JP2020085839A - Method and device for inspecting mask - Google Patents

Abstract

To provide a method and a device for inspecting a mask which can correct a change of the luminance at the time of an inspection and can precisely inspect an inspection target.SOLUTION: The method for inspection a mask includes: a step (S11) for acquiring a reference image of a mask by detecting a reflection light R as an illumination light reflected by the mask; a step (S12) for performing predetermined processing on the mask, of which reference image has been acquired; a step (S13) for acquiring an inspection image of the mask by detecting the reflection light as the illumination light reflected by the mask, on which the predetermined processing has been performed; and a step (S14) for comparing the reference image and the inspection image and inspecting the mask.SELECTED DRAWING: Figure 2

Description

The present invention relates to a mask inspection method and a mask inspection apparatus, for example, a mask inspection method and a mask inspection apparatus for inspecting a defect of a photomask used in a semiconductor manufacturing process.

Generally, a Die-to-Database comparison method for comparing a mask pattern with design data and a Die-to-Die comparison method for comparing two circuit patterns of the same shape as a method for inspecting a defect of a mask on which a pattern is formed. , And a Mask-to-Mask comparison method for comparing different masks of the same design pattern is widely known.

In either method, the mask pattern is magnified by an objective lens, and the magnified image is detected by a CCD camera for inspection.

Special table 2002-543463 gazette Japanese Patent Publication No. 2002-544555 JP, 2004-030368, A JP, 2007-192743, A JP, 2011-196728, A Japanese Patent Publication No. 2016-532902 U.S. Patent Application Publication No. 2018/238816

In the Mask-to-Mask method, a change in luminance may occur between a reference image serving as a reference and an inspection image to be inspected due to a transition of an inspection apparatus and a process such as pattern formation. .. In particular, the rate of change in luminance may be different between high luminance (hereinafter also referred to as White) and low luminance (hereinafter also referred to as Dark). These brightness changes cause a problem that a normal pattern on the mask is detected as a pseudo defect.

An object of the present invention is to provide an inspection method and an inspection device capable of accurately inspecting an inspection target by correcting a change in brightness during inspection.

The mask inspection method according to the present invention, by detecting the reflected light reflected by the mask illumination light, a step of acquiring a reference image of the mask, and a step of performing a predetermined process on the mask from which the reference image is acquired With the illumination light, by detecting the reflected light reflected by the mask that has been subjected to the predetermined processing, a step of acquiring an inspection image of the mask, the reference image, and the inspection image, Inspecting the mask by comparing. With such a configuration, it is possible to accurately inspect the inspection target.

Further, the mask inspection method according to the present invention includes a step of acquiring a reference image of the mask by using a first detection optical system that detects reflected light in which illumination light is reflected by the mask, and the first detection optical system. A step of acquiring an inspection image by detecting the reflected light reflected by the mask, which has acquired the reference image, by the illumination light using a different second detection optical system; Extracting a first brightness of the feature, a second brightness of the second feature having a brightness higher than the first brightness, and a third brightness of a third feature having a brightness higher than the second brightness. Extracting the fourth luminance of the first characteristic portion, the fifth luminance of the second characteristic portion, and the sixth luminance of the third characteristic portion from the inspection image; and the second luminance from the first luminance. A plurality of luminances up to the luminance and a plurality of luminances between the fourth luminance and the fifth luminance, and a plurality of luminances between the second luminance and the third luminance, Creating a table in which a plurality of brightness values between the fifth brightness and the sixth brightness are associated with each other; correcting the brightness of the reference image by referring to the table; and the inspection image; And inspecting the mask by comparing the corrected reference image. With such a configuration, it is possible to accurately inspect the inspection target by correcting the luminance change during the inspection.

Furthermore, the mask inspection apparatus according to the present invention illuminates the mask with illumination light, and a detection optical system for detecting reflected light reflected by the illumination light on the mask, and the reflected light detected by the detection optical system. An image processing unit that acquires a reference image of the mask based on the same, and acquires an inspection image of the mask after performing a predetermined process on the mask that acquired the reference image, and the image processing unit. Is the first brightness of the first feature, the second brightness of the second feature having a brightness higher than the first brightness, and the third feature having a brightness higher than the second brightness from the reference image. The third luminance is extracted, and the fourth luminance of the first characteristic portion, the fifth luminance of the second characteristic portion, and the sixth luminance of the third characteristic portion are extracted from the inspection image, and the first luminance is extracted. A plurality of luminances between the luminance and the second luminance and a plurality of luminances between the fourth luminance and the fifth luminance are made to correspond to each other, and a plurality of luminances between the second luminance and the third luminance are associated. A table in which a plurality of brightnesses and a plurality of brightnesses between the fifth brightness and the sixth brightness are associated with each other is created, the reference image is corrected with reference to the table, the inspection image, Inspect the mask by comparing it with the corrected reference image. With such a configuration, it is possible to accurately inspect the inspection target by correcting the luminance change during the inspection.

