Gallium oxide wafer chemical mechanical polishing method based on photocatalytic assistance

Abstract

The application discloses a method for chemical mechanical polishing of gallium oxide wafer based on photocatalytic assistance, and the gallium oxide substrate to be polished is fixed on a light-transmitting backing film for chemical mechanical polishing; in the process of the chemical mechanical polishing, the gallium oxide substrate is irradiated with ultraviolet light with a wavelength of less than 250 nm to generate electron-hole pairs, the electron-hole pairs are gathered on the surface of the gallium oxide, and the gallium oxide is oxidized and decomposed under the action of the holes. The application solves the problems of long polishing time and cleavage in the polishing process, and can further reduce the surface roughness.

Description

Photocatalytic-assisted chemical mechanical polishing method for gallium oxide wafers Technical Field

[0001] This invention belongs to the field of gallium oxide polishing technology, and specifically relates to a photocatalytically assisted chemical mechanical polishing method for gallium oxide wafers. Background Technology

[0002] Current polishing processes for gallium oxide primarily involve chemical mechanical polishing (CMP). This involves adding an acidic or alkaline pH adjuster to the polishing slurry, causing a chemical reaction on the gallium oxide surface to form a softer layer with lower hardness. Mechanical pressure is then applied to the gallium oxide using a polishing pad, and the abrasive particles, polishing pad, and polishing pad in the polishing slurry remove this soft layer, achieving surface planarization. While existing CMP processes can achieve low-roughness surfaces on gallium oxide substrates, they still struggle to address the issue of gallium oxide's susceptibility to cleavage during polishing.

[0003] Specifically, the main drawbacks of existing chemical mechanical polishing processes are:

[0004] 1. Gallium oxide has good chemical stability. At low temperatures (<100℃), the chemical reaction with acidic or alkaline pH adjusters in the polishing slurry is very slow, which leads to excessively long polishing time. On the one hand, this affects efficiency, and on the other hand, excessively long polishing time can also cause some atomic-level damage to the polished surface of gallium oxide.

[0005] 2. The gallium-oxygen bond (Ga-O) on the surface of gallium oxide has high stress sensitivity, especially on the (100) plane. Therefore, it is easy to cause cleavage of gallium oxide crystals during chemical mechanical polishing.

[0006] 3. In the chemical mechanical polishing process, due to the influence of the machining accuracy of the mechanical equipment, the polishing disk may vibrate along the Z-axis, and the mechanical stress applied to the gallium oxide (100) surface will change accordingly, causing the gallium oxide to undergo plastic deformation or even cracking.

[0007] To address the aforementioned issues, existing technologies such as CN115386301A, CN105038606A, and CN105153943A all focus on improving the polishing slurry, and no other catalytic-assisted methods have been reported. Summary of the Invention

[0008] In order to overcome the shortcomings of the prior art, the present invention aims to provide a photocatalytically assisted chemical mechanical polishing method for gallium oxide wafers, in order to solve one or all of the problems of excessive polishing time and easy cleavage during polishing, and to further reduce surface roughness.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] The photocatalytically assisted chemical mechanical polishing (CMP) method for gallium oxide wafers involves fixing the gallium oxide substrate to be polished onto a transparent backing film for CMP. During the CMP process, the gallium oxide substrate is irradiated with ultraviolet light with a wavelength λ < 250 nm to excite the generation of electron-hole pairs. The electron-hole pairs accumulate on the surface of the gallium oxide, and under the influence of the holes, the gallium oxide undergoes an oxidative decomposition reaction.

[0011] In one embodiment, the back side of the gallium oxide substrate is fixed to the light-transmitting back film, and the ultraviolet light irradiates the light-transmitting back film and passes through the light-transmitting back film to irradiate the back side of the gallium oxide substrate.

[0012] In one embodiment, the wavelength λ of the ultraviolet light is in the range of 220–250 nm, and the energy density is 100–400 μW / cm². 2 The ultraviolet light source irradiation frequency is 1–2.5 kHz.

[0013] In one embodiment, the chemical mechanical polishing includes coarse polishing and fine polishing in sequence; the coarse polishing uses an alkaline polishing slurry; the fine polishing uses an acidic polishing slurry; and the particle size of the abrasive in the alkaline polishing slurry is larger than that of the abrasive in the acidic polishing slurry.

