Cmp polishing liquid made of low temperature plasma modified photocatalyst / graphene composite abrasive and method thereof

Abstract

The application discloses a method for preparing CMP polishing liquid by using low-temperature plasma modified photocatalyst / graphene composite abrasive, and comprises the following preparation steps: (1) obtaining graphene dispersion liquid by high-pressure homogenization delamination method; (2) obtaining titanium dioxide / graphene composite material by combining sol-gel method and sintering; (3) obtaining TiO2-N / Graphene by modifying the obtained titanium dioxide / graphene composite material by low-temperature plasma nitrogen doping; and (4) preparing CMP polishing liquid by using the obtained TiO2-N / Graphene. By the above method, the graphene is prepared by physical high-pressure shearing method, the titanium dioxide / graphene composite material is synthesized by combining sol-gel method, and the nitrogen doping modification is carried out by using low-temperature plasma, so that the composite abrasive with visible light response and high photocatalytic activity is finally prepared, and the neutral polishing liquid is prepared, and the polishing liquid has the advantages of environmental protection, high efficiency and low cost, and effectively solves the problems of large pollution and low polishing efficiency of the traditional polishing liquid.

Description

Technical Field

[0001] This invention relates to the field of polishing technology, and in particular to a method for preparing CMP polishing fluid using low-temperature plasma-modified photocatalytic graphene composite abrasive. Background Technology

[0002] Third-generation wide-bandgap semiconductor materials, represented by silicon carbide (SiC), have become core materials for high-voltage, high-frequency, and high-temperature applications such as electric vehicles, high-speed rail, other rail transportation, smart grids, and aerospace due to their high breakdown electric field, high thermal conductivity, and excellent electron saturation velocity. In terms of electric vehicle applications alone, with the explosive growth of the global electric vehicle market, for example, Tesla alone requires approximately 500,000 six-inch SiC wafers per year, almost occupying the total existing global production capacity. Therefore, the market demand for high-quality, large-size SiC substrates has risen sharply.

[0003] The production process of SiC substrates generally includes: slicing, grinding and thinning, polishing and chemical mechanical polishing. Among them, the final chemical mechanical polishing is the most critical step in the processing. Considering that SiC itself has extremely high hardness and chemical inertness, with a Mohs hardness of 9.2 to 9.5, it is one of the most difficult materials to process in semiconductor manufacturing. In particular, the chemical mechanical polishing (CMP) step, which ultimately achieves an atomically smooth surface, has become a key bottleneck restricting its capacity improvement and cost reduction.

[0004] Currently, the industry commonly uses the following three polishing methods for SiC wafers: 1. Traditional CMP free abrasive polishing: This method uses free abrasive particles to roll and slide between the polishing pad and the wafer for mechanical grinding, supplemented by chemical action. The polishing fluid uses silicon dioxide (SiO2) or polycrystalline alumina (Al2O3) as the abrasive, and the polishing time is 8-12 hours in a strongly alkaline environment with a pH of 10. 2. Strong acid free abrasive polishing: This is also free abrasive polishing, but it uses a strong acid chemical solution to enhance the oxidation and corrosion of SiC. The polishing solution uses potassium permanganate (KMnO4) as the main oxidant, and is used with abrasives (such as alumina) to polish for 2-3 hours in a strong acidic environment with a pH of 2. 3. Strong acid semi-fixed abrasive polishing: The abrasive (such as silicon dioxide) is partially fixed in the resin matrix of the polishing pad, forming a semi-fixed state. It combines the high mechanical effect of fixed abrasive with the chemical effect of free abrasive. Potassium permanganate KMnO4 acidic polishing liquid is used as the chemical medium, and polishing is carried out for 2-3 hours in a strongly acidic environment with a pH of 2.

