Wafer processing path planning method and device based on paraxial machine vision

Abstract

The invention discloses a wafer processing path planning method and a wafer processing path planning device based on paraxial machine vision, and aims to solve the problem of distortion caused by non-coaxial view fields of a paraxial CCD (charge coupled device) and a galvanometer and the problem of direction control of anisotropic processing of wafers, a two-dimensional galvanometer is matched with an XYZ three-axis machine tool and a paraxial CCD camera assembly; according to the method, automatic planning of a wafer surface processing path is realized by combining a completed visual guidance process (mechanical calibration-image correction-path planning), manual intervention is reduced, the wafer processing path generated by the scheme has the characteristics of settable parameters, high precision, low cost, flexibility and controllability, and the processing path and a positioning edge of the wafer have specific directions, so that the processing efficiency is improved. Therefore, the effect of precisely processing the specific path on the surface of the wafer is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of wafer processing, and in particular to a wafer processing path planning method and device based on paraxial machine vision. Background Art

[0002] The production process of wafers determines that the outer contour of the wafer is often a standard circle. During the wafer cutting, polishing and other processing processes, the planning of the processing path has a certain impact on the processing effect. Wafers are crystals and have different characteristics in different directions. Therefore, the wafer embryo manufacturer will leave a marking line on the outer contour of the wafer. This characteristic marking line has vector characteristics and is used to indicate the crystal orientation information of the wafer. Different processing directions based on this vector will have different effects.

[0003] In the galvanometer processing system using vision guidance, there are two main vision guidance schemes: coaxial and paraxial CCD, relative to the galvanometer position. In the coaxial CCD scheme, since the CCD camera and the galvanometer are on the same optical axis, the galvanometer processing field of view and the CCD camera field of view are coaxial, and image correction is relatively simple, but the optical path structure is relatively complex, and due to the compact structure of the optical path, it is difficult to overlap the depth of field of the CCD camera and the focal plane of the galvanometer processing, the optical path cost is high, and the CCD camera field of view is often very small, making it difficult to plan the processing path of larger workpieces. In the paraxial CCD scheme, since the CCD camera and the galvanometer optical path are not coaxial, they can be placed outside the galvanometer, and the field of view size and eyepiece size of the CCD camera can be changed at will to obtain the appropriate field of view size and depth of field size. However, the field of view center of the paraxial CCD and the center of the galvanometer are not coaxial, so there is distortion between the two fields of view. When using the CCD camera field of view as the galvanometer field of view for processing, how to accurately convert the CCD field of view into the galvanometer field of view is particularly critical. Summary of the invention

[0004] In order to solve the problems existing in the above-mentioned background technology, the present invention provides a wafer processing path planning method and device based on paraxial machine vision, which utilizes a paraxial CCD camera, a two-dimensional galvanometer and an XYZ three-axis machine tool to realize automatic planning of the wafer surface processing path. The wafer processing path generated by this scheme has the characteristics of settable parameters, and the processing path and the positioning edge of the wafer have a specific direction, thereby realizing a specific path processing effect on the wafer surface, and has the advantages of low cost and low implementation difficulty.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A first aspect of the present invention provides a wafer processing path planning method based on paraxial machine vision, comprising the following steps: S1. Calibrate and synchronously control the XYZ motion axis of the machine tool. The galvanometer and the CCD camera assembly located on the side move up and down along the Z axis, and the wafer placed on the tray moves along the XY axis. S2. After the preliminary calibration of the galvanometer, the galvanometer is controlled to mark a matrix of dots on the calibration board according to the theoretical dot matrix coordinates, and the coordinates of each point on the calibration board are determined using a microscope or other magnifying device. The actual coordinates of the dot matrix mark points marked by the galvanometer on the calibration board are compared with the deviation of the theoretical coordinates, and the dynamic focusing of the galvanometer is compensated to correct the Z-axis error of the two-dimensional galvanometer at each point. S3, replace the appropriate camera eyepiece to adjust the imaging position and depth of field of the CCD camera assembly, so that the imaging plane of the CCD camera assembly is on the surface of the wafer to be processed, and at the same time adjust the camera depth of field to 1-3mm; S4. Determine the offset vector in the machine tool coordinate system between the field of view center Oc of the CCD camera assembly and the processing field of view center Og of the galvanometer The value of S5. Determine the processing size ratio of the image under the field of view of the CCD camera component and the processing field of the galvanometer k ; S6. Use the image detection method to obtain the center P (x0, y0) of the wafer and the two endpoints M (x1, y1) and N (x2, y2) of the characteristic edge under the field of view of the CCD camera component. The sign of the characteristic vector is or ; S7. The wafer processing path is composed of several groups of parallel straight lines. Different processing effects can be achieved by setting the distance between the parallel straight lines and the angle between the parallel straight lines and the characteristic vector. First, a straight line GH is made through the center P of the wafer to intersect the outer contour of the wafer at points G and H. GH is the perpendicular bisector of MN. The pixel coordinates of points G and H are obtained, and the line segment GH is discretized into a point set {Sn}, where the distance between Sn and Sn-1 is d; then a straight line is made through point Sn on GH to form an angle with the characteristic vector. Draw a straight line RQ that intersects the wafer outer contour at points Rn and Qn. The straight line set {RnQn} is the automatically planned processing path. Finally, {RnQn} is multiplied by the conversion ratio k in step S5 to obtain the processing path set in the galvanometer coordinate system. Finally, the processing head moves along the offset vector obtained in step S4. After moving, just move according to the processing path k{RnQn}.

