JPH088205B2 - Electron beam exposure method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electron beam exposure method.

2. Description of the Related Art When the electron beam exposure method is used, the irradiated electrons are scattered in the resist, and the exposure area becomes wider than the irradiation area. If the drawn figure is smaller than the electron scattering length, or if multiple drawn figures are placed closer than the electron scattering length, the effect of scattering becomes noticeable, and a pattern with the desired dimensions cannot be obtained. The effect occurs.

Hereinafter, the principle of proximity effect correction will be described first. Generally, the electron scattering intensity distribution is represented by a double Gaussian distribution as shown below, where χ _{1 is} the coordinate of the center of the irradiation beam and E (r) is the scattering intensity at the coordinate r.

Here, α represents the spread of forward scattering generated in the resist, β represents the spread of backscattering caused by reflection from the substrate, and η represents the reflection coefficient of backscattering. When the pattern represented by the area S is actually exposed with the dose Q _E , the absorption amount Q (r) at the coordinate r is Q (r) = s ₁ Q _E · E (r−χ ₁ ) d ² χ ₁ ... (2) When the resist is first removed at the coordinate r after development when the exposure dose Q _E1 is exposed to this pattern, the dissolution absorption amount Q _c of the resist is Q _c = s ₁ Q _E1 · E (r−χ ₁ ) d ² χ ₁ (3) When performing the proximity effect correction, the absorption amount Q (γ) in the equation (2) becomes larger than the dissolution absorption amount Q _c of the resist in the region where the target pattern exists in order to form the target pattern. If the irradiation area S ₁ and the irradiation quantity Q _E1 that are smaller than Q _c in the non-existing area are obtained and this irradiation area S ₁ is actually exposed to this irradiation quantity Q _E1 , the proximity effect correction is performed.

Although the principle of proximity effect correction has been described above, an inequality that satisfies the above condition is established at all points in space,
Since it is impossible to find a mathematical solution that satisfies it, the following method has been conventionally performed. That is, an evaluation point is provided at a midpoint between the target pattern and other patterns existing within a predetermined distance ε from the pattern. Next, set a certain amount of absorption as the irradiation intensity column W ₀ ＞ W ₁ ＞ W ₂・ ・ ・, set each pattern as irradiation area A ₁ , A ₂ , A ₃・ ・ ・ An, and set the irradiation quantity of all irradiation areas. Set it to W ₀ . After that, for each irradiation area Aj (j = 1,2 ... n), the evaluation points between the irradiation area A _K (k = 1,2 ... If the absorbed amount exceeds Q ₀ , and the absorbed amount W _{nj of} Aj and the irradiated amount W _nk of A _k , the larger irradiation amount W _nj is one step lower. _This is a method of determining the irradiation amount of all irradiation regions by resetting to ₊₁ or W _{nk + 1} . The above is Sugiyama, Saito, Shimizu, Tarui: Proximity effect correction in electron beam writing, IEICE (C), Vol, 62-
C, No10, P688 (1975). The above is the description of the case where the bodi-type resist is used, but the negative-type resist is exactly the same as long as it is considered that the resist remains at the portion where the resist is considered to be removed.

However, according to such a configuration, the proximity effect correction can be realized at a relatively high speed, but it is not a method for realizing the principle of the proximity effect correction, and the irradiation intensity sequence W ₀ > W ₁ > W ₂ ... However, there is a problem in that perfect proximity effect correction cannot be performed because it is empirically set depending on the pattern design rule.

The present invention has been made in consideration of the above-mentioned problems, and it is possible to calculate the irradiation area and the irradiation amount for performing proximity effect correction on an LSI having a huge number of patterns with high accuracy, easily and at high speed. An object is to provide an electron beam exposure method.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention sets a target pattern so that each side of all figures is a boundary between the figures completely or is not completely in contact with another figure. To obtain a divided figure by dividing the quadrangle or the triangle into a rectangular shape, and then setting an evaluation point near the midpoint on the side of each divided figure that does not contact another divided figure; A figure is an irradiation area, a step of assuming each of the irradiation areas and irradiation amounts, a step of obtaining an absorption amount at each of the evaluation points using the assumed irradiation areas and irradiation amounts, and a dissolution absorption amount of resist or Using the difference between the insoluble absorption amount and the absorption amount at each evaluation point, the irradiation amount for each irradiation region is determined by correcting each irradiation region by considering it as an isolated pattern and correcting the irradiation amount. And also Of.

