JP2001272766A - Method for manufacturing photomask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the influence of stray light by exactly recognizing the deterioration of the resolution of the resist occurring in the stray light and the dependence on exposure likelihood and the degree the deterioration of depth of focus. SOLUTION: The coverage in a region within a distance R from the central coordinates of a test pattern in the method for manufacturing a photomask is defined as C% and after the patterns of the mask for measurement varying in the values of R and C are exposed to the resist, the pattern line widths L formed by varying the values of R and C are measured from the formed resist patterns. The process likelihood in the regions C and R is measured from the values obtained by measuring the exposure of the line widths L and the dependence of the depth of focus. A contour graph is formed by determining the maximum depth of focus at the prescribed exposure likelihood determined from the measured process likelihood as a function of C and R. Where the prescribed maximum depth of focus is necessary, the distance Rn satisfying the same and the range Cn% of the coverage are determined and the patterns are rearranged in such a manner that the region within Rn satisfies Cn% in designing the patterns of the mask.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask used for lithography of a semiconductor, and more particularly, to correction of an LSI pattern arrangement of a photomask based on quantification of the influence of stray light which degrades a process margin of a resist pattern. The present invention relates to a method for manufacturing a photomask for applying a mask.

[0002]

2. Description of the Related Art When an LSI pattern is formed on a semiconductor substrate, a radiation-sensitive material such as a resist is applied to a film to be processed on the substrate, and exposure and development are performed using a reduction projection exposure apparatus such as a stepper or a scanner. Do. In the case of using a refractive optical type exposure apparatus in the step of forming an LSI pattern on a photosensitive material, light emitted from a light source is reflected by a reduction lens system and a projection lens system on an LSI pattern image formed on a photomask located therebetween. Is faithfully transferred to the resist. Then, the film to be processed is patterned based on the formed resist pattern.

A photomask used for this type of pattern transfer generally has a structure in which a thin-film pattern such as chromium or chromium oxide is formed as a light-shielding film on a thick glass substrate. However, when light actually passes, the difference in the refractive index between glass and chromium or between chromium and air is very large, and such light causes complicated scattering and interference in the exposure apparatus. For this reason, among the light of the total exposure amount emitted from the light source, there is light that is irradiated on the resist as light passing through an optical path other than the optical path that is theoretically expected.

[0004] Such a phenomenon is called stray light, and it becomes nonnegligible noise due to the use of a resist capable of transferring a pattern even with a short wavelength of an exposure light source or a low contrast, thereby lowering the resolution of the resist or exposing an exposure tolerance. And degrade the depth of focus. In addition, since such phenomena vary greatly depending on the coverage of chromium or chromium oxide on the mask, the coverage of the light-shielding film on the mask and the resolution of the resist deteriorate, and the exposure tolerance and the depth of focus deteriorate. Accurate grasp of the degree is indispensable for manufacturing a stable semiconductor device.

[0005]

As described above, conventionally, in the process of transferring the pattern of the photomask to the resist, the resolution of the resist is reduced due to the influence of stray light, and the exposure latitude and the depth of focus are deteriorated. However, there is a problem that such a phenomenon differs depending on the coverage of the light shielding film on the mask.

The present invention has been made in consideration of the above circumstances, and has as its object to reduce the resolving power of a resist due to stray light, and to the dependence on the degree of deterioration of exposure latitude and depth of focus. It is an object of the present invention to provide a method for manufacturing a photomask, which can accurately grasp the influence of stray light and can contribute to the realization of a lithography process in which the influence of stray light is reduced.

[0007]

(Structure) In order to solve the above problem, the present invention employs the following structure.

That is, according to the present invention, in a method for manufacturing a photomask, an opening is provided only in a region separated by a distance R from the center coordinates of a test pattern, and the coverage of the light shielding portion in the opening is defined as C% (100 ≧ C ≧ 0), the process of measuring the process allowance in the area of the coverage C% and the radius R, and the maximum depth of focus at the predetermined exposure allowance or the predetermined focus depth obtained from the measured process allowance. The maximum exposure tolerance of
A step of outputting a contour graph as a function of the coverage C% and the distance R, and a contour graph satisfying these when it is considered that a predetermined maximum depth of focus A or a certain maximum exposure latitude B is required. Distance Rn and coverage C
It is characterized by including a step of obtaining n% and a step of rearranging the pattern so that a region within the distance Rn satisfies the coverage Cn% at the time of pattern design.

