Method for flat field correction, flat field correction system and computer readable storage medium thereof

Abstract

The application discloses a flat field correction method, a flat field correction system and a computer readable storage medium thereof. The flat field correction method comprises the following steps: providing a camera to be corrected and a blank wafer; collecting a dark field image of the blank wafer; collecting a bright field image of the blank wafer; and performing flat field correction calculation processing of the camera to be corrected according to the dark field image and the bright field image of the blank wafer. In the technical scheme, the blank wafer is used as a target object for flat field correction, the blank wafer is in a dust-free environment during production, is not easy to be polluted, and has extremely high consistency of wafer surface gray scale, so that the problems of difficulty in guaranteeing sufficient size and uniformity of a flat field target in the prior art can be solved.

Description

Technical Field

[0001] This invention relates to the field of optical inspection equipment technology, and in particular to a method for flat field correction, a flat field correction system, and a computer-readable storage medium thereof. Background Technology

[0002] During camera manufacturing, due to inherent manufacturing tolerances, each sensor's brightness output exhibits a degree of non-uniformity; each pixel may respond differently to the same amount of light. When using an area scan camera, these brightness differences in the image have minimal impact because the variations across the entire image are very small. The overall image is almost unaffected, which is usually sufficient for most applications. However, when using a line scan camera, the sensor height is only a few pixels, meaning that errors produced by any single pixel will be repeated with each refresh at the same location. For example, the resulting image errors might appear as vertical stripes, significantly impacting the recorded image data.

[0003] Existing line scan camera flat field correction methods are all for correcting single-frame images. To ensure success on the first try, a flat field target with absolutely uniform color and a size larger than the camera's field of view is required, which is difficult to guarantee in actual operation. Summary of the Invention

[0004] The purpose of this invention is to provide a new method for flat field correction, in order to solve the problems in existing flat field correction methods, such as the difficulty in ensuring sufficient size and uniformity of the flat field target.

[0005] To achieve the above objectives, the present invention provides a method for flat-field correction in a first aspect, comprising:

[0006] Provide the camera to be calibrated and blank wafers;

[0007] Acquire dark-field images of the blank wafer;

[0008] Acquire a bright-field image of the blank wafer;

[0009] The flat field correction calculation is performed on the camera to be corrected based on the dark field image and bright field image of the blank wafer.

[0010] Preferably, the camera to be calibrated is a line scan camera.

[0011] Preferably, the step of acquiring the dark field image of the blank wafer includes:

[0012] Under dark field conditions, surface images of the blank wafer at n locations are acquired, where n≥1.

[0013] Preferably, the step of acquiring a bright-field image of the blank wafer includes:

[0014] Under bright field conditions, surface images of the blank wafer at m locations are acquired, where m ≥ 3;

[0015] The m positions are arranged along the same straight line, and the blank wafers at the m positions can completely cover the horizontal field of view of the camera to be calibrated.

[0016] Preferably, the bright field condition is that there is no interfering light source, and the brightness of the calibration light source is such that the gray value of the blank wafer is between 64 and 254.

[0017] Preferably, the image size of the surface image of the acquired blank wafer is w×h, where w is the number of pixels in each row and h is the number of pixels in each column.

[0018] Preferably, the flat field correction calculation process includes:

[0019] Calculate the grayscale value P1 of each column in the dark field image and the grayscale value P2 of each column in the bright field image;

[0020] The flat field correction target value T is set based on the grayscale value P2 of the bright field image;

[0021] The correction coefficient k for each column is calculated based on the grayscale value P1 of each column in the dark field image and the flat field correction target value T.

[0022] Preferably, the correction coefficient k of each column is used to correct each pixel in the image to be corrected;

[0023] Statistical verification was performed to determine whether the distribution of the corrected grayscale values ​​was uniform.

[0024] Preferably, the method for calculating the grayscale value P1 of each column in the dark field image includes: taking the mode, mean or median of all grayscale values ​​in each column of pixels that are within the statistical range of the dark field threshold as the grayscale value P1 of that column.

