CN111654242B

CN111654242B - Method and system for detecting notch on solar wafer

Info

Publication number: CN111654242B
Application number: CN202010417595.6A
Authority: CN
Inventors: 韩白权
Original assignee: Applied Materials Inc
Current assignee: Applied Materials Inc
Priority date: 2015-10-26
Filing date: 2016-09-20
Publication date: 2023-12-29
Anticipated expiration: 2036-09-20
Also published as: CN108604880B; SG10201508830PA; CN111654242A; WO2017074256A1; CN108604880A

Abstract

A notch defect detection system for detecting a notch defect at a chamfered edge of a solar wafer, the solar wafer being substantially rectangular or square in shape having a straight edge and a chamfered edge, the notch defect detection system comprising: (a) A plurality of imaging devices for picking up an image of the position of the solar wafer and horizontally positioned such that the focal plane of the imaging devices is parallel to the chamfered edge of the solar wafer; (b) A plurality of illumination devices for providing light to the imaging device when the imaging device is in operation; (c) A conveyor belt for transporting the solar wafer horizontally during a gap detection operation; (d) A sensing device that provides a signal to trigger the imaging device to begin image capture; and (e) a strobe driver triggered by the imaging device to drive the illumination device such that the imaging device provides an exposure time consistent with the illumination device, whereby the chamfer edge is at an out-of-focus position at the same location being sensed by the sensing device and the image captured by the imaging device is not sharp with a gap on the chamfer edge of the solar wafer. The invention also discloses a method for detecting the notch defect on the solar wafer.

Description

Method and system for detecting notch on solar wafer

The present application is a divisional application of the invention patent application with the application number 201680070827.7 of the application day 2016, 9 and 20, and the invention name of "method and system for detecting a notch on a solar wafer".

Technical Field

The present invention relates to a system and method for detecting a notch (chipping) in a solar wafer bevel sidewall, and more particularly to a notch detection system and method suitable for detecting a notch on any edge of a solar wafer that may cause cracking and wafer breakage.

Background

As part of the solar cell manufacturing process, solar cell manufacturers often perform inspection of solar wafers. This is to ensure that any defects on the solar wafer are identified in the beginning and that the subsequently produced solar wafer is of high quality.

Solar wafers are extremely thin silicon wafers commonly used to fabricate solar cells. In the fabrication of solar cells, the solar wafer undergoes a number of processes, such as deposition, etching, patterning, etc., to act as a substrate for the solar cell before it becomes a functional solar cell during the fabrication process. Due to the brittle nature of solar wafers, very small gaps on any edge of the solar wafer may cause cracking and ultimately wafer breakage when used in the manufacture of solar cells. Therefore, in order to increase the production yield and keep the production cost low, it is extremely critical to maintain the quality of the solar wafer from the beginning of the manufacturing process.

A notch defect may occur on the top and/or bottom surface along the straight and chamfered edges of the solar wafer (as shown in fig. 1). This type of notch can be detected by using two cameras that directly view the top and bottom surfaces of the solar wafer and take images (i.e., instant image capture) as the wafer moves (as shown in fig. 2). The gap along both the straight edge and the chamfered edge can be detected.

The notch defect may also appear on the sidewall surface along the straight edge of the solar wafer (as shown in fig. 3). This type of gap is not visible from the top and/or bottom surface and therefore an additional camera must be used. Typically, two additional cameras are placed horizontally along the wafer movement direction to view the sidewalls, and the images are taken in an instant fashion (as shown in fig. 4). To detect the gap on the leading/trailing side wall, the solar wafer is rotated 90 degrees using a mechanical rotator and then passed through two other cameras arranged similarly to the cameras prior to rotation.

In addition, notch defects may also occur on sidewall surfaces along the chamfered edges of the solar wafer (as shown in fig. 5). This type of notch is unique in that it only occurs on the sidewall of the chamfered edge that is only 45 degrees from the straight edge. Furthermore, this type of opening is not visible from the top and bottom surfaces. Although the typical depth of focus of a camera is about 2mm, the chamfer size of some single crystal solar wafers can be as high as 25mm (depending on wafer size and diameter) (as shown in fig. 6). Currently, even if horizontally positioned, the camera cannot detect the gap.

