JP4562712B2 - Charged particle beam exposure method - Google Patents

Description

  The present invention relates to a charged particle beam exposure method in which proximity effect correction is performed in order to improve the accuracy of a finished pattern dimension when creating exposure data for a charged particle beam exposure apparatus.

  When a circuit pattern is drawn by irradiating a resist film on a substrate with a charged particle beam, for example, an electron beam, a part of the electron beam incident on the resist film is scattered forward and a part of the electron beam transmitted through the resist film. Are backscattered and enter the resist film again. For this reason, even if the electron beam is incident on one point on the resist film, the influence spreads, causing a so-called proximity effect.

  The energy intensity distribution (Energy Intensity Distribution: EID) function f (X, Y) of the resist film when the electron beam is incident on the points X = 0 and Y = 0 on the resist film is expressed by the forward scattering term and the back scattering. Are expressed by the following equations that approximate each term with a Gaussian function.

ここに、ηは後方散乱係数、β_fは前方散乱半径、β_bは後方散乱半径である。これらの値は、電子ビームのエネルギー、レジスト膜の膜厚及び基板の材料などに依存し、実験により定められる。電子ビームの加速電圧が高くなるほど、β_fは小さくなり、β_bは大きくなる。

Here, the η backscattering coefficient, the beta _f forward scattering radius, the beta _b is backscattering radius. These values depend on the energy of the electron beam, the thickness of the resist film, the material of the substrate, and the like, and are determined by experiments. As the acceleration voltage of the electron beam increases, β _f decreases and β _b increases.

  In the conventional proximity effect correction method, a fixed sample point is set at the edge center point or corner of each pattern to be exposed, and the exposure intensity at each fixed sample point when the pattern is exposed is expressed by Equation (1). The amount of exposure (dose) is determined so that the sum of squares of the difference from the target value is minimized.

  However, with the high integration of LSI, the number of patterns rapidly increases and the calculation time becomes too long.

  Therefore, there has been a demand for a proximity effect correction method that can shorten the calculation time and can reduce the dimensional error of the developed pattern (finished pattern) within an allowable range.

  As one of such methods, the LSI exposure pattern arrangement surface is divided by a mesh, the pattern area density at each mesh of the mesh is calculated, and the target mesh is calculated from the peripheral mesh based on the backscattering term of Equation (1). For example, Japanese Patent No. 2502418 and Journal of Vacuum Science Technology Vol. B10, No. 6, pp. 3072-3076, have been proposed. 1992. In this method, the exposure amount is determined so that the sum of the half value of the forward scattering intensity peak and the backscattering exposure intensity is constant.

  According to this method, it is possible to prevent global variation in the pattern size due to the influence of backscattering with a simple algorithm.

  However, since the spread of the absorbed energy distribution due to forward scattering is not taken into consideration, there is no guarantee that the finished pattern size will be equal to the design width. That is, as the pattern becomes finer, the spread of the absorbed energy distribution at the half-value intensity cannot be ignored, and the finished pattern dimension becomes larger than the design width due to forward scattering.

  Therefore, the following proximity effect correction method has been proposed in Japanese Patent Application No. 11-151330.

(A) The pattern width is adjusted so that the half-value width of the forward scattering intensity distribution obtained by dividing the forward scattering term of the energy intensity distribution function by area for the pattern of interest becomes the design width, and the forward scattering intensity ε giving the half-value width _{Determine p} as the reference forward scatter intensity,
(B) An exposure intensity α _p · η by a backscattering term of the energy intensity distribution function is obtained using a pattern area density map method,
(C) A corrected exposure amount (corrected exposure amount) Qcp is determined so that Qcp times (ε _p + α _p · η) is equal to the pattern development threshold Eth.

For example, when the X direction design widths of the wide width pattern and the narrow width pattern are (X2-X1) and (X4-X3), respectively, as indicated by the wavy line in FIG. The pattern width is narrowed as shown by the solid line in FIG. The thick width pattern has a width of ε _p = 1/2 and α _p = 1, and a pattern having such values is referred to as a reference pattern. When the corrected exposure doses Qcp of the wide and narrow patterns are respectively expressed as Q ₁ and Q ₂ , (1/2 + η) Q ₁ = (ε _p + α _p · η) Q ₂ is established in the above (C). , Q ₁ <Q ₂ .

When the rectangular transmission holes 11 and 12 indicated by the solid line on the mask 10 are irradiated with the electron beams having the exposure amounts Q ₁ and Q _{2 on} the rectangular areas 13 and 14 indicated by the dotted lines, respectively, the exposure intensity on the wafer coated with the photoresist. The distribution is as shown in FIG.

  According to this method, since the inclination of the exposure intensity distribution of the pattern at the threshold Eth is steep, the variation in the pattern width with respect to the variation in the exposure condition is reduced, and a highly accurate pattern can be obtained. Further, the corrected exposure amount can be obtained in a relatively short time.

However, since the above method calculates the corrected exposure amount Qcp for each pattern, it is applicable when partial exposure is performed by selecting a block exposure pattern in a small area of, for example, 4.5 × 4.5 μm ² on the stencil mask. Can not.

  Therefore, in Japanese Patent Application No. 12-166465, the minimum value of the corrected exposure amount of each pattern in the block exposure pattern is determined as the corrected exposure amount Qcp of this block exposure pattern, and then assists the insufficient exposure intensity region in the block. Exposure is in progress.

For example, when the rectangular transmission holes 11 and 12 in FIG. 32A are irradiated with an electron beam having an exposure amount Q _{1 on} the rectangular region 15 indicated by the dotted line in FIG. 33A, the exposure on the wafer coated with the photoresist is performed. The intensity distribution is as shown in FIG. In this state, a thin line pattern cannot be developed due to insufficient exposure. Next, a rectangular transmission hole (not shown) for auxiliary exposure is irradiated with an electron beam, and auxiliary exposure (ghost exposure) of the exposure intensity distribution shown by the alternate long and short dash line in FIG. 34 is performed, thereby narrowing the width (X4-X3). The line pattern can be developed.
JP 2001-052999 A

However, the above method is based on the calculation of the corrected exposure amount for each pattern. For example, the above problem occurs even in block exposure of 4.5 × 4.5 μm ² , for example, a large area of 250 × 250 μm ² on the wafer. It cannot be applied to electron projection lithography (EPL) that performs batch exposure.

  An object of the present invention is to provide a charged particle beam exposure method using a proximity effect correction method that can further reduce variation in the dimensions of a finished pattern when a large area is collectively exposed by a charged particle projection method with a simple configuration. It is to provide.

In one aspect of the present invention, a charged particle beam exposure method for batch exposure of lipase turn by a charged particle projection,
(A) 該Pa turns irradiating a charged particle beam in a main exposure mask formed is a sensitive upper substrate collectively exposed,
(B) by irradiating a charged particle beam in the auxiliary exposure mask supplementary exposure pattern is formed simultaneously exposed on the photosensitive substrate,
The auxiliary exposure pattern has an element pattern group having an area density proportional to the shortage amount for each region where the exposure intensity is insufficient in the batch exposure in step (a).

  According to this configuration, as in the main exposure mask, large areas can be collectively subjected to auxiliary exposure, so that the exposure throughput is improved.

  Other objects, configurations and effects of the present invention will become apparent from the following description. Embodiments of the present invention will be described below with reference to the drawings. The embodiment of the present invention related to the claims is the fourth embodiment.

  First, a known energy intensity distribution function taking into account the electron beam blur δ due to the Coulomb effect or the like will be described.

The energy intensity distribution function f (X, Y) of the above equation (1) is for the case where the electron beam is incident on one point, but actually has a spread. In the electron beam exposure apparatus, the electron beam radiated from the electron gun crosses over until reaching the object to be exposed, and the electrons are subjected to Coulomb repulsion at that position to expand the electron beam (Coulomb effect). The electron beam is also expanded by aberration based on the energy distribution of the electron beam. A current density distribution at an electron beam incident point having a spread is approximated by a Gaussian function S (X, Y), and an exponent part thereof is represented by − (X ² + Y ² ) / δ ² . Also, the blur δ is obtained by using the electron beam current I _b and the constants a and b,
δ = aI _b + b
And can be approximated. For example, a = 0.03 μm / A and b = 0.05 μm. The electron beam current _Ib is a product of the current density J of the electron beam irradiated on the mask and the opening area S (selected block exposure pattern or variable rectangular opening area) of the electron beam irradiation part on the mask. This formula is expressed as
δ = aJS + b (2)
It is expressed. Usually, since the current density J is constant, the blur δ can be easily obtained from the opening area S.

  An energy intensity distribution function F (X, Y) in consideration of the beam blur δ is expressed by the following equation.

実効前方散乱半径β_f'＝（β_f ²＋δ²）^1/2及び
実効後方散乱半径β_b'＝（β_b ²＋δ²）^1/2
を用いれば、この式（３）は、上式（１）においてβ_f及びβ_bをそれぞれβ_f'及びβ_b'で置換したものと同じになる。

Effective forward scattering radius β _f ′ = (β _f ² + δ ² ) ^1/2 and effective back scattering radius β _b ′ = (β _b ² + δ ² ) ^1/2
This equation (3) is the same as the above equation (1) in which β _f and β _b are replaced by β _f ′ and β _b ′, respectively.