[0025] Preferably, the method for calculating the grayscale value P2 of each column in the brightfield image includes: taking the mode, mean or median of all grayscale values ​​within the statistical range of the brightfield threshold in each column of pixels as the grayscale value P2 of that column.

[0026] Preferably, the statistical range of the dark field threshold is (0, 5).

[0027] Preferably, the statistical range of the dark field threshold is (64, 254).

[0028] Preferably, the step of setting the flat field correction target value T based on the grayscale value P2 of the bright field image includes:

[0029] The average, median, or mode of the grayscale values ​​P2 of all columns of the brightfield image is set as the flatfield correction target value T;

[0030] Alternatively, it can be set based on specific needs or experience.

[0031] Preferably, the method for calculating the correction coefficient k for each column includes:

[0032] Based on the gray values ​​P1n in the nth column of the dark field image and P2n in the nth column of the bright field image, the correction coefficient kn = T / (P2-P1) for the nth column is calculated, where n ∈ (0, w).

[0033] Preferably, the method of correcting each pixel in the image to be corrected using the correction coefficient k of each column includes: for the gray value P at each position and the correction coefficient kn of the corresponding column, the correction value P' of each pixel is obtained by using the formula P'=(P-P1)*kn.

[0034] Preferably, the method for statistically verifying whether the distribution of the corrected grayscale values ​​is uniform includes:

[0035] The mode, mean, or median of the correction value Pn' for each pixel in each column is the corrected grayscale value Gn for that column.

[0036] Calculate the standard deviation S of the corrected gray values ​​Gn for all columns;

[0037] If S is less than the set standard deviation, it is determined that the corrected gray value distribution is uniform, and the coefficients P1 and k are obtained, thus completing the flat field correction.

[0038] On the other hand, the present invention also provides a flat field correction system, which includes:

[0039] The image acquisition module is suitable for acquiring dark-field and bright-field images of blank wafers;

[0040] The flat field correction calculation and processing module is adapted to perform flat field correction calculation and processing of the camera to be corrected based on the dark field image and bright field image of the blank wafer.

[0041] Preferably, the image acquisition module includes a wafer carrier motion unit, adapted to provide different wafer carrier positions.

[0042] Preferably, the wafer carrier motion module is adapted to carry the wafer for horizontal translation.

[0043] Preferably, the flat field correction calculation and processing module includes:

[0044] The grayscale value counting unit is suitable for counting the grayscale value P1 of each column in the dark field image and the grayscale value P2 of each column in the bright field image.

[0045] The flat field correction target value setting unit is adapted to set the flat field correction target value T according to the gray value P2 of the bright field image;

[0046] The correction coefficient calculation unit is adapted to calculate the correction coefficient k for each column based on the gray value P1 of each column of the dark field image and the flat field correction target value T.

[0047] A pixel correction unit is adapted to correct each pixel using the correction coefficient k of each column;

[0048] The calibration and verification unit is suitable for statistically verifying whether the distribution of the corrected grayscale values ​​is uniform.

[0049] In another aspect, the present invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the flat field correction method as described in any of the above claims.

[0050] Due to the application of the above-mentioned solution, the present invention has the following advantages and effects compared with the prior art:

[0051] In the technical solution of this invention, a blank wafer is used as the target object for flat-field correction. During the production process, the blank wafer is in a dust-free environment, making it less susceptible to contamination, and its surface grayscale uniformity is extremely high. Furthermore, as a semiconductor processing object, the blank wafer is readily available in semiconductor processing and testing environments, and there are devices for precisely clamping and moving the wafer, making it suitable for the standardization of actual production processes.

[0052] Furthermore, in the technical solution of this invention, the multiple bright-field images completely cover the horizontal field of view of the camera to be corrected. After image acquisition, all correction coefficients can be calculated at once. This avoids the problem of traditional flat-field correction methods requiring segmented flat-field calculations, which can easily result in obvious boundaries at the segmentation points.

[0053] Furthermore, in the technical solution of the present invention, multiple dark field images and bright field images of the blank wafer are collected as the basis for calculating the correction coefficient. Compared with the traditional technology, the amount of data for calculating the correction coefficient is larger, and a more accurate correction coefficient can be obtained.