According to the present invention, in a method of manufacturing a photomask, the outside of the pattern area within a distance R from the center coordinate of the test pattern is defined as a light-shielding area, and the coverage of the light-shielding portion in the pattern area is C% (100 ≧ C ≧ 0), using a measurement mask in which the values of R and C were respectively changed, exposing the pattern of the measurement mask to a resist on a sample,
Performing a plurality of exposures under exposure conditions with different amounts of exposure and different depths of focus; and determining, from the resist pattern formed on the sample by the exposure, each of the patterns having different exposure conditions and different values of R and C. A step of measuring the line width L; and a step of measuring the dependency of the exposure amount and the depth of focus on the line width L in a matrix based on the measured line width L. Measuring the process allowance in the area of, and the maximum focus depth at the predetermined exposure allowance or the maximum exposure allowance at the predetermined focus depth, obtained from the measured process allowance, When a predetermined maximum depth of focus A or a maximum exposure latitude B is considered necessary, a step of outputting a contour graph as a function of C% and the distance R, and an arbitrary graph in the contour graph satisfying these requirements. Distance Rn and coverage A step of determining a range Cn%, as a region within the distance Rn when pattern design of the photomask to satisfy the coverage Cn%, characterized in that it comprises a step of rearranging the pattern.

Here, preferred embodiments of the present invention include the following. (1) In the step of rearranging the pattern, if the coverage is insufficient, the dummy pattern is arranged by a predetermined area after calculating the total area of the region within the distance Rn, and if the coverage is excessive, To delete a pattern by a predetermined area. (2) The process margin in the area of the coverage C% and the radius R is obtained by simulation.

(Function) The gist of the present invention is to accurately grasp the dependency of the coverage of the light-shielding film on the mask and the resolution of the resist, the degree of deterioration of the exposure latitude and the depth of focus in designing the LSI pattern. It is to propose a test mask pattern to be used as a guideline. That is, in the present invention,
As shown in FIG. 1, it has been experimentally confirmed that the cross-sectional shape of a positive resist having a line width of 130 nm changes when exposed using masks having various Cr coverages. Provided is a method for more strictly quantitatively measuring Cr coverage dependency.

As shown in FIG. 2, the method of quantification uses a test mask in which the influence of stray light is affected only by an area within a distance Rn from the coordinates 0 of a specific pattern. Experimentally determine how far away from a particular pattern there is the effect of stray light. Actually, the Cr coverage of the mask is set to C% (100 ≧ C
≧ 0), the line width L of the specific pattern when the value of C is variously changed is measured. From a value obtained by measuring the dependency of the exposure amount and the depth of focus of the line width L in a matrix form, a process margin in a region having a certain coverage C% and a certain radius Rn is determined by a method such as ED-Tree analysis. Can be measured.

Next, for example, the maximum depth of focus (DOF) at a certain exposure latitude, obtained from these process latitudes, is calculated as a function of the coverage C% and the distance R from a specific pattern as shown in FIG. And output as a contour graph. For correction to an LSI pattern to be designed based on this graph, D is adjusted so that a finite coverage C% is obtained at the distance Rn.
Distance R shorter than the maximum distance R in the OF values (a to g)
Select n.

At the time of design, the area within a distance Rn from a specific pattern satisfies the coverage C% in the figure. For example, when the coverage is insufficient, a total area in the area is calculated and then determined. In this case, the dummy pattern is arranged in an area corresponding to a predetermined area, or when the coverage is excessive, the pattern is deleted in a predetermined area.

As described above, according to the present invention, it is possible to accurately grasp the dependency of the resolution of the resist, the exposure latitude, and the degree of deterioration of the depth of focus due to stray light. It is possible to contribute to the realization of a lithography process with reduced effects.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments.

