Mirror surface microcrack defect detection method

Abstract

The invention discloses a mirror surface microcrack defect detection method, which comprises the following steps of: firstly, pre-scanning height point information of a detected object surface, and converting the height point information into corresponding angle information; by referring to the reflection characteristics of the mirror surface, the illumination system with the adjustable special customized angle is used for projecting corresponding incident light rays with different angles, the light rays are high in collimation and strong in light collecting performance, and reflection light rays of a background area are enhanced and reflection light rays of a micro-crack area are inhibited; the light reflected by the object plane enters a customized design imaging system, and the system can only receive reflected light within a certain fixed angle range; at the moment, through fixed light filtering of the optical imaging system, the contrast ratio of the high-collimation visible light projected on the surface of the mirror surface between the microcrack defect feature and the background gray scale can be further increased, the effect of doubly expanding the tiny feature boundary is achieved, and the microcrack defect detection precision of 1 / 5-1 / 10 pixels is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of crack defect detection, and in particular relates to a method for detecting micro-crack defects on a mirror surface. Background Art

[0002] During AOI inspection, tiny surface cracks on reflective objects are often difficult to identify. Missing these defects can lead to varying degrees of losses across various industries. For example, in semiconductor chip manufacturing, cracks on the chip's mirror surface can gradually extend due to changes in temperature or stress, ultimately causing product failure.

[0003] Mirror cracks on chips often appear as cracks in the silicon substrate on the backside of the wafer. These tiny cracks, typically around 2µm in size, are difficult to detect visually, even with a high-power microscope. Furthermore, due to the wafer's thinness and brittleness, they are prone to breakage during subsequent processing, resulting in immeasurable losses. To improve chip yields and reduce costs, these cracks are typically removed during chip screening. Therefore, accurately and efficiently detecting these tiny cracks has become a pressing issue in industries such as semiconductor manufacturing.

[0004] To detect microcrack defects on the surface of grains, existing technologies can be categorized into non-optical and optical non-destructive methods. Non-optical methods typically involve ultrasonic testing, which uses the fact that cracks affect the amplitude of the ultrasonic waveform and offers good results. However, ultrasonic testing involves placing the chip in a liquid, making it susceptible to contamination and resulting in low detection efficiency. Optical non-destructive testing typically employs front-light reflection or back-light transmission methods, using infrared or near-infrared wavelengths. Front-light reflection utilizes infrared light vertically directed onto the surface of the test object, where it reflects and generates infrared optical imaging. However, the field of view of a single test with front-light reflection is often limited by resolution, resulting in slow detection speeds. Back-light transmission methods place photosensitive sensors and illumination sources on the upper and lower sides of the test object. The sensors receive infrared or near-infrared light transmitted through the object to detect microcracks. However, back-light transmission methods require high transmittance for the test chip and are generally only used for testing bare silicon wafers during the grinding process. Improvements are urgently needed. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for detecting microcrack defects on a mirror surface.

[0006] The present invention adopts the following technical solutions: A method for detecting microcrack defects on a mirror surface is implemented based on a microcrack defect detection device. The microcrack defect detection device includes an illuminator for projecting light, a detection platform for placing an object to be measured, a camera unit disposed above the detection platform, an imaging system disposed between the camera unit and the detection platform, an illumination system for reflecting light to the imaging system, and a spectral confocal sensor for collecting height information of the mirror surface. The light spot emitted by the spectral confocal sensor is sequentially projected onto the surface of the object to be measured through the illumination system and the imaging system. The light emitted by the illuminator is reflected from the illumination system to the imaging system, then projected onto the mirror surface of the object to be measured, then reflected back to the imaging system by the mirror surface, and reaches the camera unit through the imaging system. The detection method comprises the following steps: The first step is to activate the spectral confocal sensor. The light spot passes through the lighting system and imaging system in sequence to reach the surface of the object to be measured. Then, the detection platform is driven to move along the preset scanning trajectory, pre-scanning and recording the height information of the surface of the object to be measured, and obtaining multiple spectral data points. The second step is to traverse multiple spectral data points within the imaging field of view to check whether there are any spectral data points missing. The spectral data points before and after the data point loss are fitted with a linear straight line segment, and the slope is calculated and converted into the corresponding angle information. In the third step, the illuminator is adjusted according to the angle information obtained in the second step to project light corresponding to different angles. The light reaches the surface of the object to be measured through the lighting system and the imaging system in turn. Straight lines at different angles are projected onto the corresponding object surfaces at different angles, reflecting light of a uniform specific angle. The imaging system completes the absorption of the light at this specific angle and reaches the target surface of the camera unit to complete the imaging.

