Ultraviolet light catalysis assisted gallium nitride wafer polishing method

Abstract

The invention belongs to the technical field of semiconductor manufacturing, and particularly relates to an ultraviolet light catalysis assisted gallium nitride wafer polishing method which comprises the following steps: S1, fixing a ground and flushed gallium nitride wafer on a clamp of a polishing machine; s2, the sealed cabin of the polishing machine is vacuumized until the vacuum degree reaches a set vacuum degree threshold value, and then the sealed cabin is filled with oxygen until the pressure value of the oxygen in the sealed cabin reaches a set pressure threshold value; s3, an ultraviolet lamp and a heater are turned on, the ultraviolet lamp irradiates the polishing solution, the heater heats the polishing solution to a set temperature and keeps the temperature constant, and then the polishing machine is started to polish the gallium nitride wafer; and S4, cleaning the polished gallium nitride wafer. According to the method, the oxidation rate is increased, and the polishing efficiency of the gallium nitride wafer is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor manufacturing, and in particular to a gallium nitride wafer polishing method assisted by ultraviolet light catalysis. Background Art

[0002] Gallium nitride is a typical representative of the third-generation semiconductor materials. It has excellent physical and chemical properties, such as large bandgap, strong breakdown electric field, low on-resistance, high electron mobility, high conversion efficiency, high thermal conductivity, and low loss. It is widely used in communications, displays, lighting and other fields. It is one of the most promising third-generation semiconductor materials for high-power, high-frequency, and high-temperature applications, and has broad prospects for future development.

[0003] In recent years, chemical mechanical polishing has been widely used for global planarization of semiconductor wafers. Although the traditional chemical mechanical polishing method is effective, it often faces problems such as low processing efficiency and difficult to control surface quality. In order to further improve the processing efficiency and surface quality of semiconductor materials, ultraviolet photocatalysis technology has been introduced on the basis of traditional chemical mechanical polishing, and a chemical mechanical polishing method assisted by ultraviolet photocatalysis has been proposed. The chemical mechanical polishing method assisted by ultraviolet photocatalysis is an advanced surface treatment technology that combines ultraviolet photocatalysis technology with chemical mechanical polishing technology. This method uses ultraviolet light to irradiate the surface of the photocatalyst to produce hydroxyl radicals with strong oxidizing properties. These radicals can react chemically with the substances on the polishing surface to accelerate the oxidation decomposition and removal process of the material surface. However, the current chemical mechanical polishing method assisted by ultraviolet photocatalysis has the problem of low oxidation efficiency, resulting in very low polishing efficiency of gallium nitride wafers.

[0004] Therefore, based on the principle of ultraviolet photocatalytic polishing, a ultraviolet photocatalytically assisted gallium nitride wafer polishing method is proposed. Summary of the invention

[0005] The object of the present invention is to provide a gallium nitride wafer polishing method assisted by ultraviolet light catalysis to solve the problems raised in the background technology.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for polishing a gallium nitride wafer assisted by ultraviolet light catalysis, comprising the following steps:

[0008] S1: Fix the GaN wafer after grinding and washing on the fixture of the polishing machine;

[0009] S2: The sealed cabin of the polishing machine is evacuated until the vacuum degree reaches a set vacuum degree threshold, and then oxygen is filled into the sealed cabin until the pressure value of the oxygen in the sealed cabin reaches a set pressure threshold;

[0010] S3: Turn on the UV lamp and the heater, the UV lamp irradiates the polishing liquid, the heater heats the polishing liquid to a set temperature and maintains the temperature constant, and then start the polishing machine to polish the gallium nitride wafer;

[0011] S4: After polishing, the gallium nitride wafer is cleaned.

[0012] Preferably, in step S1, the gallium nitride wafer is grown from a HVPE self-stripping substrate, the gallium nitride wafer is ground using a grinder before polishing, the ground gallium nitride wafer is then rinsed with alcohol, and then the ground and rinsed gallium nitride wafer is fixed on a fixture of the polisher.

[0013] Preferably, step S1 comprises the following steps:

[0014] S11: Use paraffin wax to stick the GaN wafer to the quartz glass plate to complete the bonding;

[0015] S12: grinding the gallium nitride wafer attached to the quartz glass plate using a grinder;

[0016] S13: using alcohol to rinse the combination of the quartz glass plate and the ground gallium nitride wafer;

[0017] S14: Fixing the combination of the rinsed quartz glass plate and the ground gallium nitride wafer on a fixture of a polishing machine by vacuum adsorption.