[0054] Furthermore, in the technical solution of the present invention, a complete bright-field image or dark-field image is used as the basis for calculating the correction coefficient. The complete bright-field image or dark-field image includes multiple rows of pixels from the line scan camera, which increases the amount of data to be processed. Moreover, in the statistical data process, by setting a statistical threshold, data anomalies caused by some contamination can be better avoided.

[0055] Furthermore, in the technical solution of the present invention, setting an appropriate flat field correction target value can achieve high grayscale consistency in a wider range of optical environments. Attached Figure Description

[0056] Figure 1 A flowchart of a flat field correction method provided as an embodiment of the present invention;

[0057] Figure 2 A schematic diagram illustrating the acquisition of multiple bright-field images provided for an embodiment of the present invention;

[0058] Figure 3 A flowchart of the flat field correction calculation process provided for an embodiment of the present invention;

[0059] Figure 4 A schematic diagram of a bright-field image acquired according to an embodiment of the present invention;

[0060] Figures 5 to 6 A schematic diagram of a flat field correction system provided for an embodiment of the present invention;

[0061] Figure 7 for Figure 5 A schematic diagram of the composition of the flat field correction calculation and processing module. Detailed Implementation

[0062] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0063] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0064] In this invention, the terms “center,” “upper,” “lower,” “axial,” “bottom,” “inner,” and “outer,” etc., indicate the orientation or positional relationship based on the orientation or positional assembly relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0065] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0066] The following combination Figures 1 to 7 The method and system for flat field correction provided by this invention are described in detail.

[0067] For details, please refer to Figure 1 The present invention provides a method for flat field correction, comprising:

[0068] Step S100: Provide the camera to be calibrated and a blank wafer;

[0069] Step S200: Acquire a dark-field image of the blank wafer;

[0070] Step S300: Acquire a bright-field image of the blank wafer;

[0071] Step S400: Perform flat field correction calculation processing for the camera to be corrected based on the dark field image and bright field image of the blank wafer.

[0072] Specifically, step S100 involves providing the camera to be calibrated and a blank wafer;

[0073] In this embodiment, the camera 40 to be calibrated is a line scan camera. When using a line scan camera, the sensor height is only a few pixels, meaning that any error generated by any pixel will be repeated in every refresh at the same location. For example, the resulting image error may occur in the form of vertical stripes, which can have a significant impact on the recorded image data. In other embodiments, the camera 40 to be calibrated can also be a area scan camera.

[0074] In this embodiment, the blank wafer is a smooth wafer whose surface has not yet undergone semiconductor imaging processes such as photolithography, etching, deposition, and oxidation. During the production process, the blank wafer is in a dust-free environment, which better ensures color uniformity.

[0075] Furthermore, in some implementations, the blank wafer is placed on a wafer-carrying motion unit, which is adapted to provide different wafer-carrying positions. In some specific embodiments, the wafer-carrying motion module is adapted to carry the wafer for horizontal translation. The direction in which the wafer-carrying motion module carries the wafer for horizontal translation is perpendicular to the scanning direction of the line scan camera.

[0076] Next, step S200 is performed: acquire a dark field image of the blank wafer;

[0077] Generally, dark field images are images captured when the camera is in a non-light-sensitive state, without any lighting or sample.

[0078] Specifically, in this embodiment, the step of acquiring dark field images of the blank wafer includes: acquiring surface images of the blank wafer 60 at j locations under dark field conditions, where j≥1.

[0079] In one specific implementation, the dark field image is obtained by acquiring a surface image of the blank wafer in order to close the lens cap of the camera;

[0080] In another specific implementation, the lighting source can be turned off, the blank wafer 60 can be placed on the motion mechanism, and j images of the blank wafer at different positions can be acquired to obtain j dark field images, where j≥2.

[0081] Furthermore, in the method of turning off the lighting source, it is ensured that the entire environment is absolutely free of noise light, or that there is some light leakage in the acquisition environment after the lighting source is turned off, but the area of ​​light leakage is in a relatively stable state, so that this part of the influence can be eliminated in the subsequent algorithm processing.

[0082] Furthermore, in this embodiment, the acquired dark field image is an image of size W×H, including w columns of pixels, with each column including h pixels.

