JPH0336295B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an electron beam exposure method. especially,
Calculating the amount of pattern size correction applied to each pattern for the purpose of correcting the so-called proximity effect and calculating the irradiation amount that gives the optimum development energy intensity to each pattern can be easily, quickly and with high precision. The present invention relates to an improvement in an electron beam exposure method in which correction for the so-called proximity effect can be performed with high accuracy.

(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, as shown in FIG. 1, there is a scattering region B around the electron beam irradiation region A, and the electron beam killing 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 electron beam at the point where the distance from the center of the irradiation area is r This is the scattering intensity, and a, b, and c are constants determined by the material of the sample and the sensitivity and thickness of the resist used.

Since the width of the electron beam irradiation area A shown in FIG. 1 is usually as narrow as 0.1 to 0.2 μm, it is necessary to scan the electron beam in order to obtain a pattern with a desired width. However, as shown in Figure 1, the scattering area is quite wide, so when scanning the electron beam,
The development energy intensity (irradiation intensity) becomes relatively large in the scattering region. 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 as shown in FIG. 1, if the pattern width is narrow, the scanning speed must be lowered, that is, the irradiation amount must be increased to increase the developing 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 Conventionally used methods to correct the proximity effect include (a) considering the electron beam scattering intensity distribution, pattern shape, and the influence of scattering of the electron beam that irradiates adjacent patterns; (b) A method of irradiating an area narrower than the dimensions of the pattern to be formed, that is, a method of correcting the dimensions of each pattern. In either case, all data must be determined at the time of pattern design.

Furthermore, in the case of a direct exposure method in which a wafer is directly irradiated with an electron beam to form a pattern by lithography, it is necessary to maintain a large residual resist film thickness due to the processing process.

However, in the case of negative resists, if the irradiation dose is reduced, the remaining film thickness becomes thinner, so if we try to correct the proximity effect using a method that corrects the irradiation dose to achieve the desired pattern shape and pattern spacing. , the remaining film thickness will vary depending on the pattern shape and pattern spacing.

On the other hand, in the case of a positive resist, in order to reduce side etching and improve processing accuracy, it is desirable to have a pattern shape in which the width at the bottom surface of the resist is equal to the width at the top surface and the cross section is vertical.
Further, the pattern width when the cross-sectional shape is vertical is larger than the drawn pattern dimension, and the spread after drawing becomes more noticeable when the pattern size is large and becomes more noticeable when the film thickness is thick.

Therefore, in the case of the direct exposure method, it is necessary to maintain a large residual film thickness of the negative resist and to satisfy pattern dimensional accuracy. Further, in the case of a positive resist, in order to maintain a vertical cross-sectional shape and satisfy pattern dimensional accuracy, it is necessary to perform both dimensional correction by reducing the pattern to be drawn and dose correction at the same time.

A typical electronic exposure apparatus is constructed as shown in FIG. In the figure, 5 is the main body, 6 is the electron gun, 7 is the electron lens system, and 8 is the X
-Y deflector, 9 is the sample, 10 is the
It is a CPU, 11 is a DA converter, and 12 is an amplifier.

Since the irradiation amount and dimensional correction amount for each pattern are determined at the time of pattern design, the irradiation amount (scanning speed) and dimensional correction amount are stored in the CPU 10, and the X-Y deflector 8 is operated based on the instructions. The beam spot is driven to step forward, giving each pattern a desired development energy intensity while avoiding the so-called proximity effect, thereby enabling highly accurate pattern formation. (Same as lines 2 to 14 on page 13 of the original specification) Furthermore, as the patterns to be formed become finer and more complex, the amount of correction must be determined accurately and quantitatively in order to ensure high precision correction of the proximity effect. This has become desirable.

One way to achieve this precision is to reduce each pattern by reducing the four points a, b, c, and
Set _a sample point at d, and reduce _the length of each side by X ₁ , X ₂ ,
One idea is to use equation (1) to calculate the amount of dimensional correction applied to each pattern by creating simultaneous equations with the condition that the energy intensity at each sample point is constant. It will be done.

