Vision-based wafer pre-alignment system and method

Abstract

The invention relates to a wafer pre-alignment system and method based on vision, and the method comprises the steps: S1, dividing the edge of a wafer into at least two parts in the circumferential direction; s2, controlling a rotating mechanism to drive the wafer to rotate so as to sequentially send each edge division part of the wafer into a photographing range of a camera, and enabling the camera to photograph each edge division part of the wafer so as to obtain an image of each edge division part of the wafer; s3, processing the image of each edge division part to obtain data of each edge division part in the camera coordinate system; s4, converting data of each edge division part in the camera coordinate system into data in the world coordinate system according to a relation between the camera coordinate system and the world coordinate system; and S5, acquiring edge data of the wafer according to the data of each edge division part in the world coordinate system. According to the technical scheme of the invention, the pre-alignment of the wafer can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of wafer pre-alignment, and in particular to a vision-based wafer pre-alignment system and method. Background Art

[0002] Wafer pre-alignment technology is crucial in semiconductor manufacturing. It ensures that the wafer is initially aligned and positioned before entering the fine processing stage. Pre-alignment technology mainly uses advanced optical and visual systems to perform preliminary detection and positioning of wafers. By identifying characteristic marks on the wafer, such as notches or flat edges, the position and angle of the wafer are determined. Pre-alignment technology is indispensable in semiconductor manufacturing. By improving alignment efficiency and accuracy, it ensures that each wafer can reach the best state before entering the key processing steps, thereby improving the quality and reliability of the entire manufacturing process. How to achieve pre-alignment of wafers has become a problem that technicians in this field need to solve. Summary of the invention

[0003] In view of this, the present invention provides a vision-based wafer pre-alignment system and method, and the main technical problem to be solved is: how to achieve pre-alignment of the wafer.

[0004] In order to achieve the above object, the present invention mainly provides the following technical solutions:

[0005] An embodiment of the present invention provides a vision-based wafer pre-alignment system, which includes a camera and a rotation mechanism;

[0006] The rotating mechanism is used to drive the wafer to rotate so that the edge of the wafer passes through the photographing range of the camera in sequence.

[0007] The present invention also provides a vision-based wafer pre-alignment method for use with the vision-based wafer pre-alignment system described above, the wafer pre-alignment method comprising:

[0008] Step S1: dividing the edge of the wafer into at least two parts in the circumferential direction;

[0009] Step S2: controlling the rotating mechanism to drive the wafer to rotate, so as to sequentially send each edge portion of the wafer into the photographing range of the camera, and allowing the camera to photograph each edge portion of the wafer respectively, so as to obtain images of each edge portion of the wafer;

[0010] Step S3: Processing the images of each edge segment to obtain data of each edge segment in the camera coordinate system;

[0011] Step S4: according to the relationship between the camera coordinate system and the world coordinate system, convert the data of each edge segment in the camera coordinate system into data in the world coordinate system;

[0012] Step S5: Obtain edge data of the wafer according to the data of each edge division part in the world coordinate system.

[0013] In some implementations, the processing of the image of each edge segmented portion is specifically:

[0014] Each edge segment is subjected to filtering processing, histogram equalization processing, edge contour extraction and segmentation processing, and threshold segmentation processing in sequence.

[0015] In some embodiments, the edge data of the wafer includes round edge data of the wafer;

[0016] And / or, when the characteristic mark of the wafer is a notch set on the edge, the edge data of the wafer includes notch data;

[0017] And / or, when the characteristic mark of the wafer is a flat edge set on the edge, the edge data of the wafer includes flat edge data.

[0018] In some embodiments, when the edge data of the wafer includes round edge data of the wafer, the wafer pre-alignment method further includes:

[0019] Step S6: acquiring eccentricity information of the wafer according to the round edge data of the wafer; the eccentricity information includes at least one of an eccentricity angle and an eccentricity distance;

[0020] Step S7: judging whether the wafer needs to be corrected according to the eccentricity information.

