JPH0336292B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron beam exposure method, and more particularly to a method for forming a highly accurate electron beam exposure pattern by correcting the so-called proximity effect.

In pattern forming technology using electron beam exposure, correction of the so-called proximity effect is essential in order to improve pattern accuracy. As is well known, the proximity effect is caused by electron beam scattering (forward scattering) in the resist layer coated on the exposed object and electron beam scattering (backward scattering) from the substrate, which is the exposed object. This is a development in which the resist pattern after drawing expands to a greater extent than the electron beam irradiation pattern, which results in significant distortion of the pattern shape, especially when the distance between the patterns is less than 2 μm.
The negative effect of reducing accuracy becomes noticeable.

The electron beam scattering intensity distribution in the resist due to this scattering is expressed as a function of the distance r from the center of the beam irradiated from the outside using the following formula: f(r)=e ^-(r/A)2 +B・e ^-(r/C) It is known that the ^first term is given by forward scattering and the second term is given by backscatter. Note that in formula (1), A, B, and C are constants determined by conditions such as the thickness of the resist and the material of the substrate.

Conventionally, the most common method for correcting the proximity effect is to determine the optimal electron beam irradiation density for each pattern in advance by considering the electron beam scattering intensity distribution, pattern shape, and distance from adjacent patterns for each pattern. This method involves setting the drawing pattern to 1 or changing the drawing pattern. In either case, the amount of correction must be determined in advance at the time of creating pattern data. When forming a pattern by directly writing an electron beam on a wafer (direct exposure), it is necessary to maintain a thick residual resist film thickness due to the processing process.

However, in the case of a negative resist, the residual film thickness becomes thinner when the irradiation dose (irradiation density) is reduced, so when trying to satisfy a predetermined pattern dimension interval by proximity effect correction using irradiation dose correction, the There is a difference in the remaining film thickness.

Therefore, in the case of direct exposure, in order to maintain a large residual film thickness of the negative resist and satisfy the pattern dimensions, at the same time as making dimension corrections that deform the drawn pattern, the irradiation dose must be further increased to achieve a predetermined residual film thickness. It is necessary to perform dose correction to maintain the On the other hand, as exposure patterns become finer and more complex, it is necessary to quantitatively determine each correction amount in order to reliably correct the proximity effect.To do this, sample points are set on the sides of each pattern. One possible method is to calculate the influence from all other patterns using equation (1) above, and then use simultaneous equations to calculate the correction amount for both dimensions and irradiation amount so that the exposure intensity at each sample point is constant. It will be done.

However, when the number of patterns is on the order of 10 ⁵ to 10 ⁶ , the method of finding solutions using simultaneous equations requires a huge amount of man-hours to calculate, and even with current large-scale computers, the processing time is several hours. It is difficult to quickly determine the amount of proximity effect correction for a pattern.

Therefore, in order to make it easier to correct the irradiance of the drawing pattern, we set limits on the pattern itself so that the irradiation density can be calculated and determined based on the size of the unit pattern without considering the influence of surrounding patterns. It is proposed to do so. However, this method has the disadvantage that it cannot be applied to fine patterns and small pattern spacings because it imposes limits on pattern width and pattern spacing.

In view of these problems, it is an object of the present invention to provide an electronic method that, although an approximate method, can relatively easily determine the amount of correction for both dimensions and electron beam irradiation density, and that can also obtain highly accurate patterns. An object of the present invention is to provide a beam exposure method.

That is, the feature of the present invention is that in an electron beam exposure method in which an electron beam is irradiated onto a sample to draw a large number of independent patterns, when each independent pattern is drawn at a constant electron beam irradiation density, In calculating the drawing pattern dimensions that are reduced and corrected for the pattern dimensions to be created in consideration of the influence between patterns due to electron beam scattering, each independent pattern is made into a rectangular pattern, and one side of the rectangular pattern is The multiple influential surrounding rectangular patterns are represented by the only rectangular pattern that has the greatest proximity effect on that side, and the pattern dimensions are calculated for each side with reduction correction, and then each independent pattern is reduced. Determine the electron beam irradiation density when drawing each independent pattern so that the required residual film thickness is obtained according to the corrected pattern size, and draw the pattern with the reduced and corrected pattern size and electron beam irradiation density. By doing so, the purpose is to simplify the calculation of the correction amount.

This will be explained in detail below based on the drawings. First, when performing dimension correction, for the sake of simplicity, as mentioned above, instead of considering the influence of all other patterns on the dimension correction of a specific unit rectangular pattern, for each side, the most influential among the surrounding patterns is The influence of the pattern with the greatest influence is determined, and the pattern closest to the side of the unit rectangular pattern for which the correction amount is to be determined is selected as the pattern with the greatest influence. For example, as shown in Figure 1, a rectangular pattern
When considering the dimension correction amount x' for side X of P ₀ , other rectangular patterns that are close to and opposite this side
Among P ₁ , P ₂ , and P ₃ , the pattern P ₂ with the shortest distance
Extract and use as a representative. The reason why patterns with the minimum spacing are extracted and representative is that the electron beam scattering intensity distribution expressed by equation (1) above decreases exponentially as the distance from the beam center increases; This is because a certain pattern has a decisive influence. If there are two or more patterns at the same distance from side X, the sizes of those patterns are compared and the larger pattern is extracted as a representative. Furthermore, when the influence of two or more surrounding patterns needs to be considered, for example, when there are two patterns of the same size at approximately the same distance from side You can use this as a representative. In this way, the surrounding patterns that should be considered in determining the amount of dimensional correction for one side of a specific rectangular pattern are represented by a single rectangular pattern using the simple method of determining the amount of dimensional correction described below. This is to do so.

