JPH0763692A - Method and apparatus for inspection of pattern defect - Google Patents

Abstract

PURPOSE:To discriminate a defect due to a drop in transmissivity from a permissible small defect and to detect them by a method wherein a difference image between inspection image data and reference image data is found, a level is judged on the basis of a threshold value with reference to the difference image, a difference between a picture element noticed and its adjacent picture element is found and the level is judged by another threshold value. CONSTITUTION:An object 2, to be inspected, on an X-Y table 1 is imaged 3, it is A/D-converted 4, inspection image data at a multivalue shading level is formed, and a shading conversion circuit 6 generates reference image data on the basis of the design data and the X-Y coordinates of the object 2 to be inspected. Then, the difference in level between the inspection image data and the reference image data is computed 5, and it is output as the difference image. A judgement circuit 10 takes in the difference image, and it outputs a position exceeding a threshold value as the high level. In addition, a difference between a picture element noticed and its adjacent picture element is computed 5, the level is judged 12 by another threshold value, and it is output. A detection circuit 13 logically multiplies individual judged results by the judgement circuits 10, 12, it discriminates a defect due to a drop in transmissivity from a permissible small defect, and it detects them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern defect inspection method and apparatus for detecting thin stains or the like on a test object such as a photomask having a pattern formed thereon as a defect.

[0002]

2. Description of the Related Art FIG. 8 is a block diagram of a pattern defect inspection apparatus. An object to be inspected 2 such as a photomask is placed on the XY table 1. An image pickup device 3 such as a line sensor is arranged above the XY table 1.

The image pickup device 3 picks up an image of the object to be inspected 2 and outputs an image signal thereof. This image signal is A / D.
It is digitally converted by the converter 4 and sent to the level difference calculation circuit 5 as inspection image data of multivalued light and shade levels.

On the other hand, the grayscale conversion circuit 6 takes in the design data of the object to be inspected 2 and the XY coordinates when an image is input by the image pickup device 3 by a laser interferometer (not shown), and uses these as the design data and the XY coordinates. Based on this, reference image data for the inspection image data is generated.

The level difference calculation circuit 5 takes in the inspection image data and the reference image data, compares the gray levels between these image data, and sends the difference image data as the comparison result to the determination circuit 7.

The judgment circuit 7 compares the difference image data with a constant threshold value, and if the difference image data is equal to or larger than the threshold value, it is judged as a pattern defect. In this case, the threshold value in the determination circuit 7 is set to a value according to the defect size.

Further, in the pattern defect inspection of the photomask, the transmittance of the pattern transmitting portion is lowered in the developing process for manufacturing the photomask, that is, the light is transmitted due to a thin stain in the pattern transmitting portion caused by an etching defect or the like. It is necessary to detect a decrease in the rate as a defect.

In the defect detection of such a decrease in transmittance,
The threshold value in the judgment circuit 7 must be strictly set to a very small value in order to detect the level of light contamination. If the threshold value is not set in this way, it is difficult to detect a decrease in transmittance due to thin stains as a defect, and there is a high possibility of overlooking. However, if the threshold value is strictly set to an extremely small value, even a defect of a small size that does not need to be detected as a defect due to a pattern remaining or the like will be detected.

[0009]

As described above, in order to detect the level of light contamination, it is difficult to detect a defect unless the threshold value is strictly set to an extremely small value. On the contrary, if the threshold value is strictly set to an extremely small value, even a defect of a small size that does not need to be detected as a defect will be detected.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pattern defect inspection method and apparatus capable of detecting a defect due to a decrease in transmittance separately from a defect having an allowable small size.

[0011]

According to claim 1, difference image data between inspection image data and reference image data is obtained,
A level determination is performed on the difference image data by a first threshold value, and a difference between the pixel of interest of the difference image data and an adjacent pixel is also determined, and a level determination is performed by the second threshold value. It is a pattern defect inspection method for determining a defect on the basis of the result to achieve the above object.

According to the second aspect of the present invention, the difference image data between the inspection image data and the reference image data is obtained, and the level of the difference image data is judged by the first threshold value. This is a pattern defect inspection method for attaining the above object by performing a level determination with a second threshold value after obtaining the difference between the pixel of interest and an adjacent pixel and determining a defect based on these determination results.

According to a third aspect of the present invention, there are provided an image pickup device for picking up an image of an object to be inspected, an inspection image forming means for forming inspection image data by receiving an image signal from the image pickup device, and reference image data for the inspection image data. A reference image generating means for generating, a level difference calculating means for obtaining difference image data between the inspection image data and the reference image data, and a first determining means for performing a level determination on the difference image data with a first threshold value. And an adjoining pixel difference calculating unit that obtains a difference between the target pixel of the difference image data and an adjoining pixel, and a second threshold value for the difference obtained by the adjoining pixel difference calculating unit based on a second threshold value. A pattern defect inspecting apparatus, which includes a determining unit and a detecting unit that detects a defect based on each determination result of the first and second determining units, to achieve the above object.

