JPH0772089A - Inspecting apparatus for defect of pattern - Google Patents

Abstract

PURPOSE:To correctly inspect a defect of a photomask by the use of image data obtained by photographing an actual pattern when the defect of the photomask is to be inspected by comparing the actual pattern of the photomask with design data. CONSTITUTION:The pattern defect inspecting apparatus is provided with a means 31 for forming a design binary image based on design data and outputting design image data, a means 21 for photographing an actual pattern formed on a to-be-inspected object 19 and outputting to-be-inspected image data, and an inspecting means 81 for detecting a defect based on the comparison between the to-be-inspected image data and design image data. A second means 41 is further provided for forming a second design binary image on the basis of design data obtained by changing coordinate values of the design data and outputting second design image data. The inspecting means 81 of the apparatus detects a defect of the actual pattern on the basis of the comparing result between the to-be-inspected image data and design image data, and the comparing result between the to-be-inspected image data and second design image data.

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 defects in a photomask such as a reticle for manufacturing a semiconductor by using pattern recognition technology, and based on image data and design data based on an actual pattern of the photomask. The present invention relates to an apparatus for inspecting pattern defects by comparing with design binary image data.

[0002]

2. Description of the Related Art Today, when inspecting a photomask such as a reticle used for manufacturing a semiconductor integrated circuit, a pattern of the photomask manufactured based on design data is converted into a video signal by an image pickup device, and this signal is processed to obtain a magnetic signal. A method of inspecting a photomask for defects by comparing with the design data recorded on a tape or the like has come to be used.

An inspection apparatus for carrying out such an inspection method has an inspection image information generating means, a design image information generating means and an inspection means, and the inspection image information generating means is based on design data by an imaging device. The manufactured photomask is photographed to form an analog video signal, which is converted into N-bit digital image information, which is then sent to the inspection means as inspected image information which is binary image information, and design image information. The generating means forms a design binary image of the bit pattern based on the data corresponding to the small area of the inspection object among the design data, and the binary image corresponding to the inspection image information based on the shape of the bit pattern. The design image information, which is the information of the above, is output to the inspecting means, and the inspecting means performs the noise removal and the line width adjustment on the inspected image information and the design image information and then performs the feature detection. Etc. performed by comparing both information, and configured to store the detected disagreement as defect information (e.g. JP 64-21672).

As an example of this inspection device, as shown in FIG. 5, the design information recorded on the magnetic tape of the magnetic tape device 11 is read into the computer 13 and temporarily stored in the magnetic storage device 15. It controls a drive unit 17 to drive a moving stage 18 on which an object to be inspected 19 such as a reticle is mounted and fixed, and the moving stage 18 is extremely accurately moved by position control using a laser interferometer or the like. It is controlled.

Further, the design information for comparing with the information of the actual pattern of the object to be inspected 19 on the moving stage 18 is:
The computer 13 extracts the information of the photographing location from the magnetic storage device 15 and sends it to the design image information generating means 31, and the design image information generating means 31 stores the data of the minute portion in the data storage circuit 33 and the developing circuit 35. The image information corresponding to the shape designed by bit expansion is stored in the frame memory 37, and the information stored in the frame memory 37 is compared with the inspected image information.

The inspected image information generating means 21 for outputting the inspected image information comprises an image pickup device 23 and a binarization circuit 25. As the image pickup device 23, a CCD line sensor or the like is used. An analog video signal capable of forming a two-dimensional analog image is formed by reading a width of several mm and moving the moving stage 18 in a direction orthogonal to the line sensor, and sampling is performed 1024 times per scanning line. , 0. A digital video signal having pixels of several microns square is output from the image pickup device 23, and this digital video signal is output from the inspected image information generating means 21 as a binary image signal by the binarization circuit 25.

Further, the inspected image information from the inspected image information generating means 21 is inputted to the characteristic information generating means 61,
The image information of the required portion is extracted by the cut-out circuit 63 of the characteristic information generating means 61, the characteristic is detected by the characteristic detecting circuit 65 having a large number of templates, and the characteristic is output to the inspection means 81 as the characteristic information. The feature detection circuit 65 detects the position and the changing direction of the changing point such as a corner or a step of the actual pattern by the template, and the information of the changing direction is combined with the information indicating the position of the changing point as the characteristic information. To do.