For example, since β _b = 11.43 μm, I _b <1.5 μA and δ <0.1 μm, it can be considered that β _b ′ = β _b .

  From these, the above equation (3) is expressed by the following equation.

以上のことから、近接効果補正計算においてクーロン効果などを考慮するには、ショット毎に、開口面積Ｓに依存した実効散乱計数β_f'を計算し、その値を用いればよい。

From the above, in order to consider the Coulomb effect and the like in the proximity effect correction calculation, the effective scattering coefficient β _f ′ depending on the aperture area S is calculated for each shot and the value is used.

As described above, for example, when β _f = 0.028 μm and δ <0.1 μm, and β _f ′ is shorter than the pattern interval, when considering only the influence of forward scattering, only the target pattern needs to be considered. The influence of the surrounding pattern on the pattern is negligible. For simplicity, the effective scatter count is represented by β _f below.

  In each of the following embodiments, the mask pattern width adjustment can be regarded as a change in the design width. However, the design width is used in the repeated pattern width adjustment, and the design width is proportional to the target pattern image width ( In the calculation, since the proportionality coefficient is 1), it is considered that the design width is not changed even if the pattern width is adjusted. The design width is also the initial value of the pattern width.

  Next, an electron beam exposure method using the proximity effect correction method of Embodiment 1 of the present invention will be described.

  This proximity effect correction is a process for exposure data, and adjusts the width of a pattern formed on a mask including a block pattern that is repeatedly used and collectively exposed, and calculates a corrected exposure amount (corrected exposure amount). Is done. The pattern data on the mask included in the exposure data includes the position of each pattern, the design dimension, whether the pattern belongs to the block pattern, the size of the block pattern, and the like.

  FIG. 1 is a general flowchart showing the procedure of this proximity effect correction method.

  This method has three major steps, and includes a step S10 of self-correction (pattern width adjustment) that considers only the forward scattering term (including the effect of the Coulomb effect on beam blur) and the pattern of interest, and the forward scattering term. In step S20 for correcting the exposure amount in consideration of the backscattering term, the minimum value of the corrected exposure amounts of the plurality of patterns in the block exposure pattern is obtained as the corrected exposure amount Qcp of the block exposure pattern, and the exposure intensity in the block is insufficient. The process includes step S30 of obtaining an auxiliary exposure amount Qaux for an area and generating an auxiliary exposure shot in an area where Qaux or Qaux / Qcp is equal to or greater than a predetermined value. The feature of the first embodiment is the process of step S10, and the processes of steps S20 and S30 are the same as those of the above Japanese Patent Application No. 12-166465. However, the present embodiment is different from Japanese Patent Application No. 12-166465 in that the reference forward scattering intensity for each block exposure pattern is used in step S20.

  Hereinafter, the block exposure pattern will be described. The process for the individual pattern is the same as the process for the block exposure pattern having only one pattern.

  FIG. 2 is a detailed flowchart showing the process for one block exposure pattern in step S10 of FIG.

In the self-correction in step S10, for each block exposure pattern, the width W at the reference forward scattering intensity ε _p of the forward scattering intensity distribution of each pattern in the block is set to the design width W 0 based on the forward scattering term of the above equation (4). Adjust the pattern width to be equal. The reference forward scattering intensity ε _p is determined for each block exposure pattern.

  (S11) Substituting the sum S of the opening areas in the block into the above equation (2), the beam blur δ is obtained.

(S12) A rectangular pattern having the minimum width in the block is selected, and the half-value intensity when the half-value width of the forward scattering intensity distribution of this pattern is set to the design width is determined as the reference forward scattering intensity ε _p for block exposure. . ε _p is obtained as follows.

FIG. 3A shows a rectangular pattern whose dimensions in the X direction and the Y direction in the XY orthogonal coordinate system are W and H, respectively. The forward scattering intensity distribution F _f (x, y; W, H) of this pattern is

で表され、ここに、関数Ｇは

Where the function G is

で定義され、誤差関数ｅｒｆは次式

The error function erf is given by

で定義される。図３（Ｂ）は、ｘ軸上の前方散乱強度分布Ｆ_f（ｘ，０；Ｗ，Ｈ）を示す。ブロック内の最小幅の設計寸法Ｗ0×Ｈ0のパターンについて、Ｘ軸及びＹ軸に沿った前方散乱強度分布の半値幅がそれぞれ設計幅Ｗ0及びＨ0に等しくなるように、Ｗ及びＨを決定する。Ｗ及びＨは、次の２元連立方程式
Ｆ_f（Ｗ0／２，０；Ｗ，Ｈ）＝Ｆ_f（０，０；Ｗ，Ｈ）／２ （８）
Ｆ_f（０，Ｈ0／２；Ｗ，Ｈ）＝Ｆ_f（０，０；Ｗ，Ｈ）／２ （９）
の解である。基準前方散乱強度ε_pは、この解Ｗ及びＨを用いて次式
ε_p＝Ｆ_f（Ｗ0／２，０；Ｗ，Ｈ）／２ （１０）
で表される。

Defined by FIG. 3B shows a forward scattering intensity distribution F _f (x, 0; W, H) on the x-axis. For the pattern of the minimum width design dimension W0 × H0 in the block, W and H are determined so that the half-value widths of the forward scattering intensity distribution along the X axis and the Y axis are equal to the design widths W0 and H0, respectively. W and H are the following two simultaneous equations: F _f (W0 / 2, 0; W, H) = F _f (0, 0; W, H) / 2 (8)
F _f (0, H0 / 2; W, H) = F _f (0, 0; W, H) / 2 (9)
Is the solution. The reference forward scattering intensity ε _p is obtained by using the solutions W and H as follows: ε _p = F _f (W0 / 2, 0; W, H) / 2 (10)
It is represented by

FIG. 4 shows the numerical solution W of equation (8) for the design width W0 when H = ∞ and the effective forward scattering radius β _f = 0.04 μm. If the pattern width W is too narrow, the accuracy of the finished pattern image is deteriorated. Therefore, an allowable minimum pattern width Dm is determined based on experiments. For example, Dm = 0.04 μm. When W <Dm or when there is no solution, W = Dm is substituted into Equation (8) to obtain H, and the reference forward scattering intensity ε _p is determined based on Equation (10).

  (S13) The retry flag RF is reset, and 1 is substituted into the intra-block pattern identification number i.

  (S14) If i ≦ n, the process proceeds to step S15; otherwise, the process proceeds to step S1A. Here, n is the number of patterns in the block of interest.

(S15) For the pattern of the design dimension Wi0 × Hi0 in the block, the pattern widths Wi and Hi are determined so that the width of the forward scattering intensity distribution F _{f at} the reference forward scattering intensity ε _p is equal to the design width. That is, the following binary simultaneous equation F _f (Wi0 / 2,0; Wi, Hi) = ε _p (11)
F _f (0, Hi 0/2; Wi, Hi) = ε _p (12)
Find the solutions Wi and Hi.

(S16) If Wi or Hi deviates from the previous value Wib or Hib, respectively, δ in step S11 changes and the parameter of the function F _f changes. Therefore, the calculation in step S15 needs to be performed again for all the patterns in the block. There is. Therefore, if Wi and Hi have not converged, that is, if | Wi-Wib | or | Hi-Hib | is larger than a predetermined value, the process proceeds to step S17, and if not, the process proceeds to step S19. The initial values of the previous value Wib or Hib are the design widths Wi0 and Hi0, respectively.

  (S17) Wi and Hi are stored as Wib and Hib, respectively.

  (S18) The retry flag RF is set.

  (S19) Increment i by 1 and return to step S14.

  (S1A) If RF = 1, the process returns to step S11; otherwise, the process of FIG. 2 is terminated.

For example, as indicated by the wavy lines in FIG. 6, the X direction design widths of the wide isolated pattern and the narrow isolated pattern for individual exposure and the wide pattern and the narrow pattern for block exposure are (X2-X1) and (X4-X3), respectively. ), (X6-X5), and (X8-X7), the pattern width is narrowed as shown by the solid line by the process of step S10. When the rectangular regions 13 to 15 indicated by the dotted lines are irradiated with the electron beams to the rectangular transmission holes 11, 12, 11 </ b> A and 12 </ b> A indicated by the solid lines on the mask 10 </ b> A, an outline of the forward scattering intensity distribution on the wafer coated with the photoresist. Is as shown in FIG. In FIG. 7A, normalization is performed so that the maximum value of the forward scattering intensity distribution of an infinitely large rectangular pattern is 1. The forward scattering intensity distribution of the individual exposure is the same as in the case of the above Japanese Patent Application No. 12-166465, and the pattern width is shifted so that the half width of the forward scattering intensity distribution becomes the design width. The forward scattering intensity equal to the design width is 1/2 and ε _p for the individual exposure wide pattern and narrow pattern, respectively, and is approximately ε _p for both the block exposure thick pattern and narrow pattern. Yes, ε _p <1/2. In FIG. 6, the thick pattern 11A is narrower than the thick pattern 11 for individual exposure. As a result, the beam blur δ becomes smaller than that in the case of FIG. 33A, so that the width of the narrow pattern is slightly different from that in FIG.

