JP4591928B2 - Photomask defect inspection method and defect inspection apparatus - Google Patents

Description

  The present invention relates to a defect inspection method and a defect inspection apparatus for a photomask including a gray tone mask and a fine pattern.

In recent years, attempts have been made to reduce the number of masks using a gray-tone mask in the field of large LCD masks (Non-Patent Document 1: Monthly FPD Intelligence, May 1999).
Here, as shown in FIG. 6A, the gray tone mask has a light shielding portion 1, a transmission portion 2, and a gray tone portion 3 on a transparent substrate. The gray tone part 3 is an area in which a light shielding pattern 3a below the resolution limit of a large LCD exposure machine using a gray tone mask is formed, for example, and the transmission amount of light transmitted through this area is reduced. The film is formed for the purpose of selectively changing the film thickness of the photoresist by reducing the irradiation amount. Reference numeral 3b denotes a fine transmission portion that is less than the resolution limit of the exposure machine in the gray tone portion 3. Both the light-shielding portion 1 and the light-shielding pattern 3a are usually formed from films of the same thickness made of the same material such as chromium or a chromium compound. Both the transmissive portion 2 and the fine transmissive portion 3b are portions of the transparent substrate where a light-shielding film or the like is not formed on the transparent substrate.
The resolution limit of a large LCD exposure machine using a gray tone mask is about 3 μm for a stepper type exposure machine and about 4 μm for a mirror projection type exposure machine. For this reason, for example, in FIG. 6A, the space width of the transmission part 3b in the gray tone part 3 is set to less than 3 μm, and the line width of the light shielding pattern 3a below the resolution limit of the exposure machine is set to less than 3 μm. When the exposure is performed with the above-mentioned large LCD exposure machine, the exposure light passing through the gray tone portion 3 is insufficient in the exposure amount as a whole, so that the positive photoresist exposed through the gray tone portion 3 becomes thin. Just remain on the substrate. That is, since the resist can have a difference in solubility in the developer between the portion corresponding to the normal light-shielding portion 1 and the portion corresponding to the gray tone portion 3 depending on the exposure amount, the resist shape after development is shown in FIG. ), The portion 1 ′ corresponding to the normal light shielding portion 1 is, for example, about 1.3 μm, the portion 3 ′ corresponding to the gray tone portion 3 is, for example, about 0.3 μm, and the portion corresponding to the transmissive portion 2 is the resist. It becomes the part 2 'without. Then, the first etching of the substrate to be processed is performed in the portion 2 ′ without the resist, the resist in the thin portion 3 ′ corresponding to the gray tone portion 3 is removed by ashing or the like, and the second etching is performed in this portion. The process for two conventional masks is performed with one mask to reduce the number of masks.
Monthly FPD Intelligence, May 1999