The design image information recorded as image information in the frame memory 37 is the feature information generating means 61.
Similar to the above, the reference feature information generating means 71 detects the position and the changing direction of the change point of the edge of the reference pattern and outputs it as feature information to the inspecting means 81. The reference feature information generating means 71 includes a line width adjusting circuit and an enlarging circuit as appropriate, and measures the inspected image information and the design image information based on the design information.

The inspection means 81 compares the inspected characteristic information with the reference characteristic information by the inspection circuit 83 and stores the non-coincidence in the defect information storage device 85. In such a pattern defect inspection apparatus, since the image information to be inspected is treated as binary data, the inspection time can be shortened by the rapid processing to perform the efficient inspection. As shown in the figure, a small change before and after the threshold is a step for one pixel, but even if there is a step change close to one pixel, it may be image information without a change point. The reliability is lowered due to the quantization error, and the reliability is improved by devising the template in the feature information generating means.

It should be noted that the binarization circuit 25 in the inspected image information generating means 21 converts the N-bit multi-valued image information into binary image information by less than one pixel due to the quantization error as described above. Fixed when binarizing because the information with unevenness may be linear information, or the information of the portion that is originally a minute unevenness and should be judged as a straight line may be converted into information with unevenness for one pixel. By using a plurality of thresholds of the thresholds and arbitrary thresholds, and further, by using the edge template or the like to detect the shape of the edge, the image information is binarized to make the distinction between the straight line and the step clear, A binarization device that suppresses unevenness caused by a digitization error has also been proposed (for example, Japanese Patent Laid-Open No. 4-35171).

[0011]

Nowadays, as the density of semiconductor integrated circuits becomes higher, the precision of processing and inspection required for photomasks becomes more severe, and more precise and accurate inspection is required. . On the other hand, it is also required that inspection can be performed quickly and easily, and the inspected image information formed by capturing the photomask pattern is used as multi-valued image information, and the design image information based on the design information is also inspected image information. Comparisons are also made as image information based on combined multi-valued data, but the multi-valued design image information requires a long inspection time due to the enormous amount of data, resulting in poor efficiency. It had the drawback of being expensive.

The present invention provides a defect inspection apparatus capable of eliminating such defects and performing a quick inspection based on the design binary image information and an inspection with improved accuracy. is there.

[0013]

Design image information generating means for creating a design binary image based on design information having coordinate values indicating the position of a reference pattern and outputting design image information representing the design binary image. An inspected image information generating means for imaging an actual pattern formed on an inspected object based on the design information and outputting inspected image information corresponding to the actual pattern; the inspected image information and the design In a pattern defect inspecting apparatus comprising: an inspection unit that detects a defect in the actual pattern based on a comparison result with image information,
The coordinate value of the design information is changed based on the size of the pixel forming the image, and the second design binary image is created based on the design information with the changed coordinate value. The design means further comprises a second design image information generating means for outputting second design image information representing the value image.
The pattern defect inspection apparatus detects a defect of the actual pattern based on a comparison result of the inspection image information and the design image information and a comparison result of the inspection image information and the second design image information.

Further, design image information generating means for outputting design image information representing a design binary image, inspected image information generating means for outputting inspected image information, inspected image information and the design image information are provided. In a pattern defect inspecting apparatus comprising: inspection means for comparison;
When the actual pattern has a change point such as a step shape, it is provided with feature information generating means for outputting the feature information to be inspected indicating the position and the change direction of the change point. At least one converted design binary image
A reference image information generating means for generating information on each of the design binary images as reference image information, and detecting a feature of the design information from the design image information and the reference image information to change points. Of the defect of the actual pattern by comparing design image feature information with design image feature information for outputting design image feature information indicating the position and the changing direction of the design image feature information. In some cases, it may be used as a pattern defect inspection device for detecting

[0015]

