Catalytic polishing pad for silicon carbide substrate fine polishing and preparation method

Abstract

The application provides a polishing pad with catalysis for polishing silicon carbide substrates and a preparation method, the polishing pad is prepared by coating a damping cloth containing a chelating agent on a plastic substrate with a coating slurry and solidifying in a coagulation bath, a polyurethane porous layer obtained after pure water cleaning is immersed in a ferrous sulfate solution to generate chelation, and a polishing pad with stable catalyst effect is obtained; when the polishing pad prepared by the application is used for polishing, the chelating structure in the polishing pad is opened in a slightly acidic polishing liquid environment, trace amounts of divalent iron ions are released at the polishing interface, a Fenton reaction occurs between the divalent iron ions and hydrogen peroxide in the polishing liquid, hydroxyl radicals are generated at the polishing interface, the polishing interface can uniformly provide catalysis when polishing, and the polishing rate is effectively and uniformly improved.

Description

Technical Field

[0001] This invention relates to the field of polishing pad technology, and in particular to a catalytic polishing pad for fine polishing of silicon carbide substrates and its preparation method. Background Technology

[0002] The high C-Si bond energy in SiC crystals and its unique lattice arrangement endow SiC materials with high hardness and strong chemical stability. Therefore, the silicon carbide removal rate on wafer surfaces is very low during traditional polishing processes. Exploring auxiliary enhancement methods based on chemical mechanical polishing (CMP) is of great significance for realizing the industrial application of SiC substrate materials and improving production efficiency. Existing auxiliary enhancement methods mainly include plasma-assisted, catalyst-assisted, ultraviolet-assisted, and electric field-assisted methods. Utilizing auxiliary enhancement methods to simultaneously soften the silicon carbide surface through surface treatment and perform triboelectric removal can significantly improve the polishing rate.

[0003] In chemical mechanical polishing (CMP), chemical etching and mechanical friction occur simultaneously. Chemical etching originates from the polishing slurry, where oxidants and catalysts react chemically with the silicon carbide wafer surface to produce a thin oxide film. Mechanical friction arises from the abrasive particles, mechanical pressure, rotational speed, and polishing pad in the polishing slurry. The abrasive particles and polishing pad remove this oxide film through mechanical action. Prolonged polishing processes gradually reduce the surface roughness and improve the planarization of the silicon carbide wafer.

[0004] One of the auxiliary enhancement methods is a chemical mechanical polishing process based on the Fenton reaction. The Fenton reaction utilizes ferrous ions (Fe²⁺) to enhance the performance of the polished metal. 2+ The reaction of Fenton reaction with hydrogen peroxide (H2O2) generates highly oxidizing hydroxyl radicals (·OH). These hydroxyl radicals (·OH) possess a high redox potential and are extremely powerful oxidizing agents, effectively increasing the chemical etching rate of silicon carbide surfaces. Upon reaction with the silicon carbide wafer surface, a relatively soft and weakly bonded oxide layer is formed, which can be easily removed under mechanical friction. Other literature introduces an electric field into Fenton reaction-based chemical mechanical polishing to accelerate the conversion of ferric ions to ferrous ions at the polishing interface, thereby increasing the content of hydroxyl radicals and significantly enhancing the oxidizing activity of the polishing solution. Compared to voltage-free conditions, the polishing rate is significantly increased under applied voltage in Fenton reaction-based chemical mechanical polishing.

[0005] Currently, the industry standard for fine polishing of silicon carbide wafers typically uses a silica sol polishing slurry with a diameter of around 100nm, combined with a damping cloth polishing pad, and employs a single-sided polishing machine to polish the silicon surface of the silicon carbide wafer. Common fine polishing slurries are usually two-component (AB), requiring the addition of hydrogen peroxide before polishing, where the hydrogen peroxide acts as an oxidizing agent. This process can achieve a surface roughness of less than 0.1nm on silicon carbide substrates, but the oxidation effect of using hydrogen peroxide alone is weak, resulting in a low polishing rate. Furthermore, the Fenton reaction principle is not currently utilized in the industry for polishing slurries of silicon carbide wafers, primarily due to the presence of ferrous ions (Fe²⁺) in the solution. 2+ The ferrous oxide solution has a strong decomposition effect on hydrogen peroxide. While this helps generate highly oxidizing hydroxyl radicals (·OH), thus increasing the polishing rate to some extent, it also exacerbates the loss of hydrogen peroxide. Furthermore, the large amount of free ferrous ions in the polishing solution easily reacts with silica sol to form precipitation. Simultaneously, because the ferrous ion-catalyzed decomposition of hydrogen peroxide occurs throughout the polishing solution, the actual number of hydroxyl radicals reacting at the polishing interface is relatively small and uneven.