Conventionally, as a mask inspection method including only a light shielding portion and a transmission portion, for example, there is a comparative inspection method in which mask patterns are compared with each other using two optical systems. The method will be specifically described below.
FIG. 7A shows a state in which a white defect 11 (pinhole) is generated in the light shielding portion 1 and a black defect 12 (spot) is generated in the transmission portion 2, and an arrow indicates one lens (hereinafter referred to as an upper lens) of the comparative inspection apparatus. This shows the state of scanning.
FIG. 7B shows a transmittance signal 13 obtained along the scanning line of the lens. The transmittance signal 13 is detected by, for example, a CCD line sensor disposed in each lens unit. The level of the transmittance signal 13 is B for the light shielding unit 1 and W for the transmission unit 2, and the transmittance of the light shielding unit 1 is set to 0% and the transmittance of the transmission unit 2 is set to 100%. The transmittance signal 13 is basically composed of a pattern edge line signal (pattern shape signal) generated at the edge of the pattern (boundary between the light shielding portion and the light transmitting portion), and is generated in the light shielding portion 1 when a defect occurs. A white defect signal 11 ′ and a black defect signal 12 ′ generated in the transmission part 2 appear.
FIG. 7 (3) shows a transmittance signal 13 ′ obtained by the other lens (hereinafter referred to as the lower lens) when the same pattern as in FIG. 7 (1) and no defect occurs.
FIG. 7 (4) shows a difference signal 14 obtained by subtracting (difference) the transmittance signals obtained by the respective lenses. More specifically, the difference signal is obtained by subtracting the transmittance signal 13 ′ of FIG. 7 (3) from the transmittance signal 13 of FIG. 7 (2). In the difference signal 14, the pattern edge line signal is removed from the transmittance signal of each lens, and only the pattern defect signals 11 ′ and 12 ′ are extracted.
FIG. 7 (5) shows that the difference signal 14 obtained by extracting only the pattern defect signal sets a threshold value necessary for extracting the defect of the light shielding portion 1 and the transmission portion 2, and the white defect is detected with the threshold value 15a on the plus side. A state in which black defects are respectively detected at the negative threshold 15b is shown. If the threshold value is lowered, the detection sensitivity increases, but it is necessary to set it to a level at which pseudo defects are not detected.
In order to determine what kind of defect has occurred in which lens, for example, the upper lens circuit compares it with the signal of the lower lens (subtracts the signal of the lower lens from the signal of the upper lens), and When a white defect occurs in the light shielding portion 1, a defect signal is output on the plus side when a black defect occurs in the transmission portion 2 of the upper lens, thereby detecting a white defect and a black defect on the upper lens ( FIG. 7 (2) to (5) above. Similarly, for example, in the circuit of the lower lens, the signal of the upper lens is compared (the signal of the upper lens is subtracted from the signal of the lower lens). When a black defect occurs in the transmission part 2 of the lens, a defect signal is output on the minus side, thereby detecting a white defect and a black defect in the lower lens.

The above-described conventional comparative inspection method is an apparatus for inspecting a conventional mask including only a light-shielding portion and a transmission portion, and thus is not suitable for inspecting a gray-tone mask having a gray-tone portion.
Specifically, the conventional comparative inspection method has the following problems in inspecting the gray tone mask.
That is, the defect signal in the gray tone portion is weak because the defect itself is minute, and when a conventional comparative inspection apparatus is used, it is difficult to detect unless the threshold value is lower than the threshold value used for the normal light shielding portion inspection. It is. However, for example, when the gray tone portion is a region where a fine pattern below the resolution limit of an exposure apparatus using a gray tone mask is formed, the gray tone portion corresponds to the fine pattern as shown in FIG. A unique base signal level (noise band) 16 is produced. In the comparison inspection, the transmittance signal obtained by each lens is subtracted (difference) to obtain a difference signal, and only the pattern defect signal is extracted, but there is a slight pattern deviation between the fine light-shielding patterns in the gray tone portion. If it occurs, the base signal level is amplified (up to 2 times), and what should not be a defect is detected as a defect (pseudo defect). There is a problem that inspection is not possible.
Furthermore, since the conventional comparative inspection is for inspecting white defects and black defects, it is difficult to perform the guarantee of transmittance, which is the most important element in the gray tone mask. That is, for example, in the entire mask area, the line width of the light-shielding pattern of the gray tone portion is under (large line width) or over (small line width) with respect to the design dimension and exceeds the allowable transmittance. When the transmissivity of the semi-transmissive film constituting the gray tone part exceeds the allowable value, the difference signal is obtained because the difference signal is obtained by subtracting the transmissivity signal obtained by each lens in the comparative inspection. Therefore, there is a problem that such a transmittance defect cannot be detected. This is a problem particularly when there is no shape defect in the gray tone portion. Furthermore, in the gray tone part, it is not necessary to detect a defect as long as the transmittance is within an allowable range. However, in the conventional comparative inspection, since it is detected as a shape defect, it was detected by the conventional inspection. In some cases, however, the transmittance is within an allowable range. As a result, even those that do not necessarily have to be detected as defects are detected, and there is a problem in the accuracy (ability) of inspection.
The same problem also occurs with photomasks having fine patterns such as TFT channel portion formation photomasks and photomasks having fine and high-precision patterns such as lines and spaces with a line width of 3 μm or less. I can say that. For example, in a photomask for forming a TFT channel, there is a tendency of pattern miniaturization at a rapid pace as the TFT channel portion is miniaturized. When such a pattern is also inspected using a conventional method, a pseudo defect due to vibration of the stage of the inspection machine or image displacement of the upper and lower lenses, and other pseudo defects peculiar to a fine pattern are generated. If the sensitivity is lowered to a level at which no defect is detected, there is a problem that the sensitivity at the defect detection guarantee level cannot be obtained.

