Pattern correction method and pattern correction apparatus

Abstract

To minimize the impact on the optical image. [Solution] The pattern correction method of the embodiment includes steps 1 to 6. In the first step, information on defects in the pattern of a photomask having a pattern formed with a light-shielding film, and the optical properties of the light-shielding film and the correction film for correcting defects are obtained. In the second step, the thickness of the correction film is determined based on the optical properties of the light-shielding film and the correction film. In the third step, one or more design pieces of information are obtained that indicate the dimensions and shape of candidate patterns for the correction film, including thickness information indicating the thickness of the correction film. In the fourth step, the exposure margin is calculated for each of the one or more design pieces of information by electromagnetic field calculation using the thickness information of the correction film. In the fifth step, design pieces of information in which the exposure margin exceeds a threshold are selected from among the one or more design pieces of information. In the sixth step, the correction film is formed on the photomask according to the selected design pieces of information.

Description

Technical Field

[0001] Embodiments of the present invention relate to a pattern correction method and a pattern correction apparatus.

Background Art

[0002] In the lithography process of a semiconductor device, light irradiated from an exposure apparatus diffracts through the pattern of a photomask, and an optical image is formed by the interference of the diffracted light on the semiconductor substrate.

[0003] The pattern of the photomask is composed of a light-shielding film. When a defect is found in the pattern during the manufacturing process of the photomask, the defect is corrected by a correction film.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the optical characteristics of the correction film and the optical characteristics of the light-shielding film may not be the same. Therefore, the correction film formed on the photomask may cause the optical image formed on the semiconductor substrate to differ.

[0006] One embodiment aims to provide a pattern correction method and a pattern correction apparatus capable of suppressing the influence on the optical image.

Means for Solving the Problems

[0007] The pattern correction method of the embodiment includes steps 1 to 6. In the first step, information on defects in the pattern of a photomask having a pattern formed with a light-shielding film, and the optical properties of the light-shielding film and the correction film that corrects the defects are obtained. In the second step, the film thickness of the correction film is determined based on the optical properties of the light-shielding film and the correction film. In the third step, one or more design pieces of information are obtained that indicate the dimensions and shape of candidate patterns for the correction film, including film thickness information indicating the film thickness of the correction film. In the fourth step, the exposure margin for each of the one or more design pieces of information is calculated by electromagnetic field calculation using the film thickness information of the correction film. In the fifth step, design pieces of information whose exposure margin exceeds a threshold are selected from among the one or more design pieces of information. In the sixth step, the correction film is formed on the photomask according to the selected design pieces of information. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram illustrating a pattern defect according to an embodiment. [Figure 2] A diagram showing an overview of the various processes performed in the pattern correction system according to the embodiment. [Figure 3] A diagram showing an example of the configuration of a pattern correction system according to an embodiment. [Figure 4] A diagram showing an example of the hardware configuration of the modification pattern generation unit according to the embodiment. [Figure 5] A flowchart showing an example of the pattern modification process flow according to the embodiment. [Figure 6] A figure showing an example of design information for candidate patterns of the modified film according to the embodiment. [Figure 7] A diagram illustrating the processing flow of the computational lithography program according to the embodiment. [Figure 8] A figure showing an example of the calculation result of the exposure margin according to the embodiment. [Figure 9] A figure showing another example of the calculation result of the exposure margin according to the embodiment. [Figure 10]A figure showing another example of design information for candidate modification patterns according to the embodiment. [Modes for carrying out the invention]

[0009] Embodiments will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments described below. Furthermore, the components in the embodiments described below include those that are easily conceivable by those skilled in the art or that are substantially identical.

[0010] In the photomask manufacturing process, a desired pattern is drawn on a resist film on a glass substrate such as quartz glass, on which a light-shielding film has been formed, using an electron beam. Through development of the resist film and etching of the light-shielding film, a transfer pattern composed of light-shielding films is formed on the glass substrate.

[0011] When a pattern defect is detected by the defect inspection device, the detected pattern defect is corrected with a correction film. After that, a photomask that is guaranteed to be free of pattern defects is completed through cleaning and quality checks.

[0012] However, the optical properties of the correction film may differ from those of the light-shielding film. Therefore, if the amount of correction film formed is adjusted so that its optical properties are approximately the same as those of the light-shielding film, the thickness of the correction film may differ from that of the light-shielding film. Such differences in film thickness in the transfer pattern can cause differences in the amplitude and phase of diffracted light, resulting in a so-called three-dimensional mask effect that alters the optical image formed on the semiconductor substrate.

[0013] The 3D mask effect refers to the deviation between the optical image of a transfer pattern with a three-dimensional structure and the ideal optical image. The 3D mask effect becomes apparent when forming fine patterns on a semiconductor substrate, where the dimensions of the pattern are less than or equal to the wavelength of the exposure equipment.

[0014] In the manufacturing process of a photomask, an ILT (Inverse Lithography Technology) technique is used to perform pattern design of the photomask by solving an inverse problem with the optical image formed on a semiconductor substrate as an ideal optical image. Therefore, if the optical image formed on the semiconductor substrate is different from the ideal optical image, the accuracy of pattern design may be reduced.

[0015] To solve the above problems, the pattern correction system of the embodiment performs various processes shown in FIG. 2. First, prior to the description of FIG. 2, the pattern defect to be corrected in this embodiment will be described using FIG. 1.

[0016] In this specification, a predetermined direction along the surface of the glass substrate is defined as the X direction and the Y direction. The X direction and the Y direction are orthogonal. Also, a direction intersecting the X and Y directions is defined as the Z direction. Also, the direction of the arrow in each direction is defined as the positive direction, and the opposite direction is defined as the negative direction.