[0006] Using the above technical solution: (1) The design of separately installing the paraxial CCD and the galvanometer mirror is adopted in this application, which supports flexible replacement of the eyepiece of the CCD camera assembly to adapt to different field of view and depth of field requirements, and optimizes the imaging quality by combining with the LED ring light source, breaking through the optical path limitation of the coaxial solution, reducing the system complexity and cost, and expanding the size adaptability range of the processed parts; (2) Use the kinematic model of the XYZ three-axis machine tool, combined with a laser interferometer or a three-dimensional coordinate measuring machine (CMM) to calibrate the orthogonality error, and correct it through a compensation algorithm; at the same time, perform multiple measurements of the galvanometer marking dot matrix to generate a compensation file. Through dynamic calibration and error compensation, the motion accuracy of the multi-axis system is improved, and the impact of mechanical installation errors on the processing path is reduced; (3) Perform secondary correction on the paraxial CCD image through the perspective transformation matrix H to eliminate the tilt distortion of the field of view; combined with the offset vector And processing size ratio coefficient k , realize the precise mapping between CCD pixel coordinate system and galvanometer processing coordinate system, solve the distortion problem caused by the different axes of the paraxial CCD and galvanometer field of view, and propose a complete coordinate conversion chain (image correction → offset compensation → scale conversion) to ensure the geometric accuracy of the processing path; (4) Identify the center and outer contour of the wafer through image detection methods, and determine the direction of the feature vector. Based on the direction of the feature vector, generate the angle formed with the feature vector Parallel processing path set {RnQn}, combined with the processing size ratio coefficient k Convert to the path in the galvanometer coordinate system. Directly associate the crystal orientation information (characteristic vector) with the processing path direction to achieve directional control of the anisotropic processing effect on the wafer surface.

[0007] The present application provides a method based on paraxial CCD machine vision recognition, which uses a two-dimensional galvanometer with an XYZ three-axis machine tool, and combines it with a completed visual guidance process (calibration → correction → path generation) to realize automatic planning of wafer surface processing paths and reduce manual intervention. The wafer processing path generated by this solution has the characteristics of settable parameters, and the processing path and the positioning edge of the wafer have a specific direction, thereby achieving the effect of precise processing of specific paths on the wafer surface.

[0008] Furthermore, the specific process of replacing a suitable camera eyepiece to adjust the imaging position and depth of field of the CCD camera assembly is as follows: use a galvanometer to mark a pattern on the calibration plate, move the XY axis so that the pattern appears in the field of view of the rangefinder CCD camera assembly, and replace a suitable camera eyepiece until the CCD camera assembly clearly observes the image of the galvanometer processing plane, that is, the camera's depth of field covers the galvanometer processing focus position.

[0009] Furthermore, in the step S3, the specific process of adjusting the imaging plane of the CCD camera assembly on the surface of the wafer to be processed (parallel to the XY plane) is as follows: according to the four marking points located on the pallet and respectively located at the four vertices of the square in the machine tool coordinate system, the pixel coordinates of the four marking points in the image taken by the paraxial CCD camera assembly are observed, and the pixel coordinates in the CCD image are secondary corrected by tilting the CCD camera assembly and / or using an algorithm until the pixel coordinates of the four marking points in the CCD image are also the four vertices of the square.

[0010] Further, a mechanical holding tool of the CCD camera assembly is adjusted to perform tilt correction.