In order to solve such a problem, the applicant first uses a threshold value of a transmittance defect provided in advance for a transmittance signal obtained by scanning a pattern in a mask, not by inspection by comparison. An application was filed for a method for detecting defects (hereinafter referred to as monocular transmittance inspection) (Japanese Patent Application No. 2001-244071).
Hereinafter, a specific example of this method will be described.
FIG. 9 (1) shows a case where no defect has occurred in any of the light shielding unit 1, the transmission unit 2, and the gray tone units 3, 5, and the arrows indicate the scanning direction (inspection direction) of the lens of the inspection apparatus. Show.
FIG. 9B shows the transmittance signal 7 obtained along the scanning direction. The transmittance signal has a transmittance of 0% at the light shielding portion 1, a transmittance of 100% at the transmission portion 2, and a transmittance of 50% at the gray tone portions 3 and 5.
Here, as shown in FIG. 9 (2), for example, threshold values of the transmittance defect in the gray tone portion (upper limit side 8a, lower limit side 8b) are provided, and when these threshold values are exceeded, the transmittance defect in the gray tone portion. Is determined to have occurred.
In this case, as shown in FIG. 9 (2), thresholds of transmittance defects in the normal light shielding part and the transmissive part (transmission part side 9a, light shielding part side 9b) are further provided, and light shielding is performed when these threshold values are exceeded. This is preferable because it is possible to simultaneously detect translucency defects such as a light-blocking deterioration defect in a light-shielding part and a light-transmitting deterioration defect in a transmission part by determining that a transmittance defect has occurred in a part or a transmission part. .
Furthermore, in this case, the transmittance defect areas 10a and 10b formed by the transmittance defect extraction thresholds 8a and 8b for the gray tone part and the transmittance defect extraction thresholds 9a and 9b for the normal light shielding part and the transmission part are used. The transmittance defect can be detected regardless of the inspection area. That is, if the transmittance defect areas 10a and 10b are entered, it can be determined that there is a transmittance defect regardless of the inspection area.
According to the above inspection method, the transmittance itself can be directly inspected, and therefore, the transmittance can be guaranteed in the gray tone portion.
In addition, since it is an inspection method that does not perform pattern recognition, it is possible to avoid problems (problems in which the threshold cannot be lowered) that are caused by peculiar pattern shapes at the time of fine pattern inspection, and therefore the threshold can be lowered. Thus, it is possible to obtain a sensitivity that satisfies the required accuracy (spec) of a photomask including a gray tone mask and a fine pattern.
In addition, since a transmittance defect extraction threshold provided in advance for the transmittance signal is used instead of a pattern defect signal based on pattern comparison, a fine pattern that becomes a problem by taking a difference signal between the transmittance signals in the comparison inspection Can avoid the problem of amplification of the base signal level peculiar to the problem (the problem that the threshold cannot be lowered), and therefore the threshold can be lowered, and the sensitivity that satisfies the required accuracy of the photomask including the gray-tone mask and fine pattern can be achieved. It is possible to obtain.
Furthermore, since a comparison object is not required, inspection with a single eye is possible. Furthermore, by changing the transmittance defect extraction threshold value for the gray tone portion, it is possible to guarantee the transmittance according to the exposure conditions of the gray tone mask used by the user.

