An apparatus and method for non-destructive testing of a wafer surface

Abstract

The application relates to the field of precision detection technology, in particular to a device and method for nondestructive testing of a wafer surface. The device comprises a detection light path, a motion control module, a narrow-channel detection end, a wide-channel detection end and a data acquisition and processing module; the motion control module is used for carrying a wafer to be detected and adjusting the position; the detection light path comprises an incident light path, a wide-channel light path and a narrow-channel light path; the incident light path is used for projecting a light beam and vertically projecting the light beam onto the wafer to be detected; the narrow-channel light path is used for collecting scattered light with a diffusion angle of [5 DEG, 24 DEG] generated on the surface of the wafer to be detected and gathering the scattered light to the narrow-channel detection end; and the wide-channel light path is used for collecting scattered light with a diffusion angle of [25 DEG, 70 DEG] generated on the surface of the wafer to be detected and gathering the scattered light to the wide-channel detection end. The application can quickly and accurately identify wafer defects.

Description

Technical Field

[0001] This application relates to the field of precision testing technology, and in particular to an apparatus and method for non-destructive testing of wafer surfaces. Background Technology

[0002] Wafer surface defect detection is a critical step in semiconductor manufacturing, crucial for ensuring product quality, improving production efficiency, and reducing costs. During processing, defects may appear on the wafer surface due to environmental and process parameters, affecting wafer production yield. Wafer surface defects are typically caused by impurities or foreign matter adhering to the wafer surface during manufacturing. These defects affect the wafer's electrical and optical properties, reducing its reliability and usability. Furthermore, defective areas may accelerate physical or chemical reactions, shortening equipment lifespan. Surface defects on the wafer can also impact subsequent packaging and testing processes. For example, during packaging, wafer surface defects may lead to poor packaging or cracking of the packaging material; during testing, wafer surface defects may cause inaccurate tests or test failures. Therefore, efficient and accurate detection of wafer surface defects is of paramount importance.

[0003] Currently, several commonly used inspection methods exist in the field of wafer inspection. Electron beam inspection works by using a focused electron beam to scan the wafer surface and detect defects through signals generated by the interaction between electrons and materials. This mainly includes scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM identifies surface defects by detecting signals such as secondary electrons and backscattered electrons, while TEM observes the internal structure of the sample by using an electron beam to penetrate it. However, due to high equipment costs and relatively slow inspection speeds, it is difficult to apply to industrial production lines. Furthermore, the interaction between the electron beam and the sample can damage the sample, so caution is required in practical applications. X-ray inspection works by using X-rays to penetrate the wafer and identifying defects by analyzing the scattering and absorption of X-rays. However, its equipment is expensive and poses a certain radiation risk to operators. Electrochemical defect detection is a process that detects metallic contaminants or defects on the wafer surface through electrochemical reactions, and can effectively detect some conductive defects. However, it requires certain sample preparation and is sensitive to environmental conditions.

[0004] In addition, CN110426326B-Laser polarization device and method for detecting and distinguishing smooth surface and subsurface particles provides a method for detecting wafer surface using scattered light; in this patent text, the incident light is obliquely incident, which makes it difficult to concentrate on the wafer surface, the operation is complicated, the detection efficiency is low, and it is difficult to guarantee the detection accuracy. Summary of the Invention

[0005] To overcome the shortcomings of existing wafer defect detection methods, such as high cost, low accuracy, and high operational difficulty, this application proposes a device for non-destructive testing of wafer surfaces. The detection light is incident perpendicularly, and when the wafer is qualified, the detection light can be reflected back along the original path. Only defective wafers will produce scattered light, thereby enabling rapid and accurate identification of wafer defects.

[0006] The present invention proposes a device for non-destructive testing of wafer surfaces, comprising a detection optical path, a motion control module, a narrow-channel detection end, a wide-channel detection end, and a data acquisition and processing module; the motion control module is used to carry the wafer under test and adjust its position.