[0011] Furthermore, the specific process of using the algorithm to perform secondary correction on the pixel coordinates in the CCD image is as follows: first, obtain the transformation matrix H of the pixel coordinates of the four vertices in the CCD image at the tilted viewing angle before correction and the CCD image coordinates in the vertical downward field of view along the Z axis after correction, and then use the transformation matrix H to perform secondary correction on the pixel coordinates of the four vertices in the CCD image to obtain an imaging picture parallel to the plane of the tray.

[0012] Furthermore, the four marking points on the tray are painted with different colors respectively.

[0013] Furthermore, in step S6, >0, then the characteristic quantity is ; <0, then the characteristic quantity is .

[0014] Furthermore, in step S4, firstly, the calibration plate is placed under the galvanometer field of view, and the Z-axis distance is adjusted so that the processing focal plane of the galvanometer falls on the calibration plate. At this time, the XY-axis position of the galvanometer processing center is Og (x1, y1), and then a calibration pattern (for example, a point) is processed on the calibration plate. After completion, the Z-axis position is kept unchanged, and the XY-axis is moved so that the calibration pattern is located at the center of the CCD camera field of view. The XY-axis position at this time is recorded as Oc (x2, y2). At this time, a set of offset vectors is obtained. = (x2-x1, y2-y1), repeat the above method to measure the bias vector multiple times The value of and use its mean to represent the bias vector The value represents the offset in the machine tool coordinate system from the center point of the galvanometer processing field of view to the center point of the CCD camera component field of view.

[0015] Furthermore, in step S2, the Z axis is moved up and down so that the distance between the center point of the galvanometer optical axis and the tray is the galvanometer focal length d, and the position of the galvanometer Z axis at this time is recorded. The galvanometer is used to mark an n*n matrix target (for example, 9*9 or 25*25) on the calibration plate placed on the tray, and the dot matrix marked by the galvanometer is observed with a microscope. The deviation between the actual coordinates of the dot matrix marking points and the theoretical coordinates is compared, and a compensation file is generated to calibrate the two-dimensional galvanometer.

[0016] According to a second aspect of the present invention, a wafer processing path planning device based on paraxial machine vision is provided, which is used to implement the above-mentioned wafer processing path planning method. The device includes an XYZ three-axis machine tool, a pallet, a galvanometer and a CCD camera assembly. The pallet is installed on the XY orthogonal motion axis, the Z-axis motion axis is fixed in the middle of the gantry, the galvanometer is installed at the output end of the Z-axis motion axis, and a CCD camera assembly is fixedly installed on the side of the galvanometer. The field of view of the CCD camera assembly is downward along the Z-axis, and an LED lighting lamp ring is installed on the outer side below the galvanometer.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) This application adopts a design in which the paraxial CCD and the galvanometer are installed separately, which simplifies the optical path structure, supports flexible replacement of the eyepiece of the CCD camera assembly to adapt to different field of view and depth of field requirements, and combines with the LED ring light source to optimize the imaging quality, adapt to the imaging requirements of different wafer sizes and surface materials, break through the optical path limitations of the coaxial solution, reduce system complexity and cost, and expand the size adaptation range of the processed parts; (2) Use the kinematic model of the XYZ three-axis machine tool, combined with a laser interferometer or a three-dimensional coordinate measuring machine (CMM) to calibrate the orthogonality error, and correct it through a compensation algorithm; at the same time, perform multiple measurements of the galvanometer marking dot array to generate a compensation file. Through dynamic calibration and error compensation, the motion accuracy of the multi-axis system is improved, the impact of the accumulated mechanical installation errors on the processing path is reduced, and the overlap between the galvanometer processing focal plane and the wafer surface is improved; (3) Perform secondary correction on the paraxial CCD image through the perspective transformation matrix H to eliminate the tilt distortion of the field of view; combined with the offset vector And processing size ratio coefficient k , realize the accurate mapping between CCD pixel coordinate system and galvanometer processing coordinate system, ensure the geometric mapping accuracy of processing path, solve the distortion problem caused by the different axes of paraxial CCD and galvanometer field of view, and propose a complete coordinate transformation chain (image correction → offset compensation → scale conversion) to ensure the geometric accuracy and stability of processing path; (4) Identify the center and outer contour of the wafer through image detection methods, and determine the direction of the feature vector. Based on the direction of the feature vector, generate the angle formed with the feature vector Parallel processing path set {RnQn}, combined with the processing size ratio coefficientk Convert to the path in the galvanometer coordinate system. Directly associate the crystal orientation information (characteristic vector) with the processing path direction to achieve directional control of the anisotropic processing effect on the wafer surface and meet the requirements of the anisotropic characteristics of the wafer on the processing effect (such as directional optimization of cutting, polishing and other processes).