[0005] All existing SiC wafer polishing methods use strong acids or highly oxidizing agents (such as permanganate and hydrogen peroxide), inevitably generating toxic and harmful waste liquids. This strong chemical aggression is itself a source of pollution, and the narrow process window easily leads to excessive etching or deterioration of the wafer surface, resulting in high processing costs. Furthermore, these methods are highly corrosive to the polishing machine's piping and components, requiring additional expensive coating protection. At the same time, the core of these polishing methods relies on the chemical etching effect of highly oxidizing chemicals to soften the SiC surface. The aim is to enable the high oxidizing power of these chemicals to produce an oxidation reaction on the silicon carbide material surface, creating a softer oxide layer of SiO2, ensuring the rapid and uniform removal of micro-cracks during the chemical mechanical polishing process. The true nature of this high oxidizing power is the free radical, which is an atom or group with unpaired electrons, extremely unstable but also highly chemically active.

[0006] Based on the above research, there is an urgent need to develop an environmentally friendly, efficient, and low-cost CMP polishing slurry. On the one hand, it aims to eliminate strong acid and strong alkali systems and achieve neutralization of the polishing slurry. On the other hand, it aims to effectively shorten the polishing time and improve polishing and production efficiency. At the same time, it is necessary to significantly improve the photocatalytic activity of the photocatalyst in a wide spectral range (especially the visible light region). Summary of the Invention

[0007] The main technical problem solved by this invention is to provide a method for preparing CMP polishing slurry by using low-temperature plasma to modify photocatalytic graphene composite abrasive. Graphene is prepared by physical high-pressure shearing, and titanium dioxide / graphene composite material is synthesized by sol-gel method. Then, nitrogen doping modification is carried out by low-temperature plasma, and finally, composite abrasive with visible light response and high photocatalytic activity is prepared and formulated into a neutral polishing slurry. It is environmentally friendly, efficient and low cost, and effectively solves the problems of high pollution of traditional polishing slurry, backward traditional graphene preparation process and low polishing efficiency of SiC wafer.

[0008] To solve the above-mentioned technical problems, one technical solution adopted by the present invention is: to provide a method for preparing CMP polishing fluid using low-temperature plasma-modified photocatalyst / graphene composite abrasive, comprising the following preparation steps: (1) Graphene dispersion was obtained by high-pressure homogenization delamination method; (2) The graphene dispersion obtained above is further processed by a combination of sol-gel method and sintering method to obtain titanium dioxide / graphene composite material, and then the relevant properties are tested. (3) The titanium dioxide / graphene composite material obtained above was modified by low-temperature plasma nitrogen doping to obtain TiO2-N / Graphene, and then the relevant properties were tested. (4) Use the TiO2-N / Graphene obtained above to prepare CMP polishing fluid.

[0009] Preferably, in step (1) above, deionized water and dispersant are added to the graphite raw material, and the graphene dispersion is obtained by delamination under different pressure conditions in a high-pressure homogenizer for a certain period of time.

[0010] Preferably, the graphite raw material is selected from artificial graphite, natural graphite, crystalline graphite, or self-made reduced graphene oxide.

[0011] Preferably, the delamination pressures are 800 bar, 1400 bar, and 1600 bar, respectively, and the delamination time is 20 minutes for each.

[0012] Preferably, in step (2) above, the graphite dispersion obtained above is mixed with tetraisopropyl titanate and ethanol, and reacted in an oven at a certain temperature for a certain time to form a gel.

[0013] Preferably, the gel obtained above is sintered under an inert gas for a period of time to obtain TiO2 / Graphene composite powder, and then the relevant properties are tested.

[0014] Preferably, in step (3) above, the gas flow rate is 80 sccm, the vacuum degree is 1×10⁻³ Torr, and the power is 400 W, and the modification is carried out for 15 min to 3 h, and then the characterization test of the modification effect is performed.

[0015] Preferably, in step (4) above, the plasma-modified TiO2-N / Graphene, ethylene glycol and dispersant are dispersed by a dispersion process.

[0016] Preferably, the dispersion process uses Φ3mm ceramic balls as the grinding medium, and ball mills at 200 rpm for 10 hours to finally obtain modified photocatalyst / graphene polishing abrasive with uniform viscosity and stable performance.

[0017] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is to provide a CMP polishing slurry prepared by a method of using low-temperature plasma-modified photocatalytic graphene composite abrasive.

