Wafer eccentricity detecting and positioning method

Abstract

The invention relates to the technical field of wafer positioning, in particular to a wafer eccentricity detecting and positioning method, which comprises the following steps of: rotating a wafer along with a rotary platform, acquiring an edge image of the wafer, extracting a fine edge through sub-pixel interpolation, obtaining a wafer edge curve, performing interpolation, and calculating an eccentricity and an eccentricity angle of the wafer. Determining the position of a wafer gap, and then enabling the wafer and the revolving platform to move relatively, so that the circle center of the wafer coincides with the revolving center of the revolving platform; and driving the rotary platform to rotate by a corresponding angle according to the wafer gap position. Edge position information in the wafer rotation process is collected through a camera, the eccentric distance and the eccentric angle of the wafer relative to the rotation platform and the position of a wafer notch are calculated, eccentric correction and angle calibration of the wafer can be completed by moving the wafer and rotating the rotation platform, and the accuracy of the wafer is improved through methods of sub-pixel interpolation, spline interpolation and the like. And the wafer edge identification precision and the sampling precision are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wafer positioning, in particular to a wafer eccentricity detection and positioning method. Background Art

[0002] Wafer positioning and deflection correction are crucial during semiconductor processing. The accuracy of positioning and calibration directly impacts subsequent processing quality and yield. Wafer positioning generally involves centering and angular positioning. Existing technologies include mechanical mechanisms or wafer edge information for positioning, but these methods suffer from low accuracy and long positioning times. Summary of the Invention

[0003] The present invention aims to solve the above problems and provides a method for detecting and positioning wafer eccentricity, the technical solution of which is as follows: A wafer eccentricity detection and positioning method comprises the following steps: S1. Place the wafer on a rotary platform, which drives the wafer to rotate at a constant speed in the horizontal plane, with a rotation angle of not less than 2 ; S2. uniformly collecting images within a predetermined collection range at the edge of the wafer during wafer rotation; S3. Identifying the rough edge of the wafer in the wafer edge image, performing sub-pixel interpolation on the rough edge, and extracting the fine edge of the wafer; S4. Summarize the fine edge points of the wafer at the image acquisition position to obtain a wafer edge curve, and perform spline interpolation on the edge curve; S5. Calculate the wafer center, as well as the eccentricity and eccentricity angle between the wafer center and the rotation center of the rotary platform based on the positions of the fine edge points of the wafer; S6. Determine the wafer notch position based on the change in the edge curve; S7. Move the wafer and the rotary platform relative to each other according to the eccentricity and eccentricity angle so that the center of the wafer coincides with the rotation center of the rotary platform; drive the rotary platform to rotate the corresponding angle according to the position of the wafer notch to complete the center positioning and angle positioning of the wafer.

[0004] On the basis of the above scheme, in step S5, a plane rectangular coordinate system of the rotary platform is established, the rotation center of the rotary platform is defined as the origin of the coordinate system O, the center of the wafer is defined as point C, and the camera acquisition position is defined as point P. The length of the OP segment is L, that is, the distance between each point on the edge of the wafer and the rotation center of the rotary platform, the eccentricity between the center of the wafer and the rotation center of the rotary platform is defined as d, the radius of the wafer is defined as R, and the angle between the OC segment and the OP segment is defined as ,but (1) Find the adjacent first extreme point and second extreme point in the edge curve, where L reaches the maximum value L at the first extreme point max , L reaches the minimum value L at the second extreme point min , then (2) The eccentricity is (3).

[0005] Based on the above scheme, the phase difference between the first extreme point and the second extreme point is , calculate the phase difference between adjacent acquisition points on the wafer edge, and then calculate the phase of each point on the wafer edge relative to the first extreme point. Calculate the phase of the wafer edge at the image acquisition position relative to the first extreme point at the end of acquisition, and record the eccentricity angle.

[0006] Preferably, the adjacent difference method is used to calculate the change values of adjacent sub-pixels, a change value threshold is set, and the change value is compared with the threshold. When the change value is greater than the threshold, it is determined that the sub-pixel point is in the straight line segment of the wafer notch or on both sides of the arc segment, and when the sign of the differential value is different, the point is determined to be the center point of the arc segment of the wafer notch.

[0007] Based on the above scheme, the gap center interval is delineated with the arc center point of the wafer gap as the center, and B-spline interpolation is performed within the gap center interval. After interpolation, the adjacent sub-pixel change value is calculated using the adjacent difference method. When the sign of the differential value is different, the point is determined to be the exact center point of the wafer gap.

[0008] Preferably, the time when the rotary platform stops is later than the last sampling time of the camera, and the phase of the wafer edge image acquisition point at the predetermined position when the camera acquires the image for the last time is defined as 1. When the rotary platform stops, the phase of the wafer edge at the predetermined position is 2, when the rotary platform drives the wafer to rotate in step S7, the rotation angle should be compensated in .