[0007] Preferably, in the first step, the method for confirming the preset scanning trajectory is as follows: according to the size of the imaging field of view, the surface of the object to be measured is divided into n imaging fields of view, and the multiple imaging fields of view are divided into multiple imaging field of view groups along the Y direction, each imaging field of view group includes several imaging fields of view arranged along the X direction, and then 1 mm to the left of the uppermost imaging field of view on the left is used as the starting point M, and the starting point M is located in the middle position in the field of view height direction, and 3 mm to the right of the tail imaging field of view of the imaging field of view group is used as the stopping point N, and the detection platform is controlled to drive the object to be measured to move from point M to point N along the X direction, and then the displacement platform drives the object to be measured to move along the Y direction to complete the line feed, and so on, to form a preset scanning trajectory and complete the pre-scanning record of the height information of the spectral data points in the multiple imaging field of view groups.

[0008] Preferably, the detection platform moves at a speed of 20 mm / s in the X direction and at a speed of 20 mm / s in the Y direction.

[0009] Preferably, in the second step, when there is a spectral data point missing, the two spectral data points close to the blank area formed by the spectral data point missing are marked as point B and point C respectively, the spectral data point entering the imaging field of view is point A, and the spectral point leaving the imaging field of view is point D, and then the multiple spectral data points between point A and point B, and the multiple spectral data points between point C and point D are fitted with a linear straight line segment to obtain the two angle information α and β respectively.

[0010] Preferably, in the third step, the illuminator is adjusted according to the obtained α and β angle information to project incident light α and incident light β corresponding to different angles. The incident light α and incident light β successively reach the surface of the object to be measured through the lighting system and the imaging system, and then are reflected back to the imaging system through the mirror surface, and reach the camera unit through the imaging system. Corresponding to the imaging grayscale contrast, two overlapping images are obtained, and the two incident light irradiation areas and the middle micro-crack area are retained, which is the final test effect diagram within the imaging field of view. Similarly, the side view effect diagrams of other imaging fields are obtained, and then all the test effect diagrams are spliced ​​to obtain the completed test diagram of the surface of the object to be measured.

[0011] Preferably, the acquisition frequency of the spectral confocal sensor is 40 kHz, and the sampling interval is 0.5 μm.

[0012] Preferably, the illumination system adopts a Kohler illumination system, comprising a first lens located above the illuminator and a first beam splitter arranged above the first lens, wherein the first beam splitter is arranged at 45°.

[0013] Preferably, the imaging system adopts a telecentric imaging system, including a second beam splitter arranged above the detection table and a telecentric lens arranged above the second beam splitter, the second beam splitter is set at 45° and parallel to the first beam splitter, the light spot emitted by the spectral confocal sensor passes through the first beam splitter to the second beam splitter, and is projected onto the surface of the object to be measured; the light emitted by the illuminator passes through the first lens and is reflected by the first beam splitter to the second beam splitter, projected onto the mirror surface of the object to be measured, and then reflects the second beam splitter through the mirror surface, and reaches the camera unit through the telecentric lens.

[0014] Preferably, the camera unit adopts a CMOS camera.

[0015] Preferably, the micro-crack defect detection device further includes an angle adjustment mechanism for adjusting the illumination angle of the illuminator and a moving mechanism for driving the detection platform to move.

[0016] From the above description of the present invention, it can be seen that compared with the existing technology, the beneficial effects of the present invention are: the present invention is an optical non-destructive method for micro-crack defect detection. Compared with ultrasonic contact detection, it is highly efficient and does not damage or contaminate products, thus saving costs; compared with common front-light reflection and back-light transmission optical non-destructive testing, its application range is wider and its detection accuracy is higher; it can realize the detection of micro-cracks under low resolution (14um / pixel) conditions, and the detection accuracy can reach about 1 / 5-1 / 10 pixel.

