High-hardness ultra-high-purity silica sol as well as preparation method and application thereof

Abstract

The invention discloses high-hardness ultra-high-purity silica sol as well as a preparation method and application thereof. The preparation method comprises the following steps: 1) preparing a solution A: mixing an organic solvent, ultrapure water and an acid catalyst, adding a certain amount of an additive, and uniformly mixing; 2) preparing a solution B: uniformly mixing an organic solvent and alkoxy silane; 3) preparation of initial silica sol: adding the solution B into the solution A at one time, uniformly stirring, transferring into a closed hydrothermal kettle, and heating for reaction to obtain the initial silica sol; 4) concentration and replacement: concentrating and replacing the initial silica sol into 20 wt% of water-based silica sol; and 5) filtering: filtering the water-based silica sol to remove large particles to obtain the ultra-high-purity silica sol. The method can be used for preparing the high-hardness ultra-high-purity silica sol.

Description

Technical Field

[0001] The present invention relates to a method for preparing silica sol by acid catalysis, and particularly to a high-hardness and ultra-high-purity silica sol and its preparation method and application. Background Art

[0002] A mixture in which nano-silica particles are stably dispersed in water or other solvent systems and have colloidal properties is called silica sol. Silica sol is widely used in fields such as papermaking, casting, and catalysts. Since the third industrial revolution, with the development of the Internet and information industries, chip manufacturing has become an important field for countries to compete for. Due to its excellent properties, silica sol has been introduced into the chemical mechanical planarization (CMP) process in the chip manufacturing field.

[0003] In the conventional method for preparing silica sol by acid-catalyzed sol-gel method, the raw material silicic acid mostly exists in the form of a network structure of oligomers after the reaction, and the final sample is gel-like. If the final sample is sol-like, substances need to be added during or after synthesis to maintain stability. For example, in patent CN115650244A, alkali catalysts such as ammonia water, potassium hydroxide, and triethylamine are added to the acidic raw material so that the acidic raw material forms silica particles rather than network-structured silicic acid oligomers during the later reaction, and its principle is the same as that of alkali catalysis. In addition, for example, in patent CN102391688A, in order to keep the acidic silica sol sample stable, stabilizers such as acrylic acid are added to the final silica sol sample. Moreover, due to acid catalysis causing silicic acid to exist in the form of a network structure of oligomers, the particle hardness of the sample is extremely low, and it basically cannot meet its application in the CMP polishing field. For the preparation of silica sol by alkali catalysis, for example, patent CN101495409A uses the sol-gel method to synthesize a high-purity silica sol sample, and the hardness of its particles is also lower than 2.5 GPa, resulting in an unsatisfactory polishing rate during the CMP process and not meeting the requirements of high polishing rate. Patent CN86100503A uses the elemental silicon method to synthesize silica sol with a particle size of 15 - 20 nm, and the hardness of its sample generally does not exceed 3.5 GPa. Moreover, due to the use of a large amount of strong alkali solution, a large amount of alkali metal ions are introduced, and the sample cannot meet the requirement of ultra-high purity, which limits its application in the downstream chip CMP process. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention proposes a high-hardness and ultra-high-purity silica sol and its preparation method and application.

[0005] First, the present invention innovatively proposes a method for preparing a high-hardness and ultra-high-purity silica sol. By changing the catalytic conditions in the sol-gel process, controlling the reaction temperature, reaction pressure, and reaction time in the reaction steps, and adding a certain amount of additives to form silica particles under acid catalysis and regulate the hardness of the silica sol particles, the preparation of a high-hardness and ultra-high-purity silica sol is realized, and the polishing rate of the silica sol in CMP is improved.

[0006] Another object of the present invention is to provide a high-hardness and ultra-high-purity silica sol product.

[0007] Another object of the present invention is to provide an application of the high-hardness and ultra-high-purity silica sol in chemical mechanical polishing.

