High-purity silica sol for polishing silicon carbide substrate and preparation method thereof

Abstract

The present invention relates to a high-purity silica sol for polishing silicon carbide substrates and a preparation method thereof. The preparation method comprises: purifying tetraethoxysilane to obtain purified tetraethoxysilane, performing multi-stage reverse osmosis and electrodeionization treatment on ultrapure water to obtain treated ultrapure water; subjecting the purified tetraethoxysilane and the treated ultrapure water to a sol-gel reaction to obtain an initial silica sol; performing a hydrothermal reaction treatment to obtain silicon nanoparticles; purifying the silica sol using a continuous flow ion exchange system and a tangential flow ultrafiltration technique to obtain a high-purity silica sol; adding a stabilizer and a coupling agent to obtain a stabilized silica sol; adjusting the pH value to 9.5±0.1 to obtain a pH-controlled silica sol; performing high shear homogenization treatment on the pH-controlled silica sol, and concentrating the pH-controlled silica sol to a high-purity silica sol with a solid content of 30 wt%. The present invention provides a high-purity silica sol with good chemical stability and excellent mechanical polishing performance.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and in particular to a high-purity silica sol for polishing a silicon carbide substrate and a preparation method thereof. Background Art

[0002] Silica sol is a colloidal suspension of nano-sized silicon dioxide dispersed in a solvent. It is a non-toxic, odorless, and non-polluting non-metallic material widely used in polishing, coatings, textiles, catalysts, refractory materials, and many other fields. In recent years, with the rapid development of the semiconductor chip industry, the requirements for chemical mechanical polishing (CMP) technology have become increasingly stringent. Chemical mechanical polishing (CMP) is the most widely used polishing technique in fine polishing. It is a single-sided polishing method used to remove scratches on the silicon surface of silicon carbide wafers to achieve a smooth surface. As the only and most effective method for achieving global planarization, this technique is often used as the final step in the processing of SiC single crystal substrates and is crucial for ensuring an ultra-smooth, defect-free, and damage-free surface. High-purity silica sol, due to its extremely low metal impurity content and excellent stability, can protect semiconductor materials from damage caused by metal impurities during the fine polishing process. Therefore, ultra-high-purity silica sol has been widely used in CMP technology in recent years and is an indispensable component of modern microelectronic polishing fluids.

[0003] Polishing silicon carbide substrates is a critical process step in semiconductor manufacturing. High-purity silica sol, a key component of the polishing fluid, has a quality that directly impacts polishing results. Currently, the preparation of high-purity silica sol faces the dual challenges of increasing production rates while preventing impurities, and ensuring chemical stability while enhancing mechanical polishing performance.

[0004] Traditional silica sol preparation methods typically involve steps such as selecting a silicon source, selecting a solvent, preparing the sol, and stabilizing it. Commonly used raw materials and the preparation process may contain or generate various impurities, which require sol purification to remove. Furthermore, to achieve the desired polishing effect, the particle size distribution and concentration of the silicon nanoparticles must be adjusted. During the preparation process, purification techniques such as ion exchange and ultrafiltration are often used to ensure high purity. However, these steps often reduce production efficiency. Furthermore, to improve mechanical polishing performance, the sol needs to be uniformly mixed and concentrated, but this can affect the sol's chemical stability.

[0005] Therefore, how to ensure high purity during the efficient preparation process while maintaining chemical stability on the basis of improving mechanical polishing performance has become the main challenge facing the current silica sol preparation technology, and the existing technology needs to be improved. Summary of the Invention

[0006] In the prior art, it is necessary to ensure the high purity of high-purity silica sol during an efficient preparation process, while maintaining chemical stability on the basis of improving mechanical polishing performance. Therefore, the present invention provides a high-purity silica sol for polishing silicon carbide substrates and a preparation method thereof to solve the above problems.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a high-purity silica sol for polishing a silicon carbide substrate, which comprises the following specific steps:

[0008] S1, selecting high-purity tetraethoxysilane as a silicon source and ultrapure water as a solvent, purifying the tetraethoxysilane to obtain purified tetraethoxysilane, and simultaneously performing multi-stage reverse osmosis and electrodeionization treatment on the ultrapure water to obtain treated ultrapure water;

[0009] S2, mixing the purified tetraethoxysilane with the treated ultrapure water in a molar ratio of (1-3): (4-7), and performing a sol-gel reaction at 60±0.5°C for 4 hours to obtain an initial silica sol;

[0010] S3, subjecting the initial silica sol to a hydrothermal reaction treatment, monitoring and adjusting the hydrothermal treatment time in real time, to obtain silicon nanoparticles with an average particle size of 20±2 nm;

[0011] S4. Purifying the silica sol using a continuous flow ion exchange system and tangential flow ultrafiltration technology to obtain high-purity silica sol;

[0012] S5. Adding a stabilizer and a coupling agent to the high-purity silica sol to obtain a stabilized silica sol;

[0013] S6. Using an automatic titration system, the pH value of the stabilized silica sol is adjusted to 9.5±0.1 to obtain a pH-controlled silica sol;

[0014] S7. The silica sol after pH adjustment is subjected to high shear homogenization treatment and concentrated to a high-purity silica sol with a solid content of 30 wt%.