  However, in the monocular transmittance inspection in which the transmittance itself is directly inspected using the single transmittance signal and the transmittance defect extraction threshold as described above, since the inspection method does not perform pattern recognition, the light shielding portion and the transmissive portion It is difficult to inspect shape defects (white defects, black defects). Therefore, in order to perform high-precision inspection in a gray-tone mask having a light-shielding portion, a light-transmitting portion, and a gray-tone portion, it is necessary to perform both a comparative inspection with pattern recognition and a transmittance inspection without pattern recognition. There is a problem that a lot of inspection time is required. The same problem applies to, for example, a photomask having a fine pattern such as a TFT channel portion forming photomask, or a photomask having a fine and high-precision pattern such as a line and space having a line width of 3 μm or less.

  The present invention has been made to solve the above-described problems, and can perform defect inspection with high accuracy in a short time in a gray tone mask having a light shielding portion, a transmission portion, and a gray tone portion. It is an object to provide a method and apparatus that can.

The present invention has the following configuration.
(Structure 1) A light-shielding portion, a transmission portion, and a region in which the transmission amount is adjusted, and is a gray for the purpose of selectively changing the thickness of the photoresist by reducing the transmission amount of light transmitted through this region. A gray-tone mask defect inspection method having a tone portion,
For at least the region where the light-shielding part and the transmission part are formed, the transmittance signal obtained by scanning the pattern in the mask is used, and the pattern defect threshold value provided in advance for the pattern defect signal based on the pattern comparison is used. Detect defects by comparative inspection methods that detect defects,
At least for the gray tone portion, a gray tone mask is characterized in that a defect is detected by a method of detecting a defect using a threshold value of a transmittance defect provided in advance for a transmittance signal obtained by scanning a pattern in the mask. Defect inspection method.
(Structure 2) The gray-tone mask defect inspection method according to Structure 1, wherein the gray-tone portion is formed of a region where a light-shielding pattern equal to or less than a resolution limit of an exposure machine using a gray-tone mask is formed.
(Configuration 3) A photomask defect inspection method having a light-shielding portion, a transmission portion, and a fine pattern portion,
For at least the region where the light-shielding part and the transmission part are formed, the transmittance signal obtained by scanning the pattern in the mask is used, and the pattern defect threshold value provided in advance for the pattern defect signal based on the pattern comparison is used. Detect defects by comparative inspection methods that detect defects,
At least for a fine pattern portion, a defect is detected by a method of detecting a defect using a threshold value of a transmittance defect provided in advance for a transmittance signal obtained by scanning a pattern in the mask. Defect inspection method.
(Structure 4) The photomask defect inspection method according to Structure 3, wherein the fine pattern portion is a fine pattern that is difficult to compare and inspect.
(Structure 5) The inspection in the gray tone portion is performed separately and independently when the transmittance signal obtained by scanning the pattern in the mask is obtained by using a plurality of transmittance detecting means. The defect inspection method for a photomask according to any one of configurations 1 to 4, wherein
(Configuration 6) A light-shielding portion, a transmission portion, and a region in which the amount of transmission is adjusted. The gray is intended to selectively change the film thickness of the photoresist by reducing the amount of light transmitted through this region. A gray-tone mask defect inspection apparatus having a tone portion,
Means for scanning a pattern formed in the mask and detecting a transmittance signal;
Means for identifying which region is a light-shielding portion, a transmission portion and a gray-tone portion;
For at least the region where the light-shielding part and the transmission part are formed, the transmittance signal obtained by scanning the pattern in the mask is used, and the pattern defect threshold value provided in advance for the pattern defect signal based on the pattern comparison is used. Means for detecting defects by a comparative inspection method for detecting defects,
At least for the gray tone portion, a means for detecting a defect by a technique for detecting a defect using a threshold value of a transmittance defect provided in advance for a transmittance signal obtained by scanning the pattern in the mask;
A defect inspection apparatus comprising:
(Configuration 7) A photomask defect inspection apparatus having a light shielding part, a transmission part, and a fine pattern part,
Means for scanning a pattern formed in the mask and detecting a transmittance signal;
Means for identifying which region is the light-shielding portion, the transmission portion and the fine pattern portion;
For at least the region where the light-shielding part and the transmission part are formed, the transmittance signal obtained by scanning the pattern in the mask is used, and the pattern defect threshold value provided in advance for the pattern defect signal based on the pattern comparison is used. Means for detecting defects by a comparative inspection method for detecting defects,
Means for detecting a defect by a technique for detecting a defect using a threshold value of a transmittance defect provided in advance for a transmittance signal obtained by scanning a pattern in the mask at least for a fine pattern portion;
A defect inspection apparatus comprising:
(Structure 8) A method for producing a gray-tone mask, comprising a defect inspection step of performing a defect inspection using the method according to Structure 1 or 2.
(Structure 9) A photomask manufacturing method comprising a defect inspection step of performing a defect inspection using the method according to Structure 3 or 4.