[0008] A preparation method of a high-hardness and ultra-high-purity silica sol includes the following steps:

[0009] 1) Prepare solution A: Mix an organic solvent, ultrapure water, and an acid catalyst, and add a certain amount of an additive and mix evenly; the additive is one or more of polyacrylamide (PAM), poly(sulfobetaine methacrylate) (PSBMA), polyethylene glycol (PEG), polyvinyl alcohol (PVA), and polyvinylpyrrolidone (PVP);

[0010] 2) Prepare solution B: Mix an organic solvent and an alkoxysilane evenly;

[0011] 3) Prepare the initial silica sol: Add solution B to solution A at one time, stir evenly and then transfer to a closed hydrothermal autoclave, heat up and react to obtain the initial silica sol;

[0012] 4) Concentration and replacement: Concentrate and replace the initial silica sol with a 20 wt% aqueous silica sol;

[0013] 5) Filtration: Filter the aqueous silica sol to remove large particles to obtain an ultra-high-purity silica sol.

[0014] In a specific embodiment, in step 1), based on the total mass of the following substances being 100%, the raw material dosages are respectively: 60-70 wt% of an organic solvent (such as including but not limited to 60 wt%, 61 wt%, 62 wt%, 63 wt%, 64 wt%, 65 wt%, 66 wt%, 67 wt%, 68 wt%, 69 wt%, 70 wt%), 27-39 wt% of ultrapure water (such as including but not limited to 27 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%), and 1-3 wt% of an acid catalyst (such as including but not limited to 1 wt%, 2 wt%, 3 wt%);

[0015] Preferably, the dosage of the additive is 200-2000 ppm based on the mass of silicon dioxide, such as including but not limited to 200 ppm, 400 ppm, 600 ppm, 800 ppm, 1000 ppm, 1200 ppm, 1400 ppm, 1600 ppm, 1800 ppm, 2000 ppm, and preferably 200-1000 ppm.

[0016] In a specific embodiment, the acid catalyst is an organic acid and / or an inorganic acid;

[0017] Preferably, the organic acid is selected from at least any one of acetic acid, malonic acid, succinic acid, malic acid, and citric acid;

[0018] Preferably, the inorganic acid is selected from at least any one of hydrochloric acid, nitric acid, carbonic acid, and sulfuric acid.

[0019] Preferably, the acid catalyst is one or more of acetic acid, malic acid, or carbonic acid.

[0020] In a specific embodiment, the organic solvent is one or more of methanol, ethanol, and isopropanol. Preferably, the types of organic solvents in solution B are the same as those in solution A.

[0021] More preferably, the ultrapure water is deionized water with a resistivity ≥ 10 MΩ·cm, preferably deionized water with a resistivity ≥ 18.2 MΩ·cm.

[0022] In a specific embodiment, in step 2), the alkoxysilane is one or more of tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane;

[0023] Preferably, in step 2), the mass ratio of the organic solvent to the alkoxysilane is (0.2 - 1):1.

[0024] In a specific embodiment, in step 3), the mixing mass ratio of solution B to solution A is 1:(10 - 20).

[0025] In a specific embodiment, in step 3), the reaction conditions are: reaction temperature 140 - 220 °C, such as including but not limited to 140 °C, 160 °C, 180 °C, 200 °C, 220 °C, preferably 180 - 220 °C, reaction pressure 0.36 - 2.3 MPa(A), such as including but not limited to 1.0 MPa(A), 1.5 MPa(A), 2.0 MPa(A), preferably 1.0 - 2.3 MPa(A);

[0026] Preferably, the reaction residence time is 10 - 14 h, such as including but not limited to 10 h, 11 h, 12 h, 13 h, 14 h.

[0027] In a specific embodiment, in step 4), the concentration and replacement are carried out by heating while supplementing ultrapure water, evaporating to remove the solvent in the water, or by ultrafiltration, concentrating while supplementing ultrapure water until the content of the organic solvent in the silica sol is reduced to less than 200 ppm, preferably less than 100 ppm;

[0028] Preferably, the concentration replacement in step 4) is carried out by vacuum heating concentration or ultrafiltration membrane concentration, and the mass fraction of silica sol is concentrated to more than 20 wt%. The method of vacuum heating concentration can refer to the prior art and is well known to those skilled in the art. The equipment used for vacuum heating concentration can refer to common scraping evaporation, forced circulation evaporation or rectification in industry, and the equipment used for ultrafiltration membrane concentration can refer to common ultrafiltration membrane concentration devices in industry.

[0029] In a specific embodiment, the filtration accuracy in step 5) is 0.2 - 5 μm;

[0030] Preferably, the filtration uses a filter element made of PFA material for two - stage or three - stage filtration.