[0009] Preferably, the camera is arranged above the wafer, and a parallel coaxial surface light source is arranged below the wafer. The light source is correspondingly arranged below the camera, and the irradiation direction of the light source is upward.

[0010] Preferably, when the wafer notch is located at the first extreme point or the second extreme point, the position of the wafer notch is determined by the adjacent difference method, the extreme points covered by the wafer notch are shielded, the other extreme points are calculated and recorded, and the position information of the section where the shielded extreme points are located is fitted by interpolation.

[0011] Preferably, when the wafer notch is photographed twice or there is a wafer notch incomplete, the pixel interval of the wafer notch is calculated by the difference method, the pixel width occupied by the wafer notch is calculated, and the wafer notch with the larger pixel width is selected as the complete wafer notch image.

[0012] Preferably, the extreme value center interval is delineated with the first extreme value point and the second extreme value point as the center, B-spline interpolation is performed in the extreme value center interval, and the extreme value in the interval after interpolation is selected as the precise extreme value.

[0013] Preferably, the sub-pixel interpolation method is a one-dimensional grayscale extreme value method or a Gaussian integral curve fitting method.

[0014] The beneficial effects of the present invention are as follows: the edge position information of the wafer during rotation is collected by a camera, the eccentricity, eccentricity angle and position of the wafer notch of the wafer relative to the rotary platform are calculated, and the eccentricity correction and angle calibration of the wafer can be completed by moving the wafer and rotating the rotary platform. The calculation process is reliable and the correction accuracy is high; the wafer edge recognition accuracy and sampling accuracy are improved through methods such as sub-pixel interpolation and spline interpolation; the correction positioning can be completed with one rotation and one movement of the wafer, the operation is simple and time-saving, and the equipment cost and time cost are effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 : Schematic diagram of the device structure used in the detection method of the present invention; Figure 2 : Schematic diagram of the mathematical model of the wafer eccentrically rotating according to the present invention; Figure 3 : Schematic diagram of image acquisition by the camera of the present invention; Figure 4 : Schematic diagram of the wafer notch structure of the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments: In the present invention, unless otherwise expressly specified or limited, terms such as "mounted," "connected," "connect," and "fixed" should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; they may refer to direct connection or indirect connection through an intermediate medium; they may refer to internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0017] In the description of the present invention, it should be understood that the terms "center", "length", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying 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 one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0018] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0019] A wafer eccentricity detection and positioning method comprises the following steps: S1. Place the wafer on the rotary platform. The center of the wafer is offset from the center of rotation of the rotary platform. The rotary platform drives the wafer to rotate at a constant speed in the horizontal plane. The rotation angle is not less than 2 , ensure that the wafer rotates more than one circle; S2. uniformly collect images within a predetermined collection range at the edge of the wafer during wafer rotation; the uniformity refers to collecting images multiple times, and the time interval between two adjacent collections is the same. Preferably, if Figure 1 As shown, the camera is set above the wafer, and a parallel coaxial surface light source is set below the wafer. The light source is correspondingly set below the camera, and the light source irradiates upward. Part of the light is blocked by the wafer, and the other light is received by the camera. The camera captures an image of the edge area of the wafer; S3. Identify the rough edge of the wafer in the wafer edge image, perform sub-pixel interpolation on the rough edge, and extract the fine edge of the wafer; the sub-pixel interpolation method is a one-dimensional grayscale extreme value method or a Gaussian integral curve fitting method: The specific method of one-dimensional grayscale extreme value method is: Considering that the line array camera collects a single row of pixel data each time, this solution only considers the grayscale extreme value method in one-dimensional direction in the grayscale extreme value method, and its calculation formula is: (4) Among them, offset represents the offset, n is the proportional coefficient, represents the second-order derivative, where a, b, and c are three adjacent points in the image. After obtaining the offset value, the offset is performed with point b as the center.

[0020] When performing the interpolation operation, the gradient method is first used to obtain a coarse edge with single-pixel accuracy, and this coarse edge is used as the center point b. Then, by calculating the offset, the fine edge with sub-pixel accuracy is extracted, thereby improving the detection accuracy.

[0021] The specific method of Gaussian integral curve fitting method is: Since the backlight acquisition method is used in this solution to collect the wafer edge image changes, the change trend in the one-dimensional direction is close to the Gaussian integral curve, so the Gaussian integral curve fitting method is used for sub-pixel interpolation.

[0022] First, a rough edge with single-pixel precision is obtained through the gradient method. Then, an interval is selected with the rough edge as the center. The interval has the same number of pixels on both sides of the center point. According to the pixel position and grayscale value of each point, a Gaussian integral curve model is used for fitting to obtain the curve equation of the continuous change of each point along the edge. The second-order derivative of the curve equation is zero, which is the sub-pixel level fine edge point.