[0014] In one embodiment, the alkaline polishing slurry is prepared by adding an alkaline pH adjuster to the polishing slurry, such that the pH of the polishing slurry is 11-12; the acidic polishing slurry is prepared by adding an acidic pH adjuster to the polishing slurry, such that the pH of the polishing slurry is 1-2; the particle size of the abrasive in the alkaline polishing slurry is 40-60 nm; and the particle size of the abrasive in the acidic polishing slurry is 15-30 nm.

[0015] In one embodiment, the polishing fluid comprises abrasives, dispersants, complexing agents, defoamers, and surfactants.

[0016] In one embodiment, the coarse polishing process is as follows:

[0017] The alkaline polishing solution is heated to 90-95°C;

[0018] After the alkaline polishing slurry has fully wetted the gallium oxide substrate and the polishing pad, the polishing pad applies pressure to the gallium oxide substrate. The polishing pad pressure is 40–60 g / cm². 2 The rotation speed is 50-60 r / min, the polishing time is 2-4 h, and then the alkaline polishing solution is washed away;

[0019] The fine polishing process is as follows:

[0020] The acidic polishing solution is heated to 90-95°C;

[0021] After the acidic polishing slurry has fully wetted the gallium oxide substrate and the polishing pad, the polishing pad applies pressure to the gallium oxide substrate. The polishing pad pressure is 20–40 g / cm². 2 The rotation speed is 40-50 r / min, the polishing time is 1-2 h, and then the acidic polishing solution is washed away.

[0022] In one embodiment, during the coarse polishing process, the wavelength λ of the ultraviolet light is 220–250 nm, and the energy density is 300–400 μW / cm². 2 The irradiation frequency is 2–2.5 kHz; the ultraviolet light used for fine polishing has a wavelength λ of 240–250 nm and an energy density of 100–200 μW / cm². 2 The irradiation frequency is 1 to 1.5 kHz.

[0023] In one embodiment, the alkaline polishing solution or the acidic polishing solution is cleaned with deionized water, and the loading pressure and rotation speed of the polishing disc are reduced during the cleaning process.

[0024] In one embodiment, after the fine polishing is completed, the light-transmitting back film is removed from the polishing pad and immersed in acetone to separate the gallium oxide substrate from the light-transmitting back film.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. Ultraviolet light irradiation of gallium oxide excites electron-hole pairs, which accumulate on the surface of gallium oxide, causing an oxidative decomposition reaction. The rate of this reaction is much greater than the rate of chemical reaction of gallium oxide in the polishing solution during chemical mechanical polishing, thus greatly reducing the polishing time.

[0027] 2. Through a two-step polishing process, during the coarse polishing stage, gallium oxide reacts in an alkaline polishing solution, forming a protective layer on the polished surface. This layer shields the gallium-oxygen bonds on the underlying gallium oxide surface, reducing the sensitivity of the gallium oxide surface to mechanical stress and lowering the likelihood of gallium oxide wafer breakage during chemical mechanical polishing. During the fine polishing stage, gallium oxide reacts in an acidic polishing solution. The products dissolve more rapidly in the acidic solution under the catalysis of holes, without adversely affecting the polished surface, thus resulting in a polished surface with lower roughness. Attached Figure Description

[0028] Figure 1 is a schematic diagram of the UV adhesive being applied to the light-transmitting backing film according to the present invention.

[0029] Figure 2 is a schematic diagram of attaching a gallium oxide substrate to a light-transmitting back film according to the present invention.

[0030] Figure 3 is a schematic diagram of the gallium oxide substrate and the transparent back film of the present invention being solidified together.

[0031] Figure 4 is a schematic diagram of the implementation structure of gallium oxide chemical mechanical polishing based on photocatalysis assisted by the present invention.

[0032] Figure 5 is a schematic diagram of the two-step chemical mechanical polishing process of the present invention. Detailed Implementation

[0033] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and examples.

[0034] This invention discloses a photocatalytically assisted chemical mechanical polishing (CMP) method for gallium oxide (GaO) wafers. The GaO substrate to be polished is fixed on a transparent backing film, and then CMP is performed. During the CMP process, the GaO substrate is irradiated with ultraviolet light with a wavelength λ less than 250 nm. Upon irradiation, the GaO is excited to generate electron-hole pairs. These electron-hole pairs diffuse to the interface between the GaO and the polishing slurry under the influence of the concentration gradient and accumulate on the GaO surface. For wide-bandgap GaO semiconductors, the holes accumulated on the GaO surface can lead to the breaking of gallium-oxygen bonds, causing the GaO to undergo an oxidative decomposition reaction as follows:

[0035] 2Ga2O3+12h + →4Ga 3+ (aq) + 3O2↑

[0036] Gallium oxide reacts slowly with the pH adjuster in the polishing slurry at low temperatures below 100°C, resulting in excessively long polishing times. The present invention, namely, photocatalytically assisted gallium oxide chemical mechanical polishing, accelerates the polishing process and reduces polishing time because the oxidation-decomposition reaction rate is much higher than the chemical reaction rate of gallium oxide in the polishing slurry.