[0031] The present invention also provides a high - hardness and ultra - high - purity silica sol prepared by the method described above. The primary particle size of the particles in the silica sol is between 30 - 75 nm, the degree of association is between 1.7 - 2.3, the hardness is between 3.5 - 4 GPa, and the total metal ion content is less than 1 ppm.

[0032] The present invention also provides an application of the high - hardness and ultra - high - purity silica sol prepared by the method described above in chemical mechanical polishing.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1) The present invention creatively first proposes that in an acid - catalyzed reaction system, by changing the reaction mode, reaction temperature, reaction pressure and reaction time during the reaction stage, adding a certain amount of additives, the silica particles are formed under acid catalysis, and the hardness of the silica sol particles is adjusted, so as to achieve a high polishing rate of high - hardness and ultra - high - purity silica sol in the CMP field.

[0035] 2) Compared with traditional high - hardness silica sol, the present invention improves the purity of silica sol while ensuring the high hardness of silica sol particles, and realizes the stable application of silica sol in CMP in the IC field. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a transmission electron microscope image of the silica sol particles prepared in Example 1.

[0037] Figure 2 It is a transmission electron microscope image of the silica sol particles prepared in Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The following further illustrates the present invention through specific examples. The examples described in the present invention are only for the illustration of the present invention and do not limit the scope of the present invention.

[0039] The main raw material information used in the following examples and comparative examples is as follows:

[0040] Ultra-pure water, self-made by mili-q direct water purifier, 18.2 MΩ.cm;

[0041] Acetic acid, Suzhou Jingrui Chemical Co., Ltd., UP grade;

[0042] Malic acid, Suzhou Jingrui Chemical Co., Ltd., UP grade;

[0043] Carbonic acid, Suzhou Jingrui Chemical Co., Ltd., UP grade;

[0044] Methanol, Suzhou Jingrui Chemical Co., Ltd., UP grade;

[0045] Ethanol, Suzhou Jingrui Chemical Co., Ltd., UP grade;

[0046] Isopropanol, Suzhou Jingrui Chemical Co., Ltd., UP grade;

[0047] Tetramethoxysilane, Nantong Suojier, 99.5%;

[0048] Polyacrylamide (PAM), Suzhou Jingrui Chemical Co., Ltd., electronic grade;

[0049] Polysulfobetaine methacrylate (PSBMA), Sigma-Aldrich, product number 922390;

[0050] Polyvinyl alcohol (PVA), Suzhou Jingrui Chemical Co., Ltd., electronic grade;

[0051] Polyvinylpyrrolidone (PVP), Suzhou Jingrui Chemical Co., Ltd., electronic grade;

[0052] Other raw materials and reagents, if not otherwise specified, can be obtained through commercial channels.

[0053] The main detection methods involved in the following examples of the present invention are as follows:

[0054] The test method for solid content refers to HGT 2521-2008 industrial silica sol.

[0055] The secondary particle size of the silica sol particles is measured by a Malvern particle size analyzer Zetasizer Nano ZS90, and the primary particle size is obtained by the BET specific surface area test method to obtain the specific surface area S bet , and the primary particle size is 2727 / S bet . The degree of association is the ratio of the secondary particle size to the primary particle size.

[0056] The hardness of the silica sol particles is characterized by a nanoindentation instrument.

[0057] The concentration of metal ions is tested by Agilent 7900 ICP-MS.

[0058]

Example 1

[0059] Mix 140 g of methanol, 58 g of water, and 2 g of acetic acid, and add PSBMA with a concentration of 200 ppm relative to silica and mix evenly to obtain Solution A. Mix 5 g of methanol and 15 g of tetramethoxysilane (TMOS) evenly to obtain Solution B. Add Solution B to Solution A at one time, stir evenly, then transfer it to a hydrothermal autoclave and react at 140 °C and 0.36 MPa (A) for 10 h to obtain the initial silica sol. Then, carry out reduced-pressure heating and concentration at 10 KPa and 100 °C until it is concentrated to about 20% of the raw material volume to obtain the concentrated silica sol. Then, add ultrapure water while evaporating until the methanol content in the silica sol drops below 100 ppm, and then filter it twice with 5-μm and 0.3-μm filter elements to filter out large particles. At this time, a silica sol with a mass concentration of 20 wt%, a primary particle size of 35 nm, a secondary particle size of 70 nm, a particle hardness of 3.5 GPa, an association degree of 2, and a total metal ion content of less than 1 ppm is obtained. The content of some metal impurities is shown in Table 1.

