Silicon carbide wafer polishing method based on hot gas assistance and application

Abstract

The invention discloses a silicon carbide wafer polishing method based on hot gas assistance and application, and relates to the technical field of semiconductor material processing. The polishing method comprises the steps of gas grinding, fine grinding and chemical mechanical polishing of the silicon carbide wafer. In the gas grinding process, compressed gas in the heating area is sprayed out in the form of gas flow through the spraying area, and after the sprayed gas flow carries a grinding medium to enter the grinding area, the gas flow is sprayed to the to-be-ground face of the silicon carbide wafer for grinding treatment. Through the synergistic effect of the temperature, the air flow and the grinding medium, grinding of the to-be-ground face of the silicon carbide wafer is achieved, and the grinding effect of high removal amount is achieved. According to the method, SiC is subjected to fine grinding and chemical mechanical polishing, the whole process is implemented, the optimal balance point is found between efficiency and quality, the method has the advantages of being high in product yield and low in grinding cost, and large-scale application of SiC in the fields of new energy, 6G communication, aerospace, national defense and the like is expected to be promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor material processing, and in particular, to a polishing method and application of a silicon carbide wafer based on hot gas assistance. Background Art

[0002] As a wide-bandgap semiconductor material, silicon carbide (SiC) has excellent properties such as high breakdown electric field, high thermal conductivity, and high electron saturation drift velocity, and thus has broad application prospects in the fields of power electronic devices, radio frequency devices, and high-temperature devices. As a key substrate material for manufacturing these devices, the surface quality, crystal integrity, and subsequent device performance of silicon carbide wafers are directly affected by the surface treatment process.

[0003] In the prior art, the surface treatment of silicon carbide wafers mainly relies on methods such as mechanical grinding and chemical mechanical polishing (CMP). Although mechanical grinding has a high removal rate, it is easy to cause damage to the surface and subsurface of silicon carbide during the processing, such as cracks and defects, thereby affecting the crystal integrity and device performance of the wafers. On the other hand, although chemical mechanical polishing can obtain better surface quality, its removal efficiency is low, and the chemical reagents used may pose hazards to the environment and the health of operators. Therefore, the existing grinding methods for silicon carbide wafers generally have the problem of low efficiency, which seriously hinders the large-scale application and popularization of silicon carbide-based devices.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a polishing method and application of a silicon carbide wafer based on hot gas assistance to solve the above technical problems.

[0006] The present invention is implemented as follows:

[0007] In a first aspect, an embodiment of the present invention provides a polishing method of a silicon carbide wafer based on hot gas assistance, and the polishing method includes the following steps: gas grinding, fine grinding, and chemical mechanical polishing of the silicon carbide wafer;

[0008] Among them, the gas grinding includes:

[0009] The compressed gas in the heating zone is ejected in the form of an air flow through the ejection zone. After the ejected air flow carries the grinding medium into the grinding zone, it is ejected onto the surface to be ground of the silicon carbide wafer for grinding treatment;

[0010] Among them, the temperature of the compressed gas is 200°C - 400°C; the incident angle of the nozzle relative to the surface to be ground of the silicon carbide wafer is 80° - 100°; the amount of the grinding medium in the ejected gas per unit time and unit volume is 15 g - 30 g.

[0011] In a second aspect, an embodiment of the present invention provides an application of a silicon carbide wafer prepared by the polishing method as described above in at least one of the following fields, including new energy, 6G communication, aerospace and national defense, and semiconductor devices.

[0012] The present invention has the following beneficial effects:

[0013] In the polishing method of a silicon carbide wafer based on hot gas assistance provided by an embodiment of the present invention, after the heating zone heats the compressed gas, the injection zone carries the abrasive medium at a supersonic flow rate to jointly form a grinding zone, realizing the grinding treatment of the surface to be ground of the silicon carbide wafer; wherein, the heating zone promotes the weakening of the vibration of silicon carbide surface atoms, and the injection zone carries the abrasive medium to enhance the impact penetration ability of the grinding zone, thereby realizing low-damage and high-efficiency grinding of the silicon carbide wafer, achieving a grinding effect with a high removal rate; after precision grinding and chemical mechanical polishing, the implementation of the entire process finds the best balance between efficiency and quality, and has the characteristics of high product yield and low grinding cost, and is expected to promote the large-scale application of SiC in fields such as new energy, 6G communication, aerospace and national defense. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0015] Figure 1 It is a schematic structural diagram of the equipment used in the polishing method of a silicon carbide wafer based on hot gas assistance of the present invention;