[0023] S4. Summarize the fine edge points of the wafer at the image acquisition position to obtain a wafer edge curve, and perform spline interpolation on the edge curve; S5. Calculate the wafer center, as well as the eccentricity and eccentricity angle between the wafer center and the rotation center of the rotary platform based on the positions of the fine edge points of the wafer; Taking the numerical method as an example, a plane rectangular coordinate system of the rotary platform is established, the rotation center of the rotary platform is defined as the origin of the coordinate system O, the center of the wafer is defined as point C, and the camera acquisition position is defined as point P. The length of the OP segment is L, that is, the distance between each point on the edge of the wafer and the rotation center of the rotary platform. The eccentricity between the center of the wafer and the rotation center of the rotary platform is defined as d, the radius of the wafer is defined as R, and the angle between the OC segment and the OP segment is defined as ,but (1) Find the adjacent first extreme point and second extreme point in the edge curve, where L reaches the maximum value L at the first extreme point max , L reaches the minimum value L at the second extreme point min , then (2) The eccentricity is (3) The extreme value center interval is delineated with the first extreme value point and the second extreme value point as the center, B-spline interpolation is performed in the extreme value center interval, and the extreme value in the interval after interpolation is selected as the precise extreme value.

[0024] The phase difference between the first extreme point and the second extreme point is , calculate the phase difference between adjacent acquisition points on the wafer edge, and then calculate the phase of each point on the wafer edge relative to the first extreme point. Calculate the phase of the wafer edge at the image acquisition position relative to the first extreme point at the end of acquisition, and record the eccentricity angle.

[0025] S6. Determine the wafer notch position based on the change in the edge curve and calculate the angle of the wafer notch relative to the wafer center; S7. Move the wafer and the rotary platform relative to each other according to the eccentric distance and eccentric angle so that the center of the wafer coincides with the rotation center of the rotary platform; drive the rotary platform to rotate the corresponding angle according to the phase of the wafer notch position to complete the center positioning and angle positioning of the wafer.

[0026] Furthermore, since sampling is only performed when the rotary platform is rotating at a constant speed, the speed of the rotary platform needs to be gradually reduced until it stops after sampling. Therefore, the time when the rotary platform stops is later than the last sampling time of the camera, and the rotary platform will drive the wafer to continue rotating by a certain angle after sampling, causing errors. To solve the above problem, the phase of the wafer edge image acquisition point at the predetermined position when the camera last captured the image is defined as 1. When the rotary platform stops, the phase of the wafer edge at the predetermined position is 2, when the rotary platform drives the wafer to rotate in step S7, the rotation angle should be compensated in .

[0027] like Figure 4As shown, the wafer notch is located at the edge of the wafer, with a central angle of approximately 1°-2° and a depth of approximately 1mm. Therefore, the L value change rate at the wafer notch is significantly greater than at other points. For ease of description, the structure of the wafer notch area is simplified to two straight line segments and an arc segment between them, with the center point of the arc segment being the notch center point. In step S6, when determining the wafer notch position, the adjacent sub-pixel change value is calculated using the adjacent difference method. A change value threshold is set and the change value is compared with the threshold. When the change value is greater than the threshold, the sub-pixel point is determined to be within the straight line segment of the wafer notch or on both sides of the arc segment. When the sign of the difference value is different, the point is determined to be the center point of the wafer notch arc segment. Furthermore, the notch center interval is delineated with the arc center point of the wafer notch as the center. B-spline interpolation is performed within the notch center interval. After interpolation, the adjacent sub-pixel change value is calculated using the adjacent difference method. When the sign of the difference value is different, the point is determined to be the exact center point of the wafer notch. The phase of the precise center point is used as the basis for wafer angle adjustment, thereby improving detection and calculation accuracy.

[0028] When the wafer notch is located at the first extreme point or the second extreme point, the position of the wafer notch is determined by the adjacent difference method, the extreme points covered by the wafer notch are shielded, the other extreme points are calculated and recorded, and the position information of the segment where the shielded extreme points are located is fitted by interpolation. The segment length can be set in advance.

[0029] When the wafer notch is photographed twice or there is a wafer notch incomplete, the pixel interval of the wafer notch is calculated by the difference method, the pixel width occupied by the wafer notch is calculated, and the wafer notch with the larger pixel width is selected as the complete wafer notch image.

