Method for optimizing geometric surface type of silicon carbide cutting blade

Abstract

The invention discloses a method for optimizing the geometric surface shape of a silicon carbide cutting blade, which comprises the following steps of: forming a low-hardness oxide layer on the surface of a crystal bar through chemical corrosion pretreatment, and inhibiting linear bow deformation in combination with dynamic cutting parameters (the table speed of an inlet / outlet knife edge is 1.5-2.0 mm / H, the rocking angle of a worktable is 2 degrees and the variable-speed rocking speed). The method comprises the following specific steps: corroding a crystal bar (nitric acid with the concentration of 5 mol / L, potassium permanganate with the concentration of 0.1 mol / L, EDTA with the concentration of 0.1 mol / L, and the temperature of 50-70 DEG C) with a chemical liquid, cleaning with high-purity water, bonding with glue ab, and cutting at The edge collapse height of the cutting piece is smaller than or equal to 5 micrometers, the cutting period is shortened by 20%, meanwhile, an optimization window is provided for the follow-up chamfering process, and the method is suitable for large-scale production of silicon carbide wafers.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide (SiC) wafer cutting and processing, and particularly relates to a method for optimizing the geometric surface shape of a SiC cutting wafer by combining chemical corrosion pretreatment with dynamic cutting parameter optimization, aiming to solve the problems of edge collapse, center bulge, and cutting trajectory deviation caused by wire mesh deformation during the traditional multi-wire cutting process. Background Art

[0002] In the field of semiconductor materials, SiC has excellent physical and chemical properties. SiC single crystal materials have properties such as a wide bandgap, high thermal conductivity, high electron saturation drift velocity, and high breakdown electric field, and are widely used in the manufacture of various electronic devices. However, during the multi-wire cutting process of SiC single crystals, many challenges are faced. The poor geometric surface shape of the cutting wafer has a continuous impact on subsequent SiC single crystal processing procedures, ultimately affecting the product quality of the single crystal substrate.

[0003] Currently, traditional SiC ingot cutting methods often have some problems. For example, when the wire mesh starts to contact the ingot during the cutting process, the ingot is driven downward by the workbench and has an extrusion force on the wire mesh. The wire mesh deforms under the action of the ingot force. At this time, a wire bow appears at the part where the wire mesh contacts the ingot. During the reciprocating movement of the wire mesh at the cutting point, a horizontal lateral movement will occur, that is, the wire mesh cannot cut into the SiC ingot at the ideal position at the cutting point. Although the cutting trajectory gradually returns to normal due to the constraint of the wire mesh tension during the subsequent deep cutting process, the cutting has deviated at the initial cutting point and is not in the same plane as the subsequent cutting trajectory. The overall cutting wafer will show the phenomenon of edge collapse and center bulge. This surface shape causes irreversible damage to the cutting wafer, and at the same time, the wafer surface shape cannot be repaired into a concave shape during subsequent SiC wafer processing procedures. Therefore, during the SiC ingot cutting and processing process, ensuring the geometric surface shape of the cut wafer, cutting stability, reducing unnecessary wafer loss, and improving the final product quality of SiC single wafers are the future development trends of SiC multi-wire cutting. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for optimizing the geometric surface shape of a SiC cutting wafer to solve the problems mentioned in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A method for optimizing the geometric surface shape of a SiC cutting wafer, comprising the following steps: (1)Chemical corrosion pretreatment: Immerse the circumferential surface of the silicon carbide crystal bar in a chemical solution for corrosion to form an oxide layer with a hardness lower than that of the original crystal. The chemical solution contains nitric acid, potassium permanganate, and ethylenediaminetetraacetic acid (EDTA), with a concentration of 5 mol / L for nitric acid, 0.1 mol / L for potassium permanganate, and 0.1 mol / L for EDTA. The corrosion temperature is 50°C - 70°C, the corrosion time is 20 min - 40 min, and the corrosion depth is 20 μm - 30 μm; (2)Cleaning and drying: Use primary reverse osmosis water with a resistivity ≥ 18.2 MΩ·cm to perform overflow and circulating cleaning on the corroded crystal bar, and then dry it with a nitrogen flow rate of 10 L / min - 20 L / min and a temperature of 40°C - 60°C; (3)Crystal bar bonding: Bond the cleaned silicon carbide crystal bar to the resin strip and the cutting plate with ab glue in a mixing ratio of 1:1, and cure for 2 hours to form an integral structure; (4)Cutting parameter adjustment: Invert and fix the bonded crystal bar on the cutting equipment, set the wire mesh speed to 900 m / min for reciprocating cutting, the table speed of the cutting table at the inlet and outlet is 1.5 mm / H - 2.0 mm / H, variable-speed cutting is used in the middle process, the rocking angle of the workbench is 2°, the rocking speed in the stable state is 300° / min, and the rocking speed at the inlet and outlet is reduced to 40° / min.

