A method for cleaning the surface of a silicon carbide wafer

Abstract

The application discloses a silicon carbide wafer surface cleaning method, which comprises the following steps: providing a geopolymer dispersion liquid; immersing a silicon carbide wafer with heavy metal ions and aluminum oxide particles adsorbed on the surface in the geopolymer dispersion liquid to remove the heavy metal ions on the surface of the silicon carbide wafer; irradiating the surface of the soaked silicon carbide wafer with picosecond laser or nanosecond laser to remove the aluminum oxide particles on the surface and the residual silicon-aluminum powder after soaking and cleaning; cleaning the surface of the silicon carbide wafer and drying to obtain a complete silicon carbide wafer surface, wherein the geopolymer dispersion liquid is prepared by the following method: mixing silicate and aluminate with an alkaline solution, stirring to obtain geopolymer slurry; solidifying the geopolymer slurry, grinding the geopolymer, and then mixing the geopolymer with a dispersing agent and water to obtain the geopolymer dispersion liquid; the cleaning method is environment-friendly and improves the cleanliness of the silicon carbide wafer surface.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor preparation, and particularly relates to a silicon carbide wafer surface cleaning method. BACKGROUND

[0002] Silicon carbide, as a material with excellent electronic and thermal properties, plays a crucial role in the fields of power electronics, radio frequency power devices, etc. In the production process of silicon carbide wafers, some contaminants are inevitably left on the surface, which often affects the processing quality and final performance of the wafers. In the manufacturing process of silicon carbide wafers, a "two-step" polishing process is often used to improve the surface quality. In the first step, potassium permanganate is used in combination with alumina abrasive particles for polishing (usually rough polishing) to remove larger surface defects; in the second step, hydrogen peroxide is used in combination with silica abrasive particles for polishing (usually fine polishing) to further improve the surface flatness and smoothness. After the first step of polishing, the alumina particles and manganese metal ions left on the surface of the silicon carbide wafer not only affect the processing quality of the second step of polishing, but also are adsorbed on the surface of the silicon carbide wafer, thereby posing potential risks to subsequent device manufacturing. In the current polishing process of silicon carbide wafers, after the first step of rough polishing, an acidic liquid and brushing are usually combined to remove surface contaminants. The acidic liquid can dissolve alumina particles and manganese metal ions through chemical reaction, especially manganese metal ions, which can be converted into soluble metal ions in an acidic environment, thereby achieving removal. Brushing uses mechanical friction to help alumina particles separate from the wafer surface through physical means, improving cleaning efficiency.

[0003] Although the cleaning method combining acidic liquid and mechanical brushing can effectively remove alumina particles and manganese metal ions from the surface of silicon carbide wafers, it still has many defects. First, acidic chemicals are highly corrosive, posing a threat to the health of operators and the safety of equipment. During use, temperature, concentration and ventilation conditions need to be strictly controlled, making the operation difficult and risky. Second, the large amount of acidic waste liquid generated during cleaning contains heavy metal ions and particulate matter, which is costly to treat and can cause environmental pollution if not properly disposed of. In addition, mechanical brushing relies on physical friction to remove particles, which can enhance cleaning efficiency but also risks introducing micro-scratches and damaging the wafer surface. Especially when the surface roughness of the silicon carbide wafer is already below 0.2 nm, secondary "defects" may form on the wafer surface after cleaning, which are difficult to remove during subsequent fine polishing and ultimately affect device performance. Therefore, the traditional cleaning method has problems such as poor cleaning quality stability, heavy environmental burden and high overall cost. SUMMARY

[0004] The present application aims to solve at least one problem in the prior art and proposes a silicon carbide wafer surface cleaning method.