[0017] FIG. 1 is a schematic diagram for explaining a pattern defect 23 according to an embodiment. In FIG. 1(a), a transfer pattern 10 not including the pattern defect 23 is shown as a comparison target for FIG. 1(b), and in FIG. 1(b), a transfer pattern 10 including the pattern defect 23 is shown. The upper part of each of FIGS. 1(a) and 1(b) is a plan view of a photomask M including the transfer pattern 10, and the lower part is a cross-sectional view taken along the AA line and the BB line of FIGS. 1(a) and 1(b), respectively.

[0018] As shown in FIGS. 1(a) and 1(b), the transfer pattern 10 of the photomask M is formed on a glass substrate 11. The glass substrate 11 is made of, for example, quartz glass or the like and is formed into a rectangular shape with a 6-inch square. The transfer pattern 10 includes a light-shielding formation part 21 formed by a light-shielding film 12 and a light-transmitting part 22 (22a, 22b) where the glass substrate 11 is exposed.

[0019] The light-shielding film 12 is a film with a lower transmittance of exposure light than the glass substrate 11, and its transmittance is, for example, 6%. The light-shielding film 12 is, for example, a silicon nitride film or a molybdenum silicite film. The light-shielding film 12 is also called a phase-shift film and has the property of reversing the phase of transmitted light. In this embodiment, the thickness of the light-shielding film 12 in the light-shielding formation section 21 is defined as "T1".

[0020] As shown in Figure 1(a), each of the light-transmitting sections 22a and 22b, which are aligned along the X direction, is formed in the shape of a square with a side length of "d". Each of the light-transmitting sections 22a and 22b is surrounded by a light-shielding section 21. That is, the optical image formed by the transfer pattern 10 is a hole pattern or a dot pattern.

[0021] In contrast, in Figure 1(b), the light-transmitting portion 22b has a negative X-direction end and the adjacent light-shielding portion 21 are missing by a length "d1" toward the negative X-direction. As a result, the light-transmitting portion 22b has a rectangular shape with a longer side along the X-direction. That is, the dimensions of the light-transmitting portion 22b in Figure 1(b) are excessive (larger) by "d1" in the X-direction compared to the target dimension "d".

[0022] In this embodiment, the missing portion of the light-shielding forming portion 21 will be referred to as a pattern defect 23. That is, a pattern defect 23 is a portion of the light-shielding forming portion 21 adjacent to the end of the light-transmitting portion 22b on the negative X side that is missing by a length "d1" toward the negative X side. A pattern defect 23 is an example of a pattern defect to be corrected.

[0023] Furthermore, although the example in Figure 1(a) shows the translucent portion 22 (22a, 22b) as being formed in a square (rectangular) shape, the shape of the translucent portion 22 is not limited to this. For example, the translucent portion 22 may be formed in a groove shape extending in the X or Y direction.

[0024] Figure 2 is a diagram showing an overview of the various processes performed in the pattern correction system 1 according to the embodiment.

[0025] As shown in Figure 2, the pattern correction system 1 of this embodiment includes the following processes: detection of pattern defects 23 (step S1), selection of design information for the corrected film considering the 3D mask effect (step S2), correction of the pattern defects 23 based on the design information (step S3), and acquisition of the corrected optical image (step S4).

[0026] Step S1 involves imaging the transfer pattern 10 formed on the photomask M and detecting pattern defects 23 from the image of the captured transfer pattern 10. Step S1 is performed in the defect detection device 100 shown in Figure 3, which will be described later.

[0027] Step S2 involves performing electromagnetic field calculations that take the 3D mask effect into consideration, and selecting suitable design information from the design information of one or more candidate modified film patterns based on the calculation results. Considering the 3D mask effect in the electromagnetic field calculation means including film thickness information indicating the film thickness of the modified film pattern in the electromagnetic field calculation.

[0028] Step S3 is a process in which a modified film is formed on the transfer pattern 10 according to the design information of the selected modified film pattern. Steps S2 to S3 are performed in the pattern modification apparatus 200 shown in Figure 3. Hereafter, steps S2 to S3 may be collectively referred to as the pattern modification process.

[0029] Step S4 is a process of acquiring an optical image of the transfer pattern 10 on which the corrected film has been formed. Step S4 is mainly performed using the optical image acquisition device 300 shown in Figure 3.

[0030] Figure 3 shows an example of the configuration of the pattern correction system 1 according to the embodiment.

[0031] As shown in Figure 3, the pattern correction system 1 of the embodiment comprises a defect detection device 100, a pattern correction device 200, and an optical image acquisition device 300. The defect detection device 100, the pattern correction device 200, and the optical image acquisition device 300 are connected to each other so as to be able to communicate with one another.

[0032] The defect detection device 100 is, for example, a scanning electron microscope (SEM). The defect detection device 100 images the transfer pattern 10. The defect detection device 100 detects pattern defects 23 from the image of the transfer pattern 10. The detection of pattern defects 23 can be performed, for example, by comparing with design data or by comparing images of adjacent transfer patterns 10.

[0033] The pattern correction device 200 comprises a correction pattern generation unit 210 and a correction unit 220.

[0034] As will be described in detail later, the modified pattern generation unit 210 is configured as a computer equipped with a hardware processor such as a CPU (Central Processing Unit) and memory. The modified pattern generation unit 210 includes a data acquisition unit 211, a film thickness determination unit 212, a calculation unit 213, a selection unit 214, and a judgment unit 215.

[0035] The data acquisition unit 211 acquires an image of the pattern defect 23 detected by the defect detection device 100. The image of the pattern defect 23 is an example of information about the pattern defect 23. The data acquisition unit 211 also acquires an image of the reference pattern.

[0036] The reference pattern is a transfer pattern 10 in which no pattern defects 23 are formed. The data acquisition unit 211 may acquire an image of the reference pattern from an image captured by the defect detection device 100, or it may acquire an image of the reference pattern from the memory of the correction pattern generation unit 210 or the like.

