Preparation method of high-purity short-chain silica sol with controllable particle size

Abstract

The application relates to a preparation method of high-purity short-chain silica sol with controllable particle size. First, long-chain silica sol seed particles are prepared under acidic conditions by using active silicic acid; after adjusting the liquid environment of the seed system and adjusting the pH to alkaline, alkoxysilane is added to make the particles grow; finally, water is added for dilution, and high-purity short-chain silica sol aqueous solution with a mass fraction of 5%-20% is prepared by adopting the way of reduced pressure distillation. By adjusting the pH in the seed preparation and seed growth stages, high-purity short-chain silica sol particles with controllable particle size can be effectively prepared, and the repeatability is high and the controllability is strong.

Description

Technical Field

[0001] This invention relates to a method for preparing a high-purity short-chain silica sol with controllable particle size for chemical mechanical polishing, belonging to the field of nanomaterial preparation. Background Technology

[0002] Silica sol, composed of nano-sized silica particles, is an important raw material and end product. Due to its unique properties, it is widely used in rubber, plastics, coatings, and semiconductor processing. Currently, chemical mechanical polishing (CMP) is the most advanced technology for planarization in semiconductor processing, and silica sol, as a major consumable, has a significant impact on the final planarization effect.

[0003] Particle shape is a crucial factor affecting polishing performance. During polishing and grinding, spherical silica particles roll, resulting in a low coefficient of friction and a slow polishing rate. Simultaneously, the high specific surface area of ​​spherical particles leads to a high silanol content, making them more prone to adhering to the equipment and causing scratches.

[0004] Increasing the length of the particle chain can effectively alleviate the above situation.

[0005] CN102390837A employs a seed growth process, generating and growing seed crystals under alkaline conditions to prepare non-spherical particles with a diameter of 30–50 nm. However, the resulting particles have a narrow range of diameter variation, limiting their application in polishing scenarios. CN101402829A and CN101626979A add calcium and magnesium salts to an active silica solution to prepare potato-shaped and elongated particles to increase particle chain length. However, CMP has extremely stringent requirements for metal impurities, which can diffuse into silicon wafers or electronic devices, ultimately leading to short circuits and severely impacting product yield. Improving the purity of silica sol is a common concern in the industry. Summary of the Invention

[0006] To address the aforementioned problems, this invention innovatively proposes a method for preparing high-purity short-chain silica sol with controllable particle size. First, long-chain silica sol seed particles are prepared under acidic conditions. Then, the liquid environment of the system is adjusted and the pH is adjusted to achieve alkalinity. Alkoxysilane is added to grow the particles, thereby preparing high-purity short-chain silica sol with controllable particle size of 30-165 nm.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a high-purity short-chain silica sol with controllable particle size includes the following steps:

[0009] (1) Preparation of active polysilicic acid: Water glass was diluted with deionized water to a SiO2 content of 3-8% by mass, and then the aqueous solution was treated with cation exchange resin to control the pH value at 2-4 to obtain active silicic acid. Subsequently, the active silicic acid was alternately passed through anion and cation exchange resins to obtain active polysilicic acid with a low ion content;

[0010] (2) Seed preparation: At a certain temperature, the active polysilicic acid obtained in step (1) is stirred and reacted for a period of time to obtain silica sol seed particles;

[0011] (3) Preparation of initial silica sol: Take the seed crystals obtained in step (2), mix them with a certain proportion of organic solvent, and adjust the pH of the system to 9.5-11 using an alkaline catalyst to obtain the seed crystal growth substrate. Then, add a certain amount of seed crystal growth solution made of organic solvent and alkoxysilane dropwise to the seed crystal growth substrate, and add an alkaline catalyst to maintain the pH of the system. The reaction yields the initial silica sol.

[0012] (4) Vacuum distillation: The initial silica sol is diluted with water and distilled under reduced pressure to remove organic solvents and alkaline catalysts, resulting in a concentrated silica sol with a mass fraction of 5-20%.

[0013] In step (1), the cation exchange resin can be 001×4, 001×7 and 001×8 resin, and the anion exchange resin can be 201×4, 201×7 and 201×8 resin.

[0014] Preferably, in step (1), a low ion content means that the total metal ion content is less than 20 ppm;

[0015] Preferably, in step (2), the seed crystal preparation reaction temperature is 50-90℃, more preferably 60-70℃; and the stirring time is 1-8h.