U.S. patent No. 5,157,735, entitled "gap detection system and method", discloses a system and method for detecting a gap of a track portion of a slider of a thin film magnetic head, which obtains an image of a detection object and its boundary coordinates by tracking the boundary of the detection object from the image. The size of the opening is obtained from the coordinates of the point on the boundary, and the presence or absence of the opening is judged from the size of the opening, thereby enabling the opening defect generated on the boundary portion of the detection object to be detected with high accuracy using a simple structure.

Us patent No. 8400630 relates to a method for detecting defects in an object, the method comprising: locally illuminating the object by illuminating the object with incident light having a wavelength transparent to the object; detecting a plurality of reflected components of the incident light while also at least partially avoiding detecting a direct transmitted component of the incident light and at least partially avoiding detecting a single reflected component of the incident light; and identifying the defect by estimating an intensity difference of the detected component of the incident light.

Us patent No. 8428337 discloses a method for wafer inspection, the method comprising: directing light substantially along a first axis toward a first surface of the wafer, thereby obtaining light emanating from a second surface of the wafer along the first axis, wherein the first and second surfaces of the wafer are substantially outwardly opposed and extend substantially parallel to a plane; and directing light substantially along a second axis toward the first surface of the wafer, thereby obtaining light emanating from the second surface of the wafer along the second axis, the first axis being angularly distant from the second axis about a reference axis extending along the plane, wherein an orthogonal projection of the first axis onto the plane is substantially parallel to an orthogonal projection of the second axis onto the plane, and each of the orthogonal projections of the first axis and the second axis onto the plane is substantially orthogonal to the reference axis.

Another gap detection method is conventionally performed with the human eye, but as an alternative to such detection, various techniques for automatically detecting the gap have been proposed.

Some conventional techniques related to such a system are disclosed in, for example, japanese patent laid-open publication No. 255484/1986 and Japanese patent laid-open publication No. 13617/1987. In the former method, a straight line is applied to the boundary of the straight line portion of the binary image obtained by detection of a TV camera or the like by the least squares method (least square method), and the value of the binary image is checked along the straight line. And judging whether the notch exists or not according to the result. In the latter method, scattered light generated by the notch is detected, and for this purpose the angle of incidence and the setting of the scattered light receptors are optimized.

Disclosure of Invention

Accordingly, it is an object of the present invention to obviate the above-mentioned problems of the prior art and to provide a method of instantly detecting a notch on a chamfered sidewall of a solar wafer, which is capable of detecting the notch at a high speed without a leakage.

It is another object of the present invention to provide a system for instantly detecting a notch on a chamfered sidewall of a solar wafer, which is capable of detecting the notch at a high speed without a leakage.

It is an object of the present invention to provide a notch defect detection system for detecting a notch defect at a chamfered edge of a solar wafer, the solar wafer being of a substantially rectangular or square shape having a straight edge and a chamfered edge, the notch defect detection system comprising:

(a) A plurality of imaging devices for picking up an image of the position of the solar wafer and horizontally positioned such that the focal plane of the imaging devices is parallel to the chamfered edge of the solar wafer;

(b) A plurality of illumination devices for providing light to the imaging device when the imaging device is in operation;

(c) A conveyor belt for transporting the solar wafer horizontally during a gap detection operation;

(d) A sensing device that provides a signal to trigger the imaging device to begin image capture; and

(e) A strobe driver (strobe light driver) triggered by the imaging device to drive the illumination device such that the imaging device provides an exposure time consistent with the illumination device,

whereby the chamfer edge is located at an out-of-focus position at the same location being sensed by the sensing device and the image captured by the imaging device is not sharp with a gap on the chamfer edge of the solar wafer.

Accordingly, it is an object of the present invention to eliminate the above-mentioned problems in the prior art and to provide a gap detection system and method which have a simple structure and are capable of detecting a gap at a high speed without being missed and affected by the position or condition of a detected object.

It is another object of the present invention to provide a gap inspection system and method capable of inspecting square-shaped or structured solar wafers.