[0017] For mirror surfaces of different angles formed by microcracks, the height point information of the measured object surface is first pre-scanned and converted into corresponding angle information; referring to the mirror reflection characteristics, a specially customized angle-adjustable lighting system is used to project corresponding incident light at different angles. The light has high collimation and strong light collection, which can enhance the reflected light in the background area and suppress the reflected light in the microcrack area; the light reflected by the object surface enters the customized telecentric imaging system, which can only receive reflected light within a certain fixed angle range; at this time, the fixed light is filtered by the optical imaging system, which can further increase the contrast between the microcrack defect characteristics and the background grayscale of the highly collimated visible light projected on the mirror surface, achieving the effect of doubly expanding the boundaries of tiny features and achieving a microcrack defect detection accuracy of 1 / 5 to 1 / 10 pixels. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the structure of the micro-crack defect detection device; Figure 2 Schematic diagram of diffuse reflection; Figure 3 Schematic diagram of illumination and imaging field of view; Figure 4 This is the principle diagram of micro-crack detection; Figure 5 Schematic diagram of the imaging system; Figure 6 It is the segmentation diagram of the imaging field of view of the object being measured; Figure 7 Schematic diagram of preset scanning trajectory displacement; Figure 8 Schematic diagram of spectral data point scanning of a single imaging field of view with microcracks; Figure 9 is a schematic diagram of incident light α and incident light β; Figure 10 Schematic diagram of grayscale imaging of incident light α and incident light β; Figure 11 Schematic diagram of micro crack test; Figure 12 Schematic diagram of micro cracks taken with a high-resolution module (0.35um / pixel); Figure 13 Schematic diagram of micro cracks taken with a normal resolution module (2um / pixel); Figure 14 Schematic diagram of microcracks taken for this application (14um / pixel); In the figure, (1) illuminator, (2) lighting system, (3) angle adjustment mechanism, (4) spectral confocal sensor, (5) detection platform, (6) object surface, (7) imaging system, (8) camera unit, ① first beam splitter, ② telecentric lens, ③ second beam splitter. DETAILED DESCRIPTION

[0019] The present invention is further described below through specific embodiments.

[0020] Reference Figure 1 As shown, a microcrack defect detection device for detecting microcracks on a mirror surface comprises an illuminator (1) for projecting light, a detection platform (5) for placing a test object, a camera unit (8) arranged above the detection platform, an imaging system (7) arranged between the camera unit (8) and the detection platform (5), an illuminator (2) for reflecting light to the imaging system (7), a spectral confocal sensor (4) for collecting height information of the mirror surface, an angle adjustment mechanism (3) for adjusting the illuminator's irradiation angle, and a moving mechanism for driving the detection platform (5) to move, wherein the angle adjustment mechanism (3) and the moving mechanism are commonly used devices in the mechanical field, which can realize the adjustment of the illuminator's irradiation angle and the movement of the detection platform (5) in the X and Y directions. The specific structure thereof will not be further described here; specifically, the acquisition frequency of the spectral confocal sensor (4) is 40kHz, and the sampling interval is 0.5um. Therefore, a microcrack generally lacks 4-5 spectral data points; further, the camera unit (8) adopts a CMOS camera, and its parameters are as follows: 5M, 2448*2048; illuminator resolution 0.1°.

[0021] The illumination system (2) adopts a Kohler illumination system, comprising a first lens located above the illuminator (1) and a first beam splitter ① arranged above the first lens, wherein the first beam splitter ① is arranged at 45 degrees.

[0022] Imaging system (7) adopts a telecentric imaging system, which can only receive reflected light within a certain fixed angle range. Figure 4 、 Figure 5; At this time, the high-collimation visible light projected on the surface of the object to be tested can be filtered by the fixed light of the optical imaging system, and the contrast between the microcrack defect characteristics and the background grayscale of the highly collimated visible light projected on the surface of the object to be tested can be further increased, and finally the light and dark grayscale contrast is displayed, and the microcrack detection is completed; Specifically, the imaging system (7) includes a second beam splitter ③ arranged above the detection table (5) and a telecentric lens ② arranged above the second beam splitter ③, wherein the second beam splitter ③ is set at 45° and is parallel to the first beam splitter ①. The light spot emitted by the spectral confocal sensor (4) passes through the first beam splitter ① to the second beam splitter ③ and is projected onto the surface of the object to be tested; the light emitted by the illuminator (1) passes through the first lens and is reflected by the first beam splitter ① to the second beam splitter ③, and is projected onto the surface of the object to be tested, and then reflects the second beam splitter ③ through the surface of the object to be tested, and reaches the camera unit (8) through the telecentric lens ②; further, the Telecentric of the telecentric lens ② is less than 0.001°, and the Magnification: 0.32X.

