A polishing liquid for silicon carbide wafers and a method for preparing the same

Abstract

The present application relates to the field of grinding and polishing technology, in particular to a polishing liquid for silicon carbide wafer and a preparation method thereof. The polishing liquid comprises the following components based on the total mass of the polishing liquid: 2-10 wt% of alumina abrasive, 1-5 wt% of oxidizing agent, 0.01-0.3 wt% of compound dispersant, 0.001-0.2 wt% of auxiliary agent, and the balance is water; the polishing liquid further comprises a pH regulator to adjust the pH of the polishing liquid to 8-11; and the compound dispersant comprises an organic dispersant and an inorganic dispersant. The polishing liquid significantly improves the stability of the polishing liquid in the recycling process and effectively reduces the rate decay rate in the recycling process through the synergistic effect of the components, while maintaining a high initial polishing rate, thereby better meeting the strict requirements of semiconductor manufacturing on process window and cost control.

Description

Technical Field

[0001] This invention relates to the field of grinding and polishing technology, and in particular to a polishing slurry for silicon carbide wafers and its preparation method. Background Technology

[0002] Silicon carbide, as a core substrate material for third-generation semiconductors, has irreplaceable application value in high-temperature, high-frequency, and high-power electronic devices. As a fundamental material for device fabrication, the quality of its global surface planarization directly determines the performance of the final device. Currently, chemical mechanical polishing (CMP) has become the mainstream processing technology both domestically and internationally to achieve ultra-smooth and damage-free processing of silicon carbide wafers. In this process, the polishing slurry is a key factor affecting material removal rate and surface quality. Among numerous polishing slurry systems, alumina-based polishing slurries have become one of the important technical routes in the field of silicon carbide substrate CMP due to their excellent comprehensive performance in terms of "high-efficiency removal, low damage, and controllable cost."

[0003] However, due to their large specific surface area and high surface energy, alumina particles are prone to agglomeration and sedimentation in liquid media, especially at pH levels deviating from the isoelectric point of alumina, leading to decreased dispersion stability of the polishing slurry. Therefore, dispersants are typically used to improve the suspension of alumina particles and the stability of the system.

[0004] However, in existing silicon carbide polishing slurries, potassium permanganate is often used as an oxidant to achieve high-efficiency polishing. Because potassium permanganate has a strong oxidation potential, it can rapidly destroy the easily oxidized functional groups in most conventional organic dispersant molecules, causing molecular chain breakage and loss of their dispersion function, ultimately leading to a significant decrease in the dispersion stability of alumina particles in the system.

[0005] The aforementioned problems not only shorten the storage life of the polishing slurry but also cause dynamic changes in particle size during actual polishing, leading to fluctuations in material removal rate, performance degradation, and a significant increase in the risk of wafer surface scratches. Therefore, the insufficient dispersion stability of alumina polishing slurries has become a key bottleneck restricting the processing efficiency and surface quality consistency of silicon carbide wafers.

[0006] Based on relevant mechanistic studies in the field of particle dispersion, the key to improving the dispersion stability of alumina polishing slurry lies in effectively controlling the interaction forces between particles. For example, particle surface modification can enhance the electrostatic repulsion between particles or introduce steric hindrance effects, thereby inhibiting particle aggregation.

[0007] Currently, various dispersion strategies have been proposed and applied in practice. For example, US Patent 6258137B1 proposes coating the surface of alumina abrasive particles with a dense layer of nano-silica particles, thereby preventing direct contact between alumina particles and fundamentally inhibiting their agglomeration during processing and storage. US Patent 11130682B2, on the other hand, starts from the source, precisely controlling the microstructure (such as grain size, porosity), specific surface area, and particle size distribution of α-alumina to optimize its dispersibility and fragmentation behavior in polishing slurry, achieving a balance between high removal rate and excellent surface finish. In addition, US Patent 10329455B introduces inorganic dispersants such as aluminosilicates, allowing them to adsorb onto the abrasive surface or be uniformly dispersed in the slurry, effectively preventing particle agglomeration and sedimentation through physical barrier effects, and improving the stability of the slurry. Chinese patent CN119410272A proposes adding organic dispersants such as quaternary ammonium salts, phosphate salts, acrylates, and polyacrylates to significantly enhance the dispersion stability of the slurry by utilizing their steric hindrance effect. Although inorganic dispersants can significantly increase the Zeta potential of alumina particles through specific adsorption and achieve efficient initial dispersion through strong electrostatic repulsion, during cyclic polishing, the ionic strength of the system rises sharply with the continuous accumulation of byproducts such as potassium ions and silicates, severely compressing the electric double layer, causing the electrostatic stabilization mechanism to fail rapidly, ultimately leading to particle agglomeration and performance degradation.

[0008] Despite the existence of various dispersion strategies, in practical industrial applications, most companies still commonly use a single type of dispersant due to limitations in material costs and process complexity. These dispersants have significant limitations in improving the dispersibility of alumina polishing slurries. Specifically, they not only struggle to balance initial dispersion with long-term stability, but also fail to effectively suppress the continuous decline in material removal rate during polishing. Furthermore, as the polishing reaction proceeds, factors such as abrasive agglomeration, byproduct accumulation, and pH fluctuations further exacerbate the decline in polishing performance.

[0009] Therefore, there is an urgent need to develop a new dispersant system and its matching polishing slurry, so that in silicon carbide wafer polishing applications, it can maintain a high initial polishing rate, significantly improve cycle stability, and reduce polishing rate decay, thereby meeting the stringent requirements of semiconductor manufacturing for process window and cost control. Summary of the Invention

[0010] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a polishing slurry for silicon carbide wafers and a method for preparing the same. The polishing slurry described in this application effectively solves the problems of existing alumina polishing slurries in the silicon carbide wafer polishing process, which struggle to balance initial dispersibility and long-term stability, as well as the difficulty in effectively suppressing the decay of material removal rate.

