Silicon carbide polishing liquid and method for preparing the same

Abstract

The present application relates to polishing technology, specifically to a kind of silicon carbide polishing liquid and preparation method thereof.Polishing liquid is made of including the following raw materials: nanometer spherical mixed abrasive 15-25%, oxidizing agent 0.2-3%, dispersing agent 0.2-3%, suspending agent 0.2-3%, pure water balance;Also includes silane coupling agent, which is 1-2% of the weight of the nanometer spherical mixed abrasive.The polishing liquid of the present application is mainly suitable for the polishing process of single crystal substrate wafer, especially for the single crystal material with high hardness and slow polishing rate, especially suitable for the surface polishing treatment of silicon carbide single crystal substrate wafer.

Description

Technical Field

[0001] This invention relates to grinding and polishing technology, specifically to a silicon carbide polishing slurry and its preparation method. Background Technology

[0002] Silicon carbide (SiC) has become a third-generation semiconductor material for power semiconductor devices due to its high thermal conductivity, high breakdown field strength, large bandgap, high electron saturation drift velocity, and excellent physicochemical properties such as high temperature resistance, radiation resistance, and good chemical stability. SiC materials and devices are developing rapidly. However, SiC has extremely high hardness (Mohs hardness of 9.2) and surface tension, and is also very brittle, making machining extremely difficult and requiring a high level of technical expertise. As a substrate material, the smoothness and finish of its surface significantly affect the quality of the device. Extremely precise grinding and polishing are necessary to achieve a surface roughness Ra in the nanometer range, free of scratches and defects. This makes its fine processing steps very complex and precision machining very difficult.

[0003] The purpose of polishing is to remove mechanical damage such as scratches and pits caused by the previous grinding process and to reduce the surface roughness of the workpiece. The depth of the mechanical damage layer and the magnitude of the surface roughness are related to the abrasive grains in the grinding slurry used in the previous process. Typically, it is necessary to remove a layer of mechanical damage caused by the previous machining process by removing a layer three times the thickness of the abrasive grains in the previous grinding slurry.

[0004] Traditional multi-stage chemical mechanical polishing (CMP) methods for silicon carbide single crystal surfaces use SiO2 colloids of varying particle sizes as abrasives. Because these abrasives are relatively soft (Mohs hardness 7), significantly different from the hardness of silicon carbide crystals (Mohs hardness 9.2), the abrasive force of the SiO2 colloids on silicon carbide is minimal or nonexistent. Direct polishing with SiO2 colloids, even with the accompanying chemical reaction, results in very low polishing efficiency, and may even leave deep scratches on the crystal surface that cannot be removed. Even if a good polishing effect is achieved, the polishing time is extremely long, requiring a day or even several days. Furthermore, while potassium permanganate is currently used as an oxidant in polishing solutions, it is highly unstable, significantly affecting the pH value of the polishing solution during oxidation. Moreover, potassium permanganate is not environmentally friendly and is harmful to both human health and the environment, making its widespread use unsuitable.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The present invention aims to solve at least one of the above-mentioned technical problems.

[0007] This invention provides a silicon carbide polishing slurry and its preparation method, which is mainly applicable to the polishing process of single crystal substrates, especially for single crystal materials with high hardness and slow polishing rate, and is particularly suitable for the surface polishing treatment of silicon carbide single crystal substrates.

[0008] A polishing slurry, by weight percentage, is made from the following raw materials: 15-25% nano-spherical mixed abrasive, 0.2-3% oxidant, 0.2-3% dispersant, 0.2-3% suspending agent, and the balance being pure water; it also includes a silane coupling agent, which is 1-2% by weight of the nano-spherical mixed abrasive; the oxidant is potassium ferrate; the nano-spherical mixed abrasive is a mixture of nano-alumina powder and nano-cerium oxide powder in a weight ratio of (3-10):1; the particle size of the nano-spherical mixed abrasive is 120-600 nm; the nano-spherical mixed abrasive is spherical with a sphericity ≥0.95; the nano-alumina is a mixture of α-alumina and γ-alumina in a weight ratio of (2-5):1.

[0009] Furthermore, the polishing slurry is made from the following raw materials by weight percentage: 15-20% nano-spherical mixed abrasive, 0.5-1.5% oxidant, 0.5-2% dispersant, 0.5-2% suspending agent, and the balance being pure water; the silane coupling agent is 1-1.5% of the weight of the nano-spherical mixed abrasive.

[0010] Furthermore, in the nano-spherical mixed abrasive, the weight ratio of the nano-alumina powder and the nano-cerium oxide powder is 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1.

[0011] Furthermore, the cerium oxide micro powder is white cerium oxide micro powder with a purity of 99.9%.

[0012] Furthermore, in the nano-alumina, the weight ratio of α-alumina to γ-alumina is 2:1, 3:1, 4:1, or 5:1.

[0013] Furthermore, the particle size of the nanospherical hybrid abrasive is 120nm, 150nm, 300nm, 400nm or 600nm.

[0014] Furthermore, in the nano-spherical hybrid abrasive, the particle size of both the nano-alumina powder and the nano-cerium oxide powder is 120-600 nm.

[0015] Unless otherwise specified, the particle size mentioned in this article refers to the median particle size, i.e., D. 50 .

[0016] In this article, the sphericity of the nanospherical hybrid abrasive refers to the surface area of ​​a sphere with the same volume as the particle / the actual surface area of ​​the particle, i.e., Xmin / Xmax.

[0017] Further, the silane coupling agent includes one or more of KH-550 (γ-aminopropyltriethoxysilane), KH-560 (γ-glycidoxypropyltrimethoxysilane), and KH-570 (γ-(methacryloyloxy)propyltrimethoxysilane), preferably KH-560.

[0018] Furthermore, the pH control agent comprises a base and an acid; the base is one or more of ammonia, triethanolamine, ethylenediamine, and methylethylene glycolamine; the acid comprises cerium nitrate, or further comprises one or two of nitric acid, oxalic acid, and aluminum sulfate.

[0019] Furthermore, the content of pH control agent in the polishing solution is 1.5-4%, optionally 1.5-3%.