[0023] A method for detecting microcrack defects on a mirror surface is implemented based on the above-mentioned microcrack defect detection device, comprising the following steps: The first step is to activate the spectral confocal sensor. The light spot passes through the lighting system and imaging system in sequence to reach the surface of the object to be measured. Then, the detection platform is driven to move along the preset scanning trajectory, pre-scanning and recording the height information of the surface of the object to be measured, and obtaining multiple spectral data points. The second step is to traverse multiple spectral data points within the imaging field of view to check whether there are any spectral data points missing. The spectral data points before and after the data point loss are fitted with a linear straight line segment, and the slope is calculated and converted into the corresponding angle information. In the third step, the illuminator is adjusted according to the angle information obtained in the second step to project light corresponding to different angles. The light reaches the surface of the object to be measured through the lighting system and the imaging system in turn. Straight lines at different angles are projected onto the corresponding object surfaces at different angles, reflecting light of a uniform specific angle. The imaging system completes the absorption of the light at this specific angle and reaches the target surface of the camera unit to complete the imaging.

[0024] Among them, in the first step, the method for confirming the preset scanning trajectory is as follows: determine the maximum imaging field of view based on the illumination field of view, and then divide the object surface into n imaging fields of view according to the size of the imaging field of view, such as Figure 6 As shown in FIG, multiple imaging fields are divided into multiple imaging field groups along the Y direction. Each imaging field group includes several imaging fields arranged along the X direction. Then, 1 mm to the left of the uppermost imaging field on the left is used as the starting point M, and the starting point M is located in the middle position in the field of view height direction. 3 mm to the right of the tail imaging field of the imaging field group is used as the stopping point N. The detection platform is controlled to drive the object to be measured to move from point M to point N along the X direction, and then the displacement platform drives the object to be measured to move along the Y direction to complete the line change, as shown in FIG. Figure 7As shown, by analogy, a preset scanning trajectory is formed to complete the pre-scanning record of the height information of the spectral data points in multiple imaging field of view groups; specifically, the speed of the detection platform moving along the X direction is 20 mm / s, and the speed of moving along the Y direction is 20 mm / s.

[0025] In the second step, when there are spectral data points missing and they are all located in the same imaging field of view, refer to Figure 8 As shown, the two spectral data points close to the blank area formed by the loss of spectral data points are marked as points B and C respectively, the spectral data point entering the imaging field of view is point A, and the spectral point leaving the imaging field of view is point D, and then the multiple spectral data points between points A and B, and the multiple spectral data points between points C and D are fitted with a one-dimensional linear straight line segment, and the two angle information α and β are obtained respectively; when there is a spectral data point missing and is located in two adjacent imaging fields, the two spectral data points close to the blank area formed by the loss of spectral data points are marked as points B and C respectively, the spectral data point entering the imaging field of view where point B is located is point A, and the spectral point leaving the imaging field of view where point C is located is point D, and then the multiple spectral data points between points A and B, and the multiple spectral data points between points C and D are fitted with a one-dimensional linear straight line segment, and the two angle information α and β are obtained respectively.