[0016] Preferably, the organic solvent in step (3) is one or more of methanol, ethanol, propanol, isopropanol, acetonitrile, acetone, methyl ethyl ketone, diethyl ether, ethyl propyl ether, and cyclohexane; preferably, the organic solvent in the seed crystal growth substrate is the same as the organic solvent in the seed crystal growth solution.

[0017] The alkaline catalyst is selected from at least one of alkali metal hydroxides, ammonia, or organic amine compounds; preferably, the alkaline catalyst is selected from at least one of sodium hydroxide, potassium hydroxide, ammonia, triethanolamine, or tetramethylammonium hydroxide.

[0018] The seed growth substrate contains 1%-3% SiO2 by mass, 60%-80% organic solvent by mass, and 15%-35% water by mass.

[0019] The organic solvent in the seed crystal growth solution has a mass fraction of 0%-80%.

[0020] The alkoxysilane is one or more of tetramethoxysilane, tetraethoxysilane, or tetrapropoxysilane, preferably tetramethoxysilane;

[0021] The mass ratio of the seed growth substrate to the seed growth solution is 10:1-1:1, preferably 7.5:1-6.5:1;

[0022] The initial silica sol is prepared at a reaction temperature of 5-60℃, preferably 10-40℃; and / or, the seed growth solution is added dropwise to the seed growth substrate at a time of 0.1 min-70 min; the stirring speed is 200 r / min-1000 r / min.

[0023] Preferably, in step (4), the initial silica sol is first diluted with water to a mass fraction of 2-5%, and then heated to boiling under vacuum conditions of 5kPa-40kPa to remove the organic solvent.

[0024] The beneficial effects of this invention are as follows:

[0025] In this invention, during the preparation of high-purity short-chain silica sol, silica sol seed particles are first prepared under acidic conditions. The polysilicic acid solution flowing from the anion exchange column has small particle size and poor stability; therefore, it must be heated under acidic conditions to generate seed particles, otherwise the polysilicic acid solution easily gels. The restricted polymerization of active silicic acid under acidic conditions (limited polymerization rate and direction) is conducive to the generation of chain-like crystal nuclei, thus determining the initial morphology of the silica sol particles. Then, the seed particles with the determined morphology are effectively grown by mixing in an organic solvent and adjusting the pH of the system to alkaline, thereby obtaining short-chain silica sol. Directly adding a silicon source for seed growth without adjusting the liquid environment for seed growth easily leads to system abnormalities.

[0026] Compared to existing technologies, this invention innovatively proposes a method for preparing silica sol, which yields high-purity, short-chain silica sol with controllable particle size. This method is applicable to the chemical mechanical polishing process of semiconductor silicon wafers or electronic device crystals, offering advantages such as a high coefficient of friction, high polishing rate, and low polishing contamination. Attached Figure Description

[0027] Figure 1 (a) is a TEM image of the silica sol particles in Example 1 of the present invention.

[0028] Figure 1 (b) is a TEM image of the silica sol particles in Example 2 of the present invention.

[0029] Figure 1(c) is a TEM image of the silica sol particles in Example 3 of the present invention.

[0030] Figure 1 (d) is a TEM image of the silica sol particles in Example 4 of the present invention. Detailed Implementation

[0031] To better understand the technical solution of the present invention, the preparation method of the present invention will be further explained and illustrated below through more specific embodiments, but this does not constitute any limitation.

[0032] The main raw materials used in the following examples and comparative examples are as follows:

[0033]

[0034]

[0035] Detection method:

[0036] The appearance morphology and particle size distribution of the silica sol were characterized using TEM images taken with a JEOL JEM2100plus.

[0037] The concentration of metal ions was tested using an Agilent 5900 ICP-OES.

[0038] Example 1

[0039] 16.51 g of 28% SiO2 sodium silicate was diluted with 41.26 g of deionized water to obtain an 8% SiO2 sodium silicate aqueous solution. This solution was passed through a cation exchange column packed with 001×7 resin at a flow rate of 3 mL / min to obtain an active silicic acid solution with pH = 2.5. The active silicic acid solution was then passed through an anion exchange column packed with 201×7 resin and a cation exchange column packed with 001×7 resin at a flow rate of 8 mL / min, circulated three times, to obtain active polysilicic acid solution A.