[0007] The detection optical path includes an incident optical path, a wide-channel optical path, and a narrow-channel optical path. The incident optical path is used to project a light beam and project it perpendicularly onto the wafer under test. The narrow-channel optical path is used to collect scattered light with a diffusion angle of [5°, 24°] generated on the surface of the wafer under test and focus it onto the narrow-channel detector end. The wide-channel optical path is used to collect scattered light with a diffusion angle of [25°, 70°] generated on the surface of the wafer under test and focus it onto the wide-channel detector end. The narrow-channel detector end and the wide-channel detector end convert the collected optical signals into voltage signals and transmit them to the data acquisition and processing module to analyze the wafer surface condition.

[0008] Preferably, the wide-channel optical path uses an ellipsoidal reflector, and the narrow-channel optical path consists of a fourth lens and a reflector disposed in the ellipsoidal reflector; the reflector is used to project the scattered light collected by the fourth lens to the narrow-channel detection end; the incident optical path includes a reflective device, which projects the incident light vertically onto the lower focal point of the ellipsoidal reflector; the projection of the reflective device on the horizontal plane is covered by the projection of the fourth lens on the horizontal plane.

[0009] Preferably, it also includes a focusing optical path and a CCD camera, with the focal point of the focusing optical path coinciding with the lower focal point of the ellipsoidal reflector; the data acquisition and processing module is connected to the motion control module and the CCD camera respectively; the CCD camera captures the light spot formed on the wafer under test by the focusing optical path, and the data acquisition and processing module controls the motion control module to move to adjust the position of the wafer under test until the light spot captured by the CCD camera reaches the maximum energy state.

[0010] Preferably, the focusing optical path includes a second light source and a second fiber collimator, a fixed beam expander, and a fifth lens arranged sequentially in the light-emitting direction of the second light source.

[0011] Preferably, the angle between the direction of the beam's forward movement and the horizontal direction in the focusing optical path is 15°.

[0012] Preferably, the reflective device is a cylindrical reflector; the incident light in the detection optical path is horizontally incident on the cylindrical reflector and then vertically incident on the surface of the wafer to be tested.

[0013] Preferably, the incident optical path includes a first light source and a first fiber collimator, a first lens, a pinhole, a second lens, an adjustable beam expander, and a third lens arranged sequentially along the light output direction of the first light source.

[0014] This invention proposes a method for non-destructive testing of wafer surfaces. First, the wafer to be tested is moved to the focal point of an ellipsoidal reflector. Then, the detection optical path is activated, and a wide-channel voltage dataset {x} output from the wide-channel probe is acquired. i} and the narrow channel voltage dataset output by the narrow channel probe {y i The dataset is normalized by comparing the values ​​in the dataset with a set threshold k. Then, data points with values ​​greater than k are extracted from the two normalized datasets as defect points, and data points with values ​​less than or equal to k are marked as background points. The union of the defect points in the two datasets is taken as the defect point set, and the intersection of the background points is taken as the background point set. The defect point set and the background point set are merged and converted into a binary image. Then, the defect regions are extracted, the area of ​​each defect region is calculated, and the defect type is determined.

[0015] Preferably, before inspecting the wafer under test, the focusing optical path is calibrated so that the intersection of the focusing optical paths is located at the focal point under the ellipsoidal mirror; the calibration method is as follows:

[0016] First, use a spot analyzer to calibrate the focus of the focusing optical path; then close the focusing optical path, open the detection optical path, and find the lower focus of the ellipsoidal mirror; then simultaneously open the focusing optical path and the detection optical path, and adjust the focusing optical path so that the spot of the focusing optical path and the spot of the detection optical path are both in the state of maximum energy and the centers of the two spots coincide.

[0017] Preferably, the method for moving the wafer to be tested to the focal point of the ellipsoidal mirror is as follows:

[0018] First, turn on the focusing optical path and control the crystal under test to move toward the ellipsoidal mirror. During the movement, collect the light spot on the crystal under test and find the position with the maximum energy of the light spot, which is the focal plane under the ellipsoidal mirror. Move the crystal under test to the focal plane under the ellipsoidal mirror.

[0019] The advantages of this application are:

[0020] This application proposes a device for non-destructive testing of wafer surfaces. Based on the principle of laser scattering, it uses two channels to collect scattered light generated by defects on the wafer surface. The system rapidly scans the wafer sample, displays the voltage amplitude changes in the currently scanned area in real time, and automatically reconstructs the image of the scanned area after scanning, enabling defect identification and classification.