[0015] In one implementation, in S1 , when tetraethoxysilane is purified, it is purified by passing it through a molecular sieve column under nitrogen protection.

[0016] In one implementation, in S2, specifically including: mixing pretreated tetraethoxysilane and treated ultrapure water in a molar ratio of 1:4, stirring at a speed of 300 rpm in a constant temperature stirrer, slowly adding 0.1 mol / L hydrochloric acid solution as a catalyst, controlling the pH value between 2.0-2.5, accurately controlling the reaction temperature at 60±0.5°C, and continuing the reaction for 4 hours to obtain an initial silica sol.

[0017] In one implementation, in S3, the temperature of the hydrothermal reaction is 180° C., and the time of the hydrothermal reaction is 24 hours.

[0018] In one implementation, in S4, using a continuous flow ion exchange system specifically includes: passing the stabilized silica sol through a cation exchange resin column and an anion exchange resin column at a flow rate of 5 mL / min; using a tangential flow ultrafiltration technology specifically includes: selecting a polyethersulfone membrane with a molecular weight cutoff of 10 kDa, and concentrating and purifying at a transmembrane pressure of 0.5 MPa.

[0019] In one implementation, in S5, the stabilizer includes 0.5 wt% of polyvinyl pyrrolidone and 0.1 wt% of sodium polyacrylate, and the coupling agent is 0.05 wt% of γ-aminopropyltriethoxysilane.

[0020] In one implementation, S6 specifically includes: using an automatic titration system to slowly dropwise add 0.1 mol / L triethanolamine solution to accurately adjust the pH value of the sol to 9.5±0.1.

[0021] In one implementation, in S7, the high shear homogenization treatment specifically includes: using a high shear homogenizer to treat the sol at a rotation speed of 20,000 rpm for 15 minutes.

[0022] In one implementation, the concentrating the high-purity silica sol to a solid content of 30 wt% specifically includes: concentrating the sol at 40° C. using a vacuum rotary evaporator to adjust the solid content to 30 wt% to obtain the desired high-purity silica sol.

[0023] In a second aspect, the present invention further provides a high-purity silica sol for polishing a silicon carbide substrate, which is prepared by any of the above-mentioned methods for preparing a high-purity silica sol for polishing a silicon carbide substrate.

[0024] Beneficial effects: The method for preparing high-purity silica sol for polishing silicon carbide substrates provided by the present invention synthesizes silica sol by a sol-gel method, and optimizes the process through nanoparticle growth and regulation, efficient purification treatment, optimized addition of stabilizers and coupling agents, and precise control of pH value. While solving the purity and efficiency problems in the traditional preparation process, it also achieves improvements in chemical stability and mechanical polishing performance, and prepares a high-purity silica sol with good chemical stability and excellent mechanical polishing performance suitable for high-quality polishing of silicon carbide substrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention provides a flow chart of the steps of preparing a high-purity silica sol for polishing a silicon carbide substrate.

[0026] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the descriptions of the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" described below mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0028] See Figure 1 , Figure 1 The present invention provides a method for preparing a high-purity silica sol for polishing a silicon carbide substrate, which comprises the following specific steps:

[0029] S1, selecting high-purity tetraethoxysilane as a silicon source and ultrapure water as a solvent, purifying the tetraethoxysilane to obtain purified tetraethoxysilane, and simultaneously performing multi-stage reverse osmosis and electrodeionization treatment on the ultrapure water to obtain treated ultrapure water;

[0030] S2, mixing the purified tetraethoxysilane with the treated ultrapure water in a molar ratio of (1-3): (4-7), and performing a sol-gel reaction at 60±0.5°C for 4 hours to obtain an initial silica sol;

[0031] S3, subjecting the initial silica sol to a hydrothermal reaction treatment, monitoring and adjusting the hydrothermal treatment time in real time, to obtain silicon nanoparticles with an average particle size of 20±2 nm;

[0032] S4. Purifying the silica sol using a continuous flow ion exchange system and tangential flow ultrafiltration technology to obtain high-purity silica sol;

[0033] S5. Adding a stabilizer and a coupling agent to the high-purity silica sol to obtain a stabilized silica sol;

[0034] S6. Using an automatic titration system, the pH value of the stabilized silica sol is adjusted to 9.5±0.1 to obtain a pH-controlled silica sol;

[0035] S7. The silica sol after pH adjustment is subjected to high shear homogenization treatment and concentrated to a high-purity silica sol with a solid content of 30 wt%.