[0016] Figure 2 It is a schematic diagram of the grinding process flow of a silicon carbide wafer based on hot gas assistance;

[0017] Figure 3 It is a polishing effect diagram of a silicon carbide wafer prepared by the polishing process of Example 1;

[0018] Figure 4 It is a polishing effect diagram of a silicon carbide wafer prepared by the process of Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0020] In a first aspect, an embodiment of the present invention provides a polishing method for a silicon carbide wafer based on hot gas assistance. The polishing method includes the following steps: gas grinding, fine grinding, and chemical mechanical polishing of the silicon carbide wafer;

[0021] Among them, gas grinding includes:

[0022] The compressed gas in the heating zone is ejected in the form of an air flow through the ejection zone. After the ejection air flow carries the grinding medium into the grinding zone, it is ejected onto the surface to be ground of the silicon carbide wafer for grinding treatment;

[0023] Among them, the temperature of the compressed gas is 200°C - 400°C; the incident angle of the nozzle relative to the surface to be ground of the silicon carbide wafer is 80° - 100°; the amount of the grinding medium in the ejected gas per unit time and unit volume is 15 g - 30 g.

[0024] It should be noted that the compressed gas is used as a carrier and is ejected in a supersonic air flow. After carrying the grinding medium, it is ejected onto the surface to be ground of the silicon carbide wafer, and grinding or polishing is achieved through high-speed impact; the combination of gas-solid two-phase flow ensures the uniform distribution and directional ejection of the grinding medium. Compared with liquid media, pneumatic conveying does not require subsequent drying steps and is suitable for dry grinding scenarios. Through high-speed kinetic energy transfer and low-temperature processing, high-efficiency and low-damage precision grinding of silicon carbide wafers is achieved, which is conducive to breaking through the bottleneck of traditional processes.

[0025] The present invention does not make special limitations on the type of gas in the compressed gas, and it can be reasonably selected according to actual needs, such as air, nitrogen, argon, helium, etc. In an optional embodiment of the present invention, the compressed gas selected is compressed air, which is easy to obtain and has a low cost, and can quickly provide a high-pressure air flow to meet the requirements of high-speed grinding.

[0026] In an optional embodiment, the heating temperature of the compressed gas is 120°C - 200°C.

[0027] It should be noted that in normal-temperature air flow-assisted grinding, the kinetic energy of the grinding medium is insufficient, and it is difficult to effectively break the SiC covalent bond. After heat treatment, slight oxidation or softening may occur on the SiC surface to generate SiO2, reducing the material hardness, making the grinding medium easier to cut and reducing surface scratches.

[0028] After heating, the volume of the compressed gas expands and its density decreases. After being accelerated through the nozzle, the gas flow rate becomes faster, which is conducive to enhancing the kinetic energy of the abrasive medium, making the impact force on the SiC surface greater, and thus improving the material removal rate. Appropriate heating can reduce the interfacial friction between the abrasive medium and the gas, reduce the hygroscopicity of the abrasive medium, reduce the agglomeration of the abrasive medium, make its distribution more uniform, and make the cutting more efficient. In addition, heating the gas can reduce the temperature difference when the SiC wafer contacts the abrasive medium, relieve the microcracks caused by thermal shock, and improve the surface integrity.

[0029] Compressed gas (such as air) may generate static electricity due to friction during high-speed spraying, resulting in the adsorption of abrasive medium and debris on the nozzle or wafer surface. Heating the compressed gas can reduce the accumulation of static electricity and prevent the nozzle from being blocked.

[0030] In an alternative embodiment, the spraying distance of the nozzle relative to the surface of the silicon carbide wafer to be ground is 150 mm - 200 mm.

[0031] It should be noted that the spraying distance of the nozzle determines the contact time and coverage density between the spraying air flow (carrying the abrasive medium) and the wafer surface. If the distance is too close and the spraying is fast, it may cause excessive local erosion, resulting in surface scratches or non-uniform removal, and triggering microcracks in the silicon carbide wafer. Although the local grinding efficiency can be improved, the risk of wafer damage increases and the yield decreases; if the distance is too far, the edge area of the wafer will be insufficiently ground due to the decrease in the flow rate of the spraying air flow, the abrasive distribution is uneven, and the effective material removal rate is reduced. Therefore, reasonably regulate the spraying distance of the nozzle relative to the surface of the silicon carbide wafer to be ground to ensure that the grinding fluid uniformly covers the surface and achieve a stable material removal rate and global planarization.