[0021] This application employs a dual-channel optical path detection method, which collects scattered light over a wider range and solves the problem of small numerical aperture in traditional schemes, making it suitable for non-destructive testing of surface defects at the micro- and nano-scale. The wide channel is suitable for detecting nanoscale defects, while the narrow channel is suitable for detecting micrometer-level defects. The two channels can be used for simultaneous online detection without interference. Finally, the detection results from both channels are combined to achieve defect identification and classification.

[0022] This application allows for control of the detection spot size by adjusting the beam expander magnification. A smaller spot is suitable for detecting smaller defects, while a larger spot improves the system's detection efficiency. By adjusting the appropriate spot size to meet different detection needs, a balanced configuration of system sensitivity and detection speed can be achieved.

[0023] This application proposes an automatic focusing method for wafer surfaces, which, combined with a focusing optical path, enables the wafer to reach the inspection position more accurately. Because of the introduction of focusing, the proposed method for non-destructive testing of wafer surfaces offers advantages such as high inspection efficiency and high sensitivity compared to other methods. It is suitable for inspection tasks in various environments, and therefore has significant potential for application in the field of precision measurement. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the device structure proposed in this application;

[0025] Figure 2 This is the motion path diagram of the electronic control platform;

[0026] Figure 3 These are images of reflected light spots captured by the camera at different Z-axis positions;

[0027] Figure 4 This is a graph showing the correspondence between the Count value and the Z-axis position;

[0028] Figure 5 This is a flowchart of the data processing algorithm;

[0029] Figure 6 This is a flowchart of the measurement and testing methods in this application;

[0030] Figure 7 This is a real-time voltage signal change graph for wafer sample 1;

[0031] Figure 8 This is a surface image of wafer sample 1 reconstructed by the system;

[0032] Figure 9 This is a reconstructed image of the surface of wafer sample 2;

[0033] The diagram is labeled as follows: 10. Detection optical path, 101. First light source, 102. Fiber optic collimator, 103. First lens, 104. Pinhole, 105. Second lens, 106. Adjustable beam expander, 107. Third lens, 108. Ellipsoidal mirror, 109. Cylindrical mirror, 110. Fourth lens, 111. Plane mirror;

[0034] 20. Motion control module; 201. Electrical control platform; 202. Wafer; 203. Motor controller;

[0035] 30. Narrow channel detection end; 301. First photomultiplier tube; 302. First transimpedance amplifier;

[0036] 40. Wide-channel detection end; 401. Second photomultiplier tube; 402. Second transimpedance amplifier;

[0037] 50. Focusing optical path; 501. Second light source; 502. Second fiber collimator; 503. Fixed beam expander; 504. Fifth lens;

[0038] 60. CCD camera; 70. Data acquisition and processing module; 701. Data acquisition card; 702. Computer. Detailed Implementation

[0039] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0040] like Figure 1 As shown, the device for non-destructive testing of wafer surfaces proposed in this application is a dual-channel detection system based on laser scattering, which can dynamically adjust the spot size and achieve micro-nano-level defect detection. Figure 1 As shown, the device consists of a detection optical path 10, a motion control module 20, a narrow channel detection end 30, a wide channel detection end 40, a focusing optical path 50, a CCD camera 60, and a data acquisition and processing module 70.

[0041] The detection optical path 10 is composed of a first light source 101, a first fiber collimator 102, a first lens 103, a pinhole 104, a second lens 105, an adjustable beam expander 106, a third lens 107, an ellipsoidal reflector 108, a cylindrical reflector 109, a fourth lens 110, and a plane reflector 111.

[0042] In the detection optical path, the first fiber collimator 102, the first lens 103, the pinhole 104, the second lens 105, the adjustable beam expander 106, and the third lens 107 are arranged sequentially in the light-emitting direction of the first light source 101 to form an incident optical path, which is used to filter, collimate, and focus the emitted light from the first light source 101; so that when the incident light is reflected by the cylindrical mirror 109 to the wafer located at the lower focal point of the ellipsoidal mirror 108, it has greater light energy.

