JP3206558B2 - Aperture for electron beam writing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aperture for drawing an electron beam, which is used when drawing a resist formed on a substrate with an electron beam directly to form a circuit pattern such as a semiconductor integrated circuit.

[0002]

2. Description of the Related Art In recent years, the density of semiconductor integrated circuits has been remarkably increased, and the storage capacity of a memory element represented by a DRAM has quadrupled every three years. One of the important technologies for increasing the density of a semiconductor integrated circuit is a fine pattern forming technology.

Conventionally, a miniaturized exposure apparatus using ultraviolet light as a light source, that is, a stepper has been used to form a fine pattern on a wafer as a semiconductor substrate. However, in order to form a finer pattern, a light source is used. Wavelength is shortened,
The g-line (436 nm) of the mercury lamp has been changed to the i-line (365 nm) of the same mercury lamp, and further to KrF excimer laser light (249 nm) using krypton fluoride gas. However, the improvement of the fine pattern transfer capability, that is, the resolution by shortening the wavelength of the light source has a problem that the depth of focus decreases.

In the production of semiconductor integrated circuits,
Since the pattern transfer is repeated 10 to 30 times, the patterns are sequentially superimposed on the semiconductor substrate, resulting in a large step. Therefore, a decrease in the depth of focus makes it difficult to transfer a pattern onto a step, and makes it difficult to manufacture a semiconductor integrated circuit.

As a method of solving the above-mentioned problem of the fine pattern forming technique, an electron beam writing method in which the depth of focus is significantly larger than that of light exposure is disclosed.

In this electron beam writing method, since a semiconductor integrated circuit pattern is drawn by sequentially tracing the pattern with an electron beam having a small spot, it is possible to further miniaturize the pattern. However, the processing ability is inferior to that of ordinary light exposure. It was a problem.
However, instead of this one-stroke drawing method, batch transfer is performed using an aperture that newly forms a part of the semiconductor integrated circuit,
A partial batch electron beam lithography method for connecting these batch patterns and transferring the entire circuit pattern has been developed, and the processing capability has been dramatically improved.

FIG. 7 is a perspective view showing the structure of an electron optical system for explaining an example of an electron beam drawing apparatus using an aperture forming a part of a semiconductor integrated circuit. In this partial batch writing method, as shown in FIG. 7, an electron beam 8 from an electron gun 1 is shaped into an appropriate size and shape by a first aperture 2, and then formed on a second aperture 4 by a selective deflector 3. Irradiate. A partial collective pattern group, which is a part of the semiconductor integrated circuit pattern, is formed in the second aperture 4, and one of the pattern groups is selected by the selection deflector 3. The electron beam that has passed through the selected pattern group of the second aperture 4 is reduced by a reduction lens 5 as an objective lens, and is further collectively drawn at a desired position on a semiconductor substrate 7 by a positioning deflector 6.

FIG. 8 is a plan view of a conventional second aperture for electron beam drawing. FIGS. 9A to 9C are cross-sectional views of the second aperture of FIG. 8 taken along the line BB ′, electron beam distribution intensity diagrams of electron beams transmitted through the second aperture, and cross-sections of the resist pattern on the semiconductor substrate. The figure is shown.

In the partial batch electron beam drawing method using the second aperture as shown in FIG. 8, a pattern group formed on the second aperture 4 by the proximity effect is faithfully drawn on a resist on the semiconductor substrate 7. There is no problem. For example, as shown in FIG.
Assuming that five drawing aperture patterns up to 5 are formed as a pattern group, the electron beam passing through these pattern groups is projected onto the semiconductor substrate 7. The electron beam directly incident on the resist on the semiconductor substrate 7 is incident on the resist, is reflected on the surface of the semiconductor substrate, and returns to the semiconductor substrate again. The repetition of this incidence and reflection becomes so-called backscattered electrons, which affects the pattern to be drawn. The degree of the spread of the backscattered electrons varies depending on the acceleration voltage of the incident electron beam, the material of the semiconductor substrate, and the like, but the number of the backscattered electrons decreases as the distance from the electron beam incident position on the semiconductor substrate increases.

