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

Abstract

The invention relates to high-purity silica sol for polishing a silicon carbide substrate and a preparation method of the high-purity silica sol. The preparation method comprises the following steps: carrying out purification treatment on tetraethoxysilane to obtain purified tetraethoxysilane, and carrying out multistage reverse osmosis and electrodeionization treatment on ultrapure water to obtain treated ultrapure water; the purified tetraethoxysilane and the treated ultrapure water are subjected to a sol-gel reaction, and initial silica sol is obtained; carrying out hydrothermal reaction treatment to obtain silicon nanoparticles; purifying the silica sol by using a continuous flow ion exchange system and a tangential flow ultrafiltration technology to obtain high-purity silica sol; adding a stabilizer and a coupling agent to obtain stabilized silica sol; adjusting the pH value to 9.5 + / -0.1 to obtain silica sol after pH regulation and control; and carrying out high-shear homogenization treatment on the silica sol subjected to pH regulation and control, and concentrating to obtain the high-purity silica sol with the solid content of 30wt%. The high-purity silica sol provided by the invention is good in chemical stability and excellent in mechanical polishing performance.

Description

Technical Field

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

[0002] Silica sol is a suspended colloidal liquid in which nano-scale silicon dioxide is dispersed in a solvent. It is a non-toxic, odorless, and pollution-free non-metallic material. It is widely used in many fields such as polishing, coatings, textiles, catalysts, and refractory materials. In recent years, with the rapid development of the semiconductor chip industry, the requirements for chemical mechanical polishing (CMP) technology have become increasingly higher. Chemical mechanical polishing (CMP) is the most widely used polishing technology in fine polishing. It belongs to single-sided polishing and is used to remove scratches on the silicon surface of silicon carbide wafers to make the surface smooth. As the only most effective method to achieve global flatness, this technology is often used as the last process in the processing of SiC single crystal substrates. It is the key to ensure that the processed surface is ultra-smooth, defect-free, and damage-free. High-purity silica sol has extremely low metal impurity content and good stability, which can ensure that semiconductor materials are not damaged by metal impurities in the fine polishing process. Therefore, in recent years, ultra-high purity silica sol has been widely used in CMP technology and is one of the indispensable components in modern microelectronic polishing liquids.

[0003] Polishing of silicon carbide substrates is a key process step in semiconductor manufacturing, and high-purity silica sol, as an important component of polishing liquid, has a direct impact on the polishing effect due to its quality. Currently, in the preparation process of high-purity silica sol, there are two challenges: how to prevent the introduction of impurities while increasing the production rate, and how to improve the mechanical polishing performance while ensuring chemical stability.

[0004] The traditional method of preparing silica sol usually involves the steps of selecting silicon source, selecting solvent, preparing sol and stabilizing treatment. Commonly used raw materials and preparation processes may contain or produce various impurities, which need to be removed through the purification process of sol. At the same time, in order to obtain the ideal polishing effect, it is also necessary to adjust the particle size distribution and concentration of silicon nanoparticles. In the preparation process, in order to ensure high purity, purification treatment is often carried out by ion exchange and ultrafiltration. However, these steps often reduce production efficiency. On the other hand, in order to improve the mechanical polishing performance, the sol needs to be uniformly mixed and concentrated, but this may affect the chemical stability of the sol.

[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 in 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: 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, subjecting the initial silica sol to a hydrothermal reaction treatment, monitoring and adjusting the hydrothermal treatment time in real time, and obtaining 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; 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 pH-controlled silica sol is subjected to high shear homogenization treatment and concentrated to a high-purity silica sol with a solid content of 30 wt%.

[0008] In one implementation, in S1, when tetraethoxysilane is purified, it is purified by passing through a molecular sieve column under nitrogen protection.

[0009] In one implementation, in S2, specifically including: 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 precisely controlling the reaction temperature at 60±0.5°C, continuing the reaction for 4 hours, and obtaining an initial silica sol.

[0010] In one implementation, in S3, the temperature of the hydrothermal reaction is 180° C., and the time of the hydrothermal reaction is 24 hours.