FIG. 4 is a view showing a test pattern formed on a measurement mask, FIG. 5 is a view showing how the test pattern is exposed on a sample, and FIG. 6 is a flow chart for explaining a pattern correction operation in this embodiment. It is.

First, as shown in FIG. 4A, a test pattern having a L / S of 130 nm on the wafer is formed in a region 1 having a circular shape with a radius of 5 μm on the wafer. 2 were arranged, and a plurality of patterns having a coverage of C% in a pattern area 3 having a radius R from the center of the area 1 were prepared. Specifically, as shown in FIG. 4 (b), radii of 1 mm, 2 mm, 3 m
In the region 3 changed to m, 4 mm, and 5 mm, the coverage C% is 10%, 20%, 30%, 40%, and 50%, respectively.
The L / S pattern of 250 nm is arranged in the region 3 on the wafer and changed so as to be%, 60%, 70%, 80%, 90%, and 100%.

The outside of the region 3 having the radius R is completely covered with the light shielding film. That is, the radius R (1,
A plurality of (2, 3, 4, 5 mm) openings (pattern regions 3) are provided, and a test pattern 2 is formed in each of these openings at each of the above-described coverages.

A measurement mask having such various patterns arranged thereon was prepared, and the pattern of the measurement mask 10 was transferred onto a sample 30 by a projection lens 20 using an exposure apparatus as shown in FIG.

Specifically, a film thickness of 60
After forming a lower antireflection film 32 (AR3: manufactured by Shipley Co., Ltd.), a chemically amplified resist 33 (K
RF-M60G: JSR) was converted to PAB (Post Apply Bak).
In e), the coating is performed at 140 ° C. for 90 seconds. This sample 3
0, NA = 0.68, σ = 0.75, 2/3 annular illumination condition, KrF excimer laser exposure apparatus (NSR-S
203B: Nikon Corporation), and the above mask pattern is transferred to the resist 33 (S1).

In this transfer step, ED-
In order to perform Tree analysis, the mask pattern was transferred to a plurality of locations on the sample under different exposure conditions while changing the exposure amount and the depth of focus little by little.

After exposure, PEB (Post Exposure Bake) is performed at 140 ° C. for 90 seconds, and development is performed for 90 seconds with a 2.38% organic alkali developing solution (TMAH) (S2). The exposure amount at this time is set so that the L / S pattern of 130 nm is finished to a desired size. And the obtained L /
The dimensions of the S pattern are measured (S3). That is,
The line width of the L / S pattern different from R and C is measured for each exposure condition.

Next, the line width of the L / S pattern is 130 nm.
From a value obtained by measuring the dependence of the exposure amount and the depth of focus in a matrix on the basis of ED-Tree analysis, a certain coverage C% was obtained.
Then, the process margin in a region of a certain radius Rn is measured (S4).

Next, from the measured value of the process margin,
The maximum depth of focus (DOF) at the 10% exposure latitude is output as a contour graph as a function of the coverage C% and the distance R from the specific pattern as shown in FIG. 3 (S5).
In the figure, a, b, c, d, e, f, and g are a <b <c <d <
There is a relationship of e <f <g, and the larger the DOF, the wider the permissible coverage C% range. By the way, Rn
At a distance of DOF = d, the coverage C% is 35 to 6
5%, and when DOF = e, the coverage C% is 25 to 75%.
It has become.

At the time of design, the distance Rn from a specific pattern
For example, if the coverage is insufficient, for example, if the coverage is insufficient, a total area in the area is calculated, and then a dummy pattern is arranged for a predetermined area, so that the coverage in the area satisfies the coverage C% in the figure. If it is excessive, the pattern is deleted by a predetermined area (S6).

When the LSI pattern was transferred onto the sample using the photomask in which the pattern was rearranged in this way, the cross-sectional shape of the resist pattern was good at all positions without the tip end becoming thin or thick. It became something. That is, a lithography process in which the influence of stray light was reduced could be realized, and the pattern of the photomask could be accurately transferred onto the sample.

The present invention is not limited to the above embodiment. In the embodiment, the pattern was actually transferred to the resist using a measurement mask in order to obtain a graph as shown in FIG. 3, but it is not always necessary to perform such an experiment. Good. Further, the material of the mask is not limited to quartz or chromium, and can be appropriately changed according to specifications.

