Visual detection method for circle center, radius and angle of wafer

Abstract

The invention belongs to the field of machine vision wafer positioning detection, and provides a visual detection method for the circle center, radius and angle of a wafer. The mechanical arm sends world coordinates and digital codes, and the visual software executes a corresponding detection algorithm according to the received world coordinates and digital codes; three images are shot at three different positions of the edge of the wafer, and three representative points are obtained through calculation; fitting a circle by the three representative points, and calculating to obtain the circle center coordinate and the radius of the wafer; and shooting an image of the bevel edge of the wafer, and calculating to obtain the wafer angle. According to the invention, automatic extraction of the wafer edge can be realized, and the detection precision and efficiency are high.

Description

Technical Field

[0001] The present invention belongs to the field of machine vision wafer positioning detection, and specifically relates to a visual detection method for a wafer center, radius and angle. Background Art

[0002] Wafers are the basic raw materials for manufacturing semiconductor chips. The formation of chips includes several process links. First, extremely high-purity semiconductors are prepared into wafers through processes such as crystal pulling and slicing. Then the wafers undergo a series of semiconductor manufacturing processes to form extremely small circuit structures. Finally, they are cut, packaged, and tested to become chips, which are widely used in various electronic devices. Among them, the circuit production based on semiconductor wafers requires precise positioning of the center, radius, and angle of the wafer to ensure high-performance circuit production. However, the wafer formed by preliminary slicing is not a standard circle, and it is difficult to accurately determine its center and radius. Therefore, accurate detection of the center and radius of the wafer is the core technology of chip production.

[0003] Existing wafer inspection methods rely solely on manual measurement, such as using a high-precision vernier caliper to measure its radius, which is not only inefficient, but also cannot meet the requirements of the chip manufacturing pipeline in terms of accuracy and flexibility. Therefore, finding an efficient and accurate automatic inspection method has become an urgent need to improve wafer inspection efficiency. To this end, the present invention proposes an automatic wafer inspection method based on machine vision.

[0004] In machine vision inspection systems, edge detection algorithms are the technical basis for achieving high-precision wafer automatic inspection. Different edge detection algorithms show their own advantages and disadvantages in industrial applications: the Sobel operator performs well in simplicity and noise suppression, but its edge positioning accuracy is insufficient and may miss subtle edges. The Canny edge detection algorithm provides high edge detection accuracy and good signal-to-noise ratio, but it is highly complex and difficult to meet real-time requirements. The Laplacian operator can highlight sharp edges and is suitable for workpiece detection with rich details, but it is highly sensitive to noise and prone to false detection. The Prewitt operator is simple to implement and can effectively detect edge directions, but it also has deficiencies in accuracy and noise resistance. At the same time, the visual positioning of the wafer relies on optical detection, mainly relying on infrared light sources to penetrate the wafer for imaging, so the image clarity is not high, which easily causes the wafer imaging edge blur. In view of these problems such as low imaging quality and blurred edges, the present invention proposes an improved edge detection method. Summary of the invention

[0005] The present invention aims to solve the problems in the prior art and proposes a visual detection method for the center, radius and angle of a wafer. The present invention proposes to use a camera to extract the edge of the wafer, and obtain three precise representative points on the edge of the wafer through an algorithm, fit a circle to the representative points, and obtain the precise coordinates of the center and radius.

[0006] In order to achieve the above object, the present invention is implemented by the following technical scheme: A visual detection method for the center, radius and angle of a wafer is performed according to the following steps:

[0007] S1, the robotic arm sends the world coordinates and digital code of the current position of the wafer, and obtains images of different positions of the wafer according to the received world coordinates and digital code;

[0008] S2. Take a picture of the bevel of the wafer and obtain the wafer angle by calculating the angle between the bevel and the horizontal direction;

[0009] S3, taking three images at three different positions of the wafer edge and calculating three representative points;

[0010] S4, fitting a circle with the three representative points calculated in step S3 to obtain the coordinates of the center and radius of the wafer.

[0011] Furthermore, the specific process of collecting wafer images in step S1 is as follows:

[0012] S11, the robot arm sends communication codes 1, 2, 3, 4;

[0013] S12. The visual system performs corresponding operations according to the received communication code:

[0014] Operation 1: After receiving the communication code 1, the visual system takes a picture of the bevel side of the wafer to obtain the image img1;

[0015] Operation 2: After receiving communication code 2, the vision system takes the first picture of the wafer edge and obtains picture img2. After receiving communication code 3, the vision system takes the second picture of the wafer edge and obtains picture img3. After receiving communication code 4, the vision system takes the third picture of the wafer edge and obtains picture img4.

