Polishing liquid for polishing aluminum nitride ceramic and method for preparing the same

Abstract

The application provides a polishing liquid for polishing aluminum nitride ceramics and a preparation method thereof, and relates to the technical field of polishing materials. The preparation method of the polishing liquid for polishing aluminum nitride ceramics comprises the following steps: preparing an acidic polymer resin as a core material; using a silicon source as a raw material, coating a silica wall material on the surface of the core material through a hydrolysis condensation reaction to obtain composite microspheres for pH adjustment; using the composite microspheres, silica shear thickening particles and aluminum oxide abrasives as raw materials, adding a liquid medium, mixing and adjusting the pH value to prepare the polishing liquid. The polishing liquid prepared by the method can keep the pH value stable during the polishing process, so that the polishing liquid can keep good polishing effect.

Description

Technical Field

[0001] This invention relates to the technical field of polishing materials, and more specifically, to a polishing slurry for polishing aluminum nitride ceramics and its preparation method. Background Technology

[0002] Aluminum nitride ceramics possess excellent thermal conductivity, electrical insulation, and extremely low dielectric constant and dielectric loss. These properties make aluminum nitride ceramics widely applicable in many fields, including high-power device substrates, key components of semiconductor equipment, LED chips, and high-power amplifiers. To obtain aluminum nitride ceramic substrates with high surface quality, chemical mechanical polishing (CMP) is required, and polishing slurry is a key consumable affecting the CMP polishing effect.

[0003] Chemical mechanical polishing of aluminum nitride ceramics generally includes two processes: rough polishing and fine polishing. Rough polishing can be performed using non-woven fabric as a polishing pad and a hard polishing medium, with the pH value adjusted to around 11 to 12. The purpose of fine polishing is to optimize the roughness of the product. Considering the properties of aluminum nitride ceramic materials, fine polishing generally uses an acidic silica polishing solution with a pH value between 2 and 4.

[0004] In the aforementioned fine polishing process, the hydrolysis of aluminum nitride alters the pH and stability of the polishing solution, specifically manifesting as an increase in the pH of acidic polishing solutions. This is because aluminum nitride ceramics undergo a hydrolysis reaction upon contact with water, generating aluminum hydroxide and ammonia gas. Ammonia gas is highly soluble in water and reacts with water to form ammonium hydroxide, a weak base, thereby causing the pH of the polishing solution to rise.

[0005] An unstable pH value implies an unstable chemical corrosion rate, leading to changes in the Zeta potential of the silica abrasive and the formation of large-sized hard agglomerates. This results in an inconsistent material removal rate (MRR) throughout the polishing process, causing uneven polishing and defects such as pitting and micro-scratches on the surface of the aluminum nitride ceramic substrate due to the ploughing effect. Therefore, improving the stability of acidic silica polishing slurries to maintain a pH value of at least 5 to 6 during polishing is a key technical problem that needs to be solved in this field. Summary of the Invention

[0006] The problem addressed by this invention is how to provide an acidic silica polishing slurry that can maintain a stable pH value during the polishing process of aluminum nitride ceramics, so as to improve the polishing effect of aluminum nitride ceramic substrates.

[0007] To address the above problems, this invention provides a method for preparing a polishing slurry for polishing aluminum nitride ceramics, the method comprising: S100, Prepare an acidic polymer resin as a core material; S200: Using organosilicon as raw material, a silica wall material is coated on the surface of the core material through a hydrolysis-condensation reaction to obtain composite microspheres for pH adjustment. S300 is a polishing slurry prepared by mixing composite microspheres, silica shear-thickening particles, and alumina abrasives with a liquid medium and adjusting the pH value.

[0008] Furthermore, S100 specifically includes: S110. Mix maleic anhydride and propylene glycol methyl ether acetate evenly, then add acrylic monomer, methyl methacrylate and azobisisobutyronitrile and continue mixing evenly. Heat and pressurize to react. S120. After the reaction is complete, cool down and depressurize. Slowly pour the remaining material after removing unreacted monomers into an excess of acetone and stir rapidly. After stirring is complete, let stand, separate the solids, wash, and obtain a solid acrylic acid-methyl methacrylate copolymer, which can be used as a polymer resin.

[0009] Furthermore, in S110, by mass ratio, azobisisobutyronitrile: maleic anhydride: acrylic monomer: methyl methacrylate: propylene glycol methyl ether acetate = (0.1-0.3)(2-4):(25-30):(15-20):100.

[0010] Furthermore, in S120, the temperature conditions for the heated and pressurized reaction are 75°C to 95°C, the pressure conditions are 0.4 MPa to 0.6 MPa, and the reaction time is 3 h to 5 h.

[0011] Furthermore, the S200 specifically includes: S210, according to the mass ratio of Tween 80: polymer resin: dichloromethane = (4-8): (20-30): 100, mix Tween 80, polymer resin and dichloromethane to form a suspension; S220. According to the mass ratio of hexadecyltrimethylammonium bromide: organosilicon source: water: ethanol = (0.2-0.3): (10-15): (30-35): 100, the organosilicon source is mixed with hexadecyltrimethylammonium bromide, water and ethanol to obtain a hydrolysate. S230. Add the hydrolysate dropwise to the suspension at a mass ratio of (80-120):100, stirring simultaneously. After the addition is complete, add hydrochloric acid to adjust the pH to 3 to 4, keep warm and stir for 1.5 to 2 hours, stop keeping warm and let stand for 6 to 8 hours. S240. Centrifuge the solid, wash, and dry to obtain composite microspheres.

[0012] Furthermore, S100 specifically includes: S110. Mix maleic anhydride and propylene glycol methyl ether acetate evenly, then add acrylic monomer, methyl methacrylate and azobisisobutyronitrile and continue mixing evenly. Heat and pressurize to react. S120. After the reaction is complete, the temperature is lowered and the pressure is released to remove unreacted monomers and obtain liquid acrylic acid-methyl methacrylate copolymer. S130. Styrene monomer, water, Tween 80, N,N-methylenebisacrylamide, and azobisisobutyronitrile are mixed evenly to obtain a styrene monomer emulsion. S140. Acrylic acid-methyl methacrylate copolymer is added dropwise into styrene monomer emulsion while stirring simultaneously. After the addition is complete, an emulsion-like mixture of acrylic acid-methyl methacrylate copolymer and styrene is obtained as a polymer resin.