[0018] The present application provides a method for machine vision recognition based on paraxial CCD, aiming to solve the distortion problem caused by the non-coaxial field of view of the paraxial CCD and the galvanometer and the direction control problem of anisotropic wafer processing. It uses a two-dimensional galvanometer with an XYZ three-axis machine tool and a paraxial CCD camera assembly, and combines it with a completed visual guidance process (mechanical calibration → image correction → path planning) to realize automatic planning of the wafer surface processing path and reduce manual intervention. The wafer processing path generated by this scheme has the characteristics of settable parameters, high precision, low cost, flexible and controllable, and the processing path and the positioning edge of the wafer have a specific direction, thereby achieving the effect of precise processing of a specific path on the wafer surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] Figure 1 It is a schematic diagram of a wafer in the present invention; Figure 2 It is a structural schematic diagram of the wafer processing path planning device in the present invention; Figure 3 The image of the pallet marking points in the field of view of the front and rear CCD camera components in the present invention is corrected; Figure 4 is the offset relationship between the field of view center Oc of the CCD camera assembly and the processing field of view center Og of the galvanometer in the present invention; Figure 5 The processed part is under the field of view of the CCD camera assembly in the present invention; Figure 6 is a schematic diagram of a wafer characteristic vector in the present invention; Figure 7 A schematic diagram of a mathematical model for wafer processing path planning in the present invention; Among them, the specific drawings are marked as: XYZ three-axis machine tool 1, tray 2, wafer 3, galvanometer 4, LED lighting ring 5, CCD camera assembly 6. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Example 1 This embodiment provides a wafer processing path planning method based on paraxial machine vision, which aims to solve the distortion problem caused by the non-coaxial field of view of the paraxial CCD and the galvanometer and the direction control problem of wafer anisotropic processing. It uses a two-dimensional galvanometer with an XYZ three-axis machine tool and a paraxial CCD camera assembly, and combines the completed visual guidance process (mechanical calibration → image correction → path planning) to realize automatic planning of the wafer surface processing path and reduce manual intervention. The wafer processing path generated by the scheme has the characteristics of adjustable parameters, high precision, low cost, flexible and controllable, and the processing path and the positioning edge of the wafer have a specific direction, so as to achieve the effect of precise processing of a specific path on the wafer surface. Specifically, the following steps are included: S1. Calibrate and synchronize the XYZ axis of the machine tool. The galvanometer and the CCD camera assembly located next to it move up and down along the Z axis, and the wafer placed on the tray moves along the XY axis. Figure 1 is a schematic diagram of a wafer, P is the center of the wafer, and vector L is the characteristic vector of the wafer; S2. After the preliminary calibration of the galvanometer, the galvanometer is controlled to mark a matrix of dots on the calibration board according to the theoretical dot matrix coordinates, and the coordinates of each point on the calibration board are determined using a microscope or other magnifying device. The actual coordinates of the dot matrix mark points marked by the galvanometer on the calibration board are compared with the deviation of the theoretical coordinates, and the dynamic focusing of the galvanometer is compensated to correct the Z-axis error of the two-dimensional galvanometer at each point. S3, replace the appropriate camera eyepiece to adjust the imaging position and depth of field of the CCD camera assembly, so that the imaging plane of the CCD camera assembly is on the surface of the wafer to be processed, and at the same time adjust the camera depth of field to 1-3mm; S4. Determine the offset vector in the machine tool coordinate system between the field of view center Oc of the CCD camera assembly and the processing field of view center Og of the galvanometer The value of S5. Determine the processing size ratio of the image under the field of view of the CCD camera component and the processing field of the galvanometer k ; S6. Use the image detection method to obtain the center P (x0, y0) of the wafer and the two endpoints M (x1, y1) and N (x2, y2) of the characteristic edge under the field of view of the CCD camera component. The sign of the characteristic vector is or ; S7. The wafer processing path is composed of several groups of parallel straight lines. Different processing effects can be achieved by setting the distance between the parallel straight lines and the angle between the parallel straight lines and the characteristic vector. First, a straight line GH is made through the center P of the wafer to intersect the outer contour of the wafer at points G and H. GH is the perpendicular bisector of MN. The pixel coordinates of points G and H are obtained, and the line segment GH is discretized into a point set {Sn}, where the distance between Sn and Sn-1 is d; then a straight line is made through point Sn on GH to form an angle with the characteristic vector. Draw a straight line RQ that intersects the wafer outer contour at points Rn and Qn. The straight line set {RnQn} is the automatically planned processing path. Finally, {RnQn} is multiplied by the conversion ratio k in step S5 to obtain the processing path set in the galvanometer coordinate system. Finally, the processing head moves along the offset vector obtained in step S4. After moving, just move according to the processing path k{RnQn}.