[0005] To achieve the above object, the present application provides a silicon carbide wafer surface cleaning method, comprising the following steps:

[0006] Providing a geopolymer dispersion liquid;

[0007] Submerging the silicon carbide wafer with heavy metal ions and aluminum oxide particles adsorbed on the surface in the geopolymer dispersion liquid, and soaking the silicon carbide wafer in the geopolymer dispersion liquid at a pH of 11-13 and a temperature of 30-40°C to remove the heavy metal ions on the surface of the silicon carbide wafer;

[0008] Irradiating the surface of the soaked silicon carbide wafer with picosecond laser or nanosecond laser to remove the aluminum oxide particles on the surface of the silicon carbide wafer and the silicon-aluminum powder remaining on the surface after soaking and cleaning;

[0009] Cleaning the surface of the silicon carbide wafer with deionized water, drying, and obtaining a complete silicon carbide wafer surface;

[0010] The geopolymer dispersion liquid is prepared by mixing silicate and aluminate as precursors with an alkaline solution, stirring uniformly to obtain geopolymer slurry, and then solidifying the geopolymer slurry to form a three-dimensional network structure of geopolymer composed of AlO4 and SiO4 tetrahedral structural units, and then grinding and crushing the geopolymer, and mixing with dispersant and water to obtain the geopolymer dispersion liquid.

[0011] During the soaking and cleaning process, the three-dimensional network structure of the geopolymer will have a large number of negative charges in the alkaline environment, which can effectively adsorb positively charged metal ions such as manganese metal ions through electrostatic attraction, and form stable complexes, thereby achieving the removal of heavy metal ions on the surface of the silicon carbide wafer, and appropriately increasing the temperature of the geopolymer dispersion liquid is beneficial to cleaning, but too high temperature is not conducive to the stability of the geopolymer dispersion liquid, so the temperature is selected to be 30-40°C. The geopolymer can also remove Pb 2+ , Cu 2+ , Zn 2+ , Cd 2+ , Ni 2+ , Cr 3+ and other heavy metal ions through ion exchange adsorption.

[0012] In the laser cleaning process of irradiating the surface of the soaked silicon carbide wafer with picosecond laser or nanosecond laser, due to the obvious difference between the thermal expansion coefficient and thermal conductivity of the aluminum oxide particles and the silicon-aluminum powder and the silicon carbide wafer, such as the thermal expansion coefficient of the aluminum oxide is 1.5-1.8 times of that of the silicon carbide, after laser irradiation, the aluminum oxide particles and the silicon-aluminum powder rapidly heat up due to energy absorption, thermal expansion and thermal stress are generated, due to the low thermal conductivity, the heat is difficult to diffuse rapidly, resulting in local melting or expansion cracking inside, part of the particles may be instantaneously gasified or burst, while the silicon carbide wafer rapidly dissipates heat due to high thermal conductivity, and maintains stable structure, so that the instantaneous thermal effect and the photo pressure peeling effect induced by laser after laser irradiation make the aluminum oxide particles and the silicon-aluminum powder fall off from the surface of the silicon carbide wafer, and the surface of the silicon carbide wafer is not ablated, realizing non-contact, non-damage and high-efficiency cleaning, the process has thermodynamic selectivity and physical peeling mechanism, which significantly improves the cleaning accuracy and surface integrity. The laser width of the pulse laser is nanosecond or picosecond, the nanosecond laser can effectively penetrate the liquid layer and act on the surface particles; the picosecond laser can more accurately control the position of the beam focus, realizing high spatial selectivity cleaning, and the nanosecond laser is preferred in use, while other types of laser with pulse width such as femtosecond laser has extremely high cost, and other types of continuous wave laser is suitable for heat treatment and large-area preheating, and is not suitable for precise surface cleaning. The wavelength of the laser can be selected as 1064nm or 355nm or 532nm, preferably, the wavelength of the laser is selected as 355nm. The silicon carbide wafer has good light transmission in the visible light and infrared waveband, and the selective decontamination ability can be improved by selecting the waveband in which the wafer does not strongly absorb and the contaminant strongly absorbs.

[0013] As an optional embodiment, the solid-liquid ratio of the precursor and the alkaline solution is 1:(1-3), the precursor and the alkaline solution are mixed and then stand for 1-2 days, and the alkaline solution includes a sodium hydroxide solution or a potassium hydroxide solution.

[0014] As an optional embodiment, the precursor and the alkaline solution are uniformly stirred by using a high-speed blender after mixing, and the particle size of the precursor is 80-150μm.