[0037] In an embodiment of the present invention, the back side of the gallium oxide substrate is fixed to a light-transmitting back film. Ultraviolet light irradiates the light-transmitting back film and passes through it to irradiate the back side of the gallium oxide substrate. For example, the light-transmitting back film is selected as a high-transmittance optical quartz glass back film, which has excellent light transmission performance in the ultraviolet band, ensuring that ultraviolet light can penetrate and irradiate the back side of the gallium oxide substrate.

[0038] Figures 1, 2, and 3 of this invention illustrate the specific implementation process of fixing the back side of a gallium oxide substrate to a light-transmitting back film, including:

[0039] Using dropper 3, apply optical UV adhesive 2 to the center of the front side of the light-transmitting back film 1, as shown in Figure 1. The area of ​​optical UV adhesive 2 can be 1 / 3 of the area of ​​gallium oxide substrate 4. Attach gallium oxide substrate 4 to the center of the front side of the light-transmitting back film 1, as shown in Figure 2. Wipe away any optical UV adhesive 2 that has seeped around gallium oxide substrate 4 with lint-free paper soaked in anhydrous ethanol. Irradiate the attached gallium oxide substrate 4 with ultraviolet light source 7 for about 30 seconds to fix gallium oxide substrate 4 and light-transmitting back film 1 together, as shown in Figure 3. The optical UV adhesive 2 of this invention is a one-component UV-visible light curable modified acrylic structural adhesive that can cure rapidly under ultraviolet light irradiation. It can be used as an adhesive between gallium oxide substrate 4 and light-transmitting back film 1, and has high transmittance to short-wave ultraviolet light after curing.

[0040] Figure 4 of this invention illustrates a structure for implementing the method of this invention. A polishing pad 10 is placed on a polishing platform 9, and the tightness, height, and other parameters of the polishing pad 10 can be adjusted by an adjuster 11. The back side of the transparent back film 1 is fixed to the polishing disk 8, with the back side of the gallium oxide substrate 4 facing upwards and the front side facing downwards, toward the polishing pad 10. Polishing slurry is supplied to the polishing pad 10 using a polishing slurry supply hopper 6, and the transparent back film 1 and the gallium oxide substrate 4 are irradiated from top to bottom using an ultraviolet light source 7.

[0041] In this embodiment of the invention, the ultraviolet light source 7 is a short-wavelength tunable deep ultraviolet laser source, which can provide deep ultraviolet light with a wavelength λ < 250 nm. Further, in this embodiment, the wavelength λ of the ultraviolet light is set to a range of 220–250 nm. According to E = hc / λ, where h is Planck's constant, approximately 6.625 × 10⁻³⁴ J·s, and c is the speed of light, the ultraviolet light energy is greater than the gallium oxide bandgap Eg (4.9 eV), which can excite a large number of electron-hole pairs in gallium oxide, with an energy density of 100–400 μW / cm². 2 The irradiation frequency of the ultraviolet light source 7 is 1 to 2.5 kHz.

[0042] The parameters set in this embodiment can further ensure the generation effect and efficiency of electron-hole pairs.

[0043] In embodiments of the present invention, to reduce the possibility of gallium oxide undergoing plastic deformation or even cracking during polishing, and also to further reduce its surface roughness, a two-step chemical mechanical polishing method involving sequential coarse polishing and fine polishing is employed. Coarse polishing refers to the use of abrasive particles with a relatively larger particle size in the polishing slurry compared to fine polishing; conversely, fine polishing refers to the use of abrasive particles with a relatively smaller particle size in the polishing slurry compared to coarse polishing. In this embodiment, an alkaline polishing slurry is used for coarse polishing; an acidic polishing slurry is used for fine polishing. The alkaline polishing slurry is made by adding an alkaline pH adjuster. The acidic polishing slurry is made by adding an acidic pH adjuster.

