Solidified nano water-based silica sol polishing pad for fine polishing of SiC wafer and preparation method of solidified nano water-based silica sol polishing pad

Abstract

The invention provides a consolidated nano water-based silica sol polishing pad for SiC wafer fine polishing and a preparation method thereof.According to the polishing pad, foam slurry for consolidated abrasive damping cloth is coated on a plastic base material, then the plastic base material is placed in a segmented drying oven to be heated step by step, chemical bond combination is generated through a thermal activation curing agent and nano water-based silica sol abrasive, and the polishing pad is obtained. Solidifying the grinding material in the polyurethane resin; the foam slurry for the consolidated abrasive damping cloth comprises a thermal activation type curing agent, nano water-based silica sol, a foaming agent, a foam stabilizer, a cross-linking agent, a thickening agent and a water-based polyurethane emulsion, according to the method, the thermal activation type curing agent is added for heating and curing, so that the water-based polyurethane and the nano water-based silica sol abrasive particles are subjected to chemical reaction combination, the binding force of the nano water-based silica sol and the polyurethane resin is improved, and the abrasive material is prevented from being peeled off during polishing.

Description

Technical Field

[0001] This invention relates to the field of polishing pad technology, and in particular to a bonded nano-aqueous silica sol polishing pad for fine polishing of SiC wafers and its preparation method. Background Technology

[0002] Chemical mechanical polishing (CMP) refers to the process where, under certain pressure and in the presence of polishing materials, the workpiece being polished moves relative to the polishing pad. Through the organic combination of the abrasive action of nanoparticles and the corrosive action of oxidants, a smooth surface is formed on the surface of the workpiece being polished.

[0003] CMP based on free abrasives is a conventional method for polishing SiC wafers. A CMP process unit consists of three parts: a stage, a polishing head, and a polishing slurry delivery system. A polishing pad is attached to the stage, and a wafer is attached to the polishing head. By applying pressure to the polishing head, appropriate pressure is created between the wafer and the polishing pad. Both the stage and the polishing head can rotate, allowing relative movement between the polishing pad and the wafer. Conventional free abrasive polishing slurry polishing removes material from the wafer surface based on a three-body friction method. That is, when the abrasive is between the wafer and the polishing pad interface, the surfaces of both and the abrasive in the polishing slurry form three independent systems. In three-body friction, the abrasive is not fixed; it slides or rolls at the wafer-pad interface. Abrasive polishing slurry flows between the wafer and the polishing pad. Due to the porous structure of the polishing pad, the abrasive can be distributed relatively evenly on the polishing pad by utilizing the fluidity of the polishing slurry. Under pressure, the abrasive, which is relatively hard compared to the polishing pad material, embeds itself into the relatively soft polishing pad. Relying on the elastic support of the polishing pad, the abrasive embedded in the polishing pad scrapes the surface of the wafer. The components in the polishing slurry oxidize the silicon carbide on the wafer surface to form a relatively soft oxide layer. At the same time, the applied pressure and the mechanical shearing force of friction remove the oxide layer, achieving a trace removal of the oxide layer on the wafer surface.

[0004] Currently, the industry uses conventional wet process technology to produce damping cloth polishing pads. This process is mainly a physical coagulation process of polyurethane resin. Water is used to replace the DMF in the polyurethane resin to form a loose and porous surface. The loose and porous layer can absorb and store polishing liquid and uniformly supply polishing liquid containing abrasive to the polishing interface. The damping cloth polishing pad itself does not contain abrasive in the resin.

[0005] In this CMP process based on free abrasives, a three-body friction method is mainly used. The stability of the free abrasive dispersion and the uniformity of its supply to the polishing interface have a significant impact on the polishing effect. Furthermore, free nanoscale abrasives can become embedded in the polishing surface and pores, making them extremely difficult to clean and causing blockage of the micropores in the polishing pad. This smooths the surface of the polishing pad, ultimately leading to a gradual decrease in the material polishing rate. Simultaneously, free abrasives, especially nano-silica sol particles, are very prone to agglomeration and crystallization, resulting in scratches on the wafer surface.

[0006] Based on the shortcomings of free abrasive chemical mechanical polishing (CMP) and the ever-increasing demands for wafer planarization, 3M pioneered the Fixed Abrasive-Chemical Mechanical Polishing (FA-CMP) technology in the 1990s. In FA-CMP, the abrasive is fixed in a polishing pad, and no additional abrasive is added to the polishing slurry; instead, it contains only an aqueous solution of basic chemical components. Pressure from the polishing head can be directly transmitted to the abrasive through the polishing pad. During polishing, there is relative sliding between the abrasive and the wafer, rather than rolling, improving polishing removal efficiency. FA-CMP technology not only offers better abrasive uniformity but also involves more abrasive particles in the polishing process compared to free abrasive slurry, thus increasing the material removal rate. The abrasive fixed in the resin also prevents agglomeration, eliminating the risk of abrasive crystallization and reducing the likelihood of introducing scratch defects. Furthermore, because the abrasive is fixed in the resin, no additional abrasive needs to be added to the polishing slurry, reducing the difficulty of production, storage, and usage costs of the polishing slurry.

[0007] The fabrication of silicon carbide wafers requires grinding and chemical mechanical polishing processes to achieve an ultra-smooth surface. Polishing is divided into rough polishing and fine polishing: rough polishing aims to reduce the surface roughness of the wafer to the nanometer level; fine polishing is the final step in silicon carbide wafer fabrication, directly affecting whether the processed wafer can be used in the next epitaxial production process. The purpose of fine polishing is to further improve the surface quality of the silicon carbide substrate and reduce roughness, typically requiring the roughness of the silicon surface of the silicon carbide wafer to be below 0.2 nm.

[0008] Currently, bonded abrasives are mainly used in grinding or rough polishing processes, and have no practical application in fine polishing.

