JP7525251B2 - Method for determining sensitivity fluctuation of TDI (time delay integration) sensor, pattern inspection method, and pattern inspection device - Google Patents

Description

The present invention relates to a pattern inspection device and a pattern inspection method. For example, the present invention relates to a pattern inspection technology for inspecting pattern defects on objects that serve as samples for use in semiconductor manufacturing, and to a method for inspecting extremely small pattern defects on photomasks, wafers, liquid crystal substrates, and the like that are used when manufacturing semiconductor elements and liquid crystal displays (LCDs).

In recent years, with the increasing integration and capacity of large-scale integrated circuits (LSIs), the circuit line width required for semiconductor elements has become narrower and narrower. These semiconductor elements are manufactured by forming circuits by exposing and transferring a circuit pattern onto a wafer using a reduced projection exposure device called a stepper, using an original pattern (also called a mask or reticle, hereafter collectively referred to as a mask) on which a circuit pattern is formed. Therefore, to manufacture a mask for transferring such a fine circuit pattern onto a wafer, a pattern drawing device using an electron beam capable of drawing a fine circuit pattern is used. Such a pattern drawing device may also be used to draw a pattern circuit directly on a wafer. Alternatively, attempts are being made to develop a laser beam drawing device that draws using a laser beam other than an electron beam.

And improving yields is essential for the manufacture of LSIs, which are very costly to manufacture. However, as typified by 1-gigabit-class DRAMs (random access memories), the patterns that make up LSIs are approaching the submicron to nanometer order. One of the major factors that reduce yields is pattern defects in the masks used when exposing and transferring ultra-fine patterns onto semiconductor wafers using photolithography technology. In recent years, as the dimensions of LSI patterns formed on semiconductor wafers have become finer, the dimensions that must be detected as pattern defects have also become extremely small. For this reason, there is a need for high-precision pattern inspection equipment that inspects defects in transfer masks used in LSI manufacturing.

A known inspection method is to compare an optical image of a pattern formed on a sample such as a lithography mask at a predetermined magnification using a magnifying optical system with design data or an optical image of the same pattern on the sample. For example, there are pattern inspection methods such as "die to die inspection" which compares optical image data of the same pattern at different locations on the same mask, and "die to database inspection" which inputs drawing data (design data) converted from pattern-designed CAD data into an input format for input by a drawing device when drawing a pattern on a mask into an inspection device, generates a design image (reference image) based on this, and compares it with an optical image of the pattern, which is measurement data. In the inspection method using such an inspection device, the sample is placed on a stage, and the stage moves to scan the sample with a light beam, and the inspection is performed. The sample is irradiated with a light beam by a light source and an illumination optical system. The light transmitted through or reflected from the sample is imaged on a sensor via the optical system. The image captured by the sensor is sent to a comparison circuit as measurement data. After aligning the images, the comparison circuit compares the measurement data with the reference data according to an appropriate algorithm, and if the measurement data is not within the tolerance range, it is determined that there is a pattern defect.

Here, when imaging a pattern on a sample, a TDI sensor in which multiple optical elements (sensor pixels) are arranged two-dimensionally is used. In general, before performing mask inspection, an inspection device performs calibration such as adjusting the amount of laser light and adjusting the gain for each sensor pixel of the TDI sensor so that a TDI sensor image with appropriate gradation values for inspection is obtained. In the TDI sensor, there is a problem that the sensitivity of some sensor pixels increases during use due to deterioration, etc. If sensitivity unevenness occurs in which the sensitivity of some of the multiple sensor pixels of the TDI sensor changes after calibration performed before inspection, the sensitivity unevenness leads to gradation unevenness in the image. Therefore, there is a problem that it affects the inspection sensitivity. Therefore, it is desirable to quickly identify the area of the sensor pixels where sensitivity abnormalities have occurred during use of the TDI sensor.

Although different from TDI sensors, a technology has been disclosed for calculating a degradation index that indicates the degree of degradation based on the frequency distribution of the gradation values of a frame image in a self-luminous display device (see, for example, Patent Document 1).

JP 2008-076741 A

Therefore, one aspect of the present invention provides a method, an inspection method, and an inspection device that can quickly identify areas of an optical element where sensitivity abnormalities have occurred due to the use of a TDI sensor.

A method for determining a sensitivity fluctuation of a TDI sensor according to one aspect of the present invention includes the steps of:
a step of capturing an optical image to be inspected on a sample surface on which a plurality of graphic patterns are formed, while relatively moving a time delay integration (TDI) sensor having a two-dimensionally arranged optical element array for measuring a light quantity in an integration direction of the TDI sensor;
Setting a plurality of groups in which the optical element array is divided in an orthogonal direction perpendicular to the integration direction;
generating a plurality of sub-optical images by dividing the optical image by an imaging area width of each of the plurality of groups in an orthogonal direction and by a predetermined width in an integral direction;
creating a first histogram indicating a frequency of each gradation value for each of the plurality of sub-optical images;
creating a plurality of reference images corresponding to the plurality of sub-optical images using design pattern data on which the plurality of geometric patterns are based;
creating a second histogram indicating the frequency of each gradation value for each of the plurality of reference images;
creating a difference histogram between the first histogram and the second histogram for each sub-optical image;
a step of detecting, for each group, a shift toward higher gradation values over time that has reached a predetermined frequency in a range of gradation values greater than a gradation value adjusted for a white pattern in each difference histogram, using a plurality of difference histograms based on a plurality of sub-optical images captured over time at different positions on the sample surface;
determining a group in which a sensitivity variation has occurred based on the variation in gradation value, and outputting the result;
The present invention is characterized by comprising:

It is also preferable to determine groups in which the gradient of the gradation value fluctuation reaches a certain frequency and exceeds a threshold value.

Alternatively, it is preferable to determine the group in which the gradation value reaches a predetermined frequency and exceeds a threshold value.