[0020] In some embodiments, the pH of the polishing solution is adjusted to 10-11 using a pH control agent. The pH of the polishing solution can also be further adjusted to acidity, for example, to 2.0-3.0.

[0021] In some embodiments, the final pH of the polishing solution is controlled between 2.0 and 3.0. The pH of the polishing solution can be adjusted by an acid in a pH control agent, such as nitric acid, and stabilized by cerium nitrate.

[0022] The oxidant described in this invention is potassium ferrate. Under both acidic and alkaline conditions, potassium ferrate exhibits significantly higher oxidizing properties than potassium permanganate and potassium dichromate under the same conditions, and it is also relatively environmentally friendly. Potassium ferrate exhibits stronger oxidizing properties under acidic conditions, especially at pH values ​​below 4. Under alkaline conditions, its stability gradually increases with increasing pH, reaching relative stability at pH values ​​between 10 and 11. Therefore, this invention first prepares the polishing solution as alkaline, and then adjusts it to the required acidity when polishing is needed, maximizing the oxidizing effect of potassium ferrate.

[0023] The dispersant is one or more of modified polyacrylate, ammonium polyacrylate, modified styrene-maleic anhydride copolymer, and polyacrylamide, and may include AFCONA-4590, Dispex Ultra PA 4560, and OROTAN. TM One of 1124 and SMA3000.

[0024] The suspending agent is one or more of hydrated magnesium silicate, polyacrylic acid solution, urea-modified polyurethane solution, organic modified silicate and modified polyurea acrylate, and may be selected from RHEOART-5190, RHEOBYK-M 2600VF, OPTIGEL-WX and ZY-662.

[0025] Furthermore, the viscosity of the polishing slurry is controlled at 30-150 cp (25℃), optionally 50-80 cp (25℃), and the viscosity of the polishing slurry can be adjusted by adding dispersant and suspending agent.

[0026] In this paper, the viscosity is tested by pouring the prepared polishing slurry into the measuring cup of a rotational viscometer and reading the value as the viscosity of the polishing slurry.

[0027] Furthermore, the preparation method of the polishing slurry includes: coupling the nano-spherical mixed abrasive with a silane coupling agent. The coupling treatment method includes dispersing the nano-spherical mixed abrasive in a coupling agent solution, stirring evenly, centrifuging, collecting the precipitate, and drying.

[0028] Specifically, the coupling treatment method includes: dispersing the nano-spherical mixed abrasive in a coupling agent solution, stirring at 60-80℃ for 1-6 hours, centrifuging at 3000-4000 rpm for 2-5 minutes, collecting the precipitate, drying it, and obtaining the coupled-treated nano-mixed abrasive.

[0029] The solvent of the coupling agent solution is a mixture of ethanol and water, preferably with a mass ratio of ethanol to water of (2-6):1, and more preferably 4:1.

[0030] This invention employs a mixed abrasive of nano-spherical alumina powder and nano-spherical cerium oxide powder, wherein the sphericity of the mixed powder is ≥0.95. By using spherical abrasive to repair surface damage caused by previous processes and improve surface roughness, scratches can be effectively avoided, resulting in a smooth and flawless crystal surface. This invention combines the high-hardness alumina with the slightly lower-hardness cerium oxide powder, achieving mutual benefit. On the one hand, it ensures a high polishing rate in the polishing fluid; on the other hand, it avoids scratches and obtains better crystal quality. Furthermore, to further improve polishing performance, this invention uses a specific ratio of α-alumina and γ-alumina mixed alumina powder. Due to their different bulk densities, their properties also differ. α-alumina is harder (Mohs hardness of 9.0) and mainly plays a role in increasing the polishing rate during the polishing process, while γ-alumina powder is more brittle and has good self-sharpening properties, mainly playing a role in repairing surface damage layers and preventing scratches. The properties of α-alumina and γ-alumina are also complementary and mutually beneficial, so that the polishing liquid has both a good polishing rate and ensures that the crystal has a better surface finish. Nano-alumina powder and cerium oxide powder have high surface tension and are prone to agglomeration. By adding silane coupling agents to modify the surface of the powder, their dispersion performance and stability in the polishing liquid can be effectively improved. The dispersion and suspension properties of polishing fluid are improved by adding specific dispersants, suspending agents and other additives. This invention uses potassium ferrate, which has stronger oxidizing power and is more environmentally friendly, as an oxidant. This oxidant not only has strong oxidizing power, but is also green and environmentally friendly. Under acidic and alkaline conditions, the oxidizing power of potassium ferrate is significantly higher than that of potassium permanganate and potassium dichromate under the corresponding conditions. The oxidant can oxidize the crystal surface to form a soft layer, and the contained nano-mixed abrasive removes the soft layer. The combined use of nano-alumina and cerium oxide can accelerate the removal rate and obtain better crystal quality. The iron ions generated after the oxidation reaction of the oxidant can also stabilize the abrasive debris during polishing, which can indirectly improve the polishing rate and reduce scratches. In addition, the present invention also limits the amount of oxidant added. Since the oxidant has a certain saturation solubility, if the amount of oxidant added is too high, the oxidation rate of the crystal surface will be too fast, and the softening will be too fast. The abrasive will not have enough time to remove the soft layer that has already been formed, and a new softened layer will be formed, which will affect the quality of the polished crystal. If the amount of oxidant added is too low, the softening rate of the crystal surface will be too slow, which will affect the polishing rate.This invention uses cerium nitrate as a pH control agent. During oxidation, the oxidant consumes a large amount of hydrogen ions, leading to an increase in pH and agglomeration of the abrasive, severely affecting the polishing effect. Traditional pH control agents cannot stably maintain the pH between 2.0 and 3.0, only providing limited buffering. The cerium nitrate used in this invention can effectively and long-term stabilize the pH of the polishing solution between 2.0 and 3.0. If the pH is too high, the oxidation rate of the oxidant will be too slow, resulting in a low polishing rate; if the pH is too low, the acidity will cause the oxidant to oxidize too quickly, easily producing orange peel on the polished crystal surface, severely affecting the crystal surface quality. The polishing effect is improved by controlling the viscosity of the polishing solution, with the optimal viscosity being 30-150 cp (25℃). The viscosity of the polishing solution can be achieved by adjusting the ratio of dispersant and suspending agent. If the viscosity is too low, the polishing slurry is easily thrown off the polishing pad during the polishing process, and the abrasive cannot play an effective polishing role, affecting the polishing rate. If the viscosity is too high, the liquid flowability is relatively poor, which is not conducive to the recycling of the polishing slurry, and the chip removal ability is poor. Abrasive chips are easy to clog the polishing pad, reducing the polishing rate and easily causing scratches. In addition, due to the high surface area and high surface energy of nano-sized powders, nanoparticles are particularly prone to agglomeration and are not easy to disperse stably in the solvent. In addition to the above measures, this invention also uses a planetary ball mill for ball milling. The external force of ball milling helps to break up the agglomerated powders, thereby improving the dispersion performance of nano-sized powders.