[0043] In the detection optical path, the first light source 101 is a fiber laser that can generate violet light with a wavelength of 405nm and a horizontal polarization direction, and its power is adjustable. The output light from the first light source 101 is output through the first fiber collimator 102, and the output spot size of the first fiber collimator 102 is 0.6mm. The first fiber collimator 102 is coupled to the first lens 103 in the mounting plate by means of a thread. The parameters of the first lens 103 and the second lens 105 are consistent, and they are symmetrically distributed on both sides of the pinhole 104. Therefore, after the output light from the first lens 103 is filtered by the pinhole 104, the beam output by the second lens 105 is still a collimated beam with a spot size of 0.6mm, but the beam is more uniform. When the adjustable beam expander 106 is adjusted to a factor of 10, the beam diameter reaches 6mm after beam expansion, and the beam propagation direction is horizontal. After being focused by the third lens 107, the spot size at the focal point can reach 17μm. The focused beam enters the ellipsoidal mirror 108 through the ellipsoidal aperture, is reflected by the cylindrical mirror 109, and then incident perpendicularly on the surface of the wafer 202. At this point, the beam spot is both the focal point of the third lens 107 and the lower focal point of the ellipsoidal mirror 108. The fourth lens 110 is integrated inside the ellipsoidal mirror 108 and located above the cylindrical mirror 109. It can collect scattered light from 5-24°, which is called a narrow channel optical path. The plane mirror 111 is located above the ellipsoidal mirror 108 and can adjust the forward direction of the beam output from the fourth lens 110. Based on the confocal characteristics of the ellipsoidal mirror 108, it can collect scattered light from 25-70°.

[0044] If the surface of wafer 202 is free of defects, the reflected light will return along the original optical path in reverse, without interfering with the detection effect; if there are defects on the surface of wafer 202, scattered light at various angles will be generated. The scattered light at the micron level is mainly collected by the fourth lens 110, and the scattered light at the nanometer level is mainly collected by the ellipsoidal mirror 108.

[0045] The narrow-channel detection end 30 includes a first photomultiplier tube 301 and a first transimpedance amplifier 302. The first photomultiplier tube 301 has extremely high sensitivity and gain, and can convert the scattered light signal collected by the fourth lens 110 into a current signal; the first transimpedance amplifier 302 can convert the current signal output by the first photomultiplier tube 301 into a voltage signal for processing by the host computer.

[0046] The wide-channel detection end 40 includes a second photomultiplier tube 401 and a second transimpedance amplifier 402. The second photomultiplier tube 401 has the same specifications as the first photomultiplier tube 301. The center point of the target surface of the second photomultiplier tube 401 and the focal point on the ellipsoidal reflector 108 are the same point, which can convert the scattered light signal collected by the ellipsoidal reflector 108 into a current signal. The second transimpedance amplifier 402 can convert the current signal output by the second photomultiplier tube 401 into a voltage signal for processing by the host computer, i.e., the data acquisition and processing module 70.

[0047] The data acquisition and processing module 70 includes a data acquisition card 701 and a computer 702. The data acquisition card 701, integrated within the computer 702, acquires the voltage signals output from the first transimpedance amplifier 302 and the second transimpedance amplifier 402 for subsequent processing by the computer 702. The computer 702 analyzes and processes the signals output from the data acquisition card 701, enabling real-time display of voltage signal changes and visualization of the wafer surface image.

[0048] The system detects surface defects by using two photomultiplier tubes to receive scattered light. The intensity of the scattered light reflects the morphological characteristics of the wafer surface. There is a significant difference in the intensity of scattered light between smooth and defective regions; the signal amplitude is larger in defective regions and lower in smooth regions. Therefore, this difference can be used to distinguish between smooth and defective regions on the wafer surface. The algorithm for defect identification and classification is as follows: Figure 5 As shown, the specific process is as follows:

[0049] S11. Input wide-channel voltage dataset {x i}、 Narrow-channel voltage dataset {y i}, x i y is the voltage output by the second transimpedance amplifier 402 at the i-th detection time point. i The voltage output by the first transimpedance amplifier 302 at the i-th detection time point;

[0050] S12. For the wide-channel voltage dataset {x i} and narrow channel voltage dataset {y i Normalize them separately; let the wide-channel voltage dataset {x} be normalized. i The normalized dataset is denoted as X = {X} i}, Narrow-channel voltage dataset {y i The normalized dataset is denoted as Y = {Y} i};X i For x i The normalized value of Y i For y i The normalized value.