[0040] Take 55.02g of solution A, stir and react at 50℃ for 8h, then cool to room temperature, add 88.72g of isopropanol to the solution, add ammonia to adjust the pH to 10.0 and mix well to obtain the seed crystal growth substrate.

[0041] At 20°C, 13.42 g of isopropanol and 8.84 g of tetramethoxysilane were added dropwise to the seed growth substrate using a peristaltic pump. The addition was completed in 70 min, and 0.5 g of ammonia was added every 15 min. The reaction was carried out at 20°C and 800 r / min for 3 h to obtain the initial silica sol.

[0042] After diluting the initial silica sol with water to a mass fraction of 3.9%, it was concentrated under reduced pressure at 10 kPa and 43 °C to approximately 20%, yielding the concentrated silica sol. At this point, a short-chain silica sol with a mass concentration of 20% was obtained.

[0043] Example 2

[0044] Take 8.17 g of sodium silicate with a SiO2 mass fraction of 28% and dilute it with 33.44 g of deionized water to obtain a sodium silicate aqueous solution with a SiO2 concentration of 5.5%. Pass this solution through a cation exchange column packed with 001×7 resin at a flow rate of 4 mL / min to obtain an active silicic acid solution with pH = 2. Pass the active silicic acid solution through an anion exchange column packed with 201×7 resin and a cation exchange column packed with 001×7 resin at a flow rate of 5 mL / min, and circulate it 3 times to obtain active polysilicic acid solution A.

[0045] Take 39.63g of solution A, stir and react at 60℃ for 1h, then cool to room temperature. Add 36.69g of methanol and 68.14g of acetonitrile to the solution, add ammonia to adjust the pH to 9.5 and mix well to obtain the seed growth substrate.

[0046] At 30°C, 21.77 g of tetramethoxysilane was added dropwise to the seed growth substrate using a peristaltic pump. The addition was completed in 50 min, and 0.5 g of ammonia was added every 12 min. The reaction was carried out at 30°C and 800 r / min for 3 h to obtain the initial silica sol.

[0047] After diluting the initial silica sol with water to a mass fraction of 4.4%, it was concentrated under reduced pressure at 10 kPa and 43 °C to approximately 20%, yielding the concentrated silica sol. At this point, a short-chain silica sol with a mass concentration of 20% was obtained.

[0048] Example 3

[0049] Take 6.23 g of sodium silicate with a SiO2 mass fraction of 28% and dilute it with 50.18 g of deionized water to obtain a sodium silicate aqueous solution with a SiO2 concentration of 3.0%. Pass this solution through a cation exchange column packed with 001×7 resin at a flow rate of 10 mL / min to obtain an active silicic acid solution with pH = 2.8. Pass the active silicic acid solution through an anion exchange column packed with 201×7 resin and a cation exchange column packed with 001×7 resin at a flow rate of 5 mL / min, and circulate it 3 times to obtain active polysilicic acid solution A.

[0050] Take 53.75g of solution A, stir and react at 70℃ for 4h, then cool to room temperature. Add 100.42g of isopropanol to the solution, add ammonia to adjust the pH to 11.0 and mix well to obtain the seed crystal growth substrate.

[0051] At 40°C, a uniformly mixed mixture of 6.85g isopropanol and 15.84g tetramethoxysilane was added dropwise to the seed crystal growth substrate using a peristaltic pump. The addition was completed in 20 minutes, and 0.5g ammonia was added every 5 minutes. The mixture was stirred at 40°C and 200r / min for 3 hours to obtain the initial silica sol.

[0052] After diluting the initial silica sol with water to a mass fraction of 3.68%, it was concentrated under reduced pressure at 10 kPa and 43 °C to approximately 20%, yielding the concentrated silica sol. This resulted in a short-chain silica sol with a mass concentration of 20%.

[0053] Example 4

[0054] Take 5.78 g of sodium silicate with a SiO2 mass fraction of 28% and dilute it with 23.60 g of deionized water to obtain a sodium silicate aqueous solution with a SiO2 concentration of 5.5%. Pass this solution through a cation exchange column packed with 001×7 resin at a flow rate of 12 mL / min to obtain an active silicic acid solution with pH = 4. Pass the active silicic acid solution through an anion exchange column packed with 201×7 resin and a cation exchange column packed with 001×7 resin at a flow rate of 5 mL / min, and circulate it 3 times to obtain active polysilicic acid solution A.