[0083] In this embodiment, a line scan camera is used for image acquisition. Here, W represents the field of view of the line scan camera, and H represents the scanning distance of the line scan camera.

[0084] In other embodiments, an area scanning camera is used for image acquisition. Here, W×H represents the field of view of the area scanning camera.

[0085] Furthermore, in this embodiment, the grayscale value range of the acquired dark field image is (0, 5).

[0086] Next, step S300 is performed: acquire a bright-field image of the blank wafer;

[0087] When acquiring bright-field images of a blank wafer 60, select appropriate camera parameters to ensure image quality and sharpness. Consider using a camera with higher resolution, faster autofocus, and smaller pixel size.

[0088] Specifically, an illumination source is provided, and an image is captured to obtain a brightfield image. The brightfield condition is controlled by adjusting the brightness of the calibration source. The brightfield condition is that there are no interfering light sources, and the brightness of the calibration source is adjusted so that the grayscale value of the blank wafer is within the range of (64, 254).

[0089] Specifically, in this embodiment, the bright-field image is an image of size W×H, where W is the field of view of the line scan camera acquiring the image, and H is the scanning distance of the line scan camera. Accordingly, in this embodiment, the bright-field image includes w columns of pixels, and each column includes h pixels.

[0090] For line scan cameras, the relationship between the field of view W and the number of pixels w is: W = w × (Q / r), where Q is the unit width (pixel size) of the pixel grid that makes up the photosensitive array in the camera's image sensor, and r is the magnification of the camera lens, typically ×2, ×5, etc. By default, the field of view W of a line scan camera only includes a single row of pixels.

[0091] For example, in one embodiment, if the size Q of a single pixel in the camera's image sensor is 2.5µm, the camera pixel width w is 8192, and the camera lens magnification r is ×2, then under these hardware conditions, the field of view of a line scan camera is W = 8192 × (2.5µm / 2) = 10.24mm. Compared to area scan cameras, the difference in acquiring a whole image with a line scan camera is that it requires adjusting the camera's movement speed and sampling frequency to ensure that the pixel size in the direction of camera movement is approximately the same as the horizontal size. For example, if the camera movement distance H is 10mm, then h = 10mm / (2.5µm / 2) = 8000.

[0092] For area scanning cameras, the relationship between the field of view W×H and the number of pixels w is: W=w×(Q / r), H=h×(Q / r), where Q is the unit width (pixel size) of the pixel grid that makes up the photosensitive array in the camera's image sensor, and r is the magnification of the camera lens, typically ×1, ×2, ×5, etc. For area scanning cameras, the length and width of the pixels are the same by default.

[0093] For example, in one embodiment, if the size Q of a single pixel in the camera's image sensor is 2.5µm, the number of camera pixels w×h is 3000×4000, and the magnification r of the camera lens is ×2, then under these hardware conditions, the field of view is 3000×(2.5 / 2)=3.75mm, 4000×1.25=5mm, and the camera's field of view W×H is 3.75×5mm.

[0094] Continue to refer to Figure 2 As shown, the image acquisition position is optimized: To reduce camera displacement error, a starting point is selected as the starting point for image acquisition, and the camera scans the image along the Fc direction. After acquiring one w×h image, the blank wafer 60 is moved slightly along the Fw direction.

[0095] refer to Figure 2 , Figure 2 The diagram illustrates the acquisition of multiple bright-field images. Specifically, when the blank wafer 60 is in... Figure 2 After the image at position 1 is acquired, the blank wafer 60 is moved from position 1 to position 2, and another image acquisition is performed. Then, the blank wafer 60 is moved from position 2 to position 3, and another image acquisition is performed, and so on, until it is moved to position i. A total of i bright-field images are acquired.

[0096] The i positions are arranged along the same straight line, and the blank wafers at the i positions can completely cover the horizontal field of view of the camera to be calibrated.

[0097] Furthermore, in this embodiment, i ≥ 3, and the image size of the surface image of the blank wafer acquired in each image acquisition is W × H, where W is the field of view of the line scan camera acquiring the image, and H is the scanning distance of the line scan camera. Correspondingly, w is the number of pixels in each row of the image, and h is the number of pixels in each column.

