Method and system for detecting symmetry of optical system, device and storage medium

Abstract

A symmetry detection method and system of an optical system, a device and a storage medium, the detection method comprising: providing a target to be detected, including a to-be-detected pattern, the to-be-detected pattern having a preset region of interest, the to-be-detected pattern in the preset region of interest being axisymmetric about a first symmetry axis extending in a specific direction; acquiring an image of the preset region of interest of the target to be detected by using the optical system to obtain an image of interest, the first symmetry axis extending in the specific direction being an axis in the image of interest, and the axis being a second symmetry axis; and obtaining a symmetry representation value of the optical system in the specific direction according to the image of interest, the symmetry representation value being a difference value of detection values of two reference positions symmetric about the second symmetry axis. The symmetry representation value of the detection parameter of the optical system in the specific direction is obtained based on the image of interest being axisymmetric, so that the symmetry of the optical system is evaluated in real time and accurately.

Description

Technical Field

[0001] The present invention relates to the field of optical detection technology, and in particular to a method, system, device and storage medium for detecting the symmetry of an optical system. Background Technology

[0002] Optical measurement equipment is a device that measures objects based on optical principles. Due to its advantages such as high measurement speed, non-contact operation, and lack of contamination, optical measurement has become the most commonly used measurement method. During measurement, the optical measurement equipment uses its illumination and imaging modules to acquire an image of the object under specific illumination conditions at a specific magnification. The acquired image signal is then processed to obtain the measurement result based on the image.

[0003] Therefore, to improve the accuracy of measurement results, the optical path system of the illumination module often needs to meet highly uniform illumination conditions (e.g., uniformity of illumination intensity and angle), and the imaging module also needs to ensure the alignment of all optical elements and a good conjugate relationship between the object and image sides. When the optical system experiences uneven illumination, off-axis, tilt, or deviation from conjugate, it will cause asymmetry in the imaging signal, thus affecting the measurement results. Therefore, the symmetry of the optical system has a significant impact on the accuracy of the measurement results. Summary of the Invention

[0004] The problem addressed by the embodiments of the present invention is to provide a method, system, device, and storage medium for detecting the symmetry of an optical system, which is beneficial for real-time and accurate evaluation of the symmetry of the optical system.

[0005] To address the aforementioned problems, embodiments of the present invention provide a method for symmetry detection of an optical system, comprising: providing a target to be tested, the target to be tested including a pattern to be tested, the pattern to be tested having a preset region of interest, and the pattern to be tested in the preset region of interest being axially symmetric about a first axis of symmetry extending along a specific direction; acquiring an image of the preset region of interest of the target to be tested using the optical system to obtain an image of interest, wherein the axis along the first axis of symmetry extending along the specific direction in the image of interest is a second axis of symmetry; and acquiring a symmetry characterization value of the optical system along the specific direction based on the image of interest, wherein the symmetry characterization value is the difference between the detection values ​​of two reference positions symmetrical about the second axis of symmetry, and the detection value is positively correlated with the grayscale value of the reference positions.

[0006] Accordingly, embodiments of the present invention also provide a symmetry detection system for an optical system, comprising: a target acquisition module for providing a target, the target including a pattern, the pattern having a preset region of interest, and the pattern in the preset region of interest being axially symmetric about a first axis of symmetry extending in a specific direction; a region of interest acquisition module for acquiring an image of the preset region of interest of the target using the optical system, thereby obtaining a region of interest image, wherein the axis of the first axis of symmetry extending in the specific direction in the region of interest image is a second axis of symmetry; and a symmetry characterization value acquisition module for acquiring a symmetry characterization value of the optical system along the specific direction based on the region of interest image, wherein the symmetry characterization value is the difference between the detection values ​​of two reference positions symmetrical about the second axis of symmetry, and the detection value is positively correlated with the grayscale value of the reference position.

[0007] Accordingly, embodiments of the present invention also provide a device including at least one memory and at least one processor, wherein the memory stores one or more computer instructions, and the one or more computer instructions are executed by the processor to implement the symmetry detection method of the optical system described in the embodiments of the present invention.

[0008] Accordingly, embodiments of the present invention also provide a storage medium storing one or more computer instructions, which are used to implement the symmetry detection method of the optical system described in the embodiments of the present invention.

[0009] Compared with the prior art, the technical solution of the embodiments of the present invention has the following advantages:

[0010] In the symmetry detection method of the optical system provided in this embodiment of the invention, the test pattern of the target has a preset region of interest, and the test pattern of the preset region of interest is axially symmetric about a first axis of symmetry extending along a specific direction. An image of the preset region of interest of the target is acquired using an optical system to obtain an image of interest. The axis of the first axis of symmetry extending along the specific direction in the image of interest is a second axis of symmetry. A symmetry characterization value of the optical system along the specific direction is obtained based on the image of interest. The symmetry characterization value is the difference between the detection values ​​of two reference positions symmetrical about the second axis of symmetry. Wherein, when the optical path of the optical system has a better... When symmetry is present, the consistency of the detected values ​​of two reference positions that are symmetrical about the second axis of symmetry should be high. When the symmetry of the optical path of the optical system is poor, the detected values ​​of the two reference positions that are symmetrical about the second axis of symmetry are prone to deviation. Therefore, by using a test pattern that is symmetrical about the first axis of symmetry extending in a specific direction, and based on the image of interest corresponding to the preset region of interest, a symmetry characterization value can be obtained. This allows for real-time evaluation of the symmetry of the optical system. Moreover, the symmetry characterization value can be obtained from the same image, thus avoiding the introduction of noise into the symmetry characterization value due to multiple imaging, which is beneficial for accurately evaluating the symmetry of the optical system. Attached Figure Description

[0011] Figure 1 This is a flowchart of an embodiment of the symmetry detection method for the optical system of the present invention;

[0012] Figure 2 yes Figure 1 In step S1, a top view of an embodiment of the target to be tested;

[0013] Figure 3 yes Figure 2 An enlarged view of the pattern to be tested;

[0014] Figure 4 yes Figure 1 In step S2, a schematic diagram of an embodiment of the target image is shown;

[0015] Figure 5 yes Figure 1 In step S3, a schematic diagram of one embodiment of the template image is shown;

[0016] Figure 6 yes Figure 1 In step S3, a schematic diagram is shown after obtaining the matching region in the target image;

[0017] Figure 7 yes Figure 1 In step S3, a schematic diagram after determining the first region of interest in the image to be tested;

[0018] Figure 8 yes Figure 1 Step S4 is a schematic diagram of an embodiment;

[0019] Figure 9 yes Figure 1 In step S5, a schematic diagram of an embodiment of the symmetrical distribution of the optical system is shown.

[0020] Figure 10 yes Figure 1 In step S5, a schematic diagram of another embodiment of the symmetrical distribution of the optical system is shown.

[0021] Figure 11 This is a functional block diagram of an embodiment of the symmetry detection system of the optical system of the present invention;

[0022] Figure 12 This is a hardware structure diagram of a device provided in an embodiment of the present invention. Detailed Implementation

[0023] As is known from the background art, when an optical system experiences uneven illumination, off-axis, tilt, or deviation from conjugate, it will cause asymmetry in the imaging signal, thus affecting the measurement results. Current methods for detecting the symmetry of optical systems are insufficient for real-time and accurate assessment of their symmetry.

[0024] To address the aforementioned technical problem, embodiments of the present invention provide a method for detecting the symmetry of an optical system. (Reference) Figure 1 The diagram illustrates a flowchart of an embodiment of the symmetry detection method for the optical system of the present invention. The symmetry detection method for the optical system described in this embodiment includes the following basic steps:

[0025] Step S1: Provide a target to be tested, the target to be tested includes a pattern to be tested, the pattern to be tested has a preset region of interest, and the pattern to be tested in the preset region of interest is axially symmetric about a first axis of symmetry extending in a specific direction;

[0026] Step S2: Use the optical system to acquire an image of the preset region of interest of the target under test, and obtain an image of interest. The axis of the first axis of symmetry extending along the specific direction in the image of interest is the second axis of symmetry.

[0027] Step S3: Obtain the symmetry characterization value of the optical system along the specific direction based on the image of interest. The symmetry characterization value is the difference between the detected values ​​of two reference positions that are symmetrical about the second symmetry axis. The detected value is positively correlated with the gray value of the reference position.

