Device and method for nondestructive testing of wafer surface

Abstract

The invention relates to the technical field of precision detection, in particular to a device and a method for nondestructive testing of a wafer surface. The device provided by the invention 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 bearing a to-be-tested wafer 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 to a wafer to be measured; the narrow channel light path is used for collecting scattered light with the diffusion angle of [5 degrees, 24 degrees] 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 the diffusion angle of [25 degrees, 70 degrees] generated on the surface of the wafer to be detected and gathering the scattered light to the wide channel detection end. According to the device for nondestructive testing of the surface of the wafer, the detection light is vertically incident, the detection light can be reflected out along the original path when the wafer is qualified, and only the defective wafer can generate scattered light, so that the wafer defect can be quickly and accurately identified. According to the wafer defect detection method, the defects of high cost, low precision and high operation difficulty of a wafer defect detection method in the prior art are overcome.

Description

Technical Field

[0001] The present application relates to the field of precision detection technology, and in particular to a device and method for non-destructive detection of wafer surfaces. Background Art

[0002] Wafer surface defect detection is a key step in the semiconductor manufacturing process, and is of great significance for ensuring product quality, improving production efficiency, and reducing costs. During the processing, defects may appear on the wafer surface due to environmental and process parameters, which will affect the yield of wafer production. Defects on the wafer surface are usually caused by impurities or foreign matter attached to the wafer surface during the manufacturing process. Defects will affect the electrical and optical properties of the wafer and reduce its reliability and availability. In addition, defective areas may accelerate physical or chemical reactions and shorten the life of the equipment. Surface defects on the wafer may also have an impact on subsequent packaging and testing processes. For example, during the packaging process, defects on the wafer surface may cause poor packaging or cracking of the packaging material; during the testing process, defects on the wafer surface may cause inaccurate or failed testing. Therefore, how to efficiently and accurately detect wafer surface defects is of great significance.

[0003] At present, there are several commonly used inspection methods in the field of wafer inspection. The principle of electron beam inspection is to use a focused electron beam to scan the surface of the wafer and detect defects through the signals generated by the interaction between electrons and materials. It mainly includes scanning electron microscope (SEM) and transmission electron microscope (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 penetrating the sample with an electron beam. However, due to the high cost of equipment and the relatively slow detection speed, it is difficult to apply to industrial production lines. In addition, the interaction between the electron beam and the sample may also cause damage to the sample, so caution is required in practical applications. The principle of X-ray inspection is to use X-rays to penetrate the wafer and identify defects by analyzing the scattering and absorption of X-rays. However, its equipment cost is high and there is a certain radiation risk to the operator. Electrochemical defect detection is a process of detecting metal contaminants or defects on the surface of the wafer through electrochemical reactions, which can effectively detect some conductive defects. However, it requires certain treatment of the sample and is sensitive to environmental conditions.

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

[0005] In order to overcome the defects of the wafer defect detection methods in the above-mentioned prior art, such as high cost, low precision and great difficulty in operation, the present application proposes a device for non-destructive testing of wafer surfaces. The detection light is incident vertically, 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 provides a device for nondestructive testing of wafer surfaces, comprising a testing 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 to be tested and adjust the 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 the light beam vertically onto the wafer to be tested; 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 to be tested and gather it to the narrow channel detection end, and 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 to be tested and gather it to the wide channel detection end; the narrow channel detection end and the wide channel detection end convert the collected light signals into voltage signals and transmit them to the data acquisition and processing module to analyze the surface state of the wafer.

[0008] Preferably, the wide channel optical path adopts an ellipsoidal reflector, and the narrow channel optical path is composed of a fourth lens and a reflector arranged in the ellipsoidal reflector; the reflector is used to deliver the scattered light collected by the fourth lens to the narrow channel detection end; the incident optical path includes a reflecting device, which projects the incident light vertically to the lower focus of the ellipsoidal reflector; the projection of the reflecting 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 light path and a CCD camera, the focus of the focusing light path coincides with the lower focus of the ellipsoidal reflector; the data acquisition and processing module is respectively connected to the motion control module and the CCD camera; the CCD camera photographs the light spot formed by the focusing light path on the wafer to be tested, and the data acquisition and processing module controls the movement of the motion control module to adjust the position of the wafer to be tested until the light spot photographed by the CCD camera reaches the maximum energy state.