The invention aims to provide a method for detecting the gap defect of a solar wafer by using the detection system, which comprises the following steps:

(a) Positioning a plurality of cameras horizontally, wherein a camera focal plane of the cameras is parallel to the chamfered edge of the solar wafer;

(b) Mounting a presence sensor along the conveyor to detect the presence of a solar wafer such that the solar wafer is detected by the presence sensor before the chamfer edge enters a depth of focus (DOF) range of the camera;

(c) Transporting the solar wafer horizontally by the conveyor belt at a constant speed;

(d) Detecting the solar wafer by the presence sensor to output a true signal;

(e) Triggering the camera to capture a plurality of images of the chamfered edge at constant intervals with a signal generated by the presence sensor, and also triggering a strobe driver to provide illumination consistent with the camera exposure time;

(f) Transmitting the image that has been captured by the camera to a computer linked to the detection system;

(g) Receiving, by the computer, a series of chamfer edge images beginning outside the DOF range, within the DOF range, exiting the DOF range, and again outside the DOF range;

(h) Locating, by the computer, an image in which the chamfer edge is within the DOF range by selecting the image with the greatest image sharpness; and

(i) The sharpest image is analyzed to perform an image analysis to detect any gaps present.

The above and other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments of the present invention which is to be read in connection with the accompanying drawings.

Drawings

FIG. 1 shows a notch on a surface along an edge of a solar wafer;

FIG. 2 illustrates a conventional system for detecting a gap as shown in FIG. 1, wherein a top camera and a bottom camera are placed over a solar wafer;

FIG. 3 illustrates a typical solar wafer having a notch defect on a sidewall surface along a straight edge of the solar wafer;

FIG. 4 shows a system for detecting a breach as described in FIG. 3;

FIG. 5 illustrates a notch defect on a sidewall surface along a chamfered edge of a solar wafer;

FIG. 6 schematically illustrates a notch appearing on a sidewall surface of a chamfered edge of a solar wafer, wherein the chamfer is up to 25mm in size and the camera is in a horizontal position;

FIG. 7 schematically illustrates a system for detecting a gap in a solar wafer in accordance with the present invention;

FIG. 8 schematically illustrates the positioning of a camera according to the present invention relative to the position of a chamfer edge;

fig. 9 schematically shows the positioning of a camera according to the invention with respect to the position of the chamfer edge, wherein the solar wafer has a position change Δx on the conveyor belt;

fig. 10 schematically shows a situation where the chamfer edge according to the invention falls in the camera focal plane, even if the solar wafer position change is deltax.

Fig. 11 shows up to a number N of solar wafer 103 positions captured by the camera 101 in burst mode (burst mode) in accordance with the present invention;

FIG. 12 illustrates an example of a chamfered sidewall with a notch image taken in burst mode and their calculated edge definition in accordance with the present invention; and

fig. 13A and 13B schematically illustrate another preferred embodiment of the present invention.

Detailed Description

With reference to the figures, embodiments of the invention described below relate to a method and system for the on-the-fly detection of a notch in a chamfered sidewall of a solar wafer.

As shown, fig. 1 schematically illustrates a notch formed on a solar wafer during the fabrication of a solar cell. These common defects include a notch on the top and bottom surfaces along the chamfered edge 93, a notch on the top or bottom surface along the straight edge 92 of the solar wafer only, a notch on the top and bottom surfaces along the straight edge 91 of the solar wafer, and a notch on the top or bottom surface along the chamfered edge 90 of the solar wafer. Figures 2-4 illustrate a notch formed on a solar wafer but not on a chamfered edge. In the drawings, reference numeral 101 denotes a camera, 103 denotes a solar wafer, and a conveyor belt is denoted as 104.

Referring to fig. 5, a notch formed in the sidewall along the chamfered edge 202 of the solar wafer is shown. Conventional methods of gap detection for this case cannot be employed because this type of gap is not visible from the top and bottom surfaces of the solar wafer and appears on the side wall surface on the chamfer edge at 45 degrees to the straight edge. Although the typical depth of focus of a camera is about 2mm, the chamfer size of some single crystal silicon solar wafers can be as high as 25mm, depending on wafer size and diameter, and thus, even if the solar wafer is positioned horizontally, the camera cannot detect a notch. Fig. 6 schematically shows a notch appearing on the side wall surface of the chamfered edge of a solar wafer, wherein the chamfer is up to 25mm in size and the camera is in a horizontal position.

Exemplary embodiments of the present invention are described in more detail below, according to the illustrations provided in fig. 7-13, wherein like elements are identified with like reference numerals.