[0011] To achieve the above and other related objectives, the present invention is obtained through the following technical solution.

[0012] The first aspect of this invention discloses a polishing slurry for silicon carbide wafers. Based on the total mass of the polishing slurry, the slurry comprises the following components: 2-10 wt% alumina abrasive, 1-5 wt% oxidant, 0.01-0.3 wt% compound dispersant, 0.001-0.2 wt% additives, and the balance being water. The polishing slurry also includes a pH adjuster to adjust the pH to 8-11. The compound dispersant includes both organic and inorganic dispersants. The components of the polishing slurry work synergistically to maintain a high initial polishing rate while significantly improving cycle stability and reducing polishing rate decay, thereby meeting the stringent requirements of semiconductor manufacturing for process windows and cost control.

[0013] The content of the alumina abrasive can be 2-3 wt%, 3-4 wt%, 4-5 wt%, 5-6 wt%, 6-7 wt%, 7-8 wt%, 8-9 wt%, or 9-10 wt%. If the content of the alumina abrasive is too low, the removal rate will be low and the reaction layer cannot be effectively removed; if the content of the alumina abrasive is too high, the polishing effect will decrease, the cost will increase, and the silicon carbide wafer surface will have more scratches, higher roughness, and poor uniformity.

[0014] The content of the oxidant as described can be 1~2 wt%, 2~3 wt%, 3~4 wt%, or 4~5 wt%.

[0015] The content of the compound dispersant can be 0.01~0.015 wt%, 0.015~0.02 wt%, 0.02~0.1 wt%, 0.1~0.15 wt%, 0.15~0.2 wt%, 0.2~0.25 wt%, or 0.25~0.3 wt%.

[0016] The content of the aforementioned auxiliary agent may be 0.001~0.005 wt%, 0.005~0.01 wt%, 0.01~0.025 wt%, 0.025~0.05 wt%, 0.05~0.1 wt%, 0.1~0.15 wt%, or 0.15~0.2 wt%.

[0017] The pH adjuster adjusts the pH of the polishing solution to 8-8.5, 8.5-9, 9-9.5, 9.5-10, 10-10.5, or 10.5-11. Preferably, the pH adjuster adjusts the pH of the polishing solution to 9-10.5.

[0018] Preferably, the oxidant includes one or more of potassium permanganate, sodium permanganate, potassium periodate, and potassium iodate.

[0019] More preferably, the oxidant is potassium permanganate.

[0020] Preferably, the organic dispersant is an oxidation-resistant organic dispersant.

[0021] More preferably, the oxidation-resistant organic dispersant is selected from one or more of polycarboxylic acid copolymer salts, polyether carboxylic acid copolymer salts, and carboxylic acid copolymer salts containing sulfonic acid groups.

[0022] More preferably, the oxidation-resistant organic dispersant is selected from one or more of sodium polystyrene sulfonate, sodium maleate-acrylic acid copolymer, and sodium polyacrylate.

[0023] In this application, the number average molecular weight of the sodium polystyrene sulfonate is 50,000 to 100,000, the number average molecular weight of the sodium maleic acrylate copolymer is 3,000 to 70,000, and the number average molecular weight of the sodium polyacrylate is 1,000 to 10,000.

[0024] The number average molecular weight of the sodium polystyrene sulfonate as described can be 50,000~60,000, 60,000~70,000, 70,000~80,000, 80,000~90,000, or 90,000~100,000.

[0025] The number average molecular weight of the sodium salt of the maleic acrylate copolymer can be 3000~6000, 6000~9000, 9000~10000, 10000~20000, 20000~30000, 30000~40000, 40000~50000, 50000~60000, or 60000~70000.

[0026] The number average molecular weight of the sodium polyacrylate as described can be 1000~2000, 2000~3000, 3000~4000, 4000~5000, 5000~6000, 6000~7000, 7000~8000, 8000~9000, or 9000~10000.

[0027] Preferably, the inorganic dispersant is selected from one or more polyphosphates and silicates.

[0028] More preferably, the polyphosphate is selected from one or more of sodium hexametaphosphate, sodium pyrophosphate, sodium tripolyphosphate, and silicates.

[0029] More preferably, the silicate includes one or more of sodium silicate and magnesium aluminum silicate.

[0030] Preferably, the mass ratio of the organic dispersant to the inorganic dispersant in the compound dispersant is 1:(0.05~20).

[0031] Preferably, the alumina abrasive is selected from one or more of α-Al2O3, β-Al2O3 and γ-Al2O3.

[0032] More preferably, the alumina abrasive is α-Al2O3.

[0033] Preferably, the D of the alumina abrasive 50 The range is 0.1-0.5 μm. For example, it can be 0.1~0.15 μm, 0.15~0.2 μm, 0.2~0.25 μm, 0.25~0.3 μm, 0.3~0.4 μm, or 0.4~0.5 μm.

[0034] More preferably, the alumina abrasive has a particle size range of 0.15-0.3 μm.

[0035] Preferably, the pH adjuster is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, disodium hydrogen phosphate, and sodium dihydrogen phosphate.

[0036] More preferably, the pH adjuster is selected from potassium hydroxide and potassium carbonate.

[0037] Preferably, the additive is selected from one or more of calcium nitrate, calcium oxide, calcium hydroxide, calcium sulfate, and calcium metaborate.

[0038] More preferably, the additive is selected from one or more of calcium nitrate and calcium oxide.

[0039] The second aspect of the present invention discloses a method for preparing the polishing liquid as described above, the method comprising the following steps: stirring and mixing the raw material components.