[0006] In Fenton reaction-based chemical mechanical polishing, the inability to precisely control hydrogen peroxide consumption and hydroxyl radical generation makes it extremely difficult to maintain the stability of the polishing rate during actual operation. Furthermore, the highly unstable state of ferrous ions, which are easily oxidized by other substances, also affects the catalytic effect. Therefore, to maintain the reaction's continuity during polishing, it is necessary to continuously add ferrous salts or use ferric or zero-valent iron ions instead of ferrous ions, but this makes catalytic stability even more difficult to control. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a catalytic polishing pad for fine polishing of silicon carbide substrates and a preparation method thereof, which achieves uniform release of ferrous ions only during polishing and specifically generates highly oxidizing hydroxyl radicals at the interface between the wafer and the polishing pad, thereby providing a long-lasting and stable catalytic effect.

[0008] To achieve the above and other related objectives, the present invention provides a solvent-based polyurethane resin comprising the following raw material components by weight percentage:

[0009]

[0010] The present invention also provides a method for preparing the solvent-based polyurethane resin as described above, comprising the following steps:

[0011] 1,4-Butanediol, polybutylene adipate diol, and 1 / 7 to 1 / 5 of N,N-dimethylformamide were mixed and stirred, and the mixture was heated to 75 to 85°C. Diphenylmethane-4,4'-diisocyanate and 1 / 7 to 1 / 5 of N,N-dimethylformamide were added, and the polymerization reaction was carried out at 75 to 85°C. As the viscosity increased, 5 / 8 to 1 / 2 of N,N-dimethylformamide was added to reduce the viscosity. After reacting for 3 to 7 hours, the mixture was cooled for the first time to obtain a mixed solution. N-hydroxyethyl ethylenediamine triacetic acid was dissolved in the remaining N,N-dimethylformamide and then slowly added to the mixture. The reaction was continued for 2 to 5 hours, and then cooled for the second time to end the reaction, resulting in a solvent-based polyurethane resin containing a chelating agent.

[0012] The present invention also provides the use of the solvent-based polyurethane resin as described above in a coating slurry for damping fabric.

[0013] The present invention also provides a coating slurry for damping fabric, comprising N,N-dimethylformamide and the solvent-based polyurethane resin as described in claim 1, wherein the components are expressed in the following mass percentages:

[0014] Solvent-based polyurethane resin 60%–70%;

[0015] N,N-dimethylformamide 30%–40%.

[0016] The present invention also provides a method for preparing the coating slurry for damping fabric as described above, comprising: stirring and mixing N,N-dimethylformamide with solvent-based polyurethane resin to obtain the coating slurry for damping fabric.

[0017] The present invention also provides the use of the damping cloth coating slurry as described above in the preparation of polishing pads for fine polishing of silicon carbide wafers.

[0018] This invention also provides a method for preparing a polishing pad for fine polishing of silicon carbide wafers, comprising the following steps:

[0019] S1. The damping cloth described above is coated onto the plastic substrate by gravity using a coating slurry. The plastic substrate with the coating slurry is then immersed in a coagulation bath prepared with N,N-dimethylformamide and pure water to solidify, thereby obtaining a polyurethane porous layer.

[0020] S2. Peel the obtained polyurethane porous layer off the plastic substrate and wash it with pure water.

[0021] S3. Immerse the cleaned polyurethane porous layer in a ferrous sulfate aqueous solution to achieve chelation and obtain a polyurethane porous layer with catalytic effect. Dry and roll up the layer.

[0022] S4. The dried polyurethane porous layer with catalytic effect is pasted together with a plastic sheet, and then polished and cut to obtain the finished polishing pad. The present invention also provides a polishing pad for fine polishing of silicon carbide wafers, which is prepared by the preparation method described above.

[0023] The present invention also provides a polishing pad for fine polishing of silicon carbide wafers, which is prepared by the preparation method described above.