[0098] Next, step S400 is executed: flat field correction calculation processing of the camera to be corrected is performed based on the dark field image and bright field image of the blank wafer.

[0099] Figure 3 The diagram shows a flowchart of the flat-field correction calculation process. (Reference) Figure 3 As shown, the flat field correction calculation process includes:

[0100] Step S410: Calculate the grayscale value P1 of each column in the dark field image and the grayscale value P2 of each column in the bright field image;

[0101] refer to Figure 4 , Figure 4 The image shown is a schematic of a bright-field image that was acquired. Figure 4 As shown, the image is a W×H image, including w columns of pixels, with each column including h pixels.

[0102] Among them, the gray value P2 of the nth column of the brightfield image is one of the mode, mean or median of the gray values ​​of the h pixels in the nth column, where n∈[0,w).

[0103] The statistical range of the bright field threshold is (64, 254). Specifically, when calculating the gray value P2 of the h pixels in the nth column of the bright field image, the gray value P2 is taken as being within the range of (64, 254), and values ​​outside this range are not included in the statistics.

[0104] Furthermore, in this embodiment, when acquiring a bright-field image, if the grayscale value of the bright-field image is outside the range of (64, 254), then the risk of uneven grayscale value of the bright-field image is considered relatively high.

[0105] Accordingly, in this embodiment, the dark field image is also an image of size W×H, including w columns of pixels, each column including h pixels. The gray value P1 of the nth column of the dark field image is either the mode, mean, or median of the gray values ​​of the h pixels, n∈[0,w).

[0106] Furthermore, in this embodiment, the statistical object of the grayscale value in the nth column is the grayscale value P2 in the nth column of each dark field image.

[0107] Furthermore, if the grayscale value of the dark field image is outside the range of (0, 5), it is necessary to check whether there is severe interference light, or whether there are dead pixels or other abnormalities in the camera itself.

[0108] Next, step S420 is executed: the flat field correction target value T is set according to the gray value P2 of the bright field image;

[0109] In this embodiment, the average, median, or mode of the grayscale values ​​P2 of all columns of the brightfield image is set as the flat field correction target value T;

[0110] Specifically, for example Figure 4 In the bright-field image shown, let the grayscale value of the nth column be P2. n The grayscale values ​​from 0 to w are: P21, P22, P23, ..., P2 n P2 n+1 P2 n+2 ... P2 w Set P21, P22, P23, ..., P2 n P2 n+1 P2 n+2 ... P2 w The average, median, or mode of the values ​​is the flat field correction target value T.

[0111] Furthermore, in this embodiment, the statistical object of the grayscale value in the nth column is the grayscale value P2 in the nth column of each bright field image.

[0112] In another embodiment, the flat field correction target value T may be set according to specific needs or empirical values.

[0113] Step S430: Calculate the correction coefficient k for each column based on the grayscale value P1 of each column of the dark field image and the flat field correction target value T;

[0114] The methods for calculating the correction factor k for each column include:

[0115] Based on the gray values ​​P1n in the nth column of the dark field image and P2n in the nth column of the bright field image, the correction coefficient kn = T / (P2-P1) for the nth column is calculated, where n ∈ (0, w).

[0116] Specifically, the grayscale value P1n in the nth column of the dark field image, and the grayscale values ​​of the dark field image from columns 1 to w are respectively: P10, P11, P12, P13, ..., P1 n P1 n+1 P1 n+2 ... P1 w .

[0117] The grayscale value P2n in the nth column of the brightfield image, and the grayscale values ​​of the brightfield image in columns 1 to w are respectively: P20, P21, P22, P23, ..., P2 n P2 n+1 P2 n+2 ..., P2 w .

[0118] The correction coefficients k1, k2, ..., kn, kn+1, kn+2, ..., kw for each column are as follows:

[0119] k1 = T / (P21 - P11)

[0120] k2 = T / (P22 - P12)

[0121] k3 = T / (P23 - P13)

[0122] ...