[0032] The spraying distance can be selected as any one of 150 mm, 160 mm, 170 mm, 180 mm and 200 mm according to actual needs, or other values within the range of 150 mm - 200 mm.

[0033] In an alternative embodiment, the working pressure of the spraying air flow is 0.3 MPa - 1 MPa; preferably 0.5 MPa - 0.8 MPa.

[0034] It should be noted that reasonable control of the working pressure is to maintain the stability of the air flow, avoid the deviation of the trajectory of the abrasive medium caused by turbulence, and affect the processing consistency; it is beneficial to balance the energy consumption loss and equipment maintenance cost. The setting of the working pressure directly affects the flow rate of the spraying air flow and the spraying stability. It can be selected as any one of 0.5 MPa, 0.6 MPa, 0.7 MPa and 0.8 MPa according to needs, or other values within the range of 0.5 MPa - 0.8 MPa.

[0035] If the working pressure is too high, it may cause the grinding medium to move too fast, collide violently with the SiC surface, resulting in microcracks, scratches or a subsurface damage layer (with a depth of up to several micrometers), affecting the device reliability (such as a decrease in the breakdown voltage of power devices); if the working pressure is too low, the air flow velocity is insufficient, the grinding medium is unevenly dispersed, local agglomeration or "air shooting" occurs, and the impact energy of the grinding medium is relatively low, which can achieve a smoother surface and shallower subsurface damage, being suitable for high-precision semiconductor devices.

[0036] In an alternative embodiment, the nozzle for injecting the jet air flow in the injection zone is selected from a Laval nozzle or a plug nozzle.

[0037] It should be noted that the present invention does not particularly limit the equipment used for grinding and can be selected according to actual needs. The schematic diagram of the equipment structure is as Figure 1 shown. In the embodiments of the present invention, the equipment used is a supersonic flame spraying equipment. When the supersonic air flow (with a speed generally ≥ 340 m / s) carries the grinding medium, the kinetic energy of the grinding medium increases with the square of the speed (E k = 1 / 2mv 2 ), and the impact force is significantly enhanced, which can quickly remove the SiC material and greatly improve the material removal rate.

[0038] In the injection zone, the air flow at the injection point accelerates the subsonic air flow to supersonic through a convergent-divergent structure or directly realizes supersonic air flow injection, and the nozzle used in the equipment can be reasonably adjusted according to the situation. To prevent the high-temperature deformation of the nozzle, a water-cooled sandwich layer needs to be provided for the nozzle.

[0039] It should be noted that the present invention is based on a method for polishing silicon carbide wafers assisted by hot gas, and the equipment is equipped with a chiller system, which precisely controls the temperature of the equipment or process, absorbs and transfers heat through circulating coolant, and ensures the stable operation of the system; among them, the circulating coolant is usually water or a water-based solution.

[0040] Under supersonic conditions, the air flow density decreases, the grinding medium is more dispersed, reducing the collision and agglomeration between the grinding media, avoiding surface scratches, and at the same time maintaining high-efficiency impact. In addition, for the supersonic injection of the air flow, its short contact time (in the microsecond level) reduces the accumulation of frictional heat between the grinding medium and the SiC surface, reduces the thermal stress damage, and precisely controls the surface roughness of the SiC wafer and the depth of the subsurface.

[0041] It should be noted that the realization of supersonic air flow will generate noise, so a muffler and the like need to be added to control the noise.

[0042] By effectively adjusting the working pressure of the air flow and the concentration of the grinding medium, the impact stress can be accurately controlled to avoid the lattice fracture or microcrack propagation of SiC.

[0043] In an alternative embodiment, in the jetting zone, the incident angle of the nozzle with respect to the silicon carbide wafer is 85° - 95°.

[0044] It should be noted that reasonable control of the incident angle can homogenize the surface topography of silicon carbide and reduce directional scratches. In the embodiments of the present invention, in combination with the working pressure in the jetting zone, the jetting speed of the gas flow and the incident angle of the gas flow are directly controlled to control the cutting direction and energy distribution of the abrasive medium, achieving a balance among grinding efficiency, quality, and damage control.