[0028] When the optical path of an optical system has good symmetry, the consistency of the detected values ​​of two reference positions that are symmetrical about the second axis of symmetry should be high. When the optical path of an optical system has poor symmetry, the detected values ​​of two reference positions that are symmetrical about the second axis of symmetry are prone to deviation. Therefore, by using a test pattern that is symmetrical about the first axis of symmetry extending in a specific direction, and based on the image of interest corresponding to a preset region of interest, a symmetry characterization value can be obtained. This allows for real-time evaluation of the symmetry of the optical system. Moreover, the symmetry characterization value can be obtained from the same image, thus avoiding the introduction of noise into the symmetry characterization value due to multiple imaging, which is beneficial for accurately evaluating the symmetry of the optical system.

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0030] Reference Figures 1 to 2 , Figure 1 This is a flowchart of an embodiment of the symmetry detection method for the optical system of the present invention. In this embodiment, the optical system is a bright-field imaging system.

[0031] Reference Figure 2 and Figure 3 Step S1 is executed, providing a target to be tested 100, the target to be tested 100 including a pattern to be tested 110, the pattern to be tested 110 having a preset region of interest 110i (e.g., Figure 3 As shown in the figure), the pattern 110 to be tested in the preset region of interest 110i is axially symmetrical about a first axis of symmetry (not shown) extending in a specific direction.

[0032] The test pattern 110 of the preset region of interest 110i is axially symmetric about a first axis of symmetry extending in a specific direction. Therefore, the symmetry of the optical system in the specific direction can be evaluated by assessing the symmetry of the detection value of the image of interest corresponding to the preset region of interest 110i.

[0033] Specifically, the symmetry of the optical system is subsequently characterized by the symmetry representation value of the detected values ​​corresponding to the image of interest. After acquiring the target image of the target 100 using the optical system, the target image includes the image of the pattern 110 to be tested, and the image of interest is the image corresponding to the region of the preset region of interest 110i in the image of the target. If the symmetry of the optical system is good (e.g., small imaging optical path aberrations and good alignment and conjugate relationship between the object and image sides), then the consistency of the detected values ​​of the two parameter positions that are axially symmetric about a second symmetry axis extending in a specific direction should also be good. Therefore, the symmetry representation value of the detected values ​​corresponding to the image of interest can characterize the symmetry of the optical system, thereby evaluating the deviation of the optical path of the optical system.

[0034] In this embodiment, the preset region of interest 110i of the pattern 110 under test is axially symmetric about a first axis of symmetry extending along a specific direction, thereby preparing for the subsequent acquisition of symmetry characterization values ​​of the image of interest that is axially symmetric about a second axis of symmetry. In this embodiment, according to the evaluation requirements of the symmetry of the optical system in different specific directions, there are multiple specific directions, including mutually perpendicular first directions (such as...). Figure 2 (as shown in the X direction) and the second direction (as shown in the X direction) Figure 2 shown in the Y direction).

[0035] In this embodiment, the pattern to be tested 110 is a centrally symmetrical pattern, and the intersection of the axes of symmetry of the first and second directions is the center of symmetry 110c of the pattern to be tested (e.g., Figure 3 (As shown). Specifically, the center of symmetry 110c of the pattern to be tested is defined as the first center of symmetry 110c. Accordingly, the subsequently obtained image of interest can be centrally symmetric about the second center of symmetry of the corresponding image to be tested, thereby preparing for obtaining the symmetry characterization value of the detection value corresponding to the image of interest that is centrally symmetric about the second center of symmetry.

[0036] It is understood that in other embodiments, a specific direction may also include directions with more angles. For example, a specific direction may include a first direction, a second direction, a third direction, and a fourth direction, with the angles between the second direction, the third direction, the fourth direction and the first direction being 45°, 90°, and 135°, respectively.

[0037] In this embodiment, the pattern to be tested 110 has two first regions of interest (ROI) groups, each ROI group including two preset regions of interest 110i that are axially symmetrical. The two preset regions of interest 110i in one ROI group are aligned along a first direction (e.g., ...). Figure 2The regions of interest (as shown in the X direction) are arranged and are axially symmetric about a first axis of symmetry extending along the second direction. The two preset regions of interest 110i of the other first region of interest group are arranged along the second direction (as shown in the X direction). Figure 2 The regions are arranged in the Y direction and are axially symmetric about a first axis of symmetry extending along the first direction. Specifically, the arrangement direction of the two preset regions of interest 110i in each first region of interest group is parallel to the width direction of the preset region of interest 110i.

[0038] Accordingly, the symmetry characterization value corresponding to the image of interest symmetrically set in the first direction is subsequently obtained as the symmetry characterization value in the first direction; the symmetry characterization value corresponding to the image of interest symmetrically set in the second direction is obtained as the symmetry characterization value in the second direction, thereby evaluating the symmetry of the optical system in the first and second directions.

[0039] For example, such as Figure 3 As shown, taking the pattern 110 to be tested as a rectangle as an example, the preset region of interest 110i includes a first preset region of interest 111i symmetrically arranged in a first direction and a second preset region of interest 112i symmetrically arranged in a second direction. The rectangle includes a first dimensional direction and a second dimensional direction that are perpendicular to each other; the first direction is parallel to the first dimensional direction of the rectangle, and the second direction is parallel to the second dimensional direction of the rectangle. For example, if the pattern 110 to be tested is a rectangle, then the first dimensional direction is the length direction of the rectangle, and the second dimensional direction is the width direction of the rectangle.

[0040] Therefore, in this embodiment, the pattern to be tested 110 includes at least one grid pattern; the at least one grid pattern is centrally symmetrical. By selecting a grid pattern, the pattern to be tested 110 of the preset region of interest 110i is axially symmetrical about a first axis of symmetry extending in a specific direction.

[0041] like Figure 2 As shown, in one specific embodiment, the target 100 includes a plurality of periodically repeating test patterns 110. By selecting a target 100 with a plurality of periodically repeating test patterns 110, it is easier to obtain the symmetry distribution of the optical system after subsequently obtaining the symmetry characterization value of the image of interest. Moreover, it can reduce the influence of the differences between each test pattern 110 on the symmetry distribution of the optical system, thereby facilitating an intuitive and accurate evaluation of the symmetry of the optical system.

[0042] As an example, the plurality of test patterns 110 are arranged in a matrix along a first direction and a second direction. By arranging the plurality of test patterns 110 in a matrix, the compactness of the arrangement of the test patterns 110 is improved, thereby ensuring a sufficient number of sampling data, which is beneficial for more accurate evaluation of the symmetry of the optical system. In other embodiments, the test patterns may also be arranged in other periodic patterns.

[0043] It should be noted that the pattern under test 110 has edge information, so that the symmetry representation value of the detection value corresponding to the image of interest can be obtained by using the detection value corresponding to the edge information of the pattern under test 110. It should also be noted that the target under test 100 is formed on the object under test (not shown). As an example, the object under test is a wafer. In other embodiments, the object under test can also be a chip or a screen panel.

[0044] Continue to refer to Figure 1 and in conjunction with references Figures 4 to 7 Step S2 is executed, using the optical system to acquire an image of the preset region of interest 110i of the target 100, resulting in an image of interest 250 (e.g., ...). Figure 7 As shown in the figure, the axis of the first axis of symmetry extending in a specific direction in the image of interest 250 is the second axis of symmetry.

[0045] Subsequently, the image signal of the image of interest 250 is acquired, and the difference between the detected values ​​at two reference positions that are axially symmetric about a second axis of symmetry extending along the specific direction is calculated. It should be noted that using the detected values ​​in the image of interest 250 to calculate the symmetry characterization value helps to avoid the influence of noise in the edge detection information of the pattern under test 110 on the calculation result of the symmetry characterization value, thereby facilitating the accurate evaluation of the symmetry of the optical system.

[0046] Specifically, acquiring an image of a preset region of interest 110i of the target 100 using the optical system to obtain an image of interest 250 includes: determining a first region of interest 210i in the image 210 (e.g., ... Figure 7 As shown), the first region of interest 210i is the region of the preset region of interest 110i of the pattern to be tested 110 in the image to be tested 210, and the image to be tested 210 in the first region of interest 210i is used as the image of interest 250 (e.g. Figure 7 (As shown). In this embodiment, the first region of interest 210i is centrally symmetrical about the second center of symmetry 310c of the corresponding image to be tested 210.

[0047] In this embodiment, the pattern 110 to be tested has two first regions of interest groups, each first region of interest group including two preset regions of interest 110i that are axially symmetrical, therefore, as Figure 7As shown, determining the first region of interest 210i in the image to be tested 210 includes: determining two groups of second regions of interest in the image to be tested 210, each group of second regions of interest including two axially symmetric first regions of interest 210i.

[0048] The arrangement direction of the two first regions of interest 210i in a second region of interest group (e.g.) Figure 7 The arrangement direction of the two first regions of interest 210i perpendicular to another second region of interest group (as shown in the X direction) is as follows: Figure 7 (As shown in the Y direction). Specifically, the arrangement direction of the two first regions of interest 210i in each second region of interest group is parallel to the width direction of the first region of interest 210i.