The gist of this method for determining the amount of dimensional correction is, for example, when considering a pattern P ₀ to be corrected and an adjacent pattern P ₁ as shown in FIG.
Considering the exposure intensity distribution 10 on the pattern center line and focusing on the difference in exposure intensity at the edge of the pattern (the slope of points a' and b' in the figure), if there is an influence of the proximity effect (Figure 2 a), , when the slope is steep and the influence is small (Figure 2 b), the slope is small and flat, and how much dimension correction ( The purpose is to determine the amount of dimensional correction based on whether it is necessary to reduce the size.

FIG. 3 shows a pattern for explaining this, and the exposure intensity at points a and b in the figure is determined by the following formula.

Fa = F (γ ₁ ) + F (γ ₃ ) Fb = F (γ ₂ ) + F (γ ₄ ) (2) Here, γi (i = 1 to 4) is the distance from the center of each pattern to points a and b. F(γi) is obtained from the following equation by integrating equation (1), and S is the area irradiated by the minute beam F(γi)= _s (γ)ds (3) .

FIG. 4 shows the relationship plotted with the vertical axis representing the gradient Fb/Fa and the horizontal axis representing the dimensional correction amount l. From FIG. 4, the dimensional correction amount l ₀ corresponding to the threshold value ε can be easily found.

The operation of determining the amount of dimensional correction for each side is repeated using the above method, and this is performed for each unit rectangular pattern to complete the dimensional correction. Each dimension-corrected unit pattern can be regarded as an isolated pattern, and the irradiation necessary to obtain the required residual film thickness according to the corrected size of the pattern can be performed without considering the influence of surrounding patterns. You can find the quantity. This electron beam irradiation density Q _i is determined for each unit pattern based on the following equation.

Q _i F(γ _i )=E (4) Here, E is the development energy obtained by experiment, and F(γi) is given by equation (3).

By the above method, the correction amount for the dimensions and electron beam irradiation density is determined at the time of pattern data creation, and the data is stored in the electronic computer 6 in the apparatus as shown in FIG.
The XY deflector 4 is driven to advance the beam spot, and irradiation is performed so as to cover a predetermined pattern. FIG. 5 is a conceptual diagram of the basic configuration of a typical electron beam exposure apparatus. The electron beam exposure apparatus main body 1 has an electron gun 2, a converging electron lens system 3, and an XY deflector 4, and irradiates a thinly focused electron beam onto a resist-coated substrate and a sample 5. The position of the beam spot is determined by electronic computer 6.
DA converter 7 and amplifier 8 with pattern data from
is controlled by driving the XY deflector 4 via the XY deflector 4. The electron beam is irradiated and blanked by a blanking device in accordance with a signal from the computer 6. It is well known that control of the electron beam irradiation density can be achieved by controlling the stepping speed and blanking time of the beam spot in the above-mentioned apparatus.

By using one pattern to represent the patterns that have the above-mentioned effects, the dimensions are corrected, and the irradiation amount (density) is subsequently determined according to the size of the pattern, thereby simplifying and speeding up the process. Ru.

In the above embodiment, the case of negative resist was described, but it goes without saying that a highly accurate pattern can be obtained by applying the method according to the present invention to the case of positive resist as well.

As described above, according to the present invention, size correction and dose correction can be performed in a short time, and it is also applicable to large-scale data with patterns on the order of 10 ⁵ to 10 ⁶ . Furthermore, by performing dimension correction and dose correction simultaneously, a highly accurate pattern can be obtained. Particularly in the case of a negative resist, a predetermined residual film thickness can be maintained, so it goes without saying that significant practical effects can be obtained.

[Brief explanation of drawings]

1 to 3 are diagrams showing patterns for explaining the procedure for determining the amount of dimensional correction according to the present invention, FIG. 4 is a diagram similarly showing the relationship between the amount of dimensional correction and the exposure intensity gradient within the pattern, and FIG. The figure shows an example of the basic configuration of an electron beam exposure system.

Claims (1)

[Claims] 1. In an electron beam exposure method in which an electron beam is irradiated onto a sample to draw a large number of independent patterns, the influence between patterns due to electron beam scattering is considered when each independent pattern is drawn at a constant electron beam irradiation density. In order to obtain the drawing pattern dimensions that have been reduced and corrected for the pattern dimensions to be created by , calculate the pattern size that is reduced and corrected for each side by representing the only rectangular pattern that has the largest influence of the proximity effect on that side, and then calculate the pattern size that has been reduced and corrected for each independent pattern. An electron beam exposure method characterized by determining an electron beam irradiation density when drawing each independent pattern so as to obtain a required residual film thickness, and writing the pattern with the reduced-corrected pattern dimensions and electron beam irradiation density. .