Another aspect of the invention is to divide a target pattern into quadrilaterals or triangles in which each side of all figures is a boundary between the figures completely or a side which is not completely in contact with another figure and divides the divided figure. And a step of setting an evaluation point near a midpoint on a side that does not contact another divided figure among the sides of each divided figure, the divided figure as an irradiation area, and each irradiation area and A step of assuming an irradiation amount, a step of obtaining an absorption amount at each of the evaluation points by using the assumed irradiation region and the irradiation amount, a dissolution absorption amount or an insoluble absorption amount of resist and absorption at each evaluation point Using the difference from the quantity,
And determining the irradiation area for each of the doses by correcting each irradiation area by considering it as an isolated pattern.

Effect The present invention has the above-described configuration, and after assuming the irradiation amount or the irradiation region and evaluating the absorption amount at each evaluation point, the scattering intensity distribution of the electron beam has a very short scattering length forward scattering and a relatively long scattering length. It is possible to consider that the absorption amount at each evaluation point surrounding the divided figure depends only on the divided figure and does not depend on other divided figures by utilizing the feature of the double Gaussian distribution in which the backscattering of By doing so, it is possible to easily correct the irradiation dose or irradiation area independently for the divided figures surrounded by each evaluation point by using the difference between the absorption absorption amount or insoluble absorption amount of the resist and the absorption amount. Therefore, the calculation of the irradiation area and the irradiation amount for forming the target pattern can be performed very easily and at high speed.

Embodiment (Embodiment 1) FIG. 1 is a flow chart showing a method of setting an irradiation area from a target pattern in the first embodiment of the present invention, and determining an irradiation area and an irradiation amount performed assuming an irradiation amount. is there. The present embodiment is an embodiment that is possible when an exposure apparatus that can change the irradiation amount for each irradiation pattern is used. Hereinafter, a method of setting each irradiation area S _k for forming a target pattern and a method of calculating an optimum irradiation amount q _k for the irradiation area will be described with reference to FIG.

STEP (1) Divide the target pattern figure and set an evaluation point for the divided figure. FIG. 2 is a diagram showing a method of dividing a figure and a method of setting its evaluation point. The case where the figure shown in FIG. 2A is used as a target pattern will be described. First, the target pattern is divided into squares or triangles. That is, polygonal figures such as B and C shown in FIG. 2 (a) are respectively represented by B ₁ , B ₂ and C shown in FIG. 2 (b).
Divide into squares or triangles such as ₁ and C ₂ . Next, each of the divided figures is divided until each side completely becomes a boundary with another figure or becomes an edge which does not completely contact another figure. That is, the figure B ₂ , C ₁ having edges such as BL ₂ , CL ₂ in FIG. 2B is divided into b ₂ , b ₃ and C ₁ , C ₂ as shown in FIG. 2C. To do. If a figure other than a quadrangle or a triangle exists among the divided figures thus obtained,
Further, the above-described division is repeated twice, and finally, all the divided figures as shown in 1 to 8 of FIG. 2 (d) are constituted by quadrangles or triangles, and each side of all the divided figures is completely formed. Divide until it is at the boundary with another figure or does not touch any other figure at all. Here, since the method of further dividing the trapezoid into the quadrangle and the triangle is used in the figure division, rather than using the trapezoid as the irradiation area as it is in the calculation of the absorption amount in the later STEP (3),
It is faster to calculate by dividing into rectangle and triangle. With respect to the divided figures 1 to 8 as shown in FIG. 2 (d) obtained as described above, the respective figure areas are S _{1 to} S ₈ . Next, with respect to the above-described divided figures 1 to 8, the midpoint of the side of each side of each divided figure that is not in contact with another figure is set as an evaluation point. That is, as shown in FIG. 2D, among the sides of the i-th divided figure, the midpoint of each side that does not contact another figure is used as the evaluation point r _ij .