[0013] Further, in S110, by mass ratio, azobisisobutyronitrile: maleic anhydride: acrylic monomer: methyl methacrylate: propylene glycol methyl ether acetate = (0.1-0.3)(2-4):(15-20):(25-30):100; in S130, by mass ratio, azobisisobutyronitrile: N,N-methylenebisacrylamide: Tween 80: styrene monomer: water = (0.1-0.3):(1-2):(6-12):(20-30):100; in S140, by mass ratio, acrylic acid-methyl methacrylate copolymer: styrene monomer emulsion = (80-120):100.

[0014] Furthermore, in S120, the temperature conditions for the heated and pressurized reaction are 75°C to 90°C, the pressure conditions are 0.4 MPa to 0.6 MPa, and the reaction time is 3 h to 5 h.

[0015] Furthermore, the S200 specifically includes: S210. Mix the organosilicon source with water and ethanol at a mass ratio of (10-15):(30-35):100 to obtain a hydrolysate. S220. The polymer resin is heated and stirred for 5 to 7 hours under a protective atmosphere and at a temperature of 65°C to 70°C to obtain a mixture of acrylic acid-methyl methacrylate copolymer / polystyrene. S230. According to the mass ratio of mixture: hydrolysate = (80-120): 100, add the hydrolysate dropwise to the mixture under the heat preservation condition and stir simultaneously. After the dropwise addition is completed, add hydrochloric acid to adjust the pH value to 3 to 4, keep warm and stir for 3 to 5 hours, stop the heat preservation and let it stand and age for 6 to 8 hours. S240. Centrifuge the solid, wash it, place it in a sufficient amount of tetrahydrofuran and stir for 10 to 20 minutes. Centrifuge the solid again, wash it, and dry it to obtain composite microspheres.

[0016] The present invention also provides a polishing slurry for polishing aluminum nitride ceramics, which is obtained by the preparation method of any of the above technical solutions.

[0017] Beneficial Effects: This invention provides a method for preparing a polishing slurry for polishing aluminum nitride ceramics. The method first prepares an acidic polymer resin as a core material; then, using an organosilicon source as a raw material, a silica wall material is coated onto the surface of the core material through a hydrolysis-condensation reaction to obtain composite microspheres for pH adjustment; finally, using the composite microspheres, silica shear-thickening particles, and alumina abrasive as raw materials, a liquid medium is added for mixing and pH adjustment to obtain the polishing slurry. The polishing slurry prepared by this invention maintains a stable pH value during polishing, ensuring a stable chemical corrosion rate and preventing changes in the zeta potential of the silica shear-thickening particles, thus avoiding large-sized hard agglomerations. This ensures uniform polishing and prevents defects such as pitting and micro-scratches on the surface of aluminum nitride ceramics due to the ploughing effect. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, a detailed description of specific embodiments of the present invention will be provided below.

[0019] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available. Experimental methods in the following examples that do not specify particular conditions should be performed according to conventional methods and conditions, or as selected in the product instructions.

[0020] This invention provides a method for preparing a polishing slurry for polishing aluminum nitride ceramics. Aluminum nitride ceramics have broad application prospects in many fields, including high-power device substrates, key components of semiconductor equipment, LED chips, and high-power amplifiers. To obtain aluminum nitride ceramics with satisfactory performance, chemical mechanical polishing (CMP) is an essential step in the preparation of aluminum nitride ceramic substrates. The polishing slurries used differ between rough polishing and fine polishing of aluminum nitride ceramics.

[0021] Specifically, the purpose of rough polishing is to quickly remove the deeper damage layer (usually tens of micrometers) left by previous processes such as wire cutting, achieving a macroscopic smoothness. Therefore, hard and large-sized abrasives such as diamond, boron carbide, and silicon nitride are typically chosen. The liquid medium in the polishing slurry mainly serves to disperse the abrasives and provide lubrication and cooling. The purpose of fine polishing is to eliminate the microscopic scratches, surface and subsurface damage layers left by rough polishing, obtaining an atomically smooth surface to meet the extremely high requirements for surface quality and thermal conductivity in applications such as electronic device packaging. Therefore, silica, which can achieve shear thickening, and alumina, with suitable hardness, are the preferred polishing media for fine polishing. Fine polishing requires the use of chemical etching to achieve polishing; therefore, acidic silica polishing slurries with a pH value between 2 and 4 have broad application prospects in the market.

[0022] Polishing solutions must be highly dispersed and stable suspensions or colloids. Any abrasive agglomeration will scratch the surface like large particles, affecting the polishing effect. A unique aspect of polishing aluminum nitride ceramics is that aluminum nitride hydrolyzes during the polishing process. This hydrolysis alters the pH and stability of the polishing solution, specifically causing an increase in the pH of acidic polishing solutions. This is because aluminum nitride ceramics undergo a hydrolysis reaction upon contact with water, producing aluminum hydroxide and ammonia gas. Ammonia gas is highly soluble in water and reacts with water to form ammonium hydroxide, a weak base.

[0023] Unstable pH values ​​mean unstable chemical corrosion rates and alter the zeta potential of silica abrasives, leading to large-sized hard agglomerates. This results in the material removal rate (MRR) of the polishing process not remaining constant throughout the polishing process, causing uneven polishing and resulting in defects such as pitting and micro-scratches on the surface of aluminum nitride ceramic substrates due to the ploughing effect.

[0024] In summary, the technical problem that this invention aims to solve is how to improve the stability of acidic silica polishing slurry so that its pH value can be maintained at least within the range of 5 to 6 during the polishing process.

[0025] To address the above problems, the preparation method of the aluminum nitride ceramic polishing slurry of the present invention includes: S100, Prepare an acidic polymer resin as a core material; S200: Using organosilicon as raw material, a silica wall material is coated on the surface of the core material through a hydrolysis-condensation reaction to obtain composite microspheres for pH adjustment. S300 is a polishing slurry prepared by mixing composite microspheres, silica shear-thickening particles, and alumina abrasives with a liquid medium and adjusting the pH value.