[0009] There are already solutions and products for incorporating bonded abrasives into polyurethane polishing pads or some nonwoven polishing pads for use in grinding or rough polishing processes. Small abrasive agglomerations have minimal impact on grinding and rough polishing, and a variety of bonded abrasive types are possible, including diamond, alumina, cerium oxide, and silica powder. However, for fine polishing, only low-hardness nano-aqueous silica sol abrasives can be selected, and the silica sol abrasive particles must not agglomerate to avoid introducing scratches during polishing. Simultaneously, good bonding between the abrasive and the polishing pad resin is required to prevent excessive abrasive shedding during polishing. Conventional wet-molded damping cloth polishing pads use non-reactive polyurethane resins that do not form chemical bonds with nano-aqueous silica sol abrasives. Furthermore, because wet solidification occurs in an aqueous system, the nano-aqueous silica sol, which is typically physically blended, is easily washed away from the polyurethane resin during water washing and extrusion. Summary of the Invention

[0010] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a solidified nano-aqueous silica sol polishing pad for fine polishing of SiC wafers and its preparation method, so as to solve the technical problems of poor bonding between nano-aqueous silica sol and polyurethane resin, and easy peeling or crystallization of silica sol in polishing liquid, resulting in scratch defects.

[0011] To achieve the above and other related objectives, the present invention provides an aqueous polyurethane emulsion comprising the following raw material components by mass percentage:

[0012]

[0013] The present invention also provides a method for preparing the aqueous polyurethane emulsion as described above, comprising the following steps:

[0014] S1. Heat polybutylene adipate diol until it melts, and while maintaining the temperature, continue to add diphenylmethane-4,4'-diisocyanate to carry out the polymerization reaction. Then, add some acetone to dilute it, and then add 1,4-butanediol and 2,2-dimethylolpropionic acid to continue the reaction. Add the remaining acetone and cool down to obtain a polyurethane resin with terminal hydroxyl groups.

[0015] S2. Dimethylethanolamine is mixed with water to form an aqueous solution. The polyurethane resin with terminal hydroxyl groups obtained in step S1 is slowly added to the aqueous solution. After high-speed stirring and dispersion phase inversion, an aqueous polyurethane mixed emulsion is obtained. After removing the acetone solvent from the mixed emulsion, the aqueous polyurethane emulsion is obtained.

[0016] The present invention also provides the use of the aqueous polyurethane emulsion as described above in a foam slurry for bonded abrasive damping cloth.

[0017] This invention also provides a foam slurry for bonded abrasive damping cloth, comprising the following raw material components: a thermally activated curing agent, nano-aqueous silica sol, a foaming agent, a foam stabilizer, a crosslinking agent, a thickener, and an aqueous polyurethane emulsion as described above. The components are expressed in the following mass percentages:

[0018]

[0019] The present invention also provides a method for preparing the foam slurry for bonded abrasive damping cloth as described above, comprising: mixing waterborne polyurethane emulsion, nano-waterborne silica sol, foaming agent, foam stabilizer, crosslinking agent, thermally activated curing agent and thickener in proportion, mixing evenly and then foaming to 2.0 to 2.5 times the original volume, with a foam density of 400 to 500 g / L, to obtain the foam slurry for damping cloth.

[0020] The present invention also provides the use of the foam slurry for bonded abrasive damping cloth as described above in the preparation of polishing pads for fine polishing of silicon carbide wafers.

[0021] This invention also provides a method for preparing a polishing pad for fine polishing of silicon carbide wafers, comprising the following steps:

[0022] 1) The solidified abrasive damping cloth as described above is coated onto the plastic substrate by gravity using foam slurry. The plastic substrate with foam slurry is first slowly dried at 80-100°C, and then baked at 140-160°C to complete cross-linking and curing, thus obtaining a cured polyurethane foam porous layer.

[0023] 2) Adhere the cured polyurethane foam porous layer to the plastic sheet, then grind and cut to obtain the finished polishing pad.

[0024] The present invention also provides a polishing pad for fine polishing of silicon carbide wafers, which is prepared by the preparation method described above.

[0025] As described above, the bonded nano-aqueous silica sol polishing pad for SiC wafer fine polishing and its preparation method of the present invention have the following beneficial effects:

[0026] The present invention relates to a bonded nano-aqueous silica sol polishing pad for SiC wafer fine polishing, which uses a water-based polyurethane emulsion to make a bonded abrasive damping cloth polishing pad. The water-based polyurethane emulsion is designed and synthesized, and a crosslinking agent is used during the curing process to improve its water resistance. Simultaneously, nano-aqueous silica sol with a particle size in the range of 10–300 nm is used as the abrasive. A heat-curing method using a thermally activated curing agent allows the water-based polyurethane and the nano-aqueous silica sol abrasive particles to chemically react and bond, enhancing the adhesion between the nano-aqueous silica sol and the polyurethane resin and preventing abrasive peeling during polishing.

[0027] This invention obtains a solidified polyurethane foam porous layer with excellent abrasive properties by changing the polyurethane resin and foam slurry formulations and controlling the temperature during drying. It solves the technical problems of poor bonding between nano-aqueous silica sol and polyurethane resin, and easy crystallization of silica sol in polishing fluid causing scratch defects. Attached Figure Description

[0028] Figure 1 A schematic diagram illustrating the process of preparing a polishing pad using an aqueous polyurethane emulsion.