[0018] The beneficial effects of this invention are: This invention completely eliminates the reliance on strong acids, strong alkalis, and highly polluting chemical oxidants in traditional processes. It employs a physical high-pressure shearing method to prepare graphene and a low-temperature plasma nitrogen-doped photocatalyst, ultimately producing a neutral, environmentally friendly polishing slurry. Under visible or ultraviolet light irradiation, electrons jump from the ground state (valence band) to the excited state (conduction band), leaving holes in the ground state. Water on the photocatalyst surface reacts with these holes to generate OH radicals, achieving a completely green process from raw material synthesis to polishing application. Regarding the polishing slurry, the prepared slurry has a pH of 7-8, completely eliminating the need for strong acid (potassium permanganate, pH≈2) or strong alkali (pH≈10) chemical systems required in traditional processes. This invention eliminates the most corrosive and polluting source of waste liquid at its source; in terms of the preparation process, it is completed in a vacuum environment using only electricity and nitrogen, replacing the traditional wet chemical doping process, with no chemical solvent consumption or emission; regarding the subsequent impact on equipment, the chemical action in the polishing process relies on the •OH free radicals generated by the photocatalyst under ultraviolet light, which are converted into water after completing the oxidation reaction, leaving no harmful residues. The low-temperature plasma-modified photocatalyst / graphene composite abrasive provided by this invention offers a highly efficient, economical, and environmentally friendly polishing slurry product for the manufacture of silicon carbide chips urgently needed in fields such as electric vehicles and rail transportation, and has very good technical and market promotion value. Attached Figure Description

[0019] Figure 1 This is a morphology diagram of a graphite dispersion obtained by high-pressure homogenization delamination of artificial graphite AG according to the present invention. Figure 2 This is a morphology diagram of a graphite dispersion obtained by high-pressure homogenization delamination using natural graphite NG in this invention. Figure 3 This is a graphite dispersion morphology diagram obtained by high-pressure homogenization delamination using crystalline graphite (CG) according to the present invention. Figure 4 This is a graphite dispersion obtained by high-pressure homogenization delamination using self-made reduced graphene oxide (rGO) according to the present invention. Figure 5 These are scanning electron microscope (SEM) images of the four photocatalytic composite powders obtained in this invention: TiO2 / 5wt%AG_A, TiO2 / 5wt%NG_B, TiO2 / 5wt%CG_C, and TiO2 / 5wt%rGO. Figure 6 The XRD patterns of the four photocatalytic composite powders obtained in this invention are: TiO2 / 5wt%AG_A, TiO2 / 5wt%NG_B, TiO2 / 5wt%CG_C, and TiO2 / 5wt%rGO. Figure 7This invention uses five different light sources to conduct a methylene blue light degradation test; Figure 8 This describes the degradation test of the titanium dioxide / graphene composite material prepared in this invention under methylene blue light. Figure 9 This is a photograph of the appearance of P25 titanium dioxide after plasma modification according to the present invention. Figure 10 This is the FE-SEM morphology of P25 titanium dioxide after plasma modification according to the present invention; Figure 11 The present invention uses the FTIR spectrum of plasma-modified P25 titanium dioxide; Figure 12 The present invention uses the UV-Vis DRS spectrum of plasma-modified P25 titanium dioxide; Figure 13 The present invention utilizes plasma-modified P25 titanium dioxide methylene blue photocatalytic spectrum; Figure 14 The present invention utilizes plasma-modified TiO2 / 5wt%AG_A, TiO2 / 5wt%NG_B, TiO2 / 5wt%CG_C, and TiO2 / 5wt% rGO methylene blue photocatalytic spectra. Figure 15 This invention utilizes low-temperature plasma-modified photocatalytic graphene composite abrasive to produce a CMP polishing fluid. Figure 16 This invention compares the material removal rates after polishing using two types of polishing pads and three types of polishing liquids. Figure 17 This invention compares the surface roughness of materials polished using two types of polishing pads and three types of polishing liquids. Figure 18 This invention compares the surface morphology after polishing using two types of polishing pads and three types of polishing liquid. Detailed Implementation