[0024] As described above, the catalytic polishing pad and its preparation method for fine polishing of silicon carbide substrates of the present invention have the following beneficial effects:

[0025] This invention synthesizes a solvent-based polyurethane resin with a high molecular weight and containing a chelating agent using 1,4-butanediol, polybutylene adipate diol, N-hydroxyethyl ethylenediamine triacetic acid, diphenylmethane-4,4'-diisocyanate, and N,N-dimethylformamide. A chelating agent with active groups is grafted onto the molecular chain of the solvent-based polyurethane resin during the synthesis reaction. The polyurethane resin grafted with the chelating agent is then used to create a damping cloth polishing pad complexed with ferrous ions. During polishing, the chelating effect of the complex is weakened in the oxidant and slightly acidic polishing solution, and the ferrous ions exhibit catalytic activity, catalyzing the oxidation of hydrogen peroxide at the polishing interface. This generates more hydroxyl radicals at the polishing interface, thereby enhancing the chemical corrosion effect on the silicon carbide wafer surface.

[0026] The solvent-based polyurethane resin containing a chelating agent prepared in this invention is formulated with N,N-dimethylformamide to create a coating slurry for damping fabric. During the preparation of the polishing pad, the chelating agent forms a complex with ferrous ions, allowing the ferrous ions to exist stably within the polishing pad. During polishing, the slightly acidic polishing solution environment opens the chelated structure, releasing trace amounts of ferrous ions at the polishing interface. These ferrous ions then undergo a Fenton reaction with hydrogen peroxide in the polishing solution, generating hydroxyl radicals at the polishing interface. These radicals can specifically and efficiently oxidize the silicon carbide surface, increasing the polishing rate. Simultaneously, the trace amounts and slow release of ferrous ions prevent rapid and violent decomposition of hydrogen peroxide, maintaining a stable and efficient oxidation effect over a longer polishing time, thereby improving and stabilizing the polishing rate. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the preparation process of the catalytic polishing pads in Examples 1-3.

[0028] Figure 2 The polishing rate curves of the polishing pads prepared for Examples 1-3 and Comparative Example 1 for 40 hours of continuous polishing of silicon carbide wafers are shown. Detailed Implementation

[0029] 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.

[0030] 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.

[0031] The first aspect of this invention provides a solvent-based polyurethane resin, comprising the following raw material components by weight percentage:

[0032] 1,4-Butanediol 0.5%–3%; for example, 0.5%–1%, 1%–1.5%, 1.5%–2%, 2%–2.5%, or 2.5%–3%;

[0033] Polybutylene adipate diol 20%–30%; for example, 20%–22%, 22%–24%, 24%–26%, 26%–28%, or 28%–30%;

[0034] N-hydroxyethyl ethylenediamine triacetic acid 0.5%–5%; for example, 0.5%–1%, 1%–1.5%, 1.5%–2%, 2%–2.5%, 2.5%–3%, 3%–3.5%, 3.5%–4%, 4%–4.5%, or 4.5%–5%;

[0035] Diphenylmethane-4,4'-diisocyanate 5% to 15%; for example, 5% to 7%, 7% to 9%, 9% to 11%, 11% to 13% or 13% to 15%;

[0036] N,N-Dimethylformamide 60%–74%. For example, 60%–62%, 62%–64%, 64%–66%, 66%–68%, 68%–70%, 70%–72%, or 72%–74%.

[0037] The polybutylene adipate diol has a number-average molecular weight of 1800–3000 g / mol. For example, it can be 1800–2100 g / mol, 2100–2400 g / mol, 2400–2700 g / mol, or 2700–3000 g / mol. In a preferred embodiment of the invention, the polybutylene adipate diol has a number-average molecular weight of 2000 g / mol.

[0038] A second aspect of the present invention provides a method for preparing the solvent-based polyurethane resin as described above, comprising the following steps:

[0039] 1,4-Butanediol, polybutylene adipate diol, and 1 / 7 to 1 / 5 of N,N-dimethylformamide were mixed and stirred, and the mixture was heated to 75 to 85°C. Diphenylmethane-4,4'-diisocyanate and 1 / 7 to 1 / 5 of N,N-dimethylformamide were added, and the polymerization reaction was carried out at 75 to 85°C. As the viscosity increased, 5 / 8 to 1 / 2 of N,N-dimethylformamide was added to reduce the viscosity. After reacting for 3 to 7 hours, the mixture was cooled for the first time to obtain a mixed solution. N-hydroxyethyl ethylenediamine triacetic acid was dissolved in the remaining N,N-dimethylformamide and then slowly added to the mixture. The reaction was continued for 2 to 5 hours, and then cooled for the second time to end the reaction, resulting in a solvent-based polyurethane resin containing a chelating agent.