[0029] Figure 2 The polishing pads prepared for Examples 1-3 and Comparative Examples 1-2 are used for 40 hours of continuous polishing rate curves of silicon carbide wafers. Detailed Implementation

[0030] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0031] Please refer to the accompanying drawings. Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the presence of other method steps, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not intended to limit the order of the method steps or to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0032] The first aspect of this invention provides an aqueous polyurethane emulsion, comprising the following raw material components by mass percentage:

[0033] 1,4-Butanediol 0.2%–2%; for example, 0.2%–0.4%, 0.4%–0.6%, 0.6%–0.8%, 0.8%–1%, 1%–1.2%, 1.2%–1.4%, 1.4%–1.6%, 1.6%–1.8%, or 1.8%–2%;

[0034] Polybutylene adipate diol 10%–20%; for example, 10%–12%, 12%–14%, 14%–15%, 15%–16%, 16%–17%, 17%–18% or 18%–20%;

[0035] 2,2-Dimethylolpropionic acid 0.5%–3%; for example, 0.5%–1%, 1%–1.5%, 1.5%–2%, 2%–2.5%, or 2.5%–3%;

[0036] Diphenylmethane-4,4'-diisocyanate 5% to 10%; for example, 5% to 6%, 6% to 7%, 7% to 8%, 8% to 9% or 9% to 10%;

[0037] Acetone 15%–25%; for example, 15%–16%, 16%–17%, 17%–18%, 18%–19%, 19%–20%, 20%–21%, 21%–22%, 22%–23%, 23%–24%, or 24%–25%.

[0038] Dimethylethanolamine 0.5%–3%; for example, 0.5%–1%, 1%–1.5%, 1.5%–2%, 2%–2.5%, or 2.5%–3%;

[0039] Water content: 50%–68.8%; for example, 50%–52%, 52%–54%, 54%–56%, 56%–58%, 58%–60%, 60%–62%, 62%–64%, 64%–66%, 66%–68%, or 68%–68.8%.

[0040] In the aqueous polyurethane emulsion of the present invention, the number average molecular weight of the polybutylene adipate diol is 1800–3000 g / mol. For example, it is 1800–2000 g / mol, 2000–2200 g / mol, 2200–2400 g / mol, 2400–2700 g / mol, or 2700–3000 g / mol.

[0041] A second aspect of the present invention provides a method for preparing the aqueous polyurethane emulsion as described above, comprising the following steps:

[0042] S1. Heat polybutylene adipate diol until it melts, and while maintaining the temperature, continue to add diphenylmethane-4,4'-diisocyanate to carry out the polymerization reaction. Then, add some acetone to dilute it, and then add 1,4-butanediol and 2,2-dimethylolpropionic acid to continue the reaction. Add the remaining acetone and cool down to obtain a polyurethane resin with terminal hydroxyl groups.

[0043] S2. Dimethylethanolamine is mixed with water to form an aqueous solution. The polyurethane resin with terminal hydroxyl groups obtained in step S1 is slowly added to the aqueous solution. After high-speed stirring and dispersion phase inversion, an aqueous polyurethane mixed emulsion is obtained. After removing the acetone solvent from the mixed emulsion, the aqueous polyurethane emulsion is obtained.

[0044] In step S1, heating to melt means heating to 75–85°C. For example, 70–80°C or 80–85°C.

[0045] The polymerization reaction in step S1 takes 1 to 3 hours. For example, it takes 1 to 1.5 hours, 1.5 to 2 hours, 2 to 2.5 hours, or 2.5 to 3 hours.

[0046] The reaction time for the continued reaction described in step S1 is 2 to 5 hours. For example, it is 2 to 3 hours, 3 to 4 hours, or 4 to 5 hours.

[0047] The cooling described in step S1 refers to reducing the temperature to 50-60°C. For example, 50-55°C or 55-60°C.

[0048] The portion of acetone mentioned in step S1 is 1 / 5 to 4 / 5 of the total acetone. For example, it is 1 / 5 to 2 / 5, 2 / 5 to 3 / 5, or 3 / 5 to 4 / 5.

[0049] The remaining acetone mentioned in step S1 is 1 / 5 to 4 / 5 of the total acetone. For example, it is 1 / 5 to 2 / 5, 2 / 5 to 3 / 5, or 3 / 5 to 4 / 5.

[0050] In step S1, the molar ratio of the total hydroxyl groups in polybutylene adipate diol, 2,2-dimethylolpropionic acid, and 1,4-butanediol to the isocyanate groups in diphenylmethane-4,4'-diisocyanate (OH:NCO) is 1:1 to 1.2:1. For example, it is 1:1 to 1.05:1, 1.05:1 to 1.1:1, 1.1:1 to 1.15:1, or 1.15:1 to 1.2:1.

[0051] The stirring rate of the high-speed stirring in step S3 is 1200-1400 r / min. For example, it is 1200-1250 r / min, 1250-1300 r / min, 1300-1350 r / min or 1350-1400 r / min.

[0052] The solid content of the aqueous polyurethane resin emulsion obtained in step S2 is 30-40%. For example, it is 30-32%, 32-34%, 34-35%, 35-36%, 36-38%, or 38-40%.

[0053] The removal of acetone solvent from the mixed emulsion in step S2 is carried out by vacuum distillation.

[0054] A third aspect of the present invention provides the use of the aqueous polyurethane emulsion as described above in a foam slurry for bonded abrasive damping cloth.

[0055] A fourth aspect of this invention provides a foam slurry for bonded abrasive damping cloth, comprising the following raw material components: a thermally activated curing agent, nano-aqueous silica sol, a foaming agent, a foam stabilizer, a crosslinking agent, a thickener, and an aqueous polyurethane emulsion as described above, wherein each component is expressed in the following mass percentages:

[0056] The waterborne polyurethane emulsion comprises 50% to 70%; for example, 50% to 52%, 52% to 54%, 54% to 56%, 56% to 58%, 58% to 60%, 60% to 62%, 62% to 64%, 64% to 66%, 66% to 68%, or 68% to 70%.

[0057] The nano-aqueous silica sol comprises 2% to 12%; for example, 2% to 4%, 4% to 6%, 6% to 8%, 8% to 10%, or 10% to 12%.