In addition, various modifications can be made without departing from the scope of the present invention.

[0030]

As described above in detail, according to the present invention, the dependence of the coverage of the light shielding portion on the photomask, the resolution of the resist, the degree of exposure latitude and the degree of deterioration of the depth of focus can be accurately grasped. A lithography process that reduces the effects of stray light by conducting an experiment in advance using a measurement mask that can be used and creating a rule for the mask coverage under a specific illumination condition and using this as a guideline when designing an LSI pattern Can be realized.

[Brief description of the drawings]

FIG. 1 is a view for explaining the principle of the present invention, showing a change in a resist pattern cross-sectional shape with respect to a Cr coverage.

FIG. 2 is a view for explaining the principle of the present invention and showing a relationship between a test pattern and an opening region having a radius R.

FIG. 3 is a diagram for explaining the principle of the present invention and showing a DOF value at a certain exposure latitude as a contour line graph as a function of a coverage ratio C% and a distance R from a specific pattern.

FIG. 4 is for explaining one embodiment of the present invention,
The figure which shows the test pattern formed in the mask for a measurement.

FIG. 5 is for explaining one embodiment of the present invention,
The figure which shows a mode that a test pattern is exposed on a sample.

FIG. 6 is for explaining one embodiment of the present invention,
9 is a flowchart for explaining a pattern correction operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... L / S pattern formation area 2 ... L / S pattern 3 ... area | region (pattern area) of radius R 10 ... Measurement mask 11 ... Quartz substrate 12 ... Chrome pattern 20 ... Projection optical system 30 ... Sample 31 ... Si wafer 32 ... Anti-reflective coating 33 ... Resist

Claims (4)

[Claims] An opening is present only in a region separated by a distance R from a center coordinate of a test pattern, and a coverage of a light shielding portion in the opening is C% (100 ≧ C ≧ 0).
Measuring the process allowance in the region of radius R, and covering the maximum depth of focus at a predetermined exposure allowance or the maximum exposure allowance at a predetermined focus depth obtained from the measured process allowance. A step of outputting a contour graph as a function of the rate C% and the distance R, and a case where it is considered that a predetermined maximum depth of focus A or a certain maximum exposure latitude B is required. A step of obtaining an arbitrary distance Rn and a coverage ratio range Cn%;
and rearranging the pattern so that the area within n satisfies the coverage Cn%. 2. A method according to claim 1, wherein an area outside the pattern area within a distance R from the center coordinates of the test pattern is a light-shielding area, and a coverage of the light-shielding portion in the pattern area is C% (100 ≧ C ≧ 0)
Using measurement masks with different values of R and C,
Exposing the pattern of this measurement mask to a resist on a sample, and performing a plurality of exposures under exposure conditions with different exposure amounts and depths of focus; and from the resist pattern formed on the sample by the exposure Measuring the line width L of each pattern having different values of the exposure condition, R, and C; and determining the dependence of the exposure amount and the depth of focus on the line width L based on the measured line width L. Measuring the process latitude in the area of the coverage C% and the radius R from the values measured in the form of a matrix; and determining the maximum depth of focus at a predetermined exposure latitude obtained from the measured process latitude. A step of outputting a maximum exposure latitude at a predetermined depth of focus as a function of the coverage C% and the distance R as a contour graph, and a predetermined maximum depth of focus A or a maximum exposure latitude B is required. If you think A step of obtaining an arbitrary distance Rn and a coverage Cn% range in a contour graph satisfying the above conditions; and forming a pattern such that an area within the distance Rn satisfies the coverage Cn% at the time of photomask pattern design. And a step of rearranging the photomask. 3. A step of rearranging the patterns, when the coverage is insufficient, calculating a total area of the regions within the distance Rn, and then arranging a dummy pattern by a predetermined area, and the coverage is excessive. 3. The method according to claim 1, wherein the pattern is deleted by a predetermined area. 4. The method of manufacturing a photomask according to claim 1, wherein a process margin in the area of the coverage C% and the radius R is obtained by simulation.