[0015] As an optional embodiment, the geopolymer slurry is solidified at a temperature of 20-30℃, and the solidification time is 5-7 days.

[0016] As an optional embodiment, the particle size of the ground geopolymer powder is 100-200μm, and the dispersant includes at least one of polyvinyl alcohol, polyoxyethylene ether and polyacrylamide, by controlling the particle size of the geopolymer, the particle size of the geopolymer can be made as close as possible to the particle size of the aluminum oxide particles, so that the aluminum oxide particles and the silicon-aluminum powder can be better removed in the subsequent laser cleaning.

[0017] As an optional implementation, the silicon carbide wafer is immersed in the geopolymer dispersion liquid, and the geopolymer dispersion liquid is subjected to oscillation treatment by using an oscillator, and the oscillation frequency of the oscillator is 150 rpm-200 rpm, and the control in the oscillation frequency range is more conducive to cleaning and avoiding the breakage of the silicon carbide wafer, and the wafer will be broken if the oscillation frequency is too high.

[0018] As an optional implementation, the silicon carbide wafer is immersed in the geopolymer dispersion liquid, and the geopolymer dispersion liquid is subjected to oscillation treatment by using an oscillator, and the oscillation frequency of the oscillator is 150 rpm-200 rpm, and the control in the oscillation frequency range is more conducive to cleaning and avoiding the breakage of the silicon carbide wafer, and the wafer will be broken if the oscillation frequency is too high.

[0019] As an optional implementation, the nanosecond laser is generated by a nanosecond pulse laser, and the energy density of the nanosecond laser is 5 J / cm²-8 J / cm².

[0020] As an optional implementation, the picosecond laser is generated by a picosecond pulse laser, and the energy density of the picosecond laser is 0.4 J / cm²-0.8 J / cm².

[0021] As an optional implementation, the silicate includes at least one of sodium silicate, potassium silicate, and aluminum silicate, the aluminate includes at least one of sodium aluminate, potassium aluminate, and calcium aluminate, and the heavy metal ion includes a manganese ion.

[0022] The present application has the following beneficial effects: the present application adopts the geopolymer adsorption cleaning and laser cleaning technology linkage, can effectively remove the heavy metal ions, aluminum oxide particles and silicon-aluminum powder residues on the surface of the silicon carbide wafer, avoids introducing acidic chemicals in the cleaning process, reduces the operation safety hidden danger and the environmental pollution caused by waste liquid treatment, has higher environmental protection and lower processing cost, and the laser cleaning can accurately and effectively remove the aluminum oxide particles and the silicon-aluminum powder residues on the surface after soaking cleaning, realizes the effective cooperation with the geopolymer adsorption cleaning to solve the silicon-aluminum powder residue problem, and does not involve mechanical contact and does not introduce scratch risk, and the laser will not ablate the surface of the silicon carbide wafer, thereby maximizing the protection of the integrity of the surface of the silicon carbide wafer and improving the cleanliness of the surface of the silicon carbide wafer.

[0023] The features and advantages of the present application will be described in detail in conjunction with the embodiments and the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a process flow chart of an embodiment of the present application. DETAILED DESCRIPTION

[0025] In order to make the purposes, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application.

[0026] The present application will be described in detail below with reference to the drawings.

[0027] Embodiment 1

[0028] Referring to Figure 1 The present embodiment provides a silicon carbide wafer surface cleaning method, comprising the following steps:

[0029] S01 providing a geopolymer dispersion liquid;

[0030] S02 soaking and cleaning the silicon carbide wafer: completely immerse the silicon carbide wafer with heavy metal ions and aluminum oxide particles adsorbed on the surface in the above geopolymer dispersion liquid, and soak and react for 1 h under the condition of pH 12 and temperature 35℃. During the soaking process, the geopolymer dispersion liquid is treated by oscillation at a vibration frequency of 180 rpm by using an oscillator to remove the heavy metal ions on the surface of the silicon carbide wafer, and the heavy metal ions include manganese ions;