[0123] kn=T / (P2 n -P1 n )

[0124] kn+1=T / (P2 n+1 -P1 n+1 )

[0125] ...

[0126] kw=T / (P2 w -P1 w )

[0127] In this embodiment, the correction accuracy is improved by calculating the correction coefficient for each column.

[0128] Step S440: Correct each pixel using the correction coefficient k of each column;

[0129] In this embodiment, a new image can be acquired for this step of correction. Specifically, this step can be performed under the same lighting environment as the acquired bright-field image described above. Alternatively, it can be any image acquired in the previous steps.

[0130] The method of correcting each pixel using the correction coefficient k of each column includes: for the gray value P of each position in the selected image to be corrected and the corresponding column correction coefficient kn, the correction value P' of each pixel is obtained by using the formula P'=(P-P1)*kn.

[0131] Specifically, after the previous step, the correction coefficients k1, k2, ..., kn, kn+1, kn+2, ..., kw for each column are obtained. The method used to correct the pixels at each position in the W×H image is as follows:

[0132] For each position's grayscale value P(n, m) and the corresponding column's correction coefficient kn, calculate the correction value for each pixel.

[0133] P'(n, m) = [P(n, m) - P1] * kn

[0134] In this embodiment, each pixel in the corresponding column is corrected by the correction coefficient of each column, thereby improving the correction accuracy.

[0135] Step S450: Statistically verify whether the distribution of the corrected grayscale values ​​is uniform.

[0136] The method for statistically verifying whether the distribution of corrected gray values ​​is uniform includes: calculating the mode, mean, or median of the corrected gray value Pn' for each pixel in each column, and using this as the corrected gray value Gn for that column; and calculating the standard deviation S of the corrected gray values ​​Gn for all columns.

[0137] Specifically, the correction value for each pixel in the nth column is:

[0138] P'(n,1),P'(n,2),...,P'(n,m),...,P'(n,h)

[0139] Take the mode, mean, or median of the above h correction values ​​as the corrected grayscale value Gn for this column.

[0140] Calculate all corrected gray values ​​G in columns 1, 2, ..., n, ..., w to obtain the corrected gray values ​​G1, G2, ..., Gn, ..., Gw for all columns;

[0141] Take the standard deviation S of the corrected gray values ​​G1, G2, ..., Gn, ..., Gw of all columns;

[0142] In this embodiment, if 3S < 4, it is determined that the corrected grayscale value distribution is uniform, and coefficients P1 and k are obtained, thus completing the flat field correction.

[0143] In the ideal case, the corrected gray values ​​should be the same, with a standard deviation S of 0.

[0144] Based on the concept of Sigma in probability statistics, in this embodiment, the judgment range of the standard deviation S is set, which means that the value is distributed in (μ-3σ,μ+3σ) with a probability of 0.9973.

[0145] In other embodiments, the standard deviation S can also be set to other judgment ranges according to actual conditions and needs.

[0146] By optimizing and improving the above aspects, we can enhance the accuracy of judging whether dark-field images are greatly affected by external lighting, thus making the technical solution more complete.

[0147] In other embodiments, sampling calculations can be performed in step S430. For example, a correction coefficient k is calculated for every two columns of pixels. In subsequent calculations in steps S440 to S450, the pixels from the original two columns for which the correction coefficient k was calculated are also used for correction. This ensures that the amount of data to be processed is small, the storage and computing resources required are minimal, and the high precision requirement is still met.

[0148] refer to Figures 5 to 6 As shown, an embodiment of the present invention provides a flat field correction system, which includes:

[0149] Image acquisition module 80 is suitable for acquiring dark-field and bright-field images of blank wafers;

[0150] The flat field correction calculation and processing module 90 is adapted to perform flat field correction calculation and processing of the camera to be corrected based on the dark field image and bright field image of the blank wafer.

[0151] Specifically, the image acquisition module 80 shown includes a camera 40, the scanning field of view 50 of which is slightly larger than the surface of the blank wafer 60. The camera 40 is a line scan camera, scanning along the direction Fc perpendicular to the camera's scanning field of view 50.

[0152] The image acquisition module 80 further includes a wafer carrier motion unit 70, which is adapted to carry a blank wafer for horizontal translation and provides different wafer carrier positions.