[0058] Foaming agent 1% to 5%; for example, 1% to 2%, 2% to 3%, 3% to 4%, or 4% to 5%;

[0059] Foam stabilizer 1% to 5%; for example, 1% to 2%, 2% to 3%, 3% to 4%, or 4% to 5%;

[0060] Crosslinking agent 14%–20%; for example 14%–15%, 15%–16%, 16%–17%, 17%–18%, 18%–19% or 19%–20%;

[0061] Thermoactivated curing agent: 2%–12%; for example, 2%–4%, 4%–6%, 6%–8%, 8%–10%, or 10%–12%;

[0062] Thickener 1-4%; for example 1-2%, 2-3% or 3-4%.

[0063] The nano-aqueous silica sol is a silica sol with a particle size of 10–300 nm. For example, particle sizes of 10–20 nm, 20–50 nm, 50–100 nm, 100–150 nm, 150–200 nm, 200–250 nm, or 250–300 nm are used. The solid content of the nano-aqueous silica sol is 30–45%. For example, 30–32%, 32–34%, 34–36%, 36–38%, 38–40%, 40–42%, 42–44%, or 44–45%. In a preferred embodiment of the present invention, the nano-aqueous silica sol is a silica sol with a solid content of 40% and a particle size of 100–150 nm (Quzhou Bolainarun Electronic Materials Co., Ltd.).

[0064] The foaming agent is selected from one or more of alkyl glycosides, caprylic / capric glycerides, and fatty acid amide surfactants. In a preferred embodiment of the present invention, the foaming agent is a fatty acid amide surfactant, specifically coconut oil fatty acid diethanolamide (6501) (Guangdong Yeshi Industrial Co., Ltd.).

[0065] The foam stabilizer is selected from one or more of alkyl aminopropyl betaine, polyvinyl alcohol, lauramide propylamine oxide, dodecyl dimethylamine oxide, and polyether-modified silicone surfactants. In a preferred embodiment of the present invention, the foam stabilizer is lauramide propylamine oxide (LAO-30) (Guangdong Yeshi Industrial Co., Ltd.).

[0066] The crosslinking agent is selected from one or more of polyaziridine, polycarbodiimide, polyoxazoline, and amide alcohol multifunctional polymer crosslinking agents. In a preferred embodiment of the present invention, the crosslinking agent is a polyoxazoline crosslinking agent (WS-700) (Nippon Shokubai).

[0067] The heat-activated curing agent is selected from one or more of blocked aromatic isocyanate curing agents and blocked aliphatic isocyanate curing agents. In a preferred embodiment of the present invention, the heat-activated curing agent is a blocked aliphatic isocyanate curing agent, Imprafix 2794 (Covestro).

[0068] The thickener is selected from one or more of associative thickeners and alkali-swellable thickeners. In a preferred embodiment of the present invention, the thickener is an associative thickener, specifically ACRYSOL RM-12W thickener (Rohm and Haas).

[0069] The fifth aspect of this invention provides a method for preparing the foam slurry for bonded abrasive damping cloth as described above, comprising: mixing an aqueous polyurethane emulsion, nano-aqueous silica sol, a foaming agent, a foam stabilizer, a crosslinking agent, a thermally activated curing agent, and a thickener in a certain proportion; after mixing evenly, foaming to 2.0–2.5 times, 2.0–2.1 times, 2.1–2.2 times, 2.2–2.3 times, 2.3–2.4 times, or 2.4–2.5 times the original volume, with a foam density of 400–500 g / L, 400–420 g / L, 420–440 g / L, 440–460 g / L, 460–480 g / L, or 480–500 g / L, to obtain the foam slurry for damping cloth.

[0070] The mixing process is achieved by stirring.

[0071] The foaming process is carried out using a mechanical foaming machine.

[0072] The sixth aspect of the present invention provides the use of the foam slurry for bonded abrasive damping cloth as described above in the preparation of polishing pads for fine polishing of silicon carbide wafers.

[0073] A seventh aspect of the present invention provides a method for preparing a polishing pad for fine polishing of silicon carbide wafers, comprising the following steps:

[0074] 1) The solidified abrasive damping cloth as described in any one of claims 5 to 6 is coated onto a plastic substrate by gravity flow. The plastic substrate with foam slurry is first slowly dried at 80 to 100°C, and then baked at 140 to 160°C to complete cross-linking and curing, thereby obtaining a cured polyurethane foam porous layer.

[0075] 2) Adhere the cured polyurethane foam porous layer to the plastic sheet, then grind and cut to obtain the finished polishing pad.

[0076] In the preparation method of the present invention, during the slow drying process of the plastic substrate with foam slurry at 80-100°C, the shape of the foam slurry is fixed and the nano-aqueous silica sol particles are uniformly dispersed and fixed in the polyurethane resin.

[0077] The polishing pad preparation process of this invention differs from the traditional solvent-based wet molding process. The pore structure formed by the foam slurry is uniformly spherical, which is completely different from the teardrop-shaped pores formed by conventional solvent-based wet processes. The spherical foam has better pore elasticity and support. In addition, nano-aqueous silica sol is added to the foam slurry, which forms chemical bonds with the polyurethane resin through the action of the curing agent during the curing process, and can be firmly fixed in the polyurethane resin.