[Operation] Since the inspection device according to the present invention compares and inspects the design binary image information based on the design information and the inspected image information corresponding to the actual pattern by the inspecting means, a quick inspection is possible. Further, since the first design image information is formed based on the design information and the second design image information whose coordinate value is changed is formed, the unevenness of less than one pixel is formed from the first design image information when binarizing. Even if the information of “1” disappears, it is possible to include the unevenness of less than one pixel as the unevenness of one pixel by including the unevenness of one pixel in the second design image information by changing the coordinate value. The defect of the actual pattern is detected based on the comparison result of the image information and the inspected image information and the comparison result of the second design image information and the inspected image information. It is possible to prevent erroneous detection of a defect caused by a quantization error when creating binary design image information.

Also, when the feature of the reference pattern and the feature of the actual pattern are compared to detect the defect of the actual pattern, the reference feature information is formed based on the first designed binary image, and the coordinate value is obtained. The second reference feature information is formed based on the changed second designed binary image, and the inspection means compares the first reference feature information with the inspected feature information, and the second reference feature information and the inspected feature information. Since it is configured to detect the defect of the actual pattern based on the comparison result with the inspection feature information, it is possible to prevent erroneous detection of the defect due to the quantization error when creating the binary design image information. it can.

[0017]

The first embodiment of the defect detecting apparatus according to the present invention is as follows:
As shown in FIG. 1, an image of an object to be inspected 19 such as a reticle fixed on a moving stage 18 is captured by an image pickup device 23, and a digital video signal output from the image pickup device 23 is digitized by a binarization circuit 25. A first design image information generating means 31 and a second design image information generating means 31 which outputs the value image signal from the inspected image information generating means 21 to obtain the first design image information in which the pattern shape of a required portion is bit-developed based on the design information. Second design image information generating means 41 for outputting the design image information of, the inspected image information from the inspected image information generating means 21, the first design image information from the first design image information generating means 31, and the first design image information The inspection means 81 for comparing the second design image information from the second design image information generating means 41.

This image pickup device 23 moves the moving stage 18 in a fixed direction by a driving unit 17 and reads and scans a pattern of an object 19 to be inspected in a direction perpendicular to the moving direction. For example, one scanning line includes 1024 8-bit data. As pixel information, 0. The information of pixels in units of several microns is used as a digital video signal, and the binarization circuit 25 simply binarizes this digital video signal or binarizes it by using a plurality of threshold values. The image information to be inspected is output as binary image information.

The design information has coordinate values indicating the shape, size, and position of the reference pattern, and is stored in a magnetic tape (not shown). The design information recorded on the magnetic tape is read by a computer 13 including a central processing unit, a memory, an interface, etc. using the magnetic tape device 11 and the like. Then, the computer 13 temporarily stores this design information in the magnetic storage device 15, and based on the information from the inspection means 81, the design information of a minute range corresponding to the range read by the image pickup device 23 is generated by the first design image information generation means 31 and It is sent to the second design image information generating means 41.

The driving unit 17 for driving and controlling the movement of the moving stage 18 is also controlled by the computer 13 to move the moving stage 18 accurately at a slight speed. Further, the first design image information generating means 31 temporarily stores the design information sent from the computer 13 in the data storage circuit 33, converts it into bit pattern data of the circuit shape by the expansion circuit 35, and stores it in the frame memory 37. It is a thing.

A two-dimensional coordinate axis is defined in advance in the frame memory 37, and the bit pattern is stored in the frame memory 37 based on the coordinate value of the design information. Further, when storing in the frame memory 37, the image information in the frame memory 37 is bit-developed in the frame memory 37 so as to be equivalent to binary data of information in a range matched with the pixel size of the image pickup device 23. As shown in FIG. 3, the step difference of less than one pixel is rounded and quantized.

The second design image information generating means 41 is also
A data storage circuit 43 similar to the first design image information generating means 31.
The second design image information generating means is composed of an expansion circuit 45 and a frame memory 47, design information is stored in the data storage circuit 43, and a quantized design binary image is stored in the frame memory 47. In the expansion circuit 45 in 41, for example, the coordinate value is changed so that the coordinate value is changed from the design image information by moving the coordinate axis so as to add 0.5 pixel in the Y-shape direction, or rounding up or rounding down the one less than one pixel. And is stored in the frame memory 47.