[0020] The preferred embodiments of the present invention will now be described in detail so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0021] Example: A CMP polishing slurry prepared using low-temperature plasma-modified photocatalytic graphene composite abrasive first involves the preparation of a graphene dispersion via a high-pressure homogenization delamination method. The specific process involves selecting a high-purity carbon source material; in this embodiment, four types of carbon materials are used, as detailed in the table below. The above-mentioned graphite raw materials were added to deionized water and dispersant at a ratio of 1 wt%. The mixture was then subjected to delamination in a high-pressure homogenizer at pressures of 800 bar, 1400 bar, and 1600 bar for 20 minutes each to obtain graphene dispersions. The morphology of the delaminated graphene dispersions was observed using a field emission scanning electron microscope (FE-SEM). The morphologies of the four carbon materials under high shear delamination are shown below. Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown in the SEM, it can be seen that the layers were successfully delaminated after high-pressure shearing, but the differences between the self-made reduced graphene oxide were not significant.

[0022] Next, the obtained graphene dispersion was mixed with tetraisopropyl titanate (TTIP) and ethanol, and reacted in an oven at 85°C for 8 hours to form a gel. Then, it was sintered at 500°C for 3 hours under a N2 / Ar atmosphere to obtain four photocatalytic composite powders: TiO2 / 5wt%AG_A, TiO2 / 5wt%NG_B, TiO2 / 5wt%CG_C, and TiO2 / 5wt%rGO. The surface morphology and crystal structure were analyzed by FE-SEM and XRD. The corresponding scanning electron microscope images of these four photocatalytic composite powders are shown below. Figure 5 As shown.

[0023] Commercially available Degussa P25 titanium dioxide, composed of 80% anatase and 20% rutile, was used as a standard for testing. The JCPDS card number (JCPDS NO: 86-1157) for TiO2 anatase was used as a reference. The characteristic peaks at 2φ of 25°, 38°, 48°, 54°, 62.5°, 68.8°, and 75° refer to the (101), (004), (200), (105), (204), (116), and (215) planar nanoparticles of tetragonal anatase in TiO2. The obtained XRD patterns are shown below. Figure 6 As shown, the results confirm that in the X-ray diffraction spectrum of the prepared TiO2 / graphene composite material, TiO2 exists on the surface of graphene in the anatase crystal form, while the rutile 26° (110) after high-pressure homogenization is partially increased. The main reason is that high-pressure homogenization will produce effects such as delamination and breakage, which should be the crystal form produced by the destruction of the anatase structure.

[0024] The polishing slurry of this invention relies on a photocatalyst (plasma-modified TiO2 / graphene) to generate highly oxidizing •OH radicals under light irradiation. These radicals are key to the chemical action during polishing; they can oxidize the hard SiC surface, forming a softer oxide layer that facilitates mechanical removal. •OH radicals are extremely reactive and have a very short lifetime, making it difficult to directly measure their concentration online during polishing. Therefore, a stable, reliable, and quantitatively analyzeable indirect testing method is needed to assess the material's ability to generate •OH. Methylene blue (MB) is an organic dye molecule with strong absorption in the visible light region. It possesses perfect characteristics as a photocatalytically active probe. On the one hand, it is highly sensitive to •OH radicals, which can rapidly and completely oxidize and degrade methylene blue molecules into colorless small molecule products. On the other hand, methylene blue solutions have a characteristic absorption peak at a wavelength of λ=664 nm. By measuring the decrease in absorbance at this wavelength using a UV-Vis spectrophotometer, the degradation rate can be accurately calculated. Therefore, this is an internationally recognized standard method.

[0025] In this invention, the photocatalytic degradation of methylene blue pollutants by commercial titanium dioxide (Dequssa P25) was tested on five different UV lamp sources. Figure 7 As shown, the efficiency of both the Yuhao long-tube UV lamp and the TOSHIBA 80W long-tube UV lamp in the degradation experiment was close to 100%. The Yuhao long-tube UV 1600W is suitable for polishing machines that need to be illuminated over a large area, but when used in the methylene blue degradation experiment at the minimum power, the effect was still not good enough for this experiment, and the methylene blue was completely degraded in less than 10 minutes. Therefore, the TOSHIBA 80W long-tube UV lamp was used instead for the methylene blue experiment.