[0026] The polishing slurry of this invention is suitable for fine polishing of aluminum nitride ceramics. Its pH value is around 3 to 4, classifying it as an acidic polishing slurry for chemical-mechanical polishing. Chemical polishing is achieved through acid corrosion, while mechanical polishing is achieved through a particulate polishing medium with a certain degree of hardness. The polishing medium used in this invention includes silica shear-thickening particles and alumina abrasive.

[0027] Polishing slurries formulated with silica shear-thickening particles are based on non-Newtonian fluid properties and exhibit unique rheological behavior. Under low shear forces (such as polishing edges or flat areas), these slurries remain liquid with low viscosity, resulting in low friction and material removal rates. Under high shear forces (such as areas of concentrated contact stress like protrusions, scratches, and blemishes), the suspension instantly thickens or even becomes near-solid, forming a tiny "abrasive agglomerate" that exerts a powerful "impact" and "shear" effect on the area, preferentially removing high points. This characteristic allows silica shear-thickening particles to serve as a polishing medium, efficiently leveling surfaces without causing subsurface damage, contributing to the achievement of ultra-smooth, scratch-free surfaces.

[0028] Polishing slurries formulated with silica shear-thickening particles are often used in the final fine polishing process to achieve extremely high surface integrity and extremely low surface roughness. Alumina has a Mohs hardness of 9, lower than diamond and silicon carbide, but its material removal rate is higher than that of silica. In the polishing slurry of this invention, silica shear-thickening particles are used as the main polishing medium, supplemented with a small amount of alumina abrasive to ensure high polishing efficiency.

[0029] To formulate a polishing slurry that achieves a non-Newtonian fluid state, this invention uses water and polyethylene glycol as the liquid medium. Preferably, the molecular weight of the polyethylene glycol is between 200 and 400. In addition to the liquid medium, the polishing slurry also requires the addition of dispersants such as benzisothiazolinone, sodium polyacrylate, or sodium hexametaphosphate, as well as some additives such as preservatives and surfactants.

[0030] Preferably, in the polishing fluid of the present invention, the mass ratio of dispersant: preservative: composite microspheres: silica shear-thickening particles: alumina abrasive: polyethylene glycol: water is (0.01-1): (0.01-1): (1-8): (15-25): (1-3): (40-45): 100.

[0031] For example, the preservative is at least one or a combination of potassium sorbate, calcium sorbate, sodium sorbate.

[0032] In S300, after the composite microspheres, silica shear-thickening particles, alumina abrasive, polyethylene glycol and water as liquid media, along with dispersants and preservatives, are uniformly mixed and dispersed, an acidic reagent, such as an aqueous solution of hydrochloric acid or nitric acid, can be added to adjust the pH value. The concentration of the acidic reagent can be selected and adjusted by those skilled in the art.

[0033] Preferably, the silica shear-thickening particles have a particle size of 50 nm to 300 nm. Silica particles within this size range are sufficient to overcome Brownian motion and, when subjected to shear, can effectively collide and rub against each other to form an instantaneous solid-like phase structure, thereby generating a huge, reversible viscosity change and exerting a shear-thickening effect.

[0034] Preferably, the alumina abrasive has a particle size of 50 nm to 200 nm. Smaller particle size results in gentler cutting forces, avoiding mechanical damage. Combined with chemical corrosion, atomically smooth surfaces can be achieved.

[0035] Although adding a small amount of alumina abrasive can achieve high polishing efficiency, alumina abrasives are extremely sensitive to pH. At low pH levels (below 4), alumina particles become protonated and positively charged, and due to the repulsion of like charges, they disperse stably. However, as the pH increases, the dispersion stability of the alumina abrasive gradually decreases. Near the isoelectric point (pH 8-9), severe agglomeration and sedimentation occur, leading to deep scratches and polishing slurry failure. Besides alumina abrasives, silica shear-thickening particles also exhibit changes in zeta potential and agglomeration due to pH variations.

[0036] Therefore, the purpose of steps S100 to S300 in this invention is to prepare an acidic core material, which is then coated and added to the polishing solution. As the aluminum nitride ceramic polishing process proceeds, the acidic core material within the coating layer is gradually exposed, thereby neutralizing the hydroxide ions released from the water produced by the aluminum nitride ceramic, adjusting the pH value of the polishing solution to remain constant, preventing the agglomeration of the grinding media, and avoiding uneven polishing.

[0037] The key technical points or difficulties in achieving the above objectives are as follows: (1) It is necessary to ensure that the timing and amount of acidic substances released are matched with the hydrolysis rate of aluminum nitride ceramics, so as to ensure that the pH value of the polishing solution remains stable and avoids sharp rises or falls in the polishing solution. (2) To avoid the adverse effects of the raw materials used in the pH-adjusting composite microspheres on the properties (especially stability) of the polishing solution, it is necessary to avoid the raw material composition being too complex, and especially to avoid the rupture or damage of the coating layer affecting the stability of the polishing solution.

[0038] To address the aforementioned key technical challenges or difficulties, the present invention has made the following attempts: (1) This invention explored several different methods for preparing pH-adjustable composite microspheres. By adjusting the raw material components, proportions, and preparation processes, composite microspheres with different internal core material compositions and different external shell mechanical strengths were obtained. Furthermore, through testing, this invention obtained a process scheme that ensures minimal change in the pH value of the polishing solution under shear stress. (2) The pH-adjusting composite microspheres of the present invention use silica as the shell, and the composition of its raw materials is relatively simple. After the coating layer is broken or damaged, it will not affect the stability of the polishing solution. In order to use silica as the shell of the pH-adjusting composite microspheres, the present invention uses an organosilicon source as raw material and forms a nanoscale silica shell on the polymer surface through the sol-gel method.

[0039] (3) In this invention, different reaction systems of suspension and emulsion were tested respectively. The suspension system achieves the deposition and coating of silica on the surface of solid acidic polymer through interfacial reaction, while the emulsion system prepares partially hollow microspheres through template method, thereby adjusting the timing of the rupture of pH-adjusting composite microspheres so that they can rupture under relatively low shear strength.

[0040] (4) Test results show that by adding pH-adjusting composite microspheres, the pH value of the polishing solution of the present invention first increases and then decreases when polishing aluminum nitride. Overall, the pH value of the polishing solution of the present invention changes relatively little after the polishing process is completed.