Therefore, as shown in A of FIG. 4, when the image information as shown in B of FIG. 4 is formed in the first design image information generating means 31 by the design information having the step difference of less than one pixel, the design is performed. By changing the coordinate value of the information, C in FIG.
As shown in FIG. 4A, the step at the change point of less than one pixel is applied to the threshold value, and as shown in D of FIG. 4, the change is stored in the frame memory 47 as image information which is not lost, and the first design image information generating means 31 loses it. The information of the changed point can be complemented by the second design image information generating means 41.

Then, the first design image information generating means 31
Of the design binary image stored in the frame memory 37 of the second design image information, and the information of the design binary image stored in the frame memory 47 of the second design image information generating means 41 as the second design image information. Sent to the inspection means 81 as
At 81, the inspected image information from the inspected image information generating means 21 is compared with the first design image information.

In this comparison, although the design information and the steps in the actual pattern are almost the same, the image pickup device 23
There is a slight deviation between the pixel division in the inspection image information due to the relative positional relationship between the pixel and the actual pattern and the division when bit expansion is performed by the expansion circuit, and the inspection image information due to the quantization error during binarization. There may be a case where a mismatch for one pixel occurs between the first design image information and the first design image information.

With respect to this non-coincidence portion, if the non-coincidence between the inspection image information and the first design image information is caused by the quantization error by further comparing the second design image information and the inspection image information, As described above, since the second design image information complements the information of less than one pixel lost in the first design image information, it is possible to correct this inconsistency information so as to eliminate the inconsistent information, and to obtain an accurate real pattern. It is possible to compare with design information.

Further, as the binarization circuit 25 in the inspection image information generating means 21, not only the simple binarization with a fixed threshold value but also an arbitrary threshold value is used to round up a step less than one pixel to one pixel and inspected image information. Even in such a case, when quantization is performed by the expansion circuit 45 in the second design image information generating means 41, by similarly changing coordinate values such as rounding up, it becomes possible to perform comparative detection of minute steps. is there.

The coordinate values of the expansion circuit in the second design image information generating means 41 can be changed by adding or subtracting 0.5 pixels only in the Y-axis direction or by changing the pixel values by 0.5 pixels only in the X-axis direction. In addition to the above case, the coordinates may be moved in the oblique direction by changing 0.5 pixels in both the X-axis and Y-axis directions. That is, horizontal or diagonal edge inspection is performed by changing coordinate values in the Y-axis direction, and vertical or diagonal edge inspection is performed by changing coordinate values in the X-axis direction. By inspecting edges in the vertical and vertical directions by changing the coordinate values in both X-axis and Y-axis directions,
It enables accurate inspection.

Further, when rounding up or down, it is possible to appropriately set rounding off, and the amount of coordinate value change is not limited to 0.5 pixels, but 0.25 pixels or the like.
It is also possible to set it appropriately. Furthermore, the data storage circuit 43 in the second design image information generating means 41 is shared with the data storage circuit 33 in the first design image information generating means 31 so that the data storage circuit 43 in the second design image information generating means 41 can be used. The second design image information generating means 41 is omitted.
The developing circuit 45 in the second design image information generating means 31 is designed image information bit-developed based on the design information stored in the data storage circuit 33 in the first design image information generating means 31.
It may be stored in the frame memory 47 in 41.

Then, in another embodiment of the present invention, as shown in FIG. 2, features such as corners and steps of the actual pattern are detected based on the inspected image information from the inspected image information generating means 21. A feature information generating means 61 for forming the feature information to be inspected representing the feature and position thereof, and similarly detecting a feature such as a corner portion or a step of the reference pattern based on the design image information and representing the feature and position. The reference feature information generating means 71 for forming the reference feature information is provided, and the inspecting means 81 compares the inspected feature information with the reference feature information to inspect the defects of the actual pattern.