[0026] like Figure 8 As shown, the high-shear physical delamination method of the present invention prepares graphene, and the synthesized TiO2 / AG_A, TiO2 / NG_B, and TiO2 / CG_C photocatalytic composite materials have a photocatalytic efficiency of 85-88%, while the photocatalytic efficiency of commercially available P25 (Degussa) titanium dioxide is 92%. The photocatalytic efficiency of reduced graphene oxide prepared by the original chemical method is only 72%, mainly because physical delamination destroys the surface structure of reduced graphene oxide, resulting in poor photocatalytic effect. However, artificial graphite, natural graphite, and crystalline graphite, because their surfaces are not damaged by acidification, can retain their characteristic performance after physical delamination, so their photocatalytic efficiency is higher than that of the chemical method.

[0027] Next, commercially available Degussa P25 titanium dioxide was selected and modified according to the conditions of this invention: under a nitrogen atmosphere, a gas flow rate of 80 sccm, a vacuum degree of 1×10⁻³ Torr, and a power of 400 W, for 15 min to 3 h. The appearance of the modified titanium dioxide is as follows. Figure 9 As shown, from left to right, these represent different modification times: it can be seen that as the modification time increases, the color of P25 becomes more and more yellow, and the yellower it is, the better the nitrogen doping effect of P25.

[0028] Combination Figure 10 The SEM images show that the duration of the modification time is not visible under SEM, but it does affect the appearance of P25. EDX analysis does not detect nitrogen atom reactions. Combined with... Figure 11 FTIR analysis shows that at 3375 cm⁻¹ -1 The OH-R peak gradually broadens, indicating that the oxygen functional groups on the P25 surface are gradually replaced over time, with the peak at 1370 cm⁻¹. -1 The presence of stretching vibration peaks of NH3 indicates that N atoms have been grafted onto P25.

[0029] Combination Figure 12 The UV-Vis DRS plot of plasma-modified P25 shows that as the modification time increases, the photocatalytic wavelength of P25 gradually shifts towards the visible light red. Combined with... Figure 13 The photocatalytic spectrum of plasma-modified P25 titanium dioxide with methylene blue shows that the photocatalytic efficiency of P25 gradually increases with the increase of modification time, reaching 98% after 3 hours, which is 7% higher than that of unmodified P25.

[0030] Next, using the four photocatalytic composite powders TiO2 / 5wt%AG_A, TiO2 / 5wt%NG_B, TiO2 / 5wt%CG_C, and TiO2 / 5wt%rGO after low-temperature plasma modification according to the present invention, photocatalytic experiments on methylene blue MB pollutants were conducted under the same conditions as described above. Figure 14 As shown, P25_N2-plasma_3hr achieved a photocatalytic efficiency of 98%, while TiO2 / CGC synthesized by high-shear delamination CGC-Graphene, using the same modification parameters, also achieved a photocatalytic efficiency of 98%. At the same time, the efficiency of all samples increased by nearly 20% after nitrogen doping modification.

[0031] Finally, 15wt% of plasma-modified TiO2-N / Graphene powder, 500ml of ethylene glycol, and 1% of dispersant were dispersed by ball milling at 200 rpm for 10 hours using Φ3mm ceramic balls as the grinding medium, resulting in the modified photocatalyst / graphene polishing slurry with a uniform viscosity and stable performance of 30cp. A photograph of any of these products is shown below. Figure 15 As shown.