[0011] 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 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.

[0012] 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.

[0013] In one implementation, in 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.

[0014] 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.

[0015] In one implementation, 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.

[0016] 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 one of the above-mentioned methods for preparing a high-purity silica sol for polishing a silicon carbide substrate.

[0017] 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 by growth and regulation of nanoparticles, efficient purification treatment, optimized addition of stabilizers and coupling agents, and precise regulation 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

[0018] Figure 1 The present invention is a flowchart of the steps of preparing a method for high-purity silica sol for polishing a silicon carbide substrate.

[0019] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with 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 description of the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" described below means 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 representation of the above terms is not necessarily for the same embodiment or example. Moreover, the technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0021] See also 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: 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, subjecting the initial silica sol to a hydrothermal reaction treatment, monitoring and adjusting the hydrothermal treatment time in real time, and obtaining 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; 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 pH-controlled silica sol is subjected to high shear homogenization treatment and concentrated to a high-purity silica sol with a solid content of 30 wt%.

[0022] Specifically, in S1, when tetraethoxysilane is purified, it is purified by passing through a molecular sieve column under nitrogen protection. In the present invention, high-purity tetraethoxysilane (TEOS) is selected as the silicon source, and ultrapure water (resistivity>18.2MΩ·cm) is used as the solvent, wherein TEOS has high purity and reactivity, which is conducive to the formation of uniform silicon nanoparticles. TEOS is preliminarily purified by passing through a molecular sieve column under nitrogen protection to remove possible trace metal ions. Ultrapure water undergoes multi-stage reverse osmosis and electrodeionization treatment to ensure the extremely high purity of the solvent. 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, wherein nitric acid and sodium hydroxide can be used to dissolve the rice husk ash into a sodium silicate solution for subsequent reactions.

[0023] Specifically, in S2, it specifically includes: mixing the pretreated tetraethoxysilane with the treated ultrapure water in a molar ratio of 1:4, stirring at a speed of 300 rpm in a constant temperature stirrer, slowly dropping 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, and continuing the reaction for 4 hours to obtain an initial silica sol. This step promotes the hydrolysis and condensation reaction of TEOS by accurately controlling the reaction conditions, and forms the initial silica sol by the sol-gel method.

[0024] Specifically, in S3, the temperature of the hydrothermal reaction is 180°C, and the time of the hydrothermal reaction is 24 hours. The container of the hydrothermal reaction is a high-pressure reactor, and the growth and crystallization of silicon nanoparticles are promoted by the hydrothermal treatment process. After the hydrothermal reaction is completed, the high-pressure reactor is cooled to room temperature to obtain a preliminary silica sol. The particle size distribution is monitored in real time by dynamic light scattering (DLS) technology, 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.

[0025] Specifically, 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 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. Among them, the continuous flow ion exchange system can remove possible metal ions and other charged impurities. At the same time, the concentration and purification by tangential flow ultrafiltration technology can not only ensure the high purity of the sol, but also significantly improve the production efficiency.

[0026] 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-aminopropyl triethoxysilane. A composite stabilizer system is used in this step, in which polyvinyl pyrrolidone is the main stabilizer and sodium polyacrylate is the auxiliary stabilizer. The two additives work together through electrostatic and steric hindrance effects to effectively prevent the aggregation of silicon nanoparticles. In addition, γ-aminopropyl triethoxysilane, as a coupling agent, can enhance the interaction between silicon nanoparticles and silicon carbide substrates. The introduction of stabilizers and coupling agents can also improve the solubility and etching rate of the polishing liquid in silicon carbide.

[0027] Specifically, in S6, it specifically includes: using an automatic titration system, slowly adding 0.1 mol / L triethanolamine solution, and accurately adjusting the pH value of the sol to 9.5±0.1. Among them, the sol is accurately regulated within this pH range so that the surface of the silicon nanoparticles has a moderate negative charge, which can maintain good dispersibility without excessively corroding the silicon carbide substrate. At the same time, this pH value is also conducive to the optimal performance of the stabilizer and coupling agent.