[0031] In summary, the advantages of the polishing slurry of the present invention lie in the synergistic effect of its components, which not only overcomes the defects of the basic raw materials, but also improves other aspects of performance. By improving its own performance, the polishing effect is enhanced, and the polishing slurry of the present invention can be used for polishing silicon carbide crystals.

[0032] Of course, this invention does not limit the applications of the aforementioned polishing slurry; the polishing of silicon carbide described in this invention is merely an example. The aforementioned polishing slurry can also be used for polishing other materials or in other areas yet to be explored.

[0033] The present invention also provides a method for preparing the above-mentioned polishing fluid, comprising:

[0034] (1) Coupling-treated nano-spherical mixed abrasive: The nano-spherical mixed abrasive is dispersed in a coupling agent solution, stirred evenly, centrifuged, the precipitate is collected, and dried to obtain the coupling-treated nano-mixed abrasive;

[0035] (2) The nano-mixed abrasive obtained by coupling treatment in step (1) is mixed with potassium ferrate, dispersant, pH control agent, alkali and water, and the pH is adjusted to 10-11. The mixture is then dispersed by ball milling to obtain a mixed solution.

[0036] (3) Mix the mixed solution described in step (2) with the suspending agent and stir ultrasonically (20-30 min) to obtain a mixed alkaline solution (polishing liquid) with good suspension performance;

[0037] Optionally, the preparation method further includes:

[0038] (4) Add the acid from the pH control agent to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, and stir evenly (for example, stir for 5-10 minutes) to obtain the polishing solution.

[0039] For details on the specific coupling process in step (1), please refer to the above text.

[0040] Specifically, in step (2), a planetary ball mill is used to disperse the mixture for 2-4 hours. The grinding balls are zirconium balls with a diameter of 2 mm, and a mixed solution is obtained.

[0041] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0042] The present invention also provides a method for processing silicon carbide crystals, comprising: performing rough polishing treatment on the silicon carbide crystals using the above-mentioned polishing liquid.

[0043] Preferably, the above-mentioned polishing liquid is used in combination with a polishing pad to perform rough polishing on the silicon carbide crystal.

[0044] The rough polishing process preferably includes rough polishing of the carbon surface and / or silicon surface of the silicon carbide crystal. Specifically, the polishing time for the carbon surface is 30-60 minutes; the polishing time for the silicon surface is 30-60 minutes.

[0045] Preferably, the polishing pad has a Shore hardness of 67-69. More preferably, the polishing pad is a polyurethane polishing pad. In a specific embodiment, the polishing pad may be a polyurethane polishing pad from Universal Optics, with grooves having a spiral pattern 1.0 mm deep.

[0046] Using polishing pads with the aforementioned hardness allows them to work in conjunction with alumina micro powder in the polishing slurry, improving polishing efficiency while preventing surface scratches. If the abrasive is entirely cerium oxide micro powder, it's equivalent to a hard pad with soft abrasive, resulting in no polishing efficiency. If it's entirely alumina micro powder with a hard pad, it's prone to fine scratches. Using a specific ratio of alumina and cerium oxide, combined with polishing pads of the aforementioned hardness, can effectively eliminate scratches through chemical action while maintaining a high polishing rate.

[0047] Preferably, the conditions for coarse polishing include: a coarse polishing pressure of 350-380 g / cm³. 2The PP head rotates at 62-68 rpm, and the lower plate rotates at 60 rpm. The polishing fluid flow rate is 7-9 L / min.

[0048] The polishing fluid of this invention is used for rough polishing, which has a high polishing efficiency and high removal capacity. It can remove the abrasive debris from the silicon carbide crystal in time, which can greatly reduce the fine polishing time and significantly improve the surface quality of the crystal.

[0049] The required surface roughness can be achieved by using traditional silica polishing slurry and traditional fine polishing process.

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

[0051] (1) A mixed abrasive of nano-spherical alumina powder and nano-spherical cerium oxide powder is used. By using spherical abrasive to repair the surface loss caused by the previous process and improve the surface roughness, scratches can be effectively avoided, so as to achieve a smooth and flawless crystal surface.

[0052] (2) This invention uses a certain proportion of nano-alumina powder and nano-cerium oxide powder to form a mixed abrasive, and combines it with various additives to obtain a polishing liquid. The combination of alumina powder and cerium oxide powder avoids scratching the silicon carbide surface during the polishing process. At the same time, the alumina powder has a higher hardness, which can improve the polishing efficiency, while the cerium oxide powder has a lower hardness, which can repair the surface damage layer and surface roughness. The reasonable combination of the two achieves mutual benefit and can effectively avoid the generation of scratches while achieving a high polishing rate. The scratches are eliminated by chemical action, resulting in a crystal surface with good smoothness.

[0053] To further improve polishing performance, this invention uses a specific ratio of α-alumina and γ-alumina micro powder. Due to their different bulk densities, the two have different properties. α-alumina is harder (Mohs hardness of 9.0) and mainly plays a role in increasing the polishing rate during the polishing process, while γ-alumina micro powder is more brittle and has good self-sharpening properties. It mainly plays a role in repairing the surface damage layer and preventing scratches. The properties of α-alumina and γ-alumina are also complementary and mutually beneficial, so that the polishing liquid has both a good polishing rate and ensures a good crystal surface.