[0055] Take 27.98g of solution A, stir and react at 90℃ for 5h, then cool to room temperature. Add 41.56g of methanol and 77.19g of acetonitrile to the solution, add ammonia to adjust the pH to 10.9 and mix well to obtain the seed crystal growth substrate.

[0056] At 60°C, 9.42 g of a uniformly mixed organic solvent (a mixture with the same ratio as the organic solvent in solution A) and 12.17 g of tetramethoxysilane were added dropwise to the seed growth substrate using a peristaltic pump. The addition was completed in 5 min, and 0.5 g of ammonia was added every 1 min. The reaction was carried out at 60°C and 1000 r / min for 1.5 h to obtain the initial silica sol.

[0057] After diluting the initial silica sol with water to a mass fraction of 2.79%, it was concentrated under reduced pressure at 10 kPa and 43 °C to approximately 20%, yielding the concentrated silica sol. At this point, a short-chain silica sol with a mass concentration of 20% was obtained.

[0058] Comparative Example 1

[0059] The active polysilicic acid solution A was obtained using the same method as in Example 3.

[0060] Take 53.75g of solution A, add 100.42g of isopropanol to the solution, add ammonia to adjust the pH to 11.0 and mix well to obtain the seed growth substrate.

[0061] At 40°C, a uniformly mixed mixture of 6.85g isopropanol and 15.84g tetramethoxysilane was added dropwise to the seed crystal growth substrate using a peristaltic pump. The addition was completed in 20 minutes, and 0.5g ammonia was added every 5 minutes. The mixture was stirred at 40°C and 200r / min for 3 hours to obtain the initial silica sol.

[0062] The resulting silica sol exhibits particle aggregation, with micron-sized particles visible to the naked eye adhering to the beaker wall or depositing at the bottom of the beaker.

[0063] Comparative Example 2

[0064] The active polysilicic acid solution A was obtained using the same method as in Example 3.

[0065] Take 53.75 g of solution A, stir and react at 70℃ for 4 h, then cool to room temperature. Add 100.42 g of isopropanol to this solution to obtain the seed growth substrate. At 40℃, use a peristaltic pump to dropwise add a well-mixed mixture of 6.85 g of isopropanol and 15.84 g of tetramethoxysilane to the seed growth substrate, completing the addition over 20 min. Add 0.5 g of ammonia water every 5 min, and stir at 40℃ and 200 r / min for 3 h to obtain the initial silica sol. The obtained silica sol exhibits gelation.

[0066] Comparative Example 3

[0067] Silica sol was prepared according to the method described in Example 1 of patent CN102390837A.

[0068] Comparative Example 4

[0069] Silica sol was prepared according to the method described in Example 1 of patent CN101402829A.

[0070] Table 1 provides the particle size information for each embodiment and comparative example. Due to anomalies observed in Comparative Example 1 and Comparative Example 2, particle size data cannot be presented. As shown in Table 1, by adjusting the conditions for preparing seed crystals under acidic conditions, this patent can control the particle size within the range of 30-165 nm, achieving controllable particle size. In contrast, the particles obtained in the comparative examples have smaller particle sizes and a relatively narrower range of variation.

[0071] Table 1. Particle size (nm) of each silica sol

[0072]

[0073] Table 2 shows some of the metal impurities in each embodiment and comparative example. The metal impurity content of this patent is relatively low, while the content of some metal ions in comparative examples 3 and 4 is relatively high due to the limitations of the production process.

[0074] Comparative Example 3, prepared according to patent CN102390837A, used potassium carbonate to adjust the pH of the system and activated silicic acid to promote particle growth, resulting in a higher content of potassium and sodium ions in the final product. Comparative Example 4, prepared according to patent CN101402829A, used calcium chloride to control particle morphology and sodium hydroxide to adjust the pH of the system, resulting in a higher content of calcium and sodium ions in the final product, affecting its purity and limiting its application in semiconductor CMP.