[0078] During the drying process, the closed-type polyisocyanate heat-activated curing agent physically blended within the resin is unblocked, releasing a large number of isocyanate groups. These groups react with numerous hydroxyl groups on the polyurethane molecular chains and the surface of the nano-aqueous silica sol under the action of a catalyst, forming a cross-linked structure. This extensive cross-linking structure significantly enhances the oxidation resistance of the polyurethane resin itself, while also ensuring a stronger bond between the nano-aqueous silica sol dispersed in the foam slurry and the polyurethane resin. Furthermore, because the main structure of the waterborne polyurethane resin maintains a linear polymer structure and retains high flexibility, the added heat-activated curing agent does not affect the soft texture of the porous polyurethane layer. Simultaneously, the consolidated silica sol is less prone to agglomeration into large particles during polishing, thus improving the removal rate while avoiding defects such as scratches. Additionally, the cross-linking agent in the foam slurry can undergo a cross-linking reaction with the carboxyl groups on the waterborne polyurethane resin during drying and curing, enhancing the water resistance of the waterborne polyurethane resin and preventing softening and deformation of the polishing pad under waterborne polishing conditions. Furthermore, the dual crosslinking effect of the crosslinking agent and the heat-activated curing agent can also improve the strength of polyurethane, enhance the wear resistance and chemical resistance of the polishing pad, and maintain a long service life even when polished under oxidizing agents.

[0079] The eighth aspect of the present invention provides a polishing pad for fine polishing of silicon carbide wafers, which is prepared by the polishing pad preparation method for fine polishing of silicon carbide wafers as described above.

[0080] Example 1: Preparation of a polishing pad for fine polishing of silicon carbide wafers

[0081] 1) Synthesis of waterborne polyurethane emulsion:

[0082] formula:

[0083]

[0084] Preparation: 13.02 kg of polybutylene adipate diol (number average molecular weight 2000) was added to a reactor and heated to 80°C to melt it. 4.43 kg of MDI was added, and the polymerization reaction was maintained at 80°C for 1 hour. 3 kg of acetone was added for dilution. Then, 0.52 kg of 1,4-butanediol and 0.78 kg of 2,2-dimethylolpropionic acid were added to the reactor, and the reaction was maintained at 80°C for 4 hours. 10.02 kg of acetone was added for dilution to reduce viscosity. The temperature was lowered to 50°C to complete the reaction, yielding a product with terminal hydroxyl groups. A polyurethane resin was prepared. 45.57 kg of water and 0.41 kg of dimethylethanolamine were added to a mixing tank to form an aqueous solution. The aqueous solution was stirred at 1200 r / min, and the polyurethane resin was slowly poured into the aqueous solution and stirred to disperse, resulting in an aqueous polyurethane mixed emulsion. The solution was then distilled under reduced pressure at -0.1 MPa and 60 °C to form an azeotropic distillation, removing the acetone solvent and some water from the aqueous polyurethane mixed emulsion, yielding an aqueous polyurethane emulsion with a polyurethane solids content of 35%.

[0085] 2) Preparation of foam slurry for damping fabric:

[0086] formula:

[0087]

[0088] Preparation: 53.57 kg of waterborne polyurethane emulsion, 2.5 kg of nano-waterborne silica sol, 2.5 kg of Guangdong Yeshi 6501, 2.5 kg of Guangdong Yeshi LAO-30, 14 kg of Japanese Shokubai WS-700, 2.5 kg of Covestro Imprafix 2794, and 1.6 kg of thickener (ACRYSOL RM-12W) were stirred and mixed. After being stirred evenly, the mixture was foamed to 2.0 times its original volume using a mechanical foaming machine, that is, the foam density was 500 g / L, to obtain the foam slurry for damping cloth.

[0089] 3) Polishing Pad Preparation: Damping cloth is coated onto a PET plastic sheet with foam paste to a thickness of 1.5 mm. The plastic substrate with foam paste is placed in a segmented oven. The first segment oven is slowly dried at 90℃ for 1 hour to remove moisture from the foam paste and fix the foam shape. After drying, it is placed in the second segment oven at 150℃ for 30 minutes to complete the cross-linking reaction and cure, obtaining a cured polyurethane foam porous layer. The cured polyurethane foam porous layer is then bonded to the plastic sheet, and the polishing pad is sanded and cut to obtain the finished product. Sanding creates pores on the surface, and after adhesive backing and cutting, it is tested on a silicon carbide polishing machine.

[0090] Example 2: Preparation of a polishing pad for fine polishing of silicon carbide wafers

[0091] 1) Synthesis of waterborne polyurethane emulsion:

[0092] formula:

[0093]

[0094] Preparation: 13.28 kg of polybutylene adipate diol (number average molecular weight 2000) was added to a reactor and heated to 80°C to melt it. 4.40 kg of MDI was added, and the polymerization reaction was maintained at 80°C for 1 hour. 3 kg of acetone was added for dilution. Then, 0.46 kg of 1,4-butanediol and 0.85 kg of 2,2-dimethylolpropionic acid were added to the reactor, and the reaction was maintained at 80°C for 4 hours. 10.02 kg of acetone was added for dilution to reduce viscosity. The temperature was lowered to 50°C to complete the reaction, yielding a product with terminal hydroxyl groups. A polyurethane resin was prepared. 45.57 kg of water and 0.45 kg of dimethylethanolamine were added to a mixing tank to form an aqueous solution. The aqueous solution was stirred at 1200 r / min, and the polyurethane resin was slowly poured into the aqueous solution and stirred to disperse, resulting in an aqueous polyurethane mixed emulsion. The solution was then distilled under reduced pressure at -0.1 MPa and 60 °C to form an azeotropic distillation, removing the acetone solvent and some water from the aqueous polyurethane mixed emulsion, yielding an aqueous polyurethane emulsion with a polyurethane solids content of 35%.

[0095] 2) Preparation of foam slurry for damping fabric:

[0096] formula:

[0097]

[0098] Preparation: 54.24 kg of waterborne polyurethane emulsion, 5 kg of nano-waterborne silica sol, 2.5 kg of Guangdong Yeshi 6501, 2.5 kg of Guangdong Yeshi LAO-30, 14 kg of Japanese Shokubai WS-700, 5 kg of Covestro Imprafix 2794, and 1.7 kg of thickener (ACRYSOL RM-12W) were stirred and mixed. After being stirred evenly, the mixture was foamed to 2.1 times its original volume using a mechanical foaming machine, that is, the foam density was 476 g / L, to obtain the foam slurry for damping cloth.