(Embodiment of the Invention)
First, the inspection method of the present invention will be described with reference to FIG.
Step 1: A transmittance signal of a gray tone mask having a light shielding portion, a light transmitting portion, and a gray tone portion is obtained.
Step 2: The transmittance signal obtained in Step 1 is input to a defect determination circuit for comparison inspection, and comparison inspection is performed.
Step 3: The transmittance signal obtained in Step 1 is identified as the transmittance signal of the light-shielding portion / light-transmitting portion or the gray tone portion, and only the transmittance signal at the gray tone level is extracted.
Step 4: The transmittance signal extracted in Step 3 is input to a defect determination circuit for transmittance inspection, and the transmittance inspection is performed.

Step 1 will be described in detail.
In this step, a transmittance signal that can be used for the comparative inspection in step 2 is obtained. That is, when the comparison inspection in the process 2 is an inspection for comparing the same patterns in the same mask, each transmittance signal of the same pattern to be compared is detected using two transmittance detection means (two lines). When the comparative inspection in step 2 is an inspection for comparing the pattern and data, the transmittance signal of the pattern is obtained by one transmittance detecting means (one lens).

Next, in step 2, for example, a normal comparison inspection such as a comparison inspection for comparing patterns as described below is performed.
FIG. 2A shows a state in which a white defect 4 (pinhole) is generated in the light shielding portion 1, a black defect 5 (spot) is generated in the transmission portion 2, and a white defect 6 (pattern missing) is generated in the gray tone portion 3. Indicates a scanning state of one lens (upper lens) of the comparative inspection apparatus.
FIG. 2 (2) shows the transmittance signal 7 obtained along the scanning line. Seven levels of the transmittance signal are B for the light shielding portion 1, W for the transmission portion 2, and G for the gray tone portion 3. The transmittance of the light shielding portion 1 is 0%, and the transmittance of the transmission portion 2 is 100%. Set each. The transmittance signal 7 is basically composed of a pattern edge line signal (pattern shape signal) generated at the edge of the pattern (each boundary between the light shielding portion, the transmission portion, and the gray tone portion), and when a defect occurs, the light shielding portion. The white defect signal 4 ′ generated in 1, the black defect signal 5 ′ generated in the transmission part 2, the white defect signal 6 ′ generated in the gray tone part 3, etc. appear.
FIG. 2 (3) shows the transmittance signal 7 ′ obtained with the other lens (lower lens) when the same pattern as in FIG. 2 (1) and no defect occurs. Since the gray tone portion 3 is a fine L & S pattern, a base signal level 6 ″ (noise band) specific to the gray tone portion is generated as shown in FIG. 8 corresponding to this fine pattern.
FIG. 2 (4) is a difference signal obtained by subtracting (difference) the transmittance signals obtained by the respective lenses. More specifically, the difference signal 8 is obtained by subtracting the transmission amount signal 7 ′ in FIG. 2 (3) from the transmission signal 7 in FIG. 2 (2). In the difference signal 8, the pattern edge line signal is removed from the transmission amount signal of each lens, and only the pattern defect signals 4 ′, 5 ′, and 6 ′ are extracted.
FIG. 2 (5) shows a state in which threshold values (plus side 9a, minus side 9b) necessary for extracting defects in the light shielding portion 1 and the transmissive portion 2 are set in the difference signal 8 obtained by extracting only the pattern defect signal. Show. Here, the defect of the gray tone part 3 cannot be extracted.