[0018] Preferably, in step S2, the vacuum threshold is set to -0.1 MPa, and the pressure threshold is set to 40 KPa.

[0019] Preferably, step S2 comprises the following steps:

[0020] S21: extracting air from the sealed cabin using a second vacuum pump until the vacuum degree in the sealed cabin reaches a set vacuum degree threshold;

[0021] S22: Fill the sealed cabin with oxygen using a gas cylinder until the pressure value of the oxygen in the sealed cabin reaches a set pressure threshold.

[0022] Preferably, in step S3, the wavelength of the ultraviolet light emitted by the ultraviolet lamp is 280nm-365nm, and the set temperature is 40°C.

[0023] Preferably, in step S3, a polishing liquid containing silicon dioxide, dispersant graphene oxide, photocatalyst TiO2 and 10 wt % hydrogen peroxide is used.

[0024] Preferably, in step S3, a polyurethane polishing pad is used to polish the gallium nitride wafer during chemical mechanical polishing.

[0025] Preferably, in step S3, the rotation speed of the polishing machine's carrier is 52 rpm, and the rotation speed of the fixture is 48 rpm.

[0026] Preferably, the step S4 includes the following steps:

[0027] S41: After polishing is completed, heat the paraffin to melt it, remove the GaN wafer, put it into a wax remover, and perform ultrasonic cleaning at 40°C for 20 minutes;

[0028] S42: ultrasonically cleaning the GaN wafer for 20 minutes using a SPM solution having a volume ratio of 97 wt % H2SO4 to 30 wt % H2O2 of 4:1 to remove organic and metal contaminants on the surface;

[0029] S43: The gallium nitride wafer is then placed in 50wt% HF for ultrasonic cleaning for 10 minutes to remove adhered abrasives, oxides and paraffin.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention provides a gallium nitride wafer polishing method assisted by ultraviolet light catalysis, by filling oxygen into a sealed cabin, and the filled oxygen increases the pressure value in the sealed cabin to a set pressure threshold, the process can inhibit the decomposition of hydrogen peroxide in the polishing liquid to produce oxygen, improve the use efficiency of hydrogen peroxide, and promote more conversion of hydrogen peroxide into hydroxyl radicals; the polishing liquid is heated to a set temperature by a heater, at which temperature the rate of hydroxyl radicals generated by the photolysis reaction of hydrogen peroxide in the polishing liquid under ultraviolet light conditions can be increased, so that an oxide layer is generated faster on the wafer surface. Compared with the traditional gallium nitride wafer polishing method assisted by ultraviolet light catalysis, the oxidation rate is increased, thereby improving the polishing efficiency of the gallium nitride wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of a method for polishing a gallium nitride wafer assisted by ultraviolet catalysis according to an embodiment of the present invention;

[0033] Figure 2 is a schematic diagram of a polishing device according to an embodiment of the present invention;

[0034] Figure 3 A microscopic microscope image of a gallium nitride wafer before polishing according to an embodiment of the present invention;

[0035] Figure 4 This is a microscopic microscope image of a polished gallium nitride wafer according to an embodiment of the present invention.

[0036] Explanation of the reference numerals: 1. UV lamp, 2. Pressure gauge, 3. First vacuum pump, 4. Clamp, 5. Gas cylinder, 6. Second vacuum pump, 7. Heater, 8. Infusion tube, 9. Polishing liquid, 10. Carrying plate, 11. Sealed cabin. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Example 1

[0039] See also Figure 1 This embodiment provides a method for polishing a gallium nitride wafer assisted by ultraviolet photocatalysis. The method uses an independent GaN crystal substrate grown by an HVPE method and unintentionally doped as a gallium nitride wafer to be polished, and includes the following steps:

[0040] S1: Before polishing, the gallium nitride wafer needs to be pretreated. In this embodiment, the pretreatment includes two processes: grinding with a grinder and simple rinsing with alcohol. First, the surface of the gallium nitride wafer is ground with a grinder. During the grinding process, parameters such as grinding pressure, rotation speed and grinding time need to be controlled to avoid excessive damage to the wafer. After grinding, the wafer is simply rinsed with alcohol to remove residual grinding fluid and impurities. The rinsed wafer is fixed to the fixture 4 of the polishing machine by vacuum adsorption.