[0026] In the third step, when there are spectral data points missing and they are all located in the same imaging field of view, refer to Figures 9 to 11 As shown, according to the obtained α and β angle information, the illuminator is adjusted to project incident light α and incident light β corresponding to different angles. The incident light α and incident light β successively reach the surface of the object to be measured through the lighting system and the imaging system, and then are reflected back to the imaging system through the mirror surface, and reach the camera unit through the imaging system. Corresponding to the imaging grayscale contrast, two images will be obtained for overlapping display, and the two incident light irradiation areas and the middle micro-crack area will be retained, which is the final test effect diagram within the imaging field of view; when there is a spectral data point missing and it is located in the adjacent imaging field of view, according to the obtained α and β angles The information adjustment illuminator projects incident light α and incident light β corresponding to different angles. The incident light α and incident light β reach the surface of the object to be measured in sequence through the lighting system and the imaging system, and then are reflected back to the imaging system through the mirror surface. After reaching the camera unit through the imaging system, the corresponding imaging grayscale contrast is retained. The illumination area of ​​the two incident lights and the side crack area are retained respectively, and then the side crack areas of the two images are spliced ​​together to obtain the complete crack area; and so on, the side view effect images of other imaging fields are obtained, and then all the test effect images are spliced ​​together to obtain the complete test image of the object to be measured.

[0027] The detection principle of this application is as follows: Since the location of microcracks on the mirror surface is not fixed, they can occur at any position on the surface. The surface tilt and convexity caused by microcracks are different due to the different degree of fracture of microcracks. The angle of the light of conventional diffuse reflection of visible light is dispersed. When the light hits the mirror surface of the grain, it reaches the camera target through the conventional imaging system. Since the light is evenly reflected and diverged, Figure 2 As shown in the figure, even if there are micro cracks, the grayscale contrast between the cracks and the detection background is low, and the defect features are not obvious. When a specially customized angle-adjustable Kohler illumination system is used in conjunction with a telecentric imaging system, the illumination field of view evenly covers the entire imaging field of view, as shown in the figure. Figure 3 As shown in the figure, for the mirror surfaces with different angles formed by microcracks, the lighting system can project high-collimation light corresponding to different angles, and then reflect it back to the imaging system at a specific angle, and then reach the camera target surface. The principle of microcrack detection is as follows: Figure 4 As shown in the figure, at this time, the grayscale contrast between the crack defect feature and the detection background is obvious, achieving the effect of double expansion of the tiny feature boundary and reaching a micro-crack defect detection accuracy of 1 / 5 to 1 / 10 pixel.

[0028] Based on the present application and the existing conventional imaging system, the same microcrack defect is photographed respectively, and the obtained result graph is referred to Figures 12 to 14 As shown, among them, through Figure 14 and Figure 12 、 Figure 13 By comparison, the present invention can detect microcracks at low resolution (14um / pixel), and the detection accuracy can reach about 1 / 5-1 / 10 pixel.

[0029] The present invention is an optical non-destructive method for micro-crack defect detection. Compared with ultrasonic contact detection, it is highly efficient, does not damage or contaminate products, and saves costs. Compared with common front-light reflection and back-light transmission optical non-destructive testing, it has a wider range of applications and higher detection accuracy. It can detect micro-cracks under low resolution (14um / pixel) conditions, and the detection accuracy can reach about 1 / 5-1 / 10 pixel.

[0030] The above description is merely a preferred embodiment of the present invention and therefore cannot be used to limit the scope of the present invention. In other words, equivalent changes and modifications made according to the scope of the patent application and the contents of the specification should still fall within the scope of the patent of the present invention.

Claims

1. A method for detecting microcrack defects on a mirror surface, characterized in that: The invention is implemented based on a microcrack defect detection device, which includes an illuminator for projecting light, a detection platform for placing the object to be measured, a camera unit arranged above the detection platform, an imaging system arranged between the camera unit and the detection platform, an illumination system for reflecting light to the imaging system, and a spectral confocal sensor for collecting mirror surface height information. The light spot emitted by the spectral confocal sensor is sequentially projected onto the surface of the object to be measured through the illumination system and the imaging system. The light emitted by the illuminator is reflected by the illumination system to the imaging system, and then projected onto the mirror surface of the object to be measured. The light is then reflected back to the imaging system by the mirror surface and reaches the camera unit through the imaging system. The detection method comprises the following steps: The first step is to activate the spectral confocal sensor. The light spot passes through the lighting system and imaging system in sequence to reach the surface of the object to be measured. Then, the detection platform is driven to move along the preset scanning trajectory, pre-scanning and recording the height information of the surface of the object to be measured, and obtaining multiple spectral data points. The second step is to traverse multiple spectral data points within the imaging field of view to check whether there are any spectral data points missing. The spectral data points before and after the data point loss are fitted with a linear straight line segment, and the slope is calculated and converted into the corresponding angle information. In the third step, the illuminator is adjusted according to the angle information obtained in the second step to project light corresponding to different angles. The light reaches the surface of the object to be measured through the lighting system and the imaging system in turn. Straight lines at different angles are projected onto the corresponding object surfaces at different angles, reflecting light of a uniform specific angle. The imaging system completes the absorption of the light at this specific angle and reaches the target surface of the camera unit to complete the imaging.