Inspected image information generating means of the second embodiment
When converting the multi-valued image information output from the image pickup device 23 into binary image information, 21 is a binary image that does not lose the characteristics of the pattern by appropriately rounding up steps less than one pixel using a plurality of threshold values. The binarization circuit 25 for information is used, and the binary image information output by the binarization circuit 25 is output to the characteristic information generating means 61 as image information to be inspected.

Then, the feature information generating means 61 has a feature detection circuit 65 having a large number of templates for detecting features such as corners and steps with respect to the reference edge and a template for detecting steps of one pixel, and an image to be inspected. The cutting circuit 63 extracts the information of the local portion of the actual pattern represented by the information, and when the shape of the edge changes, the characteristic information indicating the position and the changing direction is output.

The first design image information generating means 31 records design image information bit-developed on the basis of the design information stored in the data storage circuit 33 in the frame memory 37 as in the first embodiment. The second design image information generating means 51 has a plurality of sets of frame memories and expansion circuits, each of which includes a frame memory and an expansion circuit. The embodiment shown in FIG. 53 and a second expansion circuit 57, a first frame memory 54 and a second frame memory 58 are provided.

The first expansion circuit 53 records bit expanded design image information in the first frame memory 54 based on the design information stored in the data storage circuit 33 in the first design image information generating means 31. Yes, this first expansion circuit
When the image information is formed from the design information in 53, the first
Bit expansion is performed by shifting 0.5 bits in the X coordinate direction with respect to the bit expansion of the expansion circuit 35 in the design image information generating means 31, and the second expansion circuit 57 also stores data in the first design image information generating means 31. The image information bit-developed based on the design information stored in the storage circuit 33 is stored in the second frame memory 58.
At the time of bit expansion, the bit expansion is performed by shifting the expansion circuit 35 in the first design image information generating means 31 by 0.5 pixel in the Y coordinate direction.

Then, the first design image information from the frame memory 37 in the first design image information generating means 31 and the second design from the first frame memory 54 and the second frame memory 58 in the second design image information generating means 51. The reference feature information generating means 71 to which the image information is input has a cutout circuit 73 and a feature detection circuit 75. The reference feature information generating means 71 is also a local portion from the frame memory 37 of the first design image information generating means 31 and the first frame memory 54 and the second frame memory 58 of the second design image information generating means 51 in the clipping circuit 73. The binary image information is extracted, the feature detection circuit 75 extracts information indicating changes in the corners and steps of the reference pattern by the template, and outputs the information together with information indicating the position of the change point to the inspection unit 81.

The inspecting means 81 compares the inspected feature information with the reference feature information and, if there is a mismatch, stores them in the defect information recording device 85 as defect information. The expansion circuit and the frame memory of the second design image information generating means 51 are not limited to two sets, but are composed of three sets of expansion circuits and frame memories, and have 0.25 in the X-axis and Y-axis directions.
A binary image with changed pixel coordinate values, a binary image with 0.5 pixel coordinate values changed in the X-axis and Y-axis directions, and a binary image with 0.75 pixel coordinate values changed in the X-axis and Y-axis directions. A value image may be formed and information of these binary images may be output as reference image information.

Further, in the inspected image information generating means 21, the binarization circuit 25 may be omitted, and the cutout circuit 63 and the feature detection circuit 65 may treat the multi-valued image as it is and detect the feature. In this case, minute defects can be detected stably.

[0038]

According to the present invention described in claim 1, the first design image information generating means for creating the first design binary image based on the design information, the first design binary image and the coordinate value are set. A second design image information generating means for creating a modified second design binary image, and the inspecting means receives the first design image information from the first design image information generating means and the inspected image information generating means. In addition to comparing the inspection image information, the second design image information from the second design image information and the inspection image information are also compared, so that the first design image information and the inspection image information are caused by the quantization error. Even if a mismatch occurs, the mismatch can be corrected by comparing the first design image information with the second design image information whose coordinate value has been changed and the image information to be inspected. Pattern defect inspection that can prevent false detection of There is provided a location, the present invention is first provided in a conventional pattern defect inspection apparatus
By adding a second design image information generating means similar to the design image information generating means, it is possible to easily improve the accuracy of the defect inspection apparatus.

