A method of processing an edge high stress hard brittle semiconductor material

Abstract

The application provides a processing method for edge high-stress hard brittle semiconductor material, and belongs to the technical field of semiconductor material processing. The specific method is as follows: firstly, the silicon carbide crystal ingot with edge polycrystal and slit is circularly cut by laser in the area with edge polycrystal and slit. It should be noted that the circular cutting position needs to be carried out in the symmetric direction of the crystal ingot, so as to ensure the edge high-stress area, introduce mechanical stress, and release stress on both sides at the same time, thereby reducing the risk of crystal cracking. After laser cutting, the remaining part is removed by single line, wherein the single line feeding position is in the middle of the laser cutting, and then the crystal ingot is removed. Through the improved process of the application, the edge polycrystal and slit area are circularly cut by laser cutting, the edge high stress is isolated from extending inward by laser circular cutting, the cracking problem caused by the mechanical stress introduced by the subsequent single line removal is solved, and the crystal ingot is processed quickly, with low loss and low risk.

Description

Technical Field

[0001] This invention relates to the field of semiconductor material processing technology, and specifically to a method for processing semiconductor materials with high edge stress and brittleness. Background Technology

[0002] Currently, the common method for removing stress zones at the edges of crystal ingots is rounding, which involves using diamond grinding wheels to grind away the stress areas at the edges of the crystal ingots. However, this process is prone to causing crystal ingot cracking. Furthermore, the diamond grinding wheels required for rounding are consumables and are expensive, resulting in excessively high costs for the rounding process. In addition, the portion that is ground away during rounding is completely discarded, leading to significant material waste.

[0003] The formation of cracks in silicon carbide crystals is mainly related to two factors:

[0004] Thermal stress: During crystal growth or annealing, uneven temperature distribution can generate thermal stress within the crystal. When this thermal stress exceeds the material's tolerance threshold, it can trigger crack formation.

[0005] Internal defects: Defects inside the crystal, such as inclusions and dislocations, can also become sources of stress concentration. When the stress concentration reaches a certain level, it can also lead to crystal cracking.

[0006] The appearance of these cracks not only reduces the mechanical strength of silicon carbide crystals but may also affect their electrical properties, limiting their application in high-performance electronic devices. Therefore, controlling growth conditions, optimizing the annealing process, and employing advanced growth techniques to reduce internal stress and defects are key approaches to improving the quality of silicon carbide crystals.

[0007] SiC single crystals and substrates made therefrom exhibit high brittleness (or correspondingly low ductility). During multi-stage machining of bulk SiC crystals and the aforementioned SiC substrates, they are subjected to significant mechanical forces. In particular, cracks or fissures can readily form along preferred crystal cleavage planes (e.g., type 1 and 2 in 4H-SiC), leading to damage or destruction of the SiC semi-finished cylinders and / or substrates. Especially in machining processes where mechanical forces are applied radially (i.e., perpendicular to the outer diameter), the increased likelihood of cracking along cleavage planes results in cracks in the crystal and substrate, leading to undesirable yield reductions.

[0008] DE102009048868 describes a thermal post-treatment method for SiC crystals that allows for the reduction of stress in the crystal, thereby reducing the susceptibility of SiC crystals to cracking.

[0009] CN110067020A describes a method for reducing the inherent stress within a crystal that is present during production, which in turn reduces the crystal's susceptibility to cracking.

[0010] Patent CN118559900A provides a method for processing the edge high stress hard brittle semiconductor material, which realizes rapid and low loss cutting by using diamond single wire cutting machine and diamond curve cutting machine for partial cutting and complete cutting. However, this method will introduce mechanical stress in other cleavage direction of the crystal ingot. In the actual experiment process, we found that this implementation scheme cannot reduce the cracking rate.

[0011] Patent CN113957532A provides a single crystal 4H-SiC substrate with improved cleavage resistance and a production method thereof. The single crystal 4H-SiC substrate has improved mechanical robustness, and the force applied during production and machining of the outer surface of the 4H-SiC substrate has higher mechanical robustness. The implementation scheme is to distribute the external mechanical force on a plurality of equivalent parallel cleavage planes of the force line segment L per unit length to reduce or even eliminate the occurrence of cracks, regardless of the position around the entire periphery of the SiC semi-finished product to which such external mechanical force is to be applied. The scheme is theoretically perfect, but in actual operation, it will increase the complexity of mechanical manufacturing equipment, which is not conducive to low-cost batch processing.