For example, at point a, the following formula holds true.

Q ₁ F ₁ (r ₁ ) + Q ₂ F ₂ (r ₂ ) + Q ₃ F ₃ (r ₃ ) = E ... (2) However, Qi (i = 1 to 3) is the irradiation amount for each pattern, F ₁ (r ₁ ) (i=1 to 3) is the exposure intensity for each pattern, and for example, F ₂ (r ₂ ) is expressed by the following formula.

F ₂ (r ₂ )= ∫ ^(W-x1-x3)/2 _-(W-x1-x3)/2 ∫ ^(H-x2-x4)/2 _{-(H-x2-x4)
/2} f(r)dydx...(3) However, W is the width of pattern 2, and H is the length of pattern 2.

However, as shown in equation (1), the electron beam scattering intensity distribution decreases exponentially with respect to distance and is nonlinear with respect to distance. Therefore, the above simultaneous equations often do not have a solution.

Furthermore, even if there is a theoretical solution, the number of patterns in semiconductor devices is extremely large.
Since the number is about 10 ⁶ to ^{10 7} , a long processing time is required even if a large computer with high calculation speed is used, and the method using the above simultaneous equations is not necessarily practical. . Therefore, it would be extremely convenient if it were possible to use some approximation method to easily and quickly determine the irradiation amount and the dimensional correction amount for each pattern with a realistically acceptable accuracy.

(4) Purpose of the Invention The purpose of the present invention is to meet this need, and to apply an appropriate development energy intensity to each pattern area using an electron beam that emits a specific number of electrons per unit area per unit time. In the electron beam exposure method, the irradiation amount (scanning speed) of the electron beam is controlled for each pattern, and on the other hand, in order to control the so-called proximity effect, each pattern is subjected to dimension correction. It is an object of the present invention to provide an electron beam exposure method that can easily and quickly calculate the amount (scanning speed) and the amount of dimensional correction.

(5) Structure of the Invention An object of the present invention is to reduce the amount of energy irradiation necessary to expose a first pattern and to reduce the amount of energy irradiated by the proximity effect when exposing at least one second pattern close to the first pattern. determining the ratio of the energy irradiation amount to the energy irradiation amount irradiated with the generated first pattern, deriving the dimensional correction amount of the first pattern from the ratio of the energy irradiation amount, and exposing the first pattern; This is achieved by including.

The technical idea that the present invention embodies is that, in order to form a pattern as shown in FIG. 3a, when a dimension correction is made by a length S as shown in FIG. 3b, a sample point A on the edge of the design pattern is Between the reduction rate P of the exposure intensity F and the size correction amount S, P=αS+β
As a result of simulation, it was found that there is a proportional relationship, so this law of nature was used to determine the amount of dimensional correction for each pattern. First, calculate the ratio P=F ₁ /F ₀ (rate of decrease in intensity) between the exposure intensity F ₁ when the dimension correction is applied by the length S and the exposure intensity F ₀ when the dimension correction is not applied. , and from the above proportional relationship, the pattern size to be corrected for reduction, that is, the size correction amount S is determined.

(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.

First step For each pattern i (i=1 to 3), the exposure intensity F _i (r _i ) at sample point A of pattern 1 (i=1 to
3) is calculated based on the following formula.

F ₁ (r ₁ )=∫ ^(W1-S)/2 _-(W1-S)/2 ∫ ^H1/2 _-H1/2 f(r)
dydx……(4) Fi(ri)＝∫ ^Wi/2 _-Wi/2 ∫ ^Hi/2 _-Hi/2 f(r)dydx……
(5) Second step At sample point A of pattern 1, where dimension correction is performed by length S, the following formula holds true.

Q ₁ F ₁ (r ₁ ) + Q ₂ F ₂ (r ₂ ) + Q ₃ F ₃ (r ₃ ) = E ... (6) However, Q ₁ (i = 1 to 3) is the irradiation amount of each pattern. , is calculated from the exposure intensity at sample points on the sides of each design pattern.