[0040] In the preparation method of the present invention, "1 / 7 to 1 / 5 of N,N-dimethylformamide" refers to 1 / 7 to 1 / 5 of the total amount of N,N-dimethylformamide; "5 / 8 to 1 / 2 of N,N-dimethylformamide" refers to 5 / 8 to 1 / 2 of the total amount of N,N-dimethylformamide.

[0041] The first cooling process refers to a temperature drop to 50–60°C. For example, it could be 50–52°C, 52–54°C, 54–56°C, 56–58°C, or 58–60°C.

[0042] The second cooling process involves lowering the temperature to 30–40°C. For example, it could be 30–32°C, 32–34°C, 34–36°C, 36–38°C, or 38–40°C.

[0043] The slow addition is referred to as drip addition.

[0044] The molar ratio of the isocyanate group in the diphenylmethane-4,4'-diisocyanate to the total hydroxyl groups in polybutylene adipate diol and 1,4-butanediol, NCO:OH, is 1:1 to 1.3:1. For example, it is 1:1 to 1.1:1, 1.1:1 to 1.2:1, or 1.2:1 to 1.3:1.

[0045] A third aspect of the present invention provides the use of the solvent-based polyurethane resin as described above in a coating slurry for damping fabrics.

[0046] A fourth aspect of the present invention provides a coating slurry for damping fabric, comprising N,N-dimethylformamide and the solvent-based polyurethane resin as described in claim 1, wherein the components are expressed in the following mass percentages:

[0047] Solvent-based polyurethane resin 60%–70%; for example, 60%–62%, 62%–64%, 64%–66%, 66%–68%, or 68%–70%;

[0048] N,N-dimethylformamide 30%–40%; for example, 30%–32%, 32%–34%, 34%–36%, 36%–38%, or 38%–40%.

[0049] The fifth aspect of the present invention provides a method for preparing the coating slurry for damping fabric as described above, comprising: stirring and mixing N,N-dimethylformamide with solvent-based polyurethane resin to obtain the coating slurry for damping fabric.

[0050] The sixth aspect of the present invention provides the use of the damping cloth coating slurry as described above in the preparation of a polishing pad for fine polishing of silicon carbide wafers.

[0051] 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:

[0052] S1. The damping cloth coating slurry as described in claim 5 is applied to the plastic substrate by gravity, and the plastic substrate with the coating slurry is immersed in a coagulation bath prepared with N,N-dimethylformamide and pure water to solidify, thereby obtaining a polyurethane porous layer.

[0053] S2. Peel the obtained polyurethane porous layer off the plastic substrate and wash it with pure water; remove the residual DMF in the product by washing to fix the shape of the foam cells.

[0054] S3. Immerse the cleaned polyurethane porous layer in a ferrous sulfate aqueous solution to achieve chelation and obtain a polyurethane porous layer with catalytic effect. Dry and roll up the layer.

[0055] S4. Adhere the dried polyurethane porous layer with catalytic effect to the plastic sheet, and then grind and cut it to obtain the finished polishing pad.

[0056] In both steps S1 and S2, the pure water used has a conductivity ≤10 μs / cm. For example, it can be ≤2 μs / cm, 2–4 μs / cm, 4–6 μs / cm, 6–8 μs / cm, or 8–10 μs / cm. In this invention, pure water with a conductivity of ≤10 μs / cm must be used during the coagulation and cleaning processes to prevent impurity metal ions in the water from reacting with the chelating agent in the polyurethane resin.

[0057] In step S1, the mass ratio of N,N-dimethylformamide to pure water in the coagulation bath is 10–30:70–90. For example, it can be 10–15:70–90, 15–20:70–90, 20–25:70–90, 25–30:70–90, 10–30:70–75, 10–30:75–80, 10–30:80–85, or 10–30:85–90.

[0058] The mass concentration of the ferrous sulfate aqueous solution in step S3 is 0.1% to 10%. For example, it is 0.1% to 0.5%, 0.5% to 1%, 1% to 2%, 2% to 4%, 4% to 6%, 6% to 8%, or 8% to 10%.

[0059] In the preparation method of the polishing pad of this invention, after the polyurethane porous layer is thoroughly cleaned with pure water, it needs to be immersed in a mixed solution of ferrous sulfate and pure water. This allows the chelating agent in the polyurethane resin to chelate with the ferrous ions to form a complex. The stable properties of the complex protect the ferrous ions and prevent their oxidation. After drying, the ferrous ions are chelated in the polyurethane resin. Then, through lamination, sanding, and adhesive backing processing, a damping cloth polishing pad with catalytic activity is obtained.