[0044] Gallium oxide surfaces, especially the (100) face, are highly sensitive to mechanical stress, making them prone to cleavage during polishing. In this embodiment, a two-step polishing process is used. In the first step, during rough polishing, gallium oxide reacts in an alkaline polishing solution to form a layer of [Ga(OH)4] on the polished surface. - Or other similar protective layers, which can shield the gallium-oxygen bonds on the surface of the underlying gallium oxide, reduce the sensitivity of the gallium oxide surface to mechanical stress, prevent the gallium oxide wafer from cracking, and solve the problem of easy cleavage of the gallium oxide surface, especially the (100) plane; during the second fine polishing, gallium oxide reacts in the acidic polishing solution, and under the catalysis of the holes generated by photoexcitation, the gallium salt can be accelerated to dissolve in the acidic polishing solution without adversely affecting the polished surface, thereby improving the flatness of the polished surface.

[0045] For example, the pH of the alkaline polishing solution is 11-12, and the pH of the acidic polishing solution is 1-2; the particle size of the abrasive in the alkaline polishing solution is 40-60 nm; and the particle size of the abrasive in the acidic polishing solution is 15-30 nm.

[0046] The main components of polishing slurry include abrasives, dispersants, complexing agents, defoamers, and surfactants. Among them:

[0047] The abrasive can be selected from one or more of the following: silicon dioxide, diamond, aluminum oxide, titanium oxide, and cerium oxide.

[0048] The dispersant can be an organic dispersant, more specifically one or more of triethylhexylphosphate, sodium dodecyl sulfate, methylpentanol, and polyacrylamide, used to uniformly disperse abrasive particles in the polishing fluid medium.

[0049] The complexing agent can be an alkanolamine, more specifically one or more of monoethanolamine, diethanolamine, and triethanolamine, because they are relatively stable in alkaline solutions. The complexing agent can effectively chelate the gallium metal on the surface of the gallium oxide substrate into a chelate, promoting more effective dissolution of the gallium oxide surface metal into the polishing solution.

[0050] Defoamers, also known as defoaming agents, can be one or more of the following: polydimethylsiloxane, tributyl phosphate, dimethyl silicone oil, ethylene oxide, and propylene oxide. Their function is to reduce the surface tension of the polishing slurry and inhibit foaming during the polishing process.

[0051] Surfactants can be selected from anionic surfactants such as stearic acid and sodium dodecylbenzene sulfonate, cationic surfactants such as quaternary ammonium compounds, or nonionic surfactants such as alkyl glucosides (APG) and fatty acid glycerides. Their function is twofold: firstly, to reduce the surface tension of the polishing slurry and inhibit foaming; and secondly, to increase the wettability of the gallium oxide surface, allowing the gallium oxide surface to adsorb more polishing slurry.

[0052] The alkaline pH adjuster of this invention can be selected from inorganic bases such as sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, and sodium bicarbonate, or organic bases such as methylamine, ethylamine, ethanolamine, cyclohexylamine, and tetramethylammonium hydroxide; the acidic pH adjuster can be selected from inorganic acids such as nitric acid, hydrochloric acid, sulfuric acid, hydrofluoric acid, and phosphoric acid, or organic acids such as carboxylic acid, sulfonic acid, sulfinic acid, thiocarboxylic acid, formic acid, acetic acid, benzoic acid, oxalic acid, and succinic acid.

[0053] In an embodiment of the present invention, a composition of an alkaline polishing liquid is provided, as follows:

[0054] The abrasive is silica and diamond, with a particle size of 40–60 nm; the dispersant is sodium dodecyl sulfate, with a mass fraction of 0.04–0.8% of the polishing solution; the complexing agent is monoethanolamine, with a mass fraction of 0.1–0.3% of the polishing solution; the defoamer is tributyl phosphate, with a mass fraction of 0.01–0.1% of the polishing solution; the surfactant is sodium dodecylbenzenesulfonate, with a mass fraction of 0.05–0.2% of the polishing solution; and the alkaline pH adjuster is 30% sodium hydroxide, which adjusts the pH of the polishing solution to 11–12.

[0055] In this alkaline polishing solution, gallium oxide reacts with sodium hydroxide in the following way:

[0056] Ga2O3(s) + 2OH - (aq) + 3H₂O(l) → 2[Ga(OH)₄] - (aq)

[0057] Among them, the [Ga(OH)4] produced in the reaction - It will adhere to the gallium oxide surface and shield the gallium-oxygen bonds on the gallium oxide surface, especially the (100) plane. This reduces the sensitivity of the gallium oxide surface to mechanical stress and reduces the possibility of cracking during subsequent polishing processes.

