JPH022608A - Photomask designing device for fine pattern - Google Patents

Abstract

PURPOSE:To make it possible to design a photomask pattern for forming a resist pattern as designed, even when the foundation has stepped parts, by, for example, providing a reading-out means, a foundation extracting means, a resist-film-thickness calculating means, and a pattern correcting means, all specified, in a pattern design processing section. CONSTITUTION:A memory 20 stores information concerning a photomask and the pattern of foundation; correction information concerning the thickness of the foundation and applied resist; and another correction information concerning the kind of used resist, the optical characteristics of the foundation and a patterned layer, conditions of exposure and development, data on resist-film-thickness versus transformation difference, etc. In addition, a pattern design processing section 22 is provided with a data reading-out means 50, a foundation extracting means 52 extracting the pattern of the foundation from data read out, a resist-film-thickness calculating means 54 calculating the resist-film-thickness from one correction information and the pattern of the foundation read out, and a pattern correcting means 56 performing correction for an original mask pattern to suppress the influence of the stepped parts of the foundation on the resist pattern using the other correction information and the above- mentioned resist-film-thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a photomask design apparatus for fine patterns in semiconductor integrated circuits.

(Prior art) The density of semiconductor integrated circuits is increasing, and for example, M
In the case of OS dynamic random access memory,
The number of bits per chip has quadrupled in about three years.

This increase in fertilizer density is largely due to advances in microfabrication technology. Microfabrication technology for semiconductor integrated circuits uses an exposure device that uses ultraviolet light to expose and transfer a photomask pattern onto a resist film coated on a wafer. Generally, a method is used in which the resist film is then developed to form a resist pattern.

As the resist used to create this resist pattern,
Usually, a positive type resist with good resolution is used, and this is applied onto the wafer using a spin code method so that the surface becomes a very flat resist film.

Incidentally, a photomask used for forming a resist pattern is usually designed using a photomask design apparatus for fine patterns as shown in FIG. In Figure 2, 1
0 is an external human-powered device such as a keyboard; 12 is a pattern design unit that designs a desired mask pattern based on instructions from the operator of the keyboard 10 and outputs the design result;
14 is an electron beam exposure device for forming a photomask pattern by controlling an electron beam according to a design result; 18;
Although it is not absolutely necessary, it is a monitor device that monitors the pattern during the formation of this photomask. The pattern design unit 12 takes in necessary data from the memory 20 in which design pattern data is stored in advance and the memory in response to commands from the keyboard 10, and creates data for forming a photomask pattern corresponding to the design. A pattern design processing unit 22 and a data output unit 24 that temporarily stores the data or directly outputs the data as required.
It is equipped with. Normally, this memory 20 stores, as original mask pattern data, photomask pattern dimensions that approximately match the finished resist pattern dimensions when the base of the resist film is flat. Therefore, the pattern design processing unit 22 can read out original mask pattern data from the memory 20, such as a photomask pattern specified by the designer's request or a similar photomask pattern obtained by simply reducing or enlarging it. A photomask is formed by drawing and exposing a photomask pattern by controlling the scanning of an electron beam emitted from an electron beam exposure device 14 based on the original mask pattern data. Reference numeral 26 denotes a control section for controlling the operations and timing of the keyboard 10, the electron beam exposure device 14, the monitor device M18, as well as the components of the pattern design section 12.

Therefore, when a resist pattern is formed using this conventional photomask, if the base of the resist film is flat, the photomask pattern is almost deliberately transferred as a resist pattern, and there is virtually no problem.

(Problem to be Solved by the Invention) However, when there is a step due to unevenness on the base of the resist film, the thickness of the resist film is substantially different between the top and bottom of the step. Therefore, when attempting to form a submicron fine pattern, the influence of interference due to multiple reflections of the light used for exposure begins to appear, and the patterning width differs above and below the step, resulting in a difference between the designed shape of the resist pattern and There was a problem that the actual finished shape was different.

This point will be explained using FIGS. 3 and 4.