[0051] The normalization process for the dataset is as follows: First, calculate the mean μ and standard deviation σ of the dataset; then substitute them into the following formula to calculate the normalized value Z of each dataset;

[0052]

[0053] Where the mean μ represents the center of the dataset, and the standard deviation σ represents the dispersion of each data point relative to the mean. i Let i be the i-th value in the dataset;

[0054] Calculate the wide-channel voltage dataset {x i When normalizing the values ​​of}, in the above formula, the mean μ and standard deviation σ in the dataset {x} are... i} calculate on, and z i =x i ;

[0055] Calculate the narrow channel voltage dataset {y i When normalizing the values ​​of}, in the above formula, the mean μ and standard deviation σ are in the dataset {y}. i} calculate on, and z i =y i ;

[0056] S13. Compare the values ​​in datasets X and Y with the set threshold k respectively. Mark the points in datasets X and Y that are greater than the threshold k as defect points and the points that are less than or equal to the threshold k as background points. Take the union of the defect points in the two datasets as the defect point set and the intersection of the background points as the background point set.

[0057] The threshold k is determined based on the detection requirements and defect size. Based on experience, it can be set as follows: k = 1.5 when the possible defect size is less than 30 micrometers; k = 2 when the possible defect size is between 30 and 300 micrometers; and k = 3 when the possible defect size is greater than 300 micrometers.

[0058] S14. Merge the defect point set and the background point set, and convert them into a binary image. Defect points are represented by white pixels, and background points are represented by black pixels. When a pixel value changes abruptly, it indicates that the point is a defect boundary point. This allows for the division of the defect region and the extraction of the defect area.

[0059] S15. Calculate the number of white pixels M in each defect area. Based on the area S0 of the scanned area and the total number of pixels M1 in the binary image, the area of ​​the defect S = M / M1 × S0 can be calculated. Calculate the aspect ratio of the defect and classify the defect according to the aspect ratio.

[0060] Let the diameter of the circumcircle of the defect region be its length, and the diameter of the incircle be its width. Let the aspect ratio be L. Then:

[0061] When L > 4, the identified defect is a scratch;

[0062] When 1.2 < L ≤ 4, the identified defect is a pockmark;

[0063] When 1 < L ≤ 1.2, the identified defect is a particle.

[0064] According to actual requirements, the aspect ratio definition can be further refined to facilitate enriching the defect feature database.

[0065] The focusing optical path 50 includes a second light source 501, a second fiber collimator 502, a fixed beam expander 503, and a fifth lens 504. The second fiber collimator 502, the fixed beam expander 503, and the fifth lens 504 are arranged in sequence in the light output direction of the second light source 501.

[0066] The second light source 501 is a fiber laser, which can generate purple light with a wavelength of 405 nm, the polarization direction is horizontal polarization, and the power is adjustable; the input end of the second fiber collimator 502 is connected to the optical fiber, and the output beam is a collimated beam; the fixed beam expander 503 can expand the diameter of the input collimated beam by 10 times to achieve the output of the collimated beam. The fifth lens 504 can focus the collimated beam to form a small light spot at the focal position. The focal point of the fifth lens 504 and the lower focal point of the ellipsoidal mirror 108 are the same point. The included angle between the beam propagation direction and the horizontal direction in the focusing optical path 50 is 15°.

[0067] The beam in the focusing optical path 50 is incident on the surface of the wafer 202, and reflected light will be generated. The CCD camera 60 is used to receive the reflected light and transmit the reflected light spot image to the computer 702.

[0068] In this embodiment, the debugging process of making the focal point of the fifth lens 504 and the lower focal point of the ellipsoidal mirror 108 the same point is as follows:

[0069] First, use a light spot analyzer to calibrate the focal point of the fifth lens 504;

[0070] Then, find the lower focal point of the ellipsoidal mirror 108. The lower focal point of the ellipsoidal mirror 108 is a fixed point; during operation, the second light source 501 can be turned off, the first light source 101 can be turned on, and the position where the light spot energy is the largest below the ellipsoidal mirror 108 is determined as the lower focal point of the ellipsoidal mirror 108 by measuring with a light spot analyzer;

[0071] Then, turn on the second light source 501 and the first light source 101 simultaneously, and adjust the fifth lens 504 so that the light spots in the focusing optical path and the detection optical path are both in the state of maximum energy and the centers of the two light spots coincide; at this time, the focal points of the detection optical path and the focusing optical path coincide. Since the focal point of the detection optical path is located at the lower focal point of the ellipsoidal mirror 108, the focal point of the focusing optical path 50 is located at the lower focal point of the ellipsoidal mirror 108. The focal point of the focusing optical path is at the focal length of the fifth lens 504.