[0040] Preferably, the mixing sequence is as follows: first, water is mixed evenly with dispersant, alumina abrasive, potassium permanganate, and additives in sequence; then, pH adjuster is added and mixed evenly to adjust the pH of the mixture to 8-11.

[0041] The third aspect of the present invention also discloses the use of the polishing slurry described above in the rough polishing of silicon carbide wafers.

[0042] The fourth aspect of the present invention also discloses the use of a compound dispersant in improving the dispersion stability of an alumina polishing slurry for silicon carbide wafers, said compound dispersant comprising an organic dispersant and an inorganic dispersant.

[0043] Preferably, the raw material components of the polishing liquid include an oxidant, and the polishing liquid is alkaline. The oxidant includes one or more of potassium permanganate, sodium permanganate, potassium periodate, and potassium iodate.

[0044] Preferably, the organic dispersant is an oxidation-resistant organic dispersant.

[0045] More preferably, the oxidation-resistant organic dispersant is selected from one or more of polycarboxylic acid copolymer salts, polyether carboxylic acid copolymer salts, and carboxylic acid copolymer salts containing sulfonic acid groups.

[0046] Preferably, the inorganic dispersant is selected from one or more polyphosphates and silicates.

[0047] More preferably, the polyphosphate is selected from one or more of sodium hexametaphosphate, sodium pyrophosphate, sodium tripolyphosphate, and silicates.

[0048] More preferably, the silicate includes one or more of sodium silicate and magnesium aluminum silicate.

[0049] Preferably, the mass ratio of the organic dispersant to the inorganic dispersant in the compound dispersant is 1:(0.05~20).

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] 1) In the polishing slurry described in this application, the compound dispersant, through the combination of organic and inorganic dispersants, constructs a novel composite stabilization mechanism of "electrostatic-steric synergy," overcoming the limitations of a single stabilization mode. In the compound dispersant, the inorganic dispersant adsorbs onto the particle surface through electrostatic interaction, providing strong electrostatic repulsion and achieving initial rapid dispersion of alumina particles. Simultaneously, the specially selected oxidation-resistant organic dispersant adsorbs onto the particle surface through its long-chain structure, forming a robust steric barrier. Electrostatic repulsion lays the foundation for the uniform construction of the steric barrier layer, while steric hindrance becomes the dominant force maintaining long-term stability when electrostatic interaction weakens due to the accumulation of byproducts. These two mechanisms work synergistically to achieve dual stability in storage and polishing performance.

[0052] 2) The polishing slurry disclosed in this application, through the synergistic effect of its components, can dynamically maintain a narrow distribution and high stability of abrasive particle size in the slurry, fundamentally reducing the risk of surface scratches caused by the formation of large-sized agglomerates, while ensuring a constant number of effective abrasive particles participating in the polishing reaction and stability of mechanical removal efficiency. This allows the polishing slurry, when used for polishing silicon carbide wafers, to maintain a high initial polishing rate and significantly improve cycle stability and reduce polishing rate decay, thereby ensuring that the material removal rate remains at a high level even after multiple consecutive cycles. Detailed Implementation

[0053] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0054] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0055] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0056] In this application, addressing the technical problems of existing alumina polishing slurries in silicon carbide wafer polishing processes, which struggle to balance initial dispersion performance and long-term stability, and effectively suppress the continuous decline in material removal rate, the applicant provides a polishing slurry for silicon carbide wafers and its preparation method. The polishing slurry described in this application exhibits high dispersion stability, dynamically maintaining a narrow distribution and stability of abrasive particle size within the slurry. This enables it to significantly improve its cyclic stability while maintaining a high initial polishing rate, effectively suppressing rate decay during cyclic polishing, and ensuring that the material removal rate remains at a high level even after multiple consecutive polishing cycles.

[0057] Specifically, this invention provides a specific polishing slurry and its preparation method. Based on the total mass of the polishing slurry, the slurry comprises the following components: 2-10 wt% alumina abrasive, 1-5 wt% oxidant, 0.01-0.3 wt% compound dispersant, 0.001-0.2 wt% additives, and the balance being water. The polishing slurry also includes a pH adjuster to adjust the pH to 8-11. The compound dispersant includes organic and inorganic dispersants. The synergistic effect of the components in the polishing slurry allows it to maintain a high material removal rate while effectively controlling the attenuation of the polishing rate and significantly reducing the roughness and scratches on the wafer surface. This provides a reliable technical solution for efficient, high-quality, and low-loss global planarization processing of third-generation semiconductor substrates.

[0058] The content of each raw material component in this application can be adjusted according to actual polishing and production needs.

[0059] The content of the alumina abrasive can be 2-3 wt%, 3-4 wt%, 4-5 wt%, 5-6 wt%, 6-7 wt%, 7-8 wt%, 8-9 wt%, or 9-10 wt%. If the content of the alumina abrasive is less than 2 wt%, the removal rate is low and the reaction layer cannot be effectively removed; if the content of the alumina abrasive is greater than 10 wt%, it will lead to a decrease in polishing effect and an increase in cost, while the silicon carbide wafer surface will have more scratches, higher roughness, and poor uniformity.

[0060] The content of the oxidant can be 1~2 wt%, 2~3 wt%, 3~4 wt%, or 4~5 wt%. If the oxidant content is less than 1 wt%, the chemical action of the polishing slurry is weak, the removal rate is low, and the mechanical damage is large; if the oxidant content is higher than 5 wt%, it will cause surface corrosion and pitting / fogging defects, and there will also be problems such as surface contamination by by-products.