[0037] The data acquisition unit 211 acquires the optical properties of the light-shielding film 12 constituting the light-shielding formation unit 21 and the optical properties of the modified film. Optical properties refer to at least one of the light transmittance and phase difference for a predetermined wavelength. The data acquisition unit 211 acquires the optical properties of the light-shielding film 12 and the modified film from the memory of the modified pattern generation unit 210 or the like.

[0038] As for the type of correction film, for example, a multilayer film in which a chromium film is laminated on top of a TEOS film can be used. However, the type of correction film is not limited to this. The type of correction film can be changed as needed.

[0039] The data acquisition unit 211 also acquires at least one design information for candidate patterns of the correction film to be formed on the transfer pattern 10 to correct the pattern defect 23, based on the image of the pattern defect 23 and the image of the reference pattern. The design information includes information indicating the dimensions and shape of the correction film pattern, and includes film thickness information indicating the film thickness of the correction film pattern.

[0040] The data acquisition unit 211 acquires design information for candidate patterns of the repaired film as follows. For example, the data acquisition unit 211 uses a trained model that takes an image of the pattern defect 23 as input and outputs design information for a suitable repaired film pattern to acquire information from the design information of candidate patterns of the repaired film, excluding the film thickness information. The data acquisition unit 211 then acquires the film thickness information from the film thickness determination unit 212, which will be described later. The data acquisition unit 211 may also acquire the film thickness information using a trained model.

[0041] Alternatively, the data acquisition unit 211 may acquire design information for candidate modified film patterns, including film thickness information, based on information input by the user via the input unit described later.

[0042] The data acquisition unit 211 also acquires information regarding indicators for determining whether or not there is an effect on the optical image, as described later. For example, the data acquisition unit 211 acquires such information based on information entered by the user via the input unit.

[0043] The film thickness determination unit 212 determines the film thickness of the corrected film based on the optical properties of the light-shielding film 12 and the corrected film. Specifically, the film thickness determination unit 212 determines the film thickness of the corrected film such that the optical properties of the candidate corrected film pattern are approximately equal to the optical properties of the light-shielding film 12 in the light-shielding formation unit 21. The determined film thickness is common to one or more candidate corrected film patterns acquired by the data acquisition unit 211. The film thickness information is transmitted to the data acquisition unit 211.

[0044] The calculation unit 213 uses electromagnetic field calculations to calculate the exposure margin based on the design information of one or more candidate modification film patterns. Specifically, the calculation unit 213 calculates the exposure margin of the optical image of the transfer pattern 10, assuming that each of the candidate modification film patterns, whose dimensions and shapes are specified by the design information, is formed on the transfer pattern 10. The calculation unit 213 also calculates the exposure margin of a reference pattern for comparison.

[0045] As described above, the design information for candidate correction film patterns includes information on the film thickness of the correction film patterns. That is, the calculation unit 213 performs electromagnetic field calculations using the film thickness information of the correction film patterns. This makes it possible to obtain an exposure margin that takes into account the film thickness of each candidate correction film pattern.

[0046] Exposure margin is an indicator that shows the degree to which variations in exposure conditions and unevenness on the semiconductor substrate can be tolerated during the lithography process. Exposure margin includes the rate at which a pattern of the desired dimensions can be obtained on the semiconductor substrate. Specifically, exposure margin includes the tolerance range of dose amount and the tolerance range of focus value required to form a pattern (optical image) of the target dimensions on the semiconductor substrate.

[0047] Ideally, the exposure margin of the reference pattern and the exposure margin based on the design information of the candidate pattern of the corrected film should be equal. A decrease in the exposure margin based on the candidate pattern of the corrected film relative to the exposure margin of the reference pattern means that the light intensity distribution is degraded by the corrected film, i.e., that there is an effect on the optical image. In this embodiment, the presence or absence of an effect on the optical image is determined using the exposure margin as an indicator. Specifically, the presence or absence of an effect on the optical image is determined using at least one of the allowable range of the dose amount and the allowable range of the focus value as indicators. Information indicating whether to use the allowable range of the dose amount or the allowable range of the focus value as an indicator is acquired by the data acquisition unit 211.

[0048] From this point forward, unless the tolerance range for dose and the tolerance range for focus value are distinguished individually, the tolerance range for dose and the tolerance range for focus value may be referred to as "exposure margin."

[0049] The acceptable level of impact on the optical image can be specified by setting a threshold for the exposure margin. In other words, the magnitude of the impact on the optical image can be determined by whether the exposure margin based on the design information of each candidate pattern of the corrected film exceeds the threshold.

[0050] The selection unit 214 selects design information from among the design information of one or more candidate correction film patterns, based on the exposure margin calculated by the calculation unit 213, in which the exposure margin exceeds a first threshold. Specifically, the selection unit 214 determines whether there is any design information among the design information of one or more candidate correction film patterns in which at least one of the allowable range of dose amount and the allowable range of focus value exceeds the first threshold. This makes it possible to obtain design information of candidate correction film patterns in which the impact on the optical image is acceptable.

[0051] If there is design information where the exposure margin exceeds the first threshold, the selection unit 214 selects the design information with the largest exposure margin. Specifically, if the allowable range of the dose amount is specified as an indicator for determining whether or not it affects the optical image, the selection unit 214 selects the design information with the largest allowable range of the dose amount. On the other hand, for example, if the allowable range of the focus value is specified as an indicator for determining whether or not it affects the optical image, the selection unit 214 selects the design information with the largest allowable range of the focus value.

[0052] The selection unit 214 selects the design information if there is one design information whose exposure margin exceeds the first threshold, and if there are multiple design information whose exposure margin exceeds the first threshold, it selects the design information with the largest exposure margin among the multiple design information. This makes it possible to obtain design information for a correction film pattern that has less impact on the optical image.