A pattern inspection method according to one aspect of the present invention includes:
a step of capturing an optical image to be inspected on a sample surface on which a plurality of graphic patterns are formed, while relatively moving a time delay integration (TDI) sensor having a two-dimensionally arranged optical element array for measuring a light quantity in an integration direction of the TDI sensor;
Setting a plurality of groups in which the optical element array is divided in an orthogonal direction perpendicular to the integration direction;
generating a plurality of sub-optical images by dividing the optical image by a width of an imaging area of each of the plurality of groups in an orthogonal direction and a predetermined width in an integral direction;
creating a first histogram indicating a frequency of each gradation value for each of the plurality of sub-optical images;
creating a plurality of reference images corresponding to the plurality of sub-optical images using design pattern data on which the plurality of geometric patterns are based;
creating a second histogram indicating the frequency of each gradation value for each of the plurality of reference images;
creating a difference histogram between the first histogram and the second histogram for each sub-optical image;
a step of detecting, for each group, a shift toward higher gradation values over time that has reached a predetermined frequency in a range of gradation values greater than a gradation value adjusted for a white pattern in each difference histogram, using a plurality of difference histograms based on a plurality of sub-optical images captured over time at different positions on the sample surface;
calibrating the sensitivity of the TDI sensor based on the variation in the grayscale value;
A step of comparing the sub-optical image captured by the TDI sensor whose sensitivity has been compensated by calibrating the sensitivity of the TDI sensor with a reference image corresponding to the sub-optical image, and outputting the result;
The present invention is characterized by comprising:

A pattern inspection apparatus according to one aspect of the present invention comprises:
an optical image acquisition mechanism that uses a time delay integration (TDI) sensor having a two-dimensionally arranged optical element array for measuring the amount of light, and captures an optical image to be inspected on a sample surface on which a plurality of graphic patterns are formed while relatively moving the TDI sensor in an integration direction of the TDI sensor;
a group setting unit that sets a plurality of groups into which the optical element array is divided in an orthogonal direction that is orthogonal to the integration direction;
a sub-optical image generating unit configured to generate a plurality of sub-optical images by dividing an optical image by a width of an imaging area of each of the plurality of groups in an orthogonal direction and a predetermined width in an integral direction;
a first histogram creation unit that creates a first histogram indicating a frequency of each gradation value for each of the plurality of sub-optical images;
a reference image creating unit that creates a plurality of reference images corresponding to the plurality of sub-optical images by using design pattern data on which a plurality of graphic patterns are based;
a second histogram creation unit that creates a second histogram indicating a frequency of each gradation value for each of the plurality of reference images;
a difference histogram creation unit that creates a difference histogram between the first histogram and the second histogram for each sub-optical image;
a detection unit that detects, for each group, a shift toward higher gradation values over time that has reached a predetermined frequency in a range of gradation values greater than a gradation value adjusted for a white pattern in each difference histogram, using a plurality of difference histograms based on a plurality of sub-optical images captured over time at different positions on the sample surface;
A determination unit that determines a group in which a sensitivity change has occurred based on a change in gradation value;
A comparison unit that compares the sub-optical image with a reference image corresponding to the sub-optical image;
The present invention is characterized by comprising:

According to one aspect of the present invention, it is possible to quickly identify areas of an optical element where sensitivity abnormalities have occurred due to use of a TDI sensor. As a result, high-precision inspection can be performed using a TDI sensor with compensated sensitivity.

1 is a configuration diagram showing a configuration of a pattern inspection device according to a first embodiment; 1 is a diagram showing an example of an arrangement configuration of optical elements of a TDI sensor in embodiment 1. FIG. FIG. 2 is a conceptual diagram for explaining an inspection area in the first embodiment. FIG. 2 is a flowchart showing main steps of the inspection method according to the first embodiment. FIG. 13 is a diagram showing an example of a gray scale value distribution of a TDI sensor before calibration in the first embodiment. 11 is a diagram showing an example of a gray scale value distribution of a TDI sensor in which sensitivity fluctuation occurs during use in the first embodiment. FIG. 4 is a diagram showing an example of an internal configuration of a comparison circuit according to the first embodiment; FIG. FIG. 4 is a diagram for explaining a filter process in the first embodiment. FIG. 13 is a diagram showing an example of a histogram (1) using a frame image (actual image) captured using a deteriorated sensor pixel in the first embodiment. FIG. 13 is a diagram showing an example of a histogram (2) using a reference image (reference picture) in the first embodiment. FIG. 13 is a diagram showing an example of a difference histogram between a histogram (1) using a frame image (actual image) captured using a deteriorated sensor pixel in embodiment 1 and a histogram (2) of a reference image. FIG. 13 is a diagram showing an example of a difference histogram between a histogram (1) using a frame image (actual image) captured using normal sensor pixels in embodiment 1 and a histogram (2) of a reference image. 5A to 5C are diagrams for explaining a method for determining sensitivity fluctuation in the first embodiment.

Embodiment 1.
Fig. 1 is a configuration diagram showing the configuration of a pattern inspection apparatus in embodiment 1. In Fig. 1, an inspection apparatus 100 for inspecting a substrate to be inspected, for example, a pattern formed on a mask, includes an optical image acquisition mechanism 150 and a control circuit 160.

The optical image acquisition mechanism 150 includes a light source 103, an illumination optical system 170, a movably arranged XYθ table 102, a magnification optical system 104, a TDI (time delay integration) sensor 105, a sensor circuit 106, a stripe pattern memory 123, a laser measurement system 122, and an autoloader 130. A substrate 101 transported from the autoloader 130 is placed on the XYθ table 102. The substrate 101 includes, for example, a photomask for exposure that transfers a pattern to a semiconductor substrate such as a wafer. In addition, a plurality of graphic patterns to be inspected are formed on this photomask. The substrate 101 is placed on the XYθ table 102 with the pattern-forming surface facing downwards, for example.

In the control system circuit 160, the control computer 110 that controls the entire inspection device 100 is connected to the position circuit 107, the comparison circuit 108, the reference image creation circuit 112, the autoloader control circuit 113, the table control circuit 114, the histogram creation circuits 140 and 142, the difference histogram creation circuit 144, the detection circuit 146, the judgment circuit 148, the magnetic disk device 109, the memory 111, the magnetic tape device 115, the flexible disk device (FD) 116, the CRT 117, the pattern monitor 118, and the printer 119 via the bus 120. The sensor circuit 106 is connected to the stripe pattern memory 123, and the stripe pattern memory 123 is connected to the comparison circuit 108. The XYθ table 102 is driven by the X-axis motor, the Y-axis motor, and the θ-axis motor. The XYθ table 102 is an example of a stage.