[0061] The content of the compound dispersant can be 0.01~0.015 wt%, 0.015~0.02 wt%, 0.02~0.1 wt%, 0.1~0.15 wt%, 0.15~0.2 wt%, 0.2~0.25 wt%, or 0.25~0.3 wt%. If the content of the compound dispersant is less than 0.01 wt%, the alumina abrasive particles will agglomerate due to van der Waals forces, forming hard agglomerates with a size much larger than the original particle size, thereby causing severe mechanical scratches, deep grooves, and high surface roughness on the workpiece surface. If the content of the compound dispersant is greater than 0.3 wt%, the excessive dispersant will form micelles in the solution, or the excessively thick adsorption layer will generate excessive steric hindrance, which may excessively lubricate the contact between the abrasive and the workpiece surface, weakening the effective cutting ability of the abrasive and leading to a decrease in material removal rate. Meanwhile, a large number of dispersant molecules may competitively adsorb onto the workpiece surface, hindering the effective contact between potassium permanganate oxidant and silicon carbide surface, thus weakening the chemical reaction.

[0062] The content of the aforementioned auxiliary agent may be 0.001~0.005 wt%, 0.005~0.01 wt%, 0.01~0.025 wt%, 0.025~0.05 wt%, 0.05~0.1 wt%, 0.1~0.15 wt%, or 0.15~0.2 wt%.

[0063] The pH adjuster adjusts the polishing slurry pH to 8-8.5, 8.5-9, 9-9.5, 9.5-10, 10-10.5, or 10.5-11. Preferably, the pH adjuster adjusts the polishing slurry pH to 9-10.5. Within this pH range, the polishing slurry achieves the best synergistic effect of mechanical polishing and chemical action on silicon carbide wafers. If the pH is below 8, the chemical action is weak, the softening rate of the silicon carbide wafer surface is slow, leading to difficulties in mechanical removal and low efficiency. If the pH is above 11, the chemical action is too strong, not only softening the silicon carbide wafer surface but also corroding or softening the alumina abrasive itself, causing the abrasive to "passivate," lose its cutting ability, and the polishing rate drops sharply.

[0064] In this application, the mechanism by which the polishing slurry maintains excellent dispersion stability over a long period of time is as follows:

[0065] A novel composite stability mechanism based on electrostatic-steric synergy was constructed, overcoming the limitations of a single stability mode.

[0066] In the polishing slurry of this invention, the inorganic dispersant provides a strong initial electrostatic repulsion force through characteristic adsorption, achieving rapid primary dispersion of alumina particles. Simultaneously, a specially screened, oxidation-resistant organic dispersant adsorbs onto the particle surface through its long-chain structure, forming a robust steric barrier. Electrostatic repulsion lays the foundation for the uniform construction of the steric barrier layer, while steric hindrance becomes the dominant force maintaining long-term stability when electrostatic effects weaken due to the accumulation of byproducts. These two mechanisms work synergistically to achieve dual stability in both storage and polishing performance.

[0067] It effectively suppressed the attenuation of the polishing rate during the cyclic polishing process.

[0068] Through the aforementioned mechanism, this invention can dynamically maintain a narrow distribution and stability of abrasive particle size in the polishing slurry. This not only fundamentally reduces the risk of surface scratches caused by the formation of large-sized agglomerates, but more importantly, ensures a constant number of effective abrasive particles participating in the polishing reaction and reduces the decay of the polishing rate. Therefore, the polishing slurry can significantly suppress the decay of the polishing rate, ensuring that its material removal rate remains at a high level after multiple consecutive polishing cycles.

[0069] In one specific embodiment, the oxidant includes one or more of potassium permanganate, sodium permanganate, potassium periodate, and potassium iodate.

[0070] In a more specific embodiment, the oxidant is potassium permanganate.

[0071] In one specific embodiment, the organic dispersant is an oxidation-resistant organic dispersant.

[0072] In a more specific embodiment, the oxidation-resistant organic dispersant is selected from one or more of polycarboxylic acid copolymer salts, polyether carboxylic acid copolymer salts, and carboxylic acid copolymer salts containing sulfonic acid groups. During long-term coexistence with strong oxidants, the oxidation-resistant organic dispersant provides strong steric hindrance, resisting erosion and gradually breaking down its chains. This results in low consumption of the oxidant in the system and ensures long-term dispersion.

[0073] In a further specific embodiment, the oxidation-resistant organic dispersant is selected from one or more of sodium polystyrene sulfonate, sodium maleate-acrylic acid copolymer, and sodium polyacrylate.

[0074] In this application, the number average molecular weight of the sodium polystyrene sulfonate is 50,000 to 100,000, the number average molecular weight of the sodium maleic acrylate copolymer is 3,000 to 70,000, and the number average molecular weight of the sodium polyacrylate is 1,000 to 10,000.

[0075] If the number average molecular weight of sodium polystyrene sulfonate, sodium maleic acrylate copolymer, and sodium polyacrylate is lower than the above-mentioned limits, the molecular chain of the organic dispersant is shorter, there are fewer adsorption sites on the surface of alumina particles, the adsorption strength is weaker, and it is easy to desorb under mechanical shear or thermodynamic disturbance, resulting in a decrease in dispersion stability. At the same time, when the number average molecular weight is too low, the chain length is insufficient, and an effective steric hindrance layer cannot be formed, and the particles may still agglomerate due to van der Waals forces.

[0076] If the number average molecular weight of sodium polystyrene sulfonate, sodium maleate-acrylic acid copolymer, and sodium polyacrylate exceeds the aforementioned limits, the organic dispersant chain length will be too long. This may cause it to adsorb onto multiple particles simultaneously, forming a "bridging" effect, leading to interparticle aggregation and flocculation, which in turn damages the dispersion stability. Simultaneously, high molecular weight organic dispersants may significantly increase the viscosity of the polishing slurry, affecting the hydrodynamics and particle movement during the polishing process, and even causing a decrease in polishing uniformity.