[0031] S03 laser cleaning of the silicon carbide wafer: irradiate the surface of the soaked silicon carbide wafer by using a pulsed laser with a wavelength of 355 nm and a pulse width of nanoseconds to remove the aluminum oxide particles on the surface of the silicon carbide wafer and the silicon-aluminum powder remaining on the surface after soaking and cleaning;

[0032] S04 cleaning the surface of the silicon carbide wafer with deionized water, drying, and obtaining a complete silicon carbide wafer surface;

[0033] The geopolymer dispersion liquid is prepared by the following method: mixing sodium silicate and sodium aluminate with a particle size of 150 μm as precursors with a sodium hydroxide solution at a solid-liquid ratio of 1:2, and then standing for 1 day, and then stirring uniformly by using a high-speed blender to obtain geopolymer slurry; after the above geopolymer slurry is solidified at room temperature of 25℃ for 6 days, the geopolymer with a three-dimensional network structure composed of AlO4 and SiO4 tetrahedral structural units is formed, and the geopolymer is ground and crushed into a powder with a particle size of 150 μm, and the powder, polyvinyl alcohol, and water are prepared into a geopolymer dispersion liquid by a high-energy ball milling method.

[0034] Embodiment 2

[0035] Referring to Figure 1 The present embodiment provides a silicon carbide wafer surface cleaning method, comprising the following steps:

[0036] S01 providing a geopolymer dispersion liquid;

[0037] S02 soaking cleaning silicon carbide wafer: the silicon carbide wafer with heavy metal ions and alumina particles adsorbed on the surface is completely immersed in the above geopolymer dispersion liquid, and the immersion reaction is carried out at a pH of 11 and a temperature of 40℃ for 2h. During the immersion process, the geopolymer dispersion liquid is treated by oscillation at a vibration frequency of 150 rpm using an oscillator to remove the heavy metal ions on the surface of the silicon carbide wafer, including manganese ions;

[0038] S03 laser cleaning silicon carbide wafer: the surface of the soaked silicon carbide wafer is irradiated by a pulsed laser with a wavelength of 355 nm and a pulse width of picoseconds to remove the alumina particles on the surface of the silicon carbide wafer and the silicon-aluminum powder remaining on the surface after soaking and cleaning;

[0039] S04 cleaning the surface of the silicon carbide wafer with deionized water, drying, and obtaining a complete silicon carbide wafer surface;

[0040] The geopolymer dispersion liquid is prepared as follows: potassium silicate and potassium aluminate with a particle size of 100 μm are mixed with sodium hydroxide solution at a solid-liquid ratio of 1:3, and then left to stand for 1 day. A high-speed blender is used to stir the mixture uniformly to obtain a geopolymer slurry. The geopolymer slurry is then solidified at room temperature of 30℃ for 5 days to form a geopolymer with a three-dimensional network structure composed of AlO4 and SiO4 tetrahedral structural units. The geopolymer is ground into a powder with a particle size of 100 μm. The powder is mixed with polyvinyl alcohol, polyoxyethylene ether and water by high-energy ball milling to obtain a geopolymer dispersion liquid.

[0041] Example 3

[0042] Referring to Figure 1 The present embodiment provides a method for cleaning the surface of a silicon carbide wafer, which comprises the following steps:

[0043] S01 providing a geopolymer dispersion liquid;

[0044] S02 soaking cleaning silicon carbide wafer: the silicon carbide wafer with heavy metal ions and alumina particles adsorbed on the surface is completely immersed in the above geopolymer dispersion liquid, and the immersion reaction is carried out at a pH of 11 and a temperature of 40℃ for 2h. During the immersion process, the geopolymer dispersion liquid is treated by oscillation at a vibration frequency of 150 rpm using an oscillator to remove the heavy metal ions on the surface of the silicon carbide wafer, including manganese ions;

[0045] S03 laser cleaning silicon carbide wafer: the surface of the soaked silicon carbide wafer is irradiated by a pulsed laser with a wavelength of 355 nm and a pulse width of picoseconds to remove the alumina particles on the surface of the silicon carbide wafer and the silicon-aluminum powder remaining on the surface after soaking and cleaning;

[0046] S04 washing the surface of the silicon carbide wafer with deionized water, drying, to obtain the complete silicon carbide wafer surface;