[0041] In this embodiment, step S1 at least includes the following steps:

[0042] S11: Heat the quartz glass plate, apply paraffin wax evenly on it, stick the GaN wafer on the paraffin wax and press it firmly, stop heating, wait for the paraffin wax to solidify, remove the excess paraffin wax, and complete the patch;

[0043] S12: Fix the GaN wafer after bonding on the grinding platform and start the grinder to grind. First, use a grinding head with a lower mesh number and an appropriate amount of grinding fluid to perform rough grinding on the GaN wafer. After the rough grinding reaches a certain level, replace it with a grinding head with a higher mesh number and continue fine grinding.

[0044] S13: After grinding, use alcohol to simply rinse the combination of the quartz glass plate and the ground GaN wafer to remove residual grinding fluid and impurities. During the rinsing process, the concentration of alcohol, temperature, time and other parameters must be strictly controlled to avoid damage to the wafer surface.

[0045] S14: The combination of the rinsed quartz glass plate and the ground gallium nitride wafer is fixed on the fixture 4 of the polishing machine by vacuum adsorption to continue step S2.

[0046] In step S11, in order to make the GaN wafer evenly stressed in subsequent work, the GaN wafer is glued to the center of the quartz glass plate. The purpose of removing excess wax is that the excess wax may absorb abrasive particles with larger particle sizes in the subsequent grinding process, resulting in unnecessary scratches and reducing the polishing quality.

[0047] In step S12, after the bonding is completed, the gallium nitride wafer is ground with a grinder to remove the knife marks produced during the slicing process or the large bumps on the crystal surface during the crystal growth process, improve the flatness of the wafer, and minimize the thickness of the damaged layer on the wafer surface, laying the foundation for the subsequent polishing process.

[0048] In step S13, the ground GaN wafer is simply rinsed with alcohol to remove the grinding particles and residual grinding liquid attached to the surface of the GaN wafer, ensure the smoothness and surface quality of the wafer surface, ensure the polishing efficiency, and provide a good foundation for the subsequent polishing process.

[0049] S2: Use the second vacuum pump 6 to evacuate the sealed cabin 11 of the polishing machine until the vacuum degree reaches -0.1 MPa, then open the gas cylinder 5 to fill oxygen into the sealed cabin 11 until the pressure value of the oxygen in the sealed cabin 11 reaches 40 KPa.

[0050] In this embodiment, step S2 at least includes the following steps:

[0051] S21: Start the second vacuum pump 6, the second vacuum pump 6 extracts air from the sealed cabin 11, and stops extracting air when the vacuum degree in the sealed cabin 11 reaches -0.1 MPa;

[0052] S22: Then open the gas cylinder 5, and fill the sealed cabin 11 with oxygen. When the pressure value of the oxygen in the sealed cabin 11 reaches 40KPa, stop filling with oxygen.

[0053] In step S2, the sealed cabin 11 is evacuated to ensure the purity of the environment in the sealed cabin 11, thereby preventing certain gases from having unnecessary chemical reactions with reactants or products during the polishing process, thereby affecting the polishing effect.

[0054] S3: Adoption Figure 2 The polishing machine shown in the figure polishes the gallium nitride wafer under the action of chemical corrosion and mechanical grinding, specifically:

[0055] Turn on the ultraviolet lamp 1, and the ultraviolet light emitted by the ultraviolet lamp 1 irradiates the polishing liquid 9 and the gallium nitride wafer. The polishing liquid 9 is heated by the heater 7. When the polishing liquid 9 is heated to 40°C, turn on the power of the polishing machine, start the polishing machine, rotate the carrier 10 counterclockwise, and rotate the clamp 4 clockwise. The clamp 4 drives the gallium nitride wafer to rotate clockwise. Under the action of the oxidant H2O2 in the polishing liquid 9, the hard gallium nitride is chemically converted into a softer gallium oxide layer, and the oxide layer is further removed by the mechanical action of the mutual rotation of the abrasive SiO2 and the gallium nitride and the polishing pad with a certain pressure, thereby obtaining a smooth and flat surface.

[0056] In step S3, the heater 7 heats the polishing liquid 9 to 40°C, and maintains the temperature of the polishing liquid 9 at 40°C during the subsequent polishing process to ensure the oxidation rate during the polishing process.