STEP (2) The area of each divided figure obtained in STEP (1) is set as an irradiation area, and irradiation q _k is assumed for each irradiation area. That is, the areas S _{1 to} S ₈ shown in FIG. 2D are irradiation areas, and the irradiation doses q _{1 to} q ₈ for the respective irradiation areas are, for example, q ₁ = q ₂ = q ₃ = q ₄ = q _{5 = q 6 = q 7 =} q 8 = assume q _k.

STEP (3) Irradiation amount assuming irradiation area S _k set in STEP (2)
The absorption amount Q (r _ij ) at each evaluation point r _ij for q _k is obtained as follows.

Here, r _ij is the coordinates of the evaluation point, S _k represents the kth irradiation region, _sk dr ² is the area for the region S _k , and q _k represents the irradiation amount for the kth irradiation region. . Also Sums over all illuminated areas.

STEP (4) Absorption Q (r) at each evaluation point obtained in STEP (3)
_ij ) and the dissolved absorption amount or insoluble absorption amount Q _c of the resist, and the absorption amount at the evaluation point is dominated by the irradiation region closest to the evaluation due to the characteristics of the scattering intensity distribution. to modify the dose q _k for each irradiation area S _k considers each irradiation region and the isolated pattern. That is,
The correction amount Δq _k of the dose q _k for the k-th irradiation region is the absorption amount Q at each evaluation point r _kj existing in the k-th irradiation region.
From the difference of Q _{c from} (r _kj ), we obtain as follows.

here, Is the sum of the number of evaluation points existing in the kth irradiation area. Further, d _kj represents the length of the side where the evaluation point r _kj exists in the kth irradiation area.

Here, it will be explained that the correction amount Δq _k expressed by the equation (5) becomes the correction amount when the k-th irradiation area is regarded as an isolated pattern. First, for simplification, consider a case where there is only one evaluation point r _k1 existing in the k-th irradiation area. The absorption amount Q (r _k1 ) at the evaluation point r _k1 is expressed as follows.

Next, it is assumed that the following equation is established with a certain dose q _{k ′} .

Subtracting both sides of equation (7) from both sides of equation (6) Here, the kth irradiation area is regarded as an isolated pattern. It means to consider. That is, it is considered that the absorption amount at the evaluation point r _k1 affects only the change in the irradiation amount with respect to the irradiation region in which the evaluation point exists, and does not affect the changes in the irradiation amount with respect to other irradiation regions.

If equation (9) holds, Therefore, the correction amount Δq _{k ′} to the irradiation amount q _{k ′} for which (7) is satisfied from the irradiation amount q _{k in the} equation (6) is Becomes This is a case where there is only one evaluation point r _k1 in the k-th irradiation area in the equation (5). However, when there are a plurality of evaluation points for one irradiation region, Δq _{k ′} obtained from the equation (11) from the absorption amounts at the plurality of evaluation points must be averaged. In this example, the weighted average was performed on the lengths of the sides having the evaluation points as shown in Expression (5) by regarding the evaluation points as the representative points of the sides having the evaluation points. Therefore, each irradiation dose q _k is corrected as follows with respect to the correction amount Δq _k obtained by the equation (5).

q _k = q _k −Δq _k (12) STEP (5) If all Δq _k are sufficiently small in the magnitude of the correction amount Δq _k of the irradiation amount q _k for each irradiation region s _{k in} STEP (4) , STEP (6), and if it becomes sufficiently small, the dose q _k newly obtained in STEP (4) is used as the newly assumed dose for each irradiation region, and STEP (3) Return to.