Further, the present invention according to claim 2 is
First design image information generating means for generating a first design binary image from design information, and second design image information for generating a second design binary image in which coordinate values are changed from the first design binary image. And generating the reference feature information from the first design image information and the second reference feature information from the second design image information, and setting the reference feature information and the second design image information to the feature information to be inspected, respectively. Because of the configuration for comparison, it is possible to prevent erroneous detection of a defect due to a quantization error, as in the invention described in claim 1.

[Brief description of drawings]

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

FIG. 2 is a circuit block diagram showing a second embodiment of the pattern defect inspection apparatus according to the present invention.

FIG. 3 is a diagram showing an example of a design binary image formed based on design information.

FIG. 4 is a diagram showing an example of a design binary image formed by changing coordinate values from design information.

FIG. 5 is a circuit block diagram showing an example of a conventional pattern defect inspection apparatus.

FIG. 6 is a diagram showing a quantization error when binarizing image information.

[Explanation of symbols]

11 Magnetic Tape Device 13 Computer 15 Magnetic Storage Device 17 Drive Unit 18 Moving Stage 19 Inspected Object 21 Inspected Image Information Generating Means 23 Imaging Device 25 Binary Circuit 31 First Design Image Information Generating Means 33 Data Storage Circuit 35 Expansion Circuit 37 frame memory 41,51 second
Design image information generation means 43 Data storage circuit 45 Development circuit 47 Frame memory 53 First development circuit 54 First frame memory 57 Second development circuit 58 Second frame memory 61 Feature information generation circuit 71 Reference feature information generation means 81 Inspection means 83 Inspection circuit 85 Defect information storage device

Claims (3)

[Claims] 1. A first design binary image is created based on design information having coordinate values indicating a position of a reference pattern, and first design image information representing the first design binary image is output. A first design image information generating means; an inspected image information generating means for imaging an actual pattern formed on the inspected object based on the design information and outputting inspected image information corresponding to the actual pattern; In a pattern defect inspection apparatus, which comprises an inspection unit that detects a defect in the actual pattern based on a comparison result of the inspection image information and the first design image information, the size of a pixel forming an image A second design binary image based on the design information with the coordinate values changed, and the second design representing the second design binary image. 2nd setting to output image information The inspection means further comprises total image information generation means, and the inspection means compares the comparison result between the inspection image information and the first design image information and the comparison result between the inspection image information and the second design image information. A pattern defect inspection apparatus which detects a defect in the actual pattern based on the result. 2. A first design binary image is created based on design information having coordinate values indicating the position of a reference pattern, and first design image information representing the first design binary image is output. A first design image information generating unit, and a reference feature which detects a feature of the reference pattern based on the first design image information and outputs first reference feature information representing a feature of the reference pattern and a position thereof. An information generating means, an inspected image information generating means for imaging an actual pattern formed on the inspected object based on the design information, and outputting inspected image information corresponding to the actual pattern, the inspected image Inspected characteristic information generating means for detecting a characteristic of the actual pattern based on information and outputting inspected characteristic information representing the characteristic of the actual pattern and its position, the inspected characteristic information and the first reference Feature information and In a pattern defect inspection apparatus comprising: an inspection unit for detecting a defect in the actual pattern based on a comparison result; and changing the coordinate value of the design information based on a size of a pixel forming an image, A second design image information generating unit is further provided which creates a second design binary image based on the design information with the coordinate values changed and outputs second design image information representing the second design binary image. Then, the reference feature information generating means detects the feature of the reference pattern based on the second design image information, and outputs the second reference feature information representing the feature of the reference pattern and its position, The inspecting unit determines the actual pattern based on a comparison result between the inspected feature information and the first reference feature information and a comparison result between the inspected feature information and the second reference feature information. Detect defects Pattern defect inspection apparatus according to claim Rukoto. 3. The pattern defect inspection apparatus according to claim 1, wherein the inspected image information is binary image information.