[0060]

Example 2

[0061] Mix 120 g of ethanol, 78 g of water, and 2 g of malic acid, and then add PVA with a concentration of 600 ppm relative to silica and mix evenly to obtain Solution A. Mix 5 g of ethanol and 5 g of tetramethoxysilane (TMOS) evenly to obtain Solution B. Add Solution B to Solution A at one time, stir evenly, and then transfer it to a hydrothermal autoclave and react at 160 °C and 0.62 MPa (A) for 13 h to obtain the initial silica sol. Then, carry out reduced-pressure heating and concentration at 10 KPa and 100 °C until it is concentrated to about 20% of the raw material volume to obtain the concentrated silica sol. Then, add ultrapure water while evaporating until the ethanol content in the silica sol drops below 100 ppm, and then filter it twice with 5-μm and 0.3-μm filter elements to filter out large particles. At this time, a silica sol with a mass concentration of 20 wt%, a primary particle size of 30 nm, a secondary particle size of 58.5 nm, a particle hardness of 3.65 GPa, an association degree of 1.95, and a total metal ion content of less than 1 ppm is obtained. The content of some metal impurities is shown in Table 1.

[0062]

Example 3

[0063] Mix 130 g of propanol, 68 g of water, and 2 g of carbonic acid, and add PAM with a concentration of 1000 ppm relative to silica and mix evenly to obtain Solution A. Mix 3.125 g of propanol and 9.375 g of tetramethoxysilane (TMOS) evenly to obtain Solution B. Add Solution B to Solution A at one time, stir evenly, then transfer it to a hydrothermal autoclave and react at 180 °C and 1.0 MPa (A) for 12 h to obtain the initial silica sol. Then, carry out reduced-pressure heating and concentration at 10 Kpa and 100 °C until it is concentrated to about 20% of the original volume to obtain the concentrated silica sol. Then, add ultrapure water while evaporating until the content of propanol in the silica sol drops below 100 ppm, and then filter it twice with 5-μm and 0.3-μm filter elements to filter out large particles. At this time, a silica sol with a mass concentration of 20 wt%, a primary particle size of 40 nm, a secondary particle size of 78 nm, a particle hardness of 3.76 GPa, an association degree of 1.95, and a total metal ion content of less than 1 ppm is obtained. The contents of some metal impurities are shown in Table 1.

[0064]

Example 4

[0065] Mix 140 g of isopropanol, 56 g of water, and 4 g of acetic acid, and add PVP with a concentration of 1400 ppm relative to silica and mix evenly to obtain Solution A. Mix 6.7 g of isopropanol and 13.3 g of tetramethoxysilane (TMOS) evenly to obtain Solution B. Add Solution B to Solution A at one time, stir evenly, then transfer it to a hydrothermal autoclave and react at 200 °C and 1.56 MPa (A) for 11 h to obtain the initial silica sol. Then, carry out reduced-pressure heating and concentration at 10 Kpa and 100 °C until it is concentrated to about 20% of the original volume to obtain the concentrated silica sol. Then, add ultrapure water while evaporating until the content of isopropanol in the silica sol drops below 100 ppm, and then filter it twice with 5-μm and 0.3-μm filter elements to filter out large particles. At this time, a silica sol with a mass concentration of 20 wt%, a primary particle size of 30 nm, a secondary particle size of 66 nm, a particle hardness of 3.9 GPa, an association degree of 2.2, and a total metal ion content of less than 1 ppm is obtained. The contents of some metal impurities are shown in Table 1.

[0066]

Example 5

[0067] Mix 140 g of methanol, 54 g of water, and 6 g of acetic acid, and add PSBMA and PVA with a concentration of 1000 ppm each relative to silica, and mix them evenly to obtain Solution A. Mix 5 g of methanol and 15 g of tetramethoxysilane (TMOS) evenly to obtain Solution B. Add Solution B to Solution A at once, stir evenly, then transfer it to a hydrothermal reactor and react at 220 °C and 2.3 MPa (A) for 14 h to obtain the initial silica sol. Then, carry out reduced-pressure heating and concentration at 10 Kpa and 100 °C until it is concentrated to about 20% of the original volume to obtain the concentrated silica sol. Then, add ultrapure water while evaporating until the methanol content in the silica sol drops below 100 ppm, and then filter it twice with 5-μm and 0.3-μm filter elements to filter out large particles. At this time, a silica sol with a mass concentration of 20%, a primary particle size of 45 nm, a secondary particle size of 90 nm, a particle hardness of 4.0 GPa, an association degree of 2, and a total metal ion content of less than 1 ppm is obtained. The content of some metal impurities is shown in Table 1.