[0006] Preferably, the silicon carbide crystal bar is α-type silicon carbide, the diameter of the crystal bar is 150.25 mm ± 0.25 mm, the length is 15 mm - 35 mm, a polytetrafluoroethylene mask is used during the chemical corrosion process, the mask thickness is 300 μm - 500 μm, and the diameter is the same as that of the crystal bar.

[0007] Preferably, in step (1), the pH value of the chemical solution is 2.5 - 3.5, the corrosion process is carried out in a fume hood, the face wind speed of the fume hood is 0.7 m / s - 1.0 m / s, the exhaust air volume is 1200 m³ / h - 2400 m³ / h, and the air exchange rate is 12 - 15 times to maintain a negative pressure environment.

[0008] Preferably, in step (3), the mixing and coating environment temperature of the ab glue is 25°C, the environmental humidity is 30% - 70%, and when bonding, the silicon surface of the crystal bar faces the observer and the positioning edge faces left.

[0009] Preferably, in step (4), the variable-speed cutting parameters of the cutting table are adjusted by dynamically adjusting the matching relationship between the wire mesh tension and the cutting table speed to ensure that the deformation of the wire mesh when cutting into the crystal bar is ≤ 5 μm.

[0010] Preferably, in step (2), the cleaning equipment is equipped with a filter element filtration system and a pure water storage tank, and the pure water supply pressure is stable at 0.3 MPa - 0.5 Mpa during the circulating cleaning process.

[0011] Preferably, the hardness of the oxide layer is 30%-50% of the hardness of the original silicon carbide ingot, and the material removal rate of the circumferential surface of the ingot during the cutting process is increased by 20%-40%.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: Surface profile optimization: The edge collapse of the cutting sheet is reduced by 80%, and the central protrusion height ≤ 2μm.

[0013] Efficiency improvement: The cutting cycle is shortened by 18%-22%, and the production capacity is increased by 25%.

[0014] Process compatibility: The hardness of the oxide layer is reduced, and the subsequent chamfering process time is reduced by 30%. Description of the Drawings

[0015] Figure 1 is the flow chart of the chemical etching pretreatment and cutting parameter optimization of the present invention; Figure 2 is the schematic diagram of the collapse and protrusion caused by the bow deformation of the traditional cutting wire; Figure 3 is the schematic diagram of the bonding and positioning edge direction of the ingot (the silicon side faces left); In the figure: 1 actual defect contour, 2 ideal cutting contour, 3 reciprocating cutting wire mesh, 4 central protrusion, 5 collapse area, 6 cutting material plate, 7 yellow resin strip, 8 glue layer, 9 cutting direction, 10 specified silicon side direction. Detailed Embodiments

[0016] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0017] Please refer to Figure 1 , the present invention provides a technical solution: a method for optimizing the geometric surface profile of a silicon carbide cutting sheet, including the following steps: (1) Chemical etching pretreatment: Immerse and corrode the circumferential surface of the silicon carbide ingot with a chemical solution to form an oxide layer with a hardness lower than that of the original crystal. The chemical solution contains nitric acid, potassium permanganate, and ethylenediaminetetraacetic acid (EDTA), with a concentration of nitric acid 5mol / L, potassium permanganate 0.1mol / L, and EDTA 0.1mol / L. The etching temperature is 50°C - 70°C, the etching time is 20min - 40min, and the etching depth is 20μm - 30μm; (2) Cleaning and drying: The corroded ingot is subjected to overflow and circulating cleaning with primary reverse osmosis water having a resistivity ≥ 18.2 MΩ·cm, and then dried with a nitrogen flow rate of 10 L / min - 20 L / min and a temperature of 40°C - 60°C; (3) Ingot bonding: The cleaned silicon carbide ingot is bonded to the resin strip and the cutting stock plate with ab glue having a mixing ratio of 1:1, and cured for 2 hours to form an integral structure; (4) Cutting parameter adjustment: The bonded ingot is fixed upside down on the cutting equipment, the wire mesh speed is set at 900 m / min for reciprocating cutting, the table speed of the cutting table at the inlet and outlet is 1.5 mm / H - 2.0 mm / H, variable speed cutting is used in the intermediate process, the rocking angle of the workbench is 2°, the rocking speed is 300° / min in the stable state, and the rocking speed at the inlet and outlet is reduced to 40° / min.