[0021] In some embodiments, when the characteristic mark of the wafer is a notch set on the edge, and the edge data of the wafer includes notch data, the wafer pre-alignment method further includes:

[0022] Step S8: obtaining the position of the gap according to the gap data;

[0023] Step S9: acquiring the wafer ID position according to the position of the notch and the preset notch-wafer ID position relationship;

[0024] Step S10: According to the position of the wafer ID, the rotating mechanism is controlled to drive the wafer to rotate, so as to send the wafer ID into the photographing range of the camera, and the camera is allowed to take a picture of the wafer ID to obtain an image of the wafer ID;

[0025] Step S11: Identify the wafer ID according to the wafer ID image.

[0026] In some embodiments, when the characteristic mark of the wafer is a flat edge set on the edge, and the edge data of the wafer includes flat edge data and round edge data, the wafer pre-alignment method further includes:

[0027] Step S12: According to the flat edge data and the circular edge data, the distance between the flat edge of the wafer and the center of the wafer and the perpendicular foot point corresponding to the flat edge are obtained.

[0028] By means of the above technical solution, the vision-based wafer pre-alignment system and method of the present invention has at least the following beneficial effects:

[0029] 1. The present invention can realize pre-alignment of the wafer through the steps of camera calibration, wafer edge data collection, edge image data preprocessing, coordinate system transformation and least squares fitting circle.

[0030] 2. The wafer pre-alignment system of the present invention has a wafer ID recognition function, and can maintain good pre-alignment accuracy for warped or thin wafers; in addition, the camera can also fly at high speed to improve detection efficiency.

[0031] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0033] Figure 1 is a schematic structural diagram of a vision-based wafer pre-alignment system provided by an embodiment of the present invention;

[0034] Figure 2 is a flow chart of a vision-based wafer pre-alignment method provided by an embodiment of the present invention;

[0035] Figure 3 It is a schematic diagram of coordinate system transformation;

[0036] Figure 4 It is a schematic diagram of a flat edge;

[0037] Figure 5 It is a schematic diagram of the gap;

[0038] Figure 6 It is a schematic diagram of circular edge fitting;

[0039] Figure 7 It is a schematic diagram of gap identification.

[0040] Reference numerals: 1. rotating mechanism; 2. turntable; 3. camera; 4. coaxial light source; 5. strip light source; 6. surface light source; 100. wafer. DETAILED DESCRIPTION

[0041] 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.

[0042] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0043] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0044] like Figure 1 As shown, an embodiment of the present invention provides a vision-based wafer pre-alignment system, which includes a camera 3 and a rotating mechanism 1. The rotating mechanism 1 is used to drive the wafer 100 to rotate so that the edge of the wafer 100 passes through the photographing range of the camera 3 in sequence.

[0045] In the above example, since the rotating mechanism 1 can sequentially bring the edge of the wafer 100 into the photographing range of the camera 3, the camera 3 can take pictures of the edge of the wafer 100. The camera 3 takes pictures of a portion of the edge of the wafer each time. After the wafer 100 rotates one circle, the camera 3 can obtain images of various locations on the edge of the wafer by taking pictures multiple times, so as to facilitate subsequent image processing to obtain the radius, angle information and feature mark information of the wafer 100.

[0046] In some embodiments, Figure 1As shown, the aforementioned vision-based wafer pre-alignment system may include a turntable 2, and the turntable 2 is used for mounting the wafer 100. The rotating mechanism 1 drives the wafer 100 to rotate by driving the turntable 2. The rotating mechanism 1 may include a motor to drive the turntable 2 to rotate.

[0047] The aforementioned camera 3 may be a CCD camera or the like. The aforementioned vision-based wafer pre-alignment system may further include a light source, which is used to be turned on when the camera 3 takes a picture. Among them, the light source may include a coaxial light source 4, a bar light source 5, and a surface light source 6. In a specific application example, both the coaxial light source 4 and the bar light source 5 may be located on a side of the wafer 100 close to the camera 3, and the surface light source 6 is located on a side of the wafer 100 away from the camera 3.

[0048] In some embodiments, Figure 2-7 As shown, the present invention also provides a vision-based wafer pre-alignment method for use with the vision-based wafer pre-alignment system described above. The wafer pre-alignment method includes:

[0049] Step S1: dividing the edge of the wafer 100 into at least two parts in the circumferential direction.