Note that a series of "circuits" such as the position circuit 107, the comparison circuit 108, the reference image creation circuit 112, the autoloader control circuit 113, the table control circuit 114, the histogram creation circuits 140 and 142, the difference histogram creation circuit 144, the detection circuit 146, and the judgment circuit 148 have a processing circuit. Such processing circuits include electric circuits, computers, processors, circuit boards, quantum circuits, or semiconductor devices. Alternatively, different processing circuits (separate processing circuits) may be used. For example, a series of "circuits" such as the position circuit 107, the comparison circuit 108, the reference image creation circuit 112, the autoloader control circuit 113, the table control circuit 114, the histogram creation circuits 140 and 142, the difference histogram creation circuit 144, the detection circuit 146, and the judgment circuit 148 may be configured and executed by the control computer 110. Input data or calculation results required for the position circuit 107, comparison circuit 108, reference image creation circuit 112, autoloader control circuit 113, table control circuit 114, histogram creation circuits 140, 142, difference histogram creation circuit 144, detection circuit 146, and judgment circuit 148 are stored in memory (not shown) in each circuit or in memory 111. Programs for executing the processor, etc. may be recorded on recording media such as the magnetic disk device 109, magnetic tape device 115, FD 116, or ROM (read-only memory).

In the inspection device 100, a high-magnification inspection optical system is constituted by the light source 103, the XYθ table 102, the illumination optical system 170, the magnification optical system 104, the TDI sensor 105, and the sensor circuit 106. The XYθ table 102 is driven by the table control circuit 114 under the control of the control computer 110. It can be moved by a drive system such as a three-axis (X-Y-θ) motor that drives in the X, Y, and θ directions. These X, Y, and θ motors can be, for example, step motors. The XYθ table 102 can be moved in the horizontal and rotational directions by the motors of the X, Y, and θ axes. The moving position of the substrate 101 placed on the XYθ table 102 is measured by the laser length measurement system 122 and supplied to the position circuit 107. In addition, the transport of the substrate 101 from the autoloader 130 to the XYθ table 102, and the transport process of the substrate 101 from the XYθ table 102 to the autoloader 130 are controlled by the autoloader control circuit 113.

Drawing data (design data) that is the basis for forming a pattern on the inspected substrate 101 is input from outside the inspection device 100 and stored in the magnetic disk device 109. The drawing data defines multiple graphic patterns, and each graphic pattern is usually composed of a combination of multiple element graphics. However, a graphic pattern composed of a single graphic may also exist. On the inspected substrate 101, a corresponding pattern is formed based on each of the graphic patterns defined in the drawing data.

Here, FIG. 1 shows the components necessary for explaining the first embodiment. It goes without saying that the inspection device 100 may also include other components that are normally required.

Figure 2 is a diagram showing an example of the arrangement of optical elements of the TDI sensor in embodiment 1. In Figure 2, the TDI sensor 105 has a two-dimensionally arranged photodiode (optical element) array that measures the amount of light. A photodiode array (optical element array) is composed of m1 photodiodes (optical elements) 11 (sensor pixels) in the x direction and m2 photodiodes (optical elements) in the y direction. For example, a photodiode array is composed of 1024 x 3584 photodiodes 11 in the x and y directions. The example of Figure 2 shows a case where a photodiode array is composed of 6 x 21 photodiodes 11. The example of Figure 2 also shows a case where the x direction is used as the scanning direction. In this case, the photodiode row composed of m1 photodiodes arranged in the x direction sequentially captures the same position at different times. Therefore, in the TDI sensor 105, the luminance value per pixel on the image is measured by integrating the light amount of the photodiode rows arranged in the x direction that capture the same position. In the first embodiment, a two-dimensionally arranged photodiode array is divided into a plurality of optical element groups 1 to 7 in an orthogonal direction (y direction) perpendicular to the integration direction (x direction). For example, the array is divided into a plurality of optical element groups 1 to 7 of 512 elements in the orthogonal direction (y direction). For example, in the case of a 1024 x 3584 photodiode array, each optical element group is made up of, for example, 1024 x 512 photodiodes 11. In the example of FIG. 2, each optical element group is made up of, for example, 6 x 3 photodiodes 11.

Figure 3 is a conceptual diagram for explaining the inspection area in the first embodiment. As shown in Figure 3, the inspection area 10 (whole inspection area) of the substrate 101 is virtually divided into a plurality of rectangular inspection stripes 20 with a scan width W, for example, in the Y direction. The inspection device 100 then acquires an image (stripe area image) for each inspection stripe 20. For each inspection stripe 20, an image of the figure pattern arranged within the inspection stripe 20 is captured in the longitudinal direction (X direction) of the stripe area using laser light (inspection light). In order to prevent missing images, it is preferable that the inspection stripes 20 are set so that adjacent inspection stripes 20 overlap with a predetermined margin width.

The movement of the XYθ table 102 causes the TDI sensor 105 to move continuously in the X direction relative to the substrate 101, thereby acquiring optical images. The TDI sensor 105 continuously captures optical images of a scan width W as shown in FIG. 3. In other words, the TDI sensor 105 captures optical images of the substrate 101 surface on which multiple graphic patterns are formed, while moving relatively in the integral direction of the TDI sensor 105. In the first embodiment, after capturing an optical image of one inspection stripe 20, the sensor moves in the Y direction to the position of the next inspection stripe 20, and then moves in the reverse direction to capture optical images of the scan width W in the same manner. In other words, imaging is repeated in the forward (FWD)-backward (BWD) directions, which go in opposite directions on the outward and return paths.