According to the present invention, it is possible to provide an inspection method and an inspection device that can inspect an inspection object with high accuracy.

It is a block diagram which illustrated the mask inspection apparatus which concerns on embodiment. It is a flowchart figure which illustrated the mask inspection method which concerns on embodiment. It is a flowchart figure which illustrated the details of the mask inspection method which concerns on embodiment. (A) is a figure which illustrated the reference image in the mask inspection method which concerns on embodiment, (b) is a graph which illustrated the brightness|luminance of each characteristic part of the reference image which concerns on embodiment, and a horizontal axis is abscissa. , The position of the image is shown, and the vertical axis shows the luminance. (A) is a figure which illustrated the inspection image in the mask inspection method which concerns on embodiment, (b) is a graph which illustrated the brightness|luminance of each characteristic part of the inspection image which concerns on embodiment, and a horizontal axis. , The position of the image is shown, and the vertical axis shows the luminance. In the mask inspection method according to the embodiment, it is a graph illustrating each luminance of each characteristic portion, the horizontal axis represents the luminance in the reference image, and the vertical axis represents the luminance in the inspection image. It is the figure which illustrated the lookup table in the mask inspection method which concerns on embodiment. It is a flowchart figure which illustrated the mask inspection method which concerns on the modification of embodiment.

Hereinafter, a specific configuration of this embodiment will be described with reference to the drawings. The following description shows preferred embodiments of the present invention, and the scope of the present invention is not limited to the following embodiments. In the following description, the same reference numerals indicate substantially the same contents.

(Embodiment)
A mask inspection apparatus and a mask inspection method according to the embodiment will be described. First, the configuration of the mask inspection device will be described. Then, a mask inspection method using the mask inspection apparatus will be described.

<Structure of mask inspection device>
The mask inspection apparatus of this embodiment is, for example, an inspection apparatus for a photomask used in a semiconductor manufacturing process. FIG. 1 is a configuration diagram illustrating a mask inspection apparatus 1 according to an embodiment.

As shown in FIG. 1, the mask inspection apparatus 1 includes a detection optical system 10 and an image processing unit 20. The detection optical system 10 has a beam splitter 11, an objective lens 12, a projection lens 13, and a detector 14. The image processing unit 20 has a processing unit 21 and a storage unit 22. The detection optical system 10 and the image processing unit 20 may include other optical members and the like.

Illumination light L10 generated from a light source (not shown) enters the detection optical system 10 as illumination light that illuminates the mask 30 to be inspected. The illumination light L10 that has entered the detection optical system 10 is partially reflected by the beam splitter 11 and travels toward the mask 30 to be inspected. The illumination light L10 traveling toward the mask 30 is condensed by the objective lens 12 and illuminates the pattern surface of the mask 30.

The reflected light R10 obtained by reflecting the illumination light L10 on the pattern surface of the mask 30 is condensed by the objective lens 12 and is incident on the beam splitter 11 again. A part of the reflected light R10 incident on the beam splitter 11 is transmitted and is condensed by the projection lens 13. The reflected light R10 collected by the projection lens 13 is detected by the detector 14. The detector 14 is, for example, a camera using TDI. In this way, the detection optical system 10 illuminates the mask 30 with the illumination light L10 and detects the reflected light R10 that is the illumination light L10 reflected by the mask 30.

The image processing unit 20 acquires an image of the mask 30 based on the reflected light R10 detected by the detection optical system 10. The image processing unit 20 acquires an image of the mask 30 before performing a predetermined process. The image of the mask 30 before performing the predetermined process is referred to as a reference image. Further, the image processing unit 20 acquires an image of the mask 30 after performing a predetermined process on the mask 30 that has acquired the reference image. The image of the mask 30 after performing the predetermined processing is called an inspection image. For example, the processing unit 21 in the image processing unit 20 generates an image based on the signal from the detector 14, and the storage unit 22 in the image processing unit 20 stores the generated image data.