[0054] (3) Nano-alumina powder and cerium oxide powder have high surface tension and are prone to agglomeration. Adding silane coupling agents to modify the surface of the powder can effectively improve its dispersion and stability in polishing fluids. Adding specific dispersants, suspending agents, and other additives can further improve the dispersion and suspension properties of the polishing fluid.

[0055] (4) This invention uses more environmentally friendly potassium ferrate as an oxidant. This oxidant has stronger oxidizing properties than ordinary oxidants, and even stronger than potassium permanganate and potassium dichromate. A small amount of addition can achieve good oxidizing performance, thus avoiding environmental pollution caused by adding large amounts of potassium permanganate and potassium dichromate. The oxidant can oxidize the surface of the wafer to form a soft layer. The nano-mixed abrasive contains the soft layer to be removed. The combination of nano-alumina and cerium oxide can accelerate the removal rate and obtain better crystal quality. The iron ions generated after the oxidant undergoes an oxidation reaction can also stabilize the abrasive debris during the polishing process, which can indirectly improve the polishing rate and reduce scratches. In addition, this invention also limits the amount of oxidant added. If the amount of oxidant added is too high, the oxidation rate of the crystal surface will be too fast, and the softening will be too fast. The abrasive will not have time to remove the soft layer that has already been formed, and a new softening layer will be formed, which will affect the quality of the polished crystal. If the amount of oxidant added is too low, the softening rate of the crystal surface will be too slow, which will affect the polishing rate.

[0056] (5) This invention uses cerium nitrate as a pH control agent. During the oxidation process, the oxidant consumes a large number of hydrogen ions, which leads to an increase in pH value. As a result, the abrasive will agglomerate, which seriously affects the polishing effect. Traditional pH control agents cannot stably control the pH value between 2.0 and 3.0 and can only play a limited buffering role. The cerium nitrate used in this invention can effectively stabilize the pH value of the polishing solution at 2.0-3.0 for a long time. If the pH value is too high, the oxidation rate of the oxidant will be too slow, resulting in a low polishing rate. If the pH value is too low, the oxidant will oxidize too quickly due to excessive acidity, and orange peel will easily form on the surface of the polished crystal, which seriously affects the surface quality of the crystal.

[0057] (6) The polishing effect of the polishing slurry is improved by controlling its viscosity. The optimal viscosity is 30-150 cp (25℃). This invention adjusts the viscosity of the polishing slurry by adjusting the ratio of dispersant and suspending agent. If the viscosity is too low, the polishing slurry is easily thrown off the pad during the polishing process, and the abrasive cannot play an effective polishing role, affecting the polishing rate. If the viscosity is too high, the liquid fluidity is relatively poor, which is not conducive to the recycling of the polishing slurry. Moreover, the chip removal ability is poor, and the abrasive chips are easy to clog the polishing pad, reducing the polishing rate and easily causing scratches.

[0058] (7) Due to the high surface area and high surface energy of nano-sized powders, nanoparticles are particularly easy to agglomerate and are not easy to disperse stably in solvents. In addition to the above measures, the present invention also uses a planetary ball mill for ball milling. The external force of ball milling helps to break up the agglomerated powders, thereby improving the dispersion performance of nano-sized powders.

[0059] (8) The polishing liquid of the present invention is used in conjunction with a polishing pad of a certain hardness to polish silicon carbide, which improves the polishing efficiency and avoids surface scratches. Furthermore, after rough polishing silicon carbide with the polishing liquid of the present invention, the fine polishing time can be effectively reduced and the crystal surface quality can be significantly improved. Attached Figure Description

[0060] Figure 1 The image shows the morphology of the mixed abrasive of nano-alumina powder and cerium oxide powder used in Example 1.

[0061] Figure 2 Morphology images of alumina micro powders used in different comparative proportions. Figure 2 (Left) is a morphology diagram of the alumina micro powder used in Comparative Example 7; Figure 2 (Right) is a morphology diagram of the alumina micro powder used in Comparative Example 8;

[0062] Figure 3 This is a diagram showing the dispersion state of different polishing slurries. Figure 3 (Left) is a diagram showing the dispersion state of the polishing liquid in Example 1 after 1 hour of storage; Figure 3 (Right) is a diagram showing the dispersion state of the polishing slurry in Comparative Example 1 after 1 hour.

[0063] Figure 4 The surface morphology of the silicon carbide wafer after polishing with the polishing solution obtained in Comparative Example 1 is magnified 100 times (numerous and deep scratches, number ≥15).

[0064] Figure 5 The surface morphology of the silicon carbide wafer after polishing with the polishing solution obtained in Comparative Example 7 is magnified 100 times (there are many scratches, but most of them are shallow scratches, with ≥10 scratches).

[0065] Figure 6 The image shows the surface morphology of a silicon carbide wafer polished with the polishing solution obtained in Example 1, magnified 100 times (no scratches on the surface).

[0066] Figure 7 The image shows the surface roughness of the Si and C surfaces of a silicon carbide wafer after polishing with the polishing solution obtained in Example 1. Detailed Implementation

[0067] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are only some embodiments of the present invention, not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply.

[0068] The sphericity of the nanosphere hybrid abrasives used in the following examples is ≥0.95.