FIG. 3 is a curve diagram showing the relationship between the resist film thickness (indicated in um on the horizontal axis) and the resist dimension (indicated in um on the vertical axis), where the mask dimension is 1.0 um and the exposure wavelength is 435 nm.
．． As can be understood from this figure, which is experimental data (indicated by a solid line) for a film thickness of 8 nm, the dimensions change periodically as the film thickness increases. This periodic change is caused by multiple reflections of light within the resist layer.
Therefore, when a resist film having a step is patterned using a photomask having the same size, the width of the patterning will naturally differ between the upper and lower portions of the step.

For example, as shown in the cross-sectional view of FIG.
Assume that a pattern of a base 32 is formed protrudingly on a wafer 30, and a layer to be patterned (
Also called upper layer pattern. ) 34 may have a step.

A resist material is applied by spin coating onto the wafer 30 on which the upper layer pattern 34 has been formed to form a resist layer 36 with a flat surface.
6) Patterning is performed using a conventional photomask having a pattern with dimensions almost the same as the designed finished resist dimensions. Note that the thickness of the resist layer on the lower part of the step is tl, and the thickness of the upper part is t2.

As a result of this patterning, as shown in the plan view of FIG. 4(B), the patterned resist pattern (indicated by a solid line) 40 has a width at the top of the step, with respect to the pattern of the photomask 38 shown by the - dotted line. is I22 and the width at the bottom of the step is! , then β, >12 0 For example, suppose that the resist film thickness and resist dimensions have a relationship as shown by the curve in Figure 3, and tl is 1.3 um and t2 is 1.2 μm.
Then, the size of the resist pattern formed at the top of the step is 1
2 is about 0.2 LIm shorter than the dimension β of the bottom of the step. Further, such a dimension deviation is also influenced by the type of resist, exposure conditions, and other conditions.

In this way, with conventional photomasks that are almost the same or similar to the finished resist pattern dimensions, the resist pattern dimensions are greatly affected by the underlying step, the resist material, and other conditions. It was difficult to form a fine resist pattern according to the photomask and therefore according to the design.

An object of the present invention is to predict in advance the variation in dimensions of the resist pattern caused by the step when there is a step on the base, and to correct it to the ring mask pattern data that gives the finished resist pattern dimension. An object of the present invention is to provide a photomask design device for fine patterns, which is configured to be able to design a photomask pattern for forming a resist pattern.

(Means for Solving the Problems) In order to achieve this objective, according to the present invention, first,
The memory stores, as design pattern data, information on the photomask and base patterns, correction information on the film thickness of the base and coated resist, the type of resist used, optical properties of the base and layer to be patterned, exposure and The other correction information regarding development conditions, resist film thickness vs. conversion difference data, etc. is stored.

Roughly speaking, the pattern design processing section includes a reading means for reading the aforementioned design pattern data, a base extraction means for extracting a base pattern from the read design pattern data, and a base pattern among the read design pattern data. A resist film thickness calculating means that calculates the resist film thickness from one correction information and the underlying pattern, and a ring mask using the correction information and the calculated resist film thickness of the other of the read design pattern data. A pattern correction means is provided for correcting the pattern to minimize the influence of the step difference in the base on the resist pattern to be formed.

In carrying out the present invention, this pattern correction means is applied to the resist used! ! The relationship between the resist film thickness, which depends on the type, optical properties of the base and patterned layer, exposure conditions, and development conditions, and the conversion difference, which is the difference between the mask pattern dimension and the finished resist pattern dimension, is determined, and the above-mentioned resist film It is preferable to determine the correction amount of the photomask pattern from the thickness and conversion difference.

(Function) According to the configuration of the present invention, the memory stores the original mask pattern data of the photomask that gives the finished pattern dimensions when there is no step due to unevenness on the underside of the resist film. If there is a step on the lower side, the pattern design processing section creates a mask pattern by taking into account the step shape of the base obtained from the design pattern data read from the memory, the relationship between the resist film thickness and the resist dimension, etc. The correction means corrects the original mask pattern data, and controls the electron beam writing of the exposure apparatus in response to the mask pattern data obtained from this correction. Therefore, it is possible to design a photomask having a shape and dimensions that can provide a finished resist pattern with the designed dimensions without being affected by the level difference in the base when the resist film is patterned.