[0032] In addition, to visually highlight the intrinsic performance of the polishing slurry prepared by this invention under photocatalytic working mode, this embodiment further designed two sets of independent variables to form a total of 6 experimental (AF) groups, as shown in the table below. All groups were conducted under the condition of turning on a 365nm UV light source. The independent variable 1 was the polishing slurry type (3 types); the independent variable 2 was the polishing pad type (2 types), namely IC1000 (hard pad) and Suba600 (soft pad). Six sets of comparative experiments were designed for this invention, as shown in the table below: All the above groups were polished for 1 hour using 2-inch N-type 4H-SiC wafers (Si face) under a pressure of 0.5 kg / cm², upper / lower disk rotation speeds of 100 / 60 rpm, and 365 nm UV light irradiation. Performance was evaluated using material removal rate (MRR) and surface roughness (Sa). The test results are as follows: Figure 16 , 17 As shown in Figure 18, it can be seen that the material removal rate of the polishing slurry prepared in this invention is significantly better regardless of whether IC1000 or Suba600 polishing pads are used. At the same time, the polishing performance on IC1000 polishing pads is better than that on Suba600 polishing pads, indicating that the polishing slurry of this invention has a better synergistic effect with polishing pads with higher hardness and stable surface morphology, and can achieve a surface roughness Sa of 0.44nm, which is below the industry standard of 0.5nm.

[0033] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing CMP polishing slurry using low-temperature plasma-modified photocatalyst / graphene composite abrasive, characterized in that, The preparation steps include the following: (1) Graphene dispersion was obtained by high-pressure homogenization delamination method; (2) The graphene dispersion obtained above is further processed by a combination of sol-gel method and sintering method to obtain titanium dioxide / graphene composite material, and then the relevant properties are tested. (3) The titanium dioxide / graphene composite material obtained above was modified by low-temperature plasma nitrogen doping to obtain TiO2-N / Graphene, and then the relevant properties were tested. (4) Use the TiO2-N / Graphene obtained above to prepare CMP polishing fluid.

2. The method for preparing CMP polishing slurry using low-temperature plasma-modified photocatalyst / graphene composite abrasive according to claim 1, characterized in that: In step (1) above, deionized water and dispersant are added to the graphite raw material, and the graphene dispersion is obtained by delamination under different pressure conditions in a high-pressure homogenizer for a certain period of time.

3. The method for preparing CMP polishing slurry using low-temperature plasma-modified photocatalyst / graphene composite abrasive according to claim 2, characterized in that: The graphite raw material is selected from artificial graphite, natural graphite, crystalline graphite, or self-made reduced graphene oxide.

4. The method for preparing CMP polishing slurry using low-temperature plasma-modified photocatalyst / graphene composite abrasive according to claim 2, characterized in that: The delamination pressures were selected as 800 bar, 1400 bar, and 1600 bar, respectively, and the delamination time was selected as 20 minutes for each.

5. The method for preparing CMP polishing slurry using low-temperature plasma-modified photocatalyst / graphene composite abrasive according to claim 1, characterized in that: In step (2) above, the graphite dispersion obtained above is mixed with tetraisopropyl titanate and ethanol, and reacted in an oven at a certain temperature for a certain time to form a gel.

6. The method for preparing CMP polishing slurry using low-temperature plasma-modified photocatalyst / graphene composite abrasive according to claim 5, characterized in that: The gel obtained above was sintered under an inert gas for a period of time to obtain TiO2 / Graphene composite powder, and then the relevant properties were tested.

7. The method for preparing CMP polishing slurry using low-temperature plasma-modified photocatalyst / graphene composite abrasive according to claim 1, characterized in that: In step (3) above, the gas flow rate is 80 sccm, the vacuum degree is 1×10⁻³ Torr, and the power is 400 W. The gas is modified for 15 min to 3 h, and then the modification effect is characterized by testing.

8. The method for preparing CMP polishing slurry using low-temperature plasma-modified photocatalyst / graphene composite abrasive according to claim 1, characterized in that: In step (4) above, the plasma-modified TiO2-N / Graphene, ethylene glycol and dispersant are dispersed by a dispersion process.

9. A method for preparing CMP polishing slurry using low-temperature plasma-modified photocatalyst / graphene composite abrasive according to claim 8, characterized in that: The dispersion process uses Φ3mm ceramic balls as the grinding medium and ball mills them at 200 rpm for 10 hours to finally obtain modified photocatalyst / graphene polishing abrasive with uniform viscosity and stable performance.

10. A CMP polishing slurry prepared by the method described in any one of claims 1 to 9 using low-temperature plasma-modified photocatalyst / graphene composite abrasive.

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