[0068]

Example 6

[0069] Mix 140 g of methanol, 56 g of water, and 4 g of malic acid, and add PAM and PVP with a concentration of 500 ppm each relative to silica, and mix them evenly to obtain Solution A. Mix 5 g of methanol and 15 g of tetrapropoxysilane evenly to obtain Solution B. Add Solution B to Solution A at once, stir evenly, then transfer it to a hydrothermal reactor and react at 200 °C and 1.56 MPa (A) for 11 h to obtain the initial silica sol. Then, carry out reduced-pressure heating and concentration at 10 Kpa and 100 °C until it is concentrated to about 20% of the original volume to obtain the concentrated silica sol. Then, add ultrapure water while evaporating until the methanol content in the silica sol drops below 100 ppm, and then filter it twice with 5-μm and 0.3-μm filter elements to filter out large particles. At this time, a silica sol with a mass concentration of 20 wt%, a primary particle size of 60 nm, a secondary particle size of 126 nm, a particle hardness of 3.88 GPa, an association degree of 2.1, and a total metal ion content of less than 1 ppm is obtained. The content of some metal impurities is shown in Table 1.

[0070]

Example 7

[0071] Mix 140 g of methanol, 56 g of water, and 4 g of carbonic acid, and add PSBMA, PVA, PVP, and PAM with a concentration of 500 ppm each relative to silica, and mix evenly to obtain Solution A. Mix 5 g of methanol and 15 g of tetraethoxysilane (TEOS) evenly to obtain Solution B. Add Solution B to Solution A at once, stir evenly, then transfer it to a hydrothermal reactor and react at 200 °C and 1.56 MPa (A) for 11 h to obtain the initial silica sol. Then, perform reduced-pressure heating and concentration at 10 KPa and 100 °C until it is concentrated to about 20% of the original volume to obtain the concentrated silica sol. Then, add ultrapure water while evaporating until the methanol content in the silica sol drops below 100 ppm, and then filter it through a 5-μm and a 0.3-μm filter element in series to remove large particles. At this time, a silica sol with a mass concentration of 20 wt%, a primary particle size of 45 nm, a secondary particle size of 78.75 nm, a particle hardness of 3.9 GPa, an association degree of 1.75, and a total metal ion content of less than 1 ppm is obtained. The content of some metal impurities is shown in Table 1.

[0072]

Comparative Example 1

[0073] Prepare the silica sol according to the scheme in Example 3, the difference is only that PAM is not added to Solution A.

[0074] After the reaction, concentrate and replace to obtain a silica sol with a mass concentration of 20 wt%, a primary particle size of 10 nm, a secondary particle size of 200 nm, a particle hardness of 0.6 GPa, an association degree of 20, and a total metal ion content of less than 1 ppm. The content of some metal impurities is shown in Table 1.

[0075]

Comparative Example 2

[0076] Prepare the silica sol according to the scheme in Example 1, the difference is only that the reaction conditions in the hydrothermal reactor are modified to: react at 25 °C and 0.003 MPa (A) for 2 h.

[0077] After the reaction, concentrate and replace to obtain a silica sol with a mass concentration of 20 wt%, a primary particle size of 15 nm, a secondary particle size of 330 nm, a particle hardness of 0.4 GPa, an association degree of 22, and a total metal ion content of less than 1 ppm. The content of some metal impurities is shown in Table 1.

[0078] Table 1. Content of some metal impurities in each silica sol (ppb)

[0079] Na K Cr Cu Fe Ni Ti Example 1 92 78 8 7 29 24 9 Example 2 85 69 11 9 24 16 8 Example 3 78 64 8 9 21 20 10 Example 4 89 76 11 10 20 23 11 Example 5 87 73 8 11 21 20 9 Example 6 90 78 10 10 25 23 10 Example 7 92 88 11 12 30 25 10 Comparative Example 1 93 81 10 9 24 22 8 Comparative Example 2 94 83 12 10 26 21 11

[0080] In addition, transmission electron microscope observations were respectively performed on the silica sol samples prepared in Example 1 and Comparative Example 1, as shown in Figure 1 、 Figure 2As shown. It can be seen from the figure that the silica sol sample of Example 1 presents a double-associated peanut-like structure, and the sample has excellent monodispersity, while the silica sol sample of Comparative Example 1 presents a multi-associated chain-like adhesion structure, and the sample gels after being placed for more than 24 hours.