(Embodiments) Hereinafter, embodiments of the image line patterning photomask design apparatus of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a photomask design apparatus for fine patterns according to the present invention. Components that are the same as those shown in FIG. A detailed description thereof will be omitted except for the differences in configuration from the device.

According to the present invention, the pattern design processing section 22 is configured by the reading means 5 for reading design pattern data from the memory 20.
0. Base extraction means 52 for extracting the state of the base from the design pattern data, means 54 for calculating the resist film thickness from the extracted base state and the design pattern data, and original mask from the resist film thickness and design Bakun data. It mainly consists of mask pattern correction means for correcting pattern data.

The memory 20 stores in advance various information necessary for designing a photomask as design pattern data. Generally, data designed by a CAD device can be used as this information, or, roughly speaking, required data according to the design obtained by other means can also be used. This information includes, for example, information about the photomask and the underlying pattern. As already explained, the photomask information includes various original mask pattern data such as the shape and dimensions of the mask to obtain various finished resist patterns according to the design when there is no unevenness in the lower layer of the resist film. be. The underlying pattern information includes the process and/or finished pattern of each layer under the resist film,
For example, it is data such as shape and dimensions.

Roughly speaking, the design pattern data includes process correction information regarding the film thickness of each layer below the resist film including the base layer and the film thickness of the coated resist. These are given in relation to the epitome on the wafer.

Furthermore, as design pattern data, resist film thickness vs. conversion difference data, the type of resist used to determine this conversion difference data, optical characteristics of each layer under the resist film such as the base and the layer to be buttered, There is other correction information necessary for the process, such as exposure and development conditions. here,
The conversion difference is the difference between the mask dimension and the finished resist dimension, and this difference is stored in the memory 20 along with the above-mentioned information on which it depends.
Store it in advance as a table.

Next, the operation of the apparatus of the present invention will be explained with reference to Fig. 1 and Figs. 5 to 9.

FIG. 5 is a design conceptual diagram for explaining the concept of a method of designing a photomask pattern using the apparatus of the present invention, and FIG. 6 is an explanatory diagram for explaining the design of a photomask pattern.
The figures (B) and (C) are illustrated in schematic cross-sectional views, and the figures (B) and (C) are illustrated in schematic plan views.

Now, in order to simplify the explanation, design conditions as shown in FIG. 6(A) will be set as an example. First, the case of designing a photomask that can pattern a resist film to a uniform width regardless of whether there is a step below the resist film will be described.

In FIG. 6, 60 is a substrate, 62 is a base layer that has been patterned to form a step, 64 is a layer to be patterned, and 66 is a resist film 66. This resist film 66 is patterned using a photomask. The design of the photomask used when forming the pattern of the film to be patterned 64 will be explained.

In this case, assume that various design conditions are determined as follows, as an example. The material of the base 62 is &Si○2, and its film thickness t
Let o be 5000 people. The material of the layer 64 to be patterned is polysilicon, and its thickness is 300 OA. The resist used is, for example, product number TS manufactured by Tokyo Ohka Kogyo Co., Ltd.
A positive type resist of MR8800 is used. Quasi-fabric thickness t of resist film.

is 1400OA. The exposure wavelength is 435.8 nm, and a wafer stepper device is used. For example, a developer with product number N5D-TO manufactured by Tokyo Ohka Kogyo Co., Ltd. is used as the developer.

When designing, first, the operator operates the external input unit 1 (for example, the keyboard) to read out design pattern data necessary for the design from the memory 20 by inputting a σ command to the pattern design process of the pattern design unit 12. Part 21! :give.

In response to this command, the reading means 50 of the Bakun design process F1t2 reads out design pattern data necessary for design from the memory 20. This design pattern information is shown in Figure 5.
Indicated by 0.