[0050] The edge divisions of the wafer 100 cooperate with each other to form a complete edge of the wafer 100 .

[0051] Step S2: Control the rotating mechanism 1 to drive the wafer 100 to rotate, so as to send each edge division part of the wafer 100 into the photographing range of the camera 3 in turn, and let the camera 3 take pictures of each edge division part of the wafer 100 respectively to obtain images of each edge division part of the wafer 100.

[0052] For example, the edge of the wafer 100 can be divided into N parts in the circumferential direction, where N is a positive integer greater than or equal to 2. The rotating mechanism 1 drives the wafer 100 to rotate 360 ​​degrees / N each time, so as to sequentially send the edge divisions of the wafer 100 into the photographing range of the camera 3, and let the camera 3 take pictures of each edge division respectively. Among them, the rotation angle of the wafer 100 can be collected by an encoder, and each time the wafer 100 rotates 360 degrees / N, the camera 3 is triggered to take a picture once, so as to take pictures of the corresponding edge divisions.

[0053] Step S3: Process the images of each edge segment obtained in step S2 to obtain data of each edge segment in the camera coordinate system.

[0054] The processing of the image of each edge segmentation part may specifically include: performing filtering processing, histogram equalization processing, edge contour extraction and segmentation processing, and threshold segmentation processing on each edge segmentation part in sequence.

[0055] Among them, filtering processing is used for noise removal, histogram equalization processing is used for normalization, edge contour extraction and segmentation processing is used to separate circle data from marker features (such as gaps or flat edges), and threshold segmentation processing is used to find marker features, such as finding the center of mass of the gap.

[0056] Step S4: According to the relationship between the camera coordinate system and the world coordinate system, the data of each edge segment in the camera coordinate system is converted into data in the world coordinate system.

[0057] The process of converting the data in the camera coordinate system into the data in the world coordinate system can be based on Figure 3 Understand. Figure 3 In the c ,y c ) is the camera coordinate system (the coordinate system after camera calibration), and the preset center of camera 3 is taken as the origin. w ,y w ) is the world coordinate system, and the rotation center of the turntable 2 is taken as the center.

[0058] Camera coordinate system Xc(x c ,y c ) and the world coordinate system Xw(x w ,y w ) can be expressed as follows: Xw = f + x c , Yw=-(y c -h). f is the distance between the preset center of camera 3 and the rotation center of turntable 2 at x w The deviation in the y direction is h, which is the difference between the preset center of the camera 3 and the rotation center of the turntable 2. w Deviation in direction.

[0059] According to this formula, the data point Xnc(x nc ,y nc ) can be first converted into Xnw(x nw ,y nw ); then according to the wafer rotation angle θn corresponding to the camera when capturing the image, the following formula can be used to convert the data point X'nw (x' nw , y' nw ).in,

[0060] x' nw =x nw *cos(-θn)+y nw *sin(-θn);

[0061] y' nw =-x nw *sin(-θn)+y nw *con(-θn).

[0062] Among them, x nw =f+x nc ,y nw =-(y nc -h).

[0063] Step S5: Acquire edge data of the wafer 100 according to the data of each edge segment in the world coordinate system.

[0064] The edge data of the wafer 100 may include round edge data of the wafer 100. When the characteristic mark of the wafer 100 is a notch set on the edge, the edge data of the wafer 100 may include notch data. When the characteristic mark of the wafer 100 is a flat edge set on the edge, the edge data of the wafer 100 may include flat edge data.

[0065] In the above example, the edge data of the wafer 100 can be used to achieve pre-alignment of the wafer 100. For example, the characteristic mark data of the wafer 100, such as a notch or a flat edge, can be used to compare with the preset position. If there is a deviation between the two, the wafer 100 can be driven to rotate by the rotating mechanism 1 to eliminate the deviation.

[0066] Among them, the technology of pre-aligning the wafer according to the edge data of the wafer 100 is an existing technology and will not be described in detail here.

[0067] In some embodiments, when the edge data of the wafer 100 includes round edge data of the wafer 100, the wafer pre-alignment method further includes:

[0068] Step S6: Acquire eccentricity information of the wafer 100 according to the round edge data of the wafer 100. The eccentricity information includes at least one of an eccentricity angle and an eccentricity distance.

