JPH0336296B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an electron beam exposure method. In particular, the present invention relates to improvements in methods for improving the accuracy of exposure patterns by correcting the proximity effect.

(2) Technical background In the electron beam exposure method, 0.1 to 0.2
An electron beam with a width or diameter on the order of [μm] is used to scan and irradiate the sample,
The optimum development energy intensity is given to each pattern area.

However, the electron beam is somewhat scattered in the irradiation direction (forward scattering), and is also reflected on the sample surface and scattered in the opposite direction to the irradiation direction (backward scattering). That is, a scattering region B exists around the electron beam irradiation region A, and the electron beam scattering intensity in this region is distributed exponentially as shown in the following equation.

f(r)=e ^-(r/A)2 +B・e ^-(r/C)2 ……(1) However, f(r)・ is the distance from the boundary of the irradiation area is r
is the electron beam scattering intensity at a certain point, and A, B, and C are constants determined by the material of the sample and the sensitivity and thickness of the resist used.

The width of the electron beam irradiation area A is usually 0.1 to 0.2
Since [μm] is narrow, it is necessary to scan the electron beam described above to obtain a desired width pattern. However, since the scattering region is quite wide, when the electron beam is scanned, the developing energy intensity (irradiation intensity) becomes relatively large in the scattering region. and,
The development energy intensity in this scattering region is also influenced by the shape of the pattern. This is because a given point is influenced by multiple sides surrounding it.

Since the development energy intensity in such a scattering region is not sufficient to expose the resist,
When patterns exist in an arched pattern, there is no significant negative effect, but when multiple patterns exist in close proximity, the resist is exposed to light in a wider area than the irradiated area corresponding to the pattern, that is, the scattering area, and the formation This becomes a factor that deteriorates the pattern accuracy. This effect is called the proximity effect, and it is known that when the distance between patterns is less than 2 [μm], significant distortion occurs in the pattern shape.

On the other hand, when forming a pattern by scanning an electron beam, if the pattern width is narrow, the scanning speed must be lowered, that is, the irradiation amount must be increased to increase the development energy intensity. That is, it is necessary to adjust the irradiation amount (scanning speed) in accordance with the size of the pattern.

(3) Prior art and problems The method normally used to correct the proximity effect in the prior art is to correct the size of the pattern, that is, for each pattern, (a) the above
The electron beam scattering intensity distribution f(r) given by equation (1), (b) the shape of the desired pattern, and (c)
After reducing the dimensions of the target drawing pattern in advance, taking into account the shape of the adjacent pattern and the distance from this pattern, and calculating the appropriate irradiation dose, the electron beam is applied using this reduced pattern as a reference. In this method, the desired pattern is accurately obtained as a result. In this method, all correction amounts, ie, dimension correction amounts and irradiation amount correction amounts, must be determined when creating pattern data. Furthermore, as long as we use electron beam exposure equipment at the current level of technology, we have no choice but to draw one pattern with one fixed dose; It is difficult to vary the pattern in various ways, and it is also difficult to correct patterns that make the edges of the pattern curved. As a result, pattern correction may have the opposite effect and impede pattern accuracy.

A specific example will be described with reference to FIGS. 1a and 1b. When pattern A and pattern B exist close to each other as shown in FIG. In consideration of the influence of pattern B, the dimensions of pattern A were corrected as indicated by the broken line in the figure. However, since the entire area of the corrected pattern is irradiated with the same dose, the accuracy of the area actually affected by pattern B, that is, the upper area of pattern A, is improved, but the effect of pattern B is almost unaffected. There is a disadvantage that the accuracy of the area where the pattern is not present, that is, the area below the pattern A, is conversely reduced.

In order to avoid this disadvantage, it is necessary to divide pattern A into two areas, A ₁ and A ₂ , as shown in Figure 1b. As the number of patterns increases dramatically, when the number of patterns reaches about 10 ⁵ to 10 ⁶ ,
The process is extremely cumbersome and inefficient.

