JPH05281154A - Inspection apparatus for defect of pattern - Google Patents

Abstract

PURPOSE:To eliminate the erroneous defect detection caused by the position deviations of both patterns by providing a means for inputting the two-dimensional images a material to be measured and a reference pattern, a region cutting-out means, a means, which aligns the position of the pattern of a specified region, and a defect judging means. CONSTITUTION:The design data, which ate read out of a magnetic switch disk device 11, are transferred into a DMA memory 12. After the data are developed into the bit images with a bit developing circuit 13, the images are stored in a bit memory map 14. The stored bit image data are read out with a characteristic extracting circuit 15 and read out with a reference-data forming circuit 16. The circuit 16 forms the reference pattern data in many gradations by using the read-out 14 data and the other position data, which are read out of table-position-coordinate memory 17. Meanwhile, the output of a CCD sensor 18 is converted into the pattern data to be inspected in many gradations through an A/D converter 19. Both pattern data are sent into a comparing circuit 21 through a buffer memory 20. The circuit 21 aligns the positions of both patterns in reference to the output of the circuit 15, extracts the direction of the edge of the reference Pattern, judges the defect and outputs the defect data into an output device 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting a pattern defect of a sample having a pattern such as a photomask used in a manufacturing process of a semiconductor integrated circuit.

[0002]

2. Description of the Related Art In a pattern defect inspection apparatus of this type, usually, a pattern to be inspected obtained as image data is compared with a reference pattern made from design data, and a mismatched portion is detected as a defect. Has been adopted.

This method is more reliable than the method of comparing two adjacent patterns to be inspected (die-to-die method), but on the other hand, due to alignment error, circuit pattern line width error, corner rounding, etc. When the pattern to be inspected and the design pattern are relatively misaligned, there is a possibility that a defect may be erroneously detected especially near the edges or corners of the circuit pattern.

[0004]

As described above, in the conventional pattern defect inspection apparatus which detects a defect by comparing the reference pattern with the pattern to be inspected, even the positional deviation between the reference pattern and the pattern to be inspected is detected. Also had the problem of detecting it as a defect.

Therefore, an object of the present invention is to provide a pattern defect inspection apparatus capable of eliminating erroneous defect detection due to the positional deviation of both patterns and capable of highly reliable defect detection.

[0006]

In order to achieve the above object, in a pattern defect apparatus according to the present invention, means for inputting a two-dimensional image of a pattern to be inspected and a reference pattern,
Means for cutting out a first area of the pattern to be inspected and a second area surrounding the first area, and means for cutting out a third area of the reference pattern and a fourth area surrounding the third area. , Means for aligning the pattern of the fourth area with the second area, and means for obtaining a fifth area of the third area aligned with the first area , Means for determining defects in the first area and the fifth area.

[0007]

In this structure, the pattern to be inspected and the reference pattern are aligned in the area outside the inspection area, and both patterns in the inspection area are position-corrected. Defects can be accurately detected even at edges and corners.

[0008]

Embodiments will be described below with reference to the drawings.

FIG. 1 shows a schematic structure of a pattern defect inspection apparatus according to an embodiment of the present invention.

Reference numeral 11 in the drawing denotes a magnetic disk device which stores design data used when forming a pattern. The design data read from the magnetic disk device 11 is DMA-transferred to the DMA memory 12, subsequently expanded into a bit image by the bit expansion circuit 13, and then stored in the bitmap memory 14.

The bit image data stored in the bit map memory 14 is read by the feature extraction circuit 15 and the reference data generation circuit 16. The reference data generation circuit 16 uses the data read from the bit map memory 14 and the position data read from the table position coordinate memory 16 to generate multi-tone reference pattern data. The table position coordinate memory 16 stores the position data of a table that supports a photomask to be inspected, which will be described later. Further, in generating the multi-tone reference pattern data, for example, Japanese Patent Publication No. 59-6372.
A method similar to the method shown in Japanese Patent Publication No. 5 is adopted.

On the other hand, reference numeral 18 in the drawing denotes a CCD sensor which receives an optical image of a pattern drawn on an inspected photomask (not shown) supported by a table (not shown) and converts the light intensity distribution into an electric signal. There is. The output of the CCD sensor 18 is converted into multi-tone inspected pattern data via the A / D converter 19. Then, the reference pattern data generated by the reference data generation circuit 16 and the A / D
The inspection pattern data output from the converter 19 is sent to the comparison circuit 21 via the buffer memory 20.