[0036] Specifically, in S1, tetraethoxysilane is purified by passing it through a molecular sieve column under nitrogen protection. In this invention, high-purity tetraethoxysilane (TEOS) is used as the silicon source, and ultrapure water (resistivity >18.2 MΩ·cm) is used as the solvent. TEOS has high purity and reactivity, which facilitates the formation of uniform silicon nanoparticles. TEOS is initially purified by passing it through a molecular sieve column under nitrogen protection to remove any trace metal ions. The ultrapure water undergoes multi-stage reverse osmosis and electrodeionization to ensure the solvent's extremely high purity. This step lays a pure foundation for subsequent reactions and effectively reduces the risk of impurity introduction. In another embodiment, the silicon source can also be tetramethoxysilane (Si(OCH3)4, TMOS) or rice husk ash. The rice husk ash can be dissolved into a sodium silicate solution using nitric acid and sodium hydroxide, respectively, for subsequent reactions.

[0037] Specifically, in S2, the following steps are performed: pretreated tetraethoxysilane and treated ultrapure water are mixed in a molar ratio of 1:4, stirred at 300 rpm in a thermostatic stirrer, and 0.1 mol / L hydrochloric acid solution is slowly added dropwise as a catalyst. The pH value is controlled between 2.0 and 2.5, and the reaction temperature is precisely controlled at 60 ± 0.5°C. The reaction is continued for 4 hours to obtain an initial silica sol. This step promotes the hydrolysis and condensation reactions of TEOS by precisely controlling the reaction conditions, thereby forming the initial silica sol via the sol-gel method.

[0038] Specifically, in S3, the hydrothermal reaction temperature is 180°C and the reaction time is 24 hours. The hydrothermal reaction vessel is an autoclave, and the hydrothermal treatment process promotes the growth and crystallization of silicon nanoparticles. After the hydrothermal reaction, the autoclave is cooled to room temperature to obtain a preliminary silica sol. Dynamic light scattering (DLS) technology is used to monitor the particle size distribution in real time, and the hydrothermal treatment time is adjusted to obtain silicon nanoparticles with an average particle size of 20 ± 2 nm. This step ensures the uniformity and ideal size of the silicon nanoparticles, laying the foundation for subsequent polishing performance.

[0039] Specifically, in S4, the use of a continuous flow ion exchange system includes: passing the stabilized silica sol through a cation exchange resin column and an anion exchange resin column at a flow rate of 5 mL / min; the use of tangential flow ultrafiltration technology includes: selecting a polyethersulfone membrane with a molecular weight cutoff of 10 kDa and performing concentration and purification at a transmembrane pressure of 0.5 MPa. The continuous flow ion exchange system can remove any metal ions and other charged impurities. Concentration and purification using tangential flow ultrafiltration technology not only ensures the high purity of the sol, but also significantly improves production efficiency.

[0040] Specifically, in S5, the stabilizer includes 0.5 wt% of polyvinyl pyrrolidone and 0.1 wt% of sodium polyacrylate, and the coupling agent is 0.05 wt% of γ-aminopropyltriethoxysilane. A composite stabilizer system is used in this step, wherein polyvinyl pyrrolidone is the main stabilizer and sodium polyacrylate is the auxiliary stabilizer. The two additives work together through electrostatic and steric effects to effectively prevent the aggregation of silicon nanoparticles. In addition, γ-aminopropyltriethoxysilane, as a coupling agent, can enhance the interaction between silicon nanoparticles and the silicon carbide substrate. The introduction of stabilizers and coupling agents can also improve the solubility and etching rate of the polishing liquid in silicon carbide.

[0041] Specifically, in S6, the following steps are performed: Using an automated titration system, a 0.1 mol / L triethanolamine solution is slowly added dropwise to precisely adjust the pH of the sol to 9.5 ± 0.1. Accurately controlling the sol within this pH range ensures a moderate negative charge on the surface of the silicon nanoparticles, maintaining good dispersion without excessively corroding the silicon carbide substrate. This pH also optimizes the performance of the stabilizer and coupling agent.