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

[0011] Preferably, the angle between the advancing direction of the light beam in the focusing light path and the horizontal direction is 15°.

[0012] Preferably, the reflective device is a cylindrical reflector; the incident light of the detection light 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 light 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 which are sequentially arranged along the light emitting direction of the first light source.

[0014] The present invention proposes a method for nondestructive testing of wafer surface. First, the wafer to be tested is moved to the focus below the ellipsoidal reflector, the detection optical path is turned on, and a wide channel voltage data set {x i} and the narrow channel voltage data set {y i}And perform normalization processing, compare the values ​​in the data set with the set threshold k; then extract data points greater than the k value from the two normalized data sets as defect points, and mark the data points less than or equal to the k value as background points; take the union of the defect points of the two data sets as the defect point set, and take the intersection of the background points as the background point set; merge the defect point set and the background point set, and convert them into a binary image, then extract the defect area, calculate the area of ​​each defect area and determine the defect type.

[0015] Preferably, before testing the wafer to be tested, the focusing light path is first calibrated so that the intersection of the focusing light path is located at the focus under the ellipsoidal reflector; the calibration method is:

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

[0017] Preferably, the method of moving the wafer to be tested to the focus under the ellipsoidal reflector is:

[0018] First, open the focusing light path and control the crystal to be tested to move toward the ellipsoidal reflector. During the movement, collect the light spot on the crystal to be tested and find the position with the largest light spot energy, which is the focal plane under the ellipsoidal reflector. Move the crystal to be tested to the focal plane under the ellipsoidal reflector.

[0019] The advantages of this application are:

[0020] The present application proposes a device for nondestructive testing of wafer surfaces, which uses two channels to collect scattered light generated by defects on the wafer surface based on the principle of laser scattering. The system can display the voltage amplitude changes in the current scanning area in real time by quickly scanning the wafer sample, and automatically reconstruct the scanning area image after the scanning is completed, so as to realize the identification and classification of defects.

[0021] This application uses dual-channel optical path detection to collect scattered light in a larger range, solving the problem of small numerical aperture of traditional solutions, and is suitable for non-destructive detection of surface defects at the micro-nano level. The wide channel is suitable for detecting nano-level defects, and the narrow channel is suitable for detecting micro-level defects. The two channels can realize simultaneous online detection without interfering with each other. Finally, the detection results of the two channels are combined to realize the identification and classification of defects.

[0022] This application can control the size of the detection spot by adjusting the beam expander multiple. A small spot is suitable for detecting smaller defects, while a large spot can improve the detection efficiency of the system. According to different detection requirements, the appropriate spot size is adjusted to achieve a balanced configuration of system sensitivity and detection speed.

[0023] This application proposes a method for automatic focusing of the wafer surface in combination with the focusing optical path, which can make the wafer reach the detection position more accurately. The method for non-destructive detection of the wafer surface proposed in this application has advantages such as high detection efficiency and high sensitivity compared with other methods because it introduces focusing, and can be competent for detection tasks in different environments. Therefore, this application has certain promotion significance in the field of precision measurement. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] Figure 2 It is the motion roadmap of the electronically controlled platform;

[0026] Figure 3 It is the reflected light spot image collected by the camera at different Z-axis positions;

[0027] Figure 4 This is the corresponding relationship diagram between Count value and Z-axis position;

[0028] Figure 5 It is a flow chart of the data processing algorithm;

[0029] Figure 6 is a flow chart of the method for measurement and detection of the present application;

[0030] Figure 7 This is the real-time change diagram of the voltage signal of wafer sample 1;

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

[0032] Fig. 9 is the surface image of wafer sample 2 reconstructed by the system;

[0033] Numbers in the figure: 10, detection optical path, 101, laser, 102, optical fiber collimator, 103, first lens, 104, pinhole, 105, second lens, 106, adjustable beam expander, 107, third lens, 108, ellipsoidal reflector, 109, cylindrical reflector, 110, fourth lens, 111, plane reflector;