[0049] In this embodiment, the target to be tested 100 includes multiple periodically repeated test patterns 110, and the number of test images 210 is also multiple. Therefore, a multi-target template matching method is used to determine the first region of interest 210i of each test image 210.

[0050] The steps for determining the first region of interest 210i are described in detail below with reference to the accompanying drawings.

[0051] like Figure 4 As shown, the optical system is used to acquire a target image 200 of the target 100 under test, the target image 200 including a test image 210 corresponding to the test pattern 110. Subsequently, an image of interest 250 is obtained based on the target image 200.

[0052] like Figure 5 As shown, a template image 300 of the pattern to be tested 110 is obtained. The template image 300 has a detection range (not shown), and the template image 300 includes a preset positional relationship between the second region of interest 310i and the detection range. The second region of interest 310i is the region of the preset region of interest 110i of the pattern to be tested 110 in the template image 300.

[0053] In this embodiment, since the multiple test patterns 110 are repeated, as long as a template image 300 is obtained, multiple matching regions can be obtained in the entire target image 200 through multi-target matching using the template image 300, thereby obtaining the positions of each test pattern 110 within the field of view. The template image 300 includes a preset positional relationship between the second region of interest 310i and the detection range. Therefore, after obtaining the matching regions, the first region of interest can be determined in the test image 210 based on the preset positional relationship between the second region of interest 310i in the template image 300 and the detection range.

[0054] In this embodiment, the template image 300 has two third regions of interest (ROI) groups, each ROI group including two axisymmetric second regions of interest (ROIs) 310i. The arrangement direction of the two second ROIs 310i in one of the third ROI groups (e.g., ...) Figure 5 The arrangement direction of the two second regions of interest 310i perpendicular to another third region of interest group (as shown in the X direction) Figure 5 (As shown in the Y direction). Specifically, the arrangement direction of the two second regions of interest 310i in each third region of interest group is parallel to the width direction of the second region of interest 310i.

[0055] In this embodiment, the entire area of ​​the template image 300 is used as the detection range. In other embodiments, a local area of ​​the template image can also be used as the detection range. Accordingly, during subsequent matching, the template image outside the detection range can be occluded.

[0056] In this embodiment, the center of the detection range of the template image 300 coincides with the center of symmetry 110c (i.e., the first center of symmetry 110c) of the pattern to be tested; the preset positional relationship of the second region of interest 310i relative to the detection range is the positional relationship between the second region of interest 310i and the center of the detection range. As an example, the center of the detection range is the third center of symmetry 310c of the template image 300.

[0057] In this embodiment, after obtaining the template image 300, the target image 200 is matched with the template image 300. Multiple matching regions are obtained in the target image 200. The matching region is a region composed of connected pixel positions that have a similarity greater than or equal to a preset similarity threshold with the template image 300 within the detection range. Since the multiple test patterns 110 are repeated, the template image 300 can match multiple regions in the target image 200. Therefore, the matching region is a region whose similarity to the template image 300 within the detection range is greater than or equal to the preset similarity threshold.

[0058] The preset similarity threshold should not be too large or too small. If the preset similarity threshold is too small, the matching accuracy between the target image 200 and the template image 300 will be low, which may lead to the inability to meet the positioning accuracy requirements of the image 210 under test. If the preset similarity threshold is too large, the judgment standard may be too strict, which may lead to the inability to locate the position of each image 210 under test. Therefore, in this embodiment, the preset similarity threshold ranges from 0.85 to 0.98.

[0059] Specifically, the matching process between the target image 200 and the template image 300 includes: traversing the target image 200 using a matching window of the same size as the template image 300; calculating the correlation score between the region where the matching window is located in the target image 200 and the template image 300; the correlation score is negatively correlated with the variance or standard deviation of the grayscale values ​​of each pixel in the region where the matching window is located and the grayscale values ​​of each pixel in the template image 300; and obtaining the region where the matching window in the target image 200 has a correlation score greater than or equal to a preset threshold as the matching region, with the correlation score used as the similarity. As an example, a matching window of the same size as the template image 300 is selected in the target image 200; the matching window is slid across the target image 200 in a preset sliding direction, and the correlation score between the template image 300 and the region where the current matching window is located is calculated after each slide, thereby obtaining multiple correlation scores. For example, the matching window can be slid from the top left corner of the target image 200 to the right, with each slide being the size of a column of pixels. When it reaches the far right, it slides down by the size of a row of pixels. Then, it starts sliding from the far left of the target image 200 to the left, and so on, until the matching window has traversed every pixel of the target image 200.

[0060] It should be noted that the greater the similarity, the smaller the variance or standard deviation of the grayscale values ​​of each pixel in the matching window and each pixel in the template image 300. Therefore, the correlation score is negatively correlated with the variance or standard deviation of the grayscale values ​​of the matching window region and each pixel in the template image 300. Methods for calculating the correlation score include Mean Absolute Differences (MAD), Sum of Absolute Differences (SAD), Sum of Squared Differences (SSD), Mean Squared Differences (MSD), Normalized Cross Correlation (NCC), Sequential Similarity Detection Algorithm (SSDA), or Hadamard Transform.

[0061] In this embodiment, obtaining the correlation score between the region where the matching window is located in the target image 200 and the template image 300 includes obtaining the correlation score through cross-correlation processing. Specifically, the cross-correlation processing uses two-dimensional cross-correlation (NCC2D) operation to obtain the correlation score.

[0062] As an example, the relevance score is calculated using formula (1):

[0063]

[0064] Where NCC(p,d) represents the relevance score, and I1(x,y) represents the gray value at pixel (x,y) in the template image 300. Ix(x+p,y+d) represents the average gray value of pixels in template image 300, and I2(x+p,y+d) represents the gray value at pixel (x+p,y+d) in target image 200. Wp represents the average grayscale value of the pixels in the target image 200, Wp represents the region where the matching window is located in the target image 200, and · represents the product operation.

[0065] As another example, the correlation score can also be calculated using formula (2):

[0066]

[0067] Accordingly, in this embodiment, the preset similarity threshold is the threshold of the relevance score.

[0068] like Figure 6 and Figure 7 As shown, after obtaining the matching region, the first region of interest 210i is determined in the image to be tested 210 according to the preset positional relationship between the second region of interest 310i in the template image 300 and the detection range. The relative positional relationship between the first region of interest and the matching region is the same as the preset positional relationship.

[0069] Specifically, the steps for determining the first region of interest 210i include: obtaining the position of the matching center of the matching region; and determining the first region of interest 210i in the image to be tested 210 according to a preset positional relationship and the position of the matching center, such that the relative positional relationship between the center of the first region of interest 210i and the matching center is the same as the preset positional relationship. As an example, in the target image 200, the matching center of the matching region is the second center of symmetry 210c of the image to be tested 210.

[0070] As an example, the relevance score is usually highest at the center of the matching region. Therefore, the location of the similarity peak is extracted for each matching region to obtain the location of the matching center of each matching region. In other embodiments, the contour of each matching region can also be extracted separately using morphological algorithms, and the center location can be obtained based on the contour.

[0071] Accordingly, each image to be tested 210 includes two groups of images of interest, and each group of images of interest includes two axially symmetrical images of interest 250. The arrangement direction of the two images of interest 250 in a group of images of interest (e.g., Figure 7 The arrangement direction of the two images of interest 250 (as shown in the X direction) is perpendicular to another image group of interest (e.g., Figure 7 (As shown in the Y direction). Specifically, the arrangement direction of the two image groups of interest in each image group is parallel to the width direction of the image group of interest.

[0072] Continue to refer to Figure 1 and in conjunction with references Figure 8 Step S3 is executed to obtain the symmetry characterization value of the optical system along a specific direction based on the image of interest 250. The symmetry characterization value is the difference between the detected values ​​of two reference positions that are axially symmetric about a second axis of symmetry extending along the specific direction. The detected value is positively correlated with the gray value of the reference position.

[0073] When the optical path of an optical system has good symmetry, the consistency of the detected values ​​of two reference positions that are symmetrical about a second axis of symmetry extending in a specific direction should be high. Otherwise, the detected values ​​of two reference positions that are symmetrical about a second axis of symmetry extending in a specific direction are prone to deviation. Therefore, by using the test pattern 110 that is symmetrical about a first axis of symmetry extending in a specific direction and the image of interest 250 corresponding to the preset region of interest 110i, the symmetry characterization value is obtained, thereby evaluating the symmetry of the optical system in the specific direction in real time. Moreover, the symmetry characterization value can be obtained from the same image (i.e., the target image 200), thereby avoiding the introduction of noise into the symmetry characterization value due to multiple imaging, which is beneficial for accurately evaluating the symmetry of the optical system.