[0041] (5) The test results also show that the pH-adjusting composite microspheres obtained using different raw materials and processes have different adjustment rates and degrees for the pH value of the polishing solution. This invention typically improves the process to obtain the implementation method with the best polishing effect.

[0042] In general, this invention uses acrylic acid monomers as the main raw material to prepare acidic polymer resins. Polyacrylic acid is a highly polar polymer. Each repeating unit has a hydrophilic carboxyl group, which gives polyacrylic acid a strong ability to form hydrogen bonds. Accordingly, in an aqueous medium, polyacrylic acid ionizes and releases hydrogen ions, thereby lowering the pH value of the aqueous medium.

[0043] Among numerous acidic substances (especially acidic polymers), this invention chooses polyacrylic acid because its ionization state differs under different pH conditions. Specifically, at low pH levels (below 4), the molecular chains of polyacrylic acid coil up into coils, with very low carboxyl ionization; at medium to high pH levels (above 6), the molecular chains extend and the carboxyl groups ionize; and near its isoelectric point (above 4 and below 5), polyacrylic acid is in a transitional state with some carboxyl ionization. Therefore, choosing polyacrylic acid as the core material for pH-adjusting composite microspheres not only allows for the release of acidic substances into the polishing solution but also facilitates the control of the polishing solution's pH value, ensuring stable pH changes and avoiding sudden increases or decreases. Furthermore, even if the continuous hydrolysis of aluminum nitride ceramics leads to a continuous increase in the pH of the polishing solution, the hydrogen ions generated by the ionization of polyacrylic acid carboxyl groups are insufficient to neutralize the excess hydroxide ions. However, under high pH conditions, polyacrylic acid can be adsorbed onto the surface of silica particles. The long polymer chains can form a physical barrier and cause all the encapsulated particles to repel each other due to their charge. This makes silica and alumina more stable and less prone to aggregation in a high pH environment.

[0044] After obtaining the acidic polymer resin core material, this invention uses a sol-gel method with organosilicon sources such as ethyl silicate or methyl silicate as raw materials. Under the action of an acidic catalyst, a silica shell is deposited on the surface of the core material through hydrolysis and condensation of the organosilicon source. The composite microspheres coated with the silica shell have a surface energy close to that of the polishing medium, which is beneficial for the stable storage of the polishing slurry and prevents sedimentation. During the use of the polishing slurry, shearing and grinding cause the silica shell to break down, and the acidic polymer resin core material is gradually released. The broken shell is nanoscale silica with a very small particle size prepared by the sol-gel method, which does not affect or change the properties of the polishing slurry, especially its dispersibility.

[0045] This invention employs two different technical approaches to prepare the core material, and adapts different silica wall material coating methods to the core materials obtained by different processes.

[0046] The first technical approach involves using acrylic acid monomers and methyl methacrylate as monomer raw materials, azobisisobutyronitrile (AIB) as an initiator, maleic anhydride as a grafting modifier, and propylene glycol methyl ether acetate as a reaction medium to prepare an acrylic acid-methyl methacrylate copolymer. The macromolecular chain of this copolymer contains carboxyl groups from acrylic acid, which can neutralize alkaline substances in the liquid medium to form carboxylates, thereby adjusting the pH value of the liquid medium. The carboxylates also impart hydrophilicity to the polymer chain, ensuring uniform dispersion of the acrylic acid-methyl methacrylate copolymer in aqueous or emulsion-like liquid media and maintaining the stability of the aqueous or emulsion-like liquid medium system.

[0047] The acrylic acid-methyl methacrylate copolymer obtained by heating and pressurizing is in an emulsion state. After removing unreacted monomers, a solid acrylic acid-methyl methacrylate copolymer precipitate can be obtained by pouring the acrylic acid-methyl methacrylate copolymer into excess acetone and stirring rapidly, which can then be used as a polymer resin. The purpose of adding methyl methacrylate monomer is to improve the film-forming properties of the acidic polymer resin.

[0048] Specifically, in some embodiments of the present invention, S100 specifically includes: S110. Mix maleic anhydride and propylene glycol methyl ether acetate evenly, then add acrylic monomer, methyl methacrylate and azobisisobutyronitrile and continue mixing evenly. Heat and pressurize to react. S120. After the reaction is complete, cool down and depressurize. Slowly pour the remaining material after removing unreacted monomers into an excess of acetone and stir rapidly. After stirring is complete, let stand, separate the solids, wash, and obtain a solid acrylic acid-methyl methacrylate copolymer, which can be used as a polymer resin.

[0049] Preferably, in S110, the mass ratio of azobisisobutyronitrile:maleic anhydride:acrylic monomer:methyl methacrylate:propylene glycol methyl ether acetate is (0.1-0.3)(2-4):(25-30):(15-20):100.

[0050] Preferably, in S120, the temperature conditions for the heating and pressurizing reaction are 75°C to 95°C, the pressure conditions are 0.4 MPa to 0.6 MPa, and the reaction time is 3 h to 5 h.

[0051] The first technical approach described above yielded a solid acrylic-methyl methacrylate copolymer. Subsequently, a silica film was coated onto the surface of the acrylic-methyl methacrylate copolymer via an interfacial reaction. The solid particulate acrylic-methyl methacrylate copolymer slightly swells in the water-oil mixture, serving as a heterogeneous nucleation center, where silica can gradually deposit.

[0052] To achieve the above objectives, this invention uses Tween 80 as an emulsifier, dichloromethane as the organic phase, and hexadecyltrimethylammonium bromide as a surfactant. An organosilicon source, such as ethyl silicate or methyl silicate, is uniformly dispersed in a mixture of water and ethanol, diffuses to the oil-water interface, and undergoes hydrolysis and condensation at the interface to form a silica shell, encapsulating the acrylic-methyl methacrylate copolymer emulsion droplets. After the reaction is complete, the product is collected by centrifugation and washing. The solvent in the internal oil is evaporated and removed during a drying process, thereby obtaining composite microspheres with acrylic-methyl methacrylate copolymer as the core material and silica as the wall material.