(4) Purpose of the Invention The purpose of the present invention is to eliminate this drawback, and to improve the number of divided patterns in an electron beam exposure method that corrects the proximity effect by dividing the target pattern. It is an object of the present invention to provide an electron beam exposure method in which the exposure rate is reduced and the precision of exposed patterns is improved.

(5) Structure of the Invention An object of the present invention is to provide an electron beam exposure method in which a plurality of patterns are drawn by irradiating an electron beam onto a sample. A number of sample points determined by the size and position of the surrounding patterns are set at positions determined by the sizes and positions of the surrounding patterns, and the electron beam irradiation is performed on the sample points. Calculate the scattered electron beam intensity (Fi) for each,
The scattered electron beam intensity (Fi) at each of the sample points and the scattered electrons at a point that is on the side of a pattern having the same pattern width as each of the above-mentioned patterns and where the influence of the proximity effect is negligible. Ratio (Fi/
Fo) is calculated, and if the intensity ratio (Fi/Fo) exceeds any of the set values set in multiple stages,
Divide the area including the sample points showing the intensity ratio (Fi) exceeding each step of the set value into each step, and calculate the optimal irradiation amount and optimal dimension correction amount for each pattern in the divided region. This is achieved by calculating the information and performing electron beam irradiation based on the calculated information.

FIG. 3 is a conceptual diagram showing the basic configuration of a commonly used electron beam exposure apparatus. In the figure, 6 is the main body of the electron beam exposure apparatus, 7 is the electron gun, 8 is the convergent electron lens system, 9 is the XY deflector, 10 is the sample, 11 is the CPU, and 12 is a DA converter and has 13 amplifiers.

The irradiation amount and dimensional correction amount for each pattern divided through the above steps are determined at the time of pattern design, so these values are stored in the CPU 11, and based on the instructions, the DA converter 12,
By driving the XY deflector 9 via the amplifier 13, the beam spot is stepped and a desired pattern is drawn.

(6) Embodiments of the Invention Each step of the electron beam exposure method according to an embodiment of the present invention will be described in more detail below with reference to FIG. In the figure, A is the target pattern, B,
C, D, and E are adjacent patterns that exert a proximity effect on A.

1st step: Set sample points. In the figure, sample points 1 and 2 are the middle points between the lower side of pattern C and the upper side of pattern D, and between the lower side of pattern D and the upper side of pattern E, and sample points 3,
4 and 5 are the midpoints of the lower side of pattern E, the lower side and upper side of pattern B, and the apex of pattern A.

2nd process Each sample point i of pattern A (i=1, 2,...,
5) Exposure intensity F _i (i=1, 2,..., 5)
Calculate. In other words, the exposure intensity F ₂ at point 2 is obtained as the sum of the exposure intensities exerted on sample point 2 by patterns A, B, C, D, and E.

Third step: Calculate the exposure intensity Fo, which is the average of the exposure intensity at the midpoint on each side of pattern A when the proximity effect exerted on pattern A is negligible,
The ratio of this exposure intensity Fo to the exposure intensity Fi at each sample point above, ti=Fi/Fo(i=1, 2,...,
5) Calculate.

Fourth step Depending on the precision required for the semiconductor device pattern, set values are set in multiple stages, for example 1,
The above ti is classified into one of the ranges defined by C ₁ , C ₂ , ... (1<C ₁ <C ₂ ...). In other words, for sample points 3 and 5, the influence of the surrounding patterns is extremely small, so t ₃ , t ₅ ≒1
and when 1<t ₁ , t ₄ <c ₁ , c ₁ <t 2 <c ₂ for sample points 1, 2, ₄ , as a result, sample points 1, 2, ..., 5 will be classified into the following three groups.