[0074] In this embodiment, obtaining the symmetry characterization value of the optical system along the specific direction based on the image of interest 250 includes: obtaining the symmetry characterization value of the detection value corresponding to the image of interest 250 symmetrically arranged in the first direction, as the symmetry characterization value in the first direction; and obtaining the symmetry characterization value of the detection value corresponding to the image of interest 250 symmetrically arranged in the second direction, as the symmetry characterization value in the second direction. Specifically, the difference between the detection values ​​of two reference positions symmetrical about a second axis of symmetry extending along the second direction is obtained as the symmetry characterization value in the first direction; the difference between the detection values ​​of two reference positions symmetrical about a second axis of symmetry extending along the first direction is obtained as the symmetry characterization value in the second direction.

[0075] The detected values ​​include the pixel's grayscale value, light intensity value, or charge value. In this embodiment, the detected value is described using the pixel's grayscale value as an example.

[0076] Specifically, obtaining the symmetry representation value includes: projecting the image of interest 250 along the projection direction, obtaining the correspondence between the positions of multiple pixels and the projection values ​​in the position arrangement direction as one-dimensional projection data, wherein the position arrangement direction is perpendicular to the specific direction, the projection direction is parallel to the specific direction, and the projection value is a weighted value of the detected values ​​of one or more pixels along the projection direction, wherein the detected values ​​are positively correlated with the grayscale value; selecting two reference positions that are axially symmetric about the second symmetry axis in the position arrangement direction of the one-dimensional projection data, wherein the reference positions are positions along the position arrangement direction; and obtaining the symmetry representation values ​​of the two reference positions based on the one-dimensional projection data.

[0077] One-dimensional projection data is used to represent image signals. The projection value is a weighted sum of the detected values ​​of one or more pixels along the projection direction. This allows the symmetry representation value of the detected value corresponding to the image of interest 250 to be represented based on the symmetry representation value obtained from the one-dimensional projection data. Furthermore, using one-dimensional projection data helps suppress noise, thereby improving the accuracy of the detected values.

[0078] In this embodiment, during the projection process, the image of the region between two images of interest 250 in the same image group of interest is also projected. Therefore, the two images of interest 250 in the same image group of interest correspond to one one-dimensional projection data.

[0079] Specifically, on the axis of the positional arrangement direction of the one-dimensional projection data, two reference positions that are axially symmetric about the second axis of symmetry are obtained, including: selecting two reference points that are axially symmetric about the second axis of symmetry in the positional arrangement direction of the one-dimensional projection data. Correspondingly, based on the one-dimensional projection data, a symmetry characterization value for the two reference positions is obtained, including: obtaining the difference between the projection values ​​of the two reference points as the symmetry characterization value. The better the symmetry of the optical path of the optical system, the better the symmetry of the reference points that are axially symmetric about the second axis of symmetry, and the smaller the corresponding difference in projection values ​​should be.

[0080] refer to Figure 8 , Figure 8 The graph shows the projection value as a function of the pixel position in any group of images of interest. The solid line L1 represents the curve corresponding to the one-dimensional projection data, and the dashed line L2 represents the curve of the mirrored data corresponding to the one-dimensional projection data.

[0081] Specifically, in the positional arrangement direction of the one-dimensional projection data that is symmetrical about the second axis of symmetry, two reference points that are symmetrical about the second axis of symmetry are selected, including: obtaining mirror data of the one-dimensional projection data; performing cross-correlation calculation on the one-dimensional projection data and its corresponding mirror data, and obtaining two reference points that are located at the same arrangement position in the projection direction of the one-dimensional projection data and the mirror data when the maximum cross-correlation value is obtained, wherein the arrangement position is the position along the positional arrangement direction.

[0082] In this embodiment, one-dimensional cross-correlation (NCC1D) is used to perform cross-correlation calculations on the one-dimensional projected data and its corresponding mirror data. When the cross-correlation calculation results in a maximum cross-correlation value, two reference points located at the same position in the projection direction are selected from the one-dimensional projected data and the mirror data. These are the two reference points of the one-dimensional projected data that are axially symmetric about the second axis of symmetry in the positional arrangement direction.

[0083] Specifically, in calculating the difference between the projected values ​​of two reference points, either of the two reference points is the extreme point of the one-dimensional projected data. Selecting the extreme point reduces the complexity of selecting reference points. Accordingly, the extreme point includes either the lowest point or the highest point. In this embodiment, the lowest point is taken as the extreme point; correspondingly, the difference between the projected values ​​of the two reference points is the foot difference. The position of the lowest point is the projected value of the edge signal of the pattern 110 under test; therefore, using the foot difference to characterize the symmetry representation value is more accurate.

[0084] In other embodiments, the difference between the projected values ​​of two reference points can be calculated using only one-dimensional projection data. Specifically, the one-dimensional projection data includes first projection data and second projection data located on both sides of the second axis of symmetry. In the arrangement direction of the one-dimensional projection data that is symmetrical about the second axis of symmetry, two reference points symmetrical about the second axis of symmetry are selected, including: selecting a position in the arrangement direction of the first projection data as a first reference point, and selecting a position symmetrical to the first reference point in the arrangement direction of the second projection data as a second reference point.

[0085] Accordingly, obtaining the difference between the projected values ​​of the two reference points as the symmetry representation value includes: obtaining the projected values ​​of the first reference point and the second reference point respectively; calculating the difference between the projected values ​​of the first reference point and the second reference point to obtain the symmetry representation value. Specifically, by dividing the one-dimensional projection data into first projection data and second projection data, the extreme points corresponding to the first projection data and the second projection data can be accurately obtained.

[0086] It should be noted that the preset region of interest 110i includes a first preset region of interest 111i symmetrically arranged in the first direction and a second preset region of interest 112i symmetrically arranged in the second direction. Therefore, in the process of obtaining the symmetry representation value, the value obtained in the first direction (e.g., Figure 7 The symmetry representation value of the detected value corresponding to the image of interest 250 symmetrically set in the X direction (as shown in the middle X direction) is used as the symmetry representation value in the first direction to obtain the symmetry representation value in the second direction (as shown in the middle X direction). Figure 7 The symmetry characterization value of the detected value corresponding to the image of interest 250 symmetrically set in the Y direction is used as the symmetry characterization value in the second direction, thereby evaluating the symmetry of the optical system in the first and second directions respectively.

[0087] It should also be noted that in this embodiment, the difference between the projection values ​​of the two reference points is directly used as the symmetry characterization value. In other embodiments, the normalized difference can also be used as the symmetry characterization value.

[0088] Accordingly, obtaining the symmetry representation value also includes: after calculating the difference between the projected values ​​of the two reference points, normalizing the difference between the projected values. Specifically, normalizing the difference between the projected values ​​includes: calculating the ratio of the difference between the projected values ​​to the detected value of the background of the image of interest. The detected values ​​of the background of the image of interest are usually equal, therefore, normalization can be performed using the detected value of the background of the image of interest.

[0089] Continue to refer to Figure 1 After obtaining the symmetry characterization value, the method further includes: performing step S4 to obtain the symmetry distribution of the optical system in the specific direction using the symmetry characterization values ​​of multiple test patterns 110.

[0090] The image to be tested 210 is the image to be tested corresponding to the pattern to be tested 110 located within the field of view of the imaging system. There are multiple patterns to be tested 110, and each pattern to be tested 110 has a corresponding symmetry characterization value. That is, the symmetry characterization value of each pattern to be tested 110 corresponds to the position of the pattern to be tested 110. Therefore, by using the symmetry characterization values ​​of multiple patterns to be tested 110 to obtain the symmetry distribution, the symmetry of the optical system can be evaluated more intuitively. As an example, the position of the corresponding pattern to be tested 110 is characterized by the position of the matching center of each matching region.

[0091] In this embodiment, the symmetry distribution includes a vector map, which is composed of symmetry representation value vectors corresponding to each of the test patterns 110. The symmetry representation value vector of each test pattern uses its corresponding symmetry center as the origin and its corresponding symmetry representation value in the first and second directions as the vector's coordinates. (Refer to reference...) Figure 9 , Figure 9 The arrows in the diagram represent the vectors formed by the symmetry representation values ​​of any test pattern 110 in the first and second directions. Figure 9 It can be seen that the closer to the center of the imaging system's field of view, the better the symmetry of the imaging system, thus allowing for an intuitive and accurate assessment of the symmetry of the optical system.