[0016] Furthermore, the calculation process of the wafer angle in step S2 is as follows:

[0017] S21, binarize and invert the image image1;

[0018] S22. Detect edges of the inverted image and paint 100 pixel areas at the upper, lower, left and right edges of the image in black;

[0019] S23, performing an expansion operation on the edge to make the detected edge continuous;

[0020] S24, performing straight line detection on the expanded image to obtain the wafer bevel;

[0021] S25, calculating the angle between the wafer bevel and the horizontal direction to obtain the wafer angle;

[0022] S26. Return the angle and communication code and save them.

[0023] Furthermore, the calculation process of the three representative points in step S3 is as follows:

[0024] S31, receiving three images image2, image3, image4 and their corresponding world coordinates in step S1;

[0025] S32, converting the data format of the transmitted data, converting the string format of the world coordinates into a double-precision format;

[0026] S33, binarize image2, image3, and image4 respectively and find the circle boundary;

[0027] S34, putting the coordinates of the circle boundary points of image2, image3 and image4 into three containers respectively;

[0028] S35. Obtain a representative point for each container, and perform the following operations:

[0029] Let the corresponding image coordinates of the center of the field of view be (x c ,y c ), traverse its edge points (x, y), determine the coordinates of a representative point (x p ,y p ), satisfying the condition: x p =x c And 100 <y p <1100, or y p =y c And 100 <x p <1500, calculate y p With y c The pixel deviation or x p With x c The pixel deviation is multiplied by the single pixel precision coefficient to obtain the deviation in the world coordinate system, thereby obtaining the world coordinates of the representative point.

[0030] Furthermore, the specific calculation process of the wafer center coordinates and radius in S4 is as follows:

[0031] S41. Assume the coordinates of the center of the wafer are (x0, y0), the radius is r, and the coordinates of the three representative points are A (x1, y1), B (x2, y2), and C (x3, y3). The formula for determining the circle by three points is defined as:

[0032] (x1-x0) 2 +(y1-y0) 2 =r 2 (1)

[0033] x2-x0) 2 +(y2-y0) 2 =r 2 (2)

[0034] x3-x0) 2 +(y3-y0) 2 =r 2 (3)

[0035] S42, by simplifying formula (1), formula (2), and formula (3), we can obtain:

[0036] (x1-x2)x0+(y1-y2)y0=(x1 2 -x2 2 )-(y2 2 -y1 2 ) / twenty four)

[0037] (x1-x3)x0+(y1-y3)y0=(x1 2 -x3 2 )-(y3 2 -y1 2 ) / 2 (5)

[0038] S43. Suppose a=x1-x2, b=y1-y2, c=x1-x3, d=y1-y3, e=(x1 2 -x2 2 )-(y2 2 -y1 2 ) / 2,

[0039] f=(x1 2 -x3 2 )-(y3 2 -y1 2 ) / 2, from the above formula (4) and formula (5) through the non-homogeneous linear equation system, we can get: x0 = (ed-bf) / (ad-bc), y0 = (af-ec) / (ad-bc);

[0040] S44, the (x0, y0) obtained above is the coordinate of the center of the circle, and (x0, y0) is substituted into formula (1) to calculate the radius r;

[0041] S45. Return the center coordinates (x0, y0), radius r and communication code and save them.

[0042] Compared with the prior art, the invention has the following beneficial effects.

[0043] 1. The present invention sends world coordinates and digital codes through a robotic arm, and the visual software executes a corresponding detection algorithm based on the received world coordinates and digital codes; three images are taken at three different positions of the edge of the wafer, and three representative points are calculated; a circle is fitted from the three representative points to calculate the coordinates and radius of the center of the wafer; an image is taken of the bevel of the wafer to calculate the wafer angle.

[0044] 2. The present invention proposes to determine a representative point using three images taken three times respectively, and proposes to take a point on the edge of the wafer with the same horizontal or vertical coordinate as the center point of the field of view as a representative point, and use the three representative points to fit a circle, thereby completing the determination of the center of the wafer.

[0045] 3. The algorithm of the present invention can realize an automated process flow, and it is proposed to realize it by using the interaction between a robot arm and a visual software. First, the visual software is controlled by the robot arm to take images, and then the image processed data is sent to the robot arm by the visual software, thereby realizing the automation of the entire process. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is the algorithm flow chart of the present invention;

[0047] Figure 2 It is a schematic diagram of the overall environment under the wafer inspection process;

[0048] Figure 3 (3a), (3b), (3c), and (3d) are schematic diagrams of the wafer bevel and three edge images taken by an industrial camera, respectively;

[0049] Figure 4 (4a), (4b), and (4c) are schematic diagrams of three representative points;

[0050] Figure 5 Schematic diagram of wafer bevel calculated for S2;

[0051] Figure 6 Schematic diagram of the visual inspection software interface. DETAILED DESCRIPTION

[0052] The following will describe the implementation methods of the present invention in detail with reference to the accompanying drawings and examples, so as to fully understand and implement the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects.

