A high-efficiency low-loss grinding method for laser stripping 4H-SiC wafer
By using laser-directed refining and segmented grinding, the problem of surface inhomogeneity after laser lift-off of 4H-SiC wafers was solved, achieving efficient and low-loss grinding, and improving wafer processing quality and efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANDONG UNIV
- Filing Date
- 2025-06-20
- Publication Date
- 2026-07-24
AI Technical Summary
In existing technologies, the uneven surface and multi-layered structure of 4H-SiC wafers after laser lift-off lead to problems such as low grinding efficiency, high tool wear, and poor surface quality.
A release layer is formed by laser-directed modification, and ultrasonic-assisted separation is used to identify the laser-modified layer, structural transition layer and intrinsic SiC layer. A segmented grinding strategy is adopted, and the feed rate of different regions is set. Precision grinding is performed using a diamond grinding wheel.
This technology enables low-loss, high-efficiency grinding of 4H-SiC wafers, extends grinding wheel life, improves surface quality and processing stability, and reduces processing costs.
Smart Images
Figure CN120727557B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of wide bandgap semiconductor material wafer manufacturing technology, specifically to a high-efficiency, low-damage grinding method for laser lift-off of 4H-SiC wafers. Background Technology
[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.
[0003] 4H-silicon carbide (4H-SiC), as a typical representative of third-generation wide-bandgap semiconductor materials, has significant application value in high-voltage, high-power electronic devices, 5G communications, and new energy vehicles due to its high breakdown electric field (~3 MV / cm), high thermal conductivity (~490 W / m·K), and wide bandgap characteristics. However, the extremely high hardness (Mohs hardness 9.2~9.5) and brittleness of 4H-SiC make it difficult to process. Traditional mechanical cutting methods (such as diamond wire sawing) suffer from low cutting efficiency, high material loss, and easy subsurface damage, which seriously affect the wafer processing quality and device performance.
[0004] In recent years, laser-modified cutting technology has gradually become an emerging method for SiC wafer slicing due to its advantages such as non-contact operation, high efficiency, and low damage. This technology utilizes ultrafast lasers to induce a modified layer inside SiC, achieving wafer separation through mechanical or thermal stress assistance. However, the surface of laser-cut SiC wafers often suffers from problems such as uneven modified layers, microcracks, and residual stress, affecting the electrical performance and reliability of subsequent devices. Existing grinding methods do not differentiate the treatment of the layered structure characteristics of the wafer after laser slicing, leading to problems such as processing instability, residual surface damage, insufficient stress release, and rapid wear of the grinding wheel. Summary of the Invention
[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a highly efficient and low-loss grinding method for laser-lifted 4H-SiC wafers. This method solves problems such as uneven surface after laser lift-off, low grinding efficiency caused by multi-layered structures, high tool wear, and poor surface quality. It optimizes the grinding process of laser-lifted 4H-SiC wafers, achieving rapid removal of the surface modification layer while offering advantages such as low wear, low cost, and simplified polishing.
[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: This invention provides a highly efficient and low-damage grinding method for laser lift-off of 4H-SiC wafers, comprising the following steps: Laser is used to perform directional modification of the interior of 4H-SiC crystal to form a release layer, separating the wafer from the crystal; Microscopic observation was performed on the wafer after laser ablation to identify its laser-modified layer, structural transition layer, and intrinsic SiC layer. Based on the structural characteristics of different regions, the feed parameters for segmented grinding are set so that the feed rate of the laser-modified layer is greater than that of the intrinsic SiC layer, and precision grinding is performed using an automatic thinning device and a diamond grinding wheel.
[0007] In some embodiments, when grinding the laser-modified layer, the feed rate of the diamond grinding wheel is 0.6-1 μm / s; When grinding the structural transition layer, the feed rate of the diamond grinding wheel is 0.6-1 μm / s; When grinding the intrinsic SiC layer, the feed rate of the diamond grinding wheel is 0.2-0.5 μm / s.