[0045] If the incident angle is too large, the kinetic energy is concentrated on a unit area, the cutting force is the largest, and the material removal rate (MRR) is high. It is easy to generate sharp scratches and subsurface microcracks on the surface to be ground, resulting in uneven surface topography and an increase in surface roughness (Ra) may occur; if the incident angle is too small, when the abrasive medium impacts obliquely, the cutting force is decomposed into normal and tangential components, and the normal force decreases. Although the cutting is smoother, the material removal rate decreases, the grinding process time is prolonged, and more energy is consumed.

[0046] In an alternative embodiment, the jetting moving speed is 20 mm / s - 40 mm / s;

[0047] and / or, the gas flow rate is 300 L / min - 400 L / min;

[0048] and / or, the oxygen flow rate is 200 L / min - 300 L / min;

[0049] and / or, the preheating temperature of the silicon carbide wafer is 100°C - 150°C.

[0050] It should be noted that the jetting moving speed is used to control the coverage frequency and contact time of the jetting gas flow (including the abrasive medium) on the wafer surface. An appropriate speed can optimize the abrasive cutting effect, reduce surface defects, and obtain a smoother surface. If the moving speed is too fast, the contact time between the abrasive and the wafer will be insufficient, reducing the removal efficiency; if the moving speed is too slow, surface scratches or non-uniform removal may occur due to excessive friction.

[0051] Reasonable control of the gas flow rate can ensure the uniform distribution of the abrasive medium, avoiding blockage or uneven local concentration. A too high flow rate may enhance the cutting effect but is prone to edge chipping; a too low flow rate will reduce the cutting efficiency.

[0052] An appropriate oxygen flow rate can accelerate the oxidation of the SiC surface to generate SiO2, reduce the material hardness, and thus improve the grinding efficiency.

[0053] Preheating the silicon carbide wafer can avoid wafer cracking caused by sudden temperature changes (especially crucial for SiC with high brittleness), ensure uniform temperature distribution across the entire wafer, and prevent local deformation or processing differences.

[0054] In an alternative embodiment, the material of the grinding medium is selected from at least one of diamond, cerium oxide, silicon carbide, and boron nitride.

[0055] Grinding media of each material have different characteristics, and can be reasonably selected according to actual precision requirements and process stage needs.

[0056] In the optimal embodiment of the present invention, diamond is used.

[0057] In an alternative embodiment, the amount of diamond grinding medium in the gas per unit time and per unit volume is 15 g - 30 g.

[0058] It should be noted that the amount of grinding medium in the gas per unit time and per unit volume directly affects the number of grinding media contacting the surface to be ground per unit time. If the amount of grinding medium is too much, the cutting times per unit time are too high, which is likely to form dense scratches or microcracks, and the material removal rate is greater; and too high an amount of grinding medium will accelerate nozzle wear and grinding medium breakage, increasing the consumable cost.

[0059] If the amount of grinding medium is too little and the cutting frequency is insufficient, the processing time will be prolonged, the equipment utilization rate will be reduced, and surface residual unremoved defects (such as cutting marks, oxide layers) may occur.

[0060] In an alternative embodiment of the present invention, the setting of the amount of diamond grinding medium in the gas per unit time and per unit volume is matched with parameters such as air flow pressure, temperature, nozzle design, etc. When the working pressure is high, the grinding medium concentration can be reduced to avoid nozzle blockage; when the working pressure is low, the grinding medium concentration needs to be increased to maintain efficiency.

[0061] It should be noted that in the embodiment of the present invention, according to the actual situation of silicon carbide wafer grinding, a method of periodically transporting the grinding medium for grinding can also be set, such as pneumatic pulse method, mechanical vibration method, feedback control method, etc. The device for regulating the periodic transport of the grinding medium is connected to the device for placing the grinding medium in the grinding area.

[0062] By intermittently transporting the grinding medium, it has the following characteristics: (1) enabling the grinding medium to be dispersed in the air flow for a longer time, reducing agglomeration and deposition, and prolonging the nozzle life; (2) reducing the electrostatic accumulation generated by the friction between the grinding medium and the air flow, avoiding the adsorption of the grinding medium on the wafer surface to form scratches or "agglomeration spots"; (3) avoiding the deepening of the subsurface damage layer depth of the workpiece caused by continuous high-energy collisions, which is beneficial to the reliability of the device during the period; (4) reducing the grinding medium breakage rate, reducing the risk of SiC oxidation or phase change, and reducing the consumable cost.