[0099] 3) Polishing Pad Preparation: Damping cloth is coated onto a PET plastic sheet with foam paste to a thickness of 1.5 mm. The plastic substrate with foam paste is placed in a segmented oven. The first segment oven is slowly dried at 90℃ for 1 hour to remove moisture from the foam paste and fix the foam shape. After drying, it is placed in the second segment oven at 150℃ for 30 minutes to complete the cross-linking reaction and cure, obtaining a cured polyurethane foam porous layer. The cured polyurethane foam porous layer is then bonded to the plastic sheet, and the polishing pad is sanded and cut to obtain the finished product. Sanding creates pores on the surface, and after adhesive backing and cutting, it is tested on a silicon carbide polishing machine.

[0100] Example 3: Preparation of a polishing pad for fine polishing of silicon carbide wafers

[0101] 1) Synthesis of waterborne polyurethane emulsion:

[0102] formula:

[0103]

[0104] Preparation: 13.02 kg of polybutylene adipate diol (number average molecular weight 2000) was added to a reactor and heated to 80°C to melt it. 4.18 kg of MDI was added, and the polymerization reaction was maintained at 80°C for 1 hour. 3 kg of acetone was added for dilution. Then, 0.26 kg of 1,4-butanediol and 1.04 kg of 2,2-dimethylolpropionic acid were added to the reactor, and the reaction was maintained at 80°C for 4 hours. 10.02 kg of acetone was added for dilution to reduce viscosity. The temperature was lowered to 50°C to complete the reaction, yielding a product with terminal hydroxyl groups. A polyurethane resin was prepared. 45.57 kg of water and 0.55 kg of dimethylethanolamine were added to a mixing tank to form an aqueous solution. The aqueous solution was stirred at 1200 r / min, and the polyurethane resin was slowly poured into the aqueous solution and stirred to disperse, resulting in an aqueous polyurethane mixed emulsion. The solution was then distilled under reduced pressure at -0.1 MPa and 60 °C to form an azeotropic distillation, removing the acetone solvent and some water from the aqueous polyurethane mixed emulsion, yielding an aqueous polyurethane emulsion with a polyurethane solids content of 35%.

[0105] 2) Preparation of foam slurry for damping fabric:

[0106] formula:

[0107]

[0108]

[0109] Preparation: 52.87 kg of waterborne polyurethane emulsion, 10 kg of nano-waterborne silica sol, 2.5 kg of Guangdong Yeshi 6501, 2.5 kg of Guangdong Yeshi LAO-30, 14 kg of Japanese Shokubai WS-700, 10 kg of Covestro Imprafix 2794, and 1.9 kg of thickener (ACRYSOL RM-12W) were stirred and mixed. After being stirred evenly, the mixture was foamed using a mechanical foaming machine to 2.23 times its original volume, i.e., the foam density was 448 g / L, to obtain the foam slurry for damping cloth.

[0110] 3) Polishing Pad Preparation: Damping cloth is coated onto a PET plastic sheet with foam paste to a thickness of 1.5 mm. The plastic substrate with foam paste is placed in a segmented oven. The first segment oven is slowly dried at 90℃ for 1 hour to remove moisture from the foam paste and fix the foam shape. After drying, it is placed in the second segment oven at 150℃ for 30 minutes to complete the cross-linking reaction and cure, obtaining a cured polyurethane foam porous layer. The cured polyurethane foam porous layer is then bonded to the plastic sheet, and the polishing pad is sanded and cut to obtain the finished product. Sanding creates pores on the surface, and after adhesive backing and cutting, it is tested on a silicon carbide polishing machine.

[0111] Comparative Example 1: Preparation of a polishing pad for fine polishing of silicon carbide wafers

[0112] 1) Synthesis of waterborne polyurethane emulsion:

[0113] formula:

[0114]

[0115] Preparation: 13.02 kg of polybutylene adipate diol (number average molecular weight 2000) was added to a reactor and heated to 80°C to melt it. 4.43 kg of MDI was added, and the polymerization reaction was maintained at 80°C for 1 hour. 3 kg of acetone was added for dilution. Then, 0.52 kg of 1,4-butanediol and 0.78 kg of 2,2-dimethylolpropionic acid were added to the reactor, and the reaction was maintained at 80°C for 4 hours. 10.02 kg of acetone was added for dilution to reduce viscosity. The temperature was lowered to 50°C to complete the reaction, yielding a product with terminal hydroxyl groups. A polyurethane resin was prepared. 45.57 kg of water and 0.41 kg of dimethylethanolamine were added to a mixing tank to form an aqueous solution. The aqueous solution was stirred at 1200 r / min, and the polyurethane resin was slowly poured into the aqueous solution and stirred to disperse, resulting in an aqueous polyurethane mixed emulsion. The solution was then distilled under reduced pressure at -0.1 MPa and 60 °C to form an azeotropic distillation, removing the acetone solvent and some water from the aqueous polyurethane mixed emulsion, yielding an aqueous polyurethane emulsion with a polyurethane solids content of 35%.

[0116] 2) Preparation of foam slurry for damping fabric:

[0117] formula:

[0118]

[0119] Preparation: 53.57 kg of waterborne polyurethane emulsion, 2.5 kg of Guangdong Yeshi 6501, 2.5 kg of Guangdong Yeshi LAO-30, 14 kg of Japanese Shokubai WS-700, 2.5 kg of Covestro Imprafix 2794, and 1.6 kg of thickener (ACRYSOL RM-12W) were stirred and mixed. After being stirred evenly, the mixture was foamed using a mechanical foaming machine to 2.0 times its original volume, i.e., the foam density was 500 g / L, to obtain the foam slurry for damping cloth.