[0008] Because different structural layers have significant differences in physical and mechanical properties, their sensitivities to grinding forces and thermal effects also vary. If a uniform feed rate is used, different structural layers cannot achieve optimal results, and in particular, it can easily increase the wear of the grinding wheel.
[0009] To address this issue, this invention employs a higher feed rate in the modified layer stage, enabling rapid traversal of the rough surface area of the modified layer and improving machining efficiency. In the intrinsic layer stage, the feed rate is reduced to precisely control the grinding force per unit area, suppressing microcrack propagation and stress concentration, and extending wheel life. This layered feed strategy achieves a match between machining parameters and material structural properties, effectively improving the stability of the grinding process, surface quality, and tool life.
[0010] Preferably, when grinding the laser-modified layer, the feed rate is 0.7-0.9 μm / s; When grinding the structural transition layer, the feed rate is 0.7-0.9 μm / s; When grinding the intrinsic SiC layer, the feed rate is 0.3-0.5 μm / s.
[0011] More preferably, when grinding the laser-modified layer, the feed rate is 0.8 μm / s; When grinding the structural transition layer, the feed rate is 0.8 μm / s; When grinding the intrinsic SiC layer, the feed rate is 0.4 μm / s.
[0012] In some embodiments, the laser is a femtosecond laser, a picosecond laser, or a nanosecond laser.
[0013] In some embodiments, the method of directional modification of the interior of 4H-SiC crystal using laser is as follows: The scanning path of a single laser is perpendicular to the (11-00) crystal plane of the 4H-SiC crystal; After a single scan is completed, the machine moves a set distance along a direction parallel to the (11-00) crystal plane and scans again to connect the cracks between adjacent scan paths. Repeat the above steps to complete the internal modification of the entire crystal.
[0014] In some embodiments, when separating the wafer from the crystal, ultrasonic assistance is used to propagate the modified cracks, thereby achieving the peeling of the wafer from the crystal.
[0015] In some embodiments, after grinding, the total thickness deviation (TTV), bow, warp, and residual stress on the wafer surface are measured and analyzed.
[0016] The silicon carbide crystal has a 4H single crystal structure and is suitable for wafer sizes from 6 inches to 12 inches.
[0017] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: This invention effectively controls crack propagation paths and achieves low-damage, high-integrity 4H-SiC wafer separation by combining laser-guided internal directional modification with ultrasonic-assisted exfoliation. By identifying the modified layer, structural transition layer, and intrinsic crystal region on the exfoliated surface, a segmented grinding strategy is tailored to avoid localized over-grinding and processing damage caused by traditional uniform grinding methods. Differentiated feed rates in different structural regions extend wheel life by approximately 40%, significantly reducing processing costs and improving overall processing efficiency. Simultaneously, this invention effectively releases residual stress on the wafer, significantly improving surface flatness and thickness uniformity, reducing the risk of warpage and breakage, and increasing the yield of subsequent device fabrication. Furthermore, this method is applicable to 4H-SiC wafers of different sizes from 6 inches to 12 inches, demonstrating good potential for large-scale manufacturing and widespread application. Attached Figure Description
[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0019] Figure 1 This is a schematic diagram of the process flow in an embodiment of the present invention; Figure 2 This is a schematic diagram of the overall process flow of the laser ablation and slicing technology of the present invention; Figure 3 The image shows the surface morphology of the segmented grinding process based on surface structure recognition in this invention, where (a1) is the original surface, (b1) is the surface after 20 μm removal, (c1) is the surface after 40 μm removal, and (d1) is the surface after 60 μm removal. Figure 4 The graph shows the relationship between the wear of the grinding wheel and the grinding time at different feed rates in different parts of the present invention. In this graph, (a) is the laser-modified layer, (b) is the structural transition layer, and (c) is the intrinsic SiC layer. Figure 5 The wafer surface profile (b) and stress distribution diagram (a) are shown after grinding with a 2000# grinding wheel in this invention.
[0020] Among them: 100, diamond grinding wheel; 101, silicon carbide crystal; 102, picosecond laser system; 103, modified crack; 104, wafer stripping; 105, stripping layer. Detailed Implementation
[0021] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0022] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.