[0092] In other embodiments, the symmetry distribution may also include one or more grayscale images, each of which consists of symmetry representation values ​​of the respective test patterns in the same specific direction. For example, in conjunction with a reference... Figure 10 , Figure 10 In the middle (a), a grayscale image is shown, representing the distribution of symmetry characterization values ​​in the first direction. Figure 10 Image (b) represents a grayscale image of the symmetry representation value distribution in the second direction. The grayscale image can also represent the symmetry distribution of the imaging system in any direction. Specifically, when the symmetry representation value is 0, it indicates that the imaging system has good symmetry in that specific direction. Furthermore, since the symmetry representation value is the difference between the projection values ​​of two reference points, ... Figure 10 The symmetry characterization value can be greater than 0 or less than 0, thus allowing for an intuitive and accurate assessment of the symmetry of the optical system.

[0093] Accordingly, embodiments of the present invention also provide a symmetry detection system for an optical system. (See reference) Figure 11 This diagram illustrates a functional block diagram of an embodiment of the symmetry detection system of the optical system of the present invention. The following is in conjunction with reference to... Figures 2 to 10 The symmetry detection system of the optical system described in this embodiment will be explained.

[0094] The symmetry detection system of the optical system includes: a target acquisition module 10, used to provide a target 100, the target 100 including a pattern 110, the pattern 110 having a preset region of interest 110i (e.g., Figure 3 As shown), the test pattern 110 of the preset region of interest 110i is axially symmetric about a first axis of symmetry extending along a specific direction; the image of interest acquisition module 20 is used to acquire a target image 200 of the preset region of interest 110i of the test target 100 using an optical system, to obtain an image of interest 250, wherein the axis of the first axis of symmetry extending along the specific direction in the image of interest 250 is the second axis of symmetry; the symmetry characterization value acquisition module 30 is used to acquire the symmetry characterization value of the optical system along the specific direction according to the image of interest 250, wherein the symmetry characterization value is the difference between the detection values ​​of two reference positions symmetrical about the second axis of symmetry extending along the specific direction, and the detection value is positively correlated with the gray value of the reference position.

[0095] The test pattern 110 of the preset region of interest 110i is axially symmetric about a first axis of symmetry extending along a specific direction. Therefore, the symmetry of the optical system in the specific direction can be evaluated by assessing the symmetry of the detection value of the image of interest corresponding to the preset region of interest 110i. In this embodiment, according to the requirement of evaluating the symmetry of the optical system in different specific directions, there are multiple specific directions, including mutually perpendicular first directions (such as...). Figure 2 (as shown in the X direction) and the second direction (as shown in the X direction) Figure 2 shown in the Y direction).

[0096] In one specific embodiment, the pattern to be tested 110 is a centrally symmetric pattern, and the intersection of the axes of symmetry of the first direction and the second direction is the center of symmetry 110c of the pattern to be tested. Specifically, the center of symmetry 110c of the pattern to be tested is defined as the first center of symmetry 110c. It is understood that in other embodiments, the specific direction may also include directions with more angles.

[0097] In this embodiment, the pattern to be tested 110 has two first regions of interest (ROIs), each ROI including two axially symmetrical preset regions of interest (ROIs) 110i. The two preset ROIs 110i in one ROI are arranged along a first direction and are axially symmetrical about a first axis of symmetry extending along a second direction. The two preset ROIs 110i in the other ROI are arranged along a second direction and are axially symmetrical about a first axis of symmetry extending along the first direction.

[0098] Specifically, the arrangement direction of the two preset regions of interest 110i in each first region of interest group is parallel to the width direction of the preset region of interest 110i. For example, as Figure 3 As shown, taking the pattern 110 to be tested as a rectangle as an example, the preset region of interest 110i includes a first preset region of interest 111i symmetrically arranged in a first direction and a second preset region of interest 112i symmetrically arranged in a second direction. The rectangle includes a first dimensional direction and a second dimensional direction that are perpendicular to each other; the first direction is parallel to the first dimensional direction of the rectangle, and the second direction is parallel to the second dimensional direction of the rectangle. For example, if the pattern 110 to be tested is a rectangle, then the first dimensional direction is the length direction of the rectangle, and the second dimensional direction is the width direction of the rectangle.

[0099] Therefore, in this embodiment, the pattern to be tested 110 includes at least one grid pattern; the at least one grid pattern is centrally symmetrical. By selecting a grid pattern, the pattern to be tested 110 of the preset region of interest 110i is axially symmetrical about a first axis of symmetry extending in a specific direction. Figure 2As shown, in this embodiment, the target 100 includes multiple periodically repeating test patterns 110. By selecting a target 100 with multiple periodically repeating test patterns 110, it is easier to obtain the symmetry distribution of the optical system after acquiring the symmetry characterization value of the image of interest. Furthermore, it reduces the influence of the differences between each test pattern 110 on the symmetry distribution of the optical system, thereby facilitating a more intuitive and accurate evaluation of the symmetry of the optical system. As an example, the multiple test patterns 110 are arranged in a matrix along a first direction and a second direction. In other embodiments, the test patterns can also be arranged in other periodic patterns.

[0100] It should be noted that the pattern to be tested 110 has edge information so that the symmetry representation value of the detection value corresponding to the image of interest can be obtained by using the detection value corresponding to the edge information of the pattern to be tested 110.

[0101] It should also be noted that the target under test 100 is formed on the object under test (not shown). As an example, the object under test is a wafer. In other embodiments, the object under test can also be a chip or a screen panel. In this embodiment, the image under test 210 is the image 210 corresponding to the pattern 110 under test located within the field of view of the imaging system.

[0102] The image of interest acquisition module 20 is used to acquire the image of interest 250, thereby enabling the calculation of the difference between the detected values ​​of two reference positions that are axially symmetric about an axis of symmetry extending in a specific direction by acquiring the image signal of the image of interest 250. Specifically, the image of interest acquisition module 20 is used to determine a first region of interest 210i (e.g., ...) in the image to be tested 210. Figure 7 As shown), the first region of interest 210i is the region of the preset region of interest 110i of the pattern to be tested 110 in the image to be tested 210, and the image to be tested 210 in the first region of interest 210i is used as the image of interest 250 (e.g. Figure 7 (As shown).

[0103] In this embodiment, the first region of interest 210i is centrally symmetrical about the second center of symmetry 310c of the corresponding image to be tested 210.

[0104] like Figure 7 As shown, the image of interest acquisition module 20 is used to determine two second regions of interest groups in the image to be tested 210. Each second region of interest group includes two first regions of interest 210i that are axially symmetrical. The arrangement direction of the two first regions of interest 210i in a second region of interest group (e.g., Figure 7 The arrangement direction of the two first regions of interest 210i perpendicular to another second region of interest group (as shown in the X direction) is as follows: Figure 7(As shown in the Y direction). Specifically, the arrangement direction of the two first regions of interest 210i in each second region of interest group is parallel to the width direction of the first region of interest 210i.

[0105] In this embodiment, the target to be tested 100 includes multiple periodically repeated test patterns 110, and the number of test images 210 is also multiple. Therefore, the region of interest localization module 30 uses a multi-target template matching method to determine the first region of interest 210i of each test image 210.

[0106] Specifically, the image of interest acquisition module 20 includes a target image acquisition unit (not shown), used to acquire a target image 200 of the target to be tested 100 using the optical system, the target image 200 including the test image 210 corresponding to the test pattern 110. Subsequently, an image of interest 250 is obtained based on the target image 200.

[0107] The image acquisition module 20 also includes: a template image acquisition unit (not shown), used to acquire a template image 300 of the pattern 110 to be tested (e.g., Figure 5 As shown), the template image 300 has a detection range (not shown), and the template image 300 includes a preset positional relationship between the second region of interest 310i and the detection range. The second region of interest 310i is the region of the preset region of interest 110i of the pattern to be tested 110 in the template image 300.

[0108] In this embodiment, the template image 300 has two third regions of interest groups, each third region of interest group including two axisymmetric second regions of interest 310i. The arrangement direction of the two second regions of interest 310i in a third region of interest group (e.g., Figure 5 The arrangement direction of the two second regions of interest 310i perpendicular to another third region of interest group (as shown in the X direction) Figure 5 (As shown in the Y direction). Specifically, the arrangement direction of the two second regions of interest 310i in each third region of interest group is parallel to the width direction of the second region of interest 310i.

[0109] In this embodiment, the entire area of ​​the template image 300 is used as the detection range. In other embodiments, a local area of ​​the template image can also be used as the detection range. Accordingly, during matching, the template image outside the detection range can be occluded.