[0047] The geopolymer dispersion is prepared by the following method: potassium silicate, sodium silicate and potassium aluminate, magnesium aluminate with a particle size of 80 μm are used as precursors, mixed with sodium hydroxide solution at a solid-liquid ratio of 1:1, and then placed for 2 days, stirred uniformly using a high-speed blender, to obtain a geopolymer slurry; the geopolymer slurry is then cured at 20℃ for 7 days to form a geopolymer with a three-dimensional network structure composed of AlO4 and SiO4 tetrahedral structural units, the geopolymer is ground into a powder with a particle size of 100 μm, and the powder is mixed with polyvinyl alcohol, polyacrylamide and water by high-energy ball milling to obtain the geopolymer dispersion.

[0048] The above examples are illustrative of the present application and are not limiting of the present application, any simple modification or variation of the present application is considered to be within the scope of the present application.

Claims

1. A method for cleaning a surface of a silicon carbide wafer, comprising: The method comprises the following steps: providing a geopolymer dispersion liquid; immersing the silicon carbide wafer with heavy metal ions and aluminum oxide particles adsorbed on the surface in the geopolymer dispersion liquid, soaking and reacting at a pH of 11-13 and a temperature of 30-40°C to remove the heavy metal ions on the surface of the silicon carbide wafer; irradiating the surface of the soaked silicon carbide wafer with picosecond laser or nanosecond laser to remove the aluminum oxide particles on the surface of the silicon carbide wafer and the silicon-aluminum powder remaining on the surface after soaking and cleaning; cleaning the surface of the silicon carbide wafer with deionized water and drying to obtain a complete silicon carbide wafer surface; the geopolymer dispersion liquid is prepared by mixing silicate and aluminate as precursors with an alkaline solution, stirring uniformly to obtain a geopolymer slurry, and then solidifying the geopolymer slurry to form a three-dimensional network structure of geopolymer composed of AlO4 and SiO4 tetrahedral structural units, and then grinding and crushing the geopolymer and mixing with a dispersant and water to obtain a geopolymer dispersion liquid.

2. The method of claim 1, wherein: The solid-liquid ratio of the precursors to the alkaline solution is 1: (1-3), the precursors and the alkaline solution are mixed and left to stand for 1-2 days, and the alkaline solution comprises sodium hydroxide solution or potassium hydroxide solution.

3. The method of claim 1 or 2, wherein the silicon carbide wafer surface cleaning method is characterized by: The precursors and the alkaline solution are stirred uniformly after mixing using a high-speed blender, and the particle size of the precursors is 80-150 μm.

4. The method of claim 1, wherein: The geopolymer slurry is solidified at a temperature of 20-30°C for 5-7 days.

5. The method of claim 1 or 4, wherein: The particle size of the powder after grinding and crushing the geopolymer is 100-200 μm, and the dispersant comprises at least one of polyvinyl alcohol, polyoxyethylene ether, and polyacrylamide.

6. The method of claim 1, wherein: After the silicon carbide wafer is immersed in the geopolymer dispersion liquid, the geopolymer dispersion liquid is subjected to oscillation treatment using an oscillator, and the oscillation frequency of the oscillator is 150-200 rpm.

7. The method of claim 1 or 6, wherein the silicon carbide wafer surface cleaning method is characterized by: The silicon carbide wafer is immersed in the geopolymer dispersion liquid for 1-2 h for soaking and reacting.

8. The method of claim 1, wherein: The nanosecond laser is generated by a nanosecond pulsed laser, and the energy density of the nanosecond laser is 5-8 J / cm².

9. The method of claim 1, wherein: The picosecond laser is generated by a picosecond pulsed laser, and the energy density of the picosecond laser is 0.4-0.8 J / cm².

10. The method of claim 1, wherein: the silicon carbide wafer is a 4H-SiC wafer. The silicate comprises at least one of sodium silicate, potassium silicate, and aluminum silicate, the aluminate comprises at least one of sodium aluminate, potassium aluminate, and calcium aluminate, and the heavy metal ions comprise manganese ions.

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