[0120] 3) Polishing Pad Preparation: Damping cloth is coated onto a PET plastic sheet with foam paste to a thickness of 1.5 mm. The plastic substrate with foam paste is placed in a segmented oven. The first segment oven is slowly dried at 90℃ for 1 hour to remove moisture from the foam paste and fix the foam shape. After drying, it is placed in the second segment oven at 150℃ for 30 minutes to complete the cross-linking reaction and cure, obtaining a cured polyurethane foam porous layer. The cured polyurethane foam porous layer is then bonded to the plastic sheet, and the polishing pad is sanded and cut to obtain the finished product. Sanding creates pores on the surface, and after adhesive backing and cutting, it is tested on a silicon carbide polishing machine.

[0121] Comparative Example 2: Preparation of a polishing pad for fine polishing of silicon carbide wafers

[0122] 1) Synthesis of waterborne polyurethane emulsion:

[0123] formula:

[0124]

[0125] Preparation: 13.02 kg of polybutylene adipate diol (number average molecular weight 2000) was added to a reactor and heated to 80°C to melt it. 4.43 kg of MDI was added, and the polymerization reaction was maintained at 80°C for 1 hour. 3 kg of acetone was added for dilution. Then, 0.52 kg of 1,4-butanediol and 0.78 kg of 2,2-dimethylolpropionic acid were added to the reactor, and the reaction was maintained at 80°C for 4 hours. 10.02 kg of acetone was added for dilution to reduce viscosity. The temperature was lowered to 50°C to complete the reaction, yielding a product with terminal hydroxyl groups. A polyurethane resin was prepared. 45.57 kg of water and 0.41 kg of dimethylethanolamine were added to a mixing tank to form an aqueous solution. The aqueous solution was stirred at 1200 r / min, and the polyurethane resin was slowly poured into the aqueous solution and stirred to disperse, resulting in an aqueous polyurethane mixed emulsion. The solution was then distilled under reduced pressure at -0.1 MPa and 60 °C to form an azeotropic distillation, removing the acetone solvent and some water from the aqueous polyurethane mixed emulsion, yielding an aqueous polyurethane emulsion with a polyurethane solids content of 35%.

[0126] 2) Preparation of foam slurry for damping fabric:

[0127] formula:

[0128]

[0129] Preparation: 53.57 kg of waterborne polyurethane emulsion, 2.5 kg of nano-waterborne silica sol, 2.5 kg of Guangdong Yeshi 6501, 2.5 kg of Guangdong Yeshi LAO-30, 14 kg of Japanese Shokubai WS-700, and 1.6 kg of thickener (ACRYSOL RM-12W) were stirred and mixed. After stirring evenly, the mixture was foamed to 2.0 times its original volume using a mechanical foaming machine, i.e., the foam density was 500 g / L, to obtain the foam slurry for damping cloth.

[0130] 3) Polishing Pad Preparation: Damping cloth is coated onto a PET plastic sheet with foam paste to a thickness of 1.5 mm. The plastic substrate with foam paste is placed in a segmented oven. The first segment oven is slowly dried at 90℃ for 1 hour to remove moisture from the foam paste and fix the foam shape. After drying, it is placed in the second segment oven at 150℃ for 30 minutes to complete the cross-linking reaction and cure, obtaining a cured polyurethane foam porous layer. The cured polyurethane foam porous layer is then bonded to the plastic sheet, and the polishing pad is sanded and cut to obtain the finished product. Sanding creates pores on the surface, and after adhesive backing and cutting, it is tested on a silicon carbide polishing machine.

[0131] Performance testing:

[0132] Polishing removal rate test:

[0133] Examples 1-3 and Comparative Examples 1-2 used a Mingzheng 36B polishing machine to continuously polish 6-inch conductive silicon carbide wafers for 40 hours. The polishing slurry flow rate was 100 ml / min, and the slurry was a 2% hydrogen peroxide aqueous solution. Comparative Example 1 used Brunner Run COPOL 130 polishing slurry, with hydrogen peroxide added before polishing to achieve a 2% hydrogen peroxide content. The polishing slurry flow rate was also 100 ml / min. Polishing machine parameters were: upper plate rotation speed 45 r / min, lower plate rotation speed 40 r / min, pressure 15 kPa, polishing silicon surface. The thickness difference of the silicon carbide wafer before and after polishing was measured every 2 hours to calculate the polishing rate. A total of 40 hours of polishing was performed, and the change in removal rate was observed. The results are as follows: Figure 2 As shown.

[0134] Depend on Figure 2 It can be seen that the polishing rate of Comparative Example 1 is significantly lower than that of the other examples. This is because Comparative Example 1 does not have a solidified abrasive; the silica sol exists in the COPOL 130 polishing slurry in the form of a dispersion. During the polishing process, it is carried out by three-body friction, with the abrasive exhibiting rolling and sliding friction to remove the surface material of silicon carbide. In contrast, the polishing rates of Examples 1-3 are relatively higher and more stable. This is because the nano-silica solidified in the polyurethane resin exhibits two-body friction during polishing, with sliding friction being the main mode, thus significantly increasing the amount of material removed per unit time. Comparative Example 2 shows a significant rate decrease compared to Example 1. This is because Comparative Example 2 does not use a thermally activated curing agent, and the silica sol particles in the polishing pad do not form strong chemical bonds with the polyurethane resin. The silica sol particles are very easy to detach from the resin, resulting in a gradual decrease in the polishing rate. In Examples 1-3, the use of a thermally activated curing agent enables the silica sol particles to form a strong bond with the polyurethane resin, preventing the silica sol particles from easily detaching from the resin. Furthermore, due to the numerous cross-linked structures within the cured waterborne polyurethane resin, the oxidizing agent and the frictional mechanical forces during polishing do not easily cause a decrease in resin strength, thus maintaining a stable polishing rate for a longer period. The spherical cell shape also results in more uniform physical properties during polishing, ensuring that the porous polyurethane foam layer maintains good elasticity.