[0110] In this embodiment, the center of the detection range of the template image 300 coincides with the center of symmetry 110c of the pattern to be tested (i.e., the first center of symmetry 110c); the preset positional relationship of the second region of interest 310i relative to the detection range is the positional relationship between the second region of interest 310i and the center of the detection range. As an example, the center of the detection range is the third center of symmetry 310c of the template image 300.

[0111] In this embodiment, the image of interest acquisition module 20 further includes a matching unit (not shown), which is used to perform matching processing on the target image 200 and the template image 300, and to acquire multiple matching regions in the target image 200. The matching region is a region composed of connected pixel positions that have a similarity greater than or equal to a preset similarity threshold with the template image 300 within the detection range.

[0112] Multiple test patterns 110 are repeated, and the template image 300 can match multiple regions in the target image 200. Therefore, the matching region is the region whose similarity to the template image 300 within the detection range is greater than or equal to a preset similarity threshold. In this embodiment, the preset similarity threshold ranges from 0.85 to 0.98.

[0113] The matching unit calculates the relevance score using methods including the mean absolute difference algorithm, the sum of absolute errors algorithm, the sum of squared errors algorithm, the mean sum of squared errors algorithm, the normalized cross-correlation algorithm, the sequential similarity detection algorithm, or the Hadamard transform algorithm. In this embodiment, the matching unit obtains the relevance score through cross-correlation processing. Specifically, the cross-correlation processing uses two-dimensional cross-correlation operations to obtain the relevance score. Accordingly, in this embodiment, the preset similarity threshold is the threshold for the relevance score.

[0114] like Figure 6 and Figure 7 As shown, the image of interest acquisition module 20 further includes: a positioning unit (not shown), used to locate the image based on the template image 300 (e.g., ...). Figure 5 The second region of interest 310i in the image shown is determined by the preset positional relationship between the second region of interest 310i and the detection range. The first region of interest 210i is determined in the image to be tested 210. The relative positional relationship between the first region of interest and the matching region is the same as the preset positional relationship.

[0115] Specifically, after the localization unit obtains the position of the matching center of the matching region, it determines a first region of interest 210i in the image to be tested 210 according to a preset positional relationship and the position of the matching center, such that the relative positional relationship between the center of the first region of interest 210i and the matching center is the same as the preset positional relationship. As an example, in the target image 200, the matching center of the matching region is the second center of symmetry 210c of the image to be tested 210. As an example, the relevance score at the center position of the matching region is usually the highest; therefore, the position of the similarity peak of each matching region is extracted to obtain the position of the matching center of each matching region. In other embodiments, the position of the centroid of each matching region is extracted using a morphological algorithm.

[0116] Accordingly, each image to be tested 210 includes two groups of images of interest, and each group of images of interest includes two axially symmetrical images of interest 250. The arrangement direction of the two images of interest 250 in a group of images of interest (e.g., Figure 7 The arrangement direction of the two images of interest 250 (as shown in the X direction) is perpendicular to another image group of interest (e.g., Figure 7 (As shown in the Y direction). Specifically, the arrangement direction of the two image groups of interest in each image group is parallel to the width direction of the image group of interest.

[0117] The symmetry characterization value acquisition module 30 is used to acquire the symmetry characterization value of the optical system along a specific direction based on the image of interest 250. When the optical path of the optical system has good symmetry, the consistency of the detected values ​​of the two reference positions that are axially symmetric about the second axis of symmetry extending along the specific direction should be high. Otherwise, the detected values ​​of the two reference positions that are axially symmetric about the second axis of symmetry extending along the specific direction are prone to deviation. Therefore, the test pattern 110 that is axially symmetric about the first axis of symmetry extending along the specific direction is used, and the image of interest 250 corresponding to the preset region of interest 110i is used to obtain the symmetry characterization value, thereby evaluating the symmetry of the optical system in the specific direction in real time. Moreover, the symmetry characterization value can be obtained from the same image (i.e., the target image 200), thereby avoiding the introduction of noise into the symmetry characterization value due to multiple imaging, which is beneficial for accurately evaluating the symmetry of the optical system.

[0118] In this embodiment, the symmetry characterization value acquisition module 30 acquires the difference between the detected values ​​of two reference positions symmetrical about a second symmetry axis extending along a first direction, as the symmetry characterization value in the first direction; and acquires the difference between the detected values ​​of two reference positions symmetrical about a second symmetry axis extending along a second direction, as the symmetry characterization value in the second direction.

[0119] The detected values ​​include the pixel's grayscale value, light intensity value, or charge value. In this embodiment, the detected value is the pixel's grayscale value.

[0120] Specifically, the symmetry characterization value acquisition module 30 includes: a projection unit (not shown), used to project the image of interest 250 along the projection direction, and acquire the correspondence between the positions of multiple pixels and the projection values ​​in the position arrangement direction as one-dimensional projection data, wherein the position arrangement direction is perpendicular to the specific direction, the projection direction is parallel to the specific direction, and the projection value is a weighted value of the detected values ​​of one or more pixels along the projection direction, and the detected values ​​are positively correlated with the gray value; a reference position selection unit (not shown), used to select two reference positions that are axially symmetric about a second symmetry axis in the position arrangement direction of the one-dimensional projection data, wherein the reference positions are positions along the position arrangement direction; and a symmetry characterization value acquisition unit (not shown), used to acquire the symmetry characterization values ​​of the two reference positions based on the one-dimensional projection data.

[0121] In this embodiment, during the projection process, the projection unit also projects the image of the region between two images of interest 250 in the same image group of interest. Therefore, the two images of interest 250 in the same image group of interest correspond to one one-dimensional projection data.

[0122] Specifically, the reference position selection unit is used to select two reference points that are symmetrical about the second axis of symmetry in the positional arrangement direction of the one-dimensional projection data that are symmetrical about the second axis of symmetry. Correspondingly, the symmetry characterization value acquisition unit is used to acquire the difference between the projection values ​​of the two reference points as the symmetry characterization value. The better the symmetry of the optical path of the optical system, the better the symmetry of the reference points symmetrical about the second axis of symmetry, and the smaller the corresponding difference in projection values ​​should be.

[0123] refer to Figure 8 , Figure 8 The graph shows the projection value as a function of the pixel position in any group of images of interest. The solid line L1 represents the curve corresponding to the one-dimensional projection data, and the dashed line L2 represents the curve of the mirrored data corresponding to the one-dimensional projection data.

[0124] Specifically, the reference position selection unit includes: a mirror data acquisition subunit, used to acquire mirror data of the one-dimensional projection data; a cross-correlation calculation subunit, used to perform cross-correlation calculation on the one-dimensional projection data and its corresponding mirror data; and a filtering subunit, used to acquire two reference points that have the maximum cross-correlation value and are located at the same position in the projection direction in the one-dimensional projection data and mirror data, wherein the position is along the position arrangement direction. In this embodiment, the cross-correlation calculation subunit uses one-dimensional cross-correlation operation to perform cross-correlation calculation on the one-dimensional projection data and its corresponding mirror data.

[0125] Specifically, either of the two reference points is the extreme point of the one-dimensional projection data. Selecting the extreme point reduces the complexity of selecting reference points. Accordingly, the extreme point includes either the lowest point or the highest point. In this embodiment, taking the lowest point as the extreme point, the difference between the projected values ​​of the two reference points is the foot difference. The position of the lowest point is the projected value of the edge signal of the pattern 110 under test; therefore, using the foot difference to characterize the symmetry representation value is more accurate.

[0126] In other embodiments, the difference between the projected values ​​of two reference points can be calculated using only one-dimensional projection data. Specifically, the one-dimensional projection data includes first projection data and second projection data located on both sides of the second axis of symmetry. The reference position selection unit is used to select a position as a first reference point in the positional arrangement direction of the first projection data, and to select a position symmetrical to the first reference point as a second reference point in the positional arrangement direction of the second projection data. Correspondingly, the symmetry characterization value acquisition unit is used to acquire the projection values ​​of the first reference point and the second reference point respectively; calculate the difference between the projection values ​​of the first reference point and the second reference point to obtain the symmetry characterization value.

[0127] By dividing the one-dimensional projection data into first projection data and second projection data, the maximum and minimum points corresponding to the first projection data and the second projection data can be accurately obtained.

[0128] In this embodiment, the first direction (e.g.) is obtained Figure 7 The symmetry representation value of the detected value corresponding to the image of interest 250 symmetrically set in the X direction (as shown in the middle X direction) is used as the symmetry representation value in the first direction to obtain the symmetry representation value in the second direction (as shown in the middle X direction). Figure 7 The symmetry characterization value of the detected value corresponding to the image of interest 250 symmetrically set in the Y direction is used as the symmetry characterization value in the second direction, thereby evaluating the symmetry of the optical system in the first and second directions respectively.