Therefore, the influence of the proximity effect on the drawing pattern only needs to be considered for the pattern near the incident position. That is, at the portion 33 on the semiconductor substrate 7, the influence of the backscattered electrons by the electron beam irradiated on the semiconductor substrate 7 through the drawing aperture patterns 12 and 14 in addition to the incident electrons and the backscattered electrons from the drawing aperture pattern 13. As a result, it has an electron intensity distribution as shown in FIG.
On the other hand, the portion 31 on the semiconductor substrate 7 is affected by the incident electrons and the backscattered electrons from the opening pattern 11 for drawing and the backscattered electrons by the electron beam passing through the opening pattern 12 for drawing. At this time, there is only the drawing opening pattern 12 adjacent to the drawing opening pattern 11, and therefore, the backscattered electrons are small and the influence of the proximity effect is small, so that the electron intensity is as shown in FIG. Site 3 on substrate 7
It is lower than 2-34. Now, if the electron intensity is I
At the time of o (threshold value), assuming that the transistor patterns in the portions 32 to 34 are formed to have dimensions corresponding to the opening patterns 12 to 14 for drawing, in the portions 31 and 35, FIG.
As shown in (c), the resist pattern 9 is formed by the parts 32 to
34, and sometimes the size of the resist pattern 9 is significantly reduced, and the resist pattern collapses. As described above, the pattern of the portion that is not easily affected by the proximity effect has a smaller size than the pattern of the portion that is easily affected by the proximity effect.

Therefore, in the case where the number of openings is large and the area is large near the entrance position of the aperture, it is easily affected by backscattering. Therefore, the influence of the proximity effect is approximately evaluated by the area of the pattern included inside a small circle whose radius is about the extent of backscattering with the electron beam incident position on the semiconductor substrate as the center. Assuming an array pattern transferred by the partial batch exposure method, FIG.
In the central portion 16 of the array shown in FIG. In contrast, the open end 17 of FIG.
In the corner portion 18, the area of the peripheral aperture is small, and the influence of backscattering is small. FIG. 11 shows the electron beam intensity distribution due to the back scattering at this time. In FIG. 11, symbols C0 to C3 indicate exposure intensity (electron beam intensity due to backscattering), and have a relationship of C0>C1>C2> C3. C0 has the highest exposure intensity, and C3 has the lowest exposure intensity. Since there is unevenness in the backscattering as described above, the dimension of a pattern formed when an electron beam is actually drawn is uneven.

As a countermeasure, an electron beam writing method employing a method of correcting the proximity effect is disclosed in Jpn. J. Appl.
Phys. Vol. 33, 6953 pages (1994)
(Hereinafter, referred to as a first conventional method) and JP-A-8-4
No. 5808 (hereinafter referred to as the second conventional method).

In the first conventional method described above, in an exposure method using an aperture in which a part of a semiconductor integrated circuit is formed (partial batch exposure method), the size of a shot at a corner portion is reduced as shown in FIG. The exposure amount is determined with a finer step width, and the exposure amount is compensated. When reducing the size of a shot, instead of reducing the pattern magnification on the aperture, the shaping deflector is operated, and the beam position is moved as shown by hatching in FIG. Reduce. As a result, it becomes possible to perform the proximity effect correction by the conventionally performed exposure compensation method with higher accuracy. Further, in the second aperture disclosed in the above-described second conventional method, the auxiliary opening 20 is provided further outside the outermost drawing opening pattern 19 as shown in FIG. The size of the auxiliary opening 20 is determined so that electrons smaller than the resolution limit of the resist pass through. The electron beam passing therethrough becomes auxiliary exposure for the pattern of the outermost opening with a small number of backscattered electrons, and can correct the influence of the proximity effect.

[0014]

In the above-mentioned method of reducing the shot size in the first conventional method, only one exposure amount in the same shot is determined. Generally, the electron distribution due to backscattering changes continuously depending on the position of the pattern,
There is also a difference in the exposure amount inside the shot. Therefore, in the first method, since the exposure amount in the shot is the same, it cannot be considered that the backscatter in the shot continuously varies.

