Method and equipment for efficiently detecting small surface area of crystal ingot

Abstract

The invention relates to the technical field of semiconductor processing, in particular to a method and equipment for efficiently detecting a facet area of a crystal ingot. The invention aims to provide the high-efficiency detection method for the small-surface area of the crystal ingot, which is characterized in that a laser beam is shaped into a rectangular laser to be output, point laser scanning is replaced by surface laser scanning, and a single scanning area is expanded, so that the scanning efficiency is improved, the information missing of the end surface of the crystal ingot is avoided, and the efficiency and the resolution of the detection of the end surface of the crystal ingot are higher; meanwhile, the silver reflector is adopted to obtain the light intensity distribution of the rectangular laser, and then the light intensity distribution of the reflected light of the crystal ingot is corrected, so that the influence of non-uniform light intensity of the rectangular laser on the light intensity distribution of the reflected light of the crystal ingot is avoided, and the measurement precision is improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor processing technology, and in particular to a high-efficiency detection method and device for a small face area of ​​a crystal ingot. Background Art

[0002] Semiconductor materials are resistant to high temperatures and radiation, and have excellent properties such as large bandgap width and high breakdown electric field. They have gradually become the main substrate of electronic devices and have important application prospects in the fields of communications, national defense and military industry. In the multiple processes from ingots to qualified substrate sheets, ingot cutting is the main source of material loss. At present, the main ingot cutting technologies are wire cutting and laser stripping. Compared with traditional wire cutting technology, laser stripping technology has the advantages of high production efficiency and low consumables, and has great development potential. The principle of laser stripping technology is to focus the laser at a specified depth inside the semiconductor material, process a large area of ​​modified area, and then strip the wafer. However, during the growth of the ingot, due to different doping concentrations, small facet areas and non-small facet areas with different resistivity and refractive index will be formed. When the modified laser passes through the small facet area and the non-small facet area, the depth of its focus will be inconsistent, which leads to low flatness of the stripped wafer and causes large losses in the subsequent grinding and polishing process. Therefore, accurate and efficient detection of the small facet position is an important link in improving wafer production capacity.

[0003] The existing technologies for detecting small faces of ingots mainly include fluorescence detection method and transmitted light detection method. For example, patent document CN110911268A provides a method for detecting small faces by using a shooting unit. This method uses a shooting unit to shoot the upper surface of the ingot, and uses an image processing unit to perform binarization processing on the captured image, thereby achieving the distinction between small face areas and non-small face areas. However, the ingot is relatively thick, and it is not easy to distinguish between small face areas and non-small face areas by direct shooting, which is prone to errors during implementation.

[0004] In the patent document CN115472515A, a method for detecting small faces by fluorescence is provided in the patent document entitled Ingot Processing Method and Processing Device. This method uses a laser of a specific wavelength to irradiate the ingot, and determines the small face area by detecting the intensity of the fluorescence light generated on the upper surface of the ingot. However, in the fluorescence detection step, a lens is used to focus the laser on the sample surface, and there is a problem that the laser point scanning efficiency is not high enough. In addition, the laser power density is relatively high after focusing, which can easily cause damage to the surface of the ingot.

[0005] In addition, patent document CN117316791A adopts a transmitted light detection method. This method completes the detection of the first peeled wafer by comparing the transmission intensity of the wafer and the emission intensity of the light source, and then optimizes the laser processing conditions of the next wafer according to the position information corresponding to the small face area of ​​the first wafer. However, when using laser to measure the transmittance of the wafer, it is carried out in the form of point scanning, and there are also problems of low efficiency and missing small face information.

[0006] In summary, in response to the need to detect small area surfaces of ingots, existing detection methods usually use fluorescence detection and transmitted light detection. The publicly available solutions based on optical nondestructive testing do not discuss the impact of laser energy distribution and laser coverage on scanning efficiency and measurement accuracy. Therefore, the solution needs to be further optimized to achieve efficient and accurate detection. Summary of the invention

[0007] In order to solve the above-mentioned technical problems, the purpose of the present invention is to provide an efficient detection method for the small face area of ​​a crystal ingot, which shapes the laser beam into a rectangular laser output, replaces point laser scanning with surface laser scanning, expands the single scanning area, thereby improving the scanning efficiency, and avoiding omission of information on the end face of the crystal ingot, so that the efficiency and resolution of the end face detection of the crystal ingot are higher; at the same time, the present invention uses a silver reflector to obtain the light intensity distribution of the rectangular laser, and then corrects the light intensity distribution of the reflected light from the crystal ingot, thereby avoiding the influence of the uneven light intensity of the rectangular laser on the light intensity distribution of the reflected light from the crystal ingot, and improving the measurement accuracy.

[0008] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions: An efficient detection method for a small facet area of ​​a crystal ingot comprises the following steps: 1) Optimize the laser of a specific wavelength into a flat-top beam through a homogenization system; 2) The laser beam is shaped into a rectangular beam by a beam shaping system; 3) The rectangular laser beam is reflected to the surface of the ingot through the beam splitter, and is reflected on the surface of the ingot; 4) The electric translation stage drives the surface of the ingot to move, so that the laser scans the surface of the ingot along a fixed path, and the CCD detects and records the intensity distribution of the reflected light; 5) The reflected light intensity distribution information is transmitted to the control end, and the error caused by uneven laser energy distribution is corrected in combination with a silver reflector to identify the small facet area of ​​the ingot.

[0009] Preferably, the laser emitted by the laser is a Gaussian beam with a wavelength of 300-1000 nm, an adjustable power of 0-30 W, and a beam quality factor M. 2 <1.3, spot diameter is 1~10 mm.

[0010] Preferably, the light homogenization system comprises a spatial light modulator, an aspherical lens group or a micromirror array, which is used to optimize the laser spot into a flat-top beam with uniform energy distribution.

[0011] Preferably, the beam shaping system uses a cylindrical lens group, a special prism or a Fresnel lens to compress the laser beam in one direction and collimate it in another direction, thereby outputting a rectangular spot, and the area of ​​the laser spot can be dynamically adjusted according to the size of the ingot.

[0012] Preferably, the sampling frequency of the CCD detection system is synchronized with the movement speed of the electric translation stage to ensure that a high-precision reflected light distribution image is collected at each position on the surface of the ingot to avoid data omission.

[0013] Preferably, the electric translation stage has an XYZ three-dimensional motion function, and adjusts the distance between the ingot surface and the CCD by controlling the displacement in the Z-axis direction to optimize the imaging quality of the reflected light.

[0014] Preferably, the detection of the reflected light uses a bandpass filter to filter stray light to improve the accuracy of the CCD detection signal, and the filter has high transmittance in the laser band.

[0015] Preferably, the reflected light image information collected by the CCD is corrected by the control end, and the corrected images are spliced ​​to identify the small face area of ​​the ingot; further, the control end performs Z-Score normalization processing based on the reflected light intensity distribution image collected by the CCD to eliminate the influence of uneven ambient light and laser light intensity, thereby obtaining high-precision small face area information of the ingot.

[0016] Preferably, the silver reflector is used for correcting laser energy distribution, and the collected silver reflector reflected light intensity distribution is used as a reference background image to correct the uneven reflected light distribution on the ingot surface.

[0017] Furthermore, the present invention also discloses a device for implementing the method, the device comprising: Laser, used to emit laser light of a specific wavelength; Light homogenization system, used to optimize the energy distribution of the laser spot; A beam shaping system for shaping the laser beam into a rectangular beam; A beam splitter is used to reflect part of the laser light to the surface of the ingot, and the other part is used to transmit the reflected light signal; An electric translation stage, used to carry the ingot and move it in the XY direction; CCD, used to detect and record the reflected light intensity distribution image; The control end is used to control system parameters and process reflected light data.

[0018] The present invention adopts the above-mentioned technical solution. The method adopts beam shaping technology to shape the laser beam into a rectangular beam, and expands the single scanning area by surface laser scanning, thereby avoiding the low efficiency problem caused by point scanning. At the same time, a silver reflector is used to correct the unevenness of the laser energy distribution to ensure the detection accuracy and uniformity of the reflected light intensity distribution. Through this innovative laser scanning and correction method, the present invention effectively solves the problems of low efficiency, laser damage to the ingot surface, and insufficient measurement accuracy in the existing detection technology, greatly improves the detection speed and accuracy of the small surface area of ​​the ingot, and is suitable for the production detection needs of large-scale ingots.

[0019] The technical solution of the present invention not only significantly improves the detection efficiency of the small facet area of ​​the ingot, but also ensures the accuracy of the detection results by optimizing the laser scanning mode and reflected light correction processing, providing reliable technical support for the production of high-quality wafers. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Flowchart for detecting small faces with reflected light.

[0021] Figure 2 It is a schematic diagram of the device structure of the present invention, wherein: 1 laser; 2 light homogenization system; 3 beam shaping system; 4 beam splitter; 5 crystal ingot or silver reflector; 6 electric translation stage; 7 convex lens; 8 bandpass filter; 9 CCD; 10 control end.

[0022] Figure 3 is a process diagram of laser scanning of the present invention, wherein Figure 3 (a) is a schematic diagram of the end face of the crystal ingot 501; Figure 3 (b) is a schematic diagram of a rectangular spot scanning the end face of a crystal ingot; Figure 3 (c) Schematic diagram of stitching N rectified images together. DETAILED DESCRIPTION

[0023] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] like Figure 2 As shown, the ingot facet detection device of the present invention comprises 1 a laser; 2 a light homogenization system; 3 a beam shaping system; 4 a beam splitter; 5 an ingot or a silver reflector; 6 an electric translation stage; 7 a convex lens; 8 a bandpass filter; 9 a CCD; 10 a control terminal; Laser 1, emitting laser light of a specific wavelength for ingot surface detection; homogenization system 2, optimizing the energy distribution of the laser spot; beam shaping system 3, used for shaping the laser spot to output a rectangular spot; beam splitter 4, used for reflecting the laser light and transmitting the reflected light from the upper surface containing target information; electric translation stage 6, used for loading the ingot; convex lens 7, used for converging the reflected light; bandpass filter 8, transmitting the reflected light and cutting off the stray light; CCD 9, detecting the reflected light transmitted through the bandpass filter; control terminal 10, used for controlling the laser timing, the movement of the electric translation stage, and processing the intensity distribution image of the reflected light measured by CCD 9.

[0025] like Figure 1 As shown, the method for detecting the small facet area of ​​the ingot, the ingot detection stage includes the following steps: (1) placing the crystal ingot 501 on the electric translation stage 6; (2) The laser beam of a specific wavelength is transmitted to the beam shaping system 3 after the energy distribution of the light spot is optimized by the homogenization system 2; (3) The beam shaping system 3 shapes the laser beam into a rectangular laser beam, and transmits part of the laser beam reflected by the beam splitter 4 to the upper surface of the ingot 501, where it is reflected; (4) The electric translation stage 6 drives the crystal ingot 501 to move, so that the laser scans the surface of the crystal ingot 501 along a fixed path. At the same time, the CCD 9 detects the intensity of the reflected light on the upper surface of the crystal ingot 501 at a determined sampling frequency, and transmits the intensity distribution image of the reflected light to the control end; (5) The control terminal 10 stores the intensity distribution of the reflected light of the ingot before correction collected by the CCD 9.

[0026] The light homogenization system 2 can optimize the laser beam into a flat-top beam with relatively uniform energy distribution.

[0027] The beam shaping system 3 can compress the laser beam along a certain direction to generate a rectangular laser spot of a certain area required for detection.

[0028] The laser 1 emits a Gaussian beam with a wavelength of 300-1000 nm, an adjustable power of 0-30 W, and a beam quality factor M. 2 <1.3, spot diameter 1~10 mm.

[0029] The beam splitter 4 reflects and transmits light in a ratio of 1:1, the reflected laser light is used for detecting the upper surface of the crystal ingot, and the light reflected from the upper surface of the crystal ingot 501 is used for characterizing the facet information.

[0030] When the electric translation stage 6 carries the crystal ingot, its movement is controlled by the control end 10 so that the laser beam scans along a fixed path on the surface of the crystal ingot 501 .

[0031] The moving speed of the electric translation stage 6 is 50-500 mm / s.

[0032] The electric translation stage 6 includes XYZ three-axis movement. When detecting ingots of different thicknesses, the distance between the upper surface of the ingot 501 and the CCD 9 is optimized by controlling the displacement in the Z-axis direction to achieve high-quality imaging.

[0033] The control end 10 stores each rectangular sampling area containing the intensity distribution information of the reflected light of the crystal ingot 501 collected by the CCD 9 for subsequent correction.

[0034] The bandpass filter 8 has high transmittance in the laser wavelength band.

[0035] The detection method of the ingot facet area is characterized in that the actual rectangular laser after shaping still has uneven distribution, which will affect the intensity distribution of the reflected light of the ingot, so correction is required. The correction stage includes the following steps: (1) Place a silver reflector 502 at the electric translation stage 6; (2) Without changing the parameters of the laser, the light homogenization system and the beam shaping system, the laser beam is transmitted to the beam shaping system after passing through the light homogenization system; (3) The beam shaping system outputs a rectangular laser beam, which is reflected by the beam splitter and transmitted to the upper surface of the silver reflector 502, where it is reflected; (4) CCD9 transmits the intensity distribution image of the light reflected by the silver reflector to the control terminal 10; (5) The control end 10 uses the intensity distribution of the reflected light from the silver reflector as the background, and corrects the intensity distribution of the reflected light from the ingot before correction to obtain the corrected intensity distribution of the reflected light from the ingot. The control end 10 stitches all the corrected intensity distribution images of the reflected light from the ingot together, and identifies the small facet area on the surface of the ingot according to the intensity of the reflected light from the image.

[0036] The electric translation stage 6 optimizes the distance between the upper surface of the silver reflector 502 and the CCD 9 by controlling the displacement in the Z-axis direction, thereby achieving high-quality imaging.

[0037] The control end 10 performs correction processing on the intensity distribution of the reflected light of the ingot before correction and the intensity distribution of the reflected light of the silver reflector. The rectangular area of ​​the intensity distribution of the reflected light of the ingot obtained by the above method is consistent in size and direction with the rectangular area of ​​the intensity distribution of the reflected light of the silver reflector. Therefore, it is only necessary to divide all the intensity distributions of the reflected light of the ingot before correction by the intensity distributions of the reflected light of the silver reflector, and normalize the results with Z-Score to obtain the intensity distribution of the reflected light of the ingot after correction.

[0038] The control end 10 stitches together the corrected images of the intensity distribution of the reflected light from the ingot, and identifies the facet area on the surface of the ingot according to the intensity of the reflected light.

[0039] When the laser with the same parameters is reflected on the upper surface of the ingot, due to the different reflectivity of the laser to the small facet area and the non-small facet area, reflected light with different light intensities will be obtained. The intensity distribution of the reflected light corresponds to the distribution of the small facet area, so the small facet area and the non-small facet area of ​​the ingot can be judged by the intensity of the reflected light. In addition, due to the errors of the laser, the light homogenization system and the beam shaping system, the rectangular laser beam after shaping is not uniform, which will cause the detection result to be affected by the actual rectangular laser beam distribution. The present invention uses a light homogenization system and a beam shaping system to optimize the laser beam and output a rectangular light spot with a relatively uniform energy distribution. The rectangular surface laser scans the upper surface of the ingot, covering a wider range, improving the scanning efficiency and avoiding the omission of upper surface information. At the same time, the actual distribution of the rectangular laser beam is obtained through a silver reflector, and the scanning result is corrected, thereby improving the accuracy of small facet area recognition.

[0040] Inspection equipment for the small facet area of ​​the ingot, such as Figure 2 As shown, the ingot 501 is fixed on the electric translation stage 6, and its movement path is controlled by the control end 10. The laser 1 emits a Gaussian beam, and a rectangular laser is obtained through the light homogenization system 2 and the beam shaping system 3. The rectangular laser is reflected to the upper surface of the ingot to be measured through the beam splitter 4. The laser is emitted and refracted on the upper surface, and the reflected light signal is half-transmitted and half-reflected through the beam splitter 4. The reflected light is converged by the convex lens 7, and is transmitted to the CCD9 after filtering the stray light through the bandpass filter 8. CCD9 detects and records the reflected light image and transmits it to the control end 10. Through the movement of the electric translation stage 6 in the XY direction, the laser completes the scanning of the entire upper surface of the ingot, and measures the intensity distribution images of the reflected light of N ingots to be corrected. The ingot 501 is replaced by the silver reflector 502, and the rectangular laser is reflected to the upper surface of the silver reflector 502 through the beam splitter 4 according to the same parameters of the laser 1, the light homogenization system 2, and the beam shaping system 3. The upper surface laser is emitted and refracted, and the reflected light signal is half-transmitted and half-reflected by the beam splitter 4. The transmitted reflected light is converged by the convex lens 7, and is transmitted to the CCD9 after filtering the stray light by the bandpass filter 8. The CCD9 detects and records the intensity image of the reflected light from the silver reflector 502 and transmits it to the control terminal 10. The reflected light intensity of the N crystal ingots 501 to be corrected is divided by the reflected light intensity of the silver reflector 502 and Z-Score normalized to obtain the reflected light intensity images of the N corrected crystal ingots 501. The control terminal 10 splices the reflected light images of the N corrected crystal ingots 501 together, and identifies the small face area of ​​the end face of the crystal ingot 501 according to the distribution of the reflected light intensity.

[0041] Preferably, the power density of the rectangular laser transmitted to the upper surface of the ingot 501 is not less than 0.1 W / cm 2 .

[0042] Among them, the present invention adopts a uniform light system to optimize the energy distribution of the light spot, which can be achieved through optical elements such as a spatial light modulator, an aspheric lens group, and a micromirror array.

[0043] The beam shaping system can use cylindrical lens groups, special prisms, etc. to compress the laser beam in one direction and collimate it in another direction to achieve the output of a rectangular spot. In addition, the use of optical elements with different parameters can achieve laser output with different spot areas, which is suitable for the detection of small areas of ingots of different sizes.

[0044] Figure 3 (a) is a schematic diagram of the end face of the crystal ingot 501. Figure 3 (b) is a schematic diagram of a rectangular light spot scanning the end face of a crystal ingot. Figure 3 As shown in (b), the laser of a specific wavelength forms a rectangular spot after passing through the homogenization system and the beam shaping system, and irradiates the end face of the ingot. The CCD records the reflected light image of the rectangular area. The electric translation stage 6 drives the ingot 5 to move in the XY direction at a certain speed to form a scanning path ( Figure 3 The corresponding rectangular laser scanning path in (b) is Ⅰ→Ⅱ→Ⅲ→Ⅳ→Ⅴ→Ⅵ→Ⅶ→Ⅷ→Ⅸ). After the laser completes the scanning of the end face of the ingot, the CCD records N images of the reflected light intensity distribution. The control end stitches the N corrected images together, as shown in Figure 3 As shown in (c), the non-facet region 5a and the facet region 5b of the ingot end face are identified based on the reflected light intensity distribution.