Fig. 7 schematically illustrates a system for detecting a notch defect at a chamfered edge of a solar wafer in accordance with the present invention. In a preferred embodiment of the present invention, a notch defect detection system for detecting a notch defect at a chamfered edge of a solar wafer includes a plurality of imaging devices, such as cameras 101, for picking up images of the position of the solar wafer 103. Generally, the solar wafer 103 is a substantially rectangular or square shape with straight edges and chamfered edges. In this case, a total of four cameras 101 are used for notch detection at the chamfered edge of the solar wafer 103. The system further comprises a plurality of illumination means 102 for providing light to the imaging means 101 when operating in the gap detection. The gap detection system further comprises a conveyor belt 104 for transporting the solar wafer horizontally during the gap detection operation and a sensing device 105 (presence sensor) for providing a signal to trigger the imaging device 101 to start image capturing. A strobe light driver 107 is provided in the system for triggering the imaging device 101 to drive the illumination device 102 such that the imaging device 101 provides an exposure time consistent with the illumination device 102. In other words, the gap detection system of the present preferred embodiment provides a plurality of cameras, for example, in this case, four cameras, each equipped with a lens 101 (lens), and 4 sets of illumination devices (illuminators) 102. The camera 101 is horizontally positioned and oriented such that the camera focal plane 201 is parallel to and coincides with each of the chamfered edges 202 of the solar wafer 103. The solar wafer 103 is loaded on the conveyor belt 104, and as the solar wafer 103 is transported by the conveyor belt 104, it is sensed by the presence sensor 105 installed around the conveyor belt 104 or at any suitable position, so that the presence of the solar wafer can be detected at a certain time (t 0), the presence sensor 105 triggering the camera 101 to start image capturing. The camera 101 also activates a strobe driver 107 that drives the illuminator 102 so that the camera exposure time coincides with the illumination.

In the present preferred embodiment, in view of the orientation of the camera, the chamfered edge 202 of the solar wafer 103 and the camera focal plane 201 are parallel to each other and thereby it is possible to obtain a clear image of the chamfered side wall and thereby detect a notch on the chamfered side wall of the solar wafer 103.

Fig. 8 schematically shows one corner of a breach detection system according to a preferred embodiment of the present invention. As shown, the camera focal plane 201 is directly parallel to the chamfered edge of the solar wafer 103. In order to obtain a clear image of the chamfered sidewalls, it is necessary to control the position of the solar wafer 103 on the conveyor belt 104 with high accuracy. Fig. 9 schematically illustrates the change in position Δx of the solar wafer 103 on the conveyor 104. When the solar wafer 103 has a position change Δx on the conveyor belt 104, the chamfer edge 202 may be located at an out-of-focus position at the same position being sensed by the presence sensor 105. Therefore, an image captured by the camera 101 is unclear, and the gap detection performance is affected.

Fig. 10 schematically illustrates capturing a sharp chamfer edge 202 according to the present invention. In other words, even if the solar wafer 103 position change is Δx, the chamfer edge 202 image should fall within the camera focal plane 201. To achieve this, the presence sensor 105 is moved forward so that camera image capture begins earlier. Once the camera is triggered by the presence sensor 105, it will capture images in burst mode at a fixed number of Frames Per Second (FPS) as the solar wafer 103 moves at speed v. When the camera 101 starts burst mode image capture, the chamfered edge 202 need not be at the camera focal plane 201.

Fig. 11 schematically illustrates the location of up to a number N of solar wafer 103 locations captured by the camera 101 in burst mode. The first position P1 of the solar wafer 103 is the position where the presence sensor 105 triggers the camera 101 and triggers the next image after the interval ρ, and the interval ρ can be calculated as follows:

ρ＝v/FPS

where ρ is the spacing, v is the speed of the moving solar wafer, and FPS is the fixed number of frames per second for burst mode.

Referring to fig. 11, since the camera capture is continuous while transporting the solar wafer 103, it is possible to obtain an image Pn in which the chamfer edge 202 is positioned within the depth of focus (DOF) of the camera 101, provided that the interval ρ is at least 1/2 of DOF. Thus, the camera 101 must be calculated to have a minimum FPS based on the following equation in order to ensure that the camera 101 must have a minimum FPS based on the following equation in order to ensure that the chamfer edge 202 is captured within the DOF range:

〖FPS〗_min＝(2×v×cos45°)/DOF

where FPS is the fixed number of frames per second, v is the speed of the moving solar wafer, and DOF is the focal depth range of the camera.