Next, step 3 will be described in detail.
As a method for identifying which region is a light shielding portion / transmission portion and a gray tone portion, for example, based on the transmittance signal obtained in step 1, the level of the transmittance signal in any lens is There is a method of identifying whether the light is at the light shielding part level (transmittance 0%), the transmissive part level (transmittance 100%), or the gray tone level (transmittance around 50%). FIG. 3A shows a photomask having a light shielding part, a transmission part, and a gray tone part, and an arrow indicates a scanning direction (inspection direction) of a lens of the inspection apparatus. Here, as shown in FIG. 3 (2), a certain intermediate-range transmittance is set as a gray-tone region extraction threshold value, and a transmittance signal 7 not exceeding the threshold value is a gray-tone region transmittance signal. Extract as
Note that the transmittance defect extraction threshold value is preferably set to a level exceeding the base signal level 16 specific to the gray tone portion shown in FIG. Thereby, the influence of the base signal level peculiar to the gray tone part can be eliminated. In this case, it is preferable that the transmittance defect extraction threshold is set based on the center value of the base signal level 16. In addition, by setting the transmittance defect extraction threshold at the upper limit and the lower limit of the allowable transmittance of the gray tone portion, the transmittance of the gray tone portion can be guaranteed.

Next, the inspection performed in step 4 is as follows.
In step 4, the following inspection is performed for one transmittance signal in the case of one lens, and the following inspection is separately performed for each transmittance signal in the case of two lenses.
Regarding the transmittance signal extracted in step 3, FIG. 4A shows a case where no defect is generated in the gray tone portion, and an arrow indicates a scanning direction (inspection direction) of the lens of the inspection apparatus. FIG. 4B shows the transmittance signal 7 obtained along the scanning direction. The transmittance signal is, for example, a transmittance of 50% in the gray tone portion. Then, as shown in FIG. 4 (2), for example, threshold values of the transmittance defect in the gray tone portion (upper limit side 8a, lower limit side 8b) are provided, and when these threshold values are exceeded, the transmittance defect is detected in the gray tone portion. Judge that it occurred.
FIG. 5 (1) shows a case where there is a defect in the gray tone portion. As shown in FIG. 5 (2), a change appears in the transmittance level of the defective portion. If it exceeds, it is determined that a transmittance defect has occurred in the gray tone portion.

  In the above, Step 2 and Steps 3 to 4 can be performed simultaneously with the same apparatus.

Next, the inspection apparatus of the present invention will be described.
The inspection apparatus of the present invention has means for scanning a pattern formed in a mask and detecting a transmittance signal.
Specifically, for example, a lens provided on one side of the mask, a parallel light source provided on the other side of the mask (a spot light source corresponding to the lens or a mask full-surface irradiation light source), and the mask and the lens are relative to each other. And a means for scanning the entire area of the mask (usually a mask stage moving means). The pattern formed in the mask is scanned by the parallel light source and the light receiving lens, and is arranged in each lens unit, for example. The transmittance signal is detected by the CCD line sensor.
The inspection apparatus of the present invention includes a monocular inspection machine having one lens and a compound eye inspection machine having two or more lenses. In the case of a compound eye inspection machine, for example, the same pattern portion formed in the mask is scanned with two lenses, respectively, and a transmittance signal corresponding to each lens is detected, and the same pattern formed in the mask. It has a mechanism for aligning each lens with the pattern portion.
The apparatus of the present invention has a defect determination circuit for comparison inspection. Specifically, when inspecting by comparing patterns, a circuit for obtaining a difference signal by subtracting (differing) two transmittance signals obtained by two transmittance detection means (two lenses). (Difference circuit). When the comparison inspection is an inspection for comparing the pattern and the data, one transmittance signal obtained by one transmittance detecting means (one lens) and the data are subtracted (differed) from each other to obtain a difference signal. The circuit to obtain (difference circuit). In the defect determination circuit for comparative inspection, inspection is performed on at least a region where the light shielding portion and the transmission portion are formed.
Furthermore, the apparatus of the present invention has a defect determination circuit for transmittance inspection. In the defect determination circuit for transmittance inspection, at least the gray tone portion is inspected. Specifically, when the transmittance signal in the gray tone region enters the transmittance defect area for the gray tone portion, it is determined that the transmittance defect is in the gray tone portion. In the case of a monocular inspection machine, one defect determination circuit for transmittance inspection is provided for one transmittance signal obtained by one lens. In the case of a compound eye inspection machine, two defect determination circuits for transmittance inspection are provided in order to separately and independently inspect two transmittance signals obtained by two lenses.
The apparatus of the present invention has means (for example, an identification circuit) for identifying which region is a light shielding portion / transmission portion or a gray tone portion.