[0042] Specifically, in S7, the high shear homogenization treatment specifically includes: using a high shear homogenizer to treat the sol at a speed of 20,000 rpm for 15 minutes. The high shear homogenization treatment can ensure the uniform distribution of the additives and the sufficient dispersion of the silicon nanoparticles. The high-purity silica sol concentrated to a solid content of 30 wt% specifically includes: concentrating the sol at 40°C using a vacuum rotary evaporator to adjust the solid content to 30 wt% to obtain the desired high-purity silica sol. This step not only improves the mechanical polishing performance of the sol, but also maximizes the chemical stability by controlling the concentration temperature and time.

[0043] In addition, after S7, the following steps may be performed: Inductively coupled plasma mass spectrometry (ICP-MS) is used to detect metal impurities to ensure that the total metal ion concentration is less than 1 ppb. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) are used to characterize the particle size distribution and morphology of the silicon nanoparticles. The viscosity and shear-thinning behavior of the sol are measured using a rotational rheometer to ensure that it possesses ideal rheological properties. Finally, polishing tests on silicon carbide substrates are conducted under simulated polishing conditions to evaluate material removal rate and surface roughness to verify the actual polishing performance of the sol. The resulting high-purity silica sol is then subjected to quality control and performance evaluation.

[0044] Example 1

[0045] This embodiment provides a method for preparing a high-purity silica sol for polishing a silicon carbide substrate, which includes the following specific steps:

[0046] S1, selecting high-purity tetraethoxysilane as a silicon source and ultrapure water as a solvent, purifying the tetraethoxysilane to obtain purified tetraethoxysilane, and simultaneously performing multi-stage reverse osmosis and electrodeionization treatment on the ultrapure water to obtain treated ultrapure water;

[0047] S2. Pretreated tetraethoxysilane and treated ultrapure water were mixed in a molar ratio of 1:4, stirred at 300 rpm in a thermostatic stirrer, and 0.1 mol / L hydrochloric acid solution was slowly added dropwise as a catalyst. The pH value was controlled between 2.0 and 2.5, and the reaction temperature was precisely controlled at 60 ± 0.5 °C. The reaction was continued for 4 hours to obtain an initial silica sol.

[0048] S3, subjecting the initial silica sol to a hydrothermal reaction treatment at a temperature of 180°C for 24 hours to obtain silicon nanoparticles with an average particle size of 20±2 nm;

[0049] S4. The stabilized silica sol was passed through a cation exchange resin column and an anion exchange resin column at a flow rate of 5 mL / min using a polyethersulfone membrane with a molecular weight cutoff of 10 kDa, and concentrated and purified at a transmembrane pressure of 0.5 MPa to obtain a high-purity silica sol;

[0050] S5, adding 0.5 wt % of polyvinyl pyrrolidone, 0.1 wt % of sodium polyacrylate and 0.05 wt % of γ-aminopropyltriethoxysilane to the high-purity silica sol in sequence to obtain a stabilized silica sol;

[0051] S6. Using an automatic titration system, slowly add 0.1 mol / L triethanolamine solution dropwise to accurately adjust the pH value of the sol to 9.5±0.1 to obtain a pH-controlled silica sol;

[0052] S7. The sol was treated at 20,000 rpm using a high shear homogenizer for 15 minutes, and the sol was concentrated using a vacuum rotary evaporator at 40° C. to adjust the solid content to 30 wt % to obtain a high-purity silica sol.

[0053] The high-purity silica sol obtained in Example 1 was tested for its polishing effect, particle size distribution and stability. The test showed that the average particle size was between 8 and 200 nm.

[0054] Stability testing of high-purity silica sol: 0.74 mL of a 45% triethanolamine solution was added to 100 mL of deionized water. 125 g of ammonium molybdate was slowly added with rapid stirring. The solution was heated to 60°C, and then 400 g of the 35% high-purity silica sol provided in Example 1 was quickly added. After stopping heating and stirring for 5 minutes, the viscosity of the silica sol was continuously measured using a viscometer, and the time it took for the viscosity to reach 2 Pa·s was recorded. The acceptable stability time was 9 minutes, with longer times indicating better stability. Test results demonstrate that the stability time provided by the present invention ranges from 10 to 25 minutes.

[0055] Polishing effect test of high-purity silica sol: The high-purity silica sol of Example 1 was provided for polishing, and its surface roughness was measured using an AFM scanning within a range of 5μm x 5μm. The Ra value of the high-purity silica sol provided by the present invention after polishing was measured to be below 0.37nm, which is significantly lower than the Ra value of less than 1.0nm required on the market, and has the effect of significantly reducing surface roughness.