[0053] The correction unit 220 forms a correction film pattern on the transfer pattern 10 based on the design information selected in the selection unit 214. This corrects the pattern defects 23. The correction film pattern can be formed, for example, by burning the correction film source gas onto the transfer pattern 10 with a charged particle beam. This makes it possible to form a correction film pattern on the transfer pattern 10 with dimensions and shape that have less impact on the optical image.

[0054] The determination unit 215 of the correction pattern generation unit 210 determines whether or not the correction of the pattern defect 23 was successful based on the optical image acquired by the optical image acquisition device 300, which will be described later.

[0055] Furthermore, the determination unit 215 determines whether or not the pattern defects 23 can be corrected by the correction film based on the image of the pattern defects 23 acquired by the data acquisition unit 211. Specifically, the determination unit 215 determines whether or not correction is possible depending on the size and number of pattern defects 23 included in the image of the pattern defects 23. For example, if the image of the pattern defects 23 contains multiple pattern defects 23 or if the pattern defects 23 exceed a predetermined size, the determination unit 215 determines that correction of the pattern defects 23 by the correction film is impossible. In all other cases, it determines that correction of the pattern defects 23 by the correction film is possible.

[0056] The optical image acquisition device 300 acquires an optical image of the transfer pattern 10 on which the correction film has been formed. The information, including the acquired optical image, is transmitted to the determination unit 215 of the correction pattern generation unit 210.

[0057] Figure 4 shows an example of the hardware configuration of the modification pattern generation unit 210 according to the embodiment.

[0058] As shown in Figure 4, the correction pattern generation unit 210 includes a CPU (Central Processing Unit) 201, a ROM (Read Only Memory) 202, a RAM (Random Access Memory) 203, a display unit 204, and an input unit 205. In the correction pattern generation unit 210, these components are connected via a bus line.

[0059] ROM202 stores a computer program, the modified pattern generation program 207, and the calculation lithography program 208. The modified pattern generation program 207 and the calculation lithography program 208 stored in ROM202 are loaded into RAM203 via the bus line.

[0060] The modified pattern generation program 207 is configured to execute the entire pattern modification process, and the computational lithography program 208 is configured to execute electromagnetic field calculations based on design information of candidate patterns for the modified film, as part of the pattern modification process. The modified pattern generation program 207 and the computational lithography program 208 are computer program products having a computer-readable recording medium containing multiple instructions for performing the pattern modification process and electromagnetic field calculations, which are executable by a computer. In the modified pattern generation program 207 and the computational lithography program 208, these multiple instructions cause the computer to execute the pattern modification process and electromagnetic field calculations.

[0061] The CPU 201 executes each program loaded into the RAM 203. Specifically, for example, in the pattern correction process, the CPU 201 reads the correction pattern generation program 207 from the ROM 202 according to the user's input from the input unit 205, loads it into the program storage area in the RAM 203, and executes various processes.

[0062] The display unit 204 is a display device such as a liquid crystal monitor, and displays, for example, the design information selected in the selection unit 214 based on instructions from the CPU 201. The input unit 205 is equipped with a mouse and keyboard and receives instruction information (such as design information for candidate patterns of the modified film) from the user. The instruction information entered into the input unit 205 is sent to the CPU 201.

[0063] The correction pattern generation program 207 and the calculation lithography program 208, which are executed in the correction pattern generation unit 210, are configured as modules including, for example, the calculation unit 213 mentioned above, and these are loaded into the main memory and generated in the main memory.

[0064] In Figure 3 above, each of the components of the modified pattern generation unit 210, such as the data acquisition unit 211, film thickness determination unit 212, calculation unit 213, selection unit 214, and judgment unit 215, may be implemented by the CPU 201 executing each program, or they may be implemented by dedicated hardware circuits.

[0065] The calculation lithography program 208 may be stored in a computer or other device different from the one used for generating the modified pattern 210.

[0066] Next, the flow of the pattern correction process performed in the pattern correction device 200 will be explained using Figures 5 to 9.

[0067] Figure 5 is a flowchart showing an example of the pattern correction process according to the embodiment.

[0068] Prior to step S101, the transfer pattern 10 is imaged in the defect detection device 100, and pattern defects 23 are detected.

[0069] The data acquisition unit 211 acquires an image of the pattern defect 23 detected by the defect detection device 100 (step S101).

[0070] The determination unit 215 determines whether the pattern defect 23 can be corrected based on the image of the pattern defect 23 (step S102). If the determination unit 215 determines that the pattern defect 23 cannot be corrected (step S102: No), the process ends. On the other hand, if the determination unit 215 determines that the pattern defect 23 can be corrected (step S102: Yes), the data acquisition unit 211 acquires an image of the reference pattern from, for example, the ROM 202 (step S103). The determination unit 215 determines whether the pattern defect 23 can be corrected based on the size and number of pattern defects 23 included in the image of the pattern defect 23.

[0071] The data acquisition unit 211 acquires the optical properties of the light-shielding film 12 and the optical properties of the modified film (step S104).

[0072] The film thickness determination unit 212 determines the film thickness of the modified film based on the optical properties of the light-shielding film 12 and the modified film (step S105). The film thickness determination unit 212 determines the film thickness of the modified film such that the optical properties of the pattern of the modified film are approximately equal to the optical properties of the light-shielding film 12 in the light-shielding formation unit 21. The film thickness of the pattern of the modified film determined by the film thickness determination unit 212 is, for example, "T2 (T2 > T1)".

[0073] The data acquisition unit 211 acquires one or more design information for candidate patterns of the corrected film based on the images of the pattern defect 23 and the reference pattern (step S106).

[0074] Figure 6 shows an example of design information for a candidate pattern of the modified film according to the embodiment.