According to a fourth aspect of the present invention, there are provided an image pickup device for picking up an image of an object to be inspected, an inspection image forming means for forming inspection image data by receiving an image signal from the image pickup device, and reference image data for the inspection image data. A reference image generating means for generating, a level difference calculating means for obtaining difference image data between the inspection image data and the reference image data, and a first determining means for performing a level determination on the difference image data with a first threshold value. And an adjacent pixel difference calculating means for obtaining a difference between the target pixel of the inspection image data and the adjacent pixel, and a second threshold value for the difference obtained by the adjacent pixel difference calculating means based on the second threshold value. A pattern defect inspecting apparatus, which includes a judging means and a detecting means for detecting a defect based on the judgment results of the first and second judging means, and which is intended to achieve the above object.

[0015]

According to the first aspect, the difference image data between the inspection image data and the reference image data is obtained, and the difference image data is judged by the first threshold value. At the same time, the difference between the pixel of interest of the difference image data and the pixel in the vertical and horizontal directions of the pixel of interest, for example, is obtained, and thereafter, the determination is made from the second threshold value. Then, the defect is judged by the logical product of these judgment results.

According to the second aspect, the difference image data between the inspection image data and the reference image data is determined by the first threshold value. Along with this, the pixel of interest of the inspection image data is set and the difference from the adjacent pixel is obtained in the same manner as described above, after which the second threshold value is used for determination, and the defect is determined based on these determination results.

According to the third aspect of the present invention, the image of the object to be inspected is picked up by the image pickup device to generate the inspection image data, the reference image data is generated based on the design data, and then the inspection image data and the reference image data are generated. And the difference image data is obtained.

The difference image data is judged by the first threshold value, and at the same time, the difference between the pixel of interest of the difference image data, for example, the difference between the pixel of interest and the pixels in the vertical and horizontal directions is calculated. Judgment is performed using the second threshold value, and defects are detected based on these judgment results.

According to the fourth aspect, the inspection object is imaged by the image pickup device to generate the inspection image data, and the reference image data is generated based on the design data or the like. Thereafter, the inspection image data and the reference image data are generated. And the difference image data is obtained.

The difference image data is judged by the first threshold value, and at the same time, the difference between the pixel of interest in the inspection image data and the pixel in the vertical and horizontal directions of the pixel of interest is calculated. Judgment is performed using the second threshold value, and defects are detected based on these judgment results.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. The same parts as those in FIG. 8 are designated by the same reference numerals, and detailed description thereof will be omitted. FIG. 1 is a block diagram of a pattern defect inspection apparatus. The first determination circuit 10 is connected to the output terminal of the level difference calculation circuit 5.

The first judgment circuit 10 obtains the difference between the inspection image data and the reference image data sent from the level difference calculation circuit 5, and the difference image data is leveled by a first threshold value. It has a function of making a judgment and outputting a portion where the difference image data exceeds the first threshold value as a high level.

The adjacent pixel difference calculation circuit 11 is connected to the output terminal of the level difference calculation circuit 5. The adjacent pixel difference calculation circuit 11 has a function of obtaining a difference between an adjacent pixel of the difference image image data with respect to the target pixel, for example, each pixel on the upper, lower, left, and right sides of the target pixel.

The second judgment circuit 12 makes a level judgment on the data of the difference with the adjacent pixel sent from the adjacent pixel difference calculation circuit 11 by the second threshold value, and judges the difference with the adjacent pixel. It has a function of outputting a low level where the data exceeds the second threshold value.

The detection circuit 13 performs a logical product of the determination results from the first determination circuit 10 and the second determination circuit 12,
As a result of this logical product, it has a function of detecting a high level as a defect.

Next, the operation of the apparatus configured as described above will be described. The image pickup device 3 as a line sensor picks up an image of the inspection object 2 and outputs an image signal thereof. At this time, since the XY table 1 moves in the XY directions, the imaging device 3 consequently outputs the image signal while scanning the entire surface of the inspection object 2.

This image signal is digitally converted by the A / D converter 4 and becomes multi-valued gray level inspection image data. The inspection image data is, for example, as shown in FIG. 2 (a), an acceptable small size defect Gm, and a transmittance due to a thin stain in a pattern transmitting portion caused by an etching defect or the like in a developing process for manufacturing a photomask. Has a defect Go due to a decrease in Also, FIG.
(a) shows the change of the gray level at the position of the scan S in the inspection image data.

On the other hand, the grayscale conversion circuit 6 takes in the design data of the object 2 to be inspected and the XY coordinates when an image is input by the image pickup device 3 by a laser interferometer (not shown), and uses these as the design data and the XY coordinates. Based on this, reference image data for the inspection image data is generated.