In order to use each piece of information in the read design pattern data 70 for subsequent processing, the required processing stages are shown in FIG.
4 is information on base film thickness, 76 is information on coated resist film thickness,
78 is information on the resist fi types used, 80 is information on the optical characteristics of the resist underlayer film, 82 is information on exposure and development conditions, 8
Reference numeral 4 indicates information on resist film thickness versus conversion difference data, and reference numeral 86 indicates original mask pattern data, which is photomask pattern information. FIG. 6(B) shows an example of an original photomask pattern 90 of 8 days of photomask corresponding to this original mask pattern data. Further, a base extraction process 90, a resist film thickness calculation process 92, and a pattern correction process 94, which are performed in the pattern design processing section 22, are shown respectively.

Next, using the pattern information, the base extracting means 52 extracts a pattern of the base (indicated by 62 in FIG. 6) to obtain information on the underlying layer of the resist film 66 of interest (FIG. 5, 9
0), FIG. 7 is a diagram showing the flow of this extraction operation, and FIG. 8 is an explanatory diagram thereof. This base extraction is
For example, when looking at the patterns of each layer from above, they may overlap with each other, so it is difficult to determine how far the areas of the same layer level are, or how far the areas of the upper and lower layers overlap. This is the process of extracting information. Therefore, in this embodiment, for example, pattern information is imported from the read design pattern data for the lower layer 62 and the layer to be patterned 64 (step S1).
, logical sum processing (OR processing) of both patterns (step S2
) and logical product processing (AND processing) (Step S3)!
This process is performed sequentially. For example, as illustrated in FIG. 8(A), the OR of two layer patterns 102 and 104 is
During processing, overlapping patterns at the same layer level are eliminated to obtain patterns 106 having the same layer thickness. Then, as illustrated in FIG. 8(B), two layer patterns 108 and 11 are formed.
By performing an AND process of 0, a pattern 112 of the overlapping portion is obtained. Of course, either the OR processing or the AND processing may be performed first.By this processing, regions (positions) of layers with the same thickness and regions (positions) with a step difference can be determined.

Next, the resist film calculation means 52 calculates the film thickness at each location of the resist film of interest using the data obtained by base extraction, base film thickness information 74, and applied resist film thickness information 76. (as shown in FIG. 5, 92), this calculation is performed when the film thickness of the underlayer 62 is t. If the thickness of the resist film 66 applied from the bottom of the step is t, then the thickness t2 of the resist film 66 at the top of the step is given by tz=(t+to), so it is sufficient to calculate this. , such calculation means can be implemented using conventional techniques. For example, if t,=1400OA and to=500OA, then t2=9000A.

Next, in the mask pattern correction means 56, the above-described calculated film thickness of the resist film 66, information 78 on the type of resist used, and optical property information 80 such as the reflectance of the film below the resist film 66, According to this pattern correction processing 94, which calculates the amount of correction to be applied to the original mask pattern data 86 from the exposure and development condition information 82 (indicated by 94 in FIG. 5), the The original photomask pattern corresponding to the mask pattern data 86 is shown in FIG.
If the pattern is as shown in 98 in 8), and there is a step, as explained above, the original mask pattern data 86 is corrected, and the upper side of the part where the resist film thickness is thinner due to the step is corrected. Positioned log mask pattern 9
Mask pattern data 99(
Figure 5) is given.

Next, an example of this pattern correction processing will be explained. FIG. 9 is a flow chart of the operation of the mask pattern correction means.

As already explained in FIG. 6(A), the flat area is denoted by ■, and the area above the base 62 forming the step is denoted by ■.
The thickness of the resist film 66 in region (2) is 1+, and the thickness of the resist film 66 in region H is t2. Further, in the diagrams corresponding to regions (2) and (II), mask width dimensions j&M and M2, conversion differences 8C1 and C2, mask width dimension correction amounts 8DI and C2, and resist finishing dimensions 1 and R2 are shown. 6th
The example photomask pattern 980 shown in the figure has a mask width dimension M, = M2 = M, and therefore R, = R2 = R.

First, the correction information 78, 80, 82 such as the design pattern data, type of resist, optical characteristics of the underlying film, and exposure and development conditions are read out (step 510), and the resist film depending on these information is read out. The thickness versus conversion difference data 84 is taken in (step Sl+).

