JP2002008970A - Method of correcting proximity effects in electron beam exposure, and method of manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of correcting the proximity effect in electron beam exposure, where there is neither reduction in throughput nor deterioration in TAT (time required for electron beam lithography process), and moreover there is no deterioration in dimensional accuracy. SOLUTION: In an electron beam exposure step, where electron beams are irradiated on the surface of a layer to be exposed for a pattern, scattering of the electron beams causes proximity effects, which is turn causes errors in exposure energy in the layer to be exposed to a pattern. To correct these errors, the surface of the layer to be exposed to a pattern is divided into smaller segments of a specified area causing the proximity effects. These smaller segments are ghost areas, and in a ghost light exposure step, the ghost areas are exposed to ghost light individually, with corrected exposure energy being determined for each ghost area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a proximity correction method for electron beam exposure and a method for manufacturing a semiconductor device.

[0002]

BACKGROUND OF THE INVENTION In recent years, semiconductor devices typified by memory devices have been required to have higher density, higher performance, and higher functionality.
In particular, advanced technology is also required for lithography for forming fine patterns. As a technique satisfying these requirements, an electron beam exposure method having high resolution has been used.

FIG. 6 is a schematic view of an electron beam exposure apparatus and a substrate to be exposed for explaining a conventional electron beam exposure method. The electron beam generated from the electron gun is shaped into a rectangle by the first aperture, and is irradiated onto the second aperture by the shaping deflector to form a rectangle of an arbitrary size. The rectangular shaped electron beam is applied to a predetermined position on the substrate to be exposed by a plurality of positioning deflectors, and exposes the pattern one by one like a single stroke. Or, by using the partial batch exposure method,
(Dynamic Random AccessMem
or one) or several cells of SOR
M (StaticRandom Access Mem)
A repetitive basic pattern mask for at least a part of one or several cells of (ory) is formed on the second aperture, and is exposed by one shot.

Although the electron beam itself can be formed with sufficient accuracy, when it is incident on the resist film, it is scattered in the resist and causes some forward scattering. Further, it collides with an underlying layer of silicon or the like, is reflected and returns into the resist film, and is further scattered to cause wider backscattering. The spread of such an electron beam is expressed by the equation F (r) = C ₁ · exp {− (r / σ ₁ ) ² } +
It can be approximated by a Gaussian distribution such as C ₂ · exp {− (r / σ ₂ ) ² }. In this equation, σ ₁ is the forward scattering coefficient, σ ₂
The backscattering coefficient, C ₁ and C ₂ are coefficients.

[0005] In a semiconductor device pattern that has been miniaturized along with high integration, as the distance between adjacent exposure patterns becomes smaller, the above-mentioned spread due to the scattering of electron beams overlaps and affects adjacent patterns. This is called a proximity effect.

The proximity effect will be described with reference to FIGS. FIG. 2 shows that a desired pattern to be exposed on a substrate is divided into a plurality of pattern areas which are close to each other (approximately 15 to 20 μm square when the acceleration voltage is 50 keV) based on the electron beam drawing data. FIG. The solid line in FIG. 7A is a dense pattern with a center of 1: 1 as shown in FIG.
This is the exposure intensity in the X-axis direction when approximately two sparse patterns are exposed at a certain exposure amount. TH is the resist resolution intensity at the desired dimension. The denser the pattern, the greater the effect of spreading due to electron beam scattering, and the greater the actual exposure intensity.

At the center of the pattern, the effect of the spread due to the scattering of the electron beam from the peripheral pattern increases,
The actual exposure intensity increases. Now, if the TH is determined at the point of No. 3, the resist is resolved to a desired size in the center dense pattern, but the resist may be thinner than the desired size or may not be resolved in the peripheral sparse pattern. As described above, the proximity effect is a phenomenon in which the pattern size or the like in the design changes due to the influence of the pattern density.

[0008]

2. Description of the Related Art A ghost method is one of the methods for correcting the above-mentioned proximity effect. The conventional ghost method will be described with reference to the process flow of FIG. First, as shown in FIG. 2, desired patterns to be exposed on the substrate are set to such an extent that they exert a proximity effect on each other (when the acceleration voltage is 50 keV,
(About 20 μm square). Next, a specific reference pattern area is determined (for example, area C is set as a reference pattern area), and an exposure amount in the reference pattern area is determined. Subsequently, the entire pattern area (desired pattern) is subjected to electron beam exposure according to the exposure amount determined in the previous step. At this time, as shown in FIG. 7A, the drawing intensity is substantially low around the pattern and in the sparse pattern. Therefore, as shown in FIG. 7B, the total exposure amount is constant over the entire pattern. Ghost electron beam exposure or ghost light exposure is performed only on the pattern periphery and the sparse pattern.