(i) Sample points 3, 5 (ti≒1) (ii) Sample points 1, 4 (1<ti<C ₁ ) (iii) Sample points 2 (C ₁ <ti<C ₂ ) 5th process Each of the above Divide pattern A into three regions shown in the figure to contain the group of sample points. In the case of the pattern shown in FIG. 2, the dividing line falls between sample points 1 and 2 and between sample points 2 and 5. In other words, the area including sample points 1 and 4 is
A ₁ is an area including sample point 2, A ₂ is an area including sample points 3 and 5, and A ₃ is an area including sample points 3 and 5.

6th step For each divided pattern A ₁ , A ₂ , A ₃ ,
In consideration of the spread of the pattern itself, the amount of correction of the dimensions within the pattern and the irradiation amount to obtain the target pattern dimensions are determined. Next, the inter-pattern dimension correction amount is determined by taking into account the influence of surrounding patterns.

Seventh step: Execute electron beam exposure based on the corrected dimensions and corrected doses calculated for each of the patterns A ₁ , A ₂ , and A ₃ above.

FIG. 3 is a conceptual diagram showing the basic configuration of a commonly used electron beam exposure apparatus. In the figure, 6 is the main body of the electron beam exposure apparatus, 7 is the electron gun, 8 is the convergent electron lens system, 9 is the XY deflector, 10 is the sample, 11 is the CPU, and 12 is a DA converter, and 13 is an amplifier.

The irradiation amount and dimensional correction amount for each pattern divided through the above steps are determined at the time of pattern design, so these values are stored in the CPU 11, and based on the instructions, the DA converter 12,
By driving the XY deflector 9 via the amplifier 13, the beam spot is stepped and a desired pattern is drawn.

According to this process, the number of patterns to be divided is the minimum value within a range that fully satisfies the accuracy required for semiconductor device patterns, which is not only advantageous in terms of process, but also sufficiently reduces the influence of surrounding patterns. It was confirmed that it also effectively contributes to improving pattern accuracy because it takes into account

(7) Effects of the Invention As explained above, according to the present invention, in an electron beam exposure method that corrects the proximity effect by dividing a pattern, the number of divided patterns is reduced, and furthermore, the number of divided patterns is reduced. It is possible to provide an electron beam exposure method in which the precision of exposed patterns is improved.

[Brief explanation of drawings]

FIGS. 1a and 1b are diagrams for explaining a method of correcting the proximity effect by correcting dimensions in the prior art, FIG. 2 is a diagram for explaining the configuration of the present invention, and FIG. 1 is a conceptual configuration diagram of an electron beam exposure apparatus that can be used to implement the present invention. 1, 2, 3, 4, 5...sample points, A, A ₁ ,
A ₂ , B, C, D, E...pattern, 6...electron beam exposure device main body, 7...electron gun, 8...converging electron lens system, 9...XY deflector, 10...sample, 11 ...CPU, 12...DA converter, 13...
…amplifier.

Claims (1)

[Claims] 1. In an electron beam exposure method in which a plurality of patterns are drawn by irradiating an electron beam onto a sample, on each side of each of the plurality of patterns, the size and position of the patterns around each pattern are determined. A number of sample points determined by the size and position of the patterns around each pattern are set at the positions where the electron beam is irradiated, and the scattered electron beam intensity (Fi) exerted on each of the sample points by electron beam irradiation is calculated. Calculate the scattered electron beam intensity (Fi) at each of the sample points,
Calculate the ratio (Fi/Fo) to the scattered electron beam intensity (Fo) at a point on the side of a pattern that has the same pattern width as each of the above patterns and where the influence of the proximity effect is negligible. However, if the intensity ratio (Fi/Fo) exceeds any of the set values set in multiple stages, each area containing the sample point showing the intensity ratio (Fi) exceeding each stage of the set value is The electron beam is divided into stages, the optimum irradiation amount and the optimum size correction amount are calculated for each pattern of the divided area, and electron beam irradiation is performed based on the calculated information. Beam exposure method.