[0023] Example 1 Reference Figure 1 This invention discloses an efficient and low-loss grinding optimization method for laser lift-off of 4H-SiC wafers, comprising the following steps: S1: Laser ablation process, using a picosecond laser system 102 with crystal transmission capability to perform directional modification treatment on the interior of silicon carbide crystal 101, forming a release layer 105 by laser-induced local structural changes, and promoting the expansion and penetration of modification cracks 103 under ultrasonic assistance, so as to achieve precise separation of the ablated wafer 104 from the remaining silicon carbide crystal 101.
[0024] refer to Figure 2 In this embodiment, the silicon carbide crystal 101 used is an 8-inch N-type crystal with a diameter of 200 mm.
[0025] The laser scanning path is set to be perpendicular to the (11-00) crystal plane of the 4H-SiC crystal. After a single laser processing is completed, a modified crack 103 is formed along the scanning direction. Then the worktable moves a set distance along the direction parallel to the (11-00) crystal plane and performs the next laser scan, so that adjacent modified cracks 103 are connected. The above steps are repeated to complete the internal modification of the entire crystal.
[0026] Furthermore, after laser modification is completed, silicon carbide crystal 101 is placed on an ultrasonic platform, and ultrasonic waves are used to promote the expansion and penetration of modification crack 103, ultimately peeling off a peeled wafer 104 with a thickness of approximately 650 μm.
[0027] S2: Surface structure identification and segmented grinding area division. Microscopic observation and surface analysis were performed on the laser-removed wafer 104. Based on the structural characteristics, the laser-modified layer, structural transition layer and intrinsic SiC layer were identified, and the grinding depth direction was divided into three different processing areas.
[0028] refer to Figure 3 In this embodiment, the depth range of the laser-modified layer, the structural transition layer, and the intrinsic SiC layer on the surface of the stripped wafer 104 is approximately 20 μm.
[0029] S3: Parameter setting and three-stage precision grinding. Based on the characteristics of different structural areas, the feed parameters for segmented grinding are set, and three-stage precision grinding is performed using an automatic thinning device and a diamond grinding wheel 100.
[0030] The other wafer samples obtained after peeling in step S1 are subjected to segmented grinding, with grinding settings referenced. Figure 4 The settings used in this embodiment are as follows: First interval (P1 stage, 20 μm removed), feed rate 0.8 μm / s; Second interval (P2 stage, 20 μm removed), feed rate 0.8 μm / s; The third interval (P3 stage, removing 20 μm) has a feed rate of 0.4 μm / s.
[0031] The grinding equipment used was a WG-1250 fully automatic twin-axis thinning machine manufactured by China Electronics Technology Group Corporation (CETC), paired with a 2000# resin-type diamond grinding wheel produced by Zhengzhou Abrasives & Grinding Research Institute Co., Ltd. (ZZSM).
[0032] S4: Processing result evaluation. By statistically analyzing grinding time and wheel wear, and combining a three-dimensional profilometer and stress analyzer to measure and analyze the total thickness deviation (TTV), bending, warp, and residual stress on the surface of the stripped wafer 104, a comprehensive evaluation of the processing efficiency and process stability at each stage is conducted.
[0033] refer to Figure 5 The test results of the stripped wafer 104 after being ground with a resin-type diamond 2000# grinding wheel until there were no laser processing marks on the surface are as follows: total thickness deviation (TTV) 5 μm, bending (Bow) 21.869 μm, warp (Warp) 34.777 μm, and maximum residual stress 15.33 Mpa.
[0034] The above results show that the embodiments of the present invention can effectively achieve high-quality wafer stripping, achieve efficient thinning guided by structure identification, effectively reduce tool wear while ensuring surface quality, and have excellent processing efficiency, surface quality and process stability, making them suitable for large-scale manufacturing applications.