[0053] Accordingly, S200 specifically includes: S210, according to the mass ratio of Tween 80: polymer resin: dichloromethane = (4-8): (20-30): 100, mix Tween 80, polymer resin and dichloromethane to form a suspension; S220. According to the mass ratio of hexadecyltrimethylammonium bromide: organosilicon source: water: ethanol = (0.2-0.3): (10-15): (30-35): 100, the organosilicon source is mixed with hexadecyltrimethylammonium bromide, water and ethanol to obtain a hydrolysate. S230. Add the hydrolysate dropwise to the suspension at a mass ratio of (80-120):100, stirring simultaneously. After the addition is complete, add hydrochloric acid to adjust the pH to 3 to 4, keep warm and stir for 1.5 to 2 hours, stop keeping warm and let stand for 6 to 8 hours. S240. Centrifuge the solid, wash, and dry to obtain composite microspheres.

[0054] The second technical approach of this invention also uses acrylic acid monomers and methyl methacrylate as monomer raw materials, azobisisobutyronitrile as an initiator, maleic anhydride as a grafting modifier, and propylene glycol methyl ether acetate as a reaction medium to prepare an acrylic acid-methyl methacrylate copolymer. The difference from the first approach is that it obtains an emulsion-like liquid acrylic acid-methyl methacrylate copolymer, which is then further mixed with styrene monomers. Water is used as the reaction medium, Tween 80 as the emulsifier, N,N-methylenebisacrylamide as the crosslinking agent, and azobisisobutyronitrile as the initiator. The above raw materials are then formulated to obtain a mixture of acrylic acid-methyl methacrylate copolymer and styrene monomers. This mixture is first polymerized and then mixed with an organosilicon source to obtain a reactant consisting of an acrylic acid-methyl methacrylate copolymer / polystyrene mixture as the core material and silica as the wall material.

[0055] Tetrahydrofuran is a moderately polar organic solvent. Although it contains oxygen atoms and possesses some polarity and hydrogen bond accepting ability, its polarity is far lower than that of water. Tetrahydrofuran is a good solvent for nonpolar polystyrene. However, because polypropylene is far more polar and has a much stronger ability to form hydrogen bonds than tetrahydrofuran, tetrahydrofuran cannot effectively interact with and solvate the carboxyl groups on the polypropylene chain. Therefore, polypropylene is insoluble in tetrahydrofuran, and its swelling is very limited. Therefore, by placing the reactants in a sufficient amount of tetrahydrofuran and stirring, the polystyrene acting as a template agent can be removed by extraction to obtain partially hollow composite microspheres containing an acrylic acid-methyl methacrylate copolymer.

[0056] Specifically, in some embodiments of the present invention, S100 specifically includes: S110. Mix maleic anhydride and propylene glycol methyl ether acetate evenly, then add acrylic monomer, methyl methacrylate and azobisisobutyronitrile and continue mixing evenly. Heat and pressurize to react. S120. After the reaction is complete, the temperature is lowered and the pressure is released to remove unreacted monomers and obtain liquid acrylic acid-methyl methacrylate copolymer. S130. Styrene monomer, water, Tween 80, N,N-methylenebisacrylamide, and azobisisobutyronitrile are mixed evenly to obtain a styrene monomer emulsion. S140. Acrylic acid-methyl methacrylate copolymer is added dropwise into styrene monomer emulsion while stirring simultaneously. After the addition is complete, an emulsion-like mixture of acrylic acid-methyl methacrylate copolymer and styrene is obtained as a polymer resin.

[0057] Preferably, in S110, the mass ratio of azobisisobutyronitrile:maleic anhydride:acrylic monomer:methyl methacrylate:propylene glycol methyl ether acetate = (0.1-0.3)(2-4):(15-20):(25-30):100; in S130, the mass ratio of azobisisobutyronitrile:N,N-methylenebisacrylamide:Tween 80:styrene monomer:water = (0.1-0.3):(1-2):(6-12):(20-30):100; in S140, the mass ratio of acrylic acid-methyl methacrylate copolymer:styrene monomer emulsion = (80-120):100.

[0058] Preferably, in S120, the temperature conditions for the heated and pressurized reaction are 75°C to 90°C, the pressure conditions are 0.4 MPa to 0.6 MPa, and the reaction time is 3 h to 5 h.

[0059] Accordingly, S200 specifically includes: S210. Mix the organosilicon source with water and ethanol at a mass ratio of (10-15):(30-35):100 to obtain a hydrolysate. S220. The polymer resin is heated and stirred for 5 to 7 hours under a protective atmosphere and at a temperature of 65°C to 70°C to obtain a mixture of acrylic acid-methyl methacrylate copolymer / polystyrene. S230. According to the mass ratio of mixture: hydrolysate = (80-120): 100, add the hydrolysate dropwise to the mixture under the heat preservation condition and stir simultaneously. After the dropwise addition is completed, add hydrochloric acid to adjust the pH value to 3 to 4, keep warm and stir for 3 to 5 hours, stop the heat preservation and let it stand and age for 6 to 8 hours. S240. Centrifuge the solid, wash it, place it in a sufficient amount of tetrahydrofuran and stir for 10 to 20 minutes. Centrifuge the solid again, wash it, and dry it to obtain composite microspheres.