STEP (6) Determine the irradiation dose obtained in STEP (4) as the optimum irradiation dose for the irradiation area set in STEP (2). The irradiation region and the irradiation amount obtained by the above STEP (1) to STEP (6) satisfy the condition that Δq _k represented by the equation (5) becomes zero. In Eq. (5), the values of F _kkj in one divided figure are almost equal, so _{Δq k}
= 0 means that the difference between the absorption amounts Q (r _kj ) and Q _c at the evaluation points existing in the k-th divided figure is zero when the weighted average is calculated depending on the length of the side where the evaluation points exist. It becomes the same as the condition. Therefore, considering that there may not be a dose of q _k ≧ 0 _where Q (r _ij ) = Q _c for all the set irradiation areas, the absorption at each evaluation point Considering the amount of absorption as the representative amount of the side where the evaluation point exists, the amount of absorption on the side where the evaluation point exists for the set irradiation area is Q _c under the condition of Δq _k = 0. Is the optimum condition for Since the side where the evaluation points are present is equal to the side of the target pattern, the previous condition is the optimum irradiation amount for the set irradiation area so that the absorption amount on each side of the target pattern becomes Q _c . It becomes a condition. If the absorption amount inside the irradiation area is Q _in and the absorption amount outside the irradiation area is Q _out ,
_{From in} ≧ Q _out , the irradiation area and the irradiation amount determined by STEP (1) to STEP (6) are larger than Q _c in the area where the target pattern exists, and the area where the target pattern does not exist. It can be seen that it is realized that the absorption amount at is smaller than Q _c . Further, since the function f (χ) represented by the equation (4) is the sum of the double Gaussian distributions of the extremely short distribution width and the relatively long distribution width, F _kij has the largest value when k = i, Normally, F _kKj >> F _kij (i ≠ k), so that the _steps (3) → (4) → (5) → (3) are repeated in about 2-3 times. Above STEP (1) ~ ST
It can be seen that proximity effect correction can be realized by performing exposure using the irradiation area and irradiation amount obtained by EP (6).
If the target pattern is preliminarily subjected to isotropic division or contour division before the figure division in STEP (1), the correction accuracy of this example is further improved.

(Embodiment 2) FIG. 3 is a flow chart showing a method of determining an irradiation area and an irradiation amount on the assumption of an irradiation area based on a target pattern in the second embodiment of the present invention. The present embodiment is an embodiment that is also possible when using an exposure apparatus that cannot change the irradiation amount for each irradiation pattern. A method of calculating the optimum irradiation area S _k for the irradiation dose q _k set with reference to FIG. 3 will be described below.

STEP (7) The divided figure S _k and the evaluation point r _kj are set from the target pattern by the same means as in STEP (1) of the embodiment.

STEP (8) The area of each divided figure obtained in STEP (7) is assumed to be each irradiation area, and the irradiation amount is set for the irradiation area. For example, in the dose q _k for the irradiation area S _k ,
For all k, set q _k = Q _e (= constant value).
Furthermore, at this time, the side where the evaluation point r _kj exists in each irradiation area S _k is set as the moving side L _kj, and the position of the moving side is from each moving side L _kj to the center of gravity of the irradiation area where the moving side exists. It is expressed using the distance l _kj of.

STEP (9) For the irradiation area assumed to have the irradiation dose q _k set in STEP (8), the absorption amount Q (at each evaluation point r _ij is measured by the same means as in STEP (3) of the first embodiment. r _ij ).

STEP (10) Absorption amount Q (r at each evaluation point obtained in STEP (9)
_ij ) and the dissolved absorption amount or insoluble absorption amount Q _c of the resist, the absorption amount at the evaluation point is determined from the irradiation region closest to the evaluation point by the feature of the scattering intensity distribution as in the first embodiment. Since the contribution is dominant, the irradiation region S _k is corrected with respect to the irradiation amount q _k set by regarding each irradiation region as an isolated pattern. That is, the absorption amount Q (r _kj ) at the evaluation point r _kj
The corrected movement amount Δl _kj of the moving side L _kj is obtained from the difference from Q _c as follows.

Here, L _kj represents the length of the moving side L _kj , and the function G (χ) used in Expression (13) is a function defined by Expression (14). Therefore, a new area is obtained by moving each moving side L _kj in the direction perpendicular to the moving side and the inside of the irradiation area as the positive direction by the length of the corrected moving amount Δl _kj obtained by the equation (13). Let it be the modified irradiation area.

