JPH0547969B2 - - Google Patents

Description

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

(b) Background of the technology In pattern forming technology using electron beam exposure, correction of the so-called proximity effect is essential 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 phenomenon in which the resist pattern after drawing expands to a greater extent than the electron beam irradiation pattern, and especially when the spacing between patterns becomes less than 2 μm, this results in significant distortion of the pattern shape and has a significant negative effect of reducing accuracy. .

The electron beam exposure intensity distribution in the resist due to this scattering is determined by the following equation f(r)=e-(r/A) ² +B・e-(r/ C) ² ...
It is known that the first term is given by forward scattering and the second term is given by backward scattering. 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.

Pattern spreading due to proximity effects includes spreading caused by the influence of other patterns (inter-pattern proximity effect) and spreading caused by drawing one's own pattern (intra-pattern proximity effect). The most common method for correcting the proximity effect is to set the optimal irradiation dose for each pattern in advance by considering the electron beam exposure intensity distribution, its shape, and the distance from adjacent patterns for each pattern. Alternatively, the drawing pattern may be modified. 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 drawing an electron beam on a wafer (direct exposure), it is necessary to maintain a large residual film thickness during the processing process.

However, in the case of negative resist, if the irradiation dose is reduced in order to satisfy the target pattern spacing, the remaining film thickness will become thinner. There will be a difference.

Therefore, in the case of direct exposure, the remaining film thickness of the negative resist is kept thick, and the target pattern dimensions,
In order to satisfy the spacing, it is necessary to reduce the dimensions of the drawing pattern and further increase the irradiance for correction. In other words, it is necessary to reduce the dimensions of the figure and at the same time change the irradiation dose for each figure using proximity effect correction. In order to carry out such a correction method, the amount of dimension correction and the amount of irradiation necessary to obtain the target residual film thickness and pattern dimensions are required.

(c) Prior Art and Problems Conventionally, the amount of dimensional correction for correcting the spread caused by drawing one's own pattern (intra-pattern proximity effect) has been constant regardless of the size of the pattern.

However, in the case of a negative resist, when the initial film thickness is increased, and when the rectangular size is large as shown in FIG. 1, the self-spreading becomes noticeable, and becomes more noticeable as the film thickness increases. Therefore, in the case of direct exposure, in order to maintain a large resist film thickness, a highly accurate pattern cannot be obtained with a fixed in-pattern dimension correction amount as in the conventional method.

In addition, in order to correct the irradiation amount to achieve the target residual film thickness for a pattern of any size, the size and irradiation amount of the pattern that will result in the target residual film thickness as shown in Figure 2 must be adjusted. relationship is required.

Conventionally, the relationship shown in FIG. 2 has been obtained through experiments by exposing rectangles of various sizes and plotting the point at which the film thickness becomes constant.

However, in the method of determining the relationship shown in Figure 2 through experiments, it is necessary to observe the cross-sectional shape with an electron microscope in order to measure the remaining resist film thickness at a large number of measurement points, which takes time and changes the exposure conditions. In this case, the relationship shown in FIG. 2 cannot be quickly obtained.

(d) Object of the Invention In view of these conventional problems, the object of the present invention is to pattern a photosensitive material into a pattern with a desired size and a desired residual film rate.

(e) Structure of the Invention The features of the present invention for achieving the above object are that the sensitivity curve (relationship between residual film rate and irradiation amount), which is the basic characteristic of negative resist, and the exposure intensity distribution of a pattern of arbitrary size ( (relationship between irradiation amount and pattern width) to obtain the dimensional correction amount and irradiation amount necessary to obtain the target residual film thickness and pattern dimensions, and then calculate the electronic The purpose is to perform beam writing.

(f) Embodiments of the invention A negative resist is crosslinked by electron beam irradiation,
As a result, it is a polymeric material that produces a component (gel) that is insoluble in the original solvent.

The thickness d of the insolubilized film is generally a function of the irradiation dose Q, the energy of incident electrons (acceleration voltage) E ₀ and the film thickness d ₀ before irradiation, as shown in FIG.

If the accelerating voltage E ₀ is constant, the characteristics of the negative resist are expressed as d/d ₀ =h(Q) (2) and a function of only Q.

This means that crosslinking, ie, absorption of energy from the electron beam, occurs uniformly throughout the thickness.

According to experiments conducted by the present inventors, it has been found that the ratio between the irradiation amount when a pattern appears on the resist and the irradiation amount to obtain a predetermined film remaining rate is almost constant regardless of the pattern width. In other words, the irradiation amount when a 5 micron square pattern appears in Figure 3 is Q0.
If the irradiation dose at which the desired residual film rate t1 is achieved is Q1, then the rate of increase in irradiation dose ΔQ is expressed as Q1/Q0, but if the irradiation dose at which a 1 micron square pattern appears is Q0', then The irradiation dose at which the residual film rate becomes t1 is ΔQ・
It is determined by Q0′.

Therefore, if the irradiation amount when the pattern appears is known, the irradiation amount to obtain the desired residual film rate for a pattern of any size can be determined by multiplying this by ΔQ.

Also, as shown in Figure 4, after drawing, the dimensions were corrected to satisfy the target residual film thickness and pattern dimension of 2lμm.
Consider a 2Mμm square pattern made by Sμm.