[0060] Example 1 This embodiment employs the first technical approach to prepare composite microsphere sample 1 for adjusting the pH value of the polishing solution. The preparation process is as follows: S1. Based on the mass of propylene glycol methyl ether acetate (100 parts), accurately weigh 3 parts of maleic anhydride, 27.5 parts of acrylic acid monomer, 17.5 parts of methyl methacrylate and 0.2 parts of azobisisobutyronitrile. Pour the weighed propylene glycol methyl ether acetate into a clean high-pressure reactor liner, turn on medium-speed mechanical stirring (300-400 rpm), slowly add maleic anhydride powder, stir for about 30 minutes until it is completely dissolved and a clear solution is obtained. Then slowly add acrylic acid and methyl methacrylate monomer in sequence, continue stirring for 10 minutes, and finally add azobisisobutyronitrile initiator, continue stirring for at least 15 minutes to ensure that azobisisobutyronitrile is completely dissolved and dispersed to form a uniform prepolymer solution. S2. Seal the high-pressure reactor, check its airtightness, set the reaction temperature to 85℃, start the stirrer (the speed can be increased to 400-500 rpm). As the temperature rises, the pressure inside the reactor will gradually increase. Adjust the pressure controller to stabilize the reaction pressure at 0.5MPa and maintain the reaction for 4 hours. During the reaction, the temperature and pressure should be continuously monitored and adjusted to ensure their stability. S3. After the reaction is complete, turn off the heating and allow the reactor to cool naturally to below 40°C. Then, open the pressure relief valve and reduce the pressure to atmospheric pressure before opening the reactor lid. Add the viscous polymer solution obtained from the reaction slowly (about 1-2 drops / second) dropwise to excess acetone using a constant pressure dropping funnel while stirring at high speed (800-1000 rpm). The amount of acetone should be at least 10 times the volume of the polymer solution. After the addition is complete, continue stirring for 10 minutes, then stop stirring and let it stand for 1 hour. The polymer will precipitate in the acetone as a white fibrous or flocculent solid. Filter the solid using a Buchner funnel and collect it. Wash the filter cake three times with fresh acetone to thoroughly remove residual monomers, solvents, and unreacted initiators. Transfer the filter cake to a watch glass and dry it in a vacuum drying oven at 50°C for 12 hours to obtain a white solid acrylic-methyl methacrylate copolymer resin for later use. S4. Based on the mass of dichloromethane (100 parts), accurately weigh 6 parts of Tween 80 and 25 parts of polymer resin. Add the dichloromethane to a four-necked flask. While stirring at high speed (800-1000 rpm), first dissolve the Tween 80 in the dichloromethane, then slowly add the polymer resin powder, continuing to stir until uniformly dispersed, forming a uniform and stable milky white suspension. Transfer the flask to a 58°C water bath and switch to low-speed stirring (100-200 rpm) for preheating. S5. Based on the mass of ethanol (100 parts), accurately weigh 0.2 parts of hexadecyltrimethylammonium bromide, 15 parts of ethyl silicate, and 33 parts of water. In an Erlenmeyer flask, dissolve the hexadecyltrimethylammonium bromide in the mixed solution of ethanol and water. Gently heat (40°C) and stir to accelerate the dissolution of hexadecyltrimethylammonium bromide. After the solution becomes clear, slowly add ethyl silicate with a dropper while stirring. Continue stirring for 30 minutes to allow for preliminary hydrolysis, resulting in a homogeneous and transparent hydrolysate. S6. Using a mass ratio of suspension to hydrolysate of 90:100, maintain the suspension temperature at 58℃ and stir continuously. Add the hydrolysate dropwise to the suspension at a slow rate of 2 mL / min using a constant pressure dropping funnel while stirring simultaneously. After the addition is complete, add 0.1M dilute hydrochloric acid to adjust the pH to 3.5. Keep the temperature and stir for 1.5 hours to allow ethyl silicate to undergo hydrolysis and condensation at the water / oil interface, which is stabilized by both hexadecyltrimethylammonium bromide and Tween 80, forming a silica shell on the surface of the polymer core. After the time is up, stop the temperature control and let it stand for 6 to 8 hours to age. S7. Centrifuge, wash, and dry the solids. Transfer the reaction mixture to a centrifuge tube and centrifuge at 10,000 rpm for 10 min. Collect the precipitate and wash it three times with anhydrous ethanol and deionized water alternately to remove residual surfactants, salts, and other organic matter. Transfer the washed precipitate to a petri dish and dry it in a vacuum drying oven at 60℃ for 24 h to obtain composite microspheres.

[0061] Example 2 This embodiment employs the second technical approach to prepare composite microsphere sample 2 for adjusting the pH value of the polishing solution. The preparation process is as follows: S1, the same as S1 in Example 1; S2, the same as S2 in Example 1; S3. After the reaction is complete, turn off the heating and let the reactor cool naturally to below 40°C. Then open the pressure relief valve and reduce the pressure to atmospheric pressure before opening the reactor lid. Rotate and evaporate the viscous polymer solution obtained from the reaction in a water bath at 65°C and a vacuum of less than -0.095 MPa to obtain a viscous liquid acrylic acid-methyl methacrylate copolymer. S4. Based on the mass of water (100 parts), accurately weigh 0.2 parts of azobisisobutyronitrile, 1 part of N,N-methylenebisacrylamide, 8 parts of Tween 80, and 25 parts of styrene monomer. First, add water, Tween 80, and N,N-methylenebisacrylamide to a four-necked flask, stir and heat to 40°C to completely dissolve N,N-methylenebisacrylamide. Then, slowly add styrene monomer and stir at high speed (about 800 rpm) for 10 minutes. Then, homogenize three times using a high-pressure homogenizer at 35 MPa. Transfer the emulsion back to the four-necked flask, add azobisisobutyronitrile, and stir at low speed (200 rpm) for 15 minutes to obtain a fine, milky white styrene monomer emulsion. S5. According to the mass ratio of acrylic acid-methyl methacrylate copolymer to styrene monomer emulsion = 120:100, heat the styrene monomer emulsion to 70°C under a protective atmosphere and keep stirring at a low speed (200 rpm). Add the acrylic acid-methyl methacrylate copolymer dropwise to the styrene monomer emulsion at a slow rate of about 2 mL / min using a constant pressure dropping funnel. After the addition is complete, continue stirring for 30 min to obtain a milky white acrylic acid-methyl methacrylate copolymer / styrene mixture, i.e., polymer resin (it is not necessary to allow the styrene to fully polymerize at this stage). S6. According to the mass ratio of ethyl silicate:water:ethanol = 15:33:100, ethyl silicate is slowly added dropwise to the mixture of water and ethanol while stirring at low speed (200 rpm). After the addition is complete, continue stirring for 30 minutes to obtain the hydrolysate. S7. Transfer the polymer resin to a four-necked flask, continuously introduce high-purity nitrogen into the flask as a protective atmosphere, heat to 70°C and stir (300 rpm) for 5 hours under nitrogen atmosphere to obtain a mixture of acrylic acid-methyl methacrylate copolymer / polystyrene. S8. According to the mass ratio of mixture:hydrolysate = 90:100, under the protection of nitrogen and at a temperature of 70℃, add the hydrolysate dropwise to the stirred mixture through a constant pressure dropping funnel at a rate of 3 mL / min; after the addition is complete, slowly adjust the pH of the system to 3.5 with 0.1M dilute hydrochloric acid and continue the reaction for 4 hours; then stop heating and let it stand and age for 8 hours under the protection of nitrogen. S9. Centrifuge the reaction mixture to collect the solid precipitate. Wash the precipitate three times alternately with anhydrous ethanol and deionized water. Redisperse the washed solid in sufficient tetrahydrofuran (at least 20 times the volume of the solid). Stir vigorously at room temperature for 15 min. Centrifuge the solid again, wash once with fresh tetrahydrofuran and twice with ethanol, transfer to a petri dish, and dry in a vacuum drying oven at 60℃ for 24 h to obtain composite microspheres.