[0063] In an alternative embodiment, the particle size of the grinding medium is 5 μm - 12 μm; preferably 8 μm - 10 μm.

[0064] It should be noted that the selection of the particle size of the grinding medium is a key factor determining the material removal efficiency, surface quality, and process stability. Both too coarse and too fine particle sizes of the grinding medium will bring significant drawbacks, and a trade-off needs to be made according to specific process objectives.

[0065] If the grinding medium is too coarse, when it impacts the workpiece, it is easy to form deep scratches and pits, with a large surface roughness, making it difficult to meet the requirements of high-precision devices. If the over-grinding is balanced by reducing the amount of grinding medium per unit volume, the material removal rate may not meet the requirements; moreover, gas grinding media (especially diamond) are prone to deposit inside the nozzle in a high-pressure gas flow, resulting in an increased blockage frequency and frequent shutdowns for cleaning.

[0066] If the grinding medium is too fine, its kinetic energy is low when it impacts the workpiece, and the material removal rate per unit time is low, resulting in a significant extension of the processing time and poor economy; moreover, too fine grinding media may not be able to effectively remove the tiny defects (such as cutting marks, oxide layers) remaining from the previous process, or agglomerate into clusters, forming "secondary grinding media" in the gas flow, resulting in poor surface quality.

[0067] In an alternative embodiment, the silicon carbide wafer after gas grinding is sequentially subjected to fine grinding and chemical mechanical polishing;

[0068] Among them, fine grinding includes a polyurethane honeycomb grinding pad and diamond micropowder;

[0069] Chemical mechanical polishing includes potassium permanganate and nano-silica.

[0070] In an alternative embodiment, the material removal rate of the surface to be ground of the silicon carbide wafer is 0.1 μm / min - 3.5 μm / min.

[0071] It should be noted that a high material removal rate is beneficial for high-efficiency grinding of workpieces, but its surface roughness will also be relatively large, prone to subsurface damage, with high requirements for equipment, and nozzle blockages may occur frequently; while a low material removal rate can achieve precision polishing and reduce scratches on the workpiece surface, but the processing time is significantly extended, resulting in an increase in the comprehensive cost.

[0072] In an alternative embodiment, the surface roughness Ra of the ground silicon carbide wafer is < 60 nm.

[0073] It should be noted that a small surface roughness has the following characteristics: (1) It is beneficial to reduce the interface state density, thereby improving the channel mobility of the device, reducing the threshold voltage fluctuation, and reducing the leakage risk; (2) When used as an optoelectronic device, it is beneficial to reduce light scattering and improve the ultraviolet light absorption efficiency; (3) It can reduce the initiation of microcracks, improve the mechanical reliability of the wafer in extreme environments (such as high temperature and high stress), reduce subsequent processing steps, improve the yield, and extend the wafer life. (4) It is expected to meet the requirements of high-end application scenarios, such as providing an ideal substrate for high-quality SiC epitaxial layers.

[0074] In summary, the specific implementation steps of the polishing method of the silicon carbide wafer based on hot gas assistance provided by the embodiments of the present invention are as follows (for the process schematic diagram, see Figure 2 ):

[0075] (1) Equipment inspection:

[0076] Confirm that the components of the HVOF system (such as the combustion chamber, powder feeder, cooling system, control system) are in normal condition;

[0077] Check the pressures of the gas (H2 / C3H8) and oxygen supply pipelines (0.5 MPa - 1.5 MPa);

[0078] Verify the flow rate of the cooling water circulation system (≥10 L / min).

[0079] The specific settings of the remaining equipment parameters are shown in Table 1.

[0080] Table 1 Equipment setting parameters

[0081] Parameter Setting range Control key point Gas flow rate 300 - 400 (L / min) The best state is blue - violet supersonic flame Oxygen flow rate 200 - 300 (L / min) Maintain the oxygen - fuel ratio of (1.2 - 1.5):1 Powder feeding rate 15 - 30 (g / min·L) Match with the nozzle moving speed Spraying distance 150 - 20 (mm) Too close distance is likely to cause overheating of the substrate Spraying moving speed 20 - 40 (mm / s) The scanning interval is 5 - 10 (mm) overlap Wafer pre - heating temperature 100-150(℃) Real - time monitoring with an infrared thermometer

[0082] (2) Material preparation:

[0083] Pretreatment of the silicon carbide wafer: ultrasonic cleaning with acetone → rinsing with deionized water → drying with nitrogen.