[0069] Example 1

[0070] A polishing slurry, the specific preparation method of which includes the following steps:

[0071] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0072] (2) The coupled nanosphere mixed abrasive obtained in step (1) above is mixed with 15g potassium ferrate and 20g ammonium polyacrylate (OROTAN). TM 1124), 30g of methyl ethylene glycolamine and 683g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0073] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution (ZY-662), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0074] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0075] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0076] Example 2

[0077] A polishing slurry, the specific preparation method of which includes the following steps:

[0078] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 3:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0079] (2) The coupled nanosphere mixed abrasive obtained in step (1) above is mixed with 15g potassium ferrate and 20g ammonium polyacrylate (OROTAN). TM 1124 g of methyl ethylene glycolamine and 683 g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0080] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution (ZY-662), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0081] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0082] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0083] Example 3

[0084] A polishing slurry, the specific preparation method of which includes the following steps:

[0085] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 10:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0086] (2) The coupled nanosphere mixed abrasive obtained in step (1) above is mixed with 15g potassium ferrate and 20g ammonium polyacrylate (OROTAN). TM 1124), 30g of methyl ethylene glycolamine and 683g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0087] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution (ZY-662), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0088] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0089] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0090] Example 4

[0091] A polishing slurry, the specific preparation method of which includes the following steps:

[0092] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 5:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0093] (2) The coupled nanosphere mixed abrasive obtained in step (1) above is mixed with 15g potassium ferrate and 20g ammonium polyacrylate (OROTAN). TM 1124), 30g of methyl ethylene glycolamine and 683g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0094] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution (ZY-662), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0095] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0096] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0097] Example 5

[0098] A polishing slurry, the specific preparation method of which includes the following steps:

[0099] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 2:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0100] (2) The coupled nanosphere mixed abrasive obtained in step (1) above is mixed with 15g potassium ferrate and 20g ammonium polyacrylate (OROTAN). TM 1124), 30g of methyl ethylene glycolamine and 683g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0101] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution (ZY-662), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0102] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0103] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0104] Example 6

[0105] A polishing slurry, the specific preparation method of which includes the following steps:

[0106] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 5:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0107] (2) The coupled nanosphere mixed abrasive obtained in step (1) above is mixed with 15g potassium ferrate and 20g ammonium polyacrylate (OROTAN). TM 1124), 30g of methyl ethylene glycolamine and 683g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0108] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution (ZY-662), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0109] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0110] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0111] Example 7

[0112] A polishing slurry, the specific preparation method of which includes the following steps:

[0113] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 120nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-570 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0114] (2) The nanosphere mixed abrasive obtained by coupling treatment in step (1) above is mixed with 15g potassium ferrate, 20g modified styrene-maleic anhydride copolymer (SMA3000), 30g triethanolamine and 583g water. The pH is adjusted to 10-11. After ball milling and dispersing for 4 hours using a planetary ball mill, a mixed solution is obtained.

[0115] (3) Take the above step (2) and 20g of organic modified silicate (OPTIGEL-WX), and ultrasonically stir for 20-30min to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0116] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0117] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0118] Example 8

[0119] A polishing slurry, the specific preparation method of which includes the following steps:

[0120] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 300nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-550 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0121] (2) The coupled nanosphere mixed abrasive obtained in step (1) above is mixed with 15g potassium ferrate and 20g ammonium polyacrylate (OROTAN). TM 1124), 30g of methyl ethylene glycolamine and 683g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0122] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution (ZY-662), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0123] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0124] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0125] Example 9

[0126] A polishing slurry, the specific preparation method of which includes the following steps:

[0127] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 600nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0128] (2) The coupled nanosphere mixed abrasive obtained in step (1) above is mixed with 15g potassium ferrate and 20g ammonium polyacrylate (OROTAN). TM 1124), 30g of methyl ethylene glycolamine and 683g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0129] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution (ZY-662), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0130] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0131] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0132] Example 10

[0133] A polishing slurry, the specific preparation method of which includes the following steps:

[0134] (1) Coupling-treated nano-mixed abrasive: 150g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 1.5g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0135] (2) The coupled nanosphere mixed abrasive obtained in step (1) above is mixed with 15g potassium ferrate and 20g ammonium polyacrylate (OROTAN). TM 1124), 30g of methyl ethylene glycolamine and 733.5g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0136] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution (ZY-662), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0137] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0138] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0139] Example 11

[0140] A polishing slurry, the specific preparation method of which includes the following steps:

[0141] (1) Coupling-treated nano-mixed abrasive: 250g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 5g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0142] (2) The coupled nanosphere mixed abrasive obtained in step (1) above is mixed with 15g potassium ferrate and 20g ammonium polyacrylate (OROTAN). TM 1124), 30g of methyl ethylene glycolamine and 630g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0143] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution (ZY-662), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0144] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0145] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0146] Example 12

[0147] A polishing slurry, the specific preparation method of which includes the following steps:

[0148] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0149] (2) The coupled nanosphere mixed abrasive obtained in step (1) above is mixed with 15g potassium ferrate and 20g ammonium polyacrylate (OROTAN). TM 1124), 30g of methyl ethylene glycolamine and 698g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0150] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution (ZY-662), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0151] (4) Add a certain mass of 2.5g nitric acid and 12.5g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0152] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0153] Example 13

[0154] A polishing slurry, the specific preparation method of which includes the following steps:

[0155] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0156] (2) The coupled nanosphere mixed abrasive obtained in step (1) above is mixed with 15g potassium ferrate and 20g ammonium polyacrylate (OROTAN). TM 1124), 30g of methyl ethylene glycolamine and 673g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0157] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution (ZY-662), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0158] (4) Add a certain mass of 6.6g nitric acid and 33.4g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0159] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0160] Example 14

[0161] A polishing slurry, the specific preparation method of which includes the following steps:

[0162] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0163] (2) The coupled nanosphere abrasive obtained in step (1) above is mixed with 5g potassium ferrate and 20g ammonium polyacrylate (OROTAN). TM 1124), 30g of methyl ethylene glycolamine and 693g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0164] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution ZY-662, and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, which will be kept for later use.

[0165] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0166] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0167] Example 15

[0168] A polishing slurry, the specific preparation method of which includes the following steps:

[0169] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0170] (2) The coupled nanosphere mixed abrasive obtained in step (1) above is mixed with 30g potassium ferrate and 20g ammonium polyacrylate (OROTAN).TM 1124), 30g of methyl ethylene glycolamine and 668g of water were mixed together, the pH was adjusted to 10-11, and the mixture was dispersed by ball milling for 4 hours to obtain a mixed solution.

[0171] (3) Take the solution from step (2) above and 20g of urea-modified polyurethane solution (ZY-662), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0172] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0173] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0174] Example 16

[0175] A polishing slurry, the specific preparation method of which includes the following steps:

[0176] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0177] (2) The nanosphere mixed abrasive obtained by coupling treatment in step (1) above is mixed with 15g potassium ferrate, 2g modified polyacrylate (AFCONA-4590), 30g methyl ethylene glycolamine and 691g water. The pH is adjusted to 10-11. After ball milling and dispersing for 4 hours using a planetary ball mill, a mixed solution is obtained.