[0045] The above is a description of the embodiments of the present invention. Through the above description of the disclosed embodiments, professionals and technicians in the field can implement or use the present invention. Various modifications to these embodiments will be apparent to professionals and technicians in the field. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown in this article, but will conform to the widest range consistent with the principles and novelties disclosed herein.

Claims

1. An efficient detection method for a small facet area of ​​a crystal ingot, characterized in that: The following steps are involved: 1) Optimize the laser of a specific wavelength into a flat-top beam through a homogenization system; 2) The laser beam is shaped into a rectangular beam by a beam shaping system; 3) The rectangular laser beam is reflected to the surface of the ingot through the beam splitter, and is reflected on the surface of the ingot; 4) The electric translation stage drives the surface of the ingot to move, so that the laser scans the surface of the ingot along a fixed path, and the CCD detects and records the intensity distribution of the reflected light; 5) The reflected light intensity distribution information is transmitted to the control end, and the error caused by uneven laser energy distribution is corrected in combination with a silver reflector to identify the small facet area of ​​the ingot.

2. The method according to claim 1, characterized in that The laser emitted by the laser is a Gaussian beam with a wavelength of 300-1000 nm, an adjustable power of 0-30 W, and a beam quality factor M 2 <1.3, spot diameter is 1~10 mm.

3. The method according to claim 1, characterized in that: The light homogenization system includes a spatial light modulator, an aspherical lens group or a micromirror array, and is used to optimize the laser spot into a flat-top beam with uniform energy distribution.

4. The method according to claim 1, characterized in that The beam shaping system uses a cylindrical lens group, a special prism or a Fresnel lens to compress the laser beam in one direction and collimate it in another direction, thereby outputting a rectangular spot. The area of ​​the laser spot can be dynamically adjusted according to the size of the ingot.

5. The method according to claim 1, characterized in that The sampling frequency of the CCD detection system is synchronized with the movement speed of the electric translation stage, ensuring that a high-precision reflected light distribution image is collected at each position on the surface of the ingot to avoid data omission.

6. The method according to claim 1, characterized in that The electric translation stage has an XYZ three-dimensional motion function, and adjusts the distance between the surface of the crystal ingot and the CCD by controlling the displacement in the Z-axis direction to optimize the imaging quality of the reflected light.

7. The method according to claim 1, characterized in that The detection of the reflected light adopts a bandpass filter to filter stray light to improve the accuracy of the CCD detection signal, and the filter has a high transmittance in the laser band.

8. The method according to claim 1, characterized in that: The reflected light image information collected by the CCD is corrected by the control end, and the corrected images are spliced ​​to identify the small face area of ​​the ingot; further, the control end performs Z-Score normalization processing based on the reflected light intensity distribution image collected by the CCD to eliminate the influence of uneven ambient light and laser light intensity, thereby obtaining high-precision small face area information of the ingot.

9. The method according to claim 1, characterized in that: The silver reflector is used to correct the laser energy distribution, and the collected silver reflector reflected light intensity distribution is used as a reference background image to correct the uneven reflected light distribution on the surface of the crystal ingot.

10. A device for implementing the method according to any one of claims 1 to 9, characterized in that: The equipment includes: Laser, used to emit laser light of a specific wavelength; Light homogenization system, used to optimize the energy distribution of the laser spot; A beam shaping system for shaping the laser beam into a rectangular beam; A beam splitter is used to reflect part of the laser light to the surface of the ingot, and the other part is used to transmit the reflected light signal; An electric translation stage, used to carry the ingot and move it in the XY direction; CCD, used to detect and record the reflected light intensity distribution image; The control end is used to control system parameters and process reflected light data.

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