCl excimer laser (pulse oscillation) with a wavelength of 308 nm at an energy density of 300 mJ / cm ² , to thereby form the amorphous silicon thin film 4. Is melted temporarily to be polycrystallized. The resulting polycrystalline silicon thin film 5 has an average crystal grain size of 0.3 μm.
[0027]
Next, the polycrystalline silicon thin film 5 formed as described above is patterned by photolithography to form an island-shaped polycrystalline silicon thin film 6 as shown in FIG. Next, as shown in FIG. 1D, a silicon oxide thin film 7 having a thickness of 100 nm is deposited on the island-like polycrystalline silicon thin film 6 by using plasma CVD to form a gate insulating film. Next, a molybdenum tantalum alloy layer having a thickness of 300 nm is deposited on the silicon oxide thin film 7 and patterned by photolithography to form a gate electrode 8 as shown in FIG.
[0028]
Next, as shown in FIG. 1F, P (phosphorus) as an impurity is introduced into the polycrystalline silicon thin film 5 through the silicon oxide thin film 7 by a mass separation type ion implantation apparatus using the gate electrode 8 as a mask. Implantation is performed to form a source region 9 and a drain region 10. In addition, when implanting P, not only a mass separation type ion implantation apparatus but also an amorphous amount separation type can be used.
[0029]
Next, as shown in FIG. 1 (g), a silicon oxide thin film having a thickness of 400 nm is deposited by plasma CVD to form an interlayer insulating film 11, and then irradiated with an excimer laser and previously implanted P Then, the interlayer insulating film 11 is patterned by photolithography to form contact holes.
[0030]
Next, as shown in FIG. 1H, a 400 nm-thick molybdenum tantalum alloy layer is deposited by sputtering, and this is patterned by photolithography to form the source electrode 12 and the drain electrode 13.
A polycrystalline silicon thin film transistor is completed through the above steps.
[0031]
【The invention's effect】
According to the method for producing a polycrystalline silicon thin film transistor of the present invention, a silicon nitride thin film (or silicon oxynitride thin film) by plasma CVD is used as an undercoat layer provided on a glass substrate, and this undercoat layer is The film is formed under such conditions and film thickness that the peak of the profile of the amount of released hydrogen with respect to the heating temperature appears below 600 ° C. This prevents damage to the polycrystalline silicon thin film due to hydrogen release from the undercoat layer when the amorphous silicon thin film is polycrystallized by laser beam irradiation. The diffusion of impurities can be prevented.
[0032]
If a silicon oxide thin film is further provided on the undercoat layer made of silicon nitride (or silicon oxynitride) and a polycrystalline silicon thin film is formed thereon, the space between the polycrystalline silicon thin film and the silicon oxide thin film is formed. Since an interface with few defects can be formed, a thin film transistor having excellent characteristics can be formed.
[Brief description of the drawings]
FIGS. 1A to 1H are cross-sectional views showing steps of manufacturing a polycrystalline silicon thin film transistor according to the present invention. FIGS.
FIG. 2 is a view showing the relationship between the heating temperature and the amount of released hydrogen, that is, the profile of the amount of released hydrogen for various silicon nitride thin films formed by changing the CVD conditions.
FIG. 3 is a diagram showing the relationship between the irradiation energy density of an excimer laser, the crystal grain size of a polycrystalline silicon thin film formed thereby, and the presence or absence of damage occurring in the polycrystalline silicon thin film.
[Explanation of symbols]
1 ... Glass substrate,
2 ... silicon nitride thin film,
3 ... Silicon oxide thin film,
4 Amorphous silicon thin film,
5 ... polycrystalline silicon thin film,
6 ... Island-like polycrystalline silicon thin film,
7 ... Silicon oxide thin film (gate insulating film),
8: Gate electrode,
9 ... Source region,
10 ... Drain region,
11 ... Interlayer insulating film,
12 ... Source electrode,
13: Drain electrode.

Claims (10)

Depositing a silicon nitride thin film on a glass substrate using plasma CVD;
Depositing an amorphous silicon thin film on the silicon nitride thin film;
Forming a semiconductor active layer comprising a polycrystalline silicon thin film by polycrystallizing the amorphous silicon thin film by laser beam irradiation;
In a method for producing a polycrystalline silicon thin film transistor comprising:
A method for producing a polycrystalline silicon thin film transistor, wherein a silicon nitride thin film having a peak of a profile of a hydrogen release amount with respect to a heating temperature is 600 ° C. or lower is used as the silicon nitride thin film. Depositing a silicon nitride thin film on a glass substrate using plasma CVD;
Depositing a silicon oxide thin film on the silicon nitride thin film;
Depositing an amorphous silicon thin film on the silicon oxide thin film;
Forming a semiconductor active layer comprising a polycrystalline silicon thin film by polycrystallizing the amorphous silicon thin film by laser beam irradiation;
In a method for producing a polycrystalline silicon thin film transistor comprising:
A method for producing a polycrystalline silicon thin film transistor, wherein a silicon nitride thin film having a peak of a profile of a hydrogen release amount with respect to a heating temperature is 600 ° C. or lower is used as the silicon nitride thin film. 3. The method of manufacturing a polycrystalline silicon thin film transistor according to claim 1, wherein the silicon nitride thin film has a thickness of 50 nm or more. The method for manufacturing a polycrystalline silicon thin film transistor according to any one of claims 1 to 3, wherein the amorphous silicon thin film is formed by using plasma CVD. The method for manufacturing a polycrystalline silicon thin film transistor according to any one of claims 1 to 3, wherein the amorphous silicon thin film is formed by using LPCVD or sputtering. Depositing a silicon oxynitride thin film on a glass substrate using plasma CVD;
Depositing an amorphous silicon thin film on the silicon oxynitride thin film;
Forming a semiconductor active layer comprising a polycrystalline silicon thin film by polycrystallizing the amorphous silicon thin film by laser beam irradiation;
In a method for producing a polycrystalline silicon thin film transistor comprising:
A method of manufacturing a polycrystalline silicon thin film transistor, wherein a silicon oxynitride thin film having a peak of a profile of a hydrogen release amount with respect to a heating temperature is 600 ° C. or lower is used as the silicon oxynitride thin film. Depositing a silicon oxynitride thin film on a glass substrate using plasma CVD;
Depositing a silicon oxide thin film on the silicon oxynitride thin film;
Depositing an amorphous silicon thin film on the silicon oxide thin film;
Forming a semiconductor active layer comprising a polycrystalline silicon thin film by polycrystallizing the amorphous silicon thin film by laser beam irradiation;
In a method for producing a polycrystalline silicon thin film transistor comprising:
A method of manufacturing a polycrystalline silicon thin film transistor, wherein a silicon oxynitride thin film having a peak of a profile of a hydrogen release amount with respect to a heating temperature is 600 ° C. or lower is used as the silicon oxynitride thin film. The method for manufacturing a polycrystalline silicon thin film transistor according to claim 6 or 7, wherein the thickness of the silicon oxynitride thin film is 50 nm or more. 9. The method of manufacturing a polycrystalline silicon thin film transistor according to claim 6, wherein the amorphous silicon thin film is formed by using plasma CVD. 9. The method of manufacturing a polycrystalline silicon thin film transistor according to claim 6, wherein the amorphous silicon thin film is formed using LPCVD or sputtering.

Images