JP7589107B2 - Reference image generating method and pattern inspection device - Google Patents

Description

The present invention relates to a reference image generating method and pattern inspection device used to inspect a pattern formed on a sample.

For example, in the manufacturing process of semiconductor devices, a circuit pattern is transferred onto a semiconductor substrate by reduced exposure using an exposure apparatus (also called a "stepper" or "scanner"). The exposure apparatus uses a mask (also called a "reticle") on which an original pattern (hereafter also called a "pattern") based on design data is formed.

As semiconductor devices become more highly integrated, circuit patterns are becoming finer. As circuit patterns become finer, mask patterns are becoming more complex due to the application of techniques such as optical proximity correction (OPC). For this reason, pattern inspection equipment is required to have high inspection performance that can handle complex patterns.

One pattern inspection method is the D-DB (Die to Database) method, which compares an inspection image captured by a pattern inspection device with a reference image based on design data.

Compared to the mask pattern, the pattern in the inspection image has rounded corners, dimensional shifts in the pattern, and blurring of the pattern edges due to focus deviation. These effects may cause false defects to be detected when comparing the inspection image with the reference image.

To reduce false defects in patterns like those described above, the D-DB method generates a reference image that matches the inspection image through calculations using filter coefficients. The filter coefficients are calculated based on the amount of corner rounding, dimensional shift, and edge blur of the pattern, etc.

For example, Patent Document 1 discloses a method for calculating parameters used to generate a reference image using actual images and design images that have been used in previous learning.

International Publication No. 2006/049243

As patterns become more complex, the time required to calculate filter coefficients increases. This increases the time required to generate a reference image. In other words, the setup time for pattern inspection increases, reducing the processing power of the pattern inspection device.

The present invention has been made in consideration of these points. In other words, the present invention aims to provide a reference image generation method and a pattern inspection device that can omit the calculation of filter coefficients when previously generated filter coefficients can be used in a pattern inspection device.

According to a first aspect of the present invention, a reference image generating method includes the steps of generating an unfolded image from design data, comparing first inspection parameters corresponding to inspection of a sample having a pattern on its surface with second inspection parameters corresponding to a past inspection, and, if at least a portion of the first inspection parameters match the second inspection parameters, setting second filter coefficients of the past inspection as first filter coefficients for inspection of the sample having a pattern on its surface , and creating a reference image from the unfolded image using the second filter coefficients.

According to the first aspect of the present invention, it is preferable that the reference image generating method further includes a step of calculating a first filter coefficient when at least a portion of the first inspection parameters does not match the second inspection parameters.

According to the first aspect of the present invention, at least a part of the first inspection parameters is preferably the type and minimum dimension of a pattern formed on a sample having a pattern on its surface .

According to the first aspect of the present invention, it is preferable that the reference image generating method further includes a step of calculating a first filter coefficient when the gradation value difference between the reference image created from the unfolded image and the inspection image of the sample having a pattern on its surface is equal to or greater than a predetermined threshold value using the second filter coefficient.

According to a second aspect of the present invention, a pattern inspection apparatus includes an imaging mechanism, an unfolding circuit that generates an unfolded image from design data, a search circuit that compares first inspection parameters for inspection of a sample having a pattern on its surface with second inspection parameters for a past inspection, and sets the second filter coefficient of the past inspection as a first filter coefficient for inspection of the sample having a pattern on its surface if at least a portion of the first inspection parameters match the second inspection parameters, a filter coefficient generation circuit that calculates the first filter coefficient if at least a portion of the first inspection parameters do not match the second inspection parameters, a reference circuit that creates a reference image from the unfolded image using at least one of the filter coefficients of the search circuit and the filter coefficient generation circuit, and a comparison circuit that compares the inspection image of the sample having a pattern on its surface, imaged by the imaging mechanism, with the reference image.

The reference image generation method and pattern inspection device of the present invention can reduce the time required to generate a reference image.

1 is a diagram showing an overall configuration of a pattern inspection apparatus according to an embodiment; 1 is a flowchart of a pattern inspection process according to an embodiment. 1 is a flowchart of a reference image generating process according to an embodiment.

The following describes the embodiments with reference to the drawings. The embodiments illustrate devices and methods for embodying the technical ideas of the invention. The drawings are schematic or conceptual, and the dimensions and ratios of each drawing are not necessarily the same as those in reality. The technical ideas of the present invention are not specified by the shapes, structures, arrangements, etc. of the components.