[0060] Existing technologies that simply blend chelating agents into solvent-based polyurethane resins often lead to the chelating agent detaching from the resin. The resulting metal ion complexes are prone to detachment during production, reducing their solidification within the resin and hindering their catalytic effect. Furthermore, during polishing, the complexes are subjected to chemical corrosion and mechanical friction, gradually detaching from the resin and causing a decrease in polishing speed. This invention designs and synthesizes a solvent-based polyurethane resin with grafted chelating agents. Damping cloth is produced using a traditional wet process. After a final pure water rinsing step, the damping cloth is soaked in a ferrous sulfate aqueous solution. The chelating agent in the polyurethane resin forms stable complexes with metal ions, uniformly introducing ferrous ions (metal ions react with chelating agents containing two or more coordinating atoms to form cyclic complexes. These complexes protect the metal ions from easy oxidation or reduction, exhibiting high stability) into the polishing pad, ensuring that the ferrous ions are not easily oxidized. Finally, after drying, polishing, and adhesive backing processes, a polishing pad containing ferrous ion complexes is obtained. Then, during polishing, the chelating effect of the complex in the polishing pad is weakened under the influence of oxidant and slightly acidic polishing solution. Ferrous ions exhibit catalytic activity, catalyzing the oxidation of hydrogen peroxide at the polishing interface and generating more hydroxyl radicals at the polishing interface, thereby enhancing the chemical corrosion effect on the silicon carbide wafer surface.

[0061] 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.

[0062] Example 1: Preparation of a polishing pad for fine polishing of silicon carbide wafers

[0063] 1) Synthesis of solvent-based polyurethane resin:

[0064] formula:

[0065]

[0066] Preparation: 0.65 kg of 1,4-butanediol, 8.50 kg of polybutylene adipate diol (number average molecular weight 2000) and 5 kg of DMF were added to a reactor. The temperature was raised to 80°C, and 3.17 kg of MDI and 5 kg of DMF were added to carry out the polymerization reaction. The reaction temperature was controlled at 75-85°C. As the viscosity increased, 15.84 kg of DMF was added. After reacting for 5 hours, the temperature of the material in the reactor was lowered to 50°C, and the viscosity was measured to be 56 Pa·s. 0.29 kg of N-hydroxyethyl ethylenediamine triacetic acid was dissolved in 3 kg of N,N-dimethylformamide and then added dropwise to the reactor. After reacting for 2-5 hours, the temperature was lowered to 30-40°C to complete the reaction, and a solvent-based polyurethane resin containing a chelating agent was obtained.

[0067] 2) Preparation of coating slurry for damping fabric:

[0068] formula:

[0069] Solvent-based polyurethane resin 65.00 kg;

[0070] N,N-Dimethylformamide (DMF) 35.00kg.

[0071] Preparation: 65 kg of solvent-based polyurethane resin and 35 kg of DMF were added to a mixing tank. The mixture was stirred evenly under nitrogen protection in a sealed mixing tank and then vacuumed to remove bubbles, thus obtaining the coating slurry.

[0072] 3) Polishing Pad Preparation: Damping cloth is coated onto a PET plastic sheet with a coating slurry to a thickness of 1.8 mm. The plastic substrate with the coating slurry is then immersed in a coagulation bath prepared with DMF and pure water (mass ratio 15:85) with a conductivity ≤10 μs / cm to solidify, obtaining a polyurethane porous layer. The polyurethane porous layer is peeled off from the PET plastic sheet and first washed in pure water (pure water conductivity ≤10 μs / cm) to remove residual DMF and fix the cell shape. The thoroughly cleaned polyurethane porous layer is then immersed in an aqueous solution containing ferrous sulfate (ferrous sulfate concentration 2%), allowing the chelating agent in the polyurethane porous layer to chelate with ferrous ions to form a complex, obtaining a polyurethane porous layer with catalytic activity. After drying, it is rolled up. The catalytic polyurethane porous layer is then bonded to the PET plastic sheet, and the surface is polished and cut to obtain the finished polishing pad.