[0057] In step S3, the wavelength of the ultraviolet light is preferably 280nm to 365nm. A wavelength that is too low will cause excessive oxidation on the surface of the gallium nitride wafer, increase the roughness of the gallium nitride wafer surface, and may also damage the microstructure of the gallium nitride wafer surface, affecting the polishing quality. A wavelength that is too high will reduce the photocatalytic reaction rate and reduce the polishing efficiency.

[0058] like Figure 2 The polishing machine shown includes a sealed cabin 11, an ultraviolet lamp 1, a heater 7 and an infusion tube 8. The heater 7 is arranged at the bottom of the sealed cabin 11. The upper part of the heater 7 is a carrier plate 10. The polishing pad is attached to the carrier plate 10. The polishing pad is made of polyurethane material and has certain elasticity and holes. The holes can carry a certain amount of polishing liquid 9, so that it reacts chemically with the gallium nitride wafer and forms gallium oxide with relatively low hardness on the contact surface. The elasticity can ensure that the pressure is uniform and suitable for acting on the gallium nitride wafer, so that the generated gallium oxide is rubbed off by mechanical action, and it is not easy to cause cracks. The polishing liquid 9 drips onto the polishing pad through the infusion tube 8, and the heater 7 can heat the polishing liquid 9. The ultraviolet lamp 1 is installed at the top of the sealed cabin 11. The ultraviolet lamp 1 irradiates the polishing liquid 9 to promote the oxidation of the polishing material by the polishing liquid 9.

[0059] The gallium nitride wafer is adhered to the quartz glass plate by paraffin wax, and the quartz glass plate is fixed on the fixture 4 by vacuum adsorption. The first vacuum pump 3 provides suction, and the fixture 6 provides a certain downward pressure, so that the gallium nitride wafer is pressed on the polishing liquid 9 and the polishing pad, and then the polishing liquid 9 containing an oxidant provides a chemical action, and the mechanical action is provided by the rotation in opposite directions between the fixture 4 and the carrier 10, so as to achieve the polishing of the gallium nitride wafer. The inner cavity of the sealed cabin 11 is connected with a gas cylinder 5 and a second vacuum pump 6. The gas cylinder 5 is filled with oxygen, and the gas cylinder 5 is used to fill the sealed cabin 11 with oxygen. Before the sealed cabin 11 is filled with oxygen, the second vacuum pump 6 is used to evacuate the sealed cabin 11. A pressure gauge 2 is installed at the top of the outside of the sealed cabin 11, and the pressure gauge 2 is used to measure the gas pressure value inside the sealed cabin 11.

[0060] In step S3, the polishing parameters of the gallium nitride wafer are: polishing temperature of 40°C, polishing pressure of 40KPa, carrier speed of 52rpm, fixture speed of 48rpm, polishing liquid flow rate of 80ml / min, pH value of 8, using a polyurethane polishing pad, using a polishing liquid containing silicon dioxide, dispersant graphene oxide, photocatalyst TiO2 and hydrogen peroxide (10wt%), and the polishing time is 20min.

[0061] S4: After polishing, the GaN wafer is cleaned.

[0062] In this embodiment, step S4 at least includes the following steps:

[0063] S41: After polishing is completed, the quartz glass plate is heated at high temperature until the paraffin wax is completely softened and melted, the gallium nitride wafer is removed, placed in a wax remover, and ultrasonically cleaned at 40°C for 20 minutes;

[0064] S42: ultrasonically cleaning the GaN wafer for 20 minutes using a SPM solution having a volume ratio of 97 wt % H2SO4 to 30 wt % H2O2 of 4:1 to remove organic and metal contaminants on the surface;

[0065] S43: The gallium nitride wafer is then placed in 50wt% HF for ultrasonic cleaning for 10 minutes to remove adhered abrasives, oxides and paraffin.

[0066] After step S4 is completed, the cleaned gallium nitride wafer is blown dry with nitrogen. After drying, the mass of the gallium nitride wafer before and after polishing is weighed using an electronic analytical balance to calculate the material removal rate of the gallium nitride wafer. The material removal rate is an important indicator for measuring the polishing efficiency of the gallium nitride wafer. In the ultraviolet light catalytic assisted gallium nitride wafer polishing method of this embodiment, the final material removal rate of the gallium nitride wafer is 580nm / h.