[0075] Figure 6(a) shows the design information for candidate 30a of the modified film pattern and the configuration of the transfer pattern 10A when candidate 30a of the modified film pattern is formed. Figure 6(b) shows the design information for candidate 30b of the modified film pattern and the configuration of the transfer pattern 10B when candidate 30b of the modified film pattern is formed. The upper parts of Figures 6(a) and (b) are plan views of the photomask M containing the transfer patterns 10A and 10B, respectively, and the lower parts are cross-sectional views along the CC line and DD line in Figures 6(a) and (b), respectively.

[0076] As shown in Figure 6(a), candidate pattern 30a of the corrected film is a pattern formed at a position corresponding to the pattern defect 23 (Figure 1(b)). That is, candidate pattern 30a of the corrected film is rectangular in shape with a side length of "d1" in the X direction and a side length of "d" in the Y direction. With the formation of candidate pattern 30a of the corrected film, the translucent portion 22b of the transfer pattern 10A becomes a square with a side length of "d".

[0077] The film thickness of candidate 30a for the modification film pattern is "T2", which is greater than the film thickness "T1" of the light-shielding film 12. Candidate 30a for the modification film pattern has a configuration in which a chromium film 31a is laminated on top of the TEOS film 32a.

[0078] As shown in Figure 6(b), candidate pattern 30b of the corrected film is a pattern that is formed by an excess (larger) amount of "d2" in the positive X direction relative to the position corresponding to the pattern defect 23 (Figure 1(b)). That is, candidate pattern 30b of the corrected film is rectangular in shape with a side length of "d1+d2" in the X direction and a side length of "d" in the Y direction. With the formation of candidate pattern 30b of the corrected film, the translucent portion 22b of the transfer pattern 10B becomes rectangular in shape with a side length of "d-d2" in the X direction and a side length of "d" along the Y direction, i.e., the longer side along the Y direction.

[0079] The film thickness of candidate 30b for the modified film pattern is "T2", which is greater than the film thickness "T1" of the light-shielding film 12. Candidate 30b for the modified film pattern has a configuration in which a chromium film 31b is laminated on top of the TEOS film 32b.

[0080] However, the design information for candidate modification film patterns 30a and 30b shown in Figures 6(a) and (b) is merely an example and is not limited to this.

[0081] The calculation unit 213 calculates the exposure margin for each of the design information for candidate 30a and 30b of the modified film patterns by performing electromagnetic field calculations using the film thickness information of candidate 30a and 30b (step S107). Specifically, the calculation unit 213 calculates the exposure margin for the optical images of the transfer pattern 10A on which candidate 30a of the modified film pattern is formed, and the transfer pattern 10B on which candidate 30b of the modified film pattern is formed. The calculation unit 213 also calculates the exposure margin for the optical image of a reference pattern as a comparison target.

[0082] The calculation unit 213 calculates the exposure margin for each of the above-mentioned reference pattern, transfer pattern 10A, and 10B in accordance with the instructions of the calculation lithography program 208.

[0083] Figure 7 is a diagram illustrating the processing flow of the computational lithography program 208 according to the embodiment. The processing of the computational lithography program 208 is for calculating the exposure margin by electromagnetic field calculation. The processing by the computational lithography program 208 is performed as part of the pattern correction process.

[0084] The calculation unit 213 acquires information including optical conditions necessary for calculating the exposure margin (step S301). For example, the calculation unit 213 acquires information such as the exposure wavelength, whether or not immersion exposure is performed, the range of dose and focus to be calculated, and the type of resist (positive, negative). The calculation unit 213 acquires this information, for example, through input from the user via the input unit 205.

[0085] The calculation unit 213 acquires the design information for the reference pattern, the transfer pattern 10A, and the transfer pattern 10B (step S302). The design information for the transfer pattern 10A includes the design information for candidate 30a of the modified film pattern, and the design information for the transfer pattern 10B includes the design information for candidate 30b of the modified film pattern.

[0086] The calculation unit 213 performs electromagnetic field calculations for each of the acquired reference pattern, transfer pattern 10A, and 10B (step S303). Specifically, the calculation unit 213 performs electromagnetic field calculations using the film thickness information of each of the candidate modified film patterns 30a and 30b.

[0087] The calculation unit 213 may use, for example, a finite difference time-domain method or an exact coupled wave analysis method with the region around the pattern defect 23 as the calculation domain for electromagnetic field calculations. By using these methods, an exact solution can be obtained. In addition, the calculation unit 213 may use other methods for electromagnetic field calculations, such as calculation methods using approximate mask 3D models, such as boundary layer models, domain decomposition methods, filter-based methods, machine learning methods, and deep learning methods, with the region around the pattern defect 23 as the calculation domain. By using these methods, the calculation speed of electromagnetic field calculations can be increased.

[0088] The calculation unit 213 generates a defocus dose map based on the results of the electromagnetic field calculation (step S304). Specifically, the calculation unit 213 generates a defocus dose map of the optical image in each of the reference pattern, the transfer pattern 10A, and 10B.

[0089] The defocus dose map contains information showing the transition of the dimensions (optical image) of the pattern formed on the semiconductor substrate at different dose amounts and different focus values. The calculation unit 213 calculates the exposure margin according to the defocus dose map. The calculated exposure margin reflects the film thickness information of the candidate patterns 30a and 30b of the corrected film.

[0090] This completes the processing of the calculation lithography program 208. The calculation unit 213 may also obtain a defocus dose map of the optical image of the reference pattern from a database or the like.

[0091] Figures 8 and 9 show examples of the calculated exposure margin. Figures 8 and 9 were obtained through actual experiments.

[0092] Figure 8 shows an example of the calculation results for the exposure margin according to the embodiment. In Figure 8, the horizontal axis corresponds to the dose amount, and the vertical axis corresponds to the focus value.