The comparison circuit 21 compares the reference pattern data with the pattern data to be inspected while referring to the output of the feature extraction circuit 15, and outputs defect information to the output device 22 when a defect is detected.

Here, the comparison circuit 21 compares the reference pattern data with the pattern data to be inspected as follows. That is, the comparison in the comparison circuit 21 is made up of three stages. In the first stage, the pattern to be inspected and the reference pattern are aligned, in the second stage, the edge direction of the reference pattern is extracted, and the third stage is extracted. Defect determination is performed in stages. Specifically, the following method is adopted.

First, as shown in FIG. 2A, a 6 × 6 window-shaped region is cut out from the pattern to be inspected. The window is not limited to the size of 6 × 6. From this 6 × 6 area to the central 4 × as the inspection area
The rectangular first region 23 of 4 and the annular second region 24 along the four sides of the first region 23 are cut out as alignment regions.

Further, with respect to the pattern to be inspected, the horizontal and vertical ±
8x8 from the reference pattern, assuming a position shift of 1 pixel
Cut out the window-shaped area of. From this area, there are also 9 patterns as a pattern in which the third area of 4 × 4 rectangular shape as the inspection area and the fourth area along the four sides of the third area as the alignment area are moved vertically and horizontally ± 1 pixel. cut.

Next, the inspected pattern and the reference pattern are aligned using the second region 24 set in the inspected pattern and the fourth region set in the reference pattern. As this method, as shown by 25 in FIG. 2 (b), the filter calculation of (+1, -1, -1, +1) is performed on the four pixels on the left side and the right side of the second and fourth regions. Vertically. That is, if the tone of (i, j) pixels is f _ij , the tone of the corresponding 4 pixels is (f _ij , f _{i + 1, j} , f
_{i + 2, j} , f _{i + 3, j} ) and f _ij −f _{i + 1, j} −f _{i + 2, j}
+ F _{i + 3, j} is the filter output, and the edges are f _ij and f
negatively if during _{i + 1, j,} zero if between f i _{+ 1, j} and f _{i + 2, j,} if during the _{f i + 2, j f i} + 3, j Takes a positive value.
Here, there is no difference between f _{ij and} binary.

The four pixels on the upper and lower sides are arranged in the horizontal direction. That is, the gradation of the corresponding 4 pixels is (g _ij , g
_{i, j + 1} , g _{i, j + 2} , g _{i, j + 3} ), g _ij −g
_{i, j + 1} −g _{i, j + 2} + g _{i, j + 3} is the filter output, and if the edge is between g _ij and g _{i, j + 1} , it is negative, and g _{i, j + 1} and g
_i, zero if between _{j + 2, g i, j} + 2 and g _i, a positive value if during the _{j + 3.} Therefore, the position of the edge can be obtained by this filter processing.

In this way, the edge positions on the four sides are obtained for the pattern to be inspected and the reference pattern, then the difference between the edge positions on the four sides of both patterns is obtained, and the sum of their absolute values (or squared) is obtained. Take the sum. That is, the alignment is performed at the position where the sum of absolute values (or the sum of squares) is the smallest among the nine candidates. In this way, one of the third regions of the reference pattern is selected and aligned with the first region 23 of the pattern to be inspected. The aligned third region will be referred to as a fifth region.

Next, a method for obtaining the edge direction will be described. Although the direction of the edge is not limited to the horizontal and vertical directions, an example of the vertical and horizontal directions will be described below. In order to select whether the edge is in the horizontal direction or the vertical direction, a filter for differentiating the horizontal direction and the vertical direction is applied, and the one having the smaller absolute value may be taken. 3 (a) and 3 (b) show a filter 26 for differentiating in the horizontal direction and a filter 27 for differentiating in the vertical direction in the fifth region. For example, the filter 26 is smaller than the filter 27 at the edge in the horizontal direction.

Next, a method for detecting defects will be described. In the first and third regions, the horizontal filter 28 shown in FIG. 3 (c) is used when the edge direction of the fifth region is horizontal, and the horizontal filter 28 shown in FIG. 3 (d) is used when it is vertical.
The vertical filter 29 shown in is selected. This filter is applied to the pattern to be inspected and the reference pattern, the absolute value of the difference between them is taken, and when this exceeds a threshold value, it is judged as a defect. When the filter is applied in the edge direction, it becomes 0 when there is no defect. Therefore, by matching the direction of the filter with the direction of the edge, it is possible to prevent erroneous detection due to displacement.