The present invention is not limited to the above-described embodiment.
For example, the present invention can be applied even when the gray tone portion is formed of a semi-permeable membrane.
In the above embodiment, the inspection of the gray tone portion of the gray tone mask has been described. However, the present invention is not limited thereto, and a fine pattern similar to that of the gray tone portion, such as a photomask for forming a TFT channel portion, may be used. It is applicable also to the photomask containing.
Further, in the present invention, when the transmittance signal obtained by scanning the gray tone portion as shown in FIG. 10 (1) has a periodic variation as shown in FIG. 10 (2), the signal is flattened. By performing the blurring process to achieve the same, a transmittance signal as shown in FIG. 10 (3) can be obtained, and a uniform transmittance signal of, for example, about 50%, which is the original transmittance characteristic, can be obtained. . The blurring process of the present invention is a process of blurring the obtained signal at a point where the signal is flattened most in the measurement region. This blurring process is a blurring function conventionally used in image processing. Etc. can be used. Then, by performing a transmittance defect inspection based on the blurred signal, a photomask including a gray-tone portion and a fine pattern of the gray-tone mask is detected as a pseudo-defect in the transmittance signal when the blur processing is not performed. It is possible to inspect without detecting a portion that has been processed as a pseudo defect. Therefore, it is possible to guarantee the transmittance of a portion that is detected as a pseudo defect in the transmittance signal when the blurring process is not performed. In addition, for photomasks containing gray-tone parts and fine patterns of gray-tone masks, detection of transmittance defects based on line width errors and minute protrusions at locations that are detected as pseudo-defects in the transmittance signal without blurring It becomes possible to detect a transmittance defect based on the defect.

  In the case of a gray-tone mask for LCD production, since the size is large and the inspection takes time, it is not practical in an inspection method in which both a comparative inspection and a transmittance inspection are performed separately. Therefore, the defect inspection of the present invention is not practical. The method is indispensable for putting a gray tone mask for LCD production into practical use. This is not limited to LCD (liquid crystal display) manufacturing masks, but other display devices, photomasks having fine patterns such as photomasks for forming TFT channel portions, and lines and spaces having a line width of 3 μm or less. The same applies to a photomask having such a fine and highly accurate pattern. Here, the LCD manufacturing mask includes all masks necessary for manufacturing the LCD, for example, a mask for forming a TFT (thin film transistor), a low-temperature polysilicon TFT, a color filter, and the like. Other display device manufacturing masks include all masks necessary for manufacturing organic EL (electroluminescence) displays, plasma displays, and the like. The photomask including a fine pattern is a photomask for LCD production, a display device production photomask such as an organic EL display and a plasma display, and a fine pattern for forming a TFT channel portion, a contact hole portion, etc. And a photomask having

(The invention's effect)
As described above, according to the present invention, it is possible to provide a method and apparatus capable of performing a defect inspection with high accuracy in a short time in a gray tone mask having a light shielding portion, a transmission portion, and a gray tone portion. .