<Mask inspection method>
Next, a mask inspection method using the mask inspection device 1 will be described. FIG. 2 is a flowchart illustrating the mask inspection method according to the embodiment.

As shown in step S11 of FIG. 2, the reference image of the mask 30 is acquired. Specifically, the reference image of the mask 30 is acquired by detecting the reflected light R10 that is the illumination light L10 reflected by the mask 30. By using the detection optical system 10, the mask 30 to be inspected is illuminated with the illumination light L10. Then, the detection optical system 10 detects the reflected light R10 that is the illumination light L10 reflected by the pattern surface of the mask 30. The image processing unit 20 acquires an image from the reflected light R10 detected by the detection optical system 10. The acquired image is a reference image because it is an image of the mask 30 before performing a predetermined process. The image processing unit 20 stores the acquired reference image in the storage unit 22.

Next, as shown in step S12, the mask 30 is subjected to predetermined processing. The mask 30 that performs a predetermined process is the same as the mask 30 that has acquired the reference image, or the mask 30 that has the same design (lot: lot) in which the same pattern is engraved. The predetermined process is specifically an exposure process in photolithography. Further, the predetermined process is a process of cleaning the mask. The predetermined process is not limited to the exposure process and the cleaning process as long as it is a process for the mask 30. Further, exposure processing or cleaning processing may be performed a plurality of times between the acquisition of the reference image and the acquisition of the inspection image.

Next, as shown in step S13, an inspection image of the mask 30 is acquired. Specifically, the inspection image of the mask 30 is acquired by illuminating the mask 30 that has been subjected to a predetermined process with the illumination light L10 and detecting the reflected light R10 that is the illumination light L10 reflected by the mask 30. .. The image processing unit 20 acquires an image from the reflected light R10 detected by the detection optical system 10. The image to be acquired is an inspection image because it is an image of the mask 30 after performing a predetermined process. The image processing unit 20 stores the acquired inspection image in the storage unit 22.

Next, as shown in step S14, the mask 30 is inspected by comparing the reference image and the inspection image. The details of the inspection method of the mask 30 will be described below.

FIG. 3 is a flowchart illustrating the details of the mask inspection method according to the embodiment. FIG. 4A is a diagram illustrating a reference image in the mask inspection method according to the embodiment, and FIG. 4B is a graph illustrating the luminance of each characteristic portion of the reference image according to the embodiment. The axis represents the position of the image, and the vertical axis represents the brightness. FIG. 5A is a diagram illustrating an inspection image in the mask inspection method according to the embodiment, and FIG. 5B is a graph illustrating the luminance of each characteristic portion of the inspection image according to the embodiment. The axis represents the position of the image, and the vertical axis represents the brightness.

As shown in step S21 of FIG. 3, each brightness of each characteristic portion is extracted from the reference image. For example, as illustrated in FIG. 4A, the processing unit 21 reads the reference image from the storage unit 22. In the reference image, for example, a pattern of lines and spaces 41 and a pattern of contacts 42 are formed.

In the read reference image, the processing unit 21 uses, for example, the pattern edge portion 31 as the first characteristic portion. In the acquired reference image, a drop in brightness peculiar to the reflected light is observed in the pattern edge portion 31. In such a portion where the brightness drops, the brightness may change greatly depending on the change of the condition of the mask 30 and the change of the condition of the detection optical system 10. Therefore, such a pattern edge portion 31 is extracted as the first feature point. As shown in FIG. 4B, low luminance (Dark) D1 is extracted as the luminance of the pattern edge portion 31, which is the first characteristic portion. The low brightness D1 is, for example, a gray scale of 256 steps and is 80/256.

Next, the processing unit 21 uses, for example, the absorbing film portion 32 as the second characteristic portion in the read reference image. In the acquired reference image, medium brightness is observed in the absorption film portion 32. Even with such a moderate brightness, the brightness may change significantly due to the change in the condition of the mask 30 and the change in the condition of the detection optical system 10. Therefore, such an absorbing film portion 32 is extracted as the second feature point. As shown in FIG. 4B, medium brightness (Gray) G1 is extracted as the brightness of the absorption film portion 32 that is the second characteristic portion. The medium brightness G1 is, for example, a gray scale of 256 steps and is 140/256.