It is also conceivable to add means for extracting features such as edges and corners in a plurality of directions from the reference pattern, and means for changing the threshold value according to the above features. The method disclosed in Japanese Patent Application No. 2-46227 may be used as the feature extraction method.

FIG. 4 is a schematic diagram for explaining the operation of the pattern defect inspection apparatus. The detection of a defect at a right-angled corner will be described with reference to this figure.

Corner edges are formed on the lower side and the right side of the second and fourth regions. The positions of the pattern edges on the four sides are obtained by the filter 25 shown in FIG. Reference numerals 30 to 38 are vertical and horizontal ± 1 pixel shifted reference patterns, 39 to 40 are inspection patterns, 39 is a defect-free pattern, and 40 is a defect in the corner portion.

The condition that the sum of the absolute values of the differences in the positions of the pattern edges on the four sides is the minimum is the condition indicated by 30 where the edges on the right side and the lower side coincide, and in this case, 30 is selected. Since the alignment is performed outside the inspection area as described above, the alignment can be accurately performed regardless of the presence or absence of the defect, and the reference pattern is not aligned with the defect, and the corner portion is minute. Even defects can be detected.

FIG. 5 shows an example of the result of the inspection performed by the pattern defect inspection apparatus having the above structure. Inspected pattern 4
1 and the reference pattern 42 correspond to the pattern 39 to be inspected and the reference pattern 30 in FIG. 4, and the numerical values from 0 to 10 represent the gradation. The pattern 41 to be inspected has no defect. In addition, the pixel is shifted to the upper left by one pixel with respect to the reference pattern 42, and the pattern 41 to be inspected has noise.

The inspected pattern 43 and the reference pattern 44 correspond to the inspected pattern 40 and the reference pattern 30, respectively. The pattern 43 to be inspected has a defect at the corner. The other conditions, that is, the pattern 43 to be inspected is shifted to the upper left of one pixel with respect to the reference pattern 44, and the noise on the pattern 43 to be inspected is the same.

The defect detection signal is output as shown in FIG. That is, (a) is the distribution output 45 when there is no defect.
And (b) shows the distribution output 46 when there is a defect in the corner portion. Further, FIG. 7 shows a histogram in which the horizontal axis represents the defect detection signal and the vertical axis represents the appearance frequency. When there is no defect, the average is 2, and the maximum is 6, whereas
When there is a defect, the average is 10 and the minimum is 8, and it can be seen that the defect and the noise can be separated.

[0029]

As described above, according to the present invention, it is possible to detect only defects without causing erroneous detection due to the positional deviation between the pattern to be inspected and the reference pattern.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a pattern defect inspection apparatus according to an embodiment of the present invention,

FIG. 2 is a diagram for explaining a method of aligning a pattern to be inspected with a reference pattern in the same apparatus;

FIG. 3 is a diagram for explaining a filter for aligning an inspection pattern and a reference pattern and a defect detection filter;

FIG. 4 is a schematic diagram for explaining a specific alignment example of the pattern defect inspection apparatus,

FIG. 5 is a diagram showing a specific example of defect detection,

FIG. 6 is a diagram showing an example of a detection signal,

FIG. 7 is a diagram showing a defect appearance frequency.

[Explanation of symbols]

11 ... Magnetic disk device 12 ... DMA memory 13 ... Bit expansion circuit 14 ... Bit map memory 15 ... Feature extraction circuit 16 ... Reference data generation circuit 17 ... Table position coordinate memory 18 ... CCD sensor 19 ... A / D converter 20 ... Buffer Memory 21 ... Comparison circuit 23 ... Inspection area 24 ... Alignment area 25 ... Edge position detection filter 26 ... Horizontal edge extraction filter 27 ... Vertical edge extraction filter 28 ... Horizontal edge upper defect detection filter 29 ... Vertical edge upper defect detection filter 30 ... 38 ... Reference pattern (shifted by ± 1 pixel vertically and horizontally) 39 to 40: Pattern to be inspected.

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Claims (1)

[Claims] 1. A means for inputting a two-dimensional image of a pattern to be inspected and a reference pattern; a means for cutting out a first region of the pattern to be inspected and a second region surrounding the first region; The third region of the reference pattern and the third region
Means for cutting out a fourth area surrounding the area, means for aligning the pattern of the fourth area with the second area, and means for the first area of the third area. An apparatus for inspecting a pattern defect, comprising: a means for obtaining an aligned fifth area; and a means for determining a defect in the first area and the fifth area.