  Next, with reference to FIG. 7B and FIG. 8, the contribution of forward scattering and back scattering to the exposure intensity distribution will be visually described.

  FIG. 7B is a schematic diagram showing an exposure intensity distribution obtained by adding a backscattering exposure intensity distribution to the forward scattering intensity distribution of FIG. The amount of exposure is constant and not corrected.

In this case, the backscattering component of the pattern area density α _p (α _p ≦ 1) is α _p · η, and the exposure intensity equal to the design width is expressed by ε _p + α _p · η. The thick-width isolated pattern is ε _p = 1 and α _p = 1. Although the influence of backscattering is wide-ranging, the value is relatively small unless the area is integrated, so that α _p · η of the narrow isolated pattern can be ignored.

  In FIGS. 7A and 7B, as apparent from the above equation (4), the exposure intensity is actually a value multiplied by a constant 1 / (1 + η), but this constant is omitted. Has been.

  Next, the exposure amount correction process in step S20 will be outlined.

  FIG. 8 is a schematic diagram showing the exposure intensity distribution after correcting the exposure intensity distribution of FIG. 7B.

As shown in FIG. 8, for each pattern, the corrected exposure dose Qcp times the exposure intensity (ε _p + α _p · η) equal to the design width is equal to the developing threshold Eth, that is,
(Ε _p + α _p · η) Qcp = Eth (13)
The corrected exposure amount Qcp is determined so as to satisfy the above. In FIG. 8, Q _{1 to} Q ₃ are the corrected exposure dose Qcp of the isolated thick pattern and the isolated narrow pattern and the block exposure pattern of the individual exposure, respectively.
(1/2 + η) Q ₁ = ε _p Q ₂ = (ε _p + α _p · η) Q ₃ = Eth
Q _{1 to} Q ₃ are determined so that

In the above description, the pattern area density α _p is used for simplification, but α _p is actually an effective pattern area density α _p ′ described later.

  Next, the exposure amount correction process in step S20 will be described in detail.

(S21) The surface on which the pattern to be exposed is arranged is divided into meshes of size A × A, and the area density αi, j of the i-th row and j-th column
αi, j = (area of pattern in mesh in i-th row and j-th column) / A ²
Calculate However, this pattern has the width adjusted in step S10. For example, the block shot size is a square having a side of 4.5 μm, and the square is a square having a side of 1.5 μm. Since the pattern width is not changed in steps S20 and S30, it is only necessary to calculate once.

  (S22) An effective pattern area density α′i, j described later is calculated.

  In FIG. 5, when the entire rectangular area of the (i + l) th row (j + m) column divided by the mesh is exposed, the exposure intensity al, m of the grid center point of the i-th row and j-th column due to backscattering is expressed as follows: The backscattering term of the above equation (4) is obtained by dividing the area within the mesh of the (i + l) th row and the (j + m) th column, and is expressed by the following equation.

ａl,mは、上式（４）の後方散乱項を全範囲で面積分した値が１になるように、すなわち、ａl,mの全てのｌ及びｍの値についての総和Σａl,mが１になるように規格化されている。

al, m is such that the value obtained by dividing the backscattering term of the above equation (4) by area over the entire range is 1, that is, the sum Σal, m for all l and m values of al, m is 1. It is standardized to become.

When the pattern of the area density αi + l, j + m in the grid of the (i + l) th row and the (j + m) th column is exposed with the corrected exposure amount Qi + l, j + m, the i-th row jth by backscattering. The exposure intensity in the cell of the column is approximated by η × al, m × αi + l, j + mQi + l, j + m. Considering that the influence of backscattering on a certain point is within a radius 2β _b centering on this point, it is sufficient in calculation accuracy. Therefore, when the effective pattern area density α′i, j is defined by the following equation, the exposure intensity in the cell in the i-th row and j-th column due to backscattering is approximated as ηα′i, jQcp.

ここに、整数ｌ及びｍの範囲はいずれも、−int(２β_b／Ａ)〜int(２β_b／Ａ)であり、int(ｘ)はｘの小数点以下を切り上げて整数化する関数である。上式（１５）の計算を、スムージング処理と称す。

Here, the integers l and m are both in the range of −int (2β _b / A) to int (2β _b / A), and int (x) is a function that rounds up the decimal point of x to make an integer. . The calculation of the above equation (15) is referred to as smoothing processing.

  Here, the relationship between the corrected exposure dose Qcp of the block pattern and the auxiliary exposure dose Qaux will be described. For the sake of simplicity, consider the case where auxiliary exposure is performed in units of mesh cells. Therefore, the auxiliary exposure shot size is A × A. The first to ninth meshes are included in the block exposure region, and the auxiliary exposure amount Qaux and effective pattern area density of the kth mesh are expressed as Qaux.k and α′k, respectively, and the effective pattern area density in the block when k = m. Is the maximum value.

For each mesh k, the sum of (ε _p + α′k · η) Qcp and auxiliary exposure amount Qaux.k is determined to be equal to Eth. That is, the following equation (ε _p + α′k · η) Qcp + Qaux.k = Eth (16)
When kcp is determined so that Qaux.k = 0 when k = m, the following equation is derived from equation (16).

(Ε _p + α′m · η) Qcp = Eth (17)
From the above equations (16) and (17), the following equation is derived.

Qaux.k = (α′m−α′k) ηQcp.i (18)
No auxiliary shot is generated in the area where Qaux.k = 0. In addition, Qaux.k> Δ · Qcp.i, that is,
(Α′m−α′k) η> Δ (19)
May be used as the auxiliary exposure generation condition. Here, Δ is determined by the required finished pattern dimension accuracy, for example, 0.05 or 0.01, and means that the auxiliary exposure amount to be omitted is smaller than 5% or 1% of the corrected exposure amount, respectively. is doing.

(S23) The corrected exposure amount Qcp is calculated based on the above equation (17). The above equation (17) relates to block exposure, but is also applied to a plurality of square-by-square exposure patterns. The processing in step S20 differs from the above-mentioned Japanese Patent Application No. 12-166465 only in that ε _p in equation (17) differs for each block exposure pattern.

  Next, step S30 for generating an auxiliary exposure shot will be described. This process is the same as the above-mentioned Japanese Patent Application No. 12-166465.

  (S31) The auxiliary exposure amount Qaux.k is calculated based on the above equation (17). The above equation (18) relates to block exposure, but is also applied to a plurality of square-by-square exposure patterns.

  (S32) As described above, for example, it is determined that auxiliary exposure is to be performed on the cells satisfying the condition of the above equation (19), that is, an auxiliary exposure shot is generated. The auxiliary exposure shot is performed so as to overlap the block exposure shot. In the auxiliary shot, the rectangular electron beam size is made to coincide with A × A, and exposure is performed with a focus.

  (S33) If the corrected exposure dose Qcp and the auxiliary exposure dose Qaux.k have not converged, the process returns to step S22.

  In step S22, the auxiliary exposure amount is also taken into consideration. The initial value of each corrected exposure amount Qcp is, for example, the corrected exposure amount of an isolated thick pattern.

In the first embodiment, a rectangular pattern having a minimum width in a batch exposure region (block) that is repeatedly used is selected, and is determined as a reference forward scattering intensity ε _p based on the forward scattering intensity distribution of this pattern. Since the pattern width is adjusted so that the width at the reference forward scattering intensity ε _p of the forward scattering intensity distribution of each pattern is equal to the design width, as shown in FIG. 8, the threshold value Eth of the exposure intensity distribution of the narrow-width pattern in the block The inclination at the point becomes steep, the variation in the width of the finished pattern image with respect to the variation in the exposure conditions is reduced, and a highly accurate narrow pattern can be obtained. The thick pattern has a gentler slope than in the case of Japanese Patent Application No. 12-166465, but the decrease in dimensional accuracy is small due to the large width. Therefore, the dimensional accuracy of the completed pattern image as a whole pattern is improved as compared with the conventional pattern.

  Further, as in the above Japanese Patent Application No. 12-166465, the corrected exposure amount can be obtained in a relatively short time.

Since the slope of the forward scattering intensity distribution is relatively large in the vicinity of the half-value intensity, it is not always necessary to make the half-value width of the pattern of the minimum width in the block equal to the design width in step S12, and the forward scattering intensity distribution F _f when the peak is Fmax, if equal F _f = κFmax, the width of a value within the range of kappa = 30 to 70% to the design width, dimensional accuracy of the finished pattern is improved compared with the prior art. The reason for this range limitation is that if it is lower than 30%, due to the effect of overlapping exposure intensity distributions of adjacent patterns, if it is higher than 70%, the slope of the forward scattering intensity distribution at that position is gradual. This is because becomes smaller.