[0073] Example 2: Preparation of a polishing pad for fine polishing of silicon carbide wafers

[0074] 1) Synthesis of solvent-based polyurethane resin:

[0075] formula:

[0076]

[0077] Preparation: 0.65 kg of 1,4-butanediol, 8.50 kg of polybutylene adipate diol (number average molecular weight 2000) and 5 kg of DMF were added to a reactor. The temperature was raised to 80°C, and 3.20 kg of MDI and 5 kg of DMF were added to carry out the polymerization reaction. The reaction temperature was controlled at 75-85°C. As the viscosity increased, 16.08 kg of DMF was added. After reacting for 5 hours, the temperature of the material in the reactor was lowered to 50°C, and the viscosity was measured to be 52 Pa·s. 0.59 kg of N-hydroxyethyl ethylenediamine triacetic acid was dissolved in 3 kg of N,N-dimethylformamide and then added dropwise to the reactor. After reacting for 2-5 hours, the temperature was lowered to 30-40°C to complete the reaction, and a solvent-based polyurethane resin containing a chelating agent was obtained.

[0078] 2) Preparation of coating slurry for damping fabric:

[0079] formula:

[0080] Solvent-based polyurethane resin 65.00 kg;

[0081] N,N-Dimethylformamide (DMF) 35.00kg.

[0082] Preparation: 65 kg of solvent-based polyurethane resin and 35 kg of DMF were added to a mixing tank. The mixture was stirred evenly under nitrogen protection in a sealed mixing tank and then vacuumed to remove bubbles, thus obtaining the coating slurry.

[0083] 3) Polishing Pad Preparation: Damping cloth is coated onto a PET plastic sheet with a coating slurry to a thickness of 1.8 mm. The plastic substrate with the coating slurry is then immersed in a coagulation bath prepared with DMF and pure water (mass ratio 20:80) with a conductivity ≤10 μs / cm to solidify, obtaining a polyurethane porous layer. The polyurethane porous layer is peeled off from the PET plastic sheet and first washed in pure water (pure water conductivity ≤10 μs / cm) to remove residual DMF and fix the cell shape. The thoroughly cleaned polyurethane porous layer is then immersed in an aqueous solution containing ferrous sulfate (ferrous sulfate concentration 2%), allowing the chelating agent in the polyurethane porous layer to chelate with ferrous ions to form a complex, obtaining a polyurethane porous layer with catalytic activity. After drying, it is wound up. The catalytic polyurethane porous layer is then bonded to the PET plastic sheet, and the polishing pad is obtained by grinding and cutting.

[0084] Example 3: Preparation of a polishing pad for fine polishing of silicon carbide wafers

[0085] 1) Synthesis of solvent-based polyurethane resin:

[0086] formula:

[0087]

[0088] Preparation: 0.65 kg of 1,4-butanediol, 8.50 kg of polybutylene adipate diol (number average molecular weight 2000) and 5 kg of DMF were added to a reactor. The temperature was raised to 80°C, and 3.60 kg of MDI and 5 kg of DMF were added to carry out the polymerization reaction. The reaction temperature was controlled at 75-85°C. As the viscosity increased, 18.77 kg of DMF was added. After reacting for 5 hours, the temperature of the material in the reactor was lowered to 50°C, and the viscosity was measured to be 44 Pa·s. 1.18 kg of N-hydroxyethyl ethylenediamine triacetic acid was dissolved in 3 kg of N,N-dimethylformamide and then added dropwise to the reactor. After reacting for 2-5 hours, the temperature was lowered to 30-40°C to complete the reaction, and a solvent-based polyurethane resin containing a chelating agent was obtained.

[0089] 2) Preparation of coating slurry for damping fabric:

[0090] formula:

[0091] Solvent-based polyurethane resin 65.00 kg;

[0092] N,N-Dimethylformamide (DMF) 35.00kg.

[0093] Preparation: 65 kg of solvent-based polyurethane resin and 35 kg of DMF were added to a mixing tank. The mixture was stirred evenly under nitrogen protection in a sealed mixing tank and then vacuumed to remove bubbles, thus obtaining the coating slurry.

[0094] 3) Polishing Pad Preparation: Damping cloth is coated onto a PET plastic sheet with a coating slurry to a thickness of 1.8 mm. The plastic substrate with the coating slurry is then immersed in a coagulation bath prepared with DMF and pure water (mass ratio 25:75) with a conductivity ≤10 μs / cm to solidify, obtaining a polyurethane porous layer. The polyurethane porous layer is peeled off from the PET plastic sheet and first washed in pure water (pure water conductivity ≤10 μs / cm) to remove residual DMF and fix the cell shape. The thoroughly cleaned polyurethane porous layer is then immersed in an aqueous solution containing ferrous sulfate (ferrous sulfate concentration 2%), allowing the chelating agent in the polyurethane porous layer to chelate with ferrous ions to form a complex, obtaining a polyurethane porous layer with catalytic activity. After drying, it is rolled up. The catalytic polyurethane porous layer is then bonded to the PET plastic sheet, and the surface is polished and cut to obtain the finished polishing pad.