[0018] The silicon carbide ingot is α-type silicon carbide, the ingot diameter is 150.25 mm ± 0.25 mm, the length is 15 mm - 35 mm, a polytetrafluoroethylene mask is used during the chemical corrosion process, the mask thickness is 300 μm - 500 μm, and the diameter is the same as that of the ingot.

[0019] In step (1), the pH value of the chemical solution is 2.5 - 3.5, the corrosion process is carried out in a fume hood, the face velocity of the fume hood is 0.7 m / s - 1.0 m / s, the exhaust air volume is 1200 m³ / h - 2400 m³ / h, the air exchange rate is 12 - 15 times, and a negative pressure environment is maintained.

[0020] In step (1), the pH value of the chemical solution is 2.5 - 3.5, the corrosion process is carried out in a fume hood, the face velocity of the fume hood is 0.7 m / s - 1.0 m / s, the exhaust air volume is 1200 m³ / h - 2400 m³ / h, the air exchange rate is 12 - 15 times, and a negative pressure environment is maintained.

[0021] In step (4), the variable speed cutting parameters of the cutting table are obtained by dynamically adjusting the matching relationship between the wire mesh tension and the cutting table speed to ensure that the deformation amount of the wire mesh when cutting into the ingot ≤ 5 μm.

[0022] In step (2), the cleaning equipment is equipped with a filter element filtration system and a pure water storage tank, and the pure water supply pressure is stable at 0.3 MPa - 0.5 Mpa during the circulating cleaning process.

[0023] The hardness of the oxide layer is 30% - 50% of the hardness of the original silicon carbide ingot, and the material removal rate on the circumferential surface of the ingot during cutting is increased by 20% - 40%.

[0024] Example 1: Cutting optimization under standard process parameters Ingot pretreatment: Take an α-SiC crystal bar with a diameter of 150.25 mm and a length of 25 mm, and cover the non-cutting area with a polytetrafluoroethylene mask (thickness 400 μm).

[0025] Immerse it in a mixed solution of nitric acid (5 mol / L), potassium permanganate (0.1 mol / L), and EDTA (0.1 mol / L), with pH = 3.0, temperature 60 °C, and corrode for 30 min to form a 25-μm oxide layer.

[0026] Cleaning and bonding: Use 18.2 MΩ·cm reverse osmosis water to circulate and clean for 10 min, and dry with nitrogen (flow rate 15 L / min, temperature 50 °C).

[0027] Mix 1:1 ab glue (ambient temperature 25 °C, humidity 50%), bond the crystal bar to the resin strip, with the positioning side facing left (see Figure 3 ).

[0028] Cutting parameters: The table speed at the entry cutting edge is 1.8 mm / H, the table speed at the exit cutting edge is 1.8 mm / H, and the table speed in the middle section is 1.2 mm / H.

[0029] The rocking angle of the workbench is 2°, the rocking speed in the stable section is 300 ° / min, and the rocking speed at the entry / exit cutting edges is 40 ° / min.

[0030] The wire mesh speed is 900 m / min, and the tension matching parameter ensures that the deformation of the wire mesh ≤ 5 μm.

[0031] Effect: The height of the edge collapse of the cutting disc is reduced from 15 μm in the traditional process to 3 μm, and the cutting cycle is shortened by 20%. Example 2: High-efficiency cutting with short corrosion time

[0032] Adjust the parameters: corrosion time 20 min, corrosion depth 20 μm, liquid medicine temperature 70 °C.

[0033] Cutting parameters: the table speed at the entry cutting edge is 2.0 mm / H, the table speed at the exit cutting edge is 2.0 mm / H, and the table speed in the middle section is 1.5 mm / H.

[0034] Effect: Suitable for high-production-demand scenarios, the cutting cycle is shortened by 22%, and the surface shape accuracy maintains an edge collapse ≤ 5 μm. Example 3: Optimization of large-size crystal bar cutting

[0035] Crystal bar parameters: diameter 150.5 mm, length 35 mm.

[0036] Corrosion parameters: liquid medicine pH = 2.5, corrosion for 40 min, mask thickness 500 μm.

[0037] Cutting parameters: The rocking speed of the cutting edge is 30° / min, and the wire mesh tension is increased by 10%.

[0038] Effect: The flatness uniformity of the cutting surface of large-sized wafers is improved, and the central convex height ≤ 1.5 μm. Example 4: Environmentally friendly process for low-concentration liquid medicine

[0039] Adjustment of liquid medicine: The concentration of nitric acid is 3 mol / L, the concentration of EDTA is 0.05 mol / L, and the etching time is extended to 50 min.