In step S12, the reference forward scattering intensity ε _p is adjusted so that the width at the slice level of the forward scattering intensity distribution of the pattern having the minimum design width in the batch drawing region is equal to the design width. It may be the slice level at that time. That is, the reference forward scattering intensity ε _p may be determined as ε _p = F _f (W 0/2, 0; W 0, H 0) for the pattern of the design dimension W 0 × H 0 having the minimum width in the block. If the pattern dimensions in the area to be drawn at once are extremely different, if the pattern is changed to a large pattern according to the half-value intensity of the forward scattering intensity distribution of the fine pattern, the width near the skirt of the forward scattering intensity distribution is equal to the design width. As a result, the exposure margin of a large pattern is reduced. Thus, the exposure margin of a large pattern is reduced by setting the reference forward scattering intensity ε _p to a relatively high intensity without changing the pattern of the smallest dimension. Can be reduced.

Further, in step S15, the dimension shift with respect to the pattern in the region to be collectively drawn is set so that the width at the reference forward scattering intensity ε _p of the forward scattering intensity distribution is equal to the design width with respect to the short side direction as described above. For the long side direction, the width of the forward scattering intensity distribution at F _f = κFmax may be set equal to the design width. In general, when the pattern is greatly thinned, the exposure intensity at the corner portion tends to decrease and tends to be rounded, but by doing so in the long side direction, the forward scattering intensity at the connection portion of the pattern is 2κ times the peak intensity. (If κ = 0.5, the intensity is the same as the peak intensity), and a reduction in exposure intensity at the connection portion can be reduced.

  Next, an electron beam exposure method using the proximity effect correction method according to the second embodiment of the present invention will be described with reference to FIGS.

As the pattern becomes finer, the distance between the patterns becomes shorter, and when this becomes an effective forward scattering radius β _f , the influence of forward scattering from nearby patterns occurs. The second embodiment is different from the first embodiment in that the forward scattering intensity calculation in step S15 of FIG. 2 takes into account the influence of forward scattering from nearby patterns for each side of the pattern.

FIG. 9A shows a block pattern in the batch exposure region. As shown in FIG. 9B, a non-rectangular pattern is divided into rectangles, and fixed sample points indicated by black dots are set at the midpoints of the sides of each rectangle. Fixed sample points are not set on the sides where the patterns B and C are in contact. Next, in order to capture the influence of forward scattering from nearby patterns, the forward scattering intensity at a fixed sample point set in each pattern is calculated. FIG. 10A shows the influence of forward scattering from a nearby pattern at the fixed sample point P2. The integration range of the forward scattering intensity calculation is, for example, a range of ± 2β _f in each of the X direction and the Y direction with each fixed sample point as the center. For each fixed sample point, the side corresponding to the fixed sample point is shifted in the perpendicular direction so that the forward scattering intensity becomes the reference forward scattering intensity, and the pattern width is adjusted.

In this way, when the influence of forward scattering from nearby patterns is taken in, the shift amount is generally different at the opposite sides. Therefore, as shown in FIG. 10B, when the coordinates of the lower left corner of the pattern are (X1, Y1) and the coordinates of the upper right corner are (X2, Y2), the forward scattering intensity distribution corresponding to the above equation (5) function F _f, the following equation _{F f (X, Y; X1} , X2, Y1, Y2) = G (X; X1, X2, β f)
· G (Y; Y1, Y2 , β f) (20)
Defined by In this case, in order to make the width of the forward scattering intensity distribution at the reference forward scattering intensity ε _p for the pattern of the design dimension W 0 × H 0 equal to the designed width, four fixed sample points P1, P2, P3 and P4 are used. The coordinates (X1, Y1) and (X2, Y2) are determined by calculation so that the forward scattering intensity in each of the above becomes equal to the reference forward scattering intensity ε _p . That is, the following quaternary simultaneous equations (P1) F _f of points P1~P4 (-W0 / 2,0; X1, X2, Y1, Y2) + ε1 = ε p
(P2) F _f (W0 / 2, 0; X1, X2, Y1, Y2) + ε2 = ε _p
(P3) F _f (0, −H0 / 2; X1, X2, Y1, Y2) + ε3 = ε _{p
(P4) F f (0,} H0 / 2; X1, X2, Y1, Y2) + ε4 = ε p
Solve. Here, ε1 to ε4 are forward scattering intensities from neighboring patterns excluding the pattern A at the fixed sample points P1 to P4 of the pattern A, respectively.

  The other points are the same as in the first embodiment.

  According to the second embodiment, the influence of forward scattering from nearby patterns is taken into account for each side of the pattern, so that the accuracy of the finished pattern image can be improved.

  In order to perform the dimensional shift more accurately in consideration of the influence of forward scattering, as shown in FIG. 11A, the pattern A in FIG. 10A is calculated to be composed of three divided patterns A1 to A3. In the divided patterns A1 to A3, fixed sample points are set at the midpoints of the sides that are in contact with the boundary of the pattern A, and the corresponding sides of each fixed sample point are shifted in the perpendicular direction in the same manner as described above. As a result, the width of each part of the pattern A is adjusted. Thereby, for example, a more accurately adjusted pattern as shown in FIG. 11C is obtained.

The above is an example in the case of repeatedly exposing a small area block pattern of, for example, 4.5 × 4.5 μm ² on a stencil mask to a plurality of locations on a wafer. ^{The present} invention can also be applied to an EPL in which ^two subfields are collectively transferred onto a wafer to obtain a 250 × 250 μm ² subfield image.

  Next, an electron beam exposure method using the proximity effect correction method according to the third embodiment of the present invention will be described with reference to FIGS.

  This method includes step S40 for adjusting the pattern width and step S50 for generating auxiliary exposure. Since it is a batch exposure, Qcp = 1.

For simplicity, a pattern having an infinite length in the Y-axis direction will be outlined. In the above equation (13), Qcp = 1, and the following equation: ε _p + α _p ′ · η = Eth (21)
, The reference exposure intensity (threshold) Eth = ε _p is obtained by calculating the forward scattering intensity ε _p of an isolated pattern having a design width W 0 that can be approximated as α _p ′ · η = 0. That is, the slice level is adjusted so that the width at the slice level of the forward scattering intensity distribution of the pattern with the design width W0 becomes the design width W0, and this slice level is determined as the reference exposure intensity Eth. In particular,
_{Eth = 0.5erf (W0 / β f} ) (22)
Calculate If the minimum width is selected as the design width W0, the variation in the width of the finished pattern image with respect to the variation in the exposure conditions is reduced for the reason described in the first embodiment, and the dimensional accuracy of the finished pattern image as a whole pattern is higher than that of the conventional pattern. improves.

Next, the effective pattern area density α _p ′ is calculated by the pattern area density map method described above.

Thereby, the slice level ε _p = Eth−α _p ′ · η of the forward scattering intensity distribution of each pattern is determined from the equation (21). On the other hand, the forward scattering intensity distribution is determined by the pattern width W. Therefore, the pattern width W is adjusted so that the width at the slice level of the forward scattering intensity distribution becomes the design width W0i. In particular,
epsilon _p = [erf {(W-W0i) / 2β f} + erf {(W + W0i) / 2β f} ] / 2 (23)
Find the solution W. Specifically, in calculating the effective pattern area density α _p ′, the pattern is divided into a plurality of patterns, and fixed sample points are set as shown in FIG. The pattern width W is adjusted by shifting in the vertical direction. Further, in the above formula (18), Qcp.i = 1 (Qaux.k = (α′m−α′k) η) (24)
Since the auxiliary exposure is performed in the same manner as in the block exposure, the process of step S50 is required.

  According to the third embodiment, the proximity effect correction calculation can be performed relatively easily by the algorithm as described above.

  15 (A) and 15 (B) are conceptual explanatory views of the present invention.

  FIG. 15A shows a part of the batch transfer mask 10B. A solid line is a pattern having a design dimension, and a dotted line is a pattern whose width is adjusted by the process of step S40. The pattern 16 is a rectangular pattern having the minimum design width selected in step S41, and this width is not adjusted.

  FIG. 15B shows an exposure intensity distribution in the case of performing batch exposure with the mask of FIG. A solid line and a dotted line are the cases where the pattern after design dimension and width adjustment is used, respectively. In FIG. 15B, auxiliary exposure is not included.

  Next, the process of FIG. 12 will be described in detail.

  (S41) An isolated rectangular pattern having a minimum width is selected, an XY coordinate system is defined as shown in FIG. 3A, and the widths in the X-axis direction and the Y-axis direction at the slice level of the exposure intensity distribution are respectively designed. The slice level when the slice level is adjusted to be equal to the widths W0 and H0 is obtained as the reference exposure intensity Eth. Eth is calculated by the following equation.

Eth = F (W / 2, 0; W, H) (25)
Here, F is defined by the following equation.

F (X, Y; W, H) = F _f (X, Y; W, H) + ηF _b (X, Y; W, H)
(26)
F _f (X, Y; W, H) = G (X; −W / 2, W / 2, β _f )
· G (X; -H / 2 , H / 2, β f) (27)
F _b (X, Y; W, H) = G (X; −W / 2, W / 2, β _b )
G (X; -H / 2, H / 2, β _b ) (28)
Since the isolated pattern is not affected by backscattering, the relationship of slice level = reference exposure intensity (development threshold) is not affected by the following processing. In particular, if the isolated pattern is a minimum width pattern, the variation in the width of the completed pattern image with respect to the variation in the exposure condition of the narrow pattern is reduced, and the dimensional accuracy of the completed pattern image as a whole pattern is improved as compared with the conventional pattern.