[0072] The motion control module 20 includes an electronic control platform 201 and a motor controller 203. The electronic control platform 201 is used to place the wafer 202. The motor controller 203 is connected to the computer 702 and transmits commands via serial communication, controlling the directional movement of the electronic control platform 201. The electronic control platform 201, carrying the wafer 202, is controlled by commands from the motor controller 203 to achieve precise three-dimensional movement, enabling rapid scanning and focusing of the wafer surface. The scanning path uses a serpentine scanning method, such as... Figure 2 As shown, the sequence is: Route ① (positive y-axis movement) → Route ② (negative y-axis movement) → Route ③ (positive x-axis movement) → Route ④ (positive y-axis movement) → Route ⑤ (negative y-axis movement) → Route ⑥ (positive x-axis movement) → Route ⑦ (positive y-axis movement) → Route ⑧ (negative y-axis movement).

[0073] In addition, computer 702 analyzes the reflected light spot image transmitted by CCD camera 60 to complete the automatic focusing process on the wafer surface.

[0074] The system employs a contrast-based method to achieve automatic focusing on the surface of wafer 202. If the surface of wafer 202 coincides with the lower focal plane of ellipsoidal mirror 108, the light spot energy illuminating the wafer sample surface by focusing optical path 50 is strongest, and the reflected light signal received by CCD camera 60 is strongest. If the surface of wafer sample deviates from the lower focal plane of ellipsoidal mirror 108, the position of the light spot on the surface of wafer 202 is not at the focal length of the fifth lens 504, therefore the light spot energy is slightly weaker, and the reflected light signal received by CCD camera 60 is also weaker. The computer 702 controls the Z-axis motor of the electronic control platform 201, causing the wafer to move slowly upwards. Initially, the surface of the wafer 202 deviates from the lower focal plane of the ellipsoidal reflector 108. At this time, the position of the light spot on the wafer 202 is not the focal point of the fifth lens 504, so the light spot energy is not concentrated, resulting in uneven distribution of reflected light energy. Consequently, the light spot energy received by the CCD camera 60 is uneven, and the contrast is weak. When the electronic control platform 201 moves the surface of the wafer 202 to the lower focal plane of the ellipsoidal reflector 108, the brightness of the light spot on the surface of the wafer 202 is most concentrated, and the reflected light energy is strongest. As a result, the light spot energy received by the CCD camera 60 is evenly distributed and the contrast is strongest. As the wafer 202 continues to move upwards, since its position deviates from the lower focal plane of the ellipsoidal reflector 108, the contrast signal received by the CCD camera 60 weakens, and the contrast decreases. At this time, the computer 702 controls the Z-axis motor of the electronic control platform 201 to return the wafer sample to the optimal position, namely the lower focal plane of the ellipsoidal reflector 108. Therefore, based on the contrast distribution and contrast changes of the light spot received by the CCD camera 60, it can be determined whether the wafer sample is located at the optimal focus position, and the changes in the reflected light spot image are as follows: Figure 3As shown, the light spot goes through a process from nothing to something, from dark to bright and then back to dark, which corresponds to the process of the surface of wafer 202 gradually approaching the lower focal point of ellipsoidal mirror 108, reaching the lower focal point, and then moving away from the lower focal point.

[0075] The autofocus algorithm steps are as follows:

[0076] S111. First, the Z-axis motor of the electronic control platform 201 is controlled by the computer 702 to return to the zero position, at which time Z=0; then the electronic control platform 201 is controlled to move upward. At this time, one reflected light spot image of the focusing optical path 50 is acquired per second, and the number of pixels with pixel values ​​in the range of [200,255] is calculated.

[0077] S112. Set the pixel count threshold TH = 320. Record the pixel count Count of each group of reflected light spot images and add it to array C. When the Count value is less than the threshold 320 and the Count value of the three most recent consecutive reflected light spot images decreases continuously, stop image acquisition and control the Z-axis motor to stop moving.