Next, the resist film thickness t and t2 calculated by the resist film calculation means 54 are read (step 512). In response to the resist film thicknesses t1 and t2, the optimum conversion difference data C+ and 02% resist film thickness conversion difference data 84 are selected for the regions ① and II (step 513). next,
Ring mask pattern data 8 from design pattern data 70
6 is taken in (Step 5I4), and then the correction measurement of the mask width dimension and C2 are calculated (Step 5I5).
This correction amount can be calculated by calculating and knowing the thickness of the resist film 66 at each location in the layer of interest. The dimension of the register pattern R, = R2
(This value is given in advance at the time of design.) Therefore, the photomask pattern (98 in Fig. 6 (8)) is corrected j1 (this is the mask sizing D and C2 are calculated according to the following formula.

M, -C, +[), =R.

M2 02 + C2= R2 As already explained, in this embodiment, the width 1 M (= M + = M2) of the original mask pattern 98 and the resist pattern finished dimension when patterning is performed with this original mask pattern 98! Since it is designed as R (=R+=day), in the case of the photomask pattern 98 in FIG. 6(B), there is a relationship of C2D1=02 CI between the corrections ID1 and C2 and the conversion difference. In the case of this embodiment, one of the correction amounts D
1 is the mask pattern part corresponding to area ■, so D
I=0. Therefore, the correction amount △M for the width M of the original photomask pattern 98 in the portion corresponding to the area ■, which is necessary due to the step caused by the base layer 62, is 6M=C2=02 CI, so as shown in FIG. As shown in (C), the original mask pattern data is adjusted so that the width of the original photomask pattern in the region H corresponding to the upper side of the step is larger than the width M in the region ■ by ΔM. 86. This correction step can be performed using SI6 in Figure 9.
Indicated by

In this way, the mask pattern data 99 after correction is applied to the portion corresponding to the area H is sent to the electron beam exposure bag M14 via the data output unit 24 in FIG. Figure 6 (C)
A corrected photomask pattern 100 as shown in FIG.

FIGS. 10(A) and (8) show that FIG. ), if there is a step due to the base 62,
FIG. 3 is an explanatory diagram for explaining an example of forming a resist pattern, and each diagram is schematically shown as a planar view of the resist film side from the photomask side.

FIG. 10(A) shows the arrangement of the photomask 100 and the protrusion of the base 62.
FIG. 10(B) shows a state in which the photomask 100 is patterned by exposure and development using a photomask 100. In FIG. 10(8), the photomask 100 is indicated by a dotted line. As shown in this figure, when patterning is performed using the photomask 100 that has been corrected to take into account the level difference in the base material, even the upper part of the step part of the base material 62 and the flat part without any difference in level can be patterned. , a resist pattern 67 having the same width as designed can be obtained.

By etching the underlying patterned layer 64 using this resist pattern 67 as a mask, a designed pattern can be obtained.

As described above, the photomask pattern designed according to the present invention takes into account the influence of the base level difference on the resist pattern dimensions v11v in advance, and reduces the influence of this base on the ring photomask pattern used for patterning in the case of a flat base without a level difference. It was obtained by making modifications so that it does not extend at all or substantially. Therefore, the device of this invention:
It is suitable for designing a photomask for forming a fine resist pattern of submicron size below lum.

In general, when designing a photomask using the apparatus of the present invention, if necessary design pattern data is stored in a memory in advance, changes in the process of use can be handled freely, and the scope of application is widened.

Furthermore, as in the past, by subjecting the designed photomask pattern data to an existing design rule check program, it is possible to check whether the correction by the base deviates from the design rules.

In addition, as in the past, when designing a mask pattern before making a prototype, it is also possible to check whether the process used and the design pattern are compatible.
The number of steps required to develop photomask patterns can be reduced.

It is clear that this invention is not limited only to the embodiments described above. For example, the layer structure below the resist film may have any layer structure with steps other than those shown in the embodiments. Furthermore, in addition to finishing a resist pattern with a uniform width as described above, it is also possible to design a photomask for forming a resist pattern whose pattern width varies depending on the location according to the design. In that case, all you need to do is use the above-mentioned correction scale and determine this correction!
Using l, △M=D2 =02 -CI +D+, the correction amount D of the part of the original mask pattern data corresponding to the base protrusion
2i can be calculated.