[0040] Optimization of cleaning: The supply pressure of pure water is 0.5 MPa, and the precision of the circulation filter element is 0.1 μm.

[0041] Effect: The discharge of chemical waste liquid is reduced by 30%, and the flatness accuracy is equivalent to that of the traditional process. Example 5: Process for adapting to high-humidity environment

[0042] Environmental adjustment: The mixing humidity of ab glue is 70%, and the drying temperature of nitrogen is 60 °C.

[0043] Cutting parameters: The wire mesh speed is reduced to 850 m / min, and the table speed is reduced by 10%.

[0044] Effect: Suitable for the high-humidity workshop environment, the bonding strength is increased by 15%, and the cutting yield ≥ 98%.

[0045] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made in these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for optimizing the geometric surface shape of a silicon carbide cutting disc, characterized in that, It includes the following steps: (1) Chemical corrosion pretreatment: Immerse the circumferential surface of the silicon carbide crystal bar in a chemical solution for corrosion to form an oxide layer with a hardness lower than that of the original crystal. The chemical solution contains nitric acid, potassium permanganate, and ethylenediaminetetraacetic acid (EDTA), with a concentration of 5 mol / L for nitric acid, 0.1 mol / L for potassium permanganate, and 0.1 mol / L for EDTA. The corrosion temperature is 50°C - 70°C, the corrosion time is 20 min - 40 min, and the corrosion depth is 20 μm - 30 μm; (2) Cleaning and drying: Use primary reverse osmosis water with a resistivity ≥ 18.2 MΩ·cm to perform overflow and circulation cleaning on the corroded crystal bar, and then dry it with a nitrogen flow rate of 10 L / min - 20 L / min and a temperature of 40°C - 60°C; (3) Crystal bar bonding: Bond the cleaned silicon carbide crystal bar to the resin strip and the cutting plate with ab glue in a mixing ratio of 1:1, and cure for 2 hours to form an integral structure; (4) Cutting parameter adjustment: Invert and fix the bonded crystal bar on the cutting equipment. Set the wire mesh speed to 900 m / min for reciprocating cutting. The table speed of the cutting table at the inlet and outlet is 1.5 mm / H - 2.0 mm / H. Variable-speed cutting is used in the middle process. The rocking angle of the workbench is 2°, and the rocking speed is 300° / min in the stable state, and the rocking speed at the inlet and outlet is reduced to 40° / min.

2. A method for optimizing the geometric surface shape of a silicon carbide cutting disc according to claim 1, characterized in that The silicon carbide crystal bar is α-type silicon carbide, with a crystal bar diameter of 150.25 mm ± 0.25 mm and a length of 15 mm - 35 mm. During the chemical corrosion process, a polytetrafluoroethylene mask is used, with a mask thickness of 300 μm - 500 μm and a diameter consistent with that of the crystal bar.

3. A method for optimizing the geometric surface profile of a silicon carbide cutting disc according to claim 1, characterized in that, In step (1), the pH value of the chemical solution is 2.5 - 3.

5. The corrosion process is carried out in a fume hood. The face wind speed of the fume hood is 0.7 m / s - 1.0 m / s, the exhaust air volume is 1200 m³ / h - 2400 m³ / h, and the air exchange rate is 12 - 15 times to maintain a negative pressure environment.

4. A method for optimizing the geometric surface profile of a silicon carbide cutting disc according to claim 1, characterized in that In step (3), the mixing and coating environment temperature of the ab glue is 25°C, and the environmental humidity is 30% - 70%. When bonding, the silicon surface of the crystal bar faces the observer and the positioning edge faces left.

5. A method for optimizing the geometric surface shape of a silicon carbide cutting disc according to claim 1, characterized in that, In step (4), the variable-speed cutting parameters of the cutting table are adjusted by dynamically adjusting the matching relationship between the wire mesh tension and the cutting table speed to ensure that the deformation amount of the wire mesh when cutting into the crystal bar is ≤ 5 μm.

6. A method for optimizing the geometric surface shape of a silicon carbide cutting blade according to claim 1, characterized in that, In step (2), the cleaning equipment is equipped with a filter element filtration system and a pure water storage tank. During the circulating cleaning process, the pure water supply pressure is stable at 0.3 MPa - 0.5 Mpa.

7. A method for optimizing the geometric surface shape of a silicon carbide cutting disc according to claim 1, characterized in that, The hardness of the oxide layer is 30% - 50% of the hardness of the original silicon carbide crystal bar, and the material removal rate of the circumferential surface of the crystal bar during cutting is increased by 20% - 40%.

Images