[0093] Figure 8 shows the acceptable ranges for focus value and dose amount that allow dimensions to be obtained within ±10% of the target dimensions on a semiconductor substrate. In other words, the acceptable ranges Rf and Ra shown in Figure 8 are examples of exposure margins.

[0094] The solid line in Figure 8 is the defocus dose map of the reference pattern, and the dashed line in Figure 8 is the defocus dose map of the transfer pattern 10A. The region between the two solid lines represents the tolerance range Rf of the reference pattern, and the region between the two dashed lines represents the tolerance range Ra of the transfer pattern 10A.

[0095] The area of ​​the transfer pattern 10A within the acceptable range Ra is less than half the area of ​​the reference pattern within the acceptable range Rf. This indicates that the exposure margin of the transfer pattern 10A is significantly reduced compared to the reference pattern. In other words, as shown in Figure 8, forming the pattern of the corrected film based on the design information of candidate 30a of the corrected film pattern results in a significant deterioration of the light intensity distribution, i.e., an adverse effect on the optical image.

[0096] Figure 9 shows another example of the calculation results of the exposure margin according to the embodiment. In Figure 9, the horizontal axis corresponds to the dose amount, and the vertical axis corresponds to the focus value.

[0097] Figure 9 is a modified version of Figure 8, showing the maximum focus values ​​for each dose within the acceptable range of Rf and Ra. The maximum focus values ​​(acceptable range of focus values) for each dose shown in Figure 9 are examples of exposure margins. Similarly, the maximum dose (acceptable range of dose) for each focus value is also an example of exposure margin.

[0098] In Figure 9, the solid lines connecting the black-filled square plots indicate the exposure margin of the reference pattern, the solid lines connecting the black-filled circles indicate the exposure margin of transfer pattern 10A, and the solid lines connecting the black-filled triangle plots indicate the exposure margin of transfer pattern 10B.

[0099] As shown in Figure 9, for example, the maximum focus values ​​of the reference pattern, transfer pattern 10A, and 10B at each dose are decreasing in the order of reference pattern, transfer pattern 10B, and transfer pattern 10A. Specifically, if the maximum focus value of the optical image of the reference pattern at a given dose is set to 100%, the maximum focus value of transfer pattern 10A is 30-40%, and the maximum focus value of transfer pattern 10B is 50-60%. In other words, Figure 9 shows that by forming the pattern of the corrected film based on the design information of candidate 30b of the corrected film pattern instead of candidate 30a of the corrected film pattern, the deterioration of the light intensity distribution can be suppressed, i.e., the impact on the optical image can be suppressed.

[0100] In this embodiment, the first threshold is, for example, 50% when the maximum dose amount and the maximum focus value of the reference pattern are both set to 100%.

[0101] The selection unit 214 (Figure 5) compares the exposure margin of the reference pattern calculated by the calculation unit 213 with the exposure margin of each candidate design information for the modified film pattern (step S108), and determines whether there is any design information whose exposure margin exceeds 50% as the first threshold (step S109). Specifically, the selection unit 214 compares the maximum dose amount at a predetermined focus value and the maximum focus value at a predetermined dose amount for the reference pattern, transfer pattern 10A, and 10B, and determines whether there is any design information in which at least one of the maximum dose amount and the maximum focus value exceeds 50%.

[0102] If the selection unit 214 determines that there is design information with an exposure margin of more than 50% (step S109: Yes), it selects the design information with the largest exposure margin (step S110).

[0103] Specifically, the selection unit 214 selects the design information with the largest maximum dose amount when the maximum dose amount (tolerance range of dose amount) at a predetermined focus value is specified as an indicator for determining whether or not it affects the optical image. For example, as shown in Figure 9, the maximum dose amount of transfer pattern 10A at a predetermined focus value is 65%, and the maximum dose amount of transfer pattern 10B is 75%. In this case, the selection unit 214 selects the design information of transfer pattern 10B, which has the largest maximum dose amount.

[0104] On the other hand, if the selection unit 214 is specified as an indicator for determining whether or not the maximum focus value (tolerance range of focus value) at a predetermined dose is affected by the optical image, it selects the design information with the largest maximum focus value. Although examples are omitted, the selection unit 214 selects the design information with the largest maximum focus value at a predetermined dose from among the transfer patterns 10A and 10B.

[0105] As described above, the design information for the transfer pattern 10B includes the design information for candidate 30b of the correction film pattern. That is, the selection unit 214 selects the design information for candidate 30b of the correction film pattern. In this way, design information for a candidate correction film pattern that can suppress the influence on the optical image can be obtained from among the candidate 30a and 30b of the correction film pattern.

[0106] On the other hand, if the selection unit 214 determines, for example, that there is no design information in which the exposure margin exceeds the first threshold (step S109: No), the process returns to step S106.

[0107] The modification unit 220 forms a pattern for the modified film on the transfer pattern 10 based on the design information selected in the selection unit 214 (step S111). For example, the modification unit 220 forms a pattern for the modified film on the transfer pattern 10 based on the design information of candidate 30b for the modified film pattern. In this way, a pattern for the modified film that can suppress the influence on the optical image can be obtained.

[0108] In forming the pattern of the corrected film, the correction unit 220 first loads the photomask M to be corrected into the vacuum processing layer and identifies the location of the pattern defects 23 by position alignment. After specifying the type of film to be corrected, the correction unit 220 forms the corrected film based on the design information of the candidate pattern 30b of the corrected film. This corrects the pattern defects 23. After observing the formed portion of the corrected film, the correction unit 220 removes the photomask M from the vacuum processing layer. The photomask M removed from the correction unit 220 is then loaded into the optical image acquisition device 300.