[0084] Sandblasting roughening (Al2O3 sand, #60 grit, pressure 0.3 MPa, angle 80°), the steps are as follows:

[0085] ① First, load the Al2O3 powder and perform sandblasting roughening on the SiC surface. The function of sandblasting roughening is that during the processing and storage of the SiC wafer, a natural oxide layer (such as SiO2) or adsorbed contaminants (grease, dust) will be formed. It should be noted that sandblasting can completely remove these weak boundary layers and prevent the coating from peeling off due to interface contamination.

[0086] ② Perform preheating treatment on the SiC substrate wafer;

[0087] ③ Then reload the SiC abrasive and perform spraying;

[0088] ④ Immediately perform nitrogen cooling (5 - 10 minutes) after spraying is completed.

[0089] (3) Gas grinding operation process:

[0090] ① Start the system;

[0091] ② Turn on the cooling water system → Ignite the ignition flame → Gradually increase the fuel gas / oxygen to the working pressure;

[0092] (Pay attention to observing the flame shape: A stable supersonic flame should be blue and transparent.)

[0093] ③ Formal spraying:

[0094] Keep the spray gun at an angle of 10° - 60° with the surface of the silicon carbide wafer to be ground;

[0095] Adopt a reciprocating scanning path, with an overlap of 30% - 50% between adjacent paths;

[0096] Real - time monitoring: The temperature of the silicon carbide wafer (infrared temperature measurement, maintaining < 250°C).

[0097] (4) Fine grinding:

[0098] Use a honeycomb - shaped polyurethane grinding pad; The upper disk rotates at 1 rpm - 10 rpm, the lower disk rotates at 5 rpm - 25 rpm, and the pressure is 0.01 Kg / cm 2 - 0.16 Kg / cm 2 , and perform double - sided grinding with 3μm - 5μm diamond grinding fluid.

[0099] (5) Chemical - mechanical polishing:

[0100] The polishing liquid composition is an aqueous solution of potassium permanganate and nano - silica, where the mass ratio of silica is 1% - 5%; among them, the particle size of silica is 50 nm.

[0101] In a second aspect, an embodiment of the present invention provides an application of a silicon carbide wafer prepared by the polishing method as described above in at least one of the following fields, including new energy, 6G communication, aerospace and national defense, and semiconductor devices.

[0102] The features and performance of the present invention will be further described in detail below in conjunction with embodiments.

[0103] Example 1

[0104] This example provides a polishing method for silicon carbide wafers based on hot gas assistance, which includes the following implementation steps:

[0105] (1) Equipment inspection:

[0106] Confirm that the components of the HVOF system (such as combustion chamber, powder feeder, cooling system, control system) are in normal condition;

[0107] Check the pressures of the gas (H2 / C3H8) and oxygen supply pipelines (1.2 MPa);

[0108] Verify the flow rate of the cooling water circulation system (≥2 L / min).

[0109] For the setting of other equipment parameters, please refer to Table 2 for details.

[0110] Table 2 Equipment Parameters

[0111]

[0112]

[0113] (2) Material preparation:

[0114] Pretreatment of silicon carbide wafers: ultrasonic cleaning with acetone → rinsing with deionized water → drying with nitrogen.

[0115] Sandblasting roughening (Al2O3 sand, #60 grit, pressure 0.3 MPa, angle 80°), the steps are as follows:

[0116] ① First, load the Al2O3 powder and perform sandblasting roughening on the SiC surface. The function of sandblasting roughening is that during the processing and storage of SiC wafers, a natural oxide layer (such as SiO2) or adsorbed pollutants (grease, dust) will be formed. It should be noted that sandblasting can completely remove these weak boundary layers and prevent the coating from peeling off due to interface contamination.

[0117] ② Perform preheating treatment on the SiC substrate wafer;

[0118] ③ Then reload the SiC abrasive for spraying;

[0119] ④ Immediately cool with nitrogen (8 minutes) after spraying is completed.