[0077] The number average molecular weight of the sodium polystyrene sulfonate as described can be 50,000~60,000, 60,000~70,000, 70,000~80,000, 80,000~90,000, or 90,000~100,000.

[0078] The number average molecular weight of the sodium salt of the maleic acrylate copolymer can be 3000~6000, 6000~9000, 9000~10000, 10000~20000, 20000~30000, 30000~40000, 40000~50000, 50000~60000, or 60000~70000.

[0079] The number average molecular weight of the sodium polyacrylate as described can be 1000~2000, 2000~3000, 3000~4000, 4000~5000, 5000~6000, 6000~7000, 7000~8000, 8000~9000, or 9000~10000.

[0080] In the following specific embodiments, the number average molecular weight of sodium polystyrene sulfonate is 70,000, the number average molecular weight of sodium maleic acrylate copolymer is 30,000, and the number average molecular weight of sodium polyacrylate is 6,000.

[0081] It should be noted that the selection of organic dispersants described in this application can be adjusted according to actual production or economic needs. Any organic dispersant with long branches and oxidation resistance is considered an organic dispersant described in this application.

[0082] In one specific embodiment, the inorganic dispersant is selected from one or more polyphosphates and silicates.

[0083] In a more specific embodiment, the polyphosphate includes one or more of sodium hexametaphosphate, sodium pyrophosphate, sodium tripolyphosphate, and silicates.

[0084] In a more specific embodiment, the silicate includes one or more of sodium silicate and magnesium aluminum silicate.

[0085] In one specific embodiment, the mass ratio of the organic dispersant to the inorganic dispersant in the compound dispersant is 1:(0.05~20). For example, it can be 1:(0.05~0.2), 1:(0.2~0.33), 1:(0.33~0.5), 1:(0.5~0.67), 1:(0.67~1), 1:(1~1.33), 1:(1.33~2), 1:(2~2.33), 1:(2.33~5), 1:(5~9), 1:(9~10), 1:(10~15), 1:(15~20). If the mass ratio of the organic dispersant to the inorganic dispersant is greater than 1:0.05, the proportion of organic dispersant is too high, and the storage stability of the polishing solution decreases; if the mass ratio of the organic dispersant to the inorganic dispersant is less than 1:20, the proportion of inorganic dispersant is too high, and the stability of the polishing solution decreases during cyclic polishing.

[0086] In one specific embodiment, the alumina abrasive is selected from one or more of α-Al2O3, β-Al2O3, and γ-Al2O3.

[0087] In a more specific embodiment, the alumina abrasive is α-Al2O3.

[0088] In a more specific embodiment, the alumina abrasive particle size ranges from 0.1 to 0.5 μm. For example, it can be 0.1~0.15 μm, 0.15~0.2 μm, 0.2~0.25 μm, 0.25~0.3 μm, 0.3~0.4 μm, or 0.4~0.5 μm. The alumina abrasive performs a grinding action, thereby improving the removal rate. If the alumina abrasive particle size is too small, the polishing efficiency and effect will decrease; if the alumina abrasive particle size is too large, unacceptable scratches will easily be generated on the silicon carbide wafer surface, affecting the polishing effect.

[0089] In a further specific embodiment, the alumina abrasive has a particle size range of 0.15-0.3 μm.

[0090] In one specific embodiment, the pH adjuster is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, disodium hydrogen phosphate, and sodium dihydrogen phosphate. The pH adjuster can enhance the chemical reaction between the polishing solution and the wafer surface, thereby increasing the removal rate. It should be noted that the selection of the pH adjuster includes, but is not limited to, the examples listed above; the pH adjuster can be any compound that can increase alkalinity.

[0091] In a more specific embodiment, the pH adjuster is selected from potassium hydroxide and potassium carbonate.

[0092] In one specific embodiment, the auxiliary agent is selected from one or more of calcium nitrate, calcium oxide, calcium hydroxide, calcium sulfate, and calcium metaborate. Preferably, the auxiliary agent is selected from one or more of calcium nitrate and calcium oxide.

[0093] This invention provides a specific method for preparing a polishing liquid, the method comprising the following steps: stirring and mixing the raw material components.

[0094] In one specific embodiment, the mixing sequence is as follows: first, water is mixed evenly with dispersant, alumina abrasive, potassium permanganate, and additives in sequence; then, pH adjuster is added and mixed evenly to adjust the pH of the mixture to 8-11.

[0095] It should be noted that the mixing speed and time can be adjusted by the actual equipment used for dispersion and its power, as long as the raw materials are evenly dispersed. For example, a shorter dispersion time / shorter agitator blades require a faster rotation speed; a longer dispersion time / longer agitator blades require a slower rotation speed. Similarly, a faster mixing speed requires a shorter dispersion time; a slower mixing speed requires a longer dispersion time.

[0096] The present invention also discloses the use of a compound dispersant in improving the dispersion stability of an alumina polishing slurry for silicon carbide wafers, wherein the compound dispersant comprises an organic dispersant and an inorganic dispersant.

[0097] In one specific embodiment, the raw material components of the polishing liquid include an oxidant, and the polishing liquid is alkaline. The oxidant includes one or more of potassium permanganate, sodium permanganate, potassium periodate, and potassium iodate.

[0098] In one specific embodiment, the organic dispersant is an oxidation-resistant organic dispersant.

[0099] In a more specific embodiment, the oxidation-resistant organic dispersant is selected from one or more of polycarboxylic acid copolymer salts, polyether carboxylic acid copolymer salts, and carboxylic acid copolymer salts containing sulfonic acid groups.