[0069] Step S7: Determine whether the wafer 100 needs to be corrected according to the eccentricity information. Specifically, if the eccentricity angle of the wafer 100 is within the preset range, there is no need to adjust the eccentricity angle of the wafer 100; if the eccentricity angle of the wafer 100 is not within the preset range, the eccentricity angle of the wafer 100 needs to be adjusted. Similarly, if the eccentricity of the wafer 100 is within the preset range, there is no need to adjust the eccentricity of the wafer 100; if the eccentricity is not within the preset range, the eccentricity of the wafer 100 needs to be adjusted.

[0070] In some embodiments, when the characteristic mark of the wafer 100 is a notch set on the edge, and the edge data of the wafer 100 includes notch data, the wafer pre-alignment method further includes:

[0071] Step S8: According to the gap data, the position of the gap is obtained, wherein the position information of the gap includes the position of the center of the gap.

[0072] Step S9: Obtain the wafer ID position according to the position of the notch and the preset notch-wafer ID position relationship.

[0073] The positions of the notch on the wafer 100 and the wafer ID are relatively fixed and have a specific positional relationship. Once the position of the notch on the wafer 100 is determined, the position of the wafer ID can be determined based on the notch-wafer ID positional relationship.

[0074] Step S10: According to the wafer ID position, the rotating mechanism 1 is controlled to drive the wafer 100 to rotate, so as to send the wafer ID into the photographing range of the camera 3, and the camera 3 takes a picture of the wafer ID to obtain an image of the wafer ID.

[0075] Step S11: Identify the wafer ID according to the wafer ID image. The technology of identifying characters in the image according to the image is a prior art and will not be described in detail here.

[0076] Among them, the present invention can not only realize the pre-alignment of the wafer 100, but also has the function of wafer ID recognition, and the function is more comprehensive and more practical.

[0077] In some embodiments, when the feature mark of the wafer 100 is a flat edge set on the edge, and the edge data of the wafer 100 includes flat edge data and round edge data, the wafer pre-alignment method further includes:

[0078] Step S12: According to the flat edge data and the round edge data, the distance between the flat edge of the wafer 100 and the center of the wafer circle, and the foot point of the perpendicular corresponding to the flat edge are obtained. Specifically, according to the flat edge data and the round edge data, the flat edge and the round edge of the wafer 100 can be fitted by the least square method, and then the center of the round edge and the center of the flat edge can be found, so as to calculate the distance between the flat edge and the center of the round edge, and the foot point of the perpendicular corresponding to the flat edge.

[0079] It should be noted here that: the circular edge of the wafer 100 can be fitted by the least square method according to the circular edge data of the wafer 100, so as to calculate the radius of the wafer 100 and the center position of the wafer 100 in the world coordinate system.

[0080] The wafer pre-alignment system of the present invention has a wafer ID recognition function, and can maintain good pre-alignment accuracy for warped or thin wafers 100. The camera 3 can take pictures at high speed to improve the detection efficiency.

[0081] The driver of the rotating mechanism 1 of the present invention can send a shooting signal to the camera 3. The rotating mechanism 1 drives the wafer 100 to rotate into place, which can trigger the camera 3 to collect the edge image of the wafer. Through the steps of image preprocessing, edge extraction, coordinate system conversion, least squares fitting circle, etc., the center coordinates, angle information, and wafer radius of the notch or flat edge are returned.

[0082] The wafer pre-alignment process of the present invention needs to go through the steps of camera calibration, wafer edge data collection, edge image data preprocessing, coordinate system conversion and least squares fitting circle. Camera calibration needs to perform distance calibration according to the camera installation position and the rotation center position of the rotating mechanism 1; the internal and external parameters of the camera 3 are calibrated according to the calibration plate to perform distortion correction and pixel equivalent calibration. Edge data collection requires the rotating mechanism 1 to rotate more than one circle, and trigger the camera 3 to collect images through encoder position comparison at a specified angle. Edge image data preprocessing needs to go through filtering (noise removal), histogram equalization (normalization), edge contour extraction and segmentation (segmentation of circular data and notch or flat edge data), and threshold segmentation (finding the center of mass of the notch). Among them: the segmented circular edge and flat edge data are converted to the world coordinate system, the circular edge data is least squares fitted to the circle, and the wafer center and radius are obtained (the eccentric angle and eccentricity are calculated); the notch center is directly converted to the world coordinate system to obtain the notch position information; the flat edge data is fitted by the least squares straight line to find the distance between the straight line and the center of the circle and its corresponding perpendicular foot point. The eccentricity information can be used to determine whether to perform correction. Based on the notch position information and the wafer ID position standard, the rotating mechanism 1 rotates to the wafer ID position, turns on the coaxial light and the strip light, triggers the camera 3 to capture images, and performs OCR recognition of the wafer ID.