[0153] A blank wafer 60 is placed on a wafer carrier motion unit 70, which includes at least one wafer carrier stage and a moving device connected thereto. The wafer carrier stage is adapted to hold the blank wafer 60, and the moving device is adapted to move the blank wafer 60 horizontally along the wafer carrier stage.

[0154] Each time the camera 40 completes an image acquisition, the wafer-carrying motion unit 70 slightly shifts the blank wafer 60 once, and then performs a new image acquisition, until the field of view 50 is completely covered in the horizontal direction. Figure 6 As shown in the figure, in this embodiment, blank wafer 6 0 Image acquisition is performed by translating the wafer to positions T1, T2, T3, T4, and T5 respectively. The images of the blank wafer 60 at positions T1, T2, T3, T4, and T5 can completely cover the horizontal range of the field of view 50.

[0155] In other embodiments, the blank wafer 60 can be shifted to different positions i, and a total of i (i≥3) images can be collected.

[0156] In this embodiment, the size of each captured image is W×H.

[0157] The field of view of the line scan camera acquiring the image is W, and H is the scanning distance of the line scan camera. Correspondingly, w is the number of pixels in each row of the image, and h is the number of pixels in each column.

[0158] Figure 7 As shown Figure 5 A schematic diagram of the flat-field correction calculation and processing module. (Reference) Figure 7 As shown, the flat field correction calculation and processing module includes:

[0159] The column grayscale value statistics unit 91 is adapted to count the grayscale value P1 of each column in the dark field image and the grayscale value P2 of each column in the bright field image.

[0160] The flat field correction target value setting unit 92 is adapted to set the flat field correction target value T according to the gray value P2 of the bright field image;

[0161] The correction coefficient calculation unit 93 is adapted to calculate the correction coefficient k for each column based on the gray value P1 of each column of the dark field image and the flat field correction target value T.

[0162] Pixel correction unit 94 is adapted to correct each pixel using the correction coefficient k of each column;

[0163] The calibration verification unit 95 is suitable for statistically verifying whether the distribution of the corrected gray values ​​is uniform.

[0164] In another aspect, the present invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the flat field correction method as described in any of the above claims.

[0165] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for flat-field correction, characterized in that, include: Provides a camera to be calibrated and a blank wafer, wherein the camera to be calibrated is a line scan camera; Dark-field images of the blank wafer are acquired using the camera to be calibrated; Acquiring bright-field images of the blank wafer using the camera to be calibrated includes: under bright-field conditions, acquiring surface images of the blank wafer at i positions, i ≥ 3, using the camera to be calibrated; the i positions are arranged along the same straight line, and the blank wafers at the i positions can completely cover the horizontal field of view of the camera to be calibrated; the scanning direction of the camera to be calibrated during image acquisition is perpendicular to the direction in which the wafer-carrying motion module carries the blank wafer and performs horizontal translation. Based on the dark field image and the bright field image, a flat-field correction is performed on the image to be corrected captured by the camera to obtain a corrected image. This includes: calculating the grayscale value P1 of each column in the dark field image and the grayscale value P2 of each column in the bright field image, where the grayscale value includes the mode, mean, or median of all pixel values ​​in that column; setting the mean, median, or mode of the grayscale values ​​P2 of all columns in the bright field image as the flat-field correction target value T; calculating the difference between the grayscale value P2 of each column in the bright field image and the grayscale value P1 of each column in the dark field image; performing a division operation on the flat-field correction target value T and the difference to obtain a correction coefficient k for each column; and correcting each pixel in the image to be corrected using the grayscale value P1 of each column in the dark field image and the correction coefficient k to obtain the corrected image. Statistical verification of whether the grayscale value distribution of pixels in the corrected image is uniform includes: calculating the mode, mean or median of the corrected value Pn' of each pixel in each column of the corrected image as the corrected grayscale value Gn of that column; calculating the standard deviation S of the corrected grayscale values ​​Gn of all columns; if the standard deviation S is less than the set standard deviation, it is determined that the grayscale value distribution of pixels in the corrected image is uniform.