[0100] In one specific embodiment, the inorganic dispersant is selected from one or more polyphosphates and silicates.

[0101] In a more specific embodiment, the polyphosphate is selected from one or more of sodium hexametaphosphate, sodium pyrophosphate, sodium tripolyphosphate, and silicates.

[0102] In a more specific embodiment, the silicate includes one or more of sodium silicate and magnesium aluminum silicate.

[0103] In one specific embodiment, the mass ratio of the organic dispersant to the inorganic dispersant in the compound dispersant is 1:(0.05~20).

[0104] It should be noted that the technical effect of the compound dispersant in improving the dispersion stability of the polishing slurry is also applicable to other polishing systems, such as polishing slurries for silicon carbide wafers with silicon dioxide or cerium dioxide as abrasives.

[0105] In the following embodiments of this application, the abrasive particle size D 50 Polishing rate, rate decay rate, and surface roughness were obtained through the following test methods:

[0106] 1) Abrasive particle size D 50 The particle size distribution was obtained using a Baxter 2600 particle size analyzer.

[0107] 2) The polishing rate is calculated using the following formula: Polishing rate = thickness removed (µm) / polishing time (h) = mass removed (mg) / 56.52 (g / cm) / polishing time (h)

[0108] In this study, a 6-inch silicon carbide substrate was polished using a Zhejiang Mingzheng 36B single-sided polishing machine, and the quality difference of the silicon carbide substrate before and after polishing was recorded. In the specific embodiments described below, the polishing parameters were: polishing machine platform: 915 mm; polishing slurry prepared according to the previous example; polishing slurry flow rate: 400 ml / min; polishing pressure: 238 g / cm³; lower plate rotation speed: 40 rpm; polishing time: 8 h; each run was 1 h; and water with the same pH was added each run.

[0109] 3) The rate decay rate is calculated using the following formula: Rate decay rate / % = (Initial removal rate - Removal rate after 8 hours of cyclic polishing) / Initial removal rate × 100% Ion strength I is calculated using the following formula: Ion strength = ½ × Σ(Concentration × Charge²).

[0110] 4) Surface roughness was calculated using the following method: a VEECO atomic force microscope was used for testing, with a test area of ​​5μm*5μm at each location, and the average roughness of 3 locations was calculated.

[0111] Example 1

[0112] This embodiment provides a specific polishing slurry and its preparation method. The preparation method includes the following steps: the amounts of alumina, potassium permanganate, dispersant, and additives in the polishing slurry, based on the total mass of the polishing slurry, are shown in Table 1, and the remainder is water.

[0113] (1) At room temperature, dissolve the dispersant in deionized water and stir thoroughly until completely dissolved to form a homogeneous dispersant solution A;

[0114] (2) Under the combined action of continuous mechanical stirring and ultrasound, alumina powder is slowly and evenly added to solution A. After the addition is complete, continue ultrasonic stirring for 30-60 minutes to ensure that the alumina particles are fully deagglomerated and stably dispersed to obtain a uniformly suspended slurry B;

[0115] (3) Add potassium permanganate oxidant to the obtained slurry B and stir continuously for 30 minutes to ensure that the oxidant is evenly distributed in the system to obtain mixture C;

[0116] (4) Add the auxiliary agent to the mixed solution C and stir for 30 minutes to ensure that the system is fully mixed and homogeneous, so as to obtain the mixed solution D;

[0117] (5) Add a pH adjuster to the mixed solution D, adjust the pH value to 10.5, and continue to stir and disperse for a certain period of time to obtain the alumina CMP polishing solution for SiC substrate.

[0118] Examples 2-12

[0119] In this embodiment, a specific polishing liquid and its preparation method are provided. The difference between the preparation method and that in Example 1 is that the raw material components of the polishing liquid are different, as shown in Table 1.

[0120] Comparative Examples 1-13

[0121] In this comparative example, a specific polishing slurry and its preparation method are provided. The difference between the preparation method of the polishing slurry and that of Example 1 is that the raw material components of the polishing slurry are different, as shown in Table 1.