In the following, a case will be described in which the pattern inspection device captures an optical image using a light receiving element (photodiode) as an inspection image. Note that the pattern inspection device is not limited to this. The pattern inspection device may capture an electron beam image using a scanning electron microscope (SEM) as an inspection image. Also, in this embodiment, a case will be described in which the sample to be inspected is a mask, but the sample may be any sample with a pattern on its surface, such as a wafer (semiconductor substrate) or a substrate used in a liquid crystal display device, etc.

1. Overall Configuration of Pattern Inspection Apparatus First, an example of the overall configuration of a pattern inspection apparatus 1 will be described with reference to FIG. 1. FIG. 1 is a diagram showing the overall configuration of the pattern inspection apparatus 1. Note that the example of FIG. 1 shows a configuration for acquiring an optical image by light reflected from a mask 2 (hereinafter referred to as "reflected light"), but the pattern inspection apparatus 1 is not limited to this. The pattern inspection apparatus 1 may be configured to acquire an optical image by light transmitted through the mask 2 (hereinafter referred to as "transmitted light"). Furthermore, the pattern inspection apparatus 1 may be configured to acquire an optical image by reflected light and an optical image by transmitted light.

As shown in FIG. 1, the pattern inspection device 1 includes an image acquisition mechanism 10 and a control mechanism 20.

The image acquisition mechanism 10 includes a stage 100, a stage drive unit 101, an illumination light source 102, a beam splitter 103, lenses 104 and 105, a photodiode array 106, a sensor circuit 107, a laser length measurement system 108, and an autoloader 109.

A sample (mask) 2 is placed on the stage 100. The stage 100 is movable in the X direction parallel to the surface of the stage 100 and in the Y direction parallel to the surface of the stage 100 and intersecting the X direction. The stage 100 may also be movable in the Z direction perpendicular to the surface. The stage 100 may also be rotatable around a rotation axis that is set in the Z direction.

The stage driving unit 101 has a driving mechanism for moving the stage 100 in the X direction and the Y direction. The stage driving unit 101 includes an X-axis motor 110 and a Y-axis motor 111. The X-axis motor 110 drives the stage 100 in the X direction. The Y-axis motor 111 drives the stage 100 in the Y direction. The X-axis motor 110 and the Y-axis motor 111 may be, for example, stepping motors.

The inspection area of the mask 2 is virtually divided into a number of stripes along the Y direction, for example. The stage driving unit 101 controls the movement of the stage 100 so that the light continuously scans each divided inspection frame (stripes).

The illumination light source 102 emits illumination light for inspection.

The beam splitter 103 reflects the illumination light emitted from the illumination light source 102 toward the mask 2. The beam splitter 103 also transmits the light reflected by the mask 2.

The lens 104 focuses the illumination light reflected by the beam splitter 103 onto the mask 2. The lens 104 also focuses the reflected light reflected by the mask 2 onto the beam splitter 103.

The lens 105 focuses the reflected light that passes through the beam splitter 103 onto the photodiode array 106.

The photodiode array 106 photoelectrically converts the focused light to generate an electrical signal. The photodiode array 106 transmits the generated electrical signal to the sensor circuit 107. More specifically, the photodiode array 106 includes an image sensor (not shown). As the image sensor, for example, a line sensor in which CCD cameras as image pickup elements are arranged in a line may be used. An example of the line sensor is a TDI (Time Delay Integration) sensor. For example, the TDI sensor captures an image of the pattern of the mask 2 placed on the continuously moving stage 100.

The sensor circuit 107 performs A/D (analog/digital) conversion on the electrical signal received from the photodiode array 106. The sensor circuit 107 generates an optical image based on the A/D converted electrical signal (digital signal). The sensor circuit 107 then transmits the optical image to the comparison circuit 210 of the control mechanism 20. The optical image is based on the pattern of the mask 2. In the optical image, the brightness (luminance) of each pixel obtained by dividing the imaging area on the XY plane is expressed as a gradation value. For example, when the gradation value is expressed as 8-bit data, the pixel value of each pixel is expressed as a gradation value from 0 to 255.

The laser measurement system 108 measures the position of the stage 100 in the X and Y directions (also referred to as the "stage position"). The laser measurement system 108 transmits the measured data (stage position) to the position circuit 211 of the control mechanism 20.

Multiple masks 2 are set on the autoloader 109. The autoloader 109 loads the masks 2 to be inspected onto the stage 100. The autoloader 109 also loads the masks 2 from the stage 100 after the optical images have been captured.