[0012] Therefore, based on the principle of crystal ingot cracking, the edge high stress area is treated by laser cutting to prevent cracks from extending from the high stress area to the crystal ingot. After laser processing, the edge of the crystal ingot is processed by single wire, and the laser processing + single wire cutting method is used to achieve efficient, high yield and low cost processing results. SUMMARY

[0013] The technical problem to be solved by the present application is to solve the above-mentioned problems of the prior art, and a processing method for edge high stress hard brittle semiconductor material is provided, which specifically includes the following steps:

[0014] S1. Silicon carbide crystal ingot pretreatment;

[0015] S2. Laser annular cutting stress release;

[0016] S3. Single wire cutting and rod forming.

[0017] Specifically, the step S1 is to provide a silicon carbide crystal ingot containing a polycrystalline layer and slit defects on the edge, determine the distribution range of the polycrystalline region and slit defects by optical detection or X-ray diffraction, mark the symmetry axis and defect edge position of the crystal ingot; the crystal ingot needs to be fixed on a processing platform with multi-degree-of-freedom adjustment function to ensure that the cutting direction is perpendicular to the c-axis of the crystal ingot.

[0018] Preferably, the step S2 specifically includes:

[0019] S2.1. Cutting path planning: set annular cutting path at 2-5 mm from the edge of the defect along the circumferential direction of the crystal ingot, and the two cutting paths are symmetrically distributed on both sides of the crystal ingot axis;

[0020] S2.2. Synchronous cutting: the two laser heads cut along the symmetric paths in the opposite directions (one forward and one backward) synchronously;

[0021] S2.3. Stress release mechanism: the local thermal stress generated by the symmetric cutting cancels each other out in the crystal ingot, and blocks the crack from extending to the inside of the crystal ingot.

[0022] Preferably, the process parameters of the laser cutting are: wavelength 355-1064 nm, pulse energy 0-50 J / cm 2 , repetition frequency 1 kHz-2 MHz, pulse width 1-500 fs, pulse stability -3- +3, spatial uniformity ≤3%, overlap 30%-99%, scanning speed 10-2000 mm / s, and environment control argon / nitrogen.

[0023] The step S3 is: after the laser cutting is completed, the remaining part of the rod is processed by using a diamond single-wire cutting machine.

[0024] Preferably, the step S3 specifically includes:

[0025] S3.1. Tool entry positioning: the single wire cuts into the midpoint of the symmetric axis of the laser cutting area, the tool entry direction is perpendicular to the laser cutting surface, the initial feed speed is 0.1-0.5 mm / min, and the wire tension is 5-50 N;

[0026] S3.2. Annular cutting: progressive cutting is performed along the annular groove formed by the laser pre-cutting, the cutting line speed is 1-10 m / s, and the tension and feed speed are dynamically adjusted through a closed-loop control system, so that the cutting stress is concentrated on the pre-separation interface;

[0027] S3.3. Final forming: the cutting is performed to the target size, and a cylindrical silicon carbide crystal ingot with no polycrystalline residue on the surface and slit defect peeling is obtained, which can be directly used for subsequent slicing process.

[0028] Compared with the prior art, the present application achieves the following technical effects:

[0029] Through the improved process of the present application, the edge polycrystal and the slit area are annularly cut by laser cutting, the edge high stress is isolated from extending inward by laser annular cutting, the cracking risk caused by the mechanical stress introduced by the subsequent single-wire rod extraction is reduced, and the crystal ingot is quickly, low-loss and low-risk processed. BRIEF DESCRIPTION OF DRAWINGS

[0030] For ease of illustration, the present application is described in detail below with reference to the specific embodiments and drawings.

[0031] Figure 1 The schematic diagram of the silicon carbide crystal ingot with edge polycrystal and slit.

[0032] Figure 2 The schematic diagram of the laser cutting position.

[0033] Figure 3 The schematic diagram of the single-line cutting direction.