Next, the processing unit 21 uses, for example, the pattern portion 33 as the third characteristic portion in the read reference image. In the acquired reference image, high brightness is observed in the pattern portion 33. Even with such high brightness, the brightness may change significantly due to changes in the conditions of the mask 30 and the conditions of the detection optical system 10. Therefore, such a pattern portion 33 is extracted as the third feature point. As shown in FIG. 4B, high brightness (White) W1 is extracted as the brightness of the pattern portion 33 that is the third characteristic portion. The high brightness W1 is, for example, a gray scale of 256 levels and is 230/256.

As described above, the image processing unit 20 determines, from the reference image, the low luminance D1 of the first characteristic portion, the middle luminance G1 of the second characteristic portion higher than the low luminance D1, and the higher luminance than the middle luminance G1. The high brightness W1 of the third feature portion is extracted. The image processing unit 20 may extract not only three feature points of the first to third feature portions but also four or more feature points in the reference image.

Next, as shown in step S22 of FIG. 3, each brightness of each feature is extracted from the inspection image. For example, as illustrated in FIG. 5A, the processing unit 21 reads the inspection image from the storage unit 22. Then, as shown in FIG. 5B, low luminance (Dark) D2 is extracted as the luminance of the pattern edge portion 31, which is the first characteristic portion. Similarly, medium brightness (Gray) G2 is extracted as the brightness of the absorbing film portion 32 which is the second characteristic portion, and high brightness (White) W2 is extracted as the brightness of the pattern portion 33 which is the third characteristic portion. For example, in the inspection image, the low brightness D2, the middle brightness G2, and the high brightness W2 are 70/256, 120/256, and 210/256, respectively, in 256-step gray scale.

As described above, the image processing unit 20 detects, from the inspection image, the low luminance D2 of the first characteristic portion, the middle luminance G2 of the second characteristic portion higher than the low luminance D2, and the higher luminance than the middle luminance G2. The high brightness W2 of the third feature portion is extracted. The image processing unit 20 may extract not only the three feature points from the first feature portion to the third feature portion but also four or more feature points from the inspection image.

FIG. 6 is a graph exemplifying each luminance of each characteristic portion in the mask inspection method according to the embodiment, in which the horizontal axis represents the luminance in the reference image and the vertical axis represents the luminance in the inspection image. As shown in FIG. 6, when the reference image and the inspection image have the same brightness in the same feature portion, the plot is on the straight line C. However, as in the present embodiment, the brightness in the same feature portion is the reference image. And the inspection image may be different.

For example, the slope on the graph from low brightness (D1, D2) to medium brightness (G1, G2) is different from the slope on the graph from middle brightness (G1, G2) to high brightness (W1, W2). ..

Therefore, as shown in step S23 of FIG. 3, a table is created in which the brightness of each feature point of the reference image and the brightness of each feature point of the inspection image are associated with each other. Specifically, the image processing unit 20 associates a plurality of brightnesses from the low brightness D1 to the middle brightness G1 in the reference image with a plurality of brightnesses from the low brightness D2 to the middle brightness G2 in the inspection image. At the same time, a table is created in which a plurality of luminances between the middle luminance G1 and the high luminance W1 in the reference image and a plurality of luminances between the middle luminance G2 and the high luminance W2 in the inspection image are associated with each other. The table is, for example, a lookup table (Look Up Table).

FIG. 7 is a diagram exemplifying a lookup table in the mask inspection method according to the embodiment. As shown in FIG. 7, the look-up table indicates, for example, the brightness of each feature point by the number of bits of 256.

Next, as shown in step S24 of FIG. 3, the brightness of the reference image is corrected by referring to the table. Specifically, the image processing unit 20 refers to the table and corrects the brightness of the reference image so that the brightness of the reference image corresponds to the brightness of the inspection image. For example, the image processing unit 20 corrects the low luminance D1 (80/256) of the first characteristic portion of the reference image so as to correspond to the low luminance D2 (70/256), and then the middle luminance G1 of the second characteristic portion. (140/256) is corrected so as to correspond to the medium brightness G2 (120/256).