(S42) The pattern (exposure data) is equally divided into rectangular patterns as units of dimension shift. The size of the divided pattern (divided pattern) is, for example, about (β _b / 10) × (β _b / 10), and the influence from the adjacent divided pattern on each edge of the divided pattern is uniform. Make it so that it can be considered.

  FIGS. 13A, 13C, and 13E are explanatory diagrams when one rectangular pattern indicated by a solid line is divided as indicated by a dotted line, and FIGS. (D) and FIG. 13 (F) are shown separately from each other in order to clarify the patterns divided in FIGS. 13 (A), 13 (C), and 13 (E).

  FIG. 13A shows a case where the image is simply divided at the designated size from the lower left corner. If the pattern dimension is not divisible by the designated size, a minimal pattern is generated on the right and above. In this case, the pattern disappears or the pattern width becomes negative at the time of dimensional shift, which is inappropriate.

  FIG. 13C shows a case in which the vertical and horizontal sides of the rectangular pattern are equally divided at a designated size, and the generation of a minute pattern as shown in FIG. 13A can be prevented by equally dividing the rectangular pattern. However, in the graphic change (pattern width adjustment) described later, only the side whose edge matches the original pattern is changed, so finely dividing the pattern becomes useless and complicated. It is only effective. Therefore, as shown in FIG. 13 (E), it is equally divided as in FIG. 13 (C), but only the area along the periphery of the original pattern is divided into rectangles of the same size, and each divided pattern is the original pattern. It has an edge that touches the boundary. Thereby, an unnecessary increase in the number of divided rectangular patterns can be prevented. The black dots in FIG. 13F are the same fixed sample points as in FIG.

In the following, in the case of processing for a divided pattern, a pattern that is not divided because the size is small or isolated is also referred to as a divided pattern. Further, for example, when a pattern having a design dimension of 1 × 3 μm ² is divided into three and becomes 1 × 1 μm ² , this 1 × 1 μm ² is also referred to as a design dimension.

  (S43) The pattern area density α i, j is calculated for each i and j.

  (S44) The effective pattern area density α′i, j with Qi, j = 1 and Qi + 1, j + m = 1 in the above equation (14) is calculated for each i and j.

(S45) In order to capture the influence of forward scattering from nearby patterns on the pattern divided in step S42, fixed sample points are set as shown in FIG. The forward scattering intensities ε1 to ε4 from the adjacent pattern at the sample point are calculated. Next, with respect to the divided pattern of the design dimension W0 × H0, a pair of diagonal points (X1) is formed in the same manner as in FIG. 10B so that the width at the exposure intensity distribution slice level = reference exposure intensity Eth is equal to the design width. , Y1) and (X2, Y2) are converted into the following quaternary simultaneous equations (P1) F _f (−W0 / 2, 0; X1, X2, Y1, Y2) + ε1 + α′i, j · η = Eth
(P2) F _f (W0 / 2, 0; X1, X2, Y1, Y2) + ε2 + α′i, j · η = Eth
(P3) F _f (0, −H0 / 2; X1, X2, Y1, Y2) + ε3 + α′i, j · η = Eth
(P4) F _f (0, H0 / 2; X1, X2, Y1, Y2) + ε4 + α′i, j · η = Eth
Find and solve. However, a side that does not coincide with the edge of the original pattern, such as a side marked with an X in FIG. 13F, is not moved.

  As described above, the divided pattern is regarded as a design pattern and the pattern width is adjusted in units of divided patterns, thereby improving the dimensional accuracy of the pattern before division.

  (S51 to S53) Processing similar to that of steps S31 to S33 in FIG. 1 described above is performed. Since it is determined whether or not auxiliary exposure is performed in units of cells, if the auxiliary shot is not performed, a partial exposure intensity may be insufficient in a pattern extending over a plurality of cells. Further, when the dimension is shifted, the pattern coordinates may be rounded to the minimum dimension unit of the exposure apparatus, resulting in insufficient exposure intensity. Such a lack of exposure intensity is solved by generating an auxiliary exposure shot having a grid size. In step S43, the pattern area density of auxiliary exposure is also considered. If the effective pattern area density changes due to the size shift or the auxiliary exposure shot, it is determined that the pattern does not converge and the process returns to step S43.

  FIG. 14 shows that the two design patterns indicated by the wavy lines are divided at step S42 and the surrounding sides are shifted at step S44.

In step S41, the reference exposure intensity Eth = ε _p may be determined in the same manner as in the process in step S12 in FIG. That is, in step S41, the pattern width may be adjusted. For example, an isolated rectangular pattern having the minimum design width W0 is selected, and the width at the slice level, which is a value within the range of 30 to 70% of the peak value of the forward scattering intensity distribution with respect to this pattern, is made equal to the design width. Alternatively, the slice level when the pattern width is adjusted may be determined as the reference exposure intensity Eth.

  Further, a relationship between a representative value of the design width, for example, the minimum value W0 and the reference exposure intensity Eth is calculated or empirically tabulated, and in step S41, the reference exposure intensity Eth is determined by referring to this table at W0. It may be determined.

  In step S41, the reference exposure intensity Eth may be determined, so this pattern does not have to be an isolated pattern. In this case, the pattern width is determined by the processing in steps S43 to S53.

  Also, the beam blur δ in the energy intensity distribution function is affected by the aberration of the lens of the exposure apparatus and the Coulomb effect, the area to be irradiated at once, the position in the batch irradiation area, the partial aperture area and current in the batch irradiation area. It is known to depend on density. Therefore, for more accurate correction, the effect of these on the beam blur δ is measured in advance by experiments, and the beam blur δ is obtained using the function obtained by fitting, or the experimental results are used to shorten the calculation time. And a blur δ is obtained from the table.

For example, as conceptually shown in FIG. 16, the batch irradiation region 250 × 250 μm ² is divided into 10 × 10 regions, and the beam blur δ [μm] is measured at the center of each region marked with “x”. A table is formed as shown in FIG. 15 to 16 indicate the center positions of the respective regions in the X direction and the Y direction. The beam blur δ at an arbitrary point in the collective irradiation can be obtained by two-dimensional interpolation of this table.

  Alternatively, the dependence of the beam blur δ on the collective irradiation area, the position in the collective irradiation region, the partial opening area in the collective irradiation region, and the current density is derived by simulation considering the optical system of each electron beam apparatus. The beam blur δ can be obtained from the relational expression.

  Further, for example, the position dependency of the beam blur δ within the collective irradiation region can be obtained by experiment, and the irradiation area dependency can be obtained by simulation.

  Next, an electron beam exposure method using the proximity effect correction method according to the fourth embodiment of the present invention will be described with reference to FIGS.

  In the first to third embodiments, an auxiliary exposure shot with an adjusted auxiliary exposure amount is generated in a correction area where the exposure intensity is insufficient. However, since the number of auxiliary exposure shots increases, the exposure time becomes enormous. Therefore, in the fourth embodiment of the present invention, an auxiliary exposure mask is created, and a large area is collectively subjected to auxiliary exposure as in the case of main exposure.

  18 to 20 are explanatory views showing exposure data as images. In any one of the first to third embodiments, the exposure data after adjusting the exposure amount and generating the auxiliary exposure shot is created (FIG. 18). Next, main exposure data and auxiliary exposure data are separated from the exposure data (FIGS. 19A and 19B). Finally, the auxiliary exposure data is equivalent to the exposure amount of the auxiliary exposure shot. The pattern is replaced with an area density pattern (FIG. 20), and this is used as auxiliary exposure mask data.

  Next, a method for replacing the auxiliary exposure data with an area density α pattern group having an exposure intensity equivalent to that of the auxiliary exposure shot with the exposure amount Qaux will be described.

  The exposure intensity at the center of the large pattern is 1. The exposure intensity at the center when this pattern is finely divided into pattern groups having an area density α is α. Therefore, in order to draw with the exposure amount Q0 and obtain the effect of the auxiliary exposure shot with the exposure amount Qaux, the auxiliary exposure shot is divided into pattern groups of area density α = Qaux / Q0.

  It is difficult to create a sufficiently finely divided pattern group due to the limitations of the pattern size and space that can be created on the mask. FIG. 21A and FIG. 21B each show a case where the pattern group is a mesh shape and a strip shape (both are in a lattice shape), and pattern groups having a relatively small area density and a relatively large area density are respectively shown. Use to get.

  FIG. 22 is a diagram schematically showing the forward scattering intensity distribution of the strip pattern, where the exposure intensity is high where the pattern is present and the exposure intensity is low where there is no pattern. It is important that the difference between the maximum value Emax and the minimum value Emin of the forward scattering intensity can be regarded as almost zero. The unevenness of the backscattering intensity distribution is negligible.

FIG. 23 is a diagram showing the relationship between the space width (unit is forward scattering length β _f ) and Emax−Emin (unit is arbitrary) of the strip pattern (line and space pattern) of FIG. It is. For example, when Emax−Emin ≦ 1/63 and Emax−Emin can be regarded as almost zero, a strip pattern with an area density of 50% can be created by using both pattern width and space width of 0 · 75β from FIG. Must be _f or less.