[0009]

However, the ghost exposure method causes a decrease in throughput and a deterioration in TAT (time required for an electron beam lithography process, the same applies hereinafter). The reason is that only a small area where the exposure amount is insufficient is selectively exposed. For example, in the case of electron beam ghost exposure, the throughput is reduced because a calculation processing time for determining an area with an insufficient amount of exposure is required. In addition, the two exposures of the main exposure and the ghost exposure increase the processing time for one wafer. In the case of optical ghost exposure as well, since only a small area is selectively exposed, the throughput is reduced. Further, even when the entire surface of the pattern is subjected to collective light exposure, an exposure reticle must be manufactured for each minute area, so that it takes a long time to manufacture the reticle, resulting in deterioration of the TAT.

In the ghost exposure method, dimensional accuracy is deteriorated. The reason is that correction is performed for each micro area. In the correction by ghost exposure for each minute area, it is necessary to set an arbitrary exposure amount for each minute pattern. As a result, complicated pattern division occurs, and as a result,
Degradation of dimensional accuracy occurs.

[0011] In addition, a decrease in throughput causes a decrease in dimensional accuracy. The reason is that the exposure throughput decreases and the time until the development processing increases. When the time until the development process is long, the resist exceeds the durability time until the development process, and the dimensional accuracy is deteriorated. SUMMARY OF THE INVENTION An object of the present invention is to provide a proximity effect correction method in electron beam exposure that solves at least one of the problems of the prior art. Another object of the present invention is to provide a method of manufacturing a semiconductor device that solves at least one of the problems of the above-described conventional technology.

[0012]

A proximity effect correction method in electron beam exposure according to a first aspect of the present invention is based on scattering of electron beams in an electron beam exposure step of exposing a surface of a pattern exposure target layer to electron beams. A ghost area, which is a section that defines the surface of the pattern exposure target layer in an area of a fixed area where the proximity effect occurs, so as to correct an exposure intensity error applied to the pattern exposure target layer by the proximity effect A ghost light exposure step of performing ghost light exposure of the ghost area with the correction exposure amount defined in (1). Further, the method for manufacturing a semiconductor device according to the second aspect of the present invention includes a step of exposing a pattern exposure target layer for exposing a pattern exposure target layer by correcting an exposure amount by a proximity effect correction method in electron beam exposure of the present invention. It is characterized by including.

[0013]

Next, an embodiment of the present invention will be described.

In the ghost light exposure step in the present invention, the proximity effect based on the scattering (for example, back scattering) of the electron beam in the electron beam exposure step of exposing the surface of the pattern exposure target layer to be subjected to the pattern exposure with the electron beam is performed. The surface of the pattern exposure target layer is sectioned into an area of a fixed area where the proximity effect occurs (preferably, an area of a fixed shape with a fixed area) so as to correct an exposure intensity error applied to the pattern exposure target layer. A ghost light exposure of the ghost area with a correction exposure amount determined for each ghost area, which is a section defined in the above. The pattern exposure target layer can be, for example, a resist layer in which a portion exposed to an electron beam and light is removed or remains. Further, ghost light exposure can be performed for each ghost area with a correction exposure amount determined for each ghost area.

The proximity effect correction method for electron beam exposure according to the present invention can be performed as follows. A ghost area defining step of defining a ghost area by partitioning a pattern to be exposed on the surface of the pattern exposure target layer into an area of a constant area where the proximity effect occurs (preferably, an area of a constant area and a constant shape); It can have before the ghost light exposure step. Further, the size of the ghost area can be set depending on the acceleration voltage of the electron beam in the electron beam exposure step.

Further, a step of calculating a pattern area density for calculating an area ratio of the pattern occupying the ghost area may be provided after the step of defining the ghost area. Further, the ghost light exposure step may include a correction exposure amount calculating step of determining a correction exposure amount of the ghost area according to an area ratio of the pattern occupying the ghost area.

Further, an optical stepper file creating step of creating an optical stepper file defining a correction exposure amount of the ghost area may be provided before the ghost light exposure step. Further, the ghost light exposure step may be provided before the electron beam exposure step. In the electron beam exposure step, any given exposure amount can be used regardless of the area ratio (pattern area density) of the pattern in the ghost area. Further, in the ghost light exposure step, the ghost area may be exposed to the ghost area with the corrected exposure amount by using a reticle having a light transmittance determined for each area corresponding to the ghost area, and the ghost area is adjusted to the two or more ghost areas. Ghost light exposure can be performed simultaneously on an area (particularly, two or more ghost areas having different corrected exposure amounts) or all ghost areas.