It is a figure for demonstrating the outline | summary of the defect inspection method of this invention. It is a figure for demonstrating the process 2 in embodiment. It is a figure for demonstrating the process 3 in embodiment. It is a figure for demonstrating the process 4 (when there is no defect) in embodiment. It is a figure for demonstrating the process 4 (when there exists a defect) in embodiment. It is a figure for demonstrating a gray tone mask, (1) is a fragmentary top view, (2) is a fragmentary sectional view. It is a figure for demonstrating the conventional defect inspection method. It is a figure for demonstrating the base signal level peculiar to a gray tone part. It is a figure for demonstrating the defect inspection method which concerns on the previous application by the present applicant. It is a figure for demonstrating the blurring process of the transmittance | permeability signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light-shielding part 2 Transmission part 3 Gray tone part 3a Light-shielding pattern 3b Transmission part 3c Semi-transmissive film 5 Gray tone part 7 Transmission signal 8 Difference signal 8a Transmission defect extraction threshold value (upper limit) for gray tone part
8b Transmissivity defect extraction threshold for gray tone part (lower limit)
9a Transmittance defect extraction threshold for transmission part 9b Transmittance defect extraction threshold for light shielding part 11 White defect 12 Black defect 13 Transmission signal

Claims (10)

A photomask defect inspection method having a light shielding portion, a transmission portion, and a fine pattern portion,
Scan the pattern in the photomask having the light shielding part, the light transmitting part, and the fine pattern part to obtain a transmittance signal,
For at least the region where the light shielding part and the transmission part are formed, the threshold value of the pattern defect provided in advance is determined by the difference signal of the transmittance signal based on the comparison between the same patterns in the mask or the comparison between the pattern and the data. Detect defects using comparative inspection techniques to detect defects,
A defect inspection method for a photomask, wherein at least a fine pattern portion detects a defect by a method of detecting a defect using a threshold value of a transmittance defect provided in advance for the transmittance signal by the transmittance signal .   When obtaining the transmittance signal by the scanning, each transmittance signal of the same pattern to be compared in the same mask is detected by two transmittance detecting means,
  The difference signal of the transmittance signal based on the comparison between the same patterns is used as the difference signal of the detected two transmittance signals.
The photomask defect inspection method according to claim 1, wherein:   When obtaining the transmittance signal by the scanning, one transmittance signal is detected using one transmittance detecting means,
  The difference signal of the transmittance signal based on the comparison between the pattern and the data is a difference signal based on the comparison between the one transmittance signal and the data.
The photomask defect inspection method according to claim 1, wherein:   The photomask defect inspection method according to claim 1, wherein the fine pattern portion has a pattern with a line width of 3 μm or less.   The photomask defect inspection method according to claim 1, wherein the photomask is a photomask for forming a TFT channel portion or a contact hole portion.   6. The method according to claim 1, further comprising: identifying a transmission signal of a light-shielding portion, a transmission portion, or a fine pattern portion for the transmittance signal obtained by scanning the pattern in the photomask. The photomask defect inspection method according to one item.   The defect detection method for a photomask according to any one of claims 1 to 6, wherein the defect detection by the comparative inspection method and the defect detection using a threshold of the transmittance defect are performed simultaneously. A photomask defect inspection apparatus having a light shielding part, a transmission part, and a fine pattern part,
Means for scanning a pattern formed in the mask and detecting a transmittance signal;
Means for identifying which region is the light-shielding portion, the transmission portion and the fine pattern portion;
At least for the region where the light shielding part and the transmission part are formed, the transmittance signal obtained by scanning the pattern in the mask is used, and the comparison is made between the same patterns in the mask or the comparison between the pattern and the data. Means for detecting a defect by a comparison inspection method for detecting a defect using a threshold value of a pattern defect provided in advance by a difference signal of the transmittance signal ;
At least for the fine pattern portion, means for detecting a defect by a technique for detecting a defect using a threshold value of a transmittance defect provided in advance for the transmittance signal by the transmittance signal;
A defect inspection apparatus comprising:   The defect inspection apparatus according to claim 8, comprising means for performing a blurring process for flattening the signal on the transmittance signal. A method for producing a photomask, comprising a defect inspection step of performing a defect inspection using the method according to claim 1 .

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