[0067] In summary, the present invention increases the pressure value in the sealed cabin 11 to 40KPa by filling oxygen into the sealed cabin 11, which can inhibit the decomposition of hydrogen peroxide in the polishing liquid 9 to produce oxygen, improve the use efficiency of hydrogen peroxide, and promote the conversion of more hydrogen peroxide into hydroxyl radicals; the polishing liquid 9 is heated to 40°C by the heater 7. At this temperature, the rate of hydroxyl radicals generated by the photolysis reaction of hydrogen peroxide in the polishing liquid 9 under ultraviolet light can be increased, so that the oxide layer is generated faster on the wafer surface. Compared with the traditional ultraviolet photocatalytic assisted gallium nitride wafer polishing method, the oxidation rate and polishing time are improved, thereby improving the material removal rate and polishing efficiency of the gallium nitride wafer.

[0068] Comparative Example

[0069] A method for polishing a gallium nitride wafer, using an unintentionally doped independent GaN crystal substrate grown autonomously by a HVPE method as the gallium nitride wafer to be polished, comprising the following steps:

[0070] S1: Before polishing, the gallium nitride wafer needs to be pre-treated. In this comparative example, the pre-treatment includes two processes: grinding with a grinder and simple rinsing with alcohol. First, the surface of the gallium nitride wafer is ground with a grinder. After grinding, the wafer is simply rinsed with alcohol. The rinsed wafer is fixed on the fixture 4 of the polisher by vacuum adsorption.

[0071] In this comparative example, step S1 at least includes the following steps:

[0072] S11: Heat the quartz glass plate, apply paraffin wax evenly on it, stick the GaN wafer on the paraffin wax and press it firmly, stop heating, wait for the paraffin wax to solidify, remove the excess paraffin wax, and complete the patch;

[0073] S12: Fix the GaN wafer after bonding on the grinding platform and start the grinder to grind. First, use a grinding head with a lower mesh number and an appropriate amount of grinding fluid to perform rough grinding on the GaN wafer. After the rough grinding reaches a certain level, replace it with a grinding head with a higher mesh number and continue fine grinding.

[0074] S13: After grinding is completed, the combination of the quartz glass plate and the ground gallium nitride wafer is simply rinsed with alcohol.

[0075] S14: The combination of the rinsed quartz glass plate and the ground gallium nitride wafer is fixed on the fixture 4 of the polishing machine by vacuum adsorption.

[0076] S2: The polishing machine used in this comparative example is compared with Example 1, but without heater 7, and other conditions are the same. The polishing process is as follows:

[0077] Turn on the ultraviolet lamp 1, and the ultraviolet light emitted by the ultraviolet lamp 1 irradiates the polishing liquid 9 and the gallium nitride wafer. Turn on the power of the polishing machine, start the polishing machine, make the carrier 10 rotate counterclockwise, and the clamp 4 rotate clockwise. The clamp 4 drives the gallium nitride wafer to rotate clockwise. Under the action of the oxidant H2O2 in the polishing liquid, the hard gallium nitride is chemically converted into a softer gallium oxide layer, and the oxide layer is further removed by the mechanical action of the mutual rotation of the abrasive SiO2 and the gallium nitride and the polishing pad with a certain pressure, thereby obtaining a smooth and flat surface.

[0078] The time used for polishing the gallium nitride wafer in this comparative example is 1-3 hours, which is longer than 20 minutes in the embodiment.

[0079] S3: After polishing, the GaN wafer is cleaned.

[0080] In this comparative example, step S3 at least includes the following steps:

[0081] S31: After polishing is completed, the quartz glass plate is heated at high temperature, and the paraffin is completely softened and melted, and the gallium nitride wafer is removed and placed in a wax remover, and ultrasonically cleaned at 40°C for 20 minutes;

[0082] S32: ultrasonically clean the GaN wafer for 20 minutes using a SPM solution having a volume ratio of 97 wt % H2SO4 to 30 wt % H2O2 of 4:1 to remove organic and metal contaminants on the surface;

[0083] S33: The gallium nitride wafer is then placed in 50wt% HF for ultrasonic cleaning for 10 minutes to remove adhered abrasives, oxides and paraffin.