This is a problem that the partial batch exposure method generally has when correcting the proximity effect by the exposure compensation method. In addition, there is a problem that the number of shots in the corner portion increases to reduce the shot size, and the throughput deteriorates.

In the electron beam writing aperture according to the second conventional method, an auxiliary exposure pattern having a fixed opening width is provided outside the outermost opening, and writing is performed by electrons passing through the outermost opening. The pattern is corrected with a constant intensity. However, the pattern density of the adjacent region is the same at the center 22 of the same opening as the corner 21 of the partial batch exposure pattern shown in FIG. different. Therefore, a difference occurs in the magnitude of the backscatter. Attempting to correct this with the same intensity would cause a correction error.

An object of the present invention is to provide an aperture for electron beam lithography capable of correcting unevenness of a pattern line width due to a difference in backscattered electron beam intensity between a corner portion and a central portion, which solves the above-mentioned problems in the prior art. is there.

[0018]

According to the present invention, there is provided an electron beam writing aperture which is formed by arranging a plurality of writing opening patterns to be written on a resist applied to a semiconductor substrate on a plate member. Wherein an L-shaped auxiliary exposure opening pattern for proximity effect correction having a width passing an amount of electrons equal to or less than the resolution limit of the resist is provided adjacent to a corner portion of the outermost drawing opening pattern. It is characterized by.

The L-shaped auxiliary exposure opening pattern may be formed to have the same width, and the width and length of the pattern may be variable.

The shape of the L-shaped auxiliary exposure opening pattern may be wedge-shaped, and the opening pattern area may be variable.

In the present invention, by providing the above-mentioned L-shaped auxiliary exposure opening pattern adjacent to a corner portion of the outermost drawing opening pattern, electrons transmitted through the auxiliary exposure opening pattern are added. As a result, the difference between the backscattered electrons at the corner and the center in the partial batch exposure is reduced, and the unevenness of the pattern line width due to this can be corrected.

[0022]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view of an aperture for partial electron beam writing according to an embodiment of the present invention. FIG. 2 shows FIG.
FIG. 4 is a cross-sectional view taken along line AA ′ of FIG. Aperture body 4
Is made of a material having a certain thickness, such as silicon, for blocking electrons, and a portion thereof is cut out to provide the drawing opening patterns 23 to 27 in FIG. In order to correct the proximity effect, an L-shaped auxiliary exposure opening pattern 28 is provided at the corners of the openings 23 and 27. The L-shaped auxiliary exposure opening pattern 28 is set to a size smaller than the resolution limit of the resist, and the opening itself is not resolved, but some electrons pass through the L-shaped opening.

This aperture is inserted into the electron beam lithography apparatus shown in FIG. 8, and the electron beam is made incident from the direction of the arrow shown in the sectional view of FIG.

FIG. 3 shows an L-shaped auxiliary exposure opening pattern 2.
FIG. 7 is a diagram two-dimensionally expressing exposure intensity (electron beam intensity) due to backscattering when no 8 exists. In FIG. 3, symbols C0 to C3 indicate exposure intensity, and C0>C1>C2> C
There are three relationships. In the corner portion, the amount of exposure tends to be insufficient up to a region inward from the end portion by about the back scattering diameter.

FIG. 4 shows two-dimensionally the exposure intensity (electron beam intensity) due to backscattering when the L-shaped auxiliary exposure opening pattern 28 is provided at the corners of the openings 23 and 27 as shown in FIG. Reference numerals C0 to C3 indicate the same exposure intensity as in FIG. In FIG. 4, it can be seen that the exposure intensity increases in the portion where the L-shaped auxiliary exposure opening pattern is opened, as compared with FIG.

In accordance with the change in the exposure intensity, the L-shaped auxiliary exposure opening pattern 28 in FIG. 4 uses the variable opening 28a to enlarge and reduce the size of the opening as shown in FIG. It may be possible to increase or decrease. Further, the length of the L-shaped auxiliary exposure opening pattern 28 in FIG. 4 may be variable, and the width and length of the L-shaped auxiliary exposure opening pattern 28 may be simultaneously variable. The above
The size of the variable aperture is the size of the aperture
Means various opening patterns.