[0129] It should also be noted that in this embodiment, the difference between the projection values ​​of the two reference points is directly used as the symmetry representation value. In other embodiments, the normalized difference can also be used as the symmetry representation value. Accordingly, the symmetry representation value acquisition module further includes a normalization processing unit, used to normalize the difference between the projection values. Specifically, the normalization processing unit is used to calculate the ratio of the difference between the projection values ​​to the detected value of the background of the image of interest, so as to achieve normalization processing. The detected values ​​of the background of the image of interest are usually equal, therefore, normalization processing can be performed using the detected value of the background of the image of interest.

[0130] Continue to refer to Figure 11In this embodiment, the symmetry detection system of the optical system further includes: a symmetry distribution acquisition module 40, which is used to acquire the symmetry distribution of the optical system in the specific direction by using the symmetry characterization values ​​of multiple test patterns 110.

[0131] The image to be tested 210 is the image to be tested corresponding to the pattern to be tested 110 located within the field of view of the imaging system. There are multiple patterns to be tested 110. Therefore, by using the symmetry characterization values ​​of multiple patterns to be tested 110 to obtain the symmetry distribution, the symmetry of the optical system can be evaluated more intuitively.

[0132] In this embodiment, the symmetry distribution includes a vector map, which is composed of symmetry representation value vectors corresponding to each test pattern 110. The symmetry representation value vector of each test pattern uses its corresponding symmetry center as the origin and its corresponding symmetry representation values ​​in the first and second directions as the vector's coordinates. (Refer to reference...) Figure 9 , Figure 9 The arrows in the diagram represent the vectors formed by the symmetry representation values ​​of any test pattern 110 in the first and second directions. Figure 9 It can be seen that the closer to the center of the imaging system's field of view, the better the symmetry of the imaging system, thus allowing for an intuitive and accurate assessment of the symmetry of the optical system.

[0133] In other embodiments, the symmetry distribution may also include one or more grayscale images, each grayscale image consisting of symmetry representation values ​​of the respective test patterns in the same specific direction. (Refer to reference...) Figure 10 , Figure 10 In the middle (a), a grayscale image is shown, representing the distribution of symmetry characterization values ​​in the first direction. Figure 10 Image (b) represents a grayscale image of the symmetry representation value distribution in the second direction. The grayscale image can also represent the symmetry distribution of the imaging system in any direction. Specifically, when the symmetry representation value is 0, it indicates that the imaging system has good symmetry in that specific direction. Furthermore, since the symmetry representation value is the difference between the projection values ​​of two reference points, ... Figure 10 The symmetry characterization value can be greater than 0 or less than 0, thus allowing for an intuitive and accurate assessment of the symmetry of the optical system.

[0134] This invention also provides a device that can implement the optical system symmetry detection method provided in this invention by loading a program for the above-described optical system symmetry detection method.

[0135] refer to Figure 12 The diagram illustrates the hardware structure of a device according to an embodiment of the present invention. The device in this embodiment includes: at least one processor 01, at least one communication interface 02, at least one memory 03, and at least one communication bus 04.

[0136] In this embodiment, the number of processor 01, communication interface 02, memory 03 and communication bus 04 is at least one, and the processor 01, communication interface 02 and memory 03 communicate with each other through the communication bus 04.

[0137] The communication interface 02 can be an interface of a communication module used for network communication, such as the interface of a GSM module.

[0138] The processor 01 may be a central processing unit (CPU), an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the symmetry detection method of the optical system described in this embodiment.

[0139] The memory 03 may include high-speed RAM and may also include non-volatile memory, such as at least one disk storage device. The memory 03 stores one or more computer instructions, which are executed by the processor 01 to implement the symmetry detection method for the optical system provided in the foregoing embodiments.

[0140] It should be noted that the aforementioned terminal device may also include other devices (not shown) that may not be essential to understanding the content disclosed in the embodiments of the present invention; given that these other devices may not be essential for understanding the content disclosed in the embodiments of the present invention, the embodiments of the present invention will not describe them one by one.

[0141] This invention also provides a storage medium storing one or more computer instructions for implementing the symmetry detection method of the optical system provided in the foregoing embodiments.

[0142] In the symmetry detection method of the optical system provided in this embodiment of the invention, the test pattern of the target has a preset region of interest, and the test pattern of the preset region of interest is axially symmetric about a first axis of symmetry extending along a specific direction. An image of the preset region of interest of the target is acquired using an optical system to obtain an image of interest. The axis of the first axis of symmetry extending along the specific direction in the image of interest is a second axis of symmetry. A symmetry characterization value of the optical system along the specific direction is obtained based on the image of interest. The symmetry characterization value is the difference between the detection values ​​of two reference positions symmetrical about the second axis of symmetry. Wherein, when the optical path of the optical system has a better alignment... When symmetry is achieved, the consistency of the detected values ​​of two reference positions that are symmetrical about the second axis of symmetry should be high. When the symmetry of the optical path of the optical system is poor, the detected values ​​of the two reference positions that are symmetrical about the second axis of symmetry are prone to deviation. Therefore, by using the test pattern that is symmetrical about the first axis of symmetry extending in a specific direction, and based on the image of interest corresponding to the preset region of interest, the symmetry characterization value can be obtained. This allows for real-time evaluation of the symmetry of the optical system. Moreover, the symmetry characterization value can be obtained from the same image, thus avoiding the introduction of noise into the symmetry characterization value due to multiple imaging, which is beneficial for accurately evaluating the symmetry of the optical system.

[0143] The embodiments of the present invention described above are combinations of elements and features of the present invention. Unless otherwise stated, the elements or features described are optional. Individual elements or features may be practiced without combination with other elements or features. Furthermore, embodiments of the present invention may be constructed by combining some elements and / or features. The order of operations described in the embodiments of the present invention may be rearranged. Some constructions of any embodiment may be included in another embodiment and may be replaced by corresponding constructions of another embodiment. It will be apparent to those skilled in the art that claims in the appended claims that are not expressly referenced to each other may be combined to form embodiments of the present invention, or may be included as new claims in amendments made after the filing of this application.

[0144] Embodiments of the present invention can be implemented by various means, such as hardware, firmware, software, or combinations thereof. In a hardware configuration, the method according to an exemplary embodiment of the present invention can be implemented by one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, etc.

[0145] In firmware or software configuration, embodiments of the present invention can be implemented in the form of modules, processes, functions, etc. Software code can be stored in a memory unit and executed by a processor. The memory unit is located inside or outside the processor and can send data to and receive data from the processor via various known means.

[0146] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is accorded the widest scope consistent with the principles and novel features disclosed herein.

[0147] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for detecting the symmetry of an optical system, characterized in that, include: A target to be tested is provided, the target to be tested includes a plurality of periodically repeated test patterns, the test patterns have a preset region of interest, and the test patterns in the preset region of interest are axially symmetric about a first axis of symmetry extending in a specific direction; The optical system is used to acquire a target image of the target under test, the target image including test images corresponding to a plurality of test patterns respectively; A first region of interest is determined for each image to be tested. The first region of interest is the region in the image to be tested that is a preset region of interest of the pattern to be tested. The image to be tested in the first region of interest is used as the image of interest of the image to be tested. The axis of symmetry that lies in the image of interest along the specific direction is the second axis of symmetry. For each image of interest, a symmetry characterization value of the optical system along a specific direction is obtained. The symmetry characterization value is the difference between the detected values ​​of two reference positions symmetrical about the second symmetry axis. The detected value is positively correlated with the gray value of the reference position. This includes: projecting the image of interest along a projection direction, obtaining the correspondence between the positions of multiple pixels and the projected values ​​in the position arrangement direction as one-dimensional projection data, wherein the position arrangement direction is perpendicular to the specific direction, the projection direction is parallel to the specific direction, and the projection value is a weighted value of the detected values ​​of one or more pixels along the projection direction. The detected value is positively correlated with the gray value. In the positional arrangement direction of the one-dimensional projection data, two reference positions that are axially symmetric about the second axis of symmetry are selected, and the reference positions are positions along the positional arrangement direction; based on the one-dimensional projection data, the difference between the projection values ​​of the two reference positions is obtained as a symmetry characterization value; By utilizing the symmetry characterization values ​​corresponding to the multiple patterns under test, the symmetry distribution of the optical system in the specific direction is obtained.

2. The symmetry detection method for an optical system as described in claim 1, characterized in that, The specific direction is multiple, and the multiple specific directions include a first direction and a second direction that are perpendicular to each other; Obtaining the symmetry characterization value of the optical system along the specific direction for each of the images of interest includes: obtaining the difference between the detection values ​​of two reference positions symmetrical about a second axis of symmetry extending along the second direction, as the symmetry characterization value in the first direction; The difference between the detected values ​​of two reference positions symmetrical about a second axis of symmetry extending along the first direction is obtained as a symmetry characterization value in the second direction.