[0084] After step S3 is completed, the cleaned gallium nitride wafer is blown dry with nitrogen. After drying, the mass of the gallium nitride wafer before and after polishing is weighed using an electronic analytical balance to calculate the material removal rate of the gallium nitride wafer. The material removal rate of the gallium nitride wafer in this comparative example is 110-200nm / h.

[0085] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for polishing gallium nitride wafers assisted by ultraviolet photocatalysis, characterized in that: The following steps are involved: S1: Fix the GaN wafer after grinding and washing on the fixture of the polishing machine; S2: The sealed cabin of the polishing machine is evacuated until the vacuum degree reaches a set vacuum degree threshold, and then oxygen is filled into the sealed cabin until the pressure value of the oxygen in the sealed cabin reaches a set pressure threshold; S3: Turn on the UV lamp and the heater, the UV lamp irradiates the polishing liquid, the heater heats the polishing liquid to a set temperature and maintains the temperature constant, and then start the polishing machine to polish the gallium nitride wafer; S4: After polishing, the gallium nitride wafer is cleaned.

2. The method for polishing gallium nitride wafers assisted by ultraviolet photocatalysis according to claim 1, characterized in that: In step S1, the gallium nitride wafer is grown from a HVPE self-stripping substrate, the gallium nitride wafer is ground using a grinder before polishing, and then the ground gallium nitride wafer is rinsed with alcohol, and then the ground and rinsed gallium nitride wafer is fixed on a fixture of the polisher.

3. The method for polishing gallium nitride wafers assisted by ultraviolet photocatalysis according to claim 1, characterized in that: The step S1 comprises the following steps: S11: Use paraffin wax to stick the GaN wafer to the quartz glass plate to complete the bonding; S12: grinding the gallium nitride wafer attached to the quartz glass plate using a grinder; S13: using alcohol to rinse the combination of the quartz glass plate and the ground gallium nitride wafer; S14: Fixing the combination of the rinsed quartz glass plate and the ground gallium nitride wafer on a fixture of a polishing machine by vacuum adsorption.

4. The method for polishing gallium nitride wafers assisted by ultraviolet light catalysis according to claim 1, characterized in that: In step S2, the vacuum threshold is set to -0.1 MPa, and the pressure threshold is set to 40 KPa.

5. The method for polishing gallium nitride wafers assisted by ultraviolet photocatalysis according to claim 1, characterized in that: The step S2 comprises the following steps: S21: extracting air from the sealed cabin using a second vacuum pump until the vacuum degree in the sealed cabin reaches a set vacuum degree threshold; S22: Fill the sealed cabin with oxygen using a gas cylinder until the pressure value of the oxygen in the sealed cabin reaches a set pressure threshold.

6. The method for polishing gallium nitride wafers assisted by ultraviolet photocatalysis according to claim 1, characterized in that: In step S3, the wavelength of the ultraviolet light emitted by the ultraviolet lamp is 280nm-365nm, and the set temperature is 40°C.

7. The method for polishing gallium nitride wafers assisted by ultraviolet photocatalysis according to claim 1, characterized in that: In the step S3, a polishing liquid containing silicon dioxide, graphene oxide as a dispersant, TiO2 as a photocatalyst and 10 wt % hydrogen peroxide is used.

8. The method for polishing gallium nitride wafers assisted by ultraviolet light catalysis according to claim 1, characterized in that: In the step S3, a polyurethane polishing pad is used to polish the gallium nitride wafer in chemical mechanical polishing.

9. The method for polishing gallium nitride wafers assisted by ultraviolet photocatalysis according to claim 1, characterized in that: In step S3, the rotation speed of the polishing machine's carrier is 52 rpm, and the rotation speed of the fixture is 48 rpm.

10. The method for polishing gallium nitride wafers assisted by ultraviolet photocatalysis according to claim 1, characterized in that: The step S4 includes the following steps: S41: After polishing is completed, heat the paraffin to melt, remove the GaN wafer, put it into a wax remover, and perform ultrasonic cleaning at 40°C for 20 minutes; S42: ultrasonically cleaning the GaN wafer for 20 minutes using a SPM solution having a volume ratio of 97 wt % H2SO4 to 30 wt % H2O2 of 4:1 to remove organic and metal contaminants on the surface; S43: The gallium nitride wafer is then placed in 50wt% HF for ultrasonic cleaning for 10 minutes to remove adhered abrasives, oxides and paraffin.

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