[Method of Manufacturing Semiconductor Device] The method of manufacturing a semiconductor device of the present invention includes the step of exposing the specific pattern exposure target layer. After this exposure step, the method may include a development step of developing the pattern exposure target layer after exposure to leave a pattern layer, and a base layer etching step of etching a base layer left using the pattern layer as a mask layer. it can.

[0019]

FIG. 1 shows a process flow of an embodiment of the present invention. As shown in FIG. 2, the desired patterns to be exposed on the substrate are made to have a proximity effect with each other based on the electron beam drawing data (when the acceleration voltage is 50 keV,
It is divided into a plurality of pattern areas (hereinafter referred to as ghost areas) close to each other (about 15 to 20 μm square), and the pattern area density of each ghost area is calculated.

Next, a ghost exposure amount for each ghost area is determined by drawing intensity calculation. Subsequently, a light (i-line, KrF, etc.) stepper file is created from information such as the size and position of the ghost area and the amount of ghost exposure. FIG. 3 shows an example of the stepper file. I, I
I and III indicate ghost exposure amounts of the respective ghost areas, and have a magnitude relationship of I <II <III. The size of the ghost area depends on the acceleration voltage. Acceleration voltage is 50ke
In the case of V, it is about 15 to 20 μm □. Ghost light exposure is performed using the created stepper file, followed by main electron beam exposure (exposure of a desired pattern). In the electron beam main exposure, the proximity effect correction is not performed by setting the exposure amount in consideration of the pattern density.

[Operation of Embodiment] FIG. 4 is a simple explanatory view of the correction method. FIG. 4 shows the exposure intensity in the X-axis direction when a dense pattern having a center of 1: 1 as shown in FIG. 2 and a sparse pattern having a periphery of about 1: 1.5 to 1: 2 are exposed. TH is the resist resolution intensity at the desired dimension. In the main electron beam exposure without performing the proximity effect correction, the exposure intensity is as shown by the solid line in FIG. However, due to the ghost exposure of the present invention shown by the dotted line, the actual exposure
As shown by the solid line in (b), the desired pattern is resolved according to dimensions over the entire surface of the pattern.

[Explanation of Effects] The correction method according to the embodiment of the present invention can improve the throughput and shorten the TAT. This is because ghost exposure is performed for each ghost area, and light exposure is used for the ghost exposure. For example, in the ghost exposure according to the embodiment of the present invention, the calculation processing time for judging a region having an insufficient exposure amount is unnecessary. In addition, the ghost exposure is performed by an optical stepper, and the main exposure is performed by an electron beam exposure apparatus, so that the processing time for one wafer can be reduced due to the sharing of exposure,
In addition, by performing ghost light exposure before the electron beam main exposure, the apparent sensitivity of the electron beam main exposure is increased, and the throughput is improved. Also, unlike conventional ghost light exposure, simple exposure of an area of a fixed size (ghost area) does not cause a decrease in throughput, and since the size of the ghost area is constant, there is no need to manufacture an exposure reticle. , TAT can be shortened.

In the correction method according to the embodiment of the present invention, high dimensional accuracy can be ensured. The reason is that the correction is considered in the entire pattern area. In addition, the improvement in exposure throughput shortens the time until development processing,
Since development processing can be performed within the durable time after exposure of the resist, high dimensional accuracy can be secured.

[Other Embodiments] A second embodiment of the present invention is as follows.
In the ghost exposure according to the present invention, a ghost light exposure is performed on the entire surface of the desired pattern using a reticle corresponding to the desired pattern shown in FIG. FIG. 5 shows a reticle. As shown in FIG. 3B, the desired pattern is divided into ghost areas having 5 to 10 ghost exposure levels. Therefore, the reticle shown in FIG. 5 is divided into areas corresponding to the ghost area (the area size is 60 to 80 μm in the case of a 4 to 5 times reticle), corresponding to the ghost exposure amount, and the transmittance differs for each area. . The transmittance has a magnitude relationship of I <II <III, and is controlled by the thickness of the metal surface (such as Cr) of the reticle.

[0025]

The first effect of the proximity effect correction method in electron beam exposure according to the present invention is that the proximity effect can be corrected without lowering the throughput or increasing the time required for the exposure step. . The reason is that the proximity effect correction method in the electron beam exposure of the present invention covers the pattern exposure target layer due to the proximity effect based on the scattering of the electron beam in the electron beam exposure step of exposing the surface of the pattern exposure target layer to the electron beam. The ghost area is corrected by a correction exposure amount defined for each ghost area, which is a section defined by dividing the surface of the pattern exposure target layer into an area of a constant area where the proximity effect occurs so as to correct an error in exposure intensity. Is included in the ghost light exposure step.