2. The method for flat field correction according to claim 1, characterized in that, The steps for acquiring the dark-field image of the blank wafer include: Under dark field conditions, surface images of the blank wafer at j locations are acquired, where j≥1.

3. The method for flat field correction according to claim 1, characterized in that, The bright field condition is that there is no interfering light source, and the brightness of the calibration light source makes the gray value of the blank wafer between 64 and 254.

4. The method for flat field correction according to claim 2, characterized in that, The image size of the surface image of the acquired blank wafer is w×h, where w is the number of pixels in each row and h is the number of pixels in each column.

5. The method for flat field correction according to claim 1, characterized in that, The method for calculating the grayscale value P1 of each column in the dark field image includes: taking the mode, mean or median of all grayscale values ​​in each column that are within the statistical range of the dark field threshold.

6. The method for flat field correction according to claim 1, characterized in that, The method for calculating the grayscale value P2 of each column in the bright field image includes: taking the mode, mean or median of all grayscale values ​​within the statistical range of the bright field threshold in each column of pixels as the grayscale value P2 of that column.

7. The method for flat field correction according to claim 5, characterized in that, The statistical range of the dark field threshold is (0, 5).

8. The method for flat field correction according to claim 6, characterized in that, The statistical range of the bright field threshold is (64, 254).

9. The method for flat field correction according to claim 1, characterized in that, The methods for calculating the correction factor k for each column include: Based on the gray values ​​P1n in the nth column of the dark field image and P2n in the nth column of the bright field image, the correction coefficient kn = T / (P2-P1) for the nth column is calculated, where n ∈ (0, w).

10. The method for flat field correction according to claim 1, characterized in that, The method of correcting each pixel in the image to be corrected using the correction coefficient k of each column includes: for the gray value P at each position and the correction coefficient kn of the corresponding column, the correction value P' of each pixel is obtained by using the formula P'= (P-P1)*kn.

11. A flat-field correction system, characterized in that, It includes: The image acquisition module is adapted to acquire dark-field and bright-field images of a blank wafer using a camera to be calibrated. The module includes: under bright-field conditions, acquiring surface images of the blank wafer at i positions (i ≥ 3) using the camera to be calibrated; the i positions are arranged along the same straight line, and the blank wafers at the i positions can completely cover the horizontal field of view of the camera to be calibrated; the camera to be calibrated is a line scan camera; and the scanning direction of the camera to be calibrated during image acquisition is perpendicular to the direction in which the wafer-carrying motion module horizontally translates the blank wafer. The flat-field correction calculation and processing module is adapted to perform flat-field correction calculation and processing on the camera to be corrected based on the dark-field image and bright-field image of the blank wafer, and to statistically verify whether the gray-level distribution of pixels in the corrected image is uniform. This includes: calculating the gray-level value P1 of each column in the dark-field image and the gray-level value P2 of each column in the bright-field image, where the gray-level value includes the mode, mean, or median of all pixel values ​​in that column; setting the mean, median, or mode of the gray-level values ​​P2 of all columns in the bright-field image as the flat-field correction target value T; and calculating the gray-level value P2 of each column in the bright-field image and the gray-level value P2 of the dark-field image. The difference of gray values ​​P1 in each column of the image is calculated; the difference is divided by the flat field correction target value T to obtain the correction coefficient k for each column; each pixel in the image to be corrected is corrected using the gray values ​​P1 and correction coefficient k in each column of the dark field image to obtain the corrected image; the mode, mean or median of the correction value Pn' of each pixel in each column of the corrected image is calculated as the corrected gray value Gn for that column; the standard deviation S of the corrected gray values ​​Gn for all columns is calculated; if the standard deviation S is less than the set standard deviation, it is determined that the gray values ​​of the pixels in the corrected image are uniformly distributed.

12. The flat field correction system according to claim 11, characterized in that, The image acquisition module includes a wafer carrier motion unit, which is adapted to provide different wafer carrier positions.

13. The flat field correction system according to claim 12, characterized in that, The wafer carrier motion module is adapted to carry the wafer for horizontal translation.

14. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the flat field correction method as described in any one of claims 1-10.

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