[0095] Comparative Example 1: Preparation of a polishing pad for fine polishing of silicon carbide wafers

[0096] 1) Synthesis of solvent-based polyurethane resin:

[0097] formula:

[0098]

[0099] Preparation: 0.65 kg of 1,4-butanediol, 8.50 kg of polybutylene adipate diol (number average molecular weight 2000) and 5 kg of DMF were added to a reactor. The temperature was raised to 80°C, and 3.17 kg of MDI and 5 kg of DMF were added to carry out the polymerization reaction. The reaction temperature was controlled at 75-85°C. As the viscosity increased, 18.84 kg of DMF was added. After reacting for 5 hours, the temperature of the material in the reactor was lowered to 50°C. The viscosity was measured to be 34 Pa·s. The solvent-based polyurethane resin was obtained after the reaction was completed.

[0100] 2) Preparation of coating slurry for damping fabric:

[0101] formula:

[0102] Solvent-based polyurethane resin 65.00 kg;

[0103] N,N-Dimethylformamide (DMF) 35.00kg.

[0104] Preparation: 65 kg of solvent-based polyurethane resin and 35 kg of DMF were added to a mixing tank. The mixture was stirred evenly under nitrogen protection in a sealed mixing tank and then vacuumed to remove bubbles, thus obtaining the coating slurry.

[0105] 3) Polishing Pad Preparation: Damping cloth is coated onto a PET plastic sheet with a coating slurry to a thickness of 1.8 mm. The plastic substrate with the coating slurry is then immersed in a coagulation bath prepared with DMF and pure water (mass ratio 15:85) with a conductivity ≤10 μs / cm to solidify, obtaining a polyurethane porous layer. The polyurethane porous layer is peeled off from the PET plastic sheet and first washed in pure water (pure water conductivity ≤10 μs / cm) to remove residual DMF and fix the cell shape. The thoroughly cleaned polyurethane porous layer is then immersed in an aqueous solution containing ferrous sulfate (ferrous sulfate concentration 2%) to obtain a polyurethane porous layer with catalytic activity. After drying, it is rolled up. The catalytic polyurethane porous layer is then bonded to the PET plastic sheet, and the polishing pad is obtained by grinding and cutting.

[0106] Performance testing:

[0107] Polishing Removal Rate Test: A 6-inch conductive silicon carbide wafer was continuously polished for 40 hours using a Mingzheng 36B polishing machine. The polishing slurry used was Bonaina Run COPOL 130. Hydrogen peroxide was added to the slurry before polishing, with a concentration of 2%. The slurry flow rate was 100 ml / min. Polishing machine parameters: upper plate speed 45 rpm, lower plate speed 40 rpm, 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. Results are as follows: Figure 2 As shown.

[0108] 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, and the rate fluctuates significantly. This is because the polishing pad of Comparative Example 1 does not chelate ferrous ions. Only a small amount of ferrous sulfate is absorbed in the pores when soaking in ferrous sulfate solution, but ferrous ions are not bound to the resin. Therefore, it exhibits a more obvious catalytic effect in the early stage of polishing. However, during the long-term polishing process, its oxidation ability is significantly weakened after the ferrous ions are consumed. In contrast, the polishing rates of Examples 1 to 3 are relatively higher and more stable. This is because the slightly acidic polishing solution during the polishing process causes the chelated ferrous ions in the resin to be released slowly and evenly. This causes the hydrogen peroxide in the polishing solution to decompose stably and generate strong oxidizing hydroxyl radicals, which stably play a catalytic role during the long-term polishing process. Furthermore, the presence of chelating agents in the resin can chelate more ferrous ions, which react with hydrogen peroxide to decompose and generate more hydroxyl radicals, resulting in a stronger oxidation effect on the silicon carbide surface, rapidly generating a soft oxide layer, and achieving a higher and more stable polishing rate over a long period of time.

[0109] Depend on Figure 2It can be seen that in Examples 1 to 3, as the content of chelating agent increases, the catalytic effect provided during polishing is enhanced and the polishing rate gradually increases. This is because the divalent iron ion complex formed by chelation in the polyurethane porous layer also increases with the content of chelating agent, and generates more hydroxyl radicals when reacting with hydrogen peroxide, thus exerting a stronger oxidizing effect.