[0058] In an embodiment of the present invention, an acidic polishing solution is provided with the following components:

[0059] The abrasive is silica and diamond, with a particle size of 15–30 nm; the dispersant is sodium dodecyl sulfate, with a mass fraction of 0.04–0.8% of the polishing solution; the complexing agent is monoethanolamine, with a mass fraction of 0.1–0.3% of the polishing solution; the defoamer is tributyl phosphate, with a mass fraction of 0.01–0.1% of the polishing solution; the surfactant is sodium dodecylbenzenesulfonate, with a mass fraction of 0.05–0.2% of the polishing solution; and the acidic pH adjuster is 85% phosphoric acid, which adjusts the pH of the polishing solution to 1–2.

[0060] In this acidic polishing solution, gallium oxide reacts with phosphoric acid in the following way:

[0061] Ga₂O₃ + 2H₃PO₄ → 2GaPO₄ + 3H₂O

[0062] GaPO4 → Ga 3+ (aq)+PO4 3- (aq)

[0063] That is, in acidic polishing solutions, GaPO4 decomposes into Ga. 3+ (aq) and PO4 3- (aq) dissolves in the polishing slurry, and photocatalysis accelerates this process.

[0064] The GaPO4 produced in the reaction will decompose into Ga in the acidic polishing solution. 3+ Ga 3+ It does not adhere to the gallium oxide surface, thus allowing for the formation of an ultra-smooth polished surface through polishing.

[0065] As shown in Figure 5, the specific process of the two-step chemical mechanical polishing method in this embodiment of the invention can be described as follows:

[0066] The first step is rough polishing.

[0067] The alkaline polishing solution is heated to 90-95°C using a heating device, and a suitable polishing solution flow rate is set, such as 40-80 mL / min.

[0068] After the alkaline polishing slurry has fully wetted the gallium oxide substrate and polishing pad, pressure is applied to the gallium oxide substrate through the polishing pad. The polishing pad pressure is 40–60 g / cm². 2 The rotation speed is 50-60 r / min, the polishing time is 2-4 h, and then the residual alkaline polishing solution on the gallium oxide substrate and polishing pad is cleaned off.

[0069] The second step is tossing.

[0070] The acidic polishing solution is heated to 90-95°C using a heating device, and a suitable flow rate is set, such as 40-80 mL / min.

[0071] After the acidic polishing slurry has fully wetted the gallium oxide substrate and polishing pad, pressure is applied to the gallium oxide substrate through the polishing pad. The polishing pad pressure is 20–40 g / cm². 2 The rotation speed is 40-50 r / min, the polishing time is 1-2 h, and then the residual acidic polishing solution on the gallium oxide substrate and polishing pad is cleaned off.

[0072] In embodiments of the present invention, the ultraviolet light parameters differ between the rough polishing and fine polishing processes. Specifically, the wavelength λ of the ultraviolet light during the rough polishing process is 220–250 nm, and the energy density is 300–400 μW / cm². 2The irradiation frequency is 2–2.5 kHz. During the fine polishing process, the wavelength λ of the ultraviolet light is 240–250 nm, and the energy density is 100–200 μW / cm². 2 The irradiation frequency is 1 to 1.5 kHz.

[0073] During rough polishing, the wavelength λ of ultraviolet light is relatively small, while the energy density and irradiation frequency are relatively large, resulting in a higher polishing rate. During fine polishing, the wavelength λ of ultraviolet light is relatively large, while the energy density and irradiation frequency are relatively small, which accelerates the decomposition of GaPO4 and further reduces the surface roughness of the gallium oxide substrate.

[0074] In embodiments of the present invention, deionized water can be used for cleaning after coarse and fine polishing.

[0075] For cleaning after coarse polishing, replace the alkaline polishing solution with deionized water. No heating is required. Set an appropriate polishing solution flow rate, typically 200–300 mL / min. Reduce the polishing disc loading pressure and rotation speed appropriately; for example, the polishing disc loading pressure can be set to 30–50 g / cm³. 2 Set the rotation speed to 30-40 r / min and the polishing and cleaning time to about 10 minutes to complete the cleaning.

[0076] For cleaning after fine polishing, replace the acidic polishing solution with deionized water. No heating is required. Set an appropriate polishing solution flow rate, typically 200–300 mL / min. Reduce the polishing disc loading pressure and rotation speed appropriately; for example, the polishing disc loading pressure can be set to 20–30 g / cm³. 2 Set the rotation speed to 20-30 r / min and the polishing and cleaning time to about 10 minutes to complete the cleaning.

[0077] During the cleaning process, ultraviolet light irradiation can be paused.