The control mechanism 20 includes a control computer 200, a memory unit 201, a display unit 202, an input unit 203, a communication unit 204, an autoloader control circuit 205, a stage control circuit 206, a light source control circuit 207, an unfolding circuit 208, a reference circuit 209, a comparison circuit 210, and a position circuit 211. These are connected to each other via a bus line.

The autoloader control circuit 205, the stage control circuit 206, the light source control circuit 207, the deployment circuit 208, the reference circuit 209, the comparison circuit 210, and the position circuit 211 may be configured by a program executed by the control computer 200, may be configured by hardware or firmware provided in the control computer 200, or may be configured by individual circuits controlled by the control computer 200. The following describes a case where the functions of these circuits are realized based on a program executed by the control computer 200.

The control computer 200 controls the entire pattern inspection device 1. More specifically, the control computer 200 controls the memory unit 201, the display unit 202, the input unit 203, the communication unit 204, the autoloader control circuit 205, the stage control circuit 206, the light source control circuit 207, the development circuit 208, the reference circuit 209, the comparison circuit 210, and the position circuit 211. The control computer 200 then controls the image acquisition mechanism 10 to acquire an optical image. The control computer 200 controls the control mechanism 20 to generate a reference image. The control computer 200 compares the optical image with the reference image to detect defects in the pattern. The control computer 200 includes, for example, a CPU (Central Processing Unit) not shown. The CPU executes, for example, an inspection program 223 in the memory unit 201. The control computer 200 may be, for example, a CPU device such as a microprocessor, or a computer device such as a personal computer. In addition, at least some of the functions of the control computer 200 may be performed by other integrated circuits, such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or a graphics processing unit (GPU).

The storage unit 201 stores information related to pattern inspection. More specifically, the storage unit 201 stores design data 220, inspection conditions 221, inspection data 222, inspection program 223, and the like. The storage unit 201 also stores inspection conditions 221 for pattern inspections performed in the past (hereinafter also referred to as "past inspections"). Note that the storage unit 201 may include various types of storage devices such as a magnetic disk storage device (HDD: Hard Disk Drive) or a solid state drive (SSD) as external storage.

The inspection conditions 221 include inspection parameters 224 and filter coefficients 225. Note that the inspection conditions 221 may include imaging conditions in the image acquisition mechanism 10.

The inspection parameters 224 include, for example, the product name (mask name) of the mask 2, the transmittance of the mask 2, the inspection resolution, the detection sensitivity, the calibration conditions, the algorithm conditions, and the pattern conditions.

The mask name includes, for example, a series name and a layer name. The series name is the name of a group of multiple masks 2 used in the manufacture of one semiconductor device. The layer name indicates the manufacturing process (layer) to which the mask 2 corresponds.

The transmittance of the mask 2 varies depending on the exposure conditions or the material of the pattern formed on the mask. For example, the transmittance of the mask 2 differs between exposure conditions using an ArF excimer laser and exposure conditions using a KrF excimer laser.

Inspection resolution corresponds to pixel size. For example, reducing the inspection resolution tends to make it easier to pick up small defects.

Detection sensitivity is the sensitivity in detecting defects.

Calibration conditions are the conditions for calibration that is performed before acquiring an optical image. Calibration adjusts the brightness in the optical image. For example, black and white pixel values in the optical image are adjusted to preset gradation values.

The algorithm conditions are the conditions of the algorithm used when comparing the reference image and the optical image. For example, different algorithms are applied when comparing holes, lines, or the CD (critical dimension) of patterns. Even when the same algorithm is used, the threshold used to determine defects differs depending on the inspection resolution or detection sensitivity, etc.

The pattern conditions include information on the type and minimum dimensions of the pattern to be inspected. More specifically, pattern types include holes and lines. For example, if the pattern type is a hole, the minimum dimension indicates the minimum hole diameter. Also, if the pattern type is a line, the minimum dimension indicates the minimum line width or the minimum space width. These minimum dimensions may be detected automatically, for example, using software for mask rule checking, or may be input by the device user (operator) using the input unit 203.

The filter coefficients 225 are used to generate the reference image. The filter coefficients 225 are calculated based on the amount of corner rounding of the pattern, the amount of dimensional shift, the amount of edge blurring, etc.

Inspection data 222 includes the reference image, the optical image, and data about detected defects (such as coordinates and size).

The inspection program 223 is a program for performing pattern inspection. The storage unit 201 stores the inspection program 223 as a non-transitory storage medium.

The display unit 202 is a display device such as a CRT display, a liquid crystal display, or an organic EL display. The display unit 202 may also include an audio output device.