The exposure intensity distribution of a 2Mμm square pattern is shown in FIG. Irradiation amount Q, exposure intensity distribution F
(R), the amount of development energy E is the relationship QF(R)=E, and Q=E/F(R), so the exposure intensity can be indirectly determined by Q, which is the reciprocal of the intensity distribution F(R). It shows the distribution. In FIG. 5, the vertical axis represents the irradiation amount, and the horizontal axis represents the distance from the center of the pattern to the edge.

Let Q ₁ be the irradiation amount that gives the target residual film rate t ₁ , and let Q ₀ be the irradiation amount that causes the pattern to appear, as shown in Fig. 5.
The irradiation doses Q ₀ and Q ₁ are calculated using the following formulas.

Q ₀ F(o)=E ……(3) Q ₁ F(l)=E ……(4) Here, F(R) is obtained by integrating the exposure intensity distribution equation (1) within a rectangle. , expressed by equation (5).

F(R)=∫ ^M _-M ∫ ^M _-M f(r)dxdy ...(5) Also, the positional relationship of R, r, x, and y is shown in Figure 6, and the following (6) It will look like the ceremony.

^r2 =(Rcosθ-x) ²⁺ (Rsinθ-y) ² ...(6) Also, E is the amount of development energy.

From (3) and (4), Q ₁ /Q ₀ =F(o)/F(l) (7), and Q ₁ /Q ₀ is equal to the rate of increase in irradiation dose ΔQ in FIG.

From the above, the unknown M can be obtained by solving the integral equation (7). From Figure 4, 2M=2l−2S
Because of the relationship, the dimensional correction amount S from S=l−M
can be found.

Further, the irradiation amount Q ₁ at that time can be obtained from equation (4).

Incidentally, the amount of development energy E is determined from the irradiation amount Q ₀ at which the pattern shown in FIG. 3 appears and equation (3).

As described above, by finding the dimension correction amount S for the 2 lμm square pattern, correcting (reducing) the pattern dimension, and exposing the 2Mμm square pattern with the irradiation amount Q ₁ , the target residual film rate can be achieved. t ₁ and pattern dimension 2lμm are obtained. Next, in the case of FIG. 7 where there is an influence of the proximity effect between patterns, it is determined as follows.

In Figure 7, the pattern spreads due to the drawing of the pattern itself (intra-pattern proximity effect).
The size correction amount S ₁ and the irradiation amount Q ₂ are determined by the method described above, and the size is reduced as shown by the broken line so that the target residual film rate is achieved.

Furthermore, after drawing with a dose of Q ₂ , the dimensions are reduced by S2 as indicated by the dotted line, taking into consideration the influence of surrounding patterns (proximity effect between patterns), so as to achieve the design dimensions.

S2 is calculated as follows. In Fig. 7, the design pattern dimensions and spacing are W and L, and the edge points a and c of the pattern before dimension correction (solid line in the figure)
Let G(a) and G(c) be the exposure intensities at the points, and if there is an effect of proximity effect between patterns, G(a)<G
(c), and when the influence disappears, G(a) = G
(c). From the above, in order to make the exposure intensity G(c) on the inside of the pattern and the intensity G(a) on the outside edge equal to the development energy amount E, the dimension correction is performed based on how much the dimension needs to be shifted. Quantity S2
is required.

Here, G(a) and G(c) are the following equations (8) and (9).

G(a)=Q ₂ × {F(W-S2/2)+F(3W/2+S2
/2+L)} ...(8) G(c)=Q ₂ × {F(W/2+S2/2)+F(W/2
+S2/2+L)} ...(9) Note that F(R) is given by equation (5).

Therefore, in the case of the pattern shown in FIG. 7, by performing the intra-pattern dimension correction in S1, the inter-pattern dimension correction in S2, and exposing with the irradiation dose _Q2 , the target residual film rate _t1 , pattern dimension W, and pattern can be determined. An interval L is obtained.

(g) Effects of the Invention As described above, according to the present invention, it is possible to easily obtain the dimension correction amount and irradiation amount necessary to obtain the target residual film thickness and pattern accuracy, and the correction pattern dimension and irradiation amount can be easily obtained. By performing electron beam writing based on the amount, it is possible to obtain a pattern with high precision and which guarantees the remaining film thickness.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the size of the rectangle and the spread of the pattern, Fig. 2 is a diagram showing the relationship between the size of the rectangle and the irradiation amount of the electron beam when the residual film thickness is constant, and Fig. The figure shows the relationship between the electron beam irradiation amount and the residual film rate of the photosensitive material, Figure 4 shows the relationship between the desired pattern and the electron beam irradiation pattern, and Figure 5 shows the exposure intensity distribution. , FIG. 6 is a diagram for explaining the formula, and FIG. 7 is a diagram for explaining the correction pattern. Q ₀ , Q ₁ ... electron beam irradiation amount, d, d ₀ ...
Film thickness of photosensitive material, D...Distance from the center of the pattern to the edge.

Claims (1)

[Claims] 1 Taking advantage of the fact that there is a certain proportional relationship between the amount of electron beam irradiation when a pattern appears on a negative resist and the amount of electron beam irradiation required to obtain the desired residual film rate of the resist, Determine the electron beam irradiation amount at the residual film rate, and calculate the reduced pattern size necessary to obtain the desired residual film thickness and pattern size of the resist from the relationship between the electron beam irradiation amount and pattern dimensions for a pattern with a predetermined size. An electron beam exposure method characterized in that the resist is irradiated with an electron beam using the reduced pattern size and the electron beam irradiation amount.