[0034] Figure 4 The figure of the defect-free crystal after direct rounding, without cracking.

[0035] Figure 5 The figure of the crystal after direct rounding of Comparative Example 1 with edge defects, cracking at the defect Figure 1 .

[0036] Figure 6 The figure of the crystal after direct rounding of Comparative Example 1 with edge defects, cracking at the defect Figure 2 .

[0037] Figure 7 The figure of the single-line cutting edge cracking of Comparative Examples 2-3, with the crack extending inward. DETAILED DESCRIPTION

[0038] The following is a specific embodiment of the present application and further describes the technical solutions of the present application in combination with the drawings, but the present application is not limited to these embodiments; in the following description, specific details such as specific configurations are provided only to help a comprehensive understanding of the embodiments of the present application. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present application.

[0039] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0040] The principle of laser + single-line cutting to reduce cracking: the edge defect area is a high stress area, and after direct introduction of mechanical stress, it is easy to crack towards the cleavage plane with slit / polycrystal, and the crack extends inward. By laser cutting, the high stress area is isolated from the wafer feeding area to prevent the crack from extending inward. Symmetric orientation synchronous laser cutting is adopted to uniformly release stress on the cleavage plane of the symmetric orientation, reduce the risk of cracking, and then single-line cutting from the laser cutting surface without abnormal area, and then circular cutting to obtain a wafer feeding size crystal ingot.

[0041] Example 1: Laser rod extraction + single-line cutting processing of 4H-SiC crystal ingot (diameter 150 mm)

[0042] As Figures 1-3 , step S1 (ingot pretreatment): a 4H-SiC ingot (diameter 150 mm) with edge polycrystalline layer and slit defects was provided, the defect distribution range was determined by X-ray diffraction, the ingot symmetry axis and defect edge position were marked, and the ingot was fixed on a six-degree-of-freedom machining platform, and the c-axis of the ingot was adjusted to be perpendicular to the cutting direction.

[0043] Step S2 (laser annular cutting stress release):

[0044] S2.1: two symmetric annular cutting paths (6 mm apart) were planned 3 mm away from the defect edge, and the paths were symmetrically distributed on both sides of the ingot axis.

[0045] S2.2: synchronous reverse cutting was performed using a double laser head (wavelength 1064 nm, pulse energy 30 J / cm², frequency 500 kHz, scanning speed 500 mm / s, argon environment).

[0046] S2.3: After cutting, the stress field of the ingot edge was uniformly released, and the crack propagation was limited within the laser cutting area.

[0047] Step S3 (single-wire cutting and rod forming):

[0048] S3.1: The diamond single-wire was perpendicular to the axis of the laser cutting area (feed speed 0.3 mm / min, wire tension 20 N).

[0049] S3.2: The wire was cut along the laser pre-cut groove ring (wire speed 5 m / s), the tension was dynamically adjusted to 30 N, and the feed speed was increased to 0.5 mm / min.

[0050] S3.3: A defect-free cylindrical ingot with a diameter of 142 mm was finally obtained, the surface polycrystalline layer was completely stripped, the total time consumption was 5.5 hours (laser cutting 1 hour, single-wire cutting 4.5 hours), and the material loss was 180 μm.

[0051] Effect: The ingot cracking rate is less than 5%, which can be directly used for slicing process.

[0052] Example 2: Processing of high-stress 6H-SiC ingot (diameter 200 mm)

[0053] Step S1: The ingot defect detection and fixation are the same as in Example 1, and the platform is adjusted to accommodate an 8-inch ingot. Step S2: The laser parameters are optimized to wavelength 355 nm (enhanced polycrystalline layer absorption), pulse energy 40 J / cm², frequency 1 MHz, scanning speed 300 mm / s, and nitrogen environment.

[0054] Step S3: Single wire initial feed rate 0.2 mm / min, wire tension 25 N, final gouging to a diameter of 190 mm ingot.

[0055] Result: Total time consumption 6 hours (laser 1.2 h, single wire 4.8 h), material loss 200 pm, cracking rate 4%.

[0056] Comparative Example 1: Defective Direct Spheroidization

[0057] Process: No pretreatment, directly spheroidized with diamond grinding wheel to 150 mm ingot, as shown in Figures 5-6 , the crystal with edge defects directly spheroidized, the defects cracked.