[0035] Comparative Example 1 The difference from Example 1 is that traditional grinding processes typically do not consider the layering differences in the internal structure of the material, but instead use a uniform formula for continuous processing. In a conventional grinding path, the typical removal depths of P1, P2, and P3 are approximately 55 μm, 3 μm, and 2 μm, respectively, with smaller removal amounts in stages P2 and P3. The grinding feed rate generally follows a strategy of P1>P2>P3, with typical parameter configurations of 0.6 μm / s (P1), 0.4 μm / s (P2), and 0.2 μm / s (P3).
[0036] The total thickness deviation (TTV) was 5 μm, the bow was 26.439 μm, the warp was 40.963 μm, and the maximum residual stress was 17.42 MPa. Furthermore, there were significant differences between Example 1 and Comparative Example 1 in terms of processing efficiency and grinding wheel wear.
[0037] Example 1: The grinding time was approximately 8 minutes, and the grinding wheel wear was approximately 194 μm.
[0038] Comparative Example 1: Grinding time was approximately 17 minutes. Grinding wheel wear was approximately 444 μm.
[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A highly efficient and low-destruction grinding method for laser lift-off of 4H-SiC wafers, characterized in that: Includes the following steps: Laser is used to perform directional modification of the interior of 4H-SiC crystal to form a release layer, separating the wafer from the crystal; Microscopic observation was performed on the wafer after laser ablation to identify its laser-modified layer, structural transition layer, and intrinsic SiC layer. Based on the structural characteristics of different regions, the feed parameters for segmented grinding are set so that the feed rate of the laser-modified layer is greater than that of the intrinsic SiC layer, and precision grinding is performed using an automatic thinning device and a diamond grinding wheel. When grinding the laser-modified layer, the feed rate of the diamond grinding wheel is 0.6-1 μm / s; When grinding the structural transition layer, the feed rate of the diamond grinding wheel is 0.6-1 μm / s; When grinding the intrinsic SiC layer, the feed rate of the diamond grinding wheel is 0.2-0.5 μm / s.
2. The efficient and low-damage grinding method for laser lift-off of 4H-SiC wafers according to claim 1, characterized in that: When grinding the laser-modified layer, the feed rate is 0.7-0.9 μm / s; When grinding the structural transition layer, the feed rate is 0.7-0.9 μm / s; When grinding the intrinsic SiC layer, the feed rate is 0.3-0.5 μm / s.
3. The efficient and low-damage grinding method for laser lift-off of 4H-SiC wafers according to claim 2, characterized in that: When grinding the laser-modified layer, the feed rate is 0.8 μm / s.
4. The efficient and low-damage grinding method for laser lift-off of 4H-SiC wafers according to claim 2, characterized in that: When grinding the structural transition layer, the feed rate is 0.8 μm / s.
5. The efficient and low-damage grinding method for laser lift-off of 4H-SiC wafers according to claim 2, characterized in that: When grinding the intrinsic SiC layer, the feed rate is 0.4 μm / s.
6. The efficient and low-damage grinding method for laser lift-off of 4H-SiC wafers according to claim 1, characterized in that: The laser is a femtosecond laser, picosecond laser, or nanosecond laser.
7. The efficient and low-damage grinding method for laser lift-off of 4H-SiC wafers according to claim 1, characterized in that: The method for directional modification of the interior of 4H-SiC crystal using laser is as follows: The scanning path of a single laser is perpendicular to the (11-00) crystal plane of the 4H-SiC crystal; After a single scan is completed, the machine moves a set distance along a direction parallel to the (11-00) crystal plane and scans again to connect the cracks between adjacent scan paths. Repeat the above steps to complete the internal modification of the entire crystal.
8. The efficient and low-damage grinding method for laser lift-off of 4H-SiC wafers according to claim 1, characterized in that: When separating the wafer from the crystal, ultrasonic assistance is used to propagate the modified cracks, thereby achieving the peeling of the wafer from the crystal.
9. The efficient and low-damage grinding method for laser lift-off of 4H-SiC wafers according to claim 1, characterized in that: After grinding, the total thickness deviation, bending, warping and residual stress of the wafer surface are measured and analyzed.