[0178] (3) Take the solution from step (2) above and 30g of polyacrylic acid solution (RHEOART-5190), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension properties, and keep it for later use.

[0179] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0180] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0181] Example 17

[0182] A polishing slurry, the specific preparation method of which includes the following steps:

[0183] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0184] (2) The nanosphere mixed abrasive obtained by coupling treatment in step (1) above is mixed with 15g potassium ferrate, 10g modified polyacrylate (Dispex Ultra PA 4560), 30g methyl ethylene glycolamine and 703g water. The pH is adjusted to 10-11. After ball milling and dispersing for 4 hours using a planetary ball mill, a mixed solution is obtained.

[0185] (3) Take the above step (2) and 10g of modified polyurea acrylate (RHEOBYK-M 2600VF), and ultrasonically stir for 20-30 minutes to obtain a mixed alkaline solution with good suspension performance, and keep it for later use.

[0186] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0187] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0188] Example 18

[0189] A polishing slurry, the specific preparation method of which includes the following steps:

[0190] (1) Coupling-treated nano-mixed abrasive: 200g of spherical nano-mixed abrasive with a median particle size of 400nm (wherein the weight ratio of spherical alumina micropowder to spherical cerium oxide micropowder is 7:1, and the above-mentioned spherical alumina micropowder is composed of α-alumina and γ-alumina in a weight ratio of 4:1) and 2g of KH-560 were dispersed in 100g of solvent, stirred at 60℃ for 4h, and then centrifuged at 3000rpm for 4min. The precipitate was collected, dried, and the coupling-treated nano-mixed abrasive was obtained. The solvent was a mixture of ethanol and water in a mass ratio of 4:1.

[0191] (2) The nanosphere mixed abrasive obtained by coupling treatment in step (1) above is mixed with 15g potassium ferrate, 30g modified polyacrylate (AFCONA-4590), 30g methyl ethylene glycolamine and 691g water. The pH is adjusted to 10-11. After ball milling and dispersing for 4 hours using a planetary ball mill, a mixed solution is obtained.

[0192] (3) Take the solution from step (2) above and 2g of polyacrylic acid solution (RHEOART-5190), and stir ultrasonically for 20-30 minutes to obtain a mixed alkaline solution with good suspension properties, and keep it for later use.

[0193] (4) Add a certain amount of 5g nitric acid and 25g cerium nitrate to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir for 5-10 minutes, and the polishing solution is obtained.

[0194] Furthermore, in order to avoid potassium ferrate from undergoing an oxidation reaction too early under acidic conditions and prematurely consuming hydrogen ions in the polishing solution, step (4) can be prepared temporarily before the polishing operation.

[0195] Comparative Example 1

[0196] Except that the spherical nano-hybrid abrasive was changed to a median particle size of 50 nm, everything else was the same as in Example 1.

[0197] Comparative Example 2

[0198] Except that the spherical nano-hybrid abrasive was changed to a median particle size of 1000 nm, everything else was the same as in Example 1.

[0199] Comparative Example 3

[0200] Except that the spherical alumina micro powder and the spherical cerium oxide mixed micro powder are changed to pure spherical alumina micro powder, everything else is the same as in Example 1.

[0201] Comparative Example 4

[0202] Except that the weight ratio of spherical alumina micro powder to spherical cerium oxide micro powder is changed to 1:10, everything else is the same as in Example 1.

[0203] Comparative Example 5

[0204] Except for changing the spherical alumina micro powder of mixed α-alumina and γ-alumina to all α-alumina micro powder, the rest is the same as in Example 1.

[0205] Comparative Example 6

[0206] Except that the spherical alumina micro powder is composed of α-alumina and γ-alumina in a weight ratio of 1:10, the rest is the same as in Example 1.

[0207] Comparative Example 7

[0208] Except for changing the nano-spherical mixed abrasive to nano-bulb mixed abrasive, everything else is the same as in Example 1.

[0209] Comparative Example 8

[0210] Except for changing the nano-spherical mixed abrasive into a nano-irregularly shaped mixed abrasive, everything else is the same as in Example 1.

[0211] Comparative Example 9

[0212] Except for changing the mass of the nano-spherical mixed abrasive in the polishing slurry to 500g, everything else is the same as in Example 1.

[0213] Comparative Example 10

[0214] Except for changing the mass of the nano-spherical mixed abrasive in the polishing slurry to 50g, everything else is the same as in Example 1.

[0215] Comparative Example 11

[0216] Except for the absence of the pH control agent cerium nitrate, the pH of the polishing solution increased to 6.0, and everything else was the same as in Example 1.

[0217] Comparative Example 12

[0218] The polishing solution is the same as in Example 1, except that the oxidant potassium ferrate is not added.

[0219] Comparative Example 13

[0220] The polishing solution is the same as in Example 1, except that the amount of potassium ferrate oxidant added is changed to 60g.

[0221] Comparative Example 14

[0222] The polishing slurry was identical to that in Example 1, except that no dispersant was added and the amount of suspending agent was increased to 60g.

[0223] Comparative Example 15

[0224] The polishing solution was the same as in Example 1, except that the amount of dispersant was increased to 60g and no suspending agent was added.

[0225] Experimental Example

[0226] The method for rough polishing silicon carbide crystals includes the following steps:

[0227] Six 4-inch silicon carbide wafers were attached to a ceramic disk, and polishing solutions from Examples 1-18 and Comparative Examples 1-15 were used respectively, at a concentration of 350 g / cm³. 2 Rough polishing was performed under the specified polishing pressure, with the PP head rotating at 66 rpm and the lower plate rotating at 60 rpm in the same direction. The flow rate of the polishing fluid was 8 L / min. The matching rough polishing pad was a polyurethane polishing pad from Universal Chemicals with a Shore hardness of 69 and a 1.2 mm deep spiral groove. Rough polishing improved the surface roughness after double-sided grinding to facilitate subsequent processing. Specifically, the silicon surface of the silicon carbide wafer was rough polished for 45 min, and the carbon surface of the silicon carbide wafer was rough polished for 45 min. After rough polishing, the silicon carbide wafers were washed and dried, and then the scratches were observed, and the surface roughness and polishing rate were measured. The specific test results are shown in Table 1.