[0053] like Figure 1As shown, a visual inspection method for the center, radius and angle of a wafer is performed according to the following steps:

[0054] S1. The robot arm sends the world coordinates and digital code of the current position of the wafer. The visual system obtains photos of different positions of the wafer based on the received world coordinates and digital codes. Figures (3a), (3b) and (3c) are the obtained edge images. The specific steps are as follows:

[0055] S11, the robot arm sends communication codes 1, 2, 3, 4 to the upper software;

[0056] S12. The visual system performs corresponding operations according to the received communication code:

[0057] Operation 1: After receiving the communication code 1, the visual system takes a picture of the bevel side of the wafer to obtain the image img1;

[0058] Operation 2: After receiving communication code 2, the vision system takes the first picture of the wafer edge and obtains picture img2. After receiving communication code 3, the vision system takes the second picture of the wafer edge and obtains picture img3. After receiving communication code 4, the vision system takes the third picture of the wafer edge and obtains picture img4.

[0059] S2. Take a picture of the wafer bevel and calculate the angle between the bevel and the horizontal direction to get the wafer angle. The specific steps are as follows:

[0060] S21, binarize and invert the image image1;

[0061] S22. Detect edges of the inverted image and paint 100 pixel areas at the upper, lower, left and right edges of the image in black;

[0062] S23, performing an expansion operation on the edge to make the detected edge continuous;

[0063] S24, performing straight line detection on the expanded image;

[0064] S25, calculating the angle between the straight line and the horizontal direction;

[0065] S26. Return the angle and communication code and save them.

[0066] S3, such as Figure 4 As shown, three images are taken at three different positions on the edge of the wafer, and three representative points are calculated.

[0067] S31, receiving three images image2, image3, image4 and their corresponding world coordinates in step S1;

[0068] S32, converting the data format of the transmitted data, converting the string format of the world coordinates into a double-precision format;

[0069] S33, binarize image2, image3, and image4 respectively and find the circle boundary;

[0070] S34, putting the coordinates of the circle boundary points of image2, image3 and image4 into three containers respectively;

[0071] S35. Obtain a representative point for each container, and perform the following operations:

[0072] Let the corresponding image coordinates of the center of the field of view be (x c ,y c ), traverse its edge points (x, y), determine the coordinates of a representative point (x p ,y p ), satisfying the condition: x p =x c And 100 <y p <1100, or y p =y c And 100 <x p <1500, calculate y p With y c The pixel deviation or x p With x c The pixel deviation is multiplied by the single pixel precision coefficient to obtain the deviation in the world coordinate system, thereby obtaining the world coordinates of the representative point.

[0073] S4, fitting a circle with the three representative points calculated in step S3 to obtain the center coordinates and radius of the wafer. The specific calculation process is as follows:

[0074] S41. Assume the coordinates of the center of the wafer are (x0, y0), the radius is r, and the coordinates of the three representative points are A (x1, y1), B (x2, y2), and C (x3, y3). The formula for determining the circle by three points is defined as:

[0075] (x1-x0) 2 +(y1-y0) 2 =r 2 (1)

[0076] (x2-x0) 2 +(y2-y0) 2 =r 2 (2)

[0077] (x3-x0) 2 +(y3-y0) 2 =r 2 (3)

[0078] S42, by simplifying formula (1), formula (2), and formula (3), we can obtain:

[0079] (x1-x2)x0+(y1-y2)y0=(x1 2 -x2 2 )-(y2 2 -y1 2 ) / twenty four)

[0080] (x1-x3)x0+(y1-y3)y0=(x1 2 -x3 2 )-(y3 2 -y1 2 ) / 2 (5)

[0081] S43. Suppose a=x1-x2, b=y1-y2, c=x1-x3, d=y1-y3, e=(x1 2 -x2 2 )-(y2 2 -y1 2 ) / 2, f=(x1 2 -x3 2 )-(y3 2 -y1 2 ) / 2, from the above formula (4) and formula (5) through the non-homogeneous linear equation system, we can get: x0 = (ed-bf) / (ad-bc), y0 = (af-ec) / (ad-bc);

[0082] S44, the (x0, y0) obtained above is the coordinate of the center of the circle, and (x0, y0) is substituted into formula (1) to calculate the radius r;

[0083] S45. Return the center coordinates (x0, y0), radius r and communication code and save them.