[0034] 20. motion control module, 201. electric 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 optical fiber collimator, 503, fixed beam expander, 504, fifth lens;

[0038] 60. CCD camera; 70. data acquisition processing module; 701. data acquisition card; 702. computer. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0040] like Figure 1 As shown, the present application proposes a device for nondestructive testing of wafer surfaces, which is based on a laser scattering method to build a dual-channel detection system, which can dynamically adjust the spot size and realize micro-nano level defect detection. Figure 1 As shown, the device is composed 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 optical 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 sequentially arranged in the light emitting direction of the first light source 101 to form an incident optical path for filtering, collimating and focusing the output light of the first light source 101, so that the incident light has greater light energy when it is reflected by the cylindrical reflector 109 to the wafer located at the lower focus of the ellipsoidal reflector 108.

[0043] In the detection optical path, the first light source 101 is a fiber laser, which can generate purple light with a wavelength of 405nm, a horizontal polarization direction, and adjustable power; the output light of 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 mounting plate with the first lens 103 in a threaded manner; the parameters and specifications of the first lens 103 and the second lens 105 are consistent, and the two are symmetrically distributed on both sides of the pinhole 104; therefore, after the output light of the first lens 103 is filtered by the pinhole 104, the light beam output by the second lens 105 is still a collimated light beam with a spot size of 0.6mm, but the light beam is more uniform; the adjustable beam expander 106 is adjusted to 10 times, at this time, the diameter of the light beam after expansion reaches 6mm, the forward direction of the light beam is horizontal, and after focusing by the third lens 107, the spot at the focal position can reach 17μm. The focused light beam enters the ellipsoidal reflector 108 from the ellipsoidal hole, and is vertically incident on the surface of the wafer 202 after being reflected by the cylindrical reflector 109. At this time, the light spot position is both the focus of the third lens 107 and the lower focus of the ellipsoidal reflector 108. The fourth lens 110 is integrated inside the ellipsoidal reflector 108 and is located above the cylindrical reflector 109. It can achieve 5-24° scattered light collection, which is called a narrow channel light path. The plane reflector 111 is located above the ellipsoidal reflector 108 and can adjust the forward direction of the output light beam of the fourth lens 110; according to the confocal characteristics of the ellipsoidal reflector 108, 25-70° scattered light collection can be achieved.

[0044] If there are no defects on the surface of the wafer 202, the reflected light will return in the reverse direction along the original optical path and will not interfere with the detection effect; if there are defects on the surface of the wafer 202, scattered light of 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 reflector 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 focus on the ellipsoidal reflector 108 are the same point, and the scattered light signal collected by the ellipsoidal reflector 108 can be converted 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 processing module 70 includes a data acquisition card 701 and a computer 702. The data acquisition card 701 is integrated in the computer 702 to collect the voltage signals output by 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 by the data acquisition card 701 to realize the real-time display of the voltage signal changes and the visual restoration of the wafer surface image.

[0048] The principle of the system to detect surface defects is to receive scattered light through two photomultiplier tubes. The intensity of scattered light reflects the morphological characteristics of the wafer surface. There is a clear difference in the scattered light intensity between the smooth area and the defective area. The signal amplitude of the defective area is larger, and the voltage signal amplitude of the smooth area is lower. Therefore, this difference can be used to distinguish the smooth area from the defective area on the wafer surface. The algorithm flow of defect recognition 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 data set {y i}, x i is the voltage output by the second transimpedance amplifier 402 at the i-th detection time point, y i is 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} are normalized respectively; let the wide channel voltage data set {x i The normalized data set is recorded as X = {X i}, narrow channel voltage data set {y i The normalized data set is recorded as Y = {Y i};X i For x i The normalized value of Y i for y i The normalized value of .