  However, in the present embodiment, since only the auxiliary exposure is created in the mask, there is no problem in pattern accuracy even if the electron beam is blurred to some extent, thereby making it possible to increase the effective forward scattering length. This can be realized even when a dimension as short as 0.75 times is required.

  According to the fourth embodiment, as in the main exposure mask, large areas can be collectively subjected to auxiliary exposure, so that the exposure throughput is improved.

  Next, an electron beam exposure method using the proximity effect correction method according to the fifth embodiment of the present invention will be described with reference to FIGS.

  For example, under the conditions of an effective forward scattering length of 30 nm, an effective backscattering length of 30 μm, and a backscattering coefficient of 0.6, as shown in FIG. Then, as shown in FIG. 24B, the backscattering intensity of the space portion between the patterns exceeds the reference exposure intensity Eth. Therefore, even if the pattern width is adjusted in step S45 of FIG. The width of the distribution at the reference exposure intensity Eth cannot be matched with the design width.

  However, if the pattern area density is partially reduced by changing a part of the large rectangular pattern to a lattice pattern such as a strip pattern or mesh pattern with or without beams, the backscattering intensity of the space part is the standard. Under the exposure intensity Eth, such a pattern can also be corrected.

  FIG. 25 is a general flowchart showing the procedure of the proximity effect correction method improved from the method of FIG. 12 according to the fifth embodiment of the present invention.

In FIG. 25, steps S46 to S48, S60 and S61 are added to the process of FIG. In addition, in order to generate a lattice pattern, in step S42A, for the pattern as shown in FIG. 26A, the entire area of the pattern is, for example, about (β _b / 10) as shown by the solid line in FIG. Divide evenly by size. The dotted line in FIG. 26 (B) is the mesh described above.

  (S46) Of the rectangular patterns divided in step S42A, for the divided pattern in contact with the boundary of the original pattern, for example, the divided pattern in the hatched area in FIG. 26B, step S45 in FIG. The same processing is performed to adjust the pattern width as shown in FIG. The process of step S45 is also performed on the original pattern that is small and not divided.

  The pattern of the area inside the hatched area in FIG. 24B, that is, the pattern in which all four sides of the divided pattern are in contact with the side of the other divided pattern (four-side adjacent pattern) Performs the process of step S47. Such a divided pattern does not require dimensional accuracy, but has a relatively large backscattering intensity because it is a relatively large pattern. For this reason, the four-side adjacent pattern has a great influence on the divided pattern in contact with the boundary of the original pattern, and the finished dimensions are likely to vary.

(S47) Since each divided pattern of the inner region is converted into a lattice pattern having a pattern area density α _gp as shown in FIG. 27B, for example, in the subsequent step S60, The area density α _gp is calculated by the following equation.

α _gp (F _f min + (α _p ′ / α _gpb ) η) = kEth (29)
Here, α _gp , F _f min, α _p ′, and α _gpb are all related to the divided pattern of interest, and F _f min is a minimum value Emin of the forward scattering intensity and an average intensity (Emax + Emin) / 2 of the lattice pattern. The ratio is 1 or less. α _p ′ is the minimum value of the effective pattern area density of the cell straddling the divided pattern of interest calculated in step S43. The pattern area density αi, j in the second and subsequent steps S43 of the repetitive loop of steps S43 to S53 takes into account the lattice pattern in step S47 and the dimensional shift in step S45. The pattern effective area density in S43 is a value related to the lattice pattern. α _gpb is the previous value of α _gp , its initial value is 1, and α _gpb = α _gp when determined to have converged in step S53. k is a constant larger than 1.

When converged, α _gp · F _f min is approximately equal to the minimum value of the forward scattering intensity (corresponding to the above minimum value) in the _target divided pattern having the pattern area density α _gp , and (α _gp / α _gpb ) α _p ′ · η = α _p ′ · η is the backscattering intensity in the divided pattern of _{interest having} the pattern area density α _gp . That is, the lattice pattern area density α _gp of the target divided pattern is determined so that the minimum exposure intensity of the lattice pattern in the target divided pattern is k times Eth.

Thus, by reducing the pattern area density of the inner region, the problem of variation is solved. Further, since the backscattering intensity is larger than the reference forward scattering intensity, it is possible to correct a pattern that cannot be corrected only by adjusting the pattern width. If α _gp is determined by the above equation (29), it is guaranteed that even if the minimum value of the forward scattering intensity after conversion into the lattice pattern is not exposed, the development is not disabled.

  If the value of k is too close to 1, a part of the pattern may not be developed due to fluctuations in the amount of exposure, and conversely, if it is too large, the backscattering intensity is not sufficiently reduced, so about 1.2 is appropriate.

Further, the minimum value F _f min of the forward scattering intensity varies depending on the relationship between the pitch and space width of the grating pattern and the forward scattering length. Therefore, it is appropriate to determine the minimum value F _f min based on the expected minimum pattern area density, the minimum space width required in mask formation, and the like.

Substitute α _gp for α _gpb .

(S60) A lattice pattern is generated based on the pattern area density α _gp after convergence.

For example, when the division pattern is 3 × 3 μm ² and α _gp = 0.5, if this is converted to line and space, for example, 50 line patterns with a width of 30 nm and a length of 3 μm are generated at a pitch of 60 nm. If converted into a lattice pattern, for example, 30 × 30 nm ² rectangular patterns are generated at a pitch of 42.4 nm in both the vertical and horizontal directions.

Attention should be paid to the fact that if the pattern width or space width is too small, it will be difficult to create a mask. Conversely, if the pitch or space width is too large compared to the forward scattering length, the exposure intensity will decrease locally. It is developed as a lattice pattern. In order to avoid these, a pattern generation condition is required at the time of pattern generation. For example, when the forward scattering length is 30 nm and the minimum aperture width of the mask is 30 nm, it is appropriate as one condition to fix the space width to 30 nm. It is also an appropriate condition to fix the pitch to, for example, twice the forward scattering length. Furthermore, a method of using the houndstooth pattern and the line-and-space pattern according to the value of the pattern area density α _gp is effective for reducing the difficulty of mask creation. This is because, in order to realize the same pattern area density as the line-and-space pattern using a staggered lattice under a constant pitch condition, the space must be made smaller, so that, for example, the pattern area density α _gp is 50%. By making it a houndstooth pattern if it is less than 50%, and using a line and space pattern if it is 50% or more, the generation of extremely thin beams can be suppressed, and the difficulty of mask creation can be reduced.

  (S61) Next, the pattern generated in step S60 is divided.

  The pattern shown in FIG. 27B cannot be realized because it has a donut-shaped opening for reducing the pattern edge roughness and the center part falls off. The donut pattern is usually divided into two patterns, a mask corresponding to each pattern is produced, and exposure is performed twice.

  The pattern in FIG. 27B is divided into, for example, the pattern in FIG. 28A and the pattern in FIG. The peripheral pattern is divided into a vertical pattern and a horizontal pattern, and the lattice pattern is equally divided. The reason for dividing equally is the following two points. The first point is to prevent the Coulomb effect of either of the two exposures from becoming extremely large by making the opening areas substantially the same. The second point is that it is very difficult to create a mask having a lattice pattern with a small pitch or space. However, if the mask is equally divided into two masks, the pitch is doubled and the mask can be easily created. This is because the durability of the is improved.

Note that the effective pattern area density α _p ′ used for the calculation of the pattern area density α _gp may not be the minimum value in the divided pattern, but the maximum value, the average value, the value at the grid where the pattern centroid exists, or this division You may use the weighted average value by the grid included in the pattern and straddling. As a method of calculating the pattern area density α _gp ,
α _gp = 0.5 when α _p '≧ 0.5, α _gp = 1.0 when α _p '<0.5
Or
When α _p '> 0.5, α _gp = 0.5 / α _p '
May be used.

  Also, even if the mask is an aperture mask, if there is no donut pattern in the chip and only one main exposure mask is used, one of the following methods is used.

  (1) For a pattern that was originally a part of a large pattern, the process proceeds to step S47 without performing the determination process of step S46 in FIG. 25, and the occurrence of a donut pattern is prevented.

  (2) Instead of step S61 in FIG. 25, the lattice pattern area is expanded as follows. For example, when the lattice pattern is partially generated as shown in FIG. 29B in step S60 for the pattern of FIG. 29A, it is parallel to the side having the highest backscattering intensity among the exposure boundaries of the original pattern. In addition, the lattice pattern area is extended to the exposure boundary. For example, a houndstooth pattern or a line and space pattern with a width of 30 nm is generated in the extended region.

  Further, when there is only one main exposure mask, for example, when a membrane mask that does not lack a donut pattern is used as the mask, the pattern division in step S61 may not be performed.

  Furthermore, in particular, when it is desired to accurately draw a fine pattern, pattern division may be performed so as to reduce the total pattern area on the fine pattern side in order to reduce beam blur due to the Coulomb effect near the fine pattern.

  Next, an electron beam exposure method using the proximity effect correction method according to the sixth embodiment of the present invention will be described with reference to FIG.