[0062] Comparative Example 1 In this comparative example, composite microsphere sample 3 was prepared for adjusting the pH value of the polishing solution. The preparation process is as follows: S1. Based on the mass of dichloromethane (100 parts), accurately weigh 6 parts of Tween 80 and 25 parts of D001 resin. Add the dichloromethane to a four-necked flask. Under high-speed stirring (800-1000 rpm), first dissolve the Tween 80 in the dichloromethane, then slowly add the D001 resin powder, and continue stirring until uniformly dispersed to form a suspension. Transfer the flask to a 58°C water bath and switch to low-speed stirring (100-200 rpm) for preheating. S2, the same as S5 in Example 1; S3, the same as S6 in Example 1; S4, the same as S7 in Example 1.

[0063] Example 3 In this embodiment, a series of polishing slurries were prepared. The sources of the composite microspheres used are listed in Table 1, and the preparation process is as follows: S1. Weigh the materials according to the mass ratio of dispersant: preservative: composite microspheres: silica shear-thickening particles: alumina abrasive: polyethylene glycol: water = 0.02:0.04:1.5:25:1.5:45:100; S2. First, slowly add polyethylene glycol (specifically PEG-20000) to a beaker containing water and stir magnetically (300 rpm) for about 2 hours to obtain a clear and transparent solution. Add preservative (specifically benzisothiazolinone) and dispersant (specifically sodium hexametaphosphate) and continue stirring for 15 minutes. Add silica shear thickening particles, alumina and composite microspheres in small batches while stirring continuously. After the addition is complete, sonicate homogenize for more than 30 minutes until the system becomes translucent or uniformly milky white and there are no visible agglomerates. Add 0.1M dilute hydrochloric acid to adjust the pH value to 3.5 to prepare the polishing solution.

[0064] Table 1 Comparative Example 2 Polishing slurry sample 5 was prepared in this comparative example, and its preparation process is as follows: S1. Weigh the materials according to the mass ratio of dispersant: preservative: silica shear-thickening particles: alumina abrasive: polyethylene glycol: water = 0.02:0.04:25:1.5:45:100; S2. First, slowly add polyethylene glycol (specifically PEG-20000) to a beaker containing water and stir magnetically (300 rpm) for about 2 hours to obtain a clear and transparent solution. Add preservative (specifically benzisothiazolinone) and dispersant (specifically sodium hexametaphosphate) and continue stirring for 15 minutes. Add silica shear thickening particles and alumina in small batches while stirring continuously. After the addition is complete, sonicate for more than 30 minutes until the system becomes translucent or uniformly milky white and there are no visible agglomerates. Add 0.1M dilute hydrochloric acid to adjust the pH value to 3.5 to prepare the polishing solution.

[0065] Performance testing The polishing slurry samples 1 to 5 obtained in Example 3 and Comparative Example 2 were used as polishing slurries for aluminum nitride ceramics. Thirty aluminum nitride ceramic substrate samples (30mm × 30mm × 1mm) were taken and pre-processed with a diamond abrasive disc to remove large shape errors and machining allowances, so that the surface achieves a certain flatness (target Ra < 1 micrometer); then rough polishing was performed with diamond abrasive (target Ra < 0.2 micrometers); finally, the samples were placed in an ultrasonic cleaner, cleaned with deionized water to remove all polishing slurry residue adhering to the surface, and then dried with high-purity nitrogen or clean air.

[0066] After rough polishing, fine polishing is performed. Using a CNC polishing machine and a polyurethane polishing pad, the polishing slurry samples obtained in Example 3 and Comparative Example 2 are placed in storage tanks equipped with stirring and circulation functions to polish the aluminum nitride ceramic substrate samples. One polishing slurry sample is used each time, and six aluminum nitride ceramic substrate samples are polished simultaneously using a planetary fixture. A stable flow rate (50 mL / min) is continuously supplied to the center of the polishing disc. The aluminum nitride ceramic substrate samples are securely mounted on the workpiece fixture of the polishing machine. The polishing machine is started, with the polishing disc speed at 300 rpm, polishing pressure at 10 kPa, and polishing time at 120 min. Every 20 min, a sample of polishing slurry is removed from the storage tank, and the pH value is tested using an acid-base analyzer. The test results are shown in Table 2.

[0067] Table 2 shows that the initial pH values ​​of polishing slurry samples 1 to 5 were basically the same. After use, their pH values ​​gradually increased as aluminum nitride hydrolyzed. The pH value of polishing slurry sample 5 continued to rise, while the pH value of polishing slurry sample 3 first rose, then fell, and then rose again. This indicates that the strong acid type D001 resin has a strong ability to regulate the pH of the polishing slurry, but it cannot achieve stable regulation and the fluctuations are large. For polishing slurry samples 1, 2, and 4: at 20 min, the pH increases of polishing slurry samples 1, 2, and 4 were similar; between 40 and 60 min, the increases of polishing slurry samples 2 and 4 were smaller, indicating that the acidity of polishing slurry samples 2 and 4 began to be released earlier; at 80 min, the pH values ​​of polishing slurry samples 1, 2, and 4 were similar, but the pH value of polishing slurry sample 1 decreased significantly compared to 60 min, indicating that the acidic substances in polishing slurry sample 1 began to be released relatively rapidly; between 100 and 120 min, the pH values ​​of polishing slurry samples 1, 2, and 4 were stable between 4 and 5; among them, the pH stability of polishing slurry sample 1 was slightly worse in the early stage of polishing, the pH stability of polishing slurry sample 2 was slightly worse in the later stage of polishing, and the pH stability of polishing slurry sample 4 was moderate throughout the cycle, but the overall pH adjustment time was the longest, and it could maintain a stable pH value with small fluctuations for a longer period of time.