[0083] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A vision-based wafer pre-alignment system, characterized in that: It comprises a camera (3) and a rotating mechanism (1); The rotating mechanism (1) is used to drive the wafer (100) to rotate, so that the edge of the wafer (100) passes through the photographing range of the camera (3) in sequence.

2. A vision-based wafer pre-alignment method for use with the vision-based wafer pre-alignment system of claim 1, characterized in that: The wafer pre-alignment method comprises: Step S1: dividing the edge of the wafer (100) into at least two parts in the circumferential direction; Step S2: controlling the rotating mechanism (1) to drive the wafer (100) to rotate, so as to sequentially send the edge divisions of the wafer (100) into the photographing range of the camera (3), and allowing the camera (3) to photograph the edge divisions of the wafer (100) respectively, so as to obtain images of the edge divisions of the wafer (100); Step S3: Processing the images of each edge segment to obtain data of each edge segment in the camera coordinate system; Step S4: according to the relationship between the camera coordinate system and the world coordinate system, convert the data of each edge segment in the camera coordinate system into data in the world coordinate system; Step S5: Acquire edge data of the wafer (100) based on the data of each edge division part in the world coordinate system.

3. The vision-based wafer pre-alignment method according to claim 2, characterized in that: The processing of the image of each edge segmented portion is specifically as follows: Each edge segment is subjected to filtering processing, histogram equalization processing, edge contour extraction and segmentation processing, and threshold segmentation processing in sequence.

4. The vision-based wafer pre-alignment method according to claim 2 or 3, characterized in that: The edge data of the wafer (100) includes circular edge data of the wafer (100); And / or, when the characteristic mark of the wafer (100) is a notch set on the edge, the edge data of the wafer (100) includes notch data; And / or, when the characteristic mark of the wafer (100) is a flat edge set on the edge, the edge data of the wafer (100) includes flat edge data.

5. The vision-based wafer pre-alignment method according to claim 4, characterized in that: When the edge data of the wafer (100) includes round edge data of the wafer (100), the wafer pre-alignment method further comprises: Step S6: acquiring eccentricity information of the wafer (100) according to the round edge data of the wafer (100); the eccentricity information includes at least one of an eccentricity angle and an eccentricity distance; Step S7: judging whether the wafer (100) needs to be rectified based on the eccentricity information.

6. The vision-based wafer pre-alignment method according to claim 4, characterized in that: When the characteristic mark of the wafer (100) is a notch set on the edge, and the edge data of the wafer (100) includes notch data, the wafer pre-alignment method further comprises: Step S8: obtaining the position of the gap according to the gap data; Step S9: acquiring the wafer ID position according to the position of the notch and the preset notch-wafer ID position relationship; Step S10: According to the position of the wafer ID, the rotating mechanism (1) is controlled to drive the wafer (100) to rotate so as to send the wafer ID into the photographing range of the camera (3), and the camera (3) takes a photograph of the wafer ID to obtain an image of the wafer ID; Step S11: Identify the wafer ID according to the wafer ID image.

7. The vision-based wafer pre-alignment method according to claim 4, characterized in that: When the characteristic mark of the wafer (100) is a flat edge set on the edge, and the edge data of the wafer (100) includes flat edge data and round edge data, the wafer pre-alignment method further comprises: Step S12: according to the flat edge data and the circular edge data, obtaining the distance between the flat edge of the wafer (100) and the center of the wafer, and the perpendicular foot point corresponding to the flat edge.

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