2. The method for detecting microcrack defects on a mirror surface according to claim 1, wherein: In the first step, the method for confirming the preset scanning trajectory is as follows: according to the size of the imaging field of view, the surface of the object to be measured is divided into n imaging fields of view, and the multiple imaging fields of view are divided into multiple imaging field of view groups along the Y direction. Each imaging field of view group includes several imaging fields of view arranged along the X direction. Then, 1 mm to the left of the uppermost imaging field of view on the left is used as the starting point M, and the starting point M is located in the middle position in the field of view height direction. The stopping point N is 3 mm to the right of the tail imaging field of view of the imaging field of view group. The detection platform is controlled to drive the object to be measured to move from point M to point N along the X direction. Then, the displacement platform drives the object to be measured to move along the Y direction to complete the line feed. This process is repeated to form a preset scanning trajectory and complete the pre-scanning record of the height information of the spectral data points in multiple imaging field of view groups.

3. The method for detecting microcrack defects on a mirror surface according to claim 2, wherein: The detection platform moves at a speed of 20 mm / s in the X direction and at a speed of 20 mm / s in the Y direction.

4. The method for detecting microcrack defects on a mirror surface according to claim 2, wherein: In the second step, when there is a spectral data point missing, the two spectral data points close to the blank area formed by the missing spectral data point are marked as point B and point C respectively, the spectral data point entering the imaging field of view is point A, and the spectral point leaving the imaging field of view is point D. Then, the multiple spectral data points between point A and point B, and the multiple spectral data points between point C and point D are fitted with a linear straight line segment to obtain the two angle information α and β respectively.

5. The method for detecting microcrack defects on a mirror surface according to claim 4, wherein: In the third step, the illuminator is adjusted according to the obtained α and β angle information to project incident light α and incident light β corresponding to different angles. The incident light α and incident light β reach the surface of the object to be measured in turn through the lighting system and the imaging system, and then are reflected back to the imaging system through the mirror surface. After reaching the camera unit through the imaging system, two overlapping images are obtained corresponding to the imaging grayscale contrast. The two incident light irradiation areas and the middle micro-crack area are retained, which is the final test effect image within the imaging field of view. Similarly, the side view effect images of other imaging fields are obtained, and then all the test effect images are spliced ​​to obtain the completed test image of the object to be measured.

6. The method for detecting microcrack defects on a mirror surface according to claim 1, wherein: The acquisition frequency of the spectral confocal sensor is 40 kHz, and the sampling interval is 0.5 μm.

7. The method for detecting microcrack defects on a mirror surface according to claim 1, wherein: The illumination system adopts a Kohler illumination system, which includes a first lens located above the illuminator and a first beam splitter arranged above the first lens, wherein the first beam splitter is arranged at 45 degrees.

8. The method for detecting microcrack defects on a mirror surface according to claim 7, wherein: The imaging system adopts a telecentric imaging system, including a second beam splitter arranged above the detection table and a telecentric lens arranged above the second beam splitter. The second beam splitter is set at 45 degrees and is parallel to the first beam splitter. The light spot emitted by the spectral confocal sensor passes through the first beam splitter to the second beam splitter and is projected onto the surface of the object to be measured; the light emitted by the illuminator passes through the first lens and is reflected by the first beam splitter to the second beam splitter, projected onto the mirror surface of the object to be measured, and then reflected by the second beam splitter through the mirror surface and reaches the camera unit through the telecentric lens.

9. The method for detecting microcrack defects on a mirror surface according to claim 1, wherein: The camera unit adopts a CMOS camera.

10. The method for detecting microcrack defects on a mirror surface according to claim 1, wherein: The micro-crack defect detection device further includes an angle adjustment mechanism for adjusting the illumination angle of the illuminator and a moving mechanism for driving the detection platform to move.

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