3. The symmetry detection method for an optical system as described in claim 1, characterized in that, In the process of obtaining the symmetry distribution of the optical system in a specific direction by using the symmetry characterization values ​​corresponding to the multiple test patterns respectively, the symmetry distribution includes one or more grayscale images, each of which is composed of the symmetry characterization values ​​of each test pattern in the same specific direction; or, The specific direction is multiple, including a first direction and a second direction that are perpendicular to each other, and the intersection of the first axis of symmetry of the first direction and the second direction is the center of symmetry of the pattern to be tested. The symmetry distribution includes a vector map, which is composed of symmetry representation value vectors corresponding to each of the patterns to be tested. The symmetry representation value vector of each pattern to be tested takes its corresponding symmetry center as the origin and its corresponding symmetry representation value in the first direction and the second direction as the coordinates of the vector.

4. The symmetry detection method for an optical system as described in claim 1, characterized in that, In the positional arrangement direction of the one-dimensional projection data, two reference positions that are axially symmetric about the second axis of symmetry are selected, including: in the positional arrangement direction of the one-dimensional projection data that is axially symmetric about the second axis of symmetry, two reference points that are axially symmetric about the second axis of symmetry are selected; Based on the one-dimensional projection data, the difference between the projection values ​​of the two reference positions is obtained as a symmetry characterization value, including: obtaining the difference between the projection values ​​of the two reference points as the symmetry characterization value.

5. The symmetry detection method for an optical system as described in claim 4, characterized in that, In the direction of the positional arrangement of the one-dimensional projection data that is symmetrical about the second axis of symmetry, two reference points that are symmetrical about the second axis of symmetry are selected, including: Obtain the mirror data of the one-dimensional projection data; perform cross-correlation calculation on the one-dimensional projection data and its corresponding mirror data, and obtain two reference points in the one-dimensional projection data and mirror data that are located at the same arrangement position in the projection direction when the maximum cross-correlation value is obtained, wherein the arrangement position is the position along the arrangement direction of the position. Obtaining the difference between the projection values ​​of the two reference points as the symmetry characterization value includes: obtaining the projection values ​​of each of the two reference points; calculating the difference between the projection values ​​of the two reference points to obtain the symmetry characterization value; or, The one-dimensional projection data includes first projection data and second projection data located on both sides of the second axis of symmetry. In the positional arrangement direction of the one-dimensional projection data that is symmetrical about the second axis of symmetry, two reference points that are symmetrical about the second axis of symmetry are selected, including: selecting a position in the positional arrangement direction of the first projection data as a first reference point, and selecting a position symmetrical to the first reference point in the positional arrangement direction of the second projection data as a second reference point. Obtaining the difference between the projection values ​​of the two reference points as the symmetry characterization value includes: obtaining the projection values ​​of the first reference point and the second reference point respectively; calculating the difference between the projection values ​​of the first reference point and the second reference point to obtain the symmetry characterization value.

6. The symmetry detection method for an optical system as described in claim 4, characterized in that, In the process of calculating the difference between the projected values ​​of the two reference points, either of the two reference points is the extreme point of the one-dimensional projected data, and the extreme point includes the lowest point or the highest point.

7. The symmetry detection method for an optical system as described in claim 4, characterized in that, The step of obtaining the difference between the projection values ​​of the two reference points as the symmetry characterization value includes: after calculating the difference between the projection values ​​of the two reference points, normalizing the difference between the projection values, and using the normalized difference as the symmetry characterization value. Normalizing the difference in the projected values ​​includes: calculating the ratio of the difference in the projected values ​​to the detected value of the background of the image of interest.

8. The symmetry detection method for an optical system as described in claim 1, characterized in that, The detected values ​​include the pixel's grayscale value, light intensity value, or charge value.

9. The symmetry detection method for an optical system as described in claim 1, characterized in that, Determining the first region of interest corresponding to each image to be tested includes: A template image of the pattern to be tested is obtained. The template image has a detection range and includes a preset positional relationship between a second region of interest and the detection range. The second region of interest is the region of the preset region of interest of the pattern to be tested in the template image. The target image is matched with the template image to obtain multiple matching regions in the target image. The matching region is a region composed of connected pixel positions that have a similarity to the template image within the detection range that is greater than or equal to a preset similarity threshold. After obtaining the matching region, a first region of interest is determined in the image to be tested according to the preset positional relationship between the second region of interest in the template image and the detection range. The relative positional relationship between the first region of interest and the matching region is the same as the preset positional relationship.

10. The symmetry detection method for an optical system as described in claim 9, characterized in that, The pattern to be tested is a centrally symmetrical pattern, and the pattern to be tested has a center of symmetry; The center of the detection range coincides with the center of symmetry of the pattern to be tested; The preset positional relationship between the second region of interest and the detection range is the positional relationship between the second region of interest and the center of the detection range; Determining the first region of interest in the image to be tested based on the preset positional relationship between the second region of interest in the template image and the detection range includes: obtaining the position of the matching center of the matching region; Based on the preset positional relationship and the position of the matching center, a first region of interest is determined in the image to be tested, such that the relative positional relationship between the center of the first region of interest and the matching center is the same as the preset positional relationship.

11. The detection method as described in claim 10, characterized in that, Obtaining the location of the matching center of the matching region includes: extracting the contour of each matching region using a morphological algorithm and obtaining the location of the center based on the contour; or, extracting the location of the similarity peak of each matching region to obtain the location of the matching center of each matching region.

12. The symmetry detection method for an optical system as described in claim 10, characterized in that, The matching process between the target image and the template image includes: The target image is traversed using a matching window of the same size as the template image. The correlation score between the region where the matching window is located in the target image and the template image is calculated. The correlation score is negatively correlated with the variance or standard deviation of the gray level of each pixel in the region where the matching window is located and the template image. The matching region is obtained from the target image where the relevance score is greater than or equal to a preset threshold, and the relevance score is used as the similarity.

13. The symmetry detection method for an optical system as described in claim 1, characterized in that, The pattern to be tested includes at least one grid pattern; the at least one grid pattern is centrally symmetrical.

14. A symmetry detection system for an optical system, characterized in that, include: The target acquisition module is used to provide the target to be tested, which includes multiple periodically repeated test patterns. The test patterns have a preset region of interest, and the test patterns in the preset region of interest are axially symmetric about a first axis of symmetry extending in a specific direction. An image of interest acquisition module is used to acquire a target image of the target under test using the optical system, wherein the target image includes test images corresponding to a plurality of test patterns respectively; A first region of interest is determined for each image to be tested. The first region of interest is the region in the image to be tested that is a preset region of interest of the pattern to be tested. The image to be tested in the first region of interest is used as the image of interest of the image to be tested. The axis of symmetry that lies in the image of interest along the specific direction is the second axis of symmetry. A symmetry characterization value acquisition module is used to acquire a symmetry characterization value of the optical system along the specific direction for each of the images of interest. The symmetry characterization value is the difference between the detected values ​​of two reference positions that are symmetrical about the second symmetry axis, and the detected value is positively correlated with the gray value of the reference position. The symmetry distribution acquisition module is used to acquire the symmetry distribution of the optical system in a specific direction by utilizing the symmetry characterization values ​​corresponding to the multiple patterns to be tested. The symmetry characterization value acquisition module includes: a projection unit, used to project the image of interest along the projection direction, and acquire the correspondence between the positions of multiple pixels and the projection values ​​in the position arrangement direction as one-dimensional projection data, wherein the position arrangement direction is perpendicular to the specific direction, the projection direction is parallel to the specific direction, and the projection value is a weighted value of the detected values ​​of one or more pixels along the projection direction, and the detected value is positively correlated with the gray value. The reference position selection unit is used to select two reference positions that are axially symmetric about the second axis of symmetry in the position arrangement direction of the one-dimensional projection data. The reference positions are the positions along the position arrangement direction. The symmetry characterization value acquisition unit is used to obtain the difference between the projection values ​​of the two reference positions as the symmetry characterization value based on the one-dimensional projection data.

15. A terminal device, characterized in that, It includes at least one memory and at least one processor, the memory storing one or more computer instructions, wherein the one or more computer instructions are executed by the processor to implement the symmetry detection method of the optical system as described in any one of claims 1 to 13.

16. A storage medium, characterized in that, The storage medium stores one or more computer instructions, which, when executed by a processor, implement the symmetry detection method of the optical system as described in any one of claims 1 to 13.

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