[0023] Using the above technical solution: (1) The design of separately installing the paraxial CCD and the galvanometer mirror is adopted in this application, which supports flexible replacement of the eyepiece of the CCD camera assembly to adapt to different field of view and depth of field requirements, and optimizes the imaging quality by combining with the LED ring light source, breaking through the optical path limitation of the coaxial solution, reducing the system complexity and cost, and expanding the size adaptability range of the processed parts; (2) Use the kinematic model of the XYZ three-axis machine tool, combined with a laser interferometer or a three-dimensional coordinate measuring machine (CMM) to calibrate the orthogonality error and correct it through a compensation algorithm; at the same time, perform multiple measurements of the galvanometer marking dot matrix to generate a compensation file; through dynamic calibration and error compensation, improve the motion accuracy of the multi-axis system and reduce the impact of mechanical installation errors on the processing path; (3) Perform secondary correction on the paraxial CCD image through the perspective transformation matrix H to eliminate the tilt distortion of the field of view; combined with the offset vector And processing size ratio coefficient k , realize the precise mapping between CCD pixel coordinate system and galvanometer processing coordinate system, solve the distortion problem caused by the different axes of the paraxial CCD and galvanometer field of view, and propose a complete coordinate conversion chain (image correction → offset compensation → scale conversion) to ensure the geometric accuracy of the processing path; (4) Identify the center and outer contour of the wafer through image detection methods, and determine the direction of the feature vector. Based on the direction of the feature vector, generate the angle formed with the feature vector Parallel processing path set {RnQn}, combined with the processing size ratio coefficient k Convert to the path in the galvanometer coordinate system. Directly associate the crystal orientation information (characteristic vector) with the processing path direction to achieve directional control of the anisotropic processing effect on the wafer surface.

[0024] The specific operation process of step S1 is as follows: This step completes the calibration and software control of the machine tool XYZ motion axis. Figure 2 The structure shown is installed with XYZ motion axis, tray, CCD camera assembly and LED lighting ring. The galvanometer and the CCD camera assembly located on the side move up and down along the Z axis. The wafer placed on the tray moves along the XY axis, and the reference points of the XYZ axes are set. The reference points can be set arbitrarily on the motion path of each axis, and the kinematic model is established with the reference points of each axis as the reference points. The initial coordinate system of the machine tool is established using a laser interferometer or a three-dimensional coordinate measuring machine (CMM), the orthogonality error of the X / Y / Z axes is determined, and corrected by a compensation algorithm. The software control solution can use the EtherCAT bus and the corresponding XYZ three-axis motion model of Beckhoff to achieve three-axis synchronous control of the machine tool.

[0025] The specific operation process of step S2 is as follows: Move the Z axis up and down so that the distance between the center point of the galvanometer optical axis and the pallet is the galvanometer focal length d, record the position of the galvanometer Z axis at this time, use the galvanometer to mark an n*n matrix target (for example, 9*9 or 25*25) on the calibration plate placed on the pallet (the calibration plate is a clean marking plate provided by the galvanometer manufacturer), observe the dot matrix marked by the galvanometer with a microscope, compare the deviation between the actual coordinates of the dot matrix marking points and the theoretical coordinates, generate a compensation file, and calibrate the two-dimensional galvanometer. After completing this step, the two-dimensional galvanometer can be calibrated.

[0026] The specific operation process of step S3 is as follows: First, use a galvanometer to print a pattern on the calibration plate, move the XY axis so that the pattern appears in the field of view of the rangefinder CCD camera assembly, and replace the appropriate camera eyepiece until the CCD camera assembly clearly observes the image of the galvanometer processing plane, that is, the camera's depth of field covers the galvanometer processing focus position.