In addition, the image processing unit 20 corrects the plurality of luminances between the low luminance D1 and the middle luminance G1 so as to correspond to the plurality of luminances between the low luminance D2 and the middle luminance G2. For example, correction may be performed by adding a predetermined luminance from a plurality of luminances between the low luminance D1 and the middle luminance G1, or a predetermined luminance may be set to a plurality of luminances between the low luminance D1 and the middle luminance G1. You may multiply by the coefficient of. Further, the gray scale of the inspection image may be shifted by a predetermined brightness. The image processing unit 20 may automatically perform such processing.

Further, the image processing unit 20 corrects the high brightness W1 (230/256) of the third feature portion of the reference image so as to correspond to the high brightness W2 (210/256). In addition, the image processing unit 20 corrects the plurality of luminances from the middle luminance G1 to the high luminance W1 so as to correspond to the plurality of luminances from the middle luminance G2 to the high luminance W2. The image processing unit 20 may automatically perform such processing.

Correction performed on a plurality of luminances between low luminance D1 and medium luminance G1 (addition of predetermined luminance, multiplication of a predetermined coefficient, etc.) and correction performed on a plurality of luminances between middle luminance G1 and high luminance W1 It may be different from (addition of predetermined brightness, multiplication of predetermined coefficient, etc.).

Next, as shown in step S25 of FIG. 3, the image processing unit 20 inspects the mask 30 by comparing the inspection image with the corrected reference image. Specifically, the image processing unit 20 inspects the mask 30 by comparing the inspection image with the corrected reference image to calculate a difference and detecting a defect from the calculated difference. .. In this way, the mask 30 can be inspected.

Next, the effect of this embodiment will be described. The mask inspection apparatus 1 and the mask inspection method of this embodiment inspect the mask by comparing the reference image and the inspection image. Therefore, the pattern defect on the mask 30 can be accurately inspected.

In the present embodiment, when comparing the reference image and the inspection image, the brightness of each feature point of the reference image and the brightness of each feature point of the inspection image are referred to by reference to a lookup table. , The reference image is corrected. This corrects the reference image in consideration of the change in the condition of the mask 30 and the change in the condition of the detection optical system 10. Therefore, the pseudo defect and the original defect can be distinguished, and the mask 30 can be inspected with high accuracy. The change in the condition of the mask 30 is, for example, a difference in baseline luminance due to a change in mask reflectance or the like. The change in the condition of the detection optical system 10 is, for example, a pattern profile difference due to the change in the optical system.

Further, by automatically forming the lookup table, the inspection time can be shortened and the inspection cost can be reduced.

When performing correction, for example, a plurality of sections such as low brightness (D1, D2) to medium brightness (G1, G2), medium brightness (G1, G2) to high brightness (W1, W2). It is divided into two and corrected. Accordingly, by changing the inclination of the look-up table on the way, the correction value can be optimized for each range of the brightness value.

(Modification)
Next, a modified example of the embodiment will be described. In this modification, the detection optical system that acquires the reference image and the detection optical system that acquires the inspection image are different.

FIG. 8 is a flowchart illustrating the mask inspection method according to the modification of the embodiment. As shown in step S31 of FIG. 8, a reference image of the mask 30 is acquired using the first optical detection system. The method of acquiring the reference image is the same as step S11 of the embodiment.

Next, as shown in step S32, an inspection image of the mask 30 is acquired using the second detection optical system. Here, the second detection optical system is a device different from the first detection optical system. Then, an inspection image is acquired for the same mask 30 as the mask 30 for which the reference image was acquired by the first detection optical system, or for the mask 30 of the same design (lot: lot) in which the same pattern was carved. The method of acquiring the inspection image is the same as step S13 of the embodiment except that the second detection optical system different from the first detection optical system is used.

Next, as shown in step S33, each brightness of each characteristic part is extracted from the reference image. This step is the same as step S21 of the embodiment. Next, as shown in step S34, each luminance of each characteristic portion is extracted from the inspection image. This step is also the same as step S22 of the embodiment. Next, as shown in step S35, a table is created in which each brightness of each feature point of the reference image is associated with each brightness of each feature point of the inspection image, and the table is referenced as shown in step S36. Then, the brightness of the reference image is corrected. Then, as shown in step S37, the inspection image and the corrected reference image are compared to inspect the mask 30. Steps S35 to S37 are also similar to steps S23 to S25 of the embodiment.