[0058] Result: Cracking rate 30-50%, slit defects induced radial cracks during spheroidization. Time consumption 1.5 hours, but material loss up to 4 mm (need to grind off all defect layer).

[0059] Comparative Example 2: Single Wire Cutting + Spheroidization

[0060] Process: Direct single wire cutting of the defect area and then spheroidization, as shown in Figure 7 , the cracks extended inward.

[0061] Result: Mechanical stress during single wire cutting caused 15-20% of the ingot to crack. Total time consumption 4 hours, material loss 380 pm.

[0062] Comparative Example 3: Single Wire Cutting Defects + Single Wire Gouging Ingot

[0063] Process: Stepwise single wire cutting of the defect area and then rod gouging, as shown in Figure 7 , the cracks extended inward.

[0064] Result: Cracking rate 15-20% when single wire cutting defects, total time consumption 9 hours (single wire cutting 2.5 h, rod gouging 6.5 h). Material loss 80 pm, but low efficiency and still at risk of cracking.

[0065] Table 1: Comparison of traditional processing and laser + single wire cutting

[0066] Indicator Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Cracking rate <5% <5% 30-50% 15-20% 15-20% Time (six inches) 5-6 h 5-6 h 1.5-2 h 3-5 h 8-10 h Material loss 150-200 μm 150-200 μm 3-5 mm 350-400 μm 20-100 μm

[0067] Those skilled in the art to which the present application pertains can make various modifications or supplements to the described specific embodiments or adopt similar ways to replace them, but will not deviate from the inventive concept of the present application or exceed the scope defined by the appended claims.

Claims

1. A method of processing an edge high stress hard brittle semiconductor material, characterized by, Specifically comprising the following steps: S1. Silicon carbide ingot pretreatment; S2. Laser annular cutting stress release; S3. Single-wire cutting rod extraction forming; The step S1 is specifically: providing a silicon carbide ingot with a polycrystalline layer and slit defects on the edge, determining the distribution range of the polycrystalline region and the slit defects by optical detection or X-ray diffraction, marking the symmetry axis of the ingot and the edge position of the defects; the ingot needs to be fixed on a processing platform with multi-degree-of-freedom adjustment function to ensure that the cutting direction is perpendicular to the c-axis of the ingot; The step S2 specifically comprises: S2.

1. Cutting path planning: set annular cutting paths at a distance of 2-5 mm from the edge of the defects along the circumferential direction of the ingot, and the two cutting paths are symmetrically distributed on both sides of the axis of the ingot; S2.

2. Synchronous cutting: double laser heads cut along the symmetric paths in opposite directions; S2.

3. Stress release mechanism: the local thermal stress generated by symmetric cutting cancels each other out in the ingot, blocking the crack from expanding into the ingot; The process parameters of the laser cutting are: wavelength 355-1064 nm, pulse energy 0-50 J / cm 2 , repetition frequency 1 kHz-2 MHz, pulse width 1-500 fs, pulse stability -3- +3, spatial uniformity ≤3%, overlap 30%-99%, scanning speed 10-2000 mm / s, and environment control argon or nitrogen; The step S3 is: after laser cutting, a diamond single-wire cutting machine is used for rod extraction processing of the remaining part.

2. The method of claim 1 wherein the hard and brittle semiconductor material is a gallium nitride based material. The step S3 specifically comprises: S3.

1. Tool positioning: the single wire cuts from the midpoint of the symmetric axis of the laser cutting area, the tool direction is perpendicular to the laser cutting surface, the initial feed speed is 0.1-0.5 mm / min, and the wire tension is 5-50 N; S3.

2. Annular extraction cutting: progressive extraction cutting is performed along the annular groove formed by laser pre-cutting, the cutting line speed is 1-10 m / s, and the tension and feed speed are dynamically adjusted by a closed-loop control system to concentrate the cutting stress on the pre-separation interface; S3.

3. Final forming: extract and cut to the target size to obtain a cylindrical silicon carbide ingot with no polycrystalline residue and slit defect peeling on the surface, which can be directly used for subsequent slicing process.

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