Ultrahigh-purity silicon dioxide sol as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of ultra-pure silicon dioxide sol. The preparation method comprises the following steps: 1) mixing water, an organic solvent and an organic base catalyst to obtain mother liquor; 2) under stirring, continuously adding an alkoxy silane solution into the mother liquor in the step 1) for reaction, stopping feeding when the pH value of the system is lower than 7, and then supplementing an organic base catalyst into the system to enable the pH value to be higher than 7; (3) continuing to