[0135] In summary, the waterborne polyurethane emulsion of this invention has a terminal hydroxyl structure, which can chemically bond with nano-waterborne silica sol abrasives through a thermally activated curing agent, thus solidifying the abrasives within the polyurethane resin. The main structure of the polyurethane resin maintains a linear polymer structure, exhibiting high flexibility. The carboxyl groups in the chain segments, which act as emulsifiers, can form a network cross-linked structure through a cross-linking agent, enhancing the strength, water resistance, and oxidation resistance of the polyurethane resin. The added cross-linking agent and thermally activated curing agent do not affect the overall soft texture of the prepared polishing pad, and scratches and other defects can still be avoided during polishing. The polishing pad prepared by this invention can maintain a stable polishing rate for a long time during silicon carbide polishing. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0136] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An aqueous polyurethane emulsion, characterized by, comprise the following raw material components by mass percentage:

2. A process for preparing the aqueous polyurethane emulsion according to claim 1, characterized in that, comprise the following steps: S1, heat polybutylene adipate glycol to melt, keep the temperature, continue to add diphenylmethane-4, 4'-diisocyanate for polymerization reaction, then add part of acetone dilution, then add 1, 4-butanediol and 2, 2-dimethylol propionic acid, continue to react, add the rest of acetone, and cool down to obtain polyurethane resin with terminal hydroxyl group; S2, mix dimethyl ethanolamine with water to form an aqueous solution, slowly add the polyurethane resin with terminal hydroxyl group obtained in step S1 into the aqueous solution, disperse the phase under high speed stirring, and then obtain water-based polyurethane mixed emulsion after phase inversion, and remove acetone solvent in the mixed emulsion to obtain water-based polyurethane emulsion.

3. The method for preparing an aqueous polyurethane emulsion according to claim 2, characterized by, In step S1, the heating to melt is heating to 75-85℃; And / or, the reaction time for the continuous reaction in step S1 is 2-5h; And / or, the part of acetone in step S1 is 1 / 5-4 / 5 of the total amount of acetone; And / or, the rest of acetone in step S1 is 1 / 5-4 / 5 of the total amount of acetone; And / or, the cooling in step S1 is to reduce the temperature to 50-60℃; and / or, the number average molecular weight of the polybutylene adipate glycol in step S1 is 1800-3000g / mol; And / or, the molar ratio of total hydroxyl groups in polybutylene adipate glycol, 2, 2-dimethylol propionic acid and 1, 4-butanediol to isocyanate groups in diphenylmethane-4, 4'-diisocyanate in step S1 is OH:NCO=1:1-1.2:1; And / or, the stirring rate of high speed stirring in step S2 is 1200-1400r / min; And / or, the solid content of the water-based polyurethane resin emulsion obtained in step S2 is 30-40%.

4. Use of the water-based polyurethane emulsion of claim 1 in a foam slurry for a consolidated abrasive damping cloth.

5. A consolidated abrasive damping cloth use foam slurry, characterized in that, comprise the following raw material components: heat-activated curing agent, nano water-based silica sol, foaming agent, foam stabilizer, crosslinking agent, thickening agent, and the water-based polyurethane emulsion of claim 1, each component is as follows by mass percentage:

6. The consolidated abrasive damping cloth foam slurry of claim 5, wherein, The nano water-based silica sol is silica sol with a particle size of 10-300nm; And / or, the foaming agent is selected from one or more of alkyl glycoside, caprylic acid / capric acid glyceride, fatty acid amide surfactant; And / or, the foam stabilizer is selected from one or more of alkyl acid amine propyl betaine, polyvinyl alcohol, lauryl amido propyl amine oxide, dodecyl dimethyl amine oxide, polyether modified silicone surfactant; And / or, the crosslinking agent is selected from one or more of polyaziridine, polycarbodiimide, polyoxazoline, amido alcohol multifunctional polymer crosslinking agent; And / or, the heat-activated curing agent is selected from one or more of blocked aromatic isocyanate curing agent, blocked aliphatic isocyanate curing agent; And / or, the thickening agent is selected from one or more of associative thickening agent, alkali-swellable thickening agent.

7. A method of making a foam slurry for a fixed abrasive damping cloth according to any one of claims 5-6, characterized in that, comprise: The water-based polyurethane emulsion, nano water-based silica sol, foaming agent, foam stabilizer, crosslinking agent, heat-activated curing agent and thickening agent are mixed in proportion, and after uniform mixing, the mixture is foamed to 2.0-2.5 times of the original volume, the foam density is 400-500 g / L, and the foam slurry for damping cloth is obtained.

8. Use of the foam slurry for consolidated abrasive damping cloth according to any one of claims 5-6 in the preparation of a polishing pad for fine polishing of silicon carbide wafers.

9. A method of making a polishing pad for the fine polishing of silicon carbide wafers, characterized by, The method comprises the following steps: 1) The foam slurry for consolidated abrasive damping cloth according to any one of claims 5-6 is coated on a plastic substrate by gravity flow, the plastic substrate with the foam slurry is slowly dried at 80-100 DEG C, and then baked at 140-160 DEG C after drying, to complete crosslinking and curing, and obtain a cured polyurethane foam porous layer; 2) The cured polyurethane foam porous layer is pasted to the plastic sheet, and the polishing pad product is obtained by polishing and cutting.

10. A polishing pad for the fine polishing of silicon carbide wafers, characterized by The polishing pad product is obtained by using the preparation method according to claim 9.

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