[0078] S113. The computer 702 controls the electronic control platform 201 to move the Z-axis motor in the opposite direction until it reaches the position corresponding to the maximum Count value recorded in array C, thereby completing the autofocus process.

[0079] In this embodiment, the relationship between the number of Count points and the Z-axis position is as follows: Figure 4 As shown, when Z = 3.6 mm, Count is at its maximum value, indicating that the lower focal plane of the ellipsoidal mirror coincides with the wafer surface. When Z = 6 mm, the count value is less than 320, and the last three Count values ​​decrease continuously, therefore the camera stops acquiring images.

[0080] like Figure 6 As shown, the method for non-destructive testing of wafer surfaces proposed in this embodiment uses the above-mentioned apparatus and is performed according to the following steps:

[0081] S1. Turn on the second light source 501, set the laser power to 5mw, turn on the second light source 501 and preheat for a period of time to ensure the stability of the laser output;

[0082] S2. Place the wafer 202 to be tested above the electronic control platform 201. Control the Z-axis motor of the electronic control platform 201 to first return to the zero position, and then move upward. During the motor movement, synchronously control the CCD camera 60 to acquire images of the reflected light spot. According to the above-mentioned automatic focusing method, make the wafer 202 reach the optimal detection position.

[0083] S3. Set the appropriate power of the first light source 101 and the multiple of the beam expander 106 according to the detection requirements and equipment parameters. In this embodiment, the laser power is set to 1mw and the multiple of the beam expander 106 is set to 10. Turn on the first light source 101 and preheat it for a period of time to ensure the stability of the laser output.

[0084] S4. In this embodiment, the size of the wafer sample 1 to be tested is 10×10mm. The detection area is set to 10×10mm in the computer 702, the movement speed of the electronic control platform 201 is set to 2mm / s, and the sampling rate of the acquisition card 701 is set to 10000.

[0085] S5. The scanning program is started via computer 702. The electronic control platform 201 moves according to the preset route to scan wafer sample 1 line by line. The system collects voltage data only when moving in the positive y-axis direction. At this time, the voltage amplitude change of each line can be observed in real time through the software interface. If the voltage signal is very low, it indicates that there is no defect in this area; if the voltage amplitude is high, it indicates that there is a defect in this area. Figure 7 As shown, three defect areas can be identified.

[0086] S6. After the scan is completed, the computer 702 automatically stores the voltage data acquired in this scan and performs image reconstruction on the surface area of ​​wafer sample 1 using a defect detection algorithm, such as... Figure 8 As shown. According to the algorithm classification, the defect was identified as three scratches. After calculation, the areas of the three scratches from left to right are 0.59 mm². 2 0.66mm 2 0.58mm 2 .

[0087] S7. Replace with wafer sample 2, which is 5×5mm in size, and continue testing. Repeat steps S1-S6, setting the detection area to 5×5mm, the movement speed of platform 201 to 1mm / s, and the sampling rate of acquisition card 701 to 5000. Figure 9 The surface defect area of ​​wafer sample 2 can be identified as mainly composed of pits and particles, with a particle area of ​​approximately 0.02 mm. 2 The area of ​​the pit is approximately 0.03 mm. 2 .

[0088] The detection results of wafer sample 1 and wafer sample 2 show that the detection method proposed in this application has good performance, low computational complexity, and is convenient and quick to operate.

[0089] Of course, those skilled in the art will recognize that this application is not limited to the details of the exemplary embodiments described above, but also includes the same or similar structures that can be implemented in other specific forms without departing from the spirit or essential characteristics of this application. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of this application is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this application. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0090] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0091] The technologies, shapes, and structures not described in detail in this application are all known technologies.