A second effect of the proximity effect correction method in electron beam exposure according to the present invention is that the proximity effect can be corrected while ensuring high dimensional accuracy. The reason is the same as the reason for the first effect.

A first effect of the method for manufacturing a semiconductor device of the present invention is that the exposure target layer can be exposed by correcting the proximity effect without lowering the throughput or increasing the time required for the exposure step. It is. The reason is that the method of manufacturing a semiconductor device of the present invention includes an exposure step of a pattern exposure target layer that exposes a pattern exposure target layer by correcting an exposure amount by the proximity effect correction method in electron beam exposure of the present invention. Because.

A second effect of the method of manufacturing a semiconductor device according to the present invention is that the exposure target layer can be exposed while correcting the proximity effect while ensuring high dimensional accuracy.
The reason is the same as the reason for the first effect.

[Brief description of the drawings]

FIG. 1 is a diagram showing a process flow of an embodiment of the present invention.

FIG. 2 is a diagram for explaining that a desired pattern to be exposed on a substrate is divided into ghost areas based on electron beam drawing data.

FIGS. 3A and 3B are views showing an example of a stepper file, wherein FIG. 3A shows an exposure shot map, FIG. 3B shows a desired pattern whole surface, FIG. 3C shows a peripheral portion, and FIG. Show.

FIGS. 4A and 4B are diagrams for explaining a correction method in the embodiment of the present invention, and FIG. 4A is a graph separately showing a drawing intensity of ghost exposure and a drawing intensity of electron beam main exposure. (B) is a graph showing the combined drawing intensity of the ghost exposure and the drawing intensity of the electron beam main exposure.

FIGS. 5A and 5B are views showing a reticle that can be used in the embodiment of the present invention, wherein FIG. 5A is a reticle viewed from a thickness direction, FIG. 5B is a peripheral portion, and FIG. Are respectively shown.

FIG. 6 is a schematic view of an electron beam exposure apparatus and a substrate to be exposed for explaining a conventional electron beam exposure method.

FIG. 7 is a diagram for explaining a proximity effect;
(A) is a graph showing the drawing intensity of the electron beam main exposure, and (b) is a graph obtained by combining the drawing intensity of the conventional ghost exposure and the drawing intensity of the conventional ghost exposure with the drawing intensity of the electron beam main exposure. It is a graph represented.

FIG. 8 is a diagram for explaining a conventional process flow.

Claims (9)

[Claims] A first step of exposing an electron beam to the surface of the pattern exposure target layer so as to correct an exposure intensity error applied to the pattern exposure target layer by a proximity effect based on scattering of the electron beam in an electron beam exposure step; A ghost light exposure step of performing ghost light exposure on the ghost area with a correction exposure amount determined for each ghost area, which is a section that defines the surface of the pattern exposure target layer in an area of a fixed area where an effect is generated. A proximity effect correction method in electron beam exposure. 2. A ghost area defining step of defining a ghost area by dividing a pattern to be exposed on the surface of the pattern exposure target layer into an area having a constant area where the proximity effect occurs, before the ghost light exposure step. The proximity effect correction method in electron beam exposure according to claim 1, wherein: 3. The proximity in electron beam exposure according to claim 1, wherein the size of the ghost area is set depending on an acceleration voltage of the electron beam in the electron beam exposure step. Effect correction method. 4. The electronic device according to claim 1, further comprising a pattern area density calculating step of calculating an area ratio of the pattern occupying the ghost area after the ghost area defining step. Proximity effect correction method for line exposure. 5. The method according to claim 1, further comprising a step of calculating a correction exposure amount for determining a correction exposure amount of the ghost area according to an area ratio of a pattern occupying the ghost area before the ghost light exposure step. 5. The proximity effect correction method in electron beam exposure according to any one of 1 to 4. 6. The ghost light exposure step according to claim 1, further comprising an optical stepper file creation step of creating an optical stepper file defining the ghost area correction exposure amount. 2. The proximity effect correction method in electron beam exposure according to claim 1. 7. The proximity effect correction method in electron beam exposure according to claim 1, wherein said ghost light exposure step is provided before said electron beam exposure step. 8. In the ghost light exposure step, a reticle having a light transmittance determined for each area corresponding to the ghost area so that the ghost area can be exposed to the ghost light with the correction exposure amount is used. 8. The proximity effect correction method in electron beam exposure according to claim 1, wherein the ghost area or all the ghost areas are simultaneously subjected to ghost light exposure. 9. A pattern exposure target layer exposing step of exposing a pattern exposure target layer by correcting an exposure amount by the proximity effect correction method in electron beam exposure according to any one of claims 1 to 8. A method for manufacturing a semiconductor device, comprising: