Laser modification and low-temperature impact controllable stripping method and system for single crystal silicon carbide wafer

Abstract

The invention belongs to the technical field of semiconductor material processing, and relates to a laser modification and low-temperature impact controllable stripping method and system for a single crystal silicon carbide wafer. The method comprises the following steps: pretreating the surface of a single crystal SiC crystal ingot to form a uniform rough surface; setting femtosecond laser initial parameters, and carrying out modification treatment in the crystal ingot to form a modified area; laser parameters are optimized through sweep-frequency optical coherence tomography and a CNN model, and optimal parameters are obtained; inducing to form a modified layer parallel to the surface in the crystal ingot by utilizing the parameters; coating a polymer on the surface of the modified layer and pre-cooling the crystal ingot; and applying a low-temperature impact load to promote the II-type crack to expand along the crystal face so as to realize controllable stripping. The method solves the problem that cracks are difficult to control in the laser stealth cutting technology.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor material processing technology, specifically relating to a laser-modified and low-temperature shock-controlled peeling method and system for single-crystal silicon carbide wafers. Background Technology

[0002] Single-crystal SiC, as a typical representative of third-generation wide-bandgap semiconductor materials, has significant application value in high-power electronic devices, radio frequency devices, and other fields due to its excellent physical properties (bandgap width 3.2 eV, breakdown electric field strength 3 MV / cm, thermal conductivity 490 W / (m·K)). However, its extremely high Mohs hardness (9.5) and low fracture toughness (fracture toughness K) are also significant challenges. IC ≈3.5MPa·m 1 / 2 This poses a significant challenge to wafer processing: traditional diamond wire saw cutting has inherent defects such as high material loss rate (>50%) and large wafer warpage (6-inch Warp>30 μm); while laser stealth cutting technology can reduce material loss, it is limited by the uncontrollable direction of crack propagation in the modified layer, which can easily lead to quality problems such as excessive surface roughness (Ra>5 μm) and edge breakage (>10 μm).

[0003] A thorough analysis of existing technological bottlenecks reveals three main dimensions: First, at the physical mechanism level, although femtosecond laser processing can achieve nanoscale modification through nonlinear effects such as multiphoton absorption and avalanche ionization, crack propagation still depends on subsequent mechanical separation (ultrasonic vibration / overall cryogenic cracking), resulting in type I opening cracks (perpendicular crystal plane propagation) accounting for more than 70%. Secondly, in terms of process control, the quantitative relationship between laser parameters and the three-dimensional morphology of microcracks (pore size, crack depth and distribution density characteristics) has not yet been established, resulting in a narrow process window. Finally, in terms of stress design, existing technologies simply utilize the shrinkage stress (approximately 200 MPa) generated by the difference in thermal expansion coefficients, lacking active control over the crack path, resulting in non-uniform propagation caused by edge stress concentration (warpage > 150 μm). In particular, the lack of dynamic monitoring methods for the laser-material interaction process leads to poor process stability (yield < 65%).

[0004] In summary, although laser cutting saves materials, it cannot control cracks. The underlying problem is the triple challenge of insufficient physical mechanisms, inaccurate process parameters, and uncontrollable stress direction. Summary of the Invention

[0005] The purpose of this invention is to provide a laser-modified and low-temperature shock-controlled peeling method and system for single-crystal silicon carbide wafers, solving problems such as the inability to control cracks in laser stealth cutting technology.

[0006] This invention is achieved through the following technical solution: A method for laser modification and low-temperature shock-controlled exfoliation of single-crystal silicon carbide includes the following steps: S1. Pre-treat the surface of the single-crystal SiC ingot to form a machined surface with uniform roughness; S2. Set the initial laser parameters of the femtosecond laser to perform internal modification treatment on the single-crystal SiC ingot to form a modified region; The initial laser parameters of the femtosecond laser are the pre-constructed laser parameters for inducing type II slip cracks; S3. Acquire real-time images of the modified region, monitor and optimize laser parameters using a swept-frequency optical coherence tomography method and a CNN model to obtain the optimal laser parameters; The single-crystal SiC ingot is processed using the optimal laser parameters to induce the formation of a modified layer parallel to the surface of the ingot inside the single-crystal SiC ingot; S4. Coat the surface of the modified layer with a polymer layer and pre-cool the single crystal SiC ingot. S5. Apply a low-temperature impact load to the pre-cooled ingot to promote the propagation of type II cracks along the (0001) crystal plane of single crystal SiC, and obtain the peeled SiC wafer. S6. Remove the polymer layer from the surface of the peeled-off SiC wafer and grind the surface of the peeled-off SiC wafer to obtain a finished product; S7. Repeat steps S1-S6 until the ingot processing is complete, resulting in multiple finished products.

[0007] Furthermore, in S1, the surface of the single-crystal SiC ingot is pretreated, specifically by grinding and cleaning the surface of the single-crystal SiC ingot.

[0008] Furthermore, in S2, the initial laser parameters of the femtosecond laser are: wavelength 1030 nm, pulse width 180 fs-12 ps, single pulse energy 3-20 μJ, repetition frequency 1 kHz-1 MHz, and scanning speed 0-100 mm / s.

[0009] Furthermore, in S3, real-time images of the modified region are acquired, and the laser parameters are monitored and optimized using a swept-frequency optical coherence tomography method and a CNN model to obtain the optimal laser parameters; specifically, the following processes are included: Real-time images of the modified region were acquired using a swept-frequency optical coherence tomography system, and feature information was extracted. The feature information and initial laser parameters are input into the CNN model. The CNN model outputs the predicted crack morphology and compares the similarity with the morphology of the ideal cleavage direction. If the similarity is low, the laser parameters are adjusted in real time and the process is repeated until the similarity reaches or exceeds the preset similarity. The laser parameters that correspond to a similarity level that reaches or exceeds the preset similarity level are the optimal laser parameters.

[0010] Furthermore, in S4, the pre-cooling temperature is -30°C to -50°C.

[0011] Furthermore, S5 specifically involves generating a radial temperature gradient field through a central cold source, causing the polymer-SiC interface to reach the critical temperature for glass transition.

[0012] Furthermore, the radial temperature gradient field was constructed using a liquid nitrogen injection device.

[0013] Furthermore, the radial temperature gradient field has a temperature gradient range of 3-15 K / mm, and the impact temperature is controlled between -196℃ and -50℃.

[0014] The present invention also discloses a laser-modified and cryogenic shock-controlled peeling system for single-crystal silicon carbide, including a processing system, coating equipment, precooling equipment, cryogenic shock equipment, separation equipment, and grinding equipment; The processing system includes a femtosecond laser, digital micromirror device, dual-color mirror, objective lens, three-axis moving platform, white LED light, convex lens, SS-OCT system, white LED light, CMOS image sensor, and CNN model; The sample is fixed on a three-axis moving platform; the objective lens is set above the sample, the dichroic mirror is set above the objective lens, and the white LED light is set below the three-axis moving platform. The CMOS image sensor is positioned along the refraction direction of one of the dichroic mirrors, and the CMOS image sensor communicates with the CNN model. The dichroic mirror is positioned in the reflection direction of the digital micromirror device; A convex lens is positioned in the reflection direction of one of the dichroic mirrors, and the light path of the convex lens is incident on the SS-OCT system; The processing beam output from the femtosecond laser is incident on a digital micromirror device, which is used to spatially modulate the laser wavefront using a preset holographic pattern. The modulated laser is split by a dichroic mirror, and the main processing optical path is focused by the objective lens to a predetermined depth inside the single-crystal SiC sample, inducing nonlinear absorption to form a modified layer. The backlight of white LED a is used to assist in surface topography imaging; The monitoring beam after spectral dispersion is reflected by a dichroic mirror, collimated by a convex lens, and then enters the SS-OCT system; the independent contrast beam is incident on a white LED lamp b and then synchronously introduced into the SS-OCT system, forming interference with the sample arm optical path. A CMOS image sensor is used to acquire two-dimensional morphological images of the sample modification layer, which are then fed into a CNN model. A CNN model is used to extract features from a two-dimensional topography image, perform analysis and processing, and output a predicted crack morphology. It is then spatially registered with SS-OCT data to evaluate the similarity between the predicted crack morphology and the ideal cleavage direction morphology. Based on the similarity, the laser parameters are adjusted and optimized to obtain the optimal laser parameters. Coating equipment for coating a polymer layer onto the surface of a modified layer; Pre-cooling equipment is used for pre-cooling single-crystal SiC ingots; Low-temperature impact equipment is used to apply low-temperature impact loads to pre-cooled ingots to promote the propagation of type II cracks along the (0001) crystal plane of single-crystal SiC, thereby obtaining the peeled SiC wafers; Separation equipment used to remove the polymer layer; Grinding equipment is used to grind the surface of the stripped SiC wafers.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a laser-modified and cryogenic shock-controlled peeling method for single-crystal silicon carbide wafers. First, after pretreatment of the wafer surface, a femtosecond laser is used to induce crack nucleation within the modifier layer using optimized parameters. Subsequently, a polymer is coated and pre-cooled, and a gradient temperature field is generated using a central cryogenic source to precisely propagate the crack radially. After peeling, cyclic polishing is performed. The entire process is monitored in real-time by swept-frequency optical coherence tomography (SS-OCT), and a convolutional neural network (CNN) adjusts the laser and shock parameters based on the monitoring results to achieve closed-loop control. This method, through a laser parameter-crack morphology mapping model and a central cryogenic shock path design, solves the problems of edge chipping and wafer breakage caused by type I crack propagation in traditional processes. It can complete SiC wafer peeling with high quality and low damage, significantly improving processing efficiency and yield.

[0016] This invention applies a low-temperature impact load to a pre-cooled ingot, constructing a radial temperature gradient field that decreases from the center to the outer edge. Utilizing the difference in thermal expansion coefficients between the polymer and SiC, directional tensile stress is generated within the modified layer. This enables cracks to initiate from the center and propagate along an "outward radiation" pattern, resulting in a river-like Varnaline morphology. This replaces the stress concentration caused by edge-initiated cracking in traditional processes, reducing wafer warpage by more than 50%.

[0017] Furthermore, laser parameters were monitored and optimized using swept-frequency optical coherence tomography (SS-OCT) and a CNN model to obtain the optimal laser parameters. Image analysis methods, combined with vertical microscopic imaging and swept-frequency optical coherence tomography (SS-OCT), were used to monitor the crack morphology during the femtosecond laser remodeling process. A convolutional neural network (CNN) was employed to control the process parameters in real time, inducing type II slip cracks to propagate along a predetermined direction and preventing the formation of type I opening cracks. Attached Figure Description

[0018] Figure 1 A schematic diagram of the process flow for a laser slicing method for a single-crystal SiC ingot provided in an embodiment of the present invention; Figure 2 A schematic diagram illustrating the interaction between an ultrashort pulse laser and a single-crystal SiC material, provided for an embodiment of the present invention. Figure 3 This is a structural diagram of the laser-modified and SS-OCT online monitoring system for single-crystal SiC provided in an embodiment of the present invention; Figure 4 A schematic diagram of the spatial characteristics and fracture morphology of crack nucleation in a laser-modified single-crystal SiC ingot provided in an embodiment of the present invention. Figure 5 The radial crack system induced by polymer glass transition under low-temperature impact in single-crystal SiC provided in this embodiment of the invention.

[0019] In the image, 1. Single-crystal SiC ingot; 2. Femtosecond laser; 3. Modified region; 4. Polymer; 5. SiC wafer; 6. Polishing pad; 7. Finished product; 8. Crystal lattice; 9. Electron; 10. Nanoscale pores and submicron microcrack networks; 11. Femtosecond laser; 12. Processing beam; 13. Digital micromirror device; 14. Dichroic mirror; 15. Objective lens; 16. Sample; 17. Three-axis moving platform; 18. White LED a; 19. Convex lens; 20. SS-OCT system; 21. Contrast beam; 22. White LED b; 23. CMOS image sensor; 24. CNN model; 25. Intact wafer; 26. Fragmented wafer. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0021] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0022] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0023] like Figure 1 As shown, this invention provides a schematic flowchart of a laser-modified and low-temperature shock-controlled peeling method for single-crystal silicon carbide wafers, specifically including the following processes: S1. Pre-treat the surface of the single-crystal SiC ingot 1 to form a machined surface with uniform roughness; S2. Set the initial laser parameters of the femtosecond laser 11 to perform a modification treatment on the interior of the single-crystal SiC ingot to form a modification region 3; The initial laser parameters of the femtosecond laser 11 are the pre-constructed laser parameters for inducing type II slip cracks; S3. Acquire real-time images of the modified region, monitor and optimize laser parameters using a swept-frequency optical coherence tomography method and a CNN model 24 to obtain the optimal laser parameters; The single-crystal SiC ingot is processed using the optimal laser parameters to induce the formation of a modified layer parallel to the surface of the ingot inside the single-crystal SiC ingot; The optimal laser parameters include wavelength, scanning speed, repetition frequency, pulse width, and single pulse energy.

[0024] S4. Coat the surface after laser modification with polymer 4, and pre-cool the single-crystal SiC ingot coated with polymer 4 in a low-temperature environment. S5. Apply a low-temperature impact load to the pre-cooled ingot to promote the propagation of type II cracks along the (0001) crystal plane of single crystal SiC, and obtain the peeled SiC wafer 5. S6. Remove the polymer 4 from the surface of the stripped SiC wafer 5, and then process it with a polishing pad 6 to obtain the finished product 7.

[0025] S7. Repeat S1-S6 to obtain multiple finished products 7.

[0026] A thick ingot can be peeled off into multiple wafers. After one wafer is peeled off, the remaining ingot can be recycled for further peeling.

[0027] The initial laser parameters of the femtosecond laser 11 are pre-constructed laser parameters for inducing type II slip cracks. These initial laser parameters are determined through single-factor experiments to induce type II slip cracks, avoid the formation of type I opening cracks, and prevent wafer warping or breakage. Even with a relatively reasonable parameter range determined in the early stages, dynamic adjustments are still necessary during actual processing to avoid processing risks.

[0028] The initial laser parameters of the femtosecond laser 11 are the pre-constructed laser parameters for inducing type II slip cracks. The initial laser parameters are: wavelength 1030 nm, pulse width 180 fs-12 ps, single pulse energy 3-20 μJ, repetition frequency 1 kHz-1 MHz, and scanning speed 0-100 mm / s.

[0029] The central cryogenic shock technology in S4 brings the interface between polymer 4 and SiC to the critical temperature for glass transition. By generating a radial temperature gradient field through a central cold source, low warpage peeling is achieved in the following ways: (1) Avoid stress concentration at the edges; (2) Radial crack paths are formed to release the internal stress of the crystal plane, so that the cracks can be nucleated from the center of the modified layer and propagate in a radial "radiating outward" mode; (3) Three-dimensional stress field redistribution compensates for the bending moment of conventional cold peeling process.

[0030] The radial temperature gradient field was constructed using a liquid nitrogen injection device; the temperature gradient range of the radial temperature gradient field was 3-15 K / mm, and the impact temperature was controlled between -196℃ and -50℃.

[0031] like Figure 2 As shown, a femtosecond laser 11 is used to perform a modification treatment inside the single-crystal SiC ingot 1. The specific modification mechanism is as follows: When the femtosecond laser 2 is focused inside the single-crystal SiC ingot 1, its ultrashort pulse characteristics make the interaction time between photons and the material much shorter than the thermal diffusion time of the lattice 8, thus achieving true non-thermal processing. Since single-crystal SiC is a wide-bandgap semiconductor, and the single-photon energy of the near-infrared femtosecond laser is insufficient to directly excite valence band electrons, nonlinear processes such as multiphoton absorption are required to achieve electron transitions. Under ultra-high laser intensity, electrons 9 transition from the valence band to the conduction band through multiphoton absorption or tunnel ionization, forming initial free electrons. These electrons are accelerated in the strong laser electric field, and the conduction band electron density increases exponentially through collisional ionization (avalanche effect). When the electron density 9 exceeds the critical plasma density, a local region of the material transforms into a plasma state, generating a plasma shielding effect that prevents laser energy from penetrating deeper into the material. Because the electron mass is much smaller than the ion mass, the electrons 9 in the plasma are rapidly heated and diffuse outwards, while positively charged ions remain in place due to inertia, leading to local charge separation and the formation of an extremely strong electrostatic field (Coulomb field). When the electric field strength exceeds the binding energy of the Si-C covalent bond, a Coulomb explosion occurs: ions are violently repelled under strong electrostatic repulsion, directly destroying the chemical bond and ultimately forming a nanoscale pore and submicron-scale microcrack network inside the material, thus achieving internal modification of single-crystal SiC.

[0032] like Figure 3As shown, the present invention provides a laser-modified SiC system with SS-OCT online monitoring, including a femtosecond laser 11, a digital micromirror device 13, a dichroic mirror 14, an objective lens 15, a three-axis moving platform 17, a white LED a18, a convex lens 19, an SS-OCT system 20, a white LED b22, a CMOS image sensor 23, and a CNN model 24.

[0033] The sample is fixed on the three-axis moving platform 17; the objective lens 15 is set above the sample 16, the dichroic mirror 14 is set above the objective lens 15, and the white LED light a 18 is set below the three-axis moving platform 17. The CMOS image sensor 23 is positioned in the refraction direction of one of the dichroic mirrors 14, and the CMOS image sensor 23 communicates with the CNN model 24. The dichroic mirror 14 is positioned in the reflection direction of the digital micromirror device 13; The convex lens 19 is positioned in the reflection direction of one of the dichroic mirrors 14, and the light path of the convex lens 19 is incident into the SS-OCT system 20.

[0034] The processing beam 12 output from the femtosecond laser 11 is first incident on the digital micromirror device 13, where the laser wavefront is spatially modulated by a preset holographic pattern. The modulated laser is then split by a dichroic mirror 14, and the main processing optical path is focused by a high numerical aperture objective lens 15 to a predetermined depth inside the single-crystal SiC sample 16, inducing nonlinear absorption to form a modified layer. The sample 16 is fixed on a high-precision three-axis moving platform 17, with a white LED a 18 integrated at the bottom of the platform. The backlight of the white LED a 18 is used to assist in surface morphology imaging. The split monitoring beam is reflected by the dichroic mirror 14, collimated by a convex lens 19, and then enters the SS-OCT system 20. An independent contrast beam 21 is incident on the white LED b 22 and simultaneously introduced into the SS-OCT system 20, interfering with the sample arm optical path. Simultaneously, a two-dimensional morphological image of the sample's modified layer is acquired through a CMOS image sensor 23 and spatially registered with SS-OCT data. After preprocessing to extract key features such as crack length, depth, and pore density, the image is fed into a CNN model 24 for analysis and processing to evaluate the similarity between the current crack morphology and an ideal transverse type II crack. The feedback control mechanism dynamically adjusts the output parameters of the femtosecond laser 11 based on the prediction results of the CNN model 24, achieving precise control of the femtosecond laser-modified single-crystal silicon carbide wafer.

[0035] The specific steps of the SS-OCT monitoring and CNN modulation include: S1. Obtain real-time images of the laser-modified region using SS-OCT and extract feature information; S2. Input the feature information and process parameters obtained by SS-OCT into the CNN model 24; S3 and CNN model 24 predict crack morphology based on pre-trained network weights and compare the similarity with the morphology of the ideal cleavage direction. S4. If the similarity is low, adjust the laser parameters in real time and reprocess until the similarity reaches 80% or higher.

[0036] Before its practical application, the CNN model 24 had already been trained and tested with a large amount of historical data, and it can predict crack morphology with relatively high accuracy.

[0037] like Figure 4 As shown, different laser parameter combinations result in significant differences in the morphology of the modified layer cracks formed within single-crystal silicon carbide. Type I cracks exhibit vertical propagation, which easily leads to brittle fracture of the wafer, resulting in fragmented wafer 26. In actual processing, their formation should be suppressed as much as possible through process parameter optimization. In contrast, Type II cracks exhibit ideal radial propagation behavior, with their propagation path parallel to the wafer cleavage plane, enabling controlled peeling of the intact wafer 25. Therefore, the core objective of process control is to maximize the formation probability of Type II cracks while minimizing the generation of Type I cracks.

[0038] like Figure 5 As shown, to address the warpage control problem in the processing of large-size single-crystal silicon carbide wafers, a center-loaded low-temperature impact technique is employed to control the radial propagation of cracks. Specifically, by applying a precisely controlled low-temperature impact load 27 to the central region of the wafer, the crack can be effectively induced to propagate directionally from the center to the outer edge, significantly reducing the overall stress distribution non-uniformity of the wafer and avoiding warpage deformation caused by edge stress concentration. This results in an ideal wafer with low warpage and a complete surface.

[0039] This invention proposes a center-point cold source loading technology, which applies precise low-temperature impact to the center of the wafer using a liquid nitrogen injection device. In the early stage of the low-temperature impact load, it is necessary to design the low-temperature impact path and control the interface stress. The bonding strength between the polymer and SiC and the critical conditions for glass transition under low-temperature impact are analyzed. The optimal temperature and the spatial path of the low-temperature load impact are controlled to construct a temperature gradient field that decreases from the center to the outer edge. This enables cracks to initiate from the center of the modified layer and propagate in a radial "outward radiation" mode, effectively reducing wafer warpage.

[0040] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0041] Example 1: 1. Grind the surface of a 6-inch single-crystal SiC ingot to a roughness Ra≤3 μm; 2. Linear scanning modification was performed using a femtosecond laser (wavelength 1030 nm, scanning speed 2 mm / s, pulse width 500 fs, repetition frequency 2 kHz); 3. Real-time monitoring by SS-OCT showed that the similarity between the morphology of the processed crack and the ideal crack was 75%, and the similarity was improved to 85% after adjusting the laser parameters using a CNN model. 4. After coating with a polyimide film (50 μm thick), the ingot is pre-cooled to -80°C and an impact pressure of 50 MPa is applied to the center to complete the wafer peeling under low temperature impact. 5. After stripping, the wafer warpage is <70 μm, the surface roughness Ra is <1 μm, and the remaining utilization rate reaches 90% after 10 cycles of ingot processing.

[0042] Example 2: During the cryogenic shock stage, a liquid nitrogen jet device was used to apply a -80°C cryogenic shock to the central region (5 mm in diameter) of a 6-inch wafer, maintaining a temperature gradient of 10 K / mm. The laser scanning path was optimized using a CNN model 24 to be a spiral progressive path. This verified that the crack propagated radially, forming a river-like Vanadium line morphology, reducing the warpage of the SiC wafer from 150 μm in conventional processes to below 70 μm.

[0043] Example 3: Using polyimide (CTE=50 ppm / ℃) as the interface layer, a glass transition at low temperature generates a tensile stress of 2.5 GPa. A liquid nitrogen spraying device (spraying rate 5 L / min) is used at the center of the single-crystal SiC wafer, reducing the temperature at the center point to -196℃ and the temperature at the outer edge to -80℃, forming a radially decreasing gradient field. The low-temperature impact gradient is increased to 15 K / mm, the crack propagation rate is stabilized at 0.8 mm / s, and the morphology of the Warner lines is river-like branching (in traditional processes, it is a disordered network). The peeling time is shortened to 60% of that of traditional processes, achieving stable and controllable peeling.

[0044] Example 4: 1. Laser modification of single-crystal SiC wafers (6 inches, 350 μm thick) (wavelength 1030 nm, pulse width 200 fs).

[0045] 2. At a single pulse energy of 7 μJ, a velocity of 5 mm / s, and a repetition frequency of 50 kHz, the proportion of type II slip cracks was 70%.

[0046] 3. After SS-OCT optimization and low-temperature impact peeling, the proportion of type II slip cracks increased to 95%, the chipping size of single crystal SiC decreased to 5 μm, the surface roughness Ra < 1 μm, and the wafer warpage was 55 μm.

[0047] Example 5: 1. A dynamic correlation model was established based on fracture mechanics. The thickness (350 μm), crystal orientation (0001), and elastic modulus of the polymer (epoxy resin 3.2 GPa) of the single-crystal 4H-SiC wafer were input to calculate the critical stress intensity factor K. II =1.8 MPa·m¹ / ².

[0048] 2. Monitor the crack propagation rate in real time. When the rate deviates from the theoretical value by ±10%, adjust the low-temperature impact path (from the central spiral outward expansion to the concentric circle path) to compensate for the stress field shift.

[0049] 3. For a 6-inch single-crystal SiC wafer with a thickness of 350 μm, the warpage is stable at ≤65 μm with a yield of 95%; when the thickness is extended to a wafer of 500 μm, the warpage is still controlled at 70 μm by increasing the laser power to 30 mW.

[0050] By using femtosecond lasers to induce a modified layer parallel to the crystal plane, and employing SS-OCT to acquire crack feature information in real time, the crack propagation trend is predicted using a convolutional neural network (CNN). The process parameters are dynamically adjusted to select the optimal parameter combination that induces type II slip cracks (propagating along the wafer surface) and suppresses the formation of type I opening cracks (perpendicular to the wafer surface), thus avoiding edge chipping and wafer breakage from the source and achieving directional peeling.

[0051] Improved material utilization and optimized wafer quality. Optimized laser parameters increased the processing efficiency of the modified layer by 40%, and the low-temperature impact path design reduced the peeling time to 50-60% of that of traditional processes. By precisely controlling the crack propagation path, material loss was reduced by 40%, and the utilization rate of single-crystal SiC ingots was significantly improved.

[0052] The system offers high real-time control precision and stability. By utilizing SS-OCT real-time monitoring and a CNN model for intelligent control of process parameters, precise control over crack nucleation and propagation is achieved, improving the stability and controllability of the processing.

[0053] The warpage of 6-inch single-crystal SiC is reduced to ≤70 μm, the surface roughness Ra≤1 μm, and the chipping size is controlled within 10 μm, meeting the stringent requirements for wafer flatness in high-end semiconductor devices. This avoids wafer breakage caused by Type I cracks, increasing the yield rate from over 95% compared to traditional processes.

[0054] It offers significant environmental and cost advantages. This method is applicable to single-crystal SiC wafers of varying thicknesses and crystal orientations. The central cryogenic shock technology is compatible with various polymer interface materials (such as polyimide and epoxy resin), expanding its application potential in the processing of third- and even fourth-generation semiconductors (gallium nitride, diamond, etc.). It can meet the needs of industry development and has promising application prospects.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for laser modification and low-temperature shock-controlled exfoliation of single-crystal silicon carbide, characterized in that, Includes the following steps: S1. Pre-treat the surface of the single-crystal SiC ingot to form a machined surface with uniform roughness; S2. Set the initial laser parameters of the femtosecond laser to perform internal modification treatment on the single-crystal SiC ingot to form a modified region; The initial laser parameters of the femtosecond laser are the pre-constructed laser parameters for inducing type II slip cracks; S3. Acquire real-time images of the modified region, monitor and optimize laser parameters using a swept-frequency optical coherence tomography method and a CNN model to obtain the optimal laser parameters; The single-crystal SiC ingot is processed using the optimal laser parameters to induce the formation of a modified layer parallel to the surface of the ingot inside the single-crystal SiC ingot; S4. Coat the surface of the modified layer with a polymer layer and pre-cool the single crystal SiC ingot. S5. Apply a low-temperature impact load to the pre-cooled ingot to promote the propagation of type II cracks along the (0001) crystal plane of single crystal SiC, and obtain the peeled SiC wafer. S6. Remove the polymer layer from the surface of the peeled-off SiC wafer and grind the surface of the peeled-off SiC wafer to obtain a finished product; S7. Repeat steps S1-S6 until the ingot processing is complete, resulting in multiple finished products.

2. The method for laser modification and low-temperature shock-controlled exfoliation of single-crystal silicon carbide according to claim 1, characterized in that, In S1, the surface of the single-crystal SiC ingot is pretreated, specifically by grinding and cleaning the surface of the single-crystal SiC ingot.

3. The method for laser modification and low-temperature shock-controlled exfoliation of single-crystal silicon carbide according to claim 1, characterized in that, In S2, the initial laser parameters of the femtosecond laser are: wavelength 1030 nm, pulse width 180 fs-12 ps, single pulse energy 3-20 μJ, repetition frequency 1 kHz-1 MHz, and scanning speed 0-100 mm / s.

4. The laser-modified and low-temperature shock-controlled exfoliation method for single-crystal silicon carbide according to claim 1, characterized in that, In S3, real-time images of the modified region are acquired, and laser parameters are monitored and optimized using a swept-frequency optical coherence tomography (OCT) method and a CNN model to obtain the optimal laser parameters; specifically... The process includes the following: Real-time images of the modified region were acquired using a swept-frequency optical coherence tomography system, and feature information was extracted. The feature information and initial laser parameters are input into the CNN model. The CNN model outputs the predicted crack morphology and compares the similarity with the morphology of the ideal cleavage direction. If the similarity is low, the laser parameters are adjusted in real time and the process is repeated until the similarity reaches or exceeds the preset similarity. The laser parameters that correspond to a similarity level that is above the preset similarity level are the optimal laser parameters.

5. The method for laser modification and low-temperature shock-controlled exfoliation of single-crystal silicon carbide according to claim 1, characterized in that, In S4, the pre-cooling temperature is -30℃ to -50℃.

6. The laser-modified and cryogenic shock-controlled exfoliation method for single-crystal silicon carbide according to claim 1, characterized in that, S5 specifically refers to generating a radial temperature gradient field through a central cold source, causing the polymer-SiC interface to reach the critical temperature for glass transition.

7. The method for laser modification and low-temperature shock-controlled exfoliation of single-crystal silicon carbide according to claim 6, characterized in that, The radial temperature gradient field was constructed using a liquid nitrogen injection device.

8. The laser-modified and low-temperature shock-controlled exfoliation method for single-crystal silicon carbide according to claim 6, characterized in that, The radial temperature gradient field has a temperature gradient range of 3-15 K / mm, and the impact temperature is controlled between -196℃ and -50℃.

9. A laser-modified and cryogenic shock-controlled exfoliation system for single-crystal silicon carbide, characterized in that, This includes processing systems, coating equipment, precooling equipment, cryogenic impact equipment, separation equipment, and grinding equipment; The processing system includes a femtosecond laser, digital micromirror device, dual-color mirror, objective lens, three-axis moving platform, white LED light, convex lens, SS-OCT system, white LED light, CMOS image sensor, and CNN model; The sample is fixed on a three-axis moving platform; The objective lens is positioned above the sample, the dichroic mirror is positioned above the objective lens, and the white LED light is positioned below the three-axis moving platform. The CMOS image sensor is positioned along the refraction direction of one of the dichroic mirrors, and the CMOS image sensor communicates with the CNN model. The dichroic mirror is positioned in the reflection direction of the digital micromirror device; A convex lens is positioned in the reflection direction of one of the dichroic mirrors, and the light path of the convex lens is incident on the SS-OCT system; The processing beam output from the femtosecond laser is incident on a digital micromirror device, which is used to spatially modulate the laser wavefront using a preset holographic pattern. The modulated laser is split by a dichroic mirror, and the main processing optical path is focused by the objective lens to a predetermined depth inside the single-crystal SiC sample, inducing nonlinear absorption to form a modified layer. The backlight of white LED a is used to assist in surface topography imaging; The monitoring beam after spectral dispersion is reflected by a dichroic mirror, collimated by a convex lens, and then enters the SS-OCT system; the independent contrast beam is incident on a white LED lamp b and then synchronously introduced into the SS-OCT system, forming interference with the sample arm optical path. A CMOS image sensor is used to acquire two-dimensional morphological images of the sample modification layer, which are then fed into a CNN model. A CNN model is used to extract features from a two-dimensional topography image, perform analysis and processing, and output a predicted crack morphology. It is then spatially registered with SS-OCT data to evaluate the similarity between the predicted crack morphology and the ideal cleavage direction morphology. Based on the similarity, the laser parameters are adjusted and optimized to obtain the optimal laser parameters. Coating equipment for coating a polymer layer onto the surface of a modified layer; Pre-cooling equipment is used for pre-cooling single-crystal SiC ingots; Low-temperature impact equipment is used to apply low-temperature impact loads to pre-cooled ingots to promote the propagation of type II cracks along the (0001) crystal plane of single-crystal SiC, thereby obtaining the peeled SiC wafers; Separation equipment used to remove the polymer layer; Grinding equipment is used to grind the surface of the stripped SiC wafers.

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