[0122] Table 1. Raw material composition of polishing fluid

[0123] Alumina abrasive (wt%) Oxidizing agent (potassium permanganate) (wt%) Dispersant (wt%) Additives (wt%) Example 1 3 3 Sodium tripolyphosphate (0.045) - Sodium polystyrene sulfonate (0.005) Calcium nitrate 0.05 Example 2 3 3 Sodium pyrophosphate (0.035) - Sodium polystyrene sulfonate (0.015) Calcium nitrate 0.05 Example 3 3 3 Sodium hexametaphosphate (0.06) - Sodium polystyrene sulfonate (0.04) Calcium nitrate 0.05 Example 4 3 4 Sodium tripolyphosphate (0.05g) - Sodium maleate-acrylic acid copolymer (0.05g) Calcium oxide 0.05 Example 5 3 4 Sodium tripolyphosphate (0.05) - Sodium polyacrylate (0.15) Calcium oxide 0.05 Example 6 3 4 Sodium tripolyphosphate (0.05g) - Sodium polyacrylate (0.1g) Calcium oxide 0.05 Example 7 3 4 Sodium tripolyphosphate (0.1%) - Sodium polyacrylate (0.15%) Calcium sulfate 0.05 Example 8 9 3 Sodium pyrophosphate (0.035) - Sodium polystyrene sulfonate (0.015) Calcium nitrate 0.05 Example 9 3 2 Sodium pyrophosphate (0.035) - Sodium polystyrene sulfonate (0.015) Calcium nitrate 0.05 Example 10 3 3 Sodium pyrophosphate (0.15) - Sodium polystyrene sulfonate (0.15) Calcium nitrate 0.05 Example 11 3 3 Sodium pyrophosphate (0.01) - Sodium polystyrene sulfonate (0.005) Calcium nitrate 0.05 Example 12 3 3 Sodium pyrophosphate (0.035) - Sodium polystyrene sulfonate (0.015) Calcium nitrate 0.2 Comparative Example 1 3 3 Sodium tripolyphosphate 0.05 Calcium nitrate 0.05 Comparative Example 2 3 3 Sodium pyrophosphate 0.05 Calcium nitrate 0.05 Comparative Example 3 3 3 Sodium hexametaphosphate 0.1 Calcium nitrate 0.05 Comparative Example 4 3 3 Sodium polyacrylate 0.05 Calcium nitrate 0.05 Comparative Example 5 3 3 Sodium polystyrene sulfonate 0.05 Calcium oxide 0.05 Comparative Example 6 3 3 Sodium polyacrylate 0.15 Calcium oxide 0.05 Comparative Example 7 3 4 Sodium polystyrene sulfonate 0.1 Calcium oxide 0.05 Comparative Example 8 15 3 Sodium pyrophosphate (0.035) - Sodium polystyrene sulfonate (0.015) Calcium nitrate 0.05 Comparative Example 9 3 15 Sodium pyrophosphate (0.035) - Sodium polystyrene sulfonate (0.015) Calcium nitrate 0.05 Comparative Example 10 3 3 Sodium pyrophosphate (0.25) - Sodium polystyrene sulfonate (0.15) Calcium nitrate 0.05 Comparative Example 11 3 3 Sodium pyrophosphate (0.005) - Sodium polystyrene sulfonate (0.003) Calcium nitrate 0.05 Comparative Example 12 3 3 Sodium pyrophosphate (0.035) - Sodium polystyrene sulfonate (0.015) Calcium nitrate 0.25 Comparative Example 13 3 3 Magnesium aluminum silicate (0.035) + polyethylene glycol (0.015) Calcium nitrate 0.05

[0124] The polishing slurries prepared in Examples 1-12 and Comparative Examples 1-13 were tested using the above-described test methods for initial removal rate, removal rate after 8 hours of cyclic polishing, rate decay rate, and surface roughness. The test results are shown in Table 2.

[0125] Table 2

[0126] Initial removal rate (μm / h) Removal rate (μm / h) after 8 hours of cyclic polishing Rate decay rate / % Surface roughness (nm) Example 1 1.70 1.55 8.8 0.056 Example 2 1.62 1.50 7.4 0.063 Example 3 1.58 1.46 7.6 0.058 Example 4 1.63 1.45 11.0 0.061 Example 5 1.65 1.36 17.6 0.072 Example 6 1.55 1.38 11.0 0.097 Example 7 1.54 1.26 18.2 0.087 Example 8 1.56 1.15 26.3 0.088 Example 9 1.66 1.15 30.7 0.089 Example 10 1.68 1.20 28.6 0.091 Example 11 1.58 1.18 25.3 0.093 Example 12 1.55 1.15 25.8 0.098 Comparative Example 1 1.62 0.45 72.2 0.117 Comparative Example 2 1.58 0.56 64.6 0.225 Comparative Example 3 1.54 0.44 71.4 0.135 Comparative Example 4 1.43 0.45 68.5 0.316 Comparative Example 5 1.45 0.56 61.4 0.225 Comparative Example 6 1.57 0.62 60.5 0.338 Comparative Example 7 1.54 0.54 64.9 0.442 Comparative Example 8 1.63 0.55 66.3 0.529 Comparative Example 9 1.58 0.52 67.1 0.412 Comparative Example 10 1.34 0.47 64.9 0.356 Comparative Example 11 1.62 0.51 68.5 0.576 Comparative Example 12 1.58 0.46 70.9 0.425 Comparative Example 13 1.67 0.41 75.4 0.456

[0127] The applicant further tested the abrasive particle size D of the polishing slurries prepared in Examples 1-12 and Comparative Examples 1-13 using a Baxter 2600 particle size analyzer at the following times: after preparation, after 8 hours of cyclic polishing, and after 1 month of settling. 50 The test results are shown in Table 2.

[0128] Table 2. Statistical table of abrasive particle size in polishing slurry after different placement times.

[0129] <![CDATA[Initial particle size D of alumina in the polishing liquid 50 (nm)]]> <![CDATA[After 8 hours of cyclic polishing, the alumina particle size D 50 (nm)]]> <![CDATA[Aluminum oxide particle size D after storage for 1 month 50 (nm)]]> Example 1 220 589 858 Example 2 222 547 836 Example 3 221 552 860 Example 4 230 621 887 Example 5 234 724 876 Example 6 225 620 888 Example 7 236 746 890 Example 8 238 767 945 Example 9 241 650 923 Example 10 228 594 876 Example 11 237 733 856 Example 12 232 740 934 Comparative Example 1 280 1466 1870 Comparative Example 2 287 1367 1750 Comparative Example 3 290 1255 1659 Comparative Example 4 304 1157 2036 Comparative Example 5 300 1168 2250 Comparative Example 6 297 1210 2310 Comparative Example 7 288 1159 2350 Comparative Example 8 305 1356 2426 Comparative Example 9 299 1377 2645 Comparative Example 10 310 1465 2453 Comparative Example 11 311 1645 2312 Comparative Example 12 301 1555 2561 Comparative Example 13 317 1541 2464

[0130] Test result data explanation:

[0131] With other components and preparation methods being the same, the polishing slurries corresponding to Comparative Examples 1-7 using a single dispersant, the polishing slurries corresponding to Comparative Examples 8-12 with excessive amounts of alumina abrasive, oxidant, dispersant, and additives, and the polishing slurry corresponding to Comparative Example 13 using an organic dispersant not specified in this application, all exhibited the highest removal rate decay rate (up to 75%), the largest particle size increase (up to 1541 nm), and the surface roughness of the treated wafers exceeding 0.1 nm during a continuous 8-hour cyclic polishing test. In contrast, the polishing slurries corresponding to Examples 1-12 using the technical solution of this application showed the best removal rate decay rate (7.4%), the smallest particle size increase (up to 589 nm), and the best surface roughness of the treated wafers (0.056 nm). It is evident that the material removal rate decay rate and particle size change of the polishing slurry of this application are significantly lower than those of Comparative Examples 1-13, demonstrating excellent long-term stability. Simultaneously, the surface roughness of the wafers treated with this polishing slurry is also superior to all comparative examples. The results demonstrate that when the polishing slurry described in this invention is used for polishing silicon carbide wafers, it significantly improves the stability of its repeated use while maintaining a high initial polishing rate, effectively suppresses the rate decay during the repeated polishing process, and ensures that the material removal rate remains at a high level after multiple consecutive polishing cycles.

[0132] In summary, the polishing slurry disclosed in this invention, through the synergistic effect of its components, dynamically maintains a narrow distribution and stability of abrasive particle size within the slurry. This fundamentally reduces the risk of surface scratches caused by large-sized agglomerates, ensures a constant number of effective abrasive particles participating in the polishing reaction, and reduces polishing rate decay. Consequently, when used for polishing silicon carbide wafers, this polishing slurry maintains a high initial polishing rate while significantly improving its stability during repeated use, effectively suppressing rate decay during cyclic polishing, and ensuring that the material removal rate remains at a high level after multiple consecutive polishing cycles.

[0133] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A polishing slurry for silicon carbide wafers, characterized in that, Based on the total mass of the polishing slurry, the polishing slurry comprises the following components: 2-10 wt% alumina abrasive, 1-5 wt% oxidant, 0.01-0.3 wt% compound dispersant, 0.001-0.2 wt% additives, and the balance being water; the polishing slurry also includes a pH adjuster to adjust the pH of the polishing slurry to 8-11; the compound dispersant includes organic dispersants and inorganic dispersants.

2. The polishing slurry according to claim 1, characterized in that, The organic dispersant is an oxidation-resistant organic dispersant; And / or, the inorganic dispersant is selected from one or more polyphosphates and silicates; And / or, the mass ratio of the organic dispersant to the inorganic dispersant in the compound dispersant is 1:(0.05~20); And / or, the alumina abrasive is selected from one or more of α-Al2O3, β-Al2O3 and γ-Al2O3; And / or, the D of the alumina abrasive 50 The thickness is 0.1-0.5 μm. And / or, the pH adjuster is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, disodium hydrogen phosphate, and sodium dihydrogen phosphate; And / or, the additive is selected from one or more of calcium nitrate, calcium oxide, calcium hydroxide, calcium sulfate, and calcium metaborate; And / or, the oxidizing agent includes one or more of potassium permanganate, sodium permanganate, potassium periodate, and potassium iodate.

3. The polishing slurry according to claim 2, characterized in that, The oxidation-resistant organic dispersant is selected from one or more of polycarboxylic acid copolymer salts, polyether carboxylic acid copolymer salts, and carboxylic acid copolymer salts containing sulfonic acid groups; And / or, the silicate includes one or more of sodium silicate and magnesium aluminum silicate; And / or, the alumina abrasive is α-Al2O3; And / or, the pH adjuster is selected from one or more of potassium hydroxide and potassium carbonate; And / or, the inorganic dispersant is selected from one or more of sodium hexametaphosphate, sodium pyrophosphate, sodium tripolyphosphate, and silicates.

4. The polishing slurry according to claim 3, characterized in that, The oxidation-resistant organic dispersant is selected from one or more of sodium polystyrene sulfonate, sodium maleate-acrylic acid copolymer, and sodium polyacrylate.

5. A method for preparing a polishing slurry as described in any one of claims 1 to 4, characterized in that, The preparation method includes the following steps: stirring and mixing the raw material components.

6. The preparation method according to claim 5, characterized in that, The mixing sequence is as follows: first, water is mixed evenly with dispersant, alumina abrasive, potassium permanganate, and additives in sequence; then, pH adjuster is added and mixed evenly to adjust the pH of the mixture to 8-11.

7. The use of the polishing slurry as described in any one of claims 1 to 4 in the rough polishing of silicon carbide wafers.

8. Use of a compound dispersant in improving the dispersion stability of an alumina polishing slurry for silicon carbide wafers, said compound dispersant comprising an organic dispersant and an inorganic dispersant.

9. The use according to claim 8, characterized in that, The raw material components of the polishing liquid include an oxidant, and the polishing liquid is alkaline. The oxidant includes one or more of potassium permanganate, sodium permanganate, potassium periodate, and potassium iodate. And / or, the organic dispersant is an oxidation-resistant organic dispersant; And / or, the inorganic dispersant is selected from one or more polyphosphates and silicates; And / or, the mass ratio of the organic dispersant to the inorganic dispersant in the compound dispersant is 1:(0.05~20).

10. The use according to claim 9, characterized in that, The oxidation-resistant organic dispersant is selected from one or more of polycarboxylic acid copolymer salts, polyether carboxylic acid copolymer salts, and carboxylic acid copolymer salts containing sulfonic acid groups; And / or, the polyphosphate includes one or more of sodium hexametaphosphate, sodium pyrophosphate, sodium tripolyphosphate, and silicates; And / or, the silicate includes one or more of sodium silicate and magnesium aluminum silicate.