Claims

1. An apparatus for non-destructive testing of wafer surfaces, characterized in that, It includes a detection optical path, a motion control module, a narrow channel detection end, a wide channel detection end, and a data acquisition and processing module; The motion control module is used to support the wafer under test and adjust its position; The detection optical path includes an incident optical path, a wide-channel optical path, and a narrow-channel optical path. The incident optical path projects the light beam perpendicularly onto the wafer under test. The narrow-channel optical path collects scattered light with a diffusion angle of [5°, 24°] generated on the surface of the wafer under test and focuses it onto the narrow-channel detector. The wide-channel optical path collects scattered light with a diffusion angle of [25°, 70°] generated on the surface of the wafer under test and focuses it onto the wide-channel detector. The narrow-channel and wide-channel detectors convert the collected optical signals into voltage signals and transmit them to the data acquisition and processing module to analyze the wafer surface condition. The wide-channel optical path uses an ellipsoidal reflector, and the narrow-channel optical path consists of a fourth lens and a reflector set in the ellipsoidal reflector; the reflector is used to project the scattered light collected by the fourth lens to the narrow-channel detection end; the incident optical path includes a reflective device, which projects the incident light perpendicularly to the lower focal point of the ellipsoidal reflector. The projection of the reflecting device onto the horizontal plane is covered by the projection of the fourth lens onto the horizontal plane; The reflective device uses a cylindrical reflector; the incident light in the detection optical path is horizontally incident on the cylindrical reflector and then vertically incident on the surface of the wafer to be tested.

2. The apparatus for non-destructive testing of wafer surfaces as described in claim 1, characterized in that, It also includes a focusing optical path and a CCD camera. The focal point of the focusing optical path coincides with the lower focal point of the ellipsoidal reflector. The data acquisition and processing module is connected to the motion control module and the CCD camera respectively. The CCD camera captures the light spot formed on the wafer under test by the focusing optical path. The data acquisition and processing module controls the motion control module to move and adjust the position of the wafer under test until the light spot captured by the CCD camera reaches the maximum energy state.

3. The apparatus for non-destructive testing of wafer surfaces as described in claim 2, characterized in that, The focusing optical path includes a second light source and a second fiber collimator, a fixed beam expander, and a fifth lens, which are sequentially arranged in the light-emitting direction of the second light source.

4. The apparatus for non-destructive testing of wafer surfaces as described in claim 3, characterized in that, In the focusing optical path, the angle between the direction of the beam's forward movement and the horizontal direction is 15°.

5. The apparatus for non-destructive testing of wafer surfaces as described in any one of claims 1-4, characterized in that, The incident optical path includes a first light source and a first fiber collimator, a first lens, a pinhole, a second lens, an adjustable beam expander, and a third lens arranged sequentially along the light output direction of the first light source.

6. A method for non-destructive testing of wafer surfaces using the apparatus for non-destructive testing of wafer surfaces as described in claim 2, 3, 4, or 5, characterized in that, First, the wafer under test is moved to the focal point of the ellipsoidal reflector, the detection optical path is turned on, and the wide-channel voltage dataset {x} output from the wide-channel detector is acquired. i } and the narrow channel voltage dataset output by the narrow channel probe {y i The dataset is normalized by comparing the values ​​in the dataset with a set threshold k. Then, data points with values ​​greater than k are extracted from the two normalized datasets as defect points, and data points with values ​​less than or equal to k are marked as background points. The union of the defect points in the two datasets is taken as the defect point set, and the intersection of the background points is taken as the background point set. The defect point set and the background point set are merged and converted into a binary image. Then, the defect regions are extracted, the area of ​​each defect region is calculated, and the defect type is determined.

7. The method for non-destructive testing of wafer surfaces as described in claim 6, characterized in that, Before inspecting the wafer, the focusing optical path is calibrated so that the intersection of the focusing optical path is located at the focal point of the ellipsoidal mirror; the calibration method is as follows: First, use a spot analyzer to calibrate the focus of the focusing optical path; then close the focusing optical path, open the detection optical path, and find the lower focus of the ellipsoidal mirror; then simultaneously open the focusing optical path and the detection optical path, and adjust the focusing optical path so that the spot of the focusing optical path and the spot of the detection optical path are both in the state of maximum energy and the centers of the two spots coincide.

8. The method for non-destructive testing of wafer surfaces as described in claim 7, characterized in that, The method for moving the wafer to be tested to the focal point of the ellipsoidal mirror is as follows: First, turn on the focusing optical path and control the crystal under test to move toward the ellipsoidal mirror. During the movement, collect the light spot on the crystal under test and find the position with the maximum energy of the light spot, which is the focal plane under the ellipsoidal mirror. Move the crystal under test to the focal plane under the ellipsoidal mirror.

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