For example, the dose Q ₁ of pattern 1 is calculated using the following formula.

Q ₁・F ₀ =E……(7) Q ₁ =∫ ^W1/2 _-W1/2 ∫ ^H1/2 _-H1/2 f(r)dydx=E……(8
) However, f(r) is the scattering intensity distribution, which is calculated using equation (1), E is the development energy intensity, W ₁ is the pattern width of pattern 1, and H ₁ is This is the pattern length of pattern 1.

Third step: For each pattern, a desired value of development energy intensity is applied to the pattern, which is calculated by taking into account the effects based on the electron beam irradiation applied to other patterns at the same time, as dimensional correction is applied to that pattern. Calculate the different exposure intensities. In other words, the exposure intensity F ₁ (r ₁ ) of pattern 1 subjected to dimension correction by length S is F ₁ (r ₁ )={E−Q ₂ F ₂ (r ₂ )−Q ₃ F ₃ (r ₃ )}/Q ₁
...Calculate using (9).

Fourth step: For each pattern, calculate the ratio of the exposure intensity when the pattern is subjected to dimension correction to the exposure intensity when the pattern is not subjected to dimension correction, that is, the rate of decrease in intensity. For example, for pattern 1, the ratio (reduction rate) of equation (8) and equation (9) P = F ₁
Find (r ₁ )/F ₀ .

5th step It has been found through simulation that there is a relationship between the dimensional correction amount S and the strength reduction rate P as follows: P=αS+β...(10).Using this relationship, each The size correction amount for each pattern is calculated from the reduction rate calculated in the fourth step for each pattern.

A typical electronic exposure apparatus is constructed as shown in FIG. In the figure, 5 is the main body, 6 is the electron gun, 7 is the electron lens system, and 8 is the X-
Y deflector, 9 is the sample, 10 is the CPU
11 is a DA converter, and 12 is an amplifier.

Since the irradiation amount and dimensional correction amount for each pattern are determined at the time of pattern design, the irradiation amount (scanning speed) and dimensional correction amount are stored in the CPU 6, and the X-Y deflector 8 is operated based on the instructions. The beam spot is moved step by step to provide a desired development energy intensity to each pattern while avoiding the so-called proximity effect, making it possible to form highly accurate patterns.

(7) Effects of the Invention As explained above, according to the present invention, an electron beam that emits a specific number of electrons per unit area per unit time is used to apply appropriate development energy intensity to each pattern area. controls the electron beam irradiation amount (scanning speed) for each pattern, while
In order to suppress the so-called proximity effect, in an electron beam exposure method that performs dimensional correction on each pattern, an electron beam that can easily and quickly calculate the irradiation amount (scanning speed) and the dimensional correction amount for each pattern is used. An exposure method can be provided.

[Brief explanation of drawings]

FIG. 1 is a graph showing the electron beam intensity distribution, and FIG. 2 is a diagram for explaining a method for correcting the proximity effect by correcting dimensions. Figure 3 a, b
is a diagram for explaining the technical idea of the present invention,
FIG. 4 is a diagram for explaining the configuration of the present invention, and FIG. 5 is a conceptual configuration diagram of an electronic exposure apparatus that can be used to implement the present invention. 5...Electron beam exposure device main body, 6...Electron gun, 7...Electron lens system, 8...X-Y deflector,
9...Sample, 10...CPU, 11...DA converter, 12...Amplifier.

Claims (1)

[Claims] 1 Energy irradiation amount necessary to expose the first pattern and energy irradiated with the first pattern caused by the proximity effect when exposing at least one second pattern close to the first pattern. Electron beam exposure comprising the step of determining a ratio between the energy irradiation amount and the energy irradiation amount, deriving a dimensional correction amount of the first pattern based on the ratio of the energy irradiation amount, and exposing the first pattern. Method.