Further, the numerical examples given in the above-described embodiments are not limited to these values in any way, and any suitable value can be set according to the design.

Furthermore, the reading means 50 of the pattern design processing unit 22 does not need to read out each piece of information from the memory 20 in the order explained in the explanation of the operation, but can read out the information from the memory 20 whenever necessary for processing. In addition, in the flowchart of the operation, each processing step may be replaced simultaneously or in a predetermined order in any suitable manner so as to obtain the desired processing result. I can't help you.

Further, the present invention can also be applied to photomasks that form patterns by step and repeat using a reticle.

(Effects of the Invention) As is clear from the above description, according to the photomask design apparatus for fine patterns of the present invention, mask sizing is performed by estimating in advance the dimensional variation of the resist pattern due to the step difference in the base, and thereby the electron beam exposure By controlling the apparatus, it is possible to design a photomask pattern that can form a resist pattern as designed, which does not overlap or is substantially affected by the shadow W of the base level difference, and therefore has substantially no base level difference. Therefore, if a resist pattern is formed using a photomask pattern that is optimal for the process used, a fine pattern in the submicron range can be formed with high precision.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining an embodiment of a photomask design system for fine patterns according to the present invention, FIG. 2 is a block diagram for explaining a conventional photomask design system W for fine patterns, and FIG. 4 is a characteristic curve diagram for explaining the relationship between resist film thickness and resist dimensions, which is used to explain this invention. FIG. FIG. 5 is a design concept diagram for explaining the concept of the method of designing a photomask pattern using the apparatus of the present invention. FIG. 6 is an explanatory diagram for explaining the design of a photomask pattern. FIG. 8 is a flowchart of the operation of the extraction means, FIG. 8 is an explanatory diagram of the background extraction process, FIG. 9 is a flowchart of the operation of the mask pattern correction means, and FIG. FIG. 2 is an explanatory diagram of a case where a resist film is patterned using a photomask. 10--External input unit, 12--Pattern design unit 14--Electron beam exposure device 16, 96--Photomask, 20--Memory, 24--Data output unit, 50--Reading means , 54--Resist film calculation means 56--Mask pattern correction means 60--Substrate, 62-- Base 64--
- Layer to be patterned, 66--Resist film 67...
Resist pattern 98... Ring photomask pattern 100... Photomask patterns 102 to 112... Pattern. 18.-Monitoring device 22...Pattern design processing section 26-.Control section 52-.Underground extraction means

Claims (2)

[Claims] (1) Based on the command from the external input unit, the pattern design processing unit reads the pre-stored design pattern data from the memory, performs mask pattern design processing, and sends the design processing result to the exposure device to create the mask pattern. In a photomask design device for fine patterns that controls writing, the memory stores, as design pattern data, information regarding the pattern of the photomask and the base, correction information regarding the film thickness of the base and coated resist, the type of resist used, the base, and the like. The other correction information regarding the optical characteristics of the layer to be patterned, exposure and development conditions, resist film thickness vs. conversion difference data, etc. is stored, and the pattern design processing section includes a reading means for the design pattern data, and a readout design pattern. A base extraction means for extracting a base pattern from the data; a resist film thickness calculation means for calculating a resist film thickness from the base pattern and correction information of one of the read design pattern data; and the read design pattern data. a pattern correction means that uses the correction information of the other of the two and the resist film thickness to correct the original mask pattern in order to eliminate or minimize the influence of the step of the base on the resist pattern to be formed; A photomask design device for fine patterns, characterized by comprising: (2) In the photomask design apparatus for fine patterns according to claim 1, the pattern correction means includes information on the type of resist used, the optical characteristics of the base and the layer to be patterned, the exposure conditions,
and a relationship between a resist film thickness that depends on development conditions and a conversion difference that is a difference between a mask pattern dimension and a finished resist pattern dimension, and a correction amount for the photomask pattern is determined from the resist film thickness and the conversion difference. Photomask design equipment for fine patterns.