[0027] Then, in order to determine whether the imaging plane of the CCD camera assembly and the surface of the wafer to be processed on the tray (located in the XY plane) are in parallel planes, four standard marking points are set on the tray, and their actual coordinates in the machine tool coordinate system are A (x1, y1), B (x2, y2), C (x3, y3), and D (x4, y4), which are located at the four vertices of the square respectively. In order to distinguish them, different colors are applied to the marking points to avoid position confusion when the CCD camera corresponds to the vertices. The CCD camera is moved to capture these four vertices in the center of the field of view, and these four vertices are detected in the image. Their pixel coordinates are A1 (u1, v1), B1 (u2, v2), C1 (u3, v3), and D1 (u4, v4). If A1, B1, C1, and D1 are also the four vertices of the square, it proves that the imaging plane of the CCD camera assembly is parallel to the tray plane. However, due to mechanical installation errors, a slight field of view tilt is often caused (such as Figure 3 As shown in the figure, the mechanical holding tool of the CCD camera assembly can be adjusted to make the tilt correction. If the mechanical holding mechanism cannot be fine-tuned, the algorithm can be used to perform a secondary correction on the CCD image. First, the pixel coordinates of the four vertices in the CCD image at the tilted viewing angle before correction are obtained. The transformation matrix H of the CCD image coordinates in the vertical downward field of view along the Z axis after correction is then used to perform a secondary correction on the pixel coordinates of the four vertices in the CCD image to obtain an imaging picture parallel to the plane of the tray, thereby realizing a secondary correction of the CCD field of view.

[0028] The specific steps of using the algorithm to perform secondary correction on the CCD image are as follows: Hough detection visual recognition is used to obtain the pixel coordinates of the four vertices in the CCD image before correction: A1 (u1, v1), B1 (u2, v2), C1 (u3, v3), D1 (u4, v4). The pixel coordinates of the corresponding vertex after correction are ( u i , v i ), i=1, 2, 3, 4, then ( u i , v i )and( x i , y i ) satisfies the following perspective formula: ; Among them, the perspective transformation matrix H is: ; w is the coordinate ratio between the CCD pixel coordinate system and the actual machine tool coordinate system, which can be obtained by measuring the ratio of the actual radius of the calibration point on the pallet to the CCD pixel radius. For the convenience of calculation, w=1 is taken here. For each point pair ( u i , v i ) → ( x i , y i ) can generate two equations: ; There are 8 equations for 4 point pairs, and the 8 parameters of the transformation matrix H are solved. h 11 , h 12 , h 13 , h 21 , h 22 , h 23 , h 31 , h 32 . Rewrite the equation as A · h = b The form of a homogeneous linear system of equations is solved by the least squares method or singular value decomposition, where ; ; ; Solution , then we get the solution of the perspective transformation matrix H.

[0029] Suppose the pixel set after CCD correction is , which is the pixel set of the original CCD image before correction , and then the CCD camera image can be corrected using the following formula to obtain an imaging picture that is almost parallel to the plane of the processing tray.

[0030] ; Where n is the pixel size of the CCD camera.

[0031] The specific operation process of step S4 is as follows: Since the CCD camera assembly is mounted paraxially relative to the galvanometer, there is an offset vector between the field of view center Oc of the CCD camera assembly and the processing field of view center Og of the galvanometer. , see Figure 4 In order to determine the offset vector, first place the calibration board under the galvanometer field of view, adjust the Z axis distance so that the processing focal plane of the galvanometer falls on the calibration board. At this time, the XY axis position of the galvanometer processing center is Og (x1, y1), and then process the calibration pattern (for example, a point) on the calibration board. After completion, keep the Z axis position unchanged and move the XY axis so that the calibration pattern is located at the center of the CCD camera field of view. Record the XY axis position at this time as Oc (x2, y2). At this time, a set of offset vectors is obtained. = (x2-x1, y2-y1), repeat the above method to measure the bias vector multiple times The value of and use its mean to represent the bias vector The value represents the offset in the machine tool coordinate system from the center point of the galvanometer processing field of view to the center point of the CCD camera component field of view.

[0032] The specific operation process of step S5 is as follows: Determine the processing size ratio of the image under the field of view of the CCD camera component and the processing field of view of the galvanometer k That is, use the galvanometer to mark a straight line of length f on the calibration plate, move it according to the offset vector so that the straight line appears in the field of view of the CCD camera component, and use the image to detect that the pixel length of the straight line is F, then k=f / F, and you can measure several times to find the average value. Processing size ratio k It means the conversion ratio of the processing path planned by CCD vision to the galvanometer coordinate system.

[0033] The specific operation process of step S6 is as follows: After completing the above steps, you will get a paraxial CCD vision-guided laser processing system, which will then be used to identify the workpiece and automatically plan the path.