[0120] (3) Gas grinding operation process:

[0121] ① Start the system;

[0122] ② Turn on the cooling water system → ignite the pilot flame → gradually increase the gas / oxygen to the working pressure;

[0123] (Pay attention to observing the flame shape: a stable supersonic flame should be blue and transparent)

[0124] ③ Formal spraying:

[0125] Keep the angle between the spray gun nozzle and the surface of the silicon carbide wafer to be ground at 90°;

[0126] Adopt a reciprocating scanning path with 40% overlap between adjacent paths;

[0127] Real-time monitoring: the temperature of the silicon carbide wafer (infrared temperature measurement, maintained at < 250 °C)

[0128] (4) Fine grinding:

[0129] Use a honeycomb polyurethane grinding pad; the upper platen rotates at 5 rpm, the lower platen rotates at 15 rpm, and the pressure is 0.09 Kg / cm 2 , and perform double-sided grinding with 3μm diamond grinding fluid.

[0130] (5) Chemical mechanical polishing:

[0131] The polishing fluid composition is an aqueous solution of potassium permanganate and nano-silica. Among them, the mass ratio of potassium permanganate, nano-silica and water is 7:90:3, and the particle size of silica is 50 nm.

[0132] Comparative Example 1

[0133] This comparative example provides a polishing method for silicon carbide wafers based on hot gas assistance. The difference in the implementation steps it includes compared to Example 1 is only that:

[0134] In the grinding area, the incident angle of the nozzle relative to the surface of the silicon carbide wafer to be ground is 10°.

[0135] Comparative Example 2

[0136] This comparative example provides a polishing method for silicon carbide wafers based on hot gas assistance. The difference in the implementation steps it includes compared to Example 1 is only that:

[0137] In the grinding area, the incident angle of the nozzle relative to the surface of the silicon carbide wafer to be ground is 15°.

[0138] Comparative Example 3

[0139] This comparative example provides a polishing method for silicon carbide wafers based on hot gas assistance. The difference in the implementation steps it includes compared to Example 1 is only that:

[0140] In the grinding area, the incident angle of the nozzle relative to the surface of the silicon carbide wafer to be ground is 45°.

[0141] Comparative Example 4

[0142] This comparative example provides a polishing method for silicon carbide wafers based on hot gas assistance. The difference in the implementation steps it includes compared to Example 1 is only that:

[0143] In the grinding area, the incident angle of the nozzle relative to the surface of the silicon carbide wafer to be ground is 60°.

[0144] Comparative Example 5

[0145] This comparative example provides a conventional polishing method for silicon carbide wafers, and its implementation steps are as follows:

[0146] (1) Rough grinding

[0147] Use a honeycomb polyurethane polishing pad; the upper platen speed is 3 rpm, the lower platen speed is 9 rpm, and the pressure is 0.13 Kg / cm 2 , and perform double-sided grinding with 5 μm diamond grinding fluid.

[0148] (2) Fine grinding:

[0149] Use a honeycomb polyurethane polishing pad; the upper platen speed is 5 rpm, the lower platen speed is 15 rpm, and the pressure is 0.09 Kg / cm 2 , and perform double-sided grinding with 3 μm diamond grinding fluid.

[0150] (3) Chemical mechanical polishing:

[0151] The polishing fluid composition is an aqueous solution of potassium permanganate and nano-silica. Among them, the mass ratio of potassium permanganate, nano-silica and water is 7:90:3, and the particle size of silica is 50 nm.

[0152] Test example 1

[0153] In this test example, the silicon carbide wafers prepared in Examples 1-7 and Comparative Example 1 were tested for material removal rate and surface roughness. In the relevant test methods, the calculation formula for the material removal rate is: material removal rate = (thickness of silicon carbide before grinding - thickness of silicon carbide after grinding) / time, where the thickness unit is μm and the time unit is min.

[0154] The test method for surface roughness is: use an AFM atomic force microscope to test the roughness of the wafer, and use a diamond-coated probe in contact mode to test the wafer.

[0155] The relevant test results are shown in Table 3.

[0156] Table 3 Test results

[0157]

[0158] It can be seen from the data in Table 1 that when the incident angle becomes larger or smaller, the surface roughness of the silicon carbide wafer becomes worse, and the TTV data also becomes worse. This is due to the irregular sputtering of high-speed abrasives at small incident angles, resulting in uneven action on the wafer surface.

[0159] Test example 2

[0160] This test example tests the surface structure of the silicon carbide wafers prepared in Example 1 and Comparative Example 1. The test instrument is KLA 8520 surface defect detection system.