[0228] Surface roughness test: Under the same conditions, the surface roughness was tested using an AFM testing machine (model: SPEEDFAM 36BPAW-TD); Polishing rate test: The polishing rate can be calculated by the change in the thickness of the silicon carbide wafer before and after polishing, i.e., polishing rate = amount removed before and after polishing / polishing time. The change in wafer thickness can be measured using a dial indicator; Under the same conditions, the surface scratches were observed using an optical microscope at 100x magnification.

[0229] Figure 1 Diagram of nano-spherical hybrid abrasive; Figure 2 The diagram shows a mixture of blocky (left) and irregular (right) abrasive materials. Figure 3 This is a diagram showing the polishing slurry in its static state. Figures 4-6 This is a surface morphology image of a silicon carbide wafer, in which... Figure 4 The silicon carbide wafer surface is severely scratched, with ≥15 scratches. Figure 5 Minor scratches on the silicon carbide wafer, with ≥10 scratches. Figure 6 The silicon carbide wafer has no scratches and a smooth, flat surface; Figure 7 The test images show the surface roughness of the Si and C surfaces after rough polishing.

[0230] Table 1 Comparison of Polishing Fluid Performance

[0231]

[0232]

[0233] As can be seen from Table 1, Example 1 exhibits the best overall performance, demonstrating superior dispersibility, suspension properties, and polishing effect. Figure 3(Left) is a dispersion diagram of the polishing slurry in Example 1 after 1 hour. The diagram shows that the polishing slurry is evenly dispersed and has good suspension properties. Figure 3 (Right) is a diagram showing the dispersion state of the polishing slurry of Comparative Example 1 after 1 hour. As can be seen from the diagram, the polishing slurry is dispersed very unevenly, and some abrasive particles have settled to the bottom of the bottle. Figure 6 and Figure 7 The figures show the surface morphology and surface roughness of the silicon carbide wafer polished with the polishing slurry obtained in Example 1. As can be seen from the figures, the silicon carbide wafer surface is free of scratches and has a low surface roughness, meeting the general requirements of the existing market (Ra < 0.5 nm). Table 1 shows the test data from Examples 1, 7-9, and Comparative Examples 1-2, indicating that the abrasive particle size has a significant impact on polishing performance. The abrasive particle size needs to be controlled within a suitable range (i.e., 120-600 nm). If the particle size is too small, the polishing force is insufficient, resulting in a very low polishing rate and high surface roughness. If the particle size is too large, although the polishing force is relatively strong, the large abrasive particle size easily causes new scratches. After polishing the silicon carbide wafer with the polishing slurries of Comparative Examples 1 and 2, the scratches on the wafer surface were deeper and more numerous. Specific scratch details are as follows: Figure 4 As shown in Table 1, based on the test data of Examples 1-4 and Comparative Examples 3-4, there is an optimal ratio range between spherical alumina and spherical cerium oxide micropowder. Adding an appropriate amount of cerium oxide micropowder can repair scratches and improve polishing yield, but its content should not be too high. Too high a content will result in insufficient polishing power of the polishing slurry and a low polishing rate. Comparing Examples 1, 5-6, and Comparative Examples 5-6, it can be seen that the content of α-alumina and γ-alumina micropowder also needs to be controlled within a suitable range. Adding an appropriate amount of brittle and self-sharpening γ-alumina micropowder can increase the polishing rate and improve surface roughness, but it should not be added in excess, as this will reduce the polishing rate of the polishing slurry. The content of γ-alumina micropowder should not be zero; if γ-alumina micropowder is absent, the wafer surface will have obvious scratches and a relatively high surface roughness. Based on the experimental data of Examples 1 and Comparative Examples 7-8, and... Figure 1-2 As can be seen from the micronized powder morphology images, under the same conditions, spherical abrasives showed no scratches on the crystal surface, while blocky or irregularly shaped abrasives showed obvious scratches (as shown in the image). Figure 5As shown in the figure. According to the data from Examples 1, 10-11 and Comparative Examples 9-10, the abrasive content has a great influence on the polishing effect of the polishing slurry. When there is too much abrasive (as in Comparative Example 9), the viscosity of the polishing slurry is too high. Too much abrasive can easily clog the polishing pad. On the one hand, the abrasive cannot play a good polishing role, resulting in a very low polishing rate. On the other hand, the abrasive debris can cause serious scratches due to blockage. When there is too little abrasive (as in Comparative Example 10), on the one hand, the low abrasive content leads to a very low polishing rate. On the other hand, the viscosity of the polishing slurry is too low, causing the polishing slurry to not adhere to the pad. It is easily thrown off during the polishing process and cannot play a polishing role, resulting in the rough surface of the previous process not being repaired. According to the data from Examples 1, 12-13, and Comparative Example 11, when an appropriate amount of cerium nitrate is added to the polishing solution, the polished silicon carbide wafer surface is free of scratches. However, without the addition of cerium nitrate (as in Comparative Example 11), the wafer surface shows obvious scratches. Furthermore, the cerium nitrate content also affects the polishing rate and workpiece surface roughness to some extent. According to Examples 1, 14-15, and Comparative Examples 12-13, the silicon carbide wafers polished with the polishing solutions obtained in Examples 1 and 14-15 show no scratches, while the comparative examples show... Example 12: The polishing slurry without potassium ferrate resulted in severe scratches on the wafers, a very low polishing rate, and high surface roughness. Without prior softening of the silicon carbide wafers with an oxidant, the slurry was practically ineffective at polishing them. However, if too much potassium ferrate was added (as in Comparative Example 13), the softening speed was too fast, and a new softening layer formed before the softened layer could be removed, affecting the final quality of the wafers. Especially with excessive oxidant, orange peel-like defects easily formed on the wafer surface. Examples 1, 16-18, and Comparative Examples 14 and 15 adjusted the viscosity, dispersion, and suspension properties of the polishing slurry by adjusting the ratio of dispersant and suspending agent. For example, Comparative Example 14 had poor dispersibility, and Comparative Example 15 had poor suspension. A polishing slurry viscosity of 30-150 cp yielded good overall polishing results, but excessively high or low viscosity would cause scratches. If the viscosity is too high, the grinding debris generated after grinding can easily clog the polishing pad or stick to the polishing pad, and the abrasive cannot play a good polishing role, resulting in a very low polishing rate or even serious scratches. If the viscosity is too low, the polishing liquid cannot adhere to the pad and is easily thrown off during the polishing process, thus failing to play a polishing role, resulting in a very low polishing rate, and the rough surface of the previous process cannot be well repaired, resulting in a large surface roughness of the wafer.