[0109] The correction unit 220 also determines the success or failure of the correction based on the observation results of the correction film formation area. Specifically, the correction unit 220 determines whether a correction film corresponding to the design information of the candidate correction film pattern 30b has been formed, based on the image automatically acquired when observing the correction film formation area. For example, if the correction unit 220 determines that a correction film corresponding to the design information of the candidate correction film pattern 30b has not been formed, it may terminate the pattern correction process without transporting the photomask M to the optical image acquisition device 300, considering the correction unit 220 to be non-functional. Alternatively, if the correction unit 220 determines that a correction film corresponding to the design information of the candidate correction film pattern 30b has not been formed, it may form the correction film again. In this case, the type of correction film may be changed.

[0110] The optical image acquisition device 300 acquires an optical image of the transfer pattern 10 on which the pattern of the corrected film is formed in order to determine whether the correction is successful or not (step S112). The optical image acquisition device 300 transmits the information including the optical image to the determination unit 215 of the corrected pattern generation unit 210.

[0111] The determination unit 215 determines whether the pattern defect 23 has been successfully corrected based on the optical image acquired by the optical image acquisition device 300 (step S113). Specifically, the determination unit 215 compares the exposure margin for the candidate pattern 30b of the corrected film calculated in step S107 with the exposure margin based on the optical image acquired by the optical image acquisition device 300, and determines whether the difference between these exposure margins falls below a second threshold.

[0112] If the determination unit 215 determines that the difference in exposure margin falls below the second threshold, i.e., that the correction has been successful (step S113: Yes), the pattern correction process of the embodiment is terminated.

[0113] On the other hand, if the determination unit 215 determines that the difference in exposure margin is greater than or equal to the second threshold, i.e., that the correction was unsuccessful (step S113: No), it determines whether or not the photomask M can be corrected again (step S114).

[0114] The determination unit 215 determines that further correction is possible (step S114: Yes) if the difference between the exposure margin for candidate pattern 30b of the corrected film and the exposure margin based on the optical image acquired by the optical image acquisition device 300 does not exceed a third threshold (third threshold > second threshold), and the process proceeds to step S115. After this, the photomask M is brought into the defect detection device 100, and pattern defects are imaged. The data acquisition unit 211 acquires the image of the pattern defects captured by the defect detection device 100 (step S115), and the process proceeds to step 103.

[0115] The determination unit 215 determines that the correction unit 220 is not functioning and therefore cannot be corrected again if the difference between the exposure margin for candidate pattern 30b of the corrected film and the exposure margin based on the optical image acquired by the optical image acquisition device 300 is greater than or equal to the second threshold and less than or equal to the third threshold (step S114: No), and the pattern correction process of the embodiment ends.

[0116] The determination unit 215 may determine the success or failure of the correction based on the exposure margin calculated using the computational lithography program 208, instead of the exposure margin based on the optical image acquired by the optical image acquisition device 300. In this case, the shape of the corrected transfer pattern 10 obtained by observing the corrected film formation portion performed by the correction unit 220 in step S111 may be used to calculate the exposure margin using the computational lithography program 208.

[0117] (Overview) Incidentally, in electromagnetic field calculations, the film thickness information of the correction film pattern is sometimes not taken into consideration. In this case, the exposure margin is calculated based on the two-dimensional design information of the correction film pattern. Therefore, it is difficult to accurately measure the influence of the correction film pattern on the optical image.

[0118] In contrast, in the pattern correction method and pattern correction apparatus 200 of the embodiment, the exposure margin is calculated by electromagnetic field calculation using the film thickness information of the correction film. As a result, even if, for example, the film thickness of the pattern composed of the light-shielding film 12 and the film thickness of the correction film pattern are different, the influence of the correction film pattern on the optical image can be measured with higher accuracy. Furthermore, as a result, the accuracy of pattern design using ILT technology can be improved.

[0119] Furthermore, in the pattern correction method and pattern correction apparatus 200 of the embodiment, design information in which the exposure margin exceeds a threshold is selected from among the candidate design information for the pattern of the corrected film. This makes it possible to obtain design information for the pattern of the corrected film that has less impact on the optical image. In other words, the pattern correction method and pattern correction apparatus 200 of the embodiment can suppress the impact of the pattern of the corrected film on the optical image.

[0120] (Other embodiments) In the above embodiment, the data acquisition unit 211 acquired candidate design information for the pattern of the corrected film, which differs in the X-direction dimension of the light-transmitting portion 22b. However, the shape of the candidate pattern of the corrected film is not limited to this. For example, the data acquisition unit 211 may acquire candidate design information having a shape that differs in the diagonal dimensions of the light-transmitting portion 22b, or, for example, candidate design information having a shape that differs in the distance from the center position of the light-transmitting portion 22b.

[0121] Furthermore, in the above-described embodiment, the data acquisition unit 211 acquired design information for candidate patterns of the correction film formed in a rectangular shape, but the shape of the candidate patterns of the correction film is not limited to this. The candidate patterns of the correction film may have shapes such as those shown in Figure 10.

[0122] Figure 10 shows another example of design information for candidate modification patterns according to the embodiment.

[0123] For example, candidate correction pattern 30c may have a shape with few corners, as shown in Figure 10(a). Alternatively, candidate correction pattern 30d may have a curved contour, as shown in Figure 10(b). The data acquisition unit 211 can acquire candidate correction film patterns having various shapes, such as those shown in Figures 10(a) and (b).

[0124] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0125] 1...Pattern correction system, 10, 10A, 10B...Transfer pattern, 12...Light-shielding film, 21...Light-shielding formation section, 22, 22a, 22b...Light-transmitting section, 23...Pattern defect, 30a~30d...Candidate patterns for the corrected film, 100...Defect detection device, 200...Pattern correction device, 210...Corrected pattern generation section, 211...Data acquisition section, 212...Film thickness determination section, 213...Calculation section, 214...Selection section, 215...Decision section, 220...Correction section, 300...Optical image acquisition device, M...Photomask.