In addition, in actual inspection, the stripe region image of each inspection stripe 20 is divided into multiple rectangular frame region 30 images, for example, the size of the optical element group width in the scan width direction (y direction), as shown in FIG. 3. Then, inspection is performed for each frame region 30 image. For example, it is divided into a size of 512 x 512 pixels. In the example of FIG. 3, the imaging regions of the seven optical pixel groups capture images of seven sub-stripe regions (1) to (7) into which the inspection stripe 20 is divided in the y direction. Each optical pixel group captures an image of one sub-stripe region. Then, the image of each sub-stripe region is divided into multiple frame region 30 images in the scan direction. Therefore, a reference image to be compared with the image of the frame region 30 is also created for each frame region 30.

The imaging direction is not limited to repeated forward (FWD)-backward (BWD). Imaging may be performed from one direction. For example, FWD-FWD may be repeated. Or BWD-BWD may be repeated.

Figure 4 is a flow chart showing the main steps of the inspection method in embodiment 1. In Figure 4, the inspection method in embodiment 1 performs a series of steps including a group setting step (S90), an initial calibration step (S100), a scanning step (S102), a frame image creation step (S104), a reference image creation step (S110), a histogram (1) creation step (S120), a histogram (2) creation step (S122), a difference histogram creation step (S124), a fluctuation detection step (S130), a determination step (S132), a recalibration step (S134), a positioning step (S140), and a comparison step (S142).

In the group setting step (S90), the control computer 110 (group setting unit) sets multiple optical element groups in which the photodiode array of the TDI sensor 105 is divided in an orthogonal direction perpendicular to the integration direction. In the example of Figure 2, seven optical element groups 1 to 7 are set.

As an initial calibration step (S100), before mask inspection, calibration is performed, such as adjusting the amount of laser light and adjusting the gain for each photodiode 11 of the TDI sensor 105, so that a TDI sensor image with appropriate gradation values for the inspection is obtained.

Figure 5 is a diagram showing an example of the gradation value distribution of the TDI sensor before calibration in the first embodiment. In Figure 5, the vertical axis shows the gradation value per pixel when a white pattern is imaged. The horizontal axis shows the position of the photodiode array in a direction perpendicular to the scanning direction. In addition to the deviation in sensitivity due to individual differences, the sensitivity of each photodiode 11 of the TDI sensor 105 may vary due to deterioration, for example, when the period during which the photodiode is not exposed to laser light becomes long. Therefore, before calibration, as shown in Figure 5, the gradation value obtained as an image differs depending on the position in the direction perpendicular to the scanning direction. Therefore, before inspection, the sensitivity in the direction perpendicular to the scanning direction is adjusted to be uniform by adjusting the amount of light of the laser light and adjusting the gain for each photodiode 11 of the TDI sensor 105. The example of Figure 5 shows a case where, for example, for a dynamic range of 256 gradations, when a white pattern portion is imaged, the gradation value is adjusted to, for example, 200 gradations.

As mentioned above, the TDI sensor 105 has a problem in that the sensitivity of some sensor pixels increases over time due to degradation, etc.

Figure 6 is a diagram showing an example of the gradation value distribution of a TDI sensor in which sensitivity fluctuations have occurred during use in embodiment 1. In Figure 6, the vertical axis shows the gradation value per pixel when a white pattern is captured. The horizontal axis shows the position of the photodiode array in a direction perpendicular to the scanning direction. As shown in Figure 5, after the gradation values when the white pattern part is captured are uniformly adjusted by the calibration performed before the inspection, the sensitivity of the photodiode 11 (sensor pixel) in a part of the deteriorated area fluctuates as shown in Figure 6 by using the TDI sensor 105. In the example of Figure 6, a case is shown in which some sensor pixels that had low sensitivity before the calibration shown in Figure 5 have their sensitivity increased by use, and coupled with the adjustment amount by the calibration, the sensitivity has increased significantly from the set value. When sensitivity unevenness occurs in which the sensitivity of some of the multiple sensor pixels of the TDI sensor 105 changes, the sensitivity unevenness leads to gradation unevenness in the image. Therefore, there was a problem that it affects the inspection sensitivity. Therefore, it is desirable to quickly grasp the area of the sensor pixel in which the sensitivity abnormality has occurred due to the use of the TDI sensor 105. Therefore, in the first embodiment, in parallel with the normal inspection process, changes in the gradation value histogram for each optical element group are detected to detect optical element groups that include degraded photodiodes 11 (sensor pixels) that have experienced sensitivity fluctuations.

In the scanning step (S102), the optical image acquisition mechanism 150 captures an optical image on the surface of the substrate 101 on which multiple graphic patterns are formed, while moving the TDI sensor 105 relatively in the integration direction of the TDI sensor 105. In other words, the optical image acquisition mechanism 150 scans the inspection stripe 20 with a laser beam (inspection beam) and captures a stripe region image for each inspection stripe 20 with the TDI sensor 105. Specifically, it operates as follows. The XYθ table 102 is moved to a position where the target inspection stripe 20 can be imaged. The pattern formed on the substrate 101 is irradiated with a laser beam (e.g., DUV beam) having a wavelength below the ultraviolet range, which serves as inspection beam, from an appropriate light source 103 via the illumination optical system 170. The light transmitted through the substrate 101 is focused as an optical image on the TDI sensor 105 (an example of a sensor) via the magnification optical system 104 and is incident thereon.

The image of the pattern formed on the TDI sensor 105 is photoelectrically converted by each photodiode 11 of the TDI sensor 105, and further A/D (analog-digital) converted by the sensor circuit 106. Then, pixel data of the inspection stripe 20 to be measured is stored in the stripe pattern memory 123. When capturing such pixel data (stripe area image), the dynamic range of the TDI sensor 105 uses a dynamic range with a maximum gradation when the amount of illumination light incident is, for example, 60%. The measurement data (pixel data) is, for example, 8-bit unsigned data, and represents the brightness gradation (amount of light) of each pixel. After that, the stripe area image (stripe data) is sent to the comparison circuit 108 together with data indicating the position of the substrate 101 on the XYθ table 102 output from the position circuit 107.