[0068] Table 2 The surface of the aluminum nitride ceramic substrate samples was scanned and measured using an atomic force microscope. Five detection points were selected, and the arithmetic mean roughness (Ra) of each aluminum nitride ceramic substrate sample was calculated. The test results are shown in Table 3.

[0069] Table 3 While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing a polishing slurry for polishing aluminum nitride ceramics, characterized in that, The preparation method includes: S100, Prepare an acidic polymer resin as a core material; S200: Using an organosilicon source as raw material, a silica wall material is coated on the surface of the core material through a hydrolysis-condensation reaction to obtain composite microspheres for pH adjustment. S300: Using the composite microspheres, silica shear-thickening particles, and alumina abrasive as raw materials, a liquid medium is added for mixing and the pH value is adjusted to 3-4 to prepare the polishing fluid. S100 specifically includes: S110. Mix maleic anhydride and propylene glycol methyl ether acetate evenly, then add acrylic monomer, methyl methacrylate and azobisisobutyronitrile and continue mixing evenly. Heat and pressurize to react. S120. After the reaction is complete, the temperature is reduced and the pressure is released. The remaining material after removing unreacted monomers is slowly poured into an excess of acetone and stirred rapidly. After stirring is complete, the mixture is allowed to stand, the solid is separated, washed, and a solid acrylic acid-methyl methacrylate copolymer is obtained as the polymer resin.

2. The preparation method according to claim 1, characterized in that, In S110, by mass ratio, azobisisobutyronitrile: maleic anhydride: acrylic monomer: methyl methacrylate: propylene glycol methyl ether acetate = (0.1-0.3)(2-4):(25-30):(15-20):

100.

3. The preparation method according to claim 1, characterized in that, In S120, the temperature conditions for the heating and pressurizing reaction are 75°C to 95°C, the pressure conditions are 0.4 MPa to 0.6 MPa, and the reaction time is 3 h to 5 h.

4. The preparation method according to any one of claims 1 to 3, characterized in that, S200 specifically includes: S210. Tween 80, polymer resin and dichloromethane are mixed in a mass ratio of (4-8):(20-30):100 to form a suspension. S220. According to the mass ratio of hexadecyltrimethylammonium bromide: organosilicon source: water: ethanol = (0.2-0.3): (10-15): (30-35): 100, the organosilicon source is mixed with hexadecyltrimethylammonium bromide, water and ethanol to obtain a hydrolysate; S230. According to the mass ratio of suspension to hydrolysate = (80-120):100, the hydrolysate is added dropwise to the suspension at a temperature of 55°C to 60°C while stirring simultaneously. After the addition is complete, hydrochloric acid is added to adjust the pH value to 3 to 4. The mixture is kept warm and stirred for 1.5h to 2h. The heat preservation is stopped and the mixture is allowed to stand and age for 6h to 8h. S240. Centrifuge the solid, wash, and dry to obtain the composite microspheres.

5. A method for preparing a polishing slurry for polishing aluminum nitride ceramics, characterized in that, The preparation method includes: S100, Prepare an acidic polymer resin as a core material; S200: Using an organosilicon source as raw material, a silica wall material is coated on the surface of the core material through a hydrolysis-condensation reaction to obtain composite microspheres for pH adjustment. S300: Using the composite microspheres, silica shear-thickening particles, and alumina abrasive as raw materials, a liquid medium is added for mixing and the pH value is adjusted to 3-4 to prepare the polishing fluid. S100 specifically includes: S110. Mix maleic anhydride and propylene glycol methyl ether acetate evenly, then add acrylic monomer, methyl methacrylate and azobisisobutyronitrile and continue mixing evenly. Heat and pressurize to react. S120. After the reaction is complete, the temperature is lowered and the pressure is released to remove unreacted monomers and obtain liquid acrylic acid-methyl methacrylate copolymer. S130. Styrene monomer, water, Tween 80, N,N-methylenebisacrylamide, and azobisisobutyronitrile are mixed evenly to obtain a styrene monomer emulsion. S140. The acrylic-methyl methacrylate copolymer is added dropwise into the styrene monomer emulsion while stirring simultaneously. After the addition is complete, an emulsion-like mixture of acrylic-methyl methacrylate copolymer and styrene is obtained as the polymer resin.

6. The preparation method according to claim 5, characterized in that, In S110, by mass ratio, azobisisobutyronitrile: maleic anhydride: acrylic monomer: methyl methacrylate: propylene glycol methyl ether acetate = (0.1-0.3)(2-4):(15-20):(25-30):100; In S130, by mass ratio, azobisisobutyronitrile: N,N-methylenebisacrylamide: Tween 80: styrene monomer: water = (0.1-0.3): (1-2): (6-12): (20-30): 100; In S140, the mass ratio of acrylic acid-methyl methacrylate copolymer to styrene monomer emulsion is (80-120):

100.

7. The preparation method according to claim 5, characterized in that, In S120, the temperature conditions for the heating and pressurizing reaction are 75°C to 90°C, the pressure conditions are 0.4 MPa to 0.6 MPa, and the reaction time is 3 h to 5 h.

8. The preparation method according to any one of claims 5 to 7, characterized in that, S200 specifically includes: S210. Mix the organosilicon source with water and ethanol at a mass ratio of organosilicon source: water: ethanol = (10-15): (30-35): 100 to obtain a hydrolysate. S220. The polymer resin is heated and stirred for 5 to 7 hours under a protective atmosphere and at a temperature of 65°C to 70°C to obtain a mixture of acrylic acid-methyl methacrylate copolymer / polystyrene. S230. According to the mass ratio of mixture: hydrolysate = (80-120): 100, the hydrolysate is added dropwise to the mixture under the heat preservation condition and stirred simultaneously. After the addition is completed, hydrochloric acid is added to adjust the pH value to 3 to 4. The mixture is kept warm and stirred for 3 to 5 hours. The heat preservation is stopped and the mixture is allowed to stand and age for 6 to 8 hours. S240. Centrifuge the solid, wash it, place it in a sufficient amount of tetrahydrofuran and stir for 10 to 20 minutes. Centrifuge the solid again, wash it, and dry it to obtain the composite microspheres.

9. A polishing slurry for polishing aluminum nitride ceramics, characterized in that, The polishing slurry is obtained by the preparation method as described in any one of claims 1 to 8.

Images