[0034] like Figure 5 The figure shows the workpiece under the field of view of the CCD camera component. The center P (x0, y0) of the wafer under the field of view of the CCD camera component and the two endpoints M (x1, y1) and N (x2, y2) of the characteristic edge are obtained using mature image detection methods such as Hough detection. The characteristic edge of the wafer is a vector whose direction satisfies the right-hand spiral. The processing paths at different angles relative to this vector edge will have certain differences in the wafer processing effects. Therefore, it is necessary to use an algorithm to identify the characteristic vector. still (like Figure 6 To determine the eigenvector, the following calculation is performed: ; The direction of k is perpendicular to the paper and outward, that is, the positive direction of the Z axis, so we only need to judge The sign of or .

[0035] Right now >0, then the characteristic quantity is ; <0, then the characteristic quantity is .

[0036] The specific operation process of step S7 is as follows: Assume that step S6 has determined that the direction of the feature vector is The next step is to plan the processing path. The wafer processing path is generally composed of several sets of parallel straight lines. Different processing effects can be achieved by setting the distance between the parallel straight lines and the angle between the parallel straight lines and the feature vector. First, the center P and the outer contour set of the wafer have been obtained through visual recognition, such as Figure 7 As shown, a straight line GH is drawn through the center P of the wafer and intersects the outer contour of the wafer at points G and H. GH is the perpendicular bisector of MN, and the pixel coordinates of points G and H are obtained. The line segment GH is discretized into a point set {Sn}, and the distance between Sn and Sn-1 is d. Since the pixel coordinates of GH have been determined, the point set {Sn} can be obtained. Then, through point Sn on GH, and with the feature vector Forming an angle Draw a straight line RQ that intersects the wafer outer contour at points Rn and Qn. The straight line set {RnQn} is the automatically planned processing path. Finally, {RnQn} is multiplied by the conversion ratio k in step S5 to obtain the processing path set in the galvanometer coordinate system. Finally, the processing head moves along the offset vector obtained in step S4. After the movement, the specific processing path planning method of the wafer using the paraxial vision can be realized by moving according to the processing path k{RnQn}.

[0037] Example 2 This embodiment provides a wafer processing path planning device based on paraxial machine vision, which is used to implement the above-mentioned wafer processing path planning method, such as Figure 2 As shown, the device includes an XYZ three-axis machine tool 1, a tray 2, a galvanometer 4 and a CCD camera assembly 6. The tray 2 is installed on the XY orthogonal motion axis, the wafer 3 is placed on the tray 2, the Z-axis motion axis is fixed in the middle of the gantry, the galvanometer 4 is installed at the output end of the Z-axis motion axis, and the CCD camera assembly 6 is fixedly installed on the side of the galvanometer 4. The field of view of the CCD camera assembly 6 is downward along the Z axis, and an LED lighting lamp ring 5 is installed on the outer side below the galvanometer 4.

[0038] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A wafer processing path planning method based on paraxial machine vision, characterized in that: The following steps are involved: S1. Calibrate and synchronously control the XYZ motion axis of the machine tool. The galvanometer and the CCD camera assembly located on the side move up and down along the Z axis, and the wafer to be processed placed on the tray moves along the XY axis direction; S2, comparing the deviation between the actual coordinates of the dot matrix marking points marked by the galvanometer on the calibration board and the theoretical coordinates, generating a compensation file, and calibrating the two-dimensional galvanometer; S3, replace the appropriate camera eyepiece to adjust the imaging position and depth of field of the CCD camera assembly, so that the imaging plane of the CCD camera assembly is on the surface of the wafer to be processed, and at the same time adjust the camera depth of field to 1-3mm; S4. Determine the offset vector in the machine tool coordinate system between the field of view center Oc of the CCD camera assembly and the processing field of view center Og of the galvanometer The value of S5. Determine the processing size ratio of the image under the field of view of the CCD camera component and the processing field of the galvanometer k ; S6. Use the image detection method to obtain the center P (x0, y0) of the wafer and the two endpoints M (x1, y1) and N (x2, y2) of the characteristic edge under the field of view of the CCD camera component. The sign of the characteristic vector is or ; S7. The wafer processing path is composed of several groups of parallel straight lines. Different processing effects can be achieved by setting the distance between the parallel straight lines and the angle between the parallel straight lines and the characteristic vector. First, a straight line GH is made through the center P of the wafer to intersect the outer contour of the wafer at points G and H. GH is the perpendicular bisector of MN. The pixel coordinates of points G and H are obtained, and the line segment GH is discretized into a point set {Sn}, where the distance between Sn and Sn-1 is d; then a straight line is made through point Sn on GH to form an angle with the characteristic vector. Draw a straight line RQ that intersects the wafer outer contour at points Rn and Qn. The straight line set {RnQn} is the automatically planned processing path. Finally, {RnQn} is multiplied by the conversion ratio k in step S5 to obtain the processing path set in the galvanometer coordinate system. Finally, the processing head moves along the offset vector obtained in step S4. After moving, just move according to the processing path k{RnQn}.