[0051] The normalization process of the data set is as follows: first calculate the mean μ and standard deviation σ of the data set; then substitute the following formula to calculate the normalized value Z of each data set;

[0052]

[0053] The mean μ represents the center of the data set, the standard deviation σ represents the dispersion of each data point relative to the mean, and z i is the i-th value in the data set;

[0054] Calculate the wide channel voltage data set {x i}, in the above formula, the mean μ and standard deviation σ in the data set {x i}, and z i =x i ;

[0055] Calculate the narrow channel voltage data set {y i}, in the above formula, the mean μ and standard deviation σ in the data set {y i}, and z i =y i ;

[0056] S13. Compare the values ​​in the data sets X and Y with the set threshold k respectively, mark the points in the data sets X and Y that are greater than the threshold k as defect points, and mark the points that are less than or equal to the threshold k as background points; take the union of the defect points of the two data sets as the defect point set, and take the intersection of the background points as the background point set.

[0057] The threshold k is determined according to the detection requirements and defect size. According to experience, it can be set as follows: when the possible defect size is less than 30 microns, k is 1.5; when the possible defect size is between 30-300 microns, k is 2; when the possible defect size is greater than 300 microns, k is 3.

[0058] S14. Combine the defect point set and the background point set and convert them into a binary image, where the defect point is represented by a white pixel and the background point is represented by a black pixel. When a pixel value suddenly changes, it is proved that this point is a defect boundary point, so that the defect can be divided into regions to extract the defect region.

[0059] S15. Calculate the number M of white pixels in each defect area. According to 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 defects according to the aspect ratio.

[0060] Let the diameter of the circumscribed circle of the defect area be the length, the diameter of the inscribed circle be the width, and 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 made more 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 an 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 a 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 advancing 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 at the same time, 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 electric control platform 201 and a motor controller 203; the electric control platform 201 is used to place the wafer 202. The motor controller 203 is connected to the computer 702 and transmits commands in the form of serial communication to control the directional movement of the electric control platform 201. The electric control platform 201 carries the wafer 202 and is controlled by the commands issued by the motor controller 203 to achieve precise movement in three-dimensional directions to achieve rapid scanning and focusing of the wafer surface. The scanning route adopts a serpentine scanning method, such as Figure 2 As shown, the order is: route ① (positive motion of y axis) -> route ② (negative motion of y axis) -> route ③ (positive stepping of x axis) -> route ④ (positive motion of y axis) -> route ⑤ (negative motion of y axis) -> route ⑥ (positive stepping of x axis) -> route ⑦ (positive motion of y axis) -> route ⑧ (negative motion of y axis).

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

[0074] The system uses a method based on contrast to realize the automatic focusing process of the surface of the wafer 202. If the surface of the wafer 202 coincides with the lower focal plane of the ellipsoidal reflector 108, the energy of the light spot irradiated by the focusing light path 50 onto the surface of the wafer sample is the strongest, and the reflected light signal received by the CCD camera 60 is the strongest; if the surface of the wafer sample deviates from the lower focal plane of the ellipsoidal reflector 108, the position of the light spot on the surface of the wafer 202 is not at the focal length of the fifth lens 504, so the energy of the light spot is slightly weaker, and the reflected light signal received by the CCD camera 60 is also weaker. The Z-axis motor of the electric control platform 201 is controlled by the computer 702, and the wafer moves slowly upward. Initially, the surface of the wafer 202 deviates from the lower focal plane of the ellipsoidal reflector 108. At this time, the light spot position on the wafer 202 is not the focal position of the fifth lens 504, so the light spot energy is not concentrated, resulting in uneven distribution of reflected light energy, so that the light spot energy received by the CCD camera 60 is uneven and the contrast is weak; when the electric control platform 201 drives the surface of the wafer 202 to reach the lower focal plane of the ellipsoidal reflector 108, the brightness of the light spot on the surface of the wafer 202 is the most concentrated, and the reflected light energy is the strongest, so that the light spot energy received by the CCD camera 60 is evenly distributed and the contrast is the strongest; the wafer 202 continues to move upward. Since the position of the wafer 202 deviates from the lower focal plane of the ellipsoidal reflector 108 at this time, the contrast signal received by the CCD camera 60 is weakened and the contrast becomes smaller. At this time, the computer 702 controls the Z-axis motor of the electric control platform 201 to return the wafer sample to the optimal position, that is, the lower focal plane of the ellipsoidal reflector 108. Therefore, according to the contrast distribution and contrast change of the light spot received by the CCD camera 60, it can be judged whether the wafer sample is located at the best focus position at this time. The change of the reflected light spot image is as follows: Figure 3As shown, the light spot goes from nothing to something, first dark, then bright, and then dark again, corresponding to the process that the surface of the wafer 202 gradually approaches the lower focal position of the ellipsoidal reflector 108, reaches the lower focal position, and then moves away from the lower focal position.