  According to the fifth embodiment, it is possible to separate and transfer large patterns close to each other as shown in FIG. However, if the inner region exists when the pattern is divided in step S42A, a lattice pattern is always generated. In addition, two main exposure masks are required.

  Therefore, in the sixth embodiment of the present invention, step S48 for extracting a pattern that needs to reduce the pattern area density is added to step S40B. In order to obtain information for determining which pattern to extract, the processes of steps S43 and S44 are performed before step S48.

(S48) For the meshes set in step S43 that include the pattern boundary, it is determined whether the backscattering intensity α _p ′ · η is, for example, 80% or more of the reference exposure intensity Eth, and an affirmative determination is made. Extract patterns that contain boundaries in the grid. This percentage is set high for a resist that resolves properly even at low contrast, otherwise it is set low.

  Next, after performing the figure dividing process of step S42A, the process proceeds to step S46A.

  (S46A) Similar to step S46 of FIG. 25, the same processing as step S45 of FIG. 12 is performed on the pattern (surrounding pattern) in contact with the boundary of the original pattern among the rectangular patterns divided at step S42A. Then, the pattern width is adjusted as shown in FIG. However, the process of step S47 is performed on the pattern inside the surrounding pattern only for the pattern extracted in step S48.

  The processes in steps S48 and S42A are performed only once in the repetition loop.

  Other points are the same as those of the fifth embodiment.

  Note that the present invention includes various other modifications.

  For example, the energy intensity distribution function is not limited to the above-mentioned double Gaussian, and a triple Gaussian having a third term including a fitting coefficient γ and a secondary electron scattering ratio η ′ for improving the consistency with the actual measurement may be used, You may approximate. In particular, in the second and third embodiments, in the dimension shifting step, a term that is included in the triple Gaussian and extends in a range wider than forward scattering and narrower than back scattering may be taken in.

  Further, the length of one side of the mesh cell need not be 1 / (integer) of that of the block exposure pattern.

  As is apparent from the above description, the present invention includes the following supplementary notes.

(Supplementary note 1) In a charged particle beam exposure method in which proximity effect correction is performed by adjusting the width of a pattern formed on a mask including a block pattern that is repeatedly used and collectively exposed, and calculating a correction exposure amount.
(A) determining a reference forward scattering intensity based on a forward scattering intensity distribution of a minimum width pattern included in the block pattern;
(B) For each pattern of the block pattern, adjust the pattern width so that the width of the forward scattering intensity distribution at the reference forward scattering intensity is equal to the design width,
(C) The correction exposure amount is determined so that the correction exposure amount times the sum of the reference forward scattering intensity and the back scattering intensity at the position becomes substantially the same value for each pattern.
A charged particle beam exposure method characterized by performing proximity effect correction. (1)
(Supplementary Note 2) In the step (a), the pattern at the slice level, which is a predetermined percentage of the peak value, of the forward scattering intensity distribution with respect to the minimum width pattern included in the block pattern is equal to the design width. The charged particle beam exposure method according to appendix 1, wherein the slice level when the width is adjusted is determined as the reference forward scattering intensity. (2)
(Supplementary note 3) The charged particle beam exposure method according to supplementary note 2, wherein the predetermined percentage in the step (a) is a value within a range of 30 to 70%.

  (Supplementary note 4) The charged particle beam exposure method according to supplementary note 3, wherein the predetermined percentage in the step (a) is 50%.

  (Supplementary Note 5) In the step (a), when the adjusted pattern width is smaller than a predetermined minimum value, the forward scattering intensity distribution at the slice level when the pattern width is set to the minimum value. 3. The charged particle beam exposure method according to appendix 2, wherein the slice level when the width is determined to be equal to the design width is determined as the reference forward scattering intensity.

  (Supplementary Note 6) In step (a), the slice level when the slice level is adjusted so that the width at the slice level of the forward scattering intensity distribution is equal to the design width with respect to the minimum width pattern included in the block pattern The charged particle beam exposure method according to appendix 1, wherein the level is determined as the reference forward scattering intensity.

(Appendix 7) In the step (a), the reference forward scattering intensity is determined for each block pattern. (Appendix 8) The step (c) includes:
Dividing the pattern placement surface when changing the pattern to be exposed to the pattern with the above adjusted width with a mesh,
Find the pattern area density of each mesh of the mesh,
Smoothing the pattern area density to determine the effective pattern area density,
Obtain the exposure intensity by the backscattering term as a value proportional to the effective pattern area density,
The charged particle beam exposure method according to supplementary note 1, comprising a step.

(Supplementary Note 9) In the step (c), the corrected exposure dose Qcp is determined so that Qcp (ε _p + α _p '· η) = Eth holds, where ε _p is the reference forward scattering intensity, Eth The charged particle beam exposure method according to appendix 1, wherein is a threshold value for pattern development, η is a backscattering coefficient, and α _p ′ is an effective pattern area density. (3)
(Supplementary Note 10) For each grid in which the mesh size of the mesh is smaller than the maximum size of the block pattern in step (c) and the exposure intensity is insufficient in one-shot exposure for a pattern that spans multiple meshes of the mesh The charged particle beam exposure method according to appendix 8, wherein an auxiliary exposure amount for compensating for the shortage is obtained.

(Supplementary Note 11) The above step (b)
Set a fixed sample point at the midpoint of each side for each block pattern above,
For each fixed sample point, the side corresponding to the fixed sample point is shifted in the perpendicular direction so that the intensity at the fixed sample point of the forward scattering intensity distribution becomes the reference forward scattering intensity, and the pattern width Make adjustments,
The charged particle beam exposure method according to supplementary note 1, comprising a step. (4)
(Supplementary Note 12) The above step (b)
For at least one pattern in the block pattern, divide the pattern into a plurality of rectangles,
Set a fixed sample point at the midpoint of each side of the divided rectangle that touches the boundary of the pattern,
For each fixed sample point, the side corresponding to the fixed sample point is shifted in the perpendicular direction so that the intensity at the fixed sample point of the forward scattering intensity distribution becomes the reference forward scattering intensity, and the pattern width Make adjustments,
12. A charged particle beam exposure method according to appendix 11, which comprises a step. (5)
(Supplementary note 13) In a charged particle beam exposure method in which proximity effect correction is performed by adjusting a pattern width of a mask including a plurality of patterns collectively transferred by a charged particle projection method.
(A) selecting a representative pattern of the plurality of patterns and determining a reference exposure intensity Eth based on the pattern;
(B) obtaining a backscattering intensity distribution F _b of the plurality of patterns;
(C) For each pattern, the pattern width W is adjusted so that the width at the slice level (Eth−F _b ) of the forward scattering intensity distribution becomes the design width W0i.
(D) For an area where the exposure intensity is insufficient, an auxiliary exposure amount for compensating for the shortage is obtained.
The charged particle beam exposure method characterized by the above-mentioned. (6)
(Supplementary note 14) The charged particle beam exposure method according to supplementary note 13, wherein in step (a), a rectangular pattern having a minimum design width is selected as a representative pattern from the plurality of patterns.

  (Supplementary Note 15) In step (a), an isolated rectangular pattern having the minimum design width W0 is selected as a representative pattern from the plurality of patterns, and the width at the slice level of the forward scattering intensity distribution of this pattern becomes the design width W0. The charged particle beam exposure method according to appendix 13, wherein the slice level is adjusted as described above and the slice level is determined as the reference exposure intensity Eth.

  (Supplementary Note 16) In the step (a), an isolated rectangular pattern having the minimum design width W0 is selected as a representative pattern from the plurality of patterns, and the forward scattering intensity distribution of this pattern is within the range of 30 to 70% of the peak value. 14. The charged particle beam according to appendix 13, wherein the slice level when the pattern width is adjusted so that the width at the slice level, which is a value of is equal to the design width, is determined as the reference exposure intensity Eth. Exposure method.

(Supplementary Note 17) The above step (b)
Divide the pattern placement surface on the mask with mesh,
Find the pattern area density of each mesh of the mesh,
Smoothing the pattern area density to determine the effective pattern area density,
Obtaining the backscattering intensity F _b as a value proportional to the effective pattern area density,
In the step (d), the auxiliary exposure amount is calculated in units of the mesh.
14. The charged particle beam exposure method according to supplementary note 13, wherein

(Supplementary Note 18) The above step (c)
Set a fixed sample point at the midpoint of each side for at least one pattern,
For each fixed sample point, the pattern width is adjusted by shifting the side corresponding to the fixed sample point in the perpendicular direction so that the intensity at the fixed sample point of the forward scattered intensity distribution is at the slice level. Do,
14. The charged particle beam exposure method according to appendix 13, comprising a step. (7)
(Supplementary note 19) The above step (c)
(C1) For at least one pattern, divide the pattern into a plurality of rectangles;
(C2) A fixed sample point is set at the midpoint of each side of the divided rectangle that touches the boundary of the pattern,
(C3) For each fixed sample point, the side corresponding to the fixed sample point is shifted in the perpendicular direction so that the intensity at the fixed sample point of the forward scattering intensity distribution becomes the slice level, and the pattern width Make adjustments,
14. The charged particle beam exposure method according to appendix 13, comprising a step. (8)
(Supplementary note 20) In the step (c1), only the region along the periphery of the pattern is divided into the rectangles of the same size, and each rectangle has an edge in contact with the boundary of the pattern. 19. The charged particle beam exposure method according to 19.