Figure 7 is a diagram showing an example of the internal configuration of the comparison circuit in the first embodiment. In Figure 7, the comparison circuit 108 includes storage devices 70, 71, 72, and 76 such as magnetic disk devices, a frame image creation unit 74, a positioning unit 78, and a comparison processing unit 79. A series of "~ units" such as the frame image creation unit 74, the positioning unit 78, and the comparison processing unit 79 have processing circuits. Such processing circuits include electric circuits, computers, processors, circuit boards, quantum circuits, or semiconductor devices. In addition, each "~ circuit" may use a common processing circuit (the same processing circuit). Alternatively, different processing circuits (separate processing circuits) may be used. Input data or calculation results required for the frame image creation unit 74, the positioning unit 78, and the comparison processing unit 79 are stored in a memory (not shown) in the comparison circuit 108 or in memory 111 each time.

The stripe data (stripe area image) input to the comparison circuit 108 is stored in the storage device 70.

As a frame image creation step (S104), the frame image creation unit 74 (sub-optical image generation unit) generates a plurality of frame images (sub-optical images) in which the stripe area image (optical image) is divided by the imaging area width of the individual optical element groups of the plurality of optical element groups in the orthogonal direction (y direction) perpendicular to the integration direction (scanning direction) of the TDI sensor 105 and by a predetermined width in the integration direction. Specifically, as shown in FIG. 3, the stripe area image is divided into frame images of a plurality of rectangular frame areas 30 of the size of the optical element group width. For example, it is divided into a size of 512 x 512 pixels. In the example of FIG. 3, the seven sub-stripe area images (1) to (7) in which the inspection stripe 20 is divided in the y direction by the imaging areas of the seven optical pixel groups are each divided in the x direction, thereby creating a plurality of frame images (sub-optical images) captured over time for each optical pixel group. Since each substripe region is imaged in sequence in the scanning direction, there is a time lapse between the frame image captured immediately after the start of the scan and the frame image captured near the end of the scan. This process results in the acquisition of multiple frame images (optical images) corresponding to the multiple frame regions 30. The multiple frame images are stored in the storage device 76 and sent to the histogram creation circuit 140. In this manner, image (measured image) data to be compared for inspection is generated. Thus, a reference image to be compared with the image of the frame region 30 is also created for each frame region 30.

In the reference image creation step (S110), the reference image creation circuit 112 (reference image creation unit) creates multiple reference images corresponding to multiple frame images using the design pattern data that is the basis of the multiple graphic patterns. Specifically, it operates as follows. The reference image creation circuit 112 reads out drawing data (design pattern data) for each frame area 30 of the target inspection stripe 20 from the storage device 109 via the control computer 110, and converts each graphic pattern defined in the read design pattern data into binary or multi-value image data.

The figures defined in the design pattern data are, for example, rectangles and triangles as basic figures, and the figure data stored defines the shape, size, position, etc. of each pattern figure using information such as the coordinates (x, y) at the reference position of the figure, the length of the sides, and a figure code that serves as an identifier to distinguish the type of figure, such as a rectangle or triangle.

When the design pattern data that becomes such figure data is input to the reference image creation circuit, it is expanded to data for each figure, and the figure code and figure dimensions that indicate the figure shape of the figure data are interpreted. Then, it is expanded into binary or multi-value design pattern image data as a pattern arranged in a grid with a predetermined quantization dimension as a unit, and output. In other words, the design data is read, and the occupancy rate of the figure in the design pattern is calculated for each grid that is created by virtually dividing the frame area into grids with a predetermined dimension as a unit, and n-bit occupancy data (design image data) is output. For example, it is preferable to set one grid as one pixel. Then, if one pixel has a resolution of 1/2 ⁸ (=1/256), a small area of 1/256 is assigned to the area of the figure arranged in the pixel, and the occupancy rate in the pixel is calculated. Then, it is created as 8-bit occupancy data. Such grids (inspection pixels) can be aligned with the pixels of the measurement data.

Next, the reference image creation circuit 112 applies filtering to the design image data of the design pattern, which is image data of the graphic, using a filter function.

Figure 8 is a diagram for explaining the filter processing in the first embodiment. The pixel data of the optical image captured from the substrate 101 is in a state where a filter has been applied due to the resolution characteristics of the optical system used for capturing the image, in other words, in an analog state that changes continuously, so that, for example, as shown in Figure 8, the image intensity (gray value) is different from the developed image (design image) of digital values. Therefore, the reference image creation circuit 112 creates a reference image that is close to the optical image by performing image processing (filter processing) on the developed image. This allows the design image data, which is the image data on the design side with image intensity (gray value) of digital values, to be matched to the image generation characteristics of the measurement data (optical image). The created data of the reference image of each frame region 30 is sent to the comparison circuit 108 and also to the histogram creation circuit 142. The data of the reference image input to the comparison circuit 108 is stored in the storage device 72.

In the histogram (1) creation process (S120), the histogram creation circuit 140 (first histogram creation unit) creates a histogram (1) (first histogram) that indicates the frequency of each gradation value for each frame image of the multiple frame images.

9 is a diagram showing an example of a histogram (1) using a frame image (actual image) captured using a deteriorated sensor pixel in embodiment 1. In FIG. 9, the vertical axis indicates frequency (frequency). The horizontal axis indicates gradation value. In histogram (1), the frequency of gradation values of all pixels, for example, 512 x 512 pixels, in the target frame image is shown for each gradation value. In the example of FIG. 9, the same figure pattern, for example, a line and space pattern, is arranged in each frame region 30 in the same substripe region. Of course, different patterns may be arranged in each frame region 30. In the example of FIG. 9, the case where each pixel of the frame image is defined by 256 gradations, for example, 0 to 255, is shown. In a certain substripe region, in the frame image of the frame region 30 captured immediately after the start of scanning, a peak exists in the vicinity of 200 in gradation value (gradation level), and graph A1 is shown in which the frequency remains low at gradation values above that. When a white pattern (area without a pattern) is imaged, the gradation value (gradation level) is calibrated to be, for example, 200, so that the maximum gradation is usually around 200 gradation value. Next, in a frame image of the frame area 30 imaged at a time when a predetermined time has elapsed since the start of scanning, a peak exists in the gradation value (gradation level) of around 200, and further, graph A2 is shown in which the peak is maintained even at a gradation value slightly exceeding 200. Next, in a frame image of the frame area 30 imaged at a time when further time has elapsed from the time when the frame image of graph A2 was imaged, a peak exists in the gradation value (gradation level) of around 200, and in addition, graph A3 is shown in which a second peak occurs at a gradation value even larger than that of graph A2. Next, in the frame image of the frame region 30 captured at a time when further time has passed since the frame image of the graph A3 was captured, a peak exists near the gradation value (gradation level) of 200, and a second peak occurs at a gradation value even higher than that of the graph A3, as shown in graph A4. Next, in the frame image of the frame region 30 captured at a time when further time has passed since the frame image of the graph A4 was captured, a peak exists near the gradation value (gradation level) of 200, and a second peak occurs at a gradation value even higher than that of the graph A4, as shown in graph A5. In this way, in the range of gradation values higher than the gradation value 200 adjusted for the white pattern (area without pattern), a phenomenon occurs in which the peak moves to the higher gradation side over time. In the sub-stripe region captured by the optical pixel group including the deteriorated sensor image, this phenomenon occurs because the sensitivity of the deteriorated sensor image increases due to fluctuations over time.