The input unit 203 is an input device such as a keyboard, a mouse, a touch panel, or a button switch.

The communication unit 204 is a device for connecting to a network in order to transmit and receive data to and from an external device. Various communication standards may be used for communication. For example, the communication unit 204 receives design data from an external device and transmits the results of pattern inspection to the external device.

The autoloader control circuit 205 controls the operation of the autoloader 109. The autoloader control circuit 205 operates the autoloader 109 to load the mask 2 to be inspected onto the stage 100. The autoloader control circuit 205 also operates the autoloader 109 to unload the mask 2 from the stage 100.

The stage control circuit 206 controls the stage driving unit 101. More specifically, the stage control circuit 206 acquires information on the stage position of the stage 100 measured by the laser measurement system 108 via the position circuit 211. Then, the stage control circuit 206 controls the stage driving unit 101 based on the acquired stage position information.

The light source control circuit 207 controls the illumination light source 102.

The expansion circuit 208 expands (converts) the design data 220, for example, into binary or multi-value image data. More specifically, the expansion circuit 208 expands the design data 220 stored in the storage unit 201, for example, into data for each pattern (figure), and interprets the figure code indicating the figure shape of the figure data, the figure dimensions, and the like. The expansion circuit 208 then expands the design data 220 into a binary or multi-value image (hereinafter referred to as the "expanded image") as a pattern arranged in a square with a grid of a predetermined quantization dimension as a unit. The expansion circuit 208 then calculates the occupancy rate of the figure for each pixel of the expanded image. The figure occupancy rate in each pixel calculated in this way is the pixel value of the expanded image. Below, a case will be described where the pixel value of the expanded image is expressed as an 8-bit gradation value. In this case, the pixel value of each pixel is expressed as a gradation value of 0 to 255. The expansion circuit 208 transmits the generated expanded image to the reference circuit 209.

The reference circuit 209 uses the filter coefficients to calculate the expanded image and generate a reference image. The reference circuit 209 transmits the generated reference image to the comparison circuit 210.

The reference circuit 209 includes a search circuit 230 and a filter coefficient generation circuit 231.

The search circuit 230 searches for the inspection conditions 221 of the past inspections stored in the storage unit 201 that are the same as or similar to the inspection conditions 221 of the pattern inspection to be performed this time (hereinafter referred to as "this inspection"). More specifically, the search circuit 230 compares the inspection parameters 224 of the past inspections stored in the storage unit 201 with the inspection parameters 224 of the current inspection. If all items of the inspection parameters 224 of the past inspection match the inspection parameters 224 of the current inspection, the search circuit 230 determines that the same inspection conditions 221 are present in the inspection conditions 221 of the past inspection. If some items of the inspection parameters 224 of the past inspection match the inspection parameters 224 of the current inspection, the search circuit 230 determines that similar inspection conditions 221 are present in the inspection conditions 221 of the past inspection. Some items of the inspection parameters 224 are pattern conditions, that is, the type and minimum dimensions of the pattern. Note that some items of the inspection parameters 224 may include detection sensitivity. The search circuit 230 sets the filter coefficient 225 of the same or similar inspection condition 221 as the filter coefficient 225 for the current inspection. For example, when multiple similar inspection conditions 221 are found, the search circuit 230 selects the inspection condition 221 with the most recent date (most recent) among the similar inspection conditions 221. Note that when multiple similar inspection conditions are found, the search circuit 230 may select the inspection condition 221 having the inspection parameters 224 with a high degree of matching in items other than the pattern condition, or may select the inspection condition 221 with the fewest detected defects.

When the filter coefficients 225 of the previous inspection cannot be used, that is, when the same or similar inspection conditions 221 are not found, the filter coefficient generation circuit 231 calculates the filter coefficients for the current inspection. More specifically, the filter coefficient generation circuit 231 estimates a reference image to be generated from the image data and the unfolded image of multiple estimated regions in the optical image. In other words, the filter coefficient generation circuit 231 estimates the amount of corner rounding, the amount of dimensional shift, the amount of blurring, etc. for matching the reference image to the inspection image from the image data and the unfolded image of multiple estimated regions in the optical image. Then, the filter coefficient generation circuit 231 calculates the filter coefficients based on the estimated amount of corner rounding, the amount of dimensional shift, the amount of blurring, etc. The estimated region is a region provided within the inspection region of the mask 2. The estimated region is a region used to calculate the filter coefficients and to confirm the validity of the reference image generated using the filter coefficients. It is preferable that the estimated region is set to a region in which patterns of multiple shapes are mixed. The estimated area may be set by an operator, or an area containing, for example, a critical pattern may be automatically extracted from the design data.