(Supplementary Note 21) In step (c), the forward scattering intensity distribution depends on the beam blur δ, and a relationship between the beam blur and the exposure position is obtained in advance, and the charge is determined according to the exposure position based on this relationship. 14. The charged particle beam exposure method according to appendix 13, wherein the particle beam blur δ is determined. (9)
(Additional remark 22) The pattern of the said adjusted width | variety is formed in a 1st mask blank, and the main exposure mask for collective exposure is produced,
Based on the auxiliary exposure amount obtained in the step (d), a lattice pattern having a pattern area density proportional to the auxiliary exposure amount is formed on the second mask blank to create an auxiliary exposure mask for batch exposure.
14. The charged particle beam exposure method according to appendix 13, further comprising a step.

(Supplementary note 23) In a charged particle beam exposure method in which a plurality of patterns are collectively exposed by a charged particle projection method,
(A) A main exposure mask on which the plurality of patterns are formed is irradiated with a charged particle beam to collectively expose the sensitive substrate;
(B) A pattern for auxiliary exposure is formed in an area where the exposure intensity is insufficient only with the batch exposure, and the sensitive exposure substrate is irradiated with a charged particle beam to perform batch exposure on the sensitive substrate.
The charged particle beam exposure method characterized by the above-mentioned. (10)
(Supplementary note 24) The charged particle beam exposure method according to supplementary note 23, wherein in step (b), the charged particle beam is irradiated with the focal point shifted from the sensitive substrate.

(Supplementary Note 25) Further, between the steps (b) and (c) or between (c) and (d),
(E) According to the backscattering intensity, for example, at least part of the pattern is changed to a lattice pattern according to the value of the backscattering intensity with respect to the reference exposure intensity.
14. The charged particle beam exposure method according to supplementary note 13, wherein

(Supplementary Note 26) Between the above steps (c1) and (d),
(E) If any of the four sides of the divided rectangle is in contact with the other divided rectangle side, the divided rectangle is changed to a lattice pattern.
The charged particle beam exposure method according to appendix 19, characterized by comprising steps.

  (Supplementary note 27) The charged particle beam exposure method according to supplementary note 26, wherein, in the step (e), the change is performed only when the backscattering intensity at a part of the pattern boundary exceeds a predetermined percentage of the reference exposure intensity. .

It is a general flowchart which shows the procedure of the proximity effect correction method of Example 1 of this invention. It is a detailed flowchart which shows the process with respect to one block exposure pattern of step S10 of FIG. (A) is a figure which shows the rectangular pattern whose dimension of the X direction and a Y direction in an XY orthogonal coordinate system is W and H, respectively, (B) is a front scattering term of an energy intensity distribution function about area distribution about this pattern. It is a diagram which shows forward scattering intensity distribution obtained by doing in this way. FIG. 4 is a diagram showing the pattern width (shifted width) W of the mask of FIG. 3A with respect to the half-value width (design width) W0 of FIG. 3B when the effective forward scattering radius is 0.04 μm. It is pattern area density map method explanatory drawing. It is a figure which shows the design pattern of a part of mask, the pattern shifted for proximity effect correction | amendment, and the electron beam irradiation area | region irradiated. (A) is a schematic diagram showing the relationship between the forward scattering intensity distribution corresponding to the pattern of FIG. 6 and the designed width, and (B) is an exposure intensity distribution obtained by adding the backward scattered intensity to the forward scattered intensity and the designed width. It is a schematic diagram which shows the relationship. It is a schematic diagram which shows exposure intensity distribution after correct | amending with respect to exposure intensity distribution of FIG.7 (B). (A) is a figure which shows the block pattern used for dimension shift description of the proximity effect correction method of Example 2 of this invention, (B) is a figure which shows the fixed sample point set to this pattern. (A) is explanatory drawing which shows the influence of the forward scattering from the adjacent pattern with respect to the fixed sample point P2, (B) is a figure which shows the pattern shifted asymmetrically considering this influence. (A) is a figure which shows the fixed sample point set to the divided | segmented pattern, (B) is a figure which shows what the left side pattern of (A) shifted by the influence of forward scattering. It is a general flowchart which shows the procedure of the proximity effect correction method used by the electronic projection method of Example 3 of this invention. (A), (C), and (E) are division | segmentation explanatory drawings of one rectangular pattern shown as a continuous line, (B), (D), and (F) are respectively (A), (C), and ( It is explanatory drawing shown mutually separated in order to clarify the pattern divided | segmented by E). It is explanatory drawing which shows that the two adjacent design patterns shown with a broken line were divided | segmented by step S42 of FIG. 12, and the surrounding edge was shifted by step S44 of FIG. (A) is a figure which shows a part of mask pattern before and behind a dimension shift, (B) is a schematic diagram which shows exposure intensity distribution corresponding to (A). It is a conceptual explanatory view showing a transfer pattern and a beam blur measurement point in an electron beam collective irradiation region. FIG. 17 is a table showing beam blur measurement values corresponding to beam blur measurement points in FIG. 16. FIG. It is explanatory drawing which shows the exposure data after adjusting the exposure amount and generating the auxiliary exposure shot with an image. (A) And (B) is explanatory drawing which shows the main exposure data and auxiliary exposure data which were isolate | separated from the exposure data of FIG. It is explanatory drawing which shows the auxiliary exposure mask data obtained by replacing the auxiliary exposure data of FIG. 19 (B) with a pattern having an area density equivalent to the exposure amount of the auxiliary exposure shot. (A) And (B) is explanatory drawing which shows the case where the pattern which has an area density equivalent to the exposure amount of an auxiliary exposure shot is a mesh shape and a strip shape, respectively. FIG. 22 is a diagram schematically illustrating a forward scattering intensity distribution of the strip pattern of FIG. It is a diagram showing the relationship between the space width (unit is forward scattering length β _f ) of the strip pattern of each area density and the difference between the maximum value and the minimum value of forward scattering intensity, Emax−Emin (unit is arbitrary). It is a figure which shows a part of the mask for batch transfer which has the large pattern approached used by an electronic projection method. It is a general flowchart which shows the procedure of the proximity effect correction method which improved the method of FIG. 12 of Example 5 of this invention. (A) is explanatory drawing which shows the pattern before a division | segmentation, (B) is explanatory drawing which hatches the dimension shift area | region of the pattern after a division | segmentation, and shows the mesh for pattern area density calculation with a dotted line. (A) is explanatory drawing which shows the pattern shifted in dimension by step S45 of FIG. 25, (B) was further produced | generated by step S60 of FIG. 25 based on the pattern area density calculation in step S47 of FIG. It is explanatory drawing which shows a lattice pattern. FIGS. 27A and 27B are explanatory diagrams showing patterns obtained by dividing the pattern of FIG. 27B into two in step S61 of FIG. (A) is explanatory drawing which shows the other pattern before a division | segmentation, (B) is explanatory drawing which shows the lattice pattern produced | generated by step S60 of FIG. 25 based on the pattern area density calculation by step S47 of FIG. It is. FIG. 29 is an explanatory diagram showing that the pattern of FIG. 29B is expanded in a lattice pattern area instead of step S61 of FIG. 25 so that a donut pattern is not generated. It is a general flowchart which shows the procedure of the proximity effect correction method which improved the method of FIG. 25 of Example 6 of this invention. (A) and (B) are explanatory diagrams of a proximity effect correction method for a conventional individual exposure. (A) is a design pattern of a part of a mask, a pattern shifted for proximity effect correction, and an irradiated electron beam. It is a figure which shows an irradiation area | region, (B) is a schematic diagram which shows the corrected exposure intensity distribution corresponding to the pattern of (A). (A) and (B) are explanatory diagrams of a proximity effect correction method for conventional block exposure. (A) is a design pattern of a part of a mask, a pattern shifted for proximity effect correction, and an irradiated electron beam. It is a figure which shows an irradiation area | region, (B) is a schematic diagram which shows the corrected exposure intensity distribution corresponding to the pattern of (A). FIG. 34 is a schematic diagram showing that a thin line pattern can be developed by adding auxiliary exposure to the exposure intensity distribution of FIG.

Explanation of symbols

10, 10A, 10B Mask 11, 11A, 12, 12A Shifted pattern 13-15 Electron beam irradiation area

Claims (2)

In the charged particle beam exposure method for collective exposure of the Lipa turn by the charged particle projection method,
(A) 該Pa turns irradiating a charged particle beam in a main exposure mask formed is a sensitive upper substrate collectively exposed,
(B) by irradiating a charged particle beam in the auxiliary exposure mask supplementary exposure pattern is formed simultaneously exposed on the photosensitive substrate,
The auxiliary exposure pattern has an element pattern group having an area density proportional to the shortage amount for each region where the exposure intensity is insufficient in the batch exposure in step (a).
The charged particle beam exposure method characterized by the above-mentioned.   2. The charged particle beam exposure method according to claim 1, wherein in step (b), the charged particle beam is irradiated with a focal point shifted from the sensitive substrate. 3.

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