Claims

1. A first step of obtaining information on defects in the pattern of a photomask having a pattern formed with a light-shielding film, and the optical properties of the light-shielding film and a correction film that corrects the defects, A second step of determining the thickness of the correction film based on the optical properties of the light-shielding film and the correction film, A third step of acquiring one or more design pieces of information indicating the dimensions and shape of candidate patterns for the modified film, including film thickness information indicating the film thickness of the modified film. A fourth step of calculating the exposure margin for each of the one or more design information by electromagnetic field calculation using the film thickness information of the modified film, A fifth step of selecting from the one or more design information items above the exposure margin which exceeds a threshold, A sixth step of forming the modified film on the photomask according to the selected design information, Pattern correction methods including

2. In the fourth step described above, calculating the exposure margin is This involves calculating the acceptable range of dose and focus value required to obtain the target optical image. The fifth step is, The process involves selecting the design information from among the one or more design information pieces mentioned above that has the largest tolerance range for the dose amount and the tolerance range for the focus value. The pattern modification method according to claim 1.

3. The one or more design information obtained in the third step is a plurality of design information, The fifth step is, The process involves selecting the design information with the largest exposure margin from among the aforementioned multiple design information. The pattern modification method according to claim 1.

4. The light-shielding film includes a silicon nitride film, The aforementioned modification film includes a multilayer film in which a chromium film is laminated on a TEOS film. The pattern modification method according to claim 1.

5. The aforementioned optical characteristics are The transmittance and phase difference of the light-shielding film, The pattern modification method according to claim 1.

6. The first step described above is, Based on the acquired information about defects in the pattern, a determination is made as to whether or not the defects in the pattern can be corrected. If it is determined that the defect in the aforementioned pattern can be corrected, this includes obtaining information on a reference pattern in which the defect in the aforementioned pattern does not exist. The fourth step described above is: This includes calculating the exposure margin of the aforementioned reference pattern, The fifth step is, The exposure margin for each of the one or more design information items is compared with the exposure margin of the reference pattern. It is determined whether, among the one or more design information pieces mentioned above, there is any design information piece in which the exposure margin for each of the one or more design information pieces exceeds the threshold value for the exposure margin of the reference pattern. If it is determined that there is design information that exceeds the threshold, the selection of the design information with the largest exposure margin is included. After the correction film is formed on the photomask in the sixth step, The optical image of the aforementioned photomask is obtained, Based on the exposure margin based on the optical image and the exposure margin for the design information selected in the fifth step, the success or failure of correcting the defect in the pattern is determined. If it is determined that the defect in the pattern has not been successfully corrected, the feasibility of further correcting the defect in the pattern is determined based on the exposure margin based on the optical image and the exposure margin for the design information selected in the fifth step. If it is determined that the defect in the aforementioned pattern can be corrected again, this includes reacquiring information about the defect in the aforementioned pattern. The pattern modification method according to claim 1.

7. A data acquisition unit that acquires information on defects in the pattern of a photomask having a pattern formed of a light-shielding film, the optical properties of the light-shielding film and a correction film that corrects the defects, film thickness information indicating the film thickness of the correction film determined based on the optical properties of the light-shielding film and the correction film, and one or more design pieces of information indicating the dimensions and shape of candidate patterns of the correction film, including the film thickness information of the correction film. A film thickness determination unit that determines the film thickness of the corrected film based on the optical properties of the light-shielding film and the corrected film, A calculation unit that calculates the exposure margin for each of the one or more design information by performing an electromagnetic field calculation using the film thickness information of the modified film, A selection unit that selects from the one or more design information items mentioned above that the exposure margin exceeds a threshold, A modification unit that forms the modified film on the photomask according to the selected design information, Pattern correction device.

8. The aforementioned exposure margin is, This includes the tolerance range for dose amount and the tolerance range for focus value required to obtain the target optical image. The aforementioned selection unit is From the one or more design information pieces mentioned above, select the design information piece that has the largest tolerance range for the dose amount and the tolerance range for the focus value. The pattern correction device according to claim 7.

9. The data acquisition unit, Multiple pieces of the aforementioned design information are acquired, The aforementioned selection unit is From among the multiple design information, select the design information that has the largest exposure margin. The pattern correction device according to claim 7.

10. The light-shielding film includes a silicon nitride film, The aforementioned modification film includes a multilayer film in which a chromium film is laminated on a TEOS film. The pattern correction device according to claim 7.

11. The aforementioned optical characteristics are The transmittance and phase difference of the light-shielding film, The pattern correction device according to claim 7.

12. It is further equipped with a judgment unit, The unit that makes the determination said, Based on the information regarding the defects in the aforementioned pattern, a determination is made as to whether or not the defects in the aforementioned pattern can be corrected. Based on the exposure margin for the design information selected in the selection unit and the exposure margin of the optical image of the photomask on which the corrected film is formed, the success or failure of correcting the defect in the pattern and whether or not the defect in the pattern can be corrected again are determined. The data acquisition unit, If the determination unit determines that the defect in the pattern can be corrected, it obtains information on a reference pattern in which the defect in the pattern does not exist. If the determination unit determines that the defect in the pattern can be corrected again, it obtains information about the defect in the pattern, The aforementioned arithmetic unit, The exposure margin of the aforementioned reference pattern is calculated, The aforementioned selection unit is The exposure margin for each of the one or more design information items is compared with the exposure margin of the reference pattern. It is determined whether, among the one or more design information pieces mentioned above, there is any design information piece in which the exposure margin for each of the one or more design information pieces exceeds the threshold value for the exposure margin of the reference pattern. If it is determined that there is design information that exceeds the aforementioned threshold, the design information with the largest exposure margin is selected. The pattern correction device according to claim 7.

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