[0110] In summary, this invention, by modifying the composition and manufacturing process of the polyurethane resin, allows ferrous ions to exist stably in the polishing pad in the form of a complex, thus obtaining a damping cloth polishing pad with catalytic activity. During polishing, in a slightly acidic polishing solution environment, the chelate structure in the polishing pad is opened, releasing trace amounts of ferrous ions at the polishing interface. These ferrous ions undergo a Fenton reaction with hydrogen peroxide in the polishing solution, generating hydroxyl radicals at the polishing interface. This allows the polishing interface to uniformly provide catalytic activity during polishing, thereby effectively and uniformly increasing the polishing rate. This invention achieves precise control of the Fenton reaction at the polishing interface, which is of great significance for improving the production efficiency of silicon carbide wafer fine polishing. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial application value.

[0111] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a polishing pad for fine polishing of silicon carbide wafers, characterized in that, Includes the following steps: S1. The damping cloth is coated onto the plastic substrate by gravity using a coating slurry. The plastic substrate with the coating slurry is then immersed in a coagulation bath prepared with N,N-dimethylformamide and pure water to solidify, thereby obtaining a polyurethane porous layer. S2. Peel the obtained polyurethane porous layer off the plastic substrate and wash it with pure water. S3. Immerse the cleaned polyurethane porous layer in a ferrous sulfate aqueous solution to achieve chelation and obtain a polyurethane porous layer with catalytic effect. Dry and roll up the layer. S4. Adhere the dried polyurethane porous layer with catalytic effect to the plastic sheet, and then grind and cut it to obtain the finished polishing pad. The damping cloth coating slurry described in step S1 comprises, by mass percentage, 30%~40% N,N-dimethylformamide and 60%~70% solvent-based polyurethane resin; The solvent-based polyurethane resin comprises the following raw material components by mass percentage: 1,4-Butanediol 0.5%~3%; Polybutylene adipate diol 20%~30%; N-hydroxyethyl ethylenediamine triacetic acid 0.5%~5%; Diphenylmethane-4,4'-diisocyanate 5%~15%; N,N-dimethylformamide 60%~74%.

2. The method for preparing a polishing pad for fine polishing of silicon carbide wafers as described in claim 1, characterized in that, The preparation method of the solvent-based polyurethane resin includes the following steps: 1,4-Butanediol, polybutylene adipate diol, and 1 / 7 to 1 / 5 of N,N-dimethylformamide were mixed and stirred, and the mixture was heated to 75 to 85°C. Diphenylmethane-4,4'-diisocyanate and 1 / 7 to 1 / 5 of N,N-dimethylformamide were added, and the polymerization reaction was carried out at 75 to 85°C. As the viscosity increased, 5 / 8 to 1 / 2 of N,N-dimethylformamide was added to reduce the viscosity. After reacting for 3 to 7 hours, the mixture was cooled for the first time to obtain a mixed solution. N-hydroxyethyl ethylenediamine triacetic acid was dissolved in the remaining N,N-dimethylformamide and then slowly added to the mixture. The reaction was continued for 2 to 5 hours, and then cooled for the second time to end the reaction, resulting in a solvent-based polyurethane resin containing a chelating agent.

3. The method for preparing a polishing pad for fine polishing of silicon carbide wafers as described in claim 2, characterized in that, The first cooling process involves the temperature dropping to 50-60℃. And / or, the second cooling is a temperature drop to 30~40℃; And / or, the slow addition is a dropwise addition; And / or, the molar ratio of the isocyanate group in the diphenylmethane-4,4'-diisocyanate to the total hydroxyl groups in polybutylene adipate diol and 1,4-butanediol is NCO∶OH=1∶1~1.3∶1.

4. The method for preparing a polishing pad for fine polishing of silicon carbide wafers as described in claim 1, characterized in that, The preparation method of the coating slurry for damping cloth includes: stirring and mixing N,N-dimethylformamide with solvent-based polyurethane resin to obtain the coating slurry for damping cloth.

5. The method for preparing a polishing pad for fine polishing of silicon carbide wafers as described in claim 1, characterized in that, The pure water mentioned in steps S1 and S2 is pure water with a conductivity ≤10μs / cm; And / or, the mass ratio of N,N-dimethylformamide to pure water in the coagulation bath in step S1 is 10~30:70~90; And / or, the mass concentration of the ferrous sulfate aqueous solution in step S3 is 0.1% to 10%.

6. A polishing pad for fine polishing of silicon carbide wafers, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.

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