[0078] In an embodiment of the present invention, after fine polishing and cleaning off the acidic polishing solution, the transparent back film is removed from the polishing pad and immersed in acetone to separate the gallium oxide substrate from the transparent back film.

[0079] Specifically, the integrally bonded gallium oxide substrate and transparent backing film are first cleaned in acetone for about 10 minutes to dissolve the photocured UV adhesive and separate the gallium oxide substrate from the transparent backing film. Then, the gallium oxide substrate is cleaned in isopropanol for about 2 minutes to remove any remaining acetone. It is then rinsed in deionized water for about 2 minutes to remove any remaining isopropanol from the gallium oxide surface. Finally, the gallium oxide substrate is dried using a nitrogen gun.

Claims

1. A photocatalytically assisted chemical mechanical polishing method for gallium oxide wafers, characterized in that, A gallium oxide substrate to be polished is fixed on a transparent backing film and subjected to chemical mechanical polishing (CMP). During CMP, the gallium oxide substrate is irradiated with ultraviolet light with a wavelength λ < 250 nm to excite the generation of electron-hole pairs. These electron-hole pairs accumulate on the surface of the gallium oxide substrate, and under the influence of the holes, the gallium oxide undergoes an oxidative decomposition reaction. The CMP process includes coarse polishing and fine polishing. The coarse polishing uses an alkaline polishing slurry, while the fine polishing uses an acidic polishing slurry. The abrasive particles in the alkaline polishing slurry have a larger particle size than those in the acidic polishing slurry. The coarse polishing process is as follows: the alkaline polishing slurry is heated to 90-95°C; after the alkaline polishing slurry has fully wetted the gallium oxide substrate and the polishing pad, the polishing pad applies pressure to the gallium oxide substrate at a pressure of 40-60 g / cm². 2 The rotation speed is 50-60 r / min, the polishing time is 2-4 h, and then the alkaline polishing solution is washed off; the fine polishing process is as follows: the acidic polishing solution is heated to 90-95℃; after the acidic polishing solution has fully wetted the gallium oxide substrate and the polishing pad, the polishing pad applies pressure to the gallium oxide substrate, and the polishing pad application pressure is 20-40 g / cm. 2 The rotation speed is 40-50 r / min, the polishing time is 1-2 h, and then the acidic polishing solution is washed away; during the rough polishing process, the wavelength λ of ultraviolet light is 220-250 nm, and the energy density is 300-400 μW / cm². 2 The irradiation frequency is 2~2.5kHz; the ultraviolet light used for fine polishing has a wavelength λ of 240~250nm and an energy density of 100~200μW / cm². 2 The irradiation frequency is 1~1.5kHz.

2. The photocatalytically assisted chemical mechanical polishing method for gallium oxide wafers according to claim 1, characterized in that, The back side of the gallium oxide substrate is fixed to the light-transmitting back film, and the ultraviolet light irradiates the light-transmitting back film and passes through the light-transmitting back film to irradiate the back side of the gallium oxide substrate.

3. The photocatalytically assisted chemical mechanical polishing method for gallium oxide wafers according to claim 1, characterized in that, The ultraviolet light has a wavelength λ range of 220~250nm and an energy density of 100~400μW / cm². 2 The ultraviolet light source irradiation frequency is 1~2.5kHz.

4. The photocatalytically assisted chemical mechanical polishing method for gallium oxide wafers according to claim 1, characterized in that, The alkaline polishing slurry is prepared by adding an alkaline pH adjuster to make the pH of the polishing slurry 11-12; the acidic polishing slurry is prepared by adding an acidic pH adjuster to make the pH of the polishing slurry 1-2; the abrasive particle size in the alkaline polishing slurry is 40-60 nm; and the abrasive particle size in the acidic polishing slurry is 15-30 nm.

5. The photocatalytically assisted chemical mechanical polishing method for gallium oxide wafers according to claim 4, characterized in that, The polishing fluid comprises abrasives, dispersants, complexing agents, defoamers, and surfactants.

6. The photocatalytically assisted chemical mechanical polishing method for gallium oxide wafers according to claim 1, characterized in that, The alkaline polishing solution or the acidic polishing solution is cleaned with deionized water, and the loading pressure and rotation speed of the polishing disc are reduced during the cleaning process.

7. The photocatalytically assisted chemical mechanical polishing method for gallium oxide wafers according to claim 1, characterized in that, After the fine polishing is completed, the light-transmitting back film is removed from the polishing pad and immersed in acetone to separate the gallium oxide substrate from the light-transmitting back film.

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