According to this modification, it is possible to correct the difference between the devices of the first detection optical system and the second detection optical system different from the first detection optical system. Therefore, for example, the reference image acquired by the first detection optical system can be used for different mask inspection devices. Therefore, a plurality of mask inspection devices can be compared with each other, and the error between the devices can be reduced. Further, by unifying the reference images that serve as the reference, the mask can be inspected accurately at low cost. Other configurations and effects are included in the description of the embodiments.

Although the embodiments of the present invention have been described above, the present invention includes appropriate modifications without impairing the objects and advantages thereof, and is not limited by the above embodiments. Further, the configurations of the embodiment and the modified examples may be appropriately combined.

DESCRIPTION OF SYMBOLS 1 Mask inspection apparatus 10 Detection optical system 11 Beam splitter 12 Objective lens 13 Projection lens 14 Detector 20 Image processing unit 21 Processing unit 22 Storage unit 30 Mask 31 Pattern edge portion 32 Absorption film portion 33 Pattern portion 41 Line and space 42 Contact

Claims (6)

By detecting the reflected light illumination light reflected by the mask, to obtain a reference image of the mask,
Performing a predetermined process on the mask obtained the reference image,
A step of acquiring an inspection image of the mask by detecting the reflected light reflected by the mask where the illumination light has been subjected to the predetermined processing;
Inspecting the mask by comparing the reference image and the inspection image,
A mask inspection method. From the reference image, the first brightness of the first feature, the second brightness of the second feature having a brightness higher than the first brightness, and the third brightness of the third feature having a brightness higher than the second brightness. Extracting the brightness,
Extracting the fourth brightness of the first feature, the fifth brightness of the second feature, and the sixth brightness of the third feature from the inspection image;
Corresponding a plurality of luminances between the first luminance and the second luminance and a plurality of luminances between the fourth luminance and the fifth luminance, and from the second luminance to the third luminance Forming a table in which a plurality of luminances between the first luminance and the sixth luminance are associated with each other;
Correcting the brightness of the reference image with reference to the table,
Further equipped with,
The step of inspecting the mask compares the inspection image with the corrected reference image,
The mask inspection method according to claim 1. In the step of performing the predetermined processing,
The predetermined process is a process of cleaning the mask,
The mask inspection method according to claim 1. Acquiring a reference image of the mask by using a first detection optical system that detects reflected light of illumination light reflected by the mask;
A second detection optical system different from the first detection optical system is used, and the illumination light detects the reflected light reflected by the mask that has acquired the reference image, thereby acquiring an inspection image;
From the reference image, the first brightness of the first feature, the second brightness of the second feature having a brightness higher than the first brightness, and the third brightness of the third feature having a brightness higher than the second brightness. Extracting the brightness,
Extracting from the inspection image the fourth brightness of the first feature, the fifth brightness of the second feature, and the sixth brightness of the third feature.
Corresponding a plurality of luminances between the first luminance and the second luminance and a plurality of luminances between the fourth luminance and the fifth luminance, and from the second luminance to the third luminance Creating a table in which a plurality of brightnesses between the above and a plurality of brightnesses between the fifth brightness and the sixth brightness are associated with each other;
Correcting the brightness of the reference image with reference to the table,
Inspecting the mask by comparing the inspection image and the corrected reference image,
A mask inspection method comprising. While illuminating the mask with illumination light, a detection optical system for detecting the reflected light reflected by the mask illumination light,
Based on the reflected light detected by the detection optical system, while acquiring a reference image of the mask, the inspection image of the mask after performing a predetermined process on the mask that has acquired the reference image Image processing unit to acquire,
Equipped with
The image processing unit,
From the reference image, the first brightness of the first feature, the second brightness of the second feature having a brightness higher than the first brightness, and the third brightness of the third feature having a brightness higher than the second brightness. Extract the brightness,
From the inspection image, the fourth brightness of the first feature, the fifth brightness of the second feature, and the sixth brightness of the third feature are extracted,
Corresponding a plurality of luminances between the first luminance and the second luminance and a plurality of luminances between the fourth luminance and the fifth luminance, and from the second luminance to the third luminance And a plurality of brightnesses between the fifth brightness and the sixth brightness are made to correspond to each other,
Correct the reference image by referring to the table,
Inspecting the mask by comparing the inspection image with the corrected reference image,
Mask inspection device. The predetermined process is a process of cleaning the mask,
The mask inspection apparatus according to claim 5.

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