In the histogram (2) creation step (S122), the histogram creation circuit 142 (second histogram creation unit) creates a histogram (2) (second histogram) that indicates the frequency of each gradation value for each reference image of the multiple reference images.

Figure 10 is a diagram showing an example of histogram (2) using a reference image (reference picture) in embodiment 1. In Figure 10, the vertical axis indicates frequency (frequency), and the horizontal axis indicates gradation value. Histogram (2) shows the frequency of gradation values for all pixels in the target reference image (e.g., 512 x 512 pixels) for each gradation value. Since there is no degradation of the sensor pixels in the reference image, as shown in the example of Figure 10, there is a peak at a gradation value (gradation level) of approximately 200, and graph B shows that the frequency remains low for gradation values above that.

In the difference histogram creation step (S124), the difference histogram creation circuit 144 (difference histogram creation unit) creates a difference histogram between histogram (1) and histogram (2) for each frame image. For example, the histogram (2) of the corresponding reference image is subtracted from the histogram (1) of the frame image that is the actual image. The difference calculation calculates the difference in frequency (frequency) for each gradation value.

11 is a diagram showing an example of a difference histogram between a histogram (1) using a frame image (actual image) captured using a deteriorated sensor pixel in embodiment 1 and a histogram (2) of a reference image. In Fig. 11, the vertical axis represents frequency, and the horizontal axis represents gradation value.
FIG. 12 is a diagram showing an example of a difference histogram between a histogram (1) using a frame image (actual image) captured using normal sensor pixels in the first embodiment and a histogram (2) of a reference image. In FIG. 12, the vertical axis indicates frequency. The horizontal axis indicates gradation value. Ideally, the difference frequency value becomes zero at each gradation value, but in reality, a gradation shift occurs, resulting in a difference frequency value that is not zero. In addition, in the white pattern portion, a gradation value shift occurs in the actual image. On the other hand, in the reference image, there is no shift or only a small shift occurs due to filtering. As a result, when the histogram (2) of the corresponding reference image is subtracted from the histogram (1) of the frame image that is the actual image, the difference frequency value becomes negative near the gradation value 200, as shown in FIG. 11 and FIG. 12. Here, when an image is captured using normal sensor pixels, as shown in FIG. 12, no peak movement occurs over time in the range of gradation values greater than the gradation value 200 adjusted for the white pattern (area without pattern). In contrast, when an image is captured using deteriorated sensor pixels, as shown in Fig. 11, a shift in the peak portion occurs over time in the range of gradation values greater than the gradation value 200 adjusted for the white pattern (area without pattern) (C1 to C5). Note that in the example of Fig. 11, a clear shift in the peak portion appears on the difference histogram, but this is not limited to this. The position of the gradation value that is a predetermined frequency counting from the maximum gradation value side shifts to the higher gradation value side over time. Therefore, in the first embodiment, such a shift in gradation values over time is detected.

In the variation detection step (S130), the detection circuit 146 (detection unit) detects the variation in the gradation value that has reached a predetermined frequency from the maximum gradation side in each difference histogram over time, using a plurality of difference histograms based on a plurality of frame images captured over time for each optical element group. Specifically, as shown in the difference histograms C1 to C5 in FIG. 11, it detects that the peak portion occurring in the range of gradation values greater than gradation value 200 moves toward the high gradation value side. For example, the position where the frequency reaches, for example, 100, counting from 255 gradations does not have to be the position of the maximum frequency of the peak portion. If the position where the frequency reaches, for example, 100, counting from 255 gradations, moves toward the high gradation value side over time, it can be said that the result is the same. As the predetermined frequency, it is preferable to use a value that does not fall below the base gradation value counting from the maximum gradation side. As the base gradation value, for example, the gradation value of the white pattern adjusted by calibration before inspection can be cited.

Here, a difference histogram may be created for each frame image for each substripe region, and fluctuation detection may be performed each time, but this is not limited to this. For example, it is preferable to create a difference histogram for every other frame image, every third frame, ..., every r frames (r is a natural number), and perform fluctuation detection each time. Also, for each substripe region (1) to (7) of the kth (k is a natural number) inspection stripe 20, comparison may be performed only using difference histograms for frame images in the same substripe region, but this is not limited to this. Fluctuation detection may be performed between the kth (k is a natural number) inspection stripe 20 and the k+mth (m is a natural number) inspection stripe 20 using difference histograms for frame images in corresponding substripe regions. The image obtained in the k+mth inspection stripe 20 can be compared because time has passed since the image was captured compared to the image obtained in the kth inspection stripe 20.

In the determination step (S132), the determination circuit 148 (determination unit) determines the optical element group in which sensitivity fluctuation has occurred based on the fluctuation in the gradation value.