[0234] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polishing liquid, characterized in that, The abrasive is made from the following raw materials by weight percentage: 15-25% nano-spherical mixed abrasive, 0.2-3% oxidant, 0.2-3% dispersant, 0.2-3% suspending agent, alkaline pH control agent and acidic pH control agent; it also includes a silane coupling agent, which is 1-2% of the weight of the nano-spherical mixed abrasive; and pure water as the balance. The oxidant is potassium ferrate; The nano-spherical hybrid abrasive is a mixture of nano-alumina powder and nano-cerium oxide powder in a weight ratio of (3-10):1; The particle size of the nano-spherical hybrid abrasive is 120-600 nm; The nano-spherical hybrid abrasive is spherical with a sphericity of ≥0.95; The nano-alumina is a mixed abrasive of α-alumina and γ-alumina in a weight ratio of (2-5):1; The alkaline pH control agent is one or more of ammonia, triethanolamine, ethylenediamine, and methylethylene glycolamine; the acidic pH control agent is cerium nitrate and nitric acid. The pH of the polishing solution is 2.0-3.0; The silane coupling agent includes any one or more of KH-550, KH-560, and KH-570; The dispersant is one or more of modified polyacrylate, ammonium polyacrylate, modified styrene-maleic anhydride copolymer, and polyacrylamide; The suspending agent is one or more of the following: hydrated magnesium silicate, polyacrylic acid solution, urea-modified polyurethane solution, organic modified silicate, and modified polyurea acrylate. The polishing slurry is prepared by the following method, including: (1) Coupling treatment of nano-spherical mixed abrasive: The nano-spherical mixed abrasive is dispersed in a coupling agent solution, stirred evenly, centrifuged, the precipitate is collected and dried to obtain the coupling-treated nano-mixed abrasive; (2) The nano-mixed abrasive obtained by coupling treatment in step (1) is mixed with potassium ferrate, dispersant, alkaline pH control agent and water, the pH is adjusted to 10-11, and the mixture is dispersed by ball milling to obtain a mixed solution; (3) Mix the mixed solution described in step (2) with the suspending agent and stir ultrasonically to obtain a mixed alkaline solution with good suspension performance; (4) Add the acidic pH control agent to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir evenly, and the polishing liquid is obtained.

2. The polishing slurry according to claim 1, characterized in that, The polishing slurry, by weight percentage, comprises 15-20% nano-spherical mixed abrasive, 0.5-1.5% oxidant, 0.5-2% dispersant, 0.5-2% suspending agent, and 1-1.5% silane coupling agent by weight of the nano-spherical mixed abrasive.

3. The polishing fluid according to claim 1 or 2, characterized in that, In the nano-spherical hybrid abrasive, the weight ratio of the nano-alumina powder to the nano-cerium oxide powder is 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1; and / or, the particle size of the nano-spherical hybrid abrasive is 120nm, 150nm, 300nm, 400nm, or 600nm.

4. The polishing fluid according to claim 1 or 2, characterized in that, In the nano-alumina, the weight ratio of α-alumina to γ-alumina is 2:1, 3:1, 4:1, or 5:

1.

5. The polishing fluid according to claim 1 or 2, characterized in that, The viscosity of the polishing fluid is controlled at 30-150 cp at 25°C.

6. The polishing slurry according to claim 5, characterized in that, The viscosity of the polishing fluid is controlled at 50-80 cp at 25°C.

7. A method for preparing the polishing liquid according to any one of claims 1-6, characterized in that, include: (1) Coupling treatment of nano-spherical mixed abrasive: The nano-spherical mixed abrasive is dispersed in a coupling agent solution, stirred evenly, centrifuged, the precipitate is collected and dried to obtain the coupling-treated nano-mixed abrasive; (2) The nano-mixed abrasive obtained by coupling treatment in step (1) is mixed with potassium ferrate, dispersant, alkaline pH control agent and water, the pH is adjusted to 10-11, and the mixture is dispersed by ball milling to obtain a mixed solution; (3) Mix the mixed solution described in step (2) with the suspending agent and stir ultrasonically to obtain a mixed alkaline solution with good suspension performance; (4) Add the acidic pH control agent to the mixed alkaline solution obtained in step (3) above, adjust the pH value to 2.0-3.0, stir evenly, and the polishing liquid is obtained.

8. A method for processing silicon carbide crystals, characterized in that, include: The silicon carbide crystal is coarsely polished using any one of the polishing solutions described in 1-6.

9. The method for processing silicon carbide crystals according to claim 8, characterized in that, The polishing liquid described in any one of 1-6 is used in combination with a polishing pad to perform rough polishing on the silicon carbide crystal.

10. The method for processing silicon carbide crystals according to claim 9, characterized in that, The rough polishing process includes rough polishing the carbon surface and / or silicon surface of the silicon carbide crystal.

11. The method for processing silicon carbide crystals according to claim 9, characterized in that, The polishing pad has a Shore hardness of 67-69.

12. The method for processing silicon carbide crystals according to claim 9, characterized in that, The conditions for coarse polishing include: a coarse polishing pressure of 350-380 g / cm³. 2 The PP head rotation speed is 62-68 rpm, and the lower plate rotation speed is 60 rpm; the polishing fluid flow rate is 7-9 L / min.

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