2. The wafer processing path planning method based on paraxial machine vision according to claim 1, characterized in that: In step S3, the specific process of replacing a suitable camera eyepiece to adjust the imaging position and depth of field of the CCD camera assembly is as follows: use a galvanometer to mark a pattern on the calibration plate, move the XY axis so that the pattern appears in the field of view of the rangefinder CCD camera assembly, and replace a suitable camera eyepiece until the CCD camera assembly clearly observes the image of the galvanometer processing plane.

3. The wafer processing path planning method based on paraxial machine vision according to claim 1 or 2, characterized in that: In the step S3, the specific process of adjusting the imaging plane of the CCD camera assembly on the surface of the wafer to be processed is as follows: according to the four marking points located on the tray and respectively located at the four vertices of the square in the machine tool coordinate system, the pixel coordinates of the four marking points in the image taken by the paraxial CCD camera assembly are observed, and the pixel coordinates in the CCD image are secondary corrected by tilting the CCD camera assembly and / or using an algorithm until the pixel coordinates of the four marking points in the CCD image are also the four vertices of the square.

4. The wafer processing path planning method based on paraxial machine vision according to claim 3 is characterized in that: Adjust the mechanical fixture of the CCD camera assembly for tilt correction.

5. The wafer processing path planning method based on paraxial machine vision according to claim 3, characterized in that: The specific process of using the algorithm to perform secondary correction on the pixel coordinates in the CCD image is as follows: first, obtain the transformation matrix H of the pixel coordinates of the four vertices in the CCD image at the tilted viewing angle before correction and the CCD image coordinates in the vertical downward field of view along the Z axis after correction, and then use the transformation matrix H to perform secondary correction on the pixel coordinates of the four vertices in the CCD image to obtain an imaging picture parallel to the plane of the tray.

6. The wafer processing path planning method based on paraxial machine vision according to claim 3, characterized in that: The four marking points on the tray are painted with different colors.

7. The wafer processing path planning method based on paraxial machine vision according to claim 1, characterized in that: In step S6, >0, then the characteristic quantity is ; <0, then the characteristic quantity is .

8. The wafer processing path planning method based on paraxial machine vision according to claim 1, characterized in that: In step S4, firstly, the calibration plate is placed under the galvanometer field of view, and the Z-axis distance is adjusted so that the processing focal plane of the galvanometer falls on the calibration plate. At this time, the XY-axis position of the galvanometer processing center is Og (x1, y1), and then the calibration pattern is processed on the calibration plate. After completion, the Z-axis position is kept unchanged, and the XY-axis is moved so that the calibration pattern is located at the center of the CCD camera field of view. The XY-axis position at this time is recorded as Oc (x2, y2). At this time, a set of bias vectors is obtained. = (x2-x1, y2-y1), repeat the above method to measure the bias vector multiple times The value of and use its mean to represent the bias vector The value of .

9. The wafer processing path planning method based on paraxial machine vision according to claim 1, characterized in that: In step S2, the Z axis is moved up and down so that the distance between the center point of the galvanometer optical axis and the tray is the galvanometer focal length d, and the position of the galvanometer Z axis at this time is recorded. The galvanometer is used to mark an n*n matrix target on the calibration plate placed on the tray, and the dot matrix marked by the galvanometer is observed with a microscope. The deviation between the actual coordinates of the dot matrix marking points and the theoretical coordinates is compared, and a compensation file is generated to calibrate the two-dimensional galvanometer.

10. A wafer processing path planning device based on paraxial machine vision, characterized in that: The device is used to implement the wafer processing path planning method as described in claim 1, and includes an XYZ three-axis machine tool, a pallet, a galvanometer and a CCD camera assembly. The pallet is installed on the XY orthogonal motion axis, the Z-axis motion axis is fixed in the middle of the gantry, the galvanometer is installed at the output end of the Z-axis motion axis, and the CCD camera assembly is fixedly installed on the side of the galvanometer. The field of view of the CCD camera assembly is downward along the Z axis, and an LED lighting lamp ring is installed on the outer side below the galvanometer.

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