[0075] The algorithm steps of auto focus are as follows:

[0076] S111. First, the Z-axis motor of the electric control platform 201 is controlled by the computer 702 to return to zero position, at which point Z=0; then the electric control platform 201 is controlled to move upward, at which point a reflected light spot image of the focusing light path 50 is collected per second, and the number of pixels Count whose pixel values ​​are in the range of [200,255] is calculated;

[0077] S112. Set the pixel number threshold TH=320. Record the pixel number Count of each set of reflection spot images and add it to array C. When the Count value is less than the threshold 320 and the Count values ​​of the three most recent reflection spot images decrease continuously, stop collecting images and control the Z-axis motor to stop moving;

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

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

[0080] like Figure 6 As shown, the method for nondestructive testing of wafer surface proposed in this embodiment adopts the above device 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 on the electric control platform 201, and control the Z-axis motor of the electric control platform 201 to return to the zero position first and then move upward through the computer 702. During the movement of the motor, the CCD camera 60 is synchronously controlled to collect the image of the reflected light spot, and according to the above-mentioned automatic focusing method, the wafer 202 reaches the best detection position.

[0083] S3. According to the detection requirements and equipment parameters, set the appropriate power of the first light source 101 and the multiple of the beam expander 106. 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 10×10 mm. The detection area range is set to 10×10 mm in the computer 702, the movement speed of the platform 201 is set to 2 mm / s, and the sampling rate of the acquisition card 701 is set to 10000.

[0085] S5. Start the scanning program through the computer 702, control the platform 201 to move according to the preset route, and realize the row-by-row scanning of the wafer sample 1. The system collects voltage data only when the y-axis moves in the positive direction; at this time, the voltage amplitude change of each row can be observed in real time through the software interface. If the voltage signal is very low, it means that there is no defect in this area. If the voltage amplitude is high, it means that there is a defect in this area. Figure 7 As shown, three defect areas can be distinguished.

[0086] S6. After the scanning is completed, the computer 702 automatically stores the voltage data collected this time, and reconstructs the image of the surface area of ​​the wafer sample 1 through the defect detection algorithm, such as Figure 8 As shown. According to the algorithm classification, the defect is identified as three scratches. After calculation, the area from left to right to the three scratches is 0.59mm 2 , 0.66mm 2 , 0.58mm 2 .

[0087] S7. Replace wafer sample 2 and continue testing. Its size is 5×5 mm. Repeat steps S1-S6, set the detection area to 5×5 mm, the movement speed of platform 201 to 1 mm / s, and the sampling rate of acquisition card 701 to 5000. Fig. 9 It can be identified that the surface defect area of ​​wafer sample 2 is mainly composed of pits and particles, and the particle area is about 0.02mm 2 , the pit area is about 0.03mm 2 .

[0088] Combining the test results of wafer sample 1 and wafer sample 2, it can be seen that the test method proposed in this application has good effect, low calculation complexity, and convenient and fast operation.

[0089] Of course, for those skilled in the art, the present application is not limited to the details of the above exemplary embodiments, but also includes the same or similar structures that can be implemented in other specific forms without departing from the spirit or basic characteristics of the present application. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the present application is defined by the attached claims rather than the above description, so it is intended to include all changes that fall within the meaning and scope of the equivalent elements of the claims. Any figure mark in the claims should not be regarded as limiting the claim involved.

[0090] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0091] The technologies, shapes, and structural parts not described in detail in this application are all well-known technologies.