If the difference in the exposure amount between the corner portion and the other cell edge portion is large, an L-shaped auxiliary exposure opening pattern 29 having a wedge-shaped shape as shown in FIG. The amount of line exposure can be adjusted.
This makes it possible to perform correction on various base substrates whose correction parameters change. Note that the opening area of the wedge-shaped L-shaped auxiliary exposure opening pattern 29 in FIG. 6 can be made variable.

[0029]

According to the present invention, an L-shaped auxiliary opening pattern is provided at the corners of the openings at both ends of a plurality of rectangular openings provided in parallel with the electron beam writing aperture, so that the diameter of the back scattering diameter is approximately By performing the auxiliary exposure, there is an effect that the proximity effect of the corner portion of the cell array, which is particularly affected by the proximity effect, can be corrected. In addition, since the auxiliary opening pattern can be exposed simultaneously with the circuit pattern, it is possible to prevent a decrease in throughput at the time of drawing.

[Brief description of the drawings]

FIG. 1 is a plan view of an aperture for partial batch electron beam writing according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line A-A 'of FIG.

FIG. 3 is a two-dimensional distribution diagram of exposure intensity (electron beam intensity) due to backscattering when an L-shaped auxiliary exposure aperture pattern does not exist.

FIG. 4 is a two-dimensional distribution diagram of exposure intensity (electron beam intensity) due to backscattering when an L-shaped auxiliary exposure opening pattern is provided.

FIG. 5 is a plan view of a partially collective electron beam writing aperture provided with an L-shaped auxiliary exposure opening pattern having a variable opening width.

FIG. 6 is a plan view of a partial batch electron beam writing aperture provided with an L-shaped auxiliary exposure opening pattern having a wedge-shaped opening shape.

FIG. 7 is a perspective view illustrating a configuration of an electron optical system for explaining an example of an electron beam writing apparatus.

FIG. 8 is a plan view of a conventional second aperture for electron beam writing.

9A and 9B are diagrams for explaining the features of the conventional second aperture shown in FIG. 8; FIG. 9A is a view BB ′ of the second aperture shown in FIG. 8;
FIG. 4B is a cross-sectional view taken along a line, FIG. 4B is a cross-sectional view of an electron beam distribution intensity of an electron beam transmitted through the second aperture, and FIG. 4C is a cross-sectional view of a resist pattern on a semiconductor substrate.

FIG. 10 is a plan view of a conventional second aperture for electron beam writing.

FIG. 11 is an electron beam intensity distribution by backscattering when a conventional second aperture for electron beam drawing is used.

FIG. 12 is a diagram showing a conventional proximity effect correction method by reducing the partial batch shot size.

FIG. 13 is a diagram showing a method of operating a conventional deflector to reduce a shot size.

FIG. 14 is a plan view of a conventional aperture having an auxiliary opening provided outside the outermost drawing opening pattern.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electron gun 2 first aperture 3 selective deflector 4 second aperture 5 reduction lens 6 positioning deflector 7 semiconductor substrate 8 electron beam 9 resist pattern 11-15 drawing opening pattern 16 array center 17 opening end 18 corner 23-27 Drawing opening pattern 28, 29 L-shaped auxiliary exposure opening pattern 28a Variable opening

Claims (4)

(57) [Claims] 1. An electron beam drawing aperture formed by arranging a plurality of drawing opening patterns to be drawn on a resist applied to a semiconductor substrate on a plate member, the outermost corner of the drawing opening pattern. An L-shaped auxiliary exposure aperture pattern for proximity effect correction having a width adjacent to and passing an amount of electrons equal to or less than the resolution limit of the resist is provided. 2. The electron beam writing aperture according to claim 1, wherein the width of the L-shaped auxiliary exposure opening pattern is the same. 3. The aperture for electron beam lithography according to claim 1, wherein said L-shaped auxiliary exposure opening pattern has a wedge shape. 4. The L-shaped auxiliary exposure opening pattern is
The dimensions must be smaller than the resolution limit of the resist.
The aperture for electron beam lithography according to claim 1, characterized in that:
.