This reference image data has, for example, the pattern shown in FIG. 2 (b), and FIG. 3 (b) shows the change in gray level at the same position as the position of the scan S in the inspection image data. ing.

Next, the level difference calculation circuit 5 takes in the inspection image data and the reference image data, compares the gray level difference between these image data, and sends the difference image data which is the result of this comparison. This difference image data is sent to the first determination circuit 10 and the adjacent pixel difference calculation circuit 11.

Of these, the first judgment circuit 10 takes in the difference image data from the level difference calculation circuit 5 and judges the level of the difference image data by the first threshold value.
The portion of the difference image data that exceeds the first threshold value is output as a high level.

For example, FIG. 4A shows a first threshold value for the difference image data at the scan S position, and FIG. 5A shows the result of the level judgment based on the first threshold value. As shown, a portion of the difference image data that exceeds the first threshold value is output as a high level.

On the other hand, the adjacent pixel difference calculation circuit 11 obtains the difference between the pixel of interest of the difference image image data and the adjacent pixels on the left, right, top and bottom. For example, the difference between the difference image data and the adjacent pixel in FIG. 4A will be described. The difference data between the difference image data and the adjacent pixel in the scan S direction is
As shown in (b) of the figure, it is at a high level where the gray level changes between adjacent pixels. Then, the data of the difference between these adjacent pixels is sent to the second determination circuit 12.

The second judging circuit 12 takes in the data of the difference from each adjacent pixel, judges the level of the data of the difference from the adjacent pixel by the second threshold value, and judges the difference between each adjacent pixel. A portion of the difference data exceeding the second threshold value is output as a low level.

For example, FIG. 4 (b) shows a second threshold value for the difference image data at the scan S position, and FIG. 5 (b) shows the result of level judgment based on this second threshold value. As shown, the portion of the difference image data which exceeds the second threshold value is output as a low level, that is, the second threshold value or less is output as a high level.

Next, the detection circuit 13 is the first determination circuit 10
AND the respective judgment results from the second judgment circuit 12, and as a result of the logical product, when it becomes a high level as shown in FIG. 6, the etching failure in the developing process for manufacturing the photomask, etc. Is detected as a defect Go due to a decrease in the transmittance due to thin stains in the pattern transmitting portion.

As described above, in the first embodiment, the difference image data between the inspection image data and the reference image data is obtained,
A level determination is performed on the difference image data with a first threshold value, and a level determination is performed with a second threshold value after obtaining the difference between the target pixel of the difference image data and an adjacent pixel. Since the defect is determined based on the determination result, there is a defect Go on the object 2 to be inspected due to a decrease in transmittance due to a thin stain in the pattern transmitting portion caused by etching or the like in a developing process for manufacturing a photomask. Even if the defect Gm has an acceptable small size, the defect Go due to the decrease in transmittance and the defect Gm due to the small size can be distinguished from each other, and only the defect Go due to the decrease in transmittance can be reliably detected.

Next, a second embodiment of the present invention will be described. The same parts as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. The adjacent pixel difference calculation circuit 20 uses A /
The D-converter 4 has a function of obtaining a difference between the pixel of interest of the inspection image data from the D converter 4, for example, each pixel on the upper, lower, left and right sides of the pixel of interest in the same manner as described above.

The second judgment circuit 21 judges the level of the difference data with respect to the adjacent pixel sent from the adjacent pixel difference calculation circuit 20 with the second threshold value, and the difference data with respect to the adjacent pixel. Has a function of outputting a portion where the second threshold value is exceeded as a low level.

Next, the operation of the apparatus configured as described above will be described. The image signal of the object 2 to be inspected, which is output from the image pickup device 3 as a line sensor, is digitally converted by the A / D converter 4 to become inspection image data of multivalued gray level.

As shown in FIG. 2 (a), this inspection image data has a defect Gm which is as small as allowed and a defect Go due to a decrease in transmittance. On the other hand, the grayscale conversion circuit 6 generates reference image data for the inspection image data based on the design data and the XY coordinates.

Next, the level difference calculation circuit 5 takes in the inspection image data and the reference image data, compares the gray level difference between these image data, and sends out the difference image data which is the comparison result.

At the same time, the adjacent pixel difference calculation circuit 20 obtains the difference between the pixel of interest of the inspection image data and the adjacent pixels in the vertical and horizontal directions. The first judgment circuit 10 takes in the difference image data from the level difference calculation circuit 5, judges the difference image data by a first threshold value, and exceeds the first threshold value of the difference image data. However, it is output as a high level.

Further, the second judgment circuit 21 takes in the data of the difference between the adjacent pixels and judges the level of the data of the difference between the adjacent pixels by the second threshold value, and judges the difference between the adjacent pixels. A portion of the difference data that exceeds the second threshold value is output as a low level.