Figure 13 is a diagram for explaining the method of determining sensitivity fluctuation in the first embodiment. In Figure 13, the vertical axis indicates the gradation value, and the horizontal axis indicates the frame image numbers k1 to k5 selected in chronological order. In a frame image captured by an optical element group including a normal sensor pixel, the gradation value that reaches a predetermined frequency (for example, frequency 100) from the maximum gradation side in the difference histogram does not change, for example, around 205. In contrast, in a frame image captured by an optical element group including a deteriorated sensor pixel, the gradation value that reaches a predetermined frequency (for example, frequency 100) from the maximum gradation side in the difference histogram fluctuates, for example, from around 205 to around 245. The determination circuit 148 determines an optical element group in which the gradient ΔN/Δt of the gradient value fluctuation that reaches a predetermined frequency (for example, frequency 100) exceeds a threshold value Th1. As the gradient ΔN/Δt of the gradient value fluctuation, it is preferable to use, for example, a value obtained by dividing the amount of change in the gradation value ΔN by the elapsed time Δt from the capture time of the frame image.

Alternatively, it is also preferable for the determination circuit 148 to determine the optical element group whose gradation value reaches a predetermined frequency (e.g., frequency 100) and exceeds the threshold value Th2.

It can be seen that the optical element group determined as described above contains a degraded sensor pixel (photodiode 11). The determined result is output. For example, it may be output to the magnetic disk device 109, magnetic tape device 115, flexible disk device (FD) 116, CRT 117, pattern monitor 118, or may be output from the printer 119.

As a result of the above, it is possible to quickly identify areas of optical elements where abnormalities in sensitivity have occurred due to use of the TDI sensor 105. This allows the TDI sensor 105 to be replaced. The TDI sensor 105 may be replaced even after the comparison process (S142) described below has been completed. Alternatively, the inspection may be stopped and the TDI sensor 105 may be replaced. Alternatively, if the determination indicates that a deteriorated optical element group exists, the sensitivity of the TDI sensor 105 may be calibrated again. The case of performing recalibration is described below.

In the recalibration step (S134), the sensitivity of the TDI sensor 105 is calibrated based on the variation in the gradation value. Specifically, for the optical element group in the photodiode array of the TDI sensor 105 in which the variation in gradation value has occurred, the gain of each photodiode 11 is adjusted, and correction is performed so that a base gradation value similar to that of the other normal photodiodes 11 is obtained. If there is an inspection stripe 20 that is performing a scan operation at the time when the optical element group in which the variation in gradation value has occurred is detected by judgment, recalibration should be performed after the scanning of that inspection stripe 20 is completed. In other words, it is preferable to perform recalibration during the stage movement period between the inspection stripes 20. Then, the process returns to the scanning step (S102), and the scanning of the next inspection stripe 20 is performed.

In the alignment step (S140), the alignment unit 78 reads out the frame image 30 (optical image) to be compared from the storage device 76, and also reads out the reference image to be compared from the storage device 72. Then, alignment is performed using a predetermined algorithm. For example, alignment is performed using the least squares method.

In the comparison step (S142), the comparison processing unit 79 (comparison unit) compares the frame image with the reference image corresponding to the frame image. In other words, the frame image and the reference image are compared for each frame area 30 (inspection unit area). In other words, the comparison processing unit 79 compares the frame image (optical image) of each frame area 30 of the multiple frame areas 30 (small areas) with the reference image corresponding to the frame image for each pixel to inspect the pattern for defects. Specifically, the comparison processing unit 79 compares the two for each pixel according to a predetermined judgment condition and judges the presence or absence of a defect such as a shape defect. As the judgment condition, for example, the two are compared for each pixel according to a predetermined algorithm and judge the presence or absence of a defect. For example, a difference value is calculated by subtracting the pixel value of the frame image from the pixel value of the reference image for each pixel, and if the difference value is greater than a threshold value Th, it is judged to be a defect. Then, the comparison result is output to the storage device 71. The comparison results may be output, for example, to the magnetic disk device 109, the magnetic tape device 115, the flexible disk device (FD) 116, the CRT 117, the pattern monitor 118, or from the printer 119.

When performing the above-mentioned recalibration process (S134), the comparison processing unit 79 compares a frame image captured by the TDI sensor 105, the sensitivity of which has been compensated by calibrating the sensitivity of the TDI sensor 105, with a reference image corresponding to the frame image.

In the above example, a case where die-database inspection (D-DB inspection) is performed has been described, but the present invention is not limited to this. Die-to-die inspection (D-D inspection) may also be performed. In such a case, the alignment unit 78 reads out from the storage device 76 another frame image (die 2) in which the same pattern as the frame image (die 1) to be inspected is arranged. Then, alignment is performed using a predetermined algorithm. For example, alignment is performed using the least squares method. Then, the comparison processing unit 79 (comparison unit) compares the frame image (die 1) with the frame image (die 2).

As described above, according to the first embodiment, it is possible to quickly identify areas of the optical element where sensitivity abnormalities have occurred due to use of the TDI sensor 105. As a result, it is possible to perform highly accurate inspections using the TDI sensor 105 with compensated sensitivity.

The above describes the embodiment with reference to specific examples. However, the present invention is not limited to these specific examples. For example, in the embodiment, a transmitted illumination optical system using transmitted light is shown as the illumination optical system 170, but the present invention is not limited to this. For example, a reflective illumination optical system using reflected light may be used. Alternatively, a transmitted illumination optical system and a reflective illumination optical system may be combined to use transmitted light and reflected light simultaneously.

In the above example, the base gradation value is adjusted to 200, but this is not limited to this. It may be greater than 200. Or it may be smaller. In the above example, in parallel with the normal inspection process, by detecting the change in the gradation value histogram for each optical element group, it is possible to detect an optical element group including a deteriorated photodiode 11 (sensor pixel) before the sensitivity of the photodiode 11 deteriorates to a degree that the accuracy of the inspection result cannot be tolerated. In addition, in the first embodiment, a frame image obtained by dividing the image of the substripe region is used to create a difference histogram, so that a deteriorated photodiode 11 is detected in units of optical element groups that acquire an image of the substripe region, but this is not limited to this. It is also possible to detect a deteriorated photodiode 11 in units of optical element groups that acquire an image of an area smaller or larger than the above-mentioned substripe region.

In addition, although the description of the device configuration, control method, and other parts that are not directly necessary for the explanation of the present invention have been omitted, the required device configuration and control method can be appropriately selected and used. For example, although the description of the control unit configuration that controls the inspection device 100 has been omitted, it goes without saying that the required control unit configuration can be appropriately selected and used.