[0161] The relevant SCN channel data pictures are shown in Figure 3 (Example 1) and Figure 4 (Comparative Example 1).

[0162] From Figure 3 and Figure 4 it can be seen that there are no scratches on the surface of Example 1, and the processing effect is uniform. However, in Comparative Example 1, there are some shallow scratches. This is because the sub-damage layer caused by traditional rough grinding machining is deeper. In contrast, the damage layer of the gas-assisted processing method is shallower and can be easily removed in subsequent processing. Therefore, there are no scratch phenomena in the final SCN channel image.

[0163] In summary, the polishing method provided by the embodiment of the present invention realizes the grinding of the surface to be ground of the silicon carbide wafer through the synergistic effect of the heating zone, the spraying zone and the grinding zone; for the polishing method of the silicon carbide wafer based on hot gas assistance, after the heating zone heats the compressed gas, the spraying zone and the diamond grinding medium are carried together at a supersonic flow rate to jointly form a grinding zone, realizing the grinding treatment of the surface to be ground of the silicon carbide wafer; wherein, the heating zone promotes the weakening of the vibration of the silicon carbide surface atoms, and the spraying zone and the grinding zone synergistically enhance the impact penetration ability of the diamond grinding medium, thereby realizing low-damage and high-efficiency grinding of the silicon carbide wafer and achieving a grinding effect with a high removal amount; after precision grinding and chemical mechanical polishing, the implementation of the entire process finds the best balance between efficiency and quality, and has the characteristics of high product yield and low grinding cost, and is expected to promote the large-scale application of SiC in the fields of new energy, 6G communication, aerospace and national defense.

[0164] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A hot gas assisted polishing method for silicon carbide wafers, characterized in that: The polishing method includes the following steps: gas grinding, fine grinding, and chemical mechanical polishing of the silicon carbide wafer; Among them, the gas grinding includes: The compressed gas in the heating zone is ejected in the form of an air flow through the ejection zone. After the ejected air flow carries the grinding medium into the grinding zone, it is ejected onto the surface to be ground of the silicon carbide wafer for grinding treatment; Among them, the temperature of the compressed gas is 200°C - 400°C; the incident angle of the nozzle relative to the surface to be ground of the silicon carbide wafer is 80° - 100°; the amount of the grinding medium in the ejected gas per unit time and unit volume is 15 g - 30 g.

2. The polishing method according to claim 1, wherein In the grinding zone, the ejection distance of the nozzle relative to the surface to be ground of the silicon carbide wafer is 150 mm - 200 mm.

3. The polishing method according to claim 1, wherein The working pressure of the ejected air flow is 0.3 MPa - 1 MPa; preferably 0.5 MPa - 0.8 MPa.

4. The polishing method according to claim 1, wherein The nozzle of the ejection zone is selected from a Laval nozzle or a plug nozzle.

5. The polishing method according to claim 1, wherein The ejection moving speed is 20 mm / s - 40 mm / s; and / or, the gas flow rate is 300 L / min - 400 L / min; and / or, the oxygen flow rate is 200 L / min - 300 L / min; and / or, the preheating temperature of the silicon carbide wafer is 100°C - 150°C.

6. The polishing method according to claim 1, wherein The material of the grinding medium is selected from at least one of diamond, cerium oxide, silicon carbide, and boron nitride.

7. The polishing method according to claim 1, characterized in that, The particle size of the grinding medium is 5 μm - 12 μm; preferably 8 μm - 10 μm.

8. The polishing method according to claim 1, wherein The silicon carbide wafer after gas grinding is sequentially subjected to fine grinding and chemical mechanical polishing; Among them, the fine grinding includes a honeycomb polyurethane grinding pad and diamond micropowder; The chemical mechanical polishing includes potassium permanganate and nano-silica.

9. The polishing method according to claim 1, wherein: After chemical mechanical polishing, the material removal rate of the surface to be ground of the silicon carbide wafer is 0.1 μm / min - 3.5 μm / min; and / or, the surface roughness Ra of the ground silicon carbide wafer is < 60 nm.

10. Use of a silicon carbide wafer obtained by the polishing method according to any one of claims 1 to 9 in at least one of the following fields, characterized in that: The fields include new energy, 6G communication, aerospace and national defense, and semiconductor devices.

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