The comparison circuit 210 uses an appropriate algorithm to compare the optical image received from the sensor circuit 107 with the reference image generated by the reference circuit 209. If the gradation value difference between the optical image and the reference image exceeds a preset threshold, the comparison circuit 210 determines that there is a defect at the corresponding coordinate position of the mask 2 (stage position in the X direction and Y direction). The inspection conditions 221 and the inspection data 222 are stored in the memory unit 201.

The position circuit 211 generates position data in the X and Y directions of the stage 100 based on the data received from the laser measurement system 108.

2. Flow of Pattern Inspection Next, an example of the flow of the pattern inspection will be described with reference to Fig. 2. Fig. 2 is a flowchart of the pattern inspection.

As shown in FIG. 2, the control computer 200 first controls the image acquisition mechanism 10 to perform calibration (step S1). Through the calibration, the pixel values (tone values) of the optical image acquired by the sensor circuit 107 are adjusted.

Next, the control computer 200 acquires an inspection image (optical image) of the mask 2 (step S2). The acquired optical image is sent to the comparison circuit 210.

The expansion circuit 208 executes an expansion process of the design data 220 (step S3). More specifically, the expansion circuit 208 reads out the design data 220 stored in the memory unit 201. The expansion circuit 208 then expands (converts) the design data 220 into, for example, 8-bit image data (expanded image). The expansion circuit 208 transmits the generated expanded image to the reference circuit 209.

The reference circuit 209 generates a reference image (step S4). The reference circuit 209 transmits the generated reference image to the comparison circuit 210. Details of the reference image generation process will be described later.

The comparison circuit 210 performs a comparison process (step S5). More specifically, the comparison circuit 210 first aligns the optical image with the reference image, and aligns the pattern in the optical image with the pattern in the reference image. Next, the comparison circuit 210 compares the optical image with the reference image. The comparison circuit 210 calculates the difference in pixel value (gradation value) of each pixel, and if the gradation value difference is equal to or greater than a preset threshold value, it determines that the pixel is defective.

The control computer 200 outputs the comparison result (inspection data) (step S6). The control computer 200 stores the inspection conditions 221 and the inspection data 222 in the memory unit 201. The control computer 200 then displays the inspection data 222 on the display unit 202. The control computer 200 may output the inspection data 222 to an external device (e.g., a review device, etc.) via the communication unit 204.

3. Reference Image Generation Flow Next, an example of the flow of the reference image generation process will be described with reference to Fig. 3. Fig. 3 is a flowchart of the reference image generation process. Fig. 3 corresponds to step S4 in Fig. 2.

As shown in FIG. 3, the search circuit 230 compares the inspection parameters 224 of the current inspection with the inspection parameters 224 of the previous inspection, and searches for the same or similar inspection conditions 221 (step S11).

If there are identical or similar inspection conditions 221 (step S12_Yes), that is, if at least the pattern conditions (pattern type and minimum dimensions) among the inspection parameters 224 match, the search circuit 230 sets the detected filter coefficient 225 of the previous inspection as the filter coefficient 225 of the current inspection (step S13).

The reference circuit 209 checks the validity of the set filter coefficients 225. More specifically, for example, the reference circuit 209 uses the filter coefficients 225 to generate a reference image of a preset estimated area. Next, the reference circuit 209 calculates the gradation value difference between the reference image of the estimated area and the inspection image (optical image) (step S14). Then, the reference circuit 209 checks whether the maximum value of the gradation value difference is less than a preset threshold value (step S15).

If there are no identical or similar inspection conditions 221 in step S12 (step S12_No), or if the maximum value of the gradation value difference is equal to or greater than the threshold value in step S15 (step S15_No), the filter coefficient generation circuit 231 calculates the filter coefficient 225 for the current inspection (step S16). Then, the filter coefficient generation circuit 231 sets the calculated filter coefficient in the storage unit as the filter coefficient to be used in the current inspection.

The reference circuit 209 generates a reference image using the set filter coefficient 225 (step S17). More specifically, if the maximum value of the gradation value difference is less than the threshold value in step S15 (step S15_Yes), the reference circuit 209 generates a reference image using the filter coefficient 225 of the previous inspection. On the other hand, if the filter coefficient is calculated in step S16, the reference circuit 209 generates a reference image using the calculated filter coefficient.