[0081] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, several improvements and supplements can be made without departing from the method of the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of high-hardness ultra-high-purity silica sol, characterized in that, it includes the following steps: 1) Prepare solution A: Mix organic solvent, ultrapure water, and acid catalyst, and add a certain amount of additive and mix evenly; the additive is one or more of polyacrylamide, poly(sulfobetaine methacrylate), polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone; 2) Prepare solution B: Mix organic solvent and alkoxysilane evenly; 3) Prepare initial silica sol: Add solution B to solution A at one time, stir evenly and then transfer to a closed hydrothermal autoclave, heat up and react to obtain the initial silica sol; 4) Concentration and replacement: Concentrate and replace the initial silica sol into a 20wt% aqueous silica sol; 5) Filtration: Filter the aqueous silica sol to remove large particles to obtain ultra-high-purity silica sol.

2. The preparation method of high-hardness ultra-high-purity silica sol according to claim 1, characterized in that, in step 1), based on the total mass of the following substances being 100%, the raw material dosages are respectively: 60-70wt% organic solvent, 27-39wt% ultrapure water, 1-3wt% acid catalyst; Preferably, the dosage of the additive is 200-2000 ppm based on the mass of silicon dioxide, preferably 200-1000 ppm.

3. The preparation method of high-hardness ultra-high-purity silica sol according to claim 1 or 2, characterized in that, the acid catalyst is organic acid and / or inorganic acid; Preferably, the organic acid is selected from at least one of acetic acid, malonic acid, succinic acid, malic acid, and citric acid; Preferably, the inorganic acid is selected from at least one of hydrochloric acid, nitric acid, carbonic acid, and sulfuric acid.

4. The preparation method of high-hardness ultra-high-purity silica sol according to any one of claims 1-3, characterized in that, the organic solvent is one or more of methanol, ethanol, and isopropanol.

5. The preparation method of high-hardness ultra-high-purity silica sol according to any one of claims 1-4, characterized in that, in step 2), the alkoxysilane is one or more of tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane; Preferably, in step 2), the mass ratio of organic solvent to alkoxysilane is (0.2-1):

1.

6. The preparation method of high-hardness ultra-high-purity silica sol according to any one of claims 1-5, characterized in that, in step 3), the mixing mass ratio of solution B to solution A is 1:(10-20).

7. The preparation method of high-hardness ultra-high-purity silica sol according to any one of claims 1-6, characterized in that, in step 3), the reaction conditions are: reaction temperature 140-220 °C, preferably 180-220 °C, reaction pressure 0.36-2.3 MPaA, preferably 1.0-2.3 MPaA; Preferably, the reaction residence time is 10-14 h.

8. The preparation method of high-hardness ultra-high-purity silica sol according to any one of claims 1-7, characterized in that, In the concentration replacement in step 4), ultrapure water is supplemented while heating, the solvent in the water is evaporated, or an ultrafiltration method is adopted to concentrate while supplementing ultrapure water until the content of the organic solvent in the silica sol is reduced to less than 200 ppm, preferably less than 100 ppm. Preferably, the concentration replacement in step 4) adopts vacuum heating concentration or ultrafiltration membrane concentration to concentrate the mass fraction of the silica sol to more than 20 wt%.

9. The method for preparing a high-hardness and ultra-high-purity silica sol according to any one of claims 1-8, characterized in that the filtration accuracy in step 5) is 0.2-5 μm; Preferably, the filtration uses a filter element made of PFA material for two-stage or three-stage filtration.

10. A high-hardness and ultra-high-purity silica sol prepared by the method according to any one of claims 1-9, characterized in that the primary particle size of the particles in the silica sol is between 30-75 nm, the degree of association is between 1.7-2.3, the hardness is between 3.5-4 GPa, and the total content of metal ions is less than 1 ppm.

11. An application of the high-hardness and ultra-high-purity silica sol prepared by the method according to any one of claims 1-9 in chemical mechanical polishing.

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