For example, given a typical conveyor belt travel speed of 200mm/s and a camera 101 depth of focus (DOF) of 2mm, the minimum FPS required to obtain a clear chamfer sidewall image is calculated to be about 141 frames per second. This can be achieved by using a modern CMOS sensor camera with an Area-Of-Interest (AOI) set to a thin window sufficient to cover the thickness Of the solar wafer 103 plus some margin.

In the preferred embodiment of the present invention, it is also important to calculate the number of images N required in burst mode to ensure that the chamfered edge 202 of the solar wafer 103 has passed through the camera focal plane 201 regardless of the positional change Δx.

N_min＝(ΔX×FPS)/(v×cos45°)

Where N is the number of images, deltaX is the change in position, FPS is the fixed number of frames per second, and v is the speed of the moving solar wafer.

For example, given a typical change in position ΔX of + -5 mm, a minimum number of images to be captured in burst mode of 10 will be found. The actual number should be greater after considering the location of the presence sensor 105.

It has been mentioned previously that when the presence sensor 105 senses the solar wafer 103, the camera 101 starts burst mode image capture. This results in a number N of images being sent to the computer 106 connected to the gap detection system. It will be noted that only one from the N images collected need be selected for gap detection.

Fig. 12 shows a series of chamfered sidewalls with a gap image with calculated edge sharpness taken in burst mode according to the present invention. As shown, since image 7 in the series of images has the highest edge definition, this image is selected for gap detection. Note that the chamfer edge 202 has transitioned from out-of-focus to in-focus and then from in-focus to out-of-focus. In addition, it will be noted that the chamfer edge 202 does not stay at the same position due to the 45 degree orientation of the camera relative to the direction of solar wafer movement.

Accordingly, the present invention provides a method of detecting a notch defect of a solar wafer using the above disclosed detection system. The method comprises the following steps: a plurality of cameras are positioned horizontally with the camera focal plane of the cameras parallel to the chamfered edge of the solar wafer. A presence sensor is mounted along the conveyor belt to detect the presence of the solar wafer and positioned such that when the presence sensor detects the solar wafer, the chamfered edge of the solar wafer is detected before the chamfered edge enters a depth of focus (DOF) range of the camera. The solar wafers are transported at a constant speed by conveyor 104. When the solar wafer 103 is transported and reaches the presence sensor 105, the presence sensor 105 detects the solar wafer 103 and thus sets the output signal of the system to true. The output signal is connected to the camera 101 and the signal triggers the camera 101 to capture multiple images (or burst mode) of the chamfered edge at constant intervals. At the same time that the camera 101 captures an image, the camera 101 also activates the strobe driver 107 to provide illumination consistent with the camera exposure time. The image captured by the camera is transmitted to the computer. At the end of the plurality of image captures, the computer 106 receives a series of chamfer edge images beginning outside the DOF range, entering the DOF range, within the DOF range, exiting the DOF range, and again outside the DOF range.

According to the invention, software is loaded into the computer 106, which will locate an image in which the chamfer edge is within the DOF range by selecting the image with the greatest image sharpness. The software will then perform an image analysis using the sharpest image to detect the presence of a gap.

Fig. 13A and 13B schematically show possible modifications of the gap detection system in another preferred embodiment of the present invention. It will be noted that the number of cameras employed can be reduced to two. This can be achieved by placing two beam splitters 301 on each side of the conveyor belt 104. The beam splitter 301 allows the camera 101 to capture the leading chamfer edge (leading chamfer edge) 302 first and then the trailing chamfer edge (trailing chamfer edge) 303 next, as long as the leading and trailing chamfer edges are not present at the same time in the camera focal plane, which can be done by controlling the gap between the solar wafers.

While there have been described what are at present considered to be the preferred embodiments of the invention, it will be understood that various modifications thereof may be made, and it is intended by the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

Claims

1. A gap detection system, comprising:

a conveyor belt configured to transport wafers; and

a plurality of cameras for imaging the bevel edges of the wafer, the plurality of cameras being positioned such that a focal plane of each camera is parallel to at least one bevel edge of the wafer when the wafer is transported on the conveyor belt.