All other methods for determining sensitivity fluctuations in time delay integration (TDI) sensors, pattern inspection methods, and pattern inspection devices that incorporate the elements of the present invention and that can be modified by a person skilled in the art are within the scope of the present invention.

10 Inspection area 11 Photodiode 20 Inspection stripe 30 Frame area 70, 71, 72, 76 Storage device 74 Frame image generating section 78 Alignment section 79 Comparison processing section 100 Inspection device 101 Substrate 102 XYθ table 103 Light source 104 Magnification optical system 105 TDI sensor 106 Sensor circuit 107 Position circuit 108 Comparison circuit 109 Magnetic disk device 110 Control computer 111 Memory 112 Reference image creation circuit 113 Autoloader control circuit 114 Table control circuit 115 Magnetic tape device 116 FD
117 CRT
118 Pattern monitor 119 Printer 120 Bus 122 Laser length measurement system 123 Stripe pattern memory 130 Autoloader 140, 142 Histogram creation circuit 144 Difference histogram creation circuit 146 Detection circuit 148 Judgment circuit 150 Optical image acquisition mechanism 160 Control circuit 170 Illumination optical system

Claims (5)

a step of capturing an optical image to be inspected on a sample surface on which a plurality of graphic patterns are formed, by using a time delay integration (TDI) sensor having a two-dimensionally arranged optical element array for measuring a light quantity, while relatively moving the TDI sensor in an integration direction of the TDI sensor;
setting a plurality of groups in which the optical element array is divided in an orthogonal direction perpendicular to the integration direction;
generating a plurality of sub-optical images by dividing the optical image by a width of an imaging area of each of the plurality of groups in the orthogonal direction and a predetermined width in the integral direction;
creating a first histogram indicating a frequency of each gradation value for each of the plurality of sub-optical images;
creating a plurality of reference images corresponding to the plurality of sub-optical images using design pattern data on which the plurality of geometric patterns are based;
creating a second histogram indicating a frequency of each gradation value for each of the plurality of reference images;
creating a difference histogram between the first histogram and the second histogram for each of the sub-optical images;
a step of detecting, for each group, a shift toward higher gradation values over time that has reached a predetermined frequency in a range of gradation values greater than a gradation value adjusted for a white pattern in each difference histogram, using a plurality of difference histograms based on a plurality of sub-optical images captured over time at different positions on the sample surface;
determining a group in which a sensitivity variation has occurred based on the variation in the gradation value, and outputting the result;
A method for determining a sensitivity fluctuation of a TDI sensor, comprising: The method for determining the sensitivity fluctuation of a TDI sensor according to claim 1, characterized in that a group is determined in which the gradient of the fluctuation in the gradation value that has reached the predetermined frequency exceeds a threshold value. The method for determining sensitivity fluctuations of a TDI sensor according to claim 1, characterized in that a group is determined in which the gradation value that has reached the specified frequency exceeds a threshold value. a step of capturing an optical image to be inspected on a sample surface on which a plurality of graphic patterns are formed, by using a time delay integration (TDI) sensor having a two-dimensionally arranged optical element array for measuring a light quantity, while relatively moving the TDI sensor in an integration direction of the TDI sensor;
setting a plurality of groups in which the optical element array is divided in an orthogonal direction perpendicular to the integration direction;
generating a plurality of sub-optical images by dividing the optical image by a width of an imaging area of each of the plurality of groups in the orthogonal direction and a predetermined width in the integral direction;
creating a first histogram indicating a frequency of each gradation value for each of the plurality of sub-optical images;
creating a plurality of reference images corresponding to the plurality of sub-optical images using design pattern data on which the plurality of geometric patterns are based;
creating a second histogram indicating a frequency of each gradation value for each of the plurality of reference images;
creating a difference histogram between the first histogram and the second histogram for each of the sub-optical images;
a step of detecting, for each group, a shift toward higher gradation values over time that has reached a predetermined frequency in a range of gradation values greater than a gradation value adjusted for a white pattern in each difference histogram, using a plurality of difference histograms based on a plurality of sub-optical images captured over time at different positions on the sample surface;
calibrating the sensitivity of the TDI sensor based on the variation in the grayscale value;
A step of comparing the sub-optical image captured by the TDI sensor whose sensitivity has been compensated by calibrating the sensitivity of the TDI sensor with a reference image corresponding to the sub-optical image, and outputting the result;
A pattern inspection method comprising: an optical image acquisition mechanism that uses a time delay integration (TDI) sensor having a two-dimensionally arranged optical element array for measuring light quantity, and captures an optical image to be inspected on a sample surface on which a plurality of graphic patterns are formed while relatively moving the TDI sensor in an integration direction of the TDI sensor;
a group setting unit that sets a plurality of groups into which the optical element array is divided in an orthogonal direction that is orthogonal to the integration direction;
a sub-optical image generating unit configured to generate a plurality of sub-optical images obtained by dividing the optical image by a width of an imaging area of each of the plurality of groups in the orthogonal direction and a predetermined width in the integral direction;
a first histogram creation unit that creates a first histogram indicating a frequency of each gradation value for each sub-optical image of the plurality of sub-optical images;
a reference image creation unit that creates a plurality of reference images corresponding to the plurality of sub-optical images by using design pattern data on which the plurality of figure patterns are based;
a second histogram creation unit that creates a second histogram indicating a frequency of each gradation value for each of the plurality of reference images;
a difference histogram creation unit that creates a difference histogram between the first histogram and the second histogram for each of the sub-optical images;
a detection unit that detects, for each group, a shift toward a higher gradation value over time that has reached a predetermined frequency in a range of gradation values greater than a gradation value adjusted for a white pattern in each difference histogram, using a plurality of difference histograms based on a plurality of sub-optical images captured over time at different positions on the sample surface;
a determination unit that determines a group in which a sensitivity change has occurred based on the change in the gradation value;
A comparison unit that compares the sub-optical image with a reference image corresponding to the sub-optical image;
A pattern inspection device comprising:

Images