Claims

1. A device for nondestructive 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 carry the wafer to be tested 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 is used to project a light beam and project the light beam vertically onto the wafer to be tested; 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 to be tested and gather it to the narrow channel detection end, and 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 to be tested and gather it to the wide channel detection end; The narrow channel detection end and the wide channel detection end convert the collected optical signals into voltage signals and transmit them to the data acquisition and processing module to analyze the surface status of the wafer.

2. The device for nondestructive testing of wafer surface according to claim 1, characterized in that: The wide channel optical path adopts an ellipsoid reflector, and the narrow channel optical path is composed of a fourth lens and a reflector arranged in the ellipsoid reflector; the reflector is used to deliver the scattered light collected by the fourth lens to the narrow channel detection end; the incident optical path includes a reflector, and the reflector projects the incident light vertically to the lower focus of the ellipsoid reflector; The projection of the reflective device on the horizontal plane is covered by the projection of the fourth lens on the horizontal plane.

3. The device for nondestructive testing of wafer surface according to claim 2, characterized in that: It also includes a focusing light path and a CCD camera, the focus of the focusing light path coincides with the lower focus of the ellipsoidal reflector; the data acquisition and processing module are respectively connected to the motion control module and the CCD camera; the CCD camera captures the light spot formed by the focusing light path on the wafer to be tested, and the data acquisition and processing module controls the movement of the motion control module to adjust the position of the wafer to be tested until the light spot captured by the CCD camera reaches the maximum energy state.

4. The device for nondestructive testing of wafer surface according to claim 3, characterized in that: The focusing optical path includes a second light source and a second optical fiber collimator, a fixed beam expander and a fifth lens which are sequentially arranged in the light emitting direction of the second light source.

5. The device for nondestructive testing of wafer surface according to claim 4, characterized in that: The angle between the forward direction of the light beam in the focusing optical path and the horizontal direction is 15°.

6. The device for nondestructive testing of wafer surface according to claim 2, characterized in that: The reflective device adopts a cylindrical reflector; the incident light of the detection light path is horizontally incident on the cylindrical reflector, and then vertically incident on the surface of the wafer to be tested.

7. The device for nondestructive testing of wafer surface according to any one of claims 1 to 6, characterized in that: The incident light 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 which are sequentially arranged along the light emitting direction of the first light source.

8. A method for nondestructive testing of wafer surfaces using the device for nondestructive testing of wafer surfaces as claimed in claim 3, 4, 5 or 7, characterized in that: First, the wafer to be tested is moved to the focus under the ellipsoid reflector, the detection optical path is turned on, and the wide channel voltage data set {x i } and the narrow channel voltage data set {y i }And perform normalization processing, compare the values ​​in the data set with the set threshold k; then extract data points greater than the k value from the two normalized data sets as defect points, and mark the data points less than or equal to the k value as background points; take the union of the defect points of the two data sets as the defect point set, and take the intersection of the background points as the background point set; merge the defect point set and the background point set, and convert them into a binary image, then extract the defect area, calculate the area of ​​each defect area and determine the defect type.

9. The method for nondestructive testing of wafer surface according to claim 8, characterized in that: Before testing the wafer to be tested, the focusing light path is calibrated so that the intersection of the focusing light path is located at the focus under the ellipsoid reflector; the calibration method is: First, use a spot analyzer to calibrate the focus of the focusing light path; then close the focusing light path, open the detection light path, and find the lower focus of the ellipsoidal reflector; then open the focusing light path and the detection light path at the same time, and adjust the focusing light path so that the light spots of the focusing light path and the detection light path are both in the maximum energy state and the centers of the two light spots coincide.

10. The method for nondestructive testing of wafer surface according to claim 9, characterized in that: The method of moving the wafer to be tested to the focus under the ellipsoidal reflector is: First, open the focusing light path and control the crystal to be tested to move toward the ellipsoidal reflector. During the movement, collect the light spot on the crystal to be tested and find the position with the largest light spot energy, which is the focal plane under the ellipsoidal reflector. Move the crystal to be tested to the focal plane under the ellipsoidal reflector.

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