STEP (11) In STEP (10), if all Δl _kj are sufficiently small in the magnitude of the corrected moving amount Δl _kj of the moving side L _kj in each irradiation region S _k , go to STEP (12), if not, The modified irradiation area is used as the newly assumed irradiation area.
Return to EP (9).

STEP (12) The irradiation area obtained in STEP (10) is determined as the optimum irradiation area for the irradiation amount set in STEP (8).
In the irradiation area and irradiation amount obtained by the above STEP (7) to STEP (12), Δl _kj represented by the equation (13) becomes zero. That is, the condition that the absorption amount Q (r _ij ) of all evaluation points is equal to the dissolved absorption amount or the insoluble absorption amount Q _c of the resist is completely satisfied. Therefore, if exposure is performed using the irradiation amount and irradiation region obtained in the second embodiment, the proximity effect correction is realized with higher accuracy than in the first embodiment. In addition, the second embodiment is similar to the first embodiment.
If the target pattern is preliminarily subjected to isotropic division or contour division or other preliminary division before the figure division in STEP (1), the correction accuracy of this embodiment is further improved. The irradiation area obtained in this embodiment can also be used as a mask size for collective electron beam transfer.

By combining the first embodiment and the second embodiment, more effective proximity effect correction can be realized. For example, in Example 2, by using the irradiation amount set in STEP (2) as the irradiation amount obtained in Example 1, more accurate proximity effect correction is realized, and STEP (9) →
The number of repetitions of (10) → (11) → (9) is reduced, and the calculation can be performed faster than when the second embodiment is performed alone. Example
In 1 and 2, the evaluation point was set to the midpoint of the divided figure, but it may be near the midpoint.

EFFECTS OF THE INVENTION As can be seen from the above description, according to the present invention, it is possible to obtain an irradiation amount and an irradiation area for realizing proximity effect correction, and complete proximity effect correction is realized with extremely high accuracy. Further, the present invention can be realized at high speed even for an LSI pattern having an enormous number of patterns, since the previous irradiation amount and irradiation region are obtained by a simple calculation.

[Brief description of drawings]

FIG. 1 is a flow chart showing a method of setting an irradiation area from a target pattern in the first embodiment of the present invention and deciding the irradiation area and the irradiation quantity assuming the irradiation quantity;
The figure shows the method of dividing the figure and the method of setting the evaluation points,
FIG. 3 is a flow chart showing a method of determining an irradiation area and an irradiation amount by assuming an irradiation area from a target pattern in the second embodiment of the present invention. 1-8 ... Divided figure.

Front page continued (72) Inventor Noboru Nomura Osaka Prefecture Kadoma City 1006 Kadoma, Matsushita Electric Industrial Co., Ltd. References JP-A-1-270317 (JP, A) JP-A-59-112621 (JP, A)

Claims (2)

[Claims] 1. A step of dividing a target pattern into quadrangles or triangles in which each side of all figures is a boundary between the figures completely or a side which is not completely in contact with another figure to obtain a divided figure. After that, among the sides of each of the divided figures, a step of setting an evaluation point near a midpoint on a side that is not in contact with another divided figure, and the divided figure is an irradiation area, and each irradiation area and an irradiation amount. And a step of obtaining an absorption amount at each of the evaluation points using the assumed irradiation area and irradiation amount, and a dissolution absorption amount or insoluble absorption amount of the resist and an absorption amount at each evaluation point And the irradiation amount is determined for each irradiation region by correcting each irradiation region by considering it as an isolated pattern. 2. A step of dividing a target pattern into quadrangles or triangles in which each side of all figures is a boundary between the figures completely or a side which is not completely in contact with another figure to obtain a divided figure. After that, among the sides of each of the divided figures, a step of setting an evaluation point near a midpoint on a side that is not in contact with another divided figure, and the divided figure is an irradiation area, and each irradiation area and an irradiation amount. And a step of obtaining an absorption amount at each of the evaluation points using the assumed irradiation area and irradiation amount, and a dissolution absorption amount or insoluble absorption amount of the resist and an absorption amount at each evaluation point And deciding the irradiation region for each of the doses by correcting each irradiation region by considering it as an isolated pattern and correcting the irradiation region.