Next, the detection circuit 13 is the first determination circuit 10
AND the respective judgment results from the second judgment circuit 21 are performed, and a high level is detected from the result of the logical product as a defect Go due to a decrease in transmittance.

As described above, in the second embodiment, the difference image data between the inspection image data and the reference image data is obtained,
The difference image data is level-determined by the first threshold value, and the level determination is performed by the second threshold value after obtaining the difference between the target pixel of the inspection image data and the adjacent pixel. Since the defect is determined based on the determination result, the inspected object 2 has the defect Go of reduced transmittance and the defect Gm of an acceptable small size as in the first embodiment. Also, the defect Go having a reduced transmittance and the defect Gm having a small size can be distinguished from each other to reliably detect only the defect Go due to a reduced transmittance.

The present invention is not limited to the above embodiments, and may be modified within the scope of the invention. In each of the above-described embodiments, only the defect Go due to the decrease in the transmittance is detected, but the determination circuit for detecting the pattern defect of the inspection object 2 with respect to the level difference calculation circuit 5 (for example, shown in FIG. 8). The judgment circuit 7) is connected to detect the pattern defect of the inspection object 2 and the defect Go due to the decrease of the transmittance.
May be performed together with the detection of

Further, the adjacent pixel difference calculation circuits 11 and 20 obtain the difference between the target pixel of the difference image data and the inspection image data with respect to the upper, lower, left, and right adjacent pixels, respectively. In addition to ± 45 ° to the pixel of interest
You may make it obtain | require the difference with four adjacent pixels in the diagonal direction. Further, the inspection object 2 is not limited to the photomask,
If a pattern is formed, it can be applied to detect the pattern defect.

[0049]

As described above in detail, according to the present invention, it is possible to provide a pattern defect inspection method and apparatus capable of detecting a defect caused by a decrease in transmittance separately from a defect having a small allowable size.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a pattern defect inspection apparatus according to the present invention.

FIG. 2 is a schematic diagram of inspection image data and reference image data.

FIG. 3 is a diagram showing a gray level change in inspection image data and reference image data.

FIG. 4 is a diagram showing a determination operation according to each threshold value of first and second determination circuits.

FIG. 5 is a diagram showing a determination result by first and second determination circuits.

FIG. 6 is a diagram showing a defect detection result.

FIG. 7 is a configuration diagram showing a second embodiment of the pattern defect inspection apparatus according to the present invention.

FIG. 8 is a configuration diagram of a conventional device.

[Explanation of symbols]

1 ... XY table, 2 ... Inspected object, 3 ... Imaging device, 4 ...
A / D converter, 5 ... Level difference calculation circuit, 10 ... First determination circuit, 11, 20 ... Adjacent pixel difference calculation circuit, 12, 21
... second determination circuit, 13 ... detection circuit.

Claims (4)

[Claims] 1. A difference image data between inspection image data and reference image data is obtained, a level judgment is performed on the difference image data by a first threshold value, and at the same time, the difference image data is adjacent to a pixel of interest. Second, finding the difference with the pixel
The pattern defect inspection method is characterized in that the level is judged based on the threshold value and the defect is judged based on these judgment results. 2. The difference image data between the inspection image data and the reference image data is obtained, and the level judgment is performed on the difference image data by a first threshold value. A pattern defect inspecting method, characterized in that after a difference from a pixel is obtained, a level judgment is performed by a second threshold value, and a defect is judged based on these judgment results. 3. An image pickup device for picking up an image of an object to be inspected, an inspection image creating means for creating inspection image data by receiving an image signal from the image pickup device, and a reference image for generating reference image data for the inspection image data. Generating means, level difference calculating means for obtaining difference image data between the inspection image data and the reference image data, and first determining means for performing level determination on the difference image data with a first threshold value. An adjoining pixel difference calculating means for obtaining a difference between the pixel of interest and the adjoining pixel of the difference image data;
A pattern defect comprising: a second judging means for making a level judgment based on the threshold value of 1; and a detecting means for detecting a defect based on each judgment result of the first and second judging means. Inspection device. 4. An image pickup device for picking up an image of an object to be inspected, an inspection image creating means for creating inspection image data by receiving an image signal from the image pickup device, and a reference image for generating reference image data for the inspection image data. Generating means, level difference calculating means for obtaining difference image data between the inspection image data and the reference image data, and first determining means for performing level determination on the difference image data with a first threshold value. An adjoining pixel difference calculating unit that obtains a difference between the target pixel of the inspection image data and an adjoining pixel;
A pattern defect comprising: a second judging means for making a level judgment based on the threshold value of 1; and a detecting means for detecting a defect based on the judgment results of the first and second judging means. Inspection device.