[0084] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A visual inspection method for wafer center, radius and angle, characterized by: Follow these steps: S1, the robotic arm sends the world coordinates and digital code of the current position of the wafer, and obtains images of different positions of the wafer according to the received world coordinates and digital code; S2. Take a picture of the bevel of the wafer and obtain the wafer angle by calculating the angle between the bevel and the horizontal direction; S3, taking three images at three different positions of the wafer edge and calculating three representative points; S4, fitting a circle with the three representative points calculated in step S3 to obtain the coordinates of the center and radius of the wafer.

2. The visual inspection method for wafer center, radius and angle according to claim 1, characterized in that: The specific process of collecting wafer images in step S1 is as follows: S11, the robot arm sends communication codes 1, 2, 3, 4; S12. The visual system performs corresponding operations according to the received communication code: Operation 1: After receiving the communication code 1, the visual system takes a picture of the bevel side of the wafer to obtain the image img1; Operation 2: After receiving communication code 2, the vision system takes the first picture of the wafer edge and obtains picture img2. After receiving communication code 3, the vision system takes the second picture of the wafer edge and obtains picture img3. After receiving communication code 4, the vision system takes the third picture of the wafer edge and obtains picture img4.

3. The visual inspection method for wafer center, radius and angle according to claim 2, characterized in that: The calculation process of the wafer angle in step S2 is as follows: S21, binarize and invert the image image1; S22. Detect edges of the inverted image and paint 100 pixel areas at the upper, lower, left and right edges of the image in black; S23, performing an expansion operation on the edge to make the detected edge continuous; S24, performing straight line detection on the expanded image to obtain the wafer bevel; S25, calculating the angle between the wafer bevel and the horizontal direction to obtain the wafer angle; S26. Return the angle and communication code and save them.

4. The visual inspection method for wafer center, radius and angle according to claim 3, characterized in that: The calculation process of the three representative points in step S3 is as follows: S31, receiving three images image2, image3, image4 and their corresponding world coordinates in step S1; S32, converting the data format of the transmitted data, converting the string format of the world coordinates into a double-precision format; S33, binarize image2, image3, and image4 respectively and find the circle boundary; S34, putting the coordinates of the circle boundary points of image2, image3 and image4 into three containers respectively; S35. Obtain a representative point for each container, and perform the following operations: Let the corresponding image coordinates of the center of the field of view be (x c ,y c ), traverse its edge points (x, y), determine a representative point coordinate (x p ,y p ), satisfying the condition: X p =X c And 100 <y p <1100, or y p =y c And 100 <x p <1500, calculate y p With y c The pixel deviation or x p With x c The pixel deviation is multiplied by the single pixel precision coefficient to obtain the deviation in the world coordinate system, thereby obtaining the world coordinates of the representative point.

5. The visual inspection method for wafer center, radius and angle according to claim 4, characterized in that: The specific calculation process of the wafer center coordinates and radius in S4 is as follows: S41. Assume the coordinates of the center of the wafer are (x0, y0), the radius is r, and the coordinates of the three representative points are A (x1, y1), B (x2, y2), and C (x3, y3). The formula for determining the circle by three points is defined as: (x1-x0) 2 +(y1-y0) 2 =r 2 (1) (x2-x0) 2 +(y2-y0) 2 =r 2 (2) <h2 style=";text-align:left;direction:ltr">(x3-x0)<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +(y3-y0)<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> =r<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> (3) S42, by simplifying formula (1), formula (2), and formula (3), we can obtain: <h2 style=";text-align:left;direction:ltr">(x1-x2)x0+(y1-y2)y0=(x1<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> -x2<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> )-(y2<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> -y1<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> ) / 2 (4) <h2 style=";text-align:left;direction:ltr">(x1-x3)x0+(y1-y3)y0=(x1<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> -x3<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> )-(y3<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> -y1<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> ) / 2 (5) S43. Suppose a=x1-x2, b=y1-y2, c=x1-x3, d=y1-y3, e=(x1 2 -x2 2 )-(y2 2 -y1 2 ) / 2, f=(x1 2 -x3 2 )-(y3 2 -y1 2 ) / 2, from the above formula (4) and formula (5) through the non-homogeneous linear equation system, we can get: x0 = (ed-bf) / (ad-bc), y0 = (af-ec) / (ad-bc); S44, the (x0, y0) obtained above is the coordinate of the center of the circle, and (x0, y0) is substituted into formula (1) to calculate the radius r; S45. Return the center coordinates (x0, y0), radius r and communication code and save them.

Images