[0030] The present invention has been described above by way of examples, but the present invention is not limited to the above specific embodiments. Any changes or modifications based on the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A wafer eccentricity detection and positioning method, characterized in that: The following steps are involved: S1. Place the wafer on a rotary platform, which drives the wafer to rotate at a constant speed in the horizontal plane, with a rotation angle of not less than 2 ; S2. uniformly collecting images within a predetermined collection range at the edge of the wafer during wafer rotation; S3. Identifying the rough edge of the wafer in the wafer edge image, performing sub-pixel interpolation on the rough edge, and extracting the fine edge of the wafer; S4. Summarize the fine edge points of the wafer at the image acquisition position to obtain a wafer edge curve, and perform spline interpolation on the edge curve; S5. Calculate the wafer center, as well as the eccentricity and eccentricity angle between the wafer center and the rotation center of the rotary platform based on the positions of the fine edge points of the wafer; S6. Determine the wafer notch position based on the change in the edge curve; S7. Move the wafer and the rotary platform relative to each other according to the eccentricity and eccentricity angle so that the center of the wafer coincides with the rotation center of the rotary platform; drive the rotary platform to rotate the corresponding angle according to the position of the wafer notch to complete the center positioning and angle positioning of the wafer.

2. The wafer eccentricity detection and positioning method according to claim 1, characterized in that: In step S5, a plane rectangular coordinate system of the rotary platform is established, the rotation center of the rotary platform is defined as the origin of the coordinate system O, the center of the wafer is defined as point C, and the camera acquisition position is defined as point P. The length of the OP segment is L, that is, the distance between each point on the edge of the wafer and the rotation center of the rotary platform, the eccentricity between the center of the wafer and the rotation center of the rotary platform is defined as d, the wafer radius is defined as R, and the angle between the OC segment and the OP segment is defined as ,but （1） Find the adjacent first extreme point and second extreme point in the edge curve, where L reaches the maximum value L at the first extreme point max , L reaches the minimum value L at the second extreme point min , then （2） The eccentricity is （3）。 3. The wafer eccentricity detection and positioning method according to claim 2, characterized in that: The phase difference between the first extreme point and the second extreme point is , calculate the phase difference between adjacent acquisition points on the wafer edge, and then calculate the phase of each point on the wafer edge relative to the first extreme point. Calculate the phase of the wafer edge at the image acquisition position relative to the first extreme point at the end of acquisition, and record the eccentricity angle.

4. The wafer eccentricity detection and positioning method according to claim 1, characterized in that: The adjacent difference method is used to calculate the change values of adjacent sub-pixels, and a change value threshold is set. The change value is compared with the threshold. When the change value is greater than the threshold, it is determined that the sub-pixel point is in the straight line segment of the wafer notch or on both sides of the arc segment. When the sign of the differential value is different, the point is determined to be the center point of the arc segment of the wafer notch.

5. The wafer eccentricity detection and positioning method according to claim 4, characterized in that: The gap center interval is delineated with the arc center point of the wafer gap as the center, and B-spline interpolation is performed within the gap center interval. After interpolation, the adjacent sub-pixel change value is calculated using the adjacent difference method. When the difference value sign is different, the point is determined to be the exact center point of the wafer gap.

6. The wafer eccentricity detection and positioning method according to claim 1, characterized in that: The time when the rotary platform stops is later than the last sampling time of the camera. The phase of the wafer edge image acquisition point at the predetermined position when the camera acquires the image for the last time is defined as 1. When the rotary platform stops, the phase of the wafer edge at the predetermined position is 2, when the rotary platform drives the wafer to rotate in step S7, the rotation angle should be compensated in .

7. The wafer eccentricity detection and positioning method according to claim 1, characterized in that: The camera is set above the wafer, and a parallel coaxial surface light source is set below the wafer. The light source is correspondingly set below the camera, and the irradiation direction of the light source is upward.

8. The wafer eccentricity detection and positioning method according to claim 2, characterized in that: When the wafer notch is located at the first extreme point or the second extreme point, the position of the wafer notch is determined by the adjacent difference method, the extreme points covered by the wafer notch are shielded, the other extreme points are calculated and recorded, and the position information of the section where the shielded extreme points are located is fitted by interpolation.

9. The wafer eccentricity detection and positioning method according to claim 2, characterized in that: When the wafer notch is photographed twice or there is a wafer notch incomplete, the pixel interval of the wafer notch is calculated by the difference method, the pixel width occupied by the wafer notch is calculated, and the wafer notch with the larger pixel width is selected as the complete wafer notch image.

10. The wafer eccentricity detection and positioning method according to claim 2, characterized in that: The extreme value center interval is delineated with the first extreme value point and the second extreme value point as the center, B-spline interpolation is performed in the extreme value center interval, and the extreme value in the interval after interpolation is selected as the precise extreme value.

11. The wafer eccentricity detection and positioning method according to claim 1, characterized in that: The sub-pixel interpolation method is a one-dimensional grayscale extreme value method or a Gaussian integral curve fitting method.

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