4. Effects of the Present Embodiment With the configuration according to the present embodiment, the inspection parameters of the current inspection and the previous inspection can be compared, and if the inspection conditions are the same or similar, the filter coefficients of the corresponding previous inspection can be set as the filter coefficients of the current inspection. This makes it possible to omit the process of calculating the filter coefficients. As a result, the time required to generate a reference image can be shortened. In other words, the processing capacity of the pattern inspection device can be improved.

Furthermore, with the configuration according to this embodiment, if the gradation value difference between the reference image and the inspection image (optical image) is equal to or greater than a preset threshold value, a filter coefficient can be calculated to generate a reference image. This makes it possible to suppress deviations between the reference image and the inspection image (optical image) that would occur if filter coefficients from a previous inspection were used.

3, if a plurality of inspection conditions 221 are found and if the maximum value of the gradation value difference is equal to or greater than a threshold value in step S15, the pattern inspection device 1 may not calculate the filter coefficients, but may instead set the filter coefficients 225 of other past inspections that were not selected in step S13 as the filter coefficients 225 of the current inspection again.

In addition, after calculating the filter coefficients in step S16 of FIG. 3, the process may proceed to step S14 to check the validity of the calculated filter coefficients. Then, in step S15, if the maximum value of the gradation value difference is equal to or greater than a threshold value, the estimated region may be changed and the filter coefficients may be calculated again.

The present invention is not limited to the above-described embodiment, and various modifications can be made in the implementation stage without departing from the gist of the invention. The embodiments may be implemented in appropriate combination, in which case the combined effects can be obtained. Furthermore, the above-described embodiment includes various inventions, and various inventions can be extracted by combinations selected from the multiple constituent elements disclosed. For example, if the problem can be solved and an effect can be obtained even if some constituent elements are deleted from all the constituent elements shown in the embodiment, the configuration from which these constituent elements are deleted can be extracted as an invention.

1...Pattern inspection device, 2...Sample, 10...Image acquisition mechanism, 20...Control mechanism, 100...Stage, 101...Stage drive unit, 102...Illumination light source, 103...Beam splitter, 104, 105...Lens, 106...Photodiode array, 107...Sensor circuit, 108...Laser length measurement system, 109...Autoloader, 110...X-axis motor, 111...Y-axis motor, 200...Control computer, 201...Memory unit, 202... Display unit, 203...input unit, 204...communication unit, 205...autoloader control circuit, 206...stage control circuit, 207...light source control circuit, 208...expansion circuit, 209...reference circuit, 210...comparison circuit, 211...position circuit, 220...design data, 221...inspection conditions, 222...inspection data, 223...inspection program, 224...inspection parameters, 225...filter coefficient, 230...search circuit, 231...filter coefficient generation circuit

Claims (5)

generating an expanded image from the design data;
comparing first inspection parameters corresponding to an inspection of the specimen having a patterned surface with second inspection parameters corresponding to a previous inspection;
setting second filter coefficients of the previous inspection as first filter coefficients for an inspection of the specimen having a patterned surface if at least a portion of the first inspection parameters match the second inspection parameters;
generating a reference image from the unfolded image using the second filter coefficients;
Equipped with
Reference image generation method. calculating the first filter coefficients if the at least some of the first inspection parameters do not match the second inspection parameters.
The reference image generating method according to claim 1 . the at least a portion of the first inspection parameters being a type and a minimum dimension of a pattern formed on the sample having a pattern on a surface of the sample;
3. The method for generating a reference image according to claim 1. calculating the first filter coefficient when a gradation value difference between the reference image created from the developed image and an inspection image of the sample having a pattern on a surface thereof is equal to or greater than a preset threshold value using the second filter coefficient;
The reference image generating method according to claim 1 . An imaging mechanism;
an unfolded circuit for generating an unfolded image from design data;
a search circuit that compares first inspection parameters for an inspection of a sample having a pattern on its surface with second inspection parameters for a previous inspection, and sets the second filter coefficients for the previous inspection as first filter coefficients for the inspection of the sample having a pattern on its surface if at least a portion of the first inspection parameters match the second inspection parameters;
a filter coefficient generating circuit for calculating the first filter coefficients when the at least some of the first test parameters do not match the second test parameters;
a reference circuit that generates a reference image from the expanded image by using at least one of the filter coefficients of the search circuit and the filter coefficient generation circuit;
a comparison circuit that compares an inspection image of the sample having a pattern on a surface thereof, the inspection image being captured by the imaging mechanism, with the reference image.
Pattern inspection equipment.