[0075] Table 2. Metal impurity content (ppm) of various silica sols

[0076] Example 1 5 <1 <1 <1 <1 <1 <1 Example 2 4 <1 <1 <1 <1 <1 <1 Example 3 5 <1 <1 <1 <1 <1 <1 Example 4 2 <1 <1 <1 <1 <1 <1 Comparative Example 3 124 633 2 <1 3 8 11 Comparative Example 4 550 30 10 7 14 1350 22

[0077] Figure 1 TEM images of Embodiments 1, 2, 3, and 4 of the present invention are provided, respectively corresponding to... Figure 1 The figures a, b, c, and d are shown in the diagram. As can be seen from the figure, all particles in the examples are short-chain in shape, but exhibit different particle sizes. The difference between Comparative Example 1 and the examples lies in whether, after obtaining the active polysilicic acid, it is heated and stirred under acidic conditions to prepare seed crystals. Without the step of obtaining seed crystals under acidic conditions, after adjusting the pH to alkaline, the excessively high concentration of active silicic acid will undergo nucleation, leading to particle agglomeration. The difference between Comparative Example 2 and the examples lies in whether, after obtaining seed crystals under acidic conditions, a catalyst is added to adjust the pH to alkaline. Directly adding a silicon source under acidic conditions will lead to gelation.

[0078] Although the present invention has been described in detail through the preferred embodiments described above, it should be understood that the above description should not be considered as a limitation of the present invention. Those skilled in the art will understand that modifications or adjustments can be made to the present invention based on the teachings of this specification. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing a high-purity short-chain silica sol with controllable particle size, characterized in that, It includes the following steps: (1) Preparation of active polysilicic acid: Water glass was diluted with deionized water and then treated with cation exchange resin to control the pH value to acidic to obtain active silicic acid; then, the active silicic acid was purified to obtain active polysilicic acid with low ion content. (2) Seed preparation: The active polysilicic acid obtained in step (1) is stirred and reacted at 50-90℃ for a period of time to obtain silica sol seed particles; (3) Preparation of initial silica sol: Take the seed crystals obtained in step (2), mix them with organic solvent, add an alkaline catalyst to adjust the pH of the system to 9.5~11, and obtain the seed crystal growth base solution; then, add the seed crystal growth solution made of organic solvent and alkoxysilane dropwise to the seed crystal growth base solution, and add an alkaline catalyst to maintain the pH of the system stable, and the reaction yields the initial silica sol. (4) Vacuum distillation: Dilute the initial silica sol with water to remove organic solvents and alkaline catalysts to obtain concentrated silica sol.

2. The preparation method according to claim 1, characterized in that, In step (1), the water glass is diluted with deionized water to a SiO2 mass fraction of 3-8%; and / or, the pH value is controlled at 2-4.

3. The preparation method according to claim 1, characterized in that, In step (2), the reaction temperature is 60-70℃ and the stirring time is 1-8h.

4. The preparation method according to claim 1, characterized in that, The organic solvent in step (3) is one or more of methanol, ethanol, propanol, isopropanol, acetonitrile, acetone, methyl ethyl ketone, diethyl ether, ethyl propyl ether, and cyclohexane.

5. The preparation method according to claim 1, characterized in that, The alkaline catalyst mentioned in step (3) is selected from at least one of alkali metal hydroxides, ammonia, or organic amine compounds.

6. The preparation method according to claim 5, characterized in that, In step (3), the alkaline catalyst is selected from at least one of sodium hydroxide, potassium hydroxide, ammonia, triethanolamine or tetramethylammonium hydroxide.

7. The preparation method according to any one of claims 1-6, characterized in that, In step (3), the mass fraction of SiO2 in the seed growth substrate is 1%-3%, the mass fraction of organic solvent is 60%-80%, and the mass fraction of water is 15%-35%.

8. The preparation method according to claim 1, characterized in that, The organic solvent mass fraction in the seed growth solution described in step (3) is 0%-80%.

9. The preparation method according to any one of claims 1-6, characterized in that, The alkoxysilane mentioned in step (3) is one or more of tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

10. The preparation method according to any one of claims 1-6, characterized in that, In step (3), the initial silica sol is prepared at a reaction temperature of 5-60℃; and / or, the seed growth solution is added dropwise to the seed growth substrate at a time of 0.1 min-70 min.

11. The preparation method according to claim 1, characterized in that, In step (4), the initial silica sol is first diluted with water to a mass fraction of 2-5%, and then the organic solvent is removed under vacuum conditions of 5kPa-40kPa.

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