[0056] In summary, the method for preparing high-purity silica sol for polishing silicon carbide substrates provided by the present invention synthesizes silica sol by a sol-gel method, and optimizes the process through nanoparticle growth and regulation, efficient purification treatment, optimized addition of stabilizers and coupling agents, and precise control of pH value. While solving the purity and efficiency problems in the traditional preparation process, it also achieves improvements in chemical stability and mechanical polishing performance, and prepares a high-purity silica sol with good chemical stability and excellent mechanical polishing performance suitable for high-quality polishing of silicon carbide substrates.

[0057] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing high-purity silica sol for polishing silicon carbide substrates, characterized in that: The specific steps include: S1, selecting high-purity tetraethoxysilane as a silicon source and ultrapure water as a solvent, purifying the tetraethoxysilane to obtain purified tetraethoxysilane, and simultaneously performing multi-stage reverse osmosis and electrodeionization treatment on the ultrapure water to obtain treated ultrapure water; S2, mixing the purified tetraethoxysilane with the treated ultrapure water in a molar ratio of (1-3): (4-7), and performing a sol-gel reaction at 60±0.5°C for 4 hours to obtain an initial silica sol; S3, performing a hydrothermal reaction treatment on the initial silica sol, monitoring and adjusting the hydrothermal treatment time in real time, to obtain silicon nanoparticles with an average particle size of 20±2 nm; S4. Purifying the silica sol using a continuous flow ion exchange system and tangential flow ultrafiltration technology to obtain high-purity silica sol; S5. Adding a stabilizer and a coupling agent to the high-purity silica sol to obtain a stabilized silica sol, wherein the stabilizer comprises 0.5 wt % of polyvinyl pyrrolidone and 0.1 wt % of sodium polyacrylate, and the coupling agent is 0.05 wt % of γ-aminopropyltriethoxysilane; S6. Using an automatic titration system, the pH value of the stabilized silica sol is adjusted to 9.5±0.1 to obtain a pH-controlled silica sol; S7. The silica sol after pH adjustment is subjected to high shear homogenization treatment and concentrated to a high-purity silica sol with a solid content of 30 wt%.

2. The method for preparing high-purity silica sol for polishing silicon carbide substrates according to claim 1, characterized in that: In S1, when tetraethoxysilane is purified, it is purified by passing through a molecular sieve column under nitrogen protection.

3. The method for preparing high-purity silica sol for polishing silicon carbide substrates according to claim 1, characterized in that: In S2, it specifically includes: mixing the pretreated tetraethoxysilane and the treated ultrapure water in a molar ratio of 1:4, stirring at a speed of 300 rpm in a constant temperature stirrer, slowly adding 0.1 mol / L hydrochloric acid solution as a catalyst, controlling the pH value between 2.0-2.5, and accurately controlling the reaction temperature at 60±0.5°C. The reaction is continued for 4 hours to obtain an initial silica sol.

4. The method for preparing high-purity silica sol for polishing silicon carbide substrates according to claim 1, characterized in that: In S3, the temperature of the hydrothermal reaction is 180° C., and the time of the hydrothermal reaction is 24 hours.

5. The method for preparing high-purity silica sol for polishing silicon carbide substrates according to claim 1, characterized in that: In S4, the use of a continuous flow ion exchange system specifically includes: passing the stabilized silica sol through a cation exchange resin column and an anion exchange resin column at a flow rate of 5 mL / min; the use of a tangential flow ultrafiltration technology specifically includes: selecting a polyethersulfone membrane with a molecular weight cutoff of 10 kDa, and concentrating and purifying at a transmembrane pressure of 0.5 MPa.

6. The method for preparing high-purity silica sol for polishing silicon carbide substrates according to claim 1, characterized in that: In S6, specifically including: using an automatic titration system, slowly adding 0.1 mol / L triethanolamine solution to accurately adjust the pH value of the sol to 9.5±0.

1.

7. The method for preparing high-purity silica sol for polishing silicon carbide substrates according to claim 1, characterized in that: In S7, the high shear homogenization treatment specifically includes: using a high shear homogenizer to treat the sol at a rotation speed of 20,000 rpm for 15 minutes.

8. The method for preparing high-purity silica sol for polishing silicon carbide substrates according to claim 1, characterized in that: The high-purity silica sol concentrated to a solid content of 30 wt % specifically includes: concentrating the sol at 40° C. using a vacuum rotary evaporator to adjust the solid content to 30 wt % to obtain the desired high-purity silica sol.

9. A high-purity silica sol for polishing a silicon carbide substrate, characterized in that: The high-purity silica sol for polishing silicon carbide substrates is prepared by the preparation method of high-purity silica sol for polishing silicon carbide substrates according to any one of claims 1 to 8.

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