2. The system of claim 1, further comprising:

a presence sensor configured to trigger image capture by the plurality of cameras.

3. The system of claim 1, wherein the plurality of cameras comprises four cameras.

4. The system of claim 3, wherein each camera is positioned to obtain an image of a different one of the chamfered edges.

5. The system of claim 1, further comprising:

a plurality of illuminators configured to illuminate the wafer when the camera captures an image of the chamfered edge.

6. The system of claim 5, further comprising:

a lamp driver configured to drive the plurality of illuminators.

7. The system of claim 6, wherein the lamp driver is configured to trigger the plurality of cameras to drive the plurality of illuminators.

8. The system of claim 6, wherein the lamp driver is configured to drive the plurality of illuminators in response to signals provided by the plurality of cameras.

9. The system of claim 8, further comprising:

10. The system of claim 9, wherein exposure times of the plurality of cameras are consistent with illumination from the illuminator.

11. The system of claim 1, wherein the plurality of cameras are configured to capture images in burst mode.

12. The system of claim 11, wherein the burst mode captures images at a fixed number of frames per second of at least (2 x v x cos45 °)/depth of focus (DOF), where v is a speed at which the wafer moves in a first direction and DOF is a depth of focus of the plurality of cameras.

13. The system of claim 1, further comprising:

a computer that receives a series of chamfer edge images from the plurality of cameras, including (a) images from outside one side of a depth of focus range, (b) images into the depth of focus range, (c) images within the depth of focus range, (d) images out of the depth of focus range, and (e) images outside the other side of the depth of focus range.

14. The system of claim 13, wherein the computer selects an image with the greatest sharpness from the series of chamfer edge images.

15. The system of claim 13, wherein the computer analyzes the series of chamfer edge images to detect the presence of a wafer gap.

16. A gap detection system, comprising:

a conveyor belt configured to transport wafers;

a presence sensor configured to detect the presence of the wafer;

a plurality of cameras having a focal plane, the plurality of cameras oriented to

Capturing an image of a chamfered edge of the wafer in response to a signal provided by the presence sensor while the wafer is positioned on the conveyor belt, the focal plane of each camera being parallel to at least one chamfered edge of the wafer; and

a plurality of illuminators positioned to provide light to the camera when capturing an image.

17. The system of claim 16, wherein the plurality of cameras comprises four cameras positioned and oriented horizontally to capture an image of each of the chamfered edges of the wafer.

18. The system of claim 16, further comprising:

a lamp driver configured to trigger the plurality of cameras and drive the plurality of illuminators.

19. The system of claim 16, wherein exposure times of the plurality of cameras are consistent with illumination from the illuminator.

20. The system of claim 16, further comprising:

21. The system of claim 20, wherein the computer selects an image with the greatest sharpness from the series of chamfer edge images.

22. The system of claim 20, wherein the computer analyzes the series of chamfer edge images to detect the presence of a wafer gap.

23. A method for detecting wafer gap defects, the method comprising:

transporting the wafer on a conveyor belt;

capturing images of the chamfered edges of the wafers transported on the conveyor belt by a plurality of cameras, the focal plane of each camera being parallel to at least one chamfered edge of the wafer; and

illuminating the chamfered edge of the wafer while capturing an image of the chamfered edge.

24. The method of claim 23, wherein capturing an image of the chamfered edge of the wafer transported on the conveyor belt further comprises:

the image acquisition is started before the wafer enters the depth of focus range of the plurality of cameras.

25. The method of claim 23, wherein capturing an image of the chamfered edge of the wafer transported on the conveyor belt further comprises:

a burst image is captured.

26. The method of claim 23, further comprising:

receiving, by a computer, a series of chamfer edge images from the plurality of cameras, including (a) images from outside one side of a depth of focus range, (b) images into the depth of focus range, (c) images within the depth of focus range, (d) images out of the depth of focus range, and (e) images outside the other side of the depth of focus range.

27. The method of claim 26, further comprising:

an image having the greatest image clarity is selected from the series of chamfer edge images.

28. The method of claim 27, further comprising:

wafer notch defects are detected from the selected image.