[0028] 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 additives and the full dispersion of silicon nanoparticles. The high-purity silica sol concentrated to a solid content of 30 wt% specifically includes: concentrating the sol at 40°C by a vacuum rotary evaporator, adjusting the solid content to 30 wt%, and obtaining 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.

[0029] In addition, after S7, it can also include: using inductively coupled plasma mass spectrometry (ICP-MS) to detect the metal impurity content to ensure that the total metal ion concentration is less than 1 ppb. Use dynamic light scattering (DLS) and transmission electron microscopy (TEM) to characterize the particle size distribution and morphology of silicon nanoparticles. The viscosity and shear thinning behavior of the sol are measured by a rotational rheometer to ensure that it has ideal rheological properties. Finally, a polishing test of the silicon carbide substrate is carried out under simulated polishing conditions to evaluate the material removal rate and surface roughness to verify the actual polishing performance of the sol. The final high-purity silica sol is subjected to quality control and performance evaluation.

[0030] Example 1 This embodiment provides a method for preparing a high-purity silica sol for polishing a silicon carbide substrate, which comprises the following specific steps: 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. Pretreated tetraethoxysilane and treated ultrapure water were mixed in a molar ratio of 1:4, stirred at 300 rpm in a constant temperature stirrer, and 0.1 mol / L hydrochloric acid solution was slowly added as a catalyst, the pH value was controlled between 2.0-2.5, the reaction temperature was accurately controlled at 60±0.5°C, and the reaction was continued for 4 hours to obtain an initial silica sol; 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; S4, 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 polyethersulfone membrane with a molecular weight cutoff of 10 kDa, and concentrating and purifying it under a transmembrane pressure of 0.5 MPa to obtain a high-purity silica sol; 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; S6. Using an automatic titration system, slowly dropwise add 0.1 mol / L triethanolamine solution to accurately adjust the pH value of the sol to 9.5±0.1 to obtain a pH-controlled silica sol; S7. Use a high shear homogenizer to treat the sol at a rotation speed of 20,000 rpm for 15 minutes, concentrate the sol at 40°C using a vacuum rotary evaporator, and adjust the solid content to 30 wt% to obtain a high-purity silica sol.

[0031] The high-purity silica sol obtained in Example 1 was tested for its polishing effect, particle size distribution and stability. The average particle size was found to be between 8 and 200 nm.

[0032] Stability test of high-purity silica sol: add 0.74 mL of triethanolamine solution with a mass fraction of 45% to 100 mL of deionized water, slowly add 125 g of ammonium molybdate under rapid stirring, heat the solution to 60 ° C, and then quickly add 400 g of high-purity silica sol provided in Example 1 with a mass fraction of 35%, stop heating and stir for 5 minutes, and continuously measure the viscosity of the silica sol with a viscometer, and record the time when the viscosity reaches 2 Pa·S. The qualified stability time is 9 minutes, and the longer the time, the better the stability of the silica sol. The test results show that the qualified stability time provided by the present invention is between 10 and 25 minutes.

[0033] 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 by scanning with AFM within the range of 5μmx 5μm. It was measured that the Ra value of the high-purity silica sol provided by the present invention after polishing was below 0.37nm, which is compared with the Ra value of less than 1.0nm required on the market, and has the effect of significantly reducing the surface roughness.

[0034] 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 by 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 that is suitable for high-quality polishing of silicon carbide substrates.

[0035] 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 specification 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, subjecting the initial silica sol to a hydrothermal reaction treatment, monitoring and adjusting the hydrothermal treatment time in real time, and obtaining 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; 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 pH-controlled silica sol 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, specifically including: 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, continuing the reaction for 4 hours, and obtaining 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 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.

7. 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.

8. 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.

9. 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. by a vacuum rotary evaporator to adjust the solid content to 30 wt % to obtain the desired high-purity silica sol.

10. 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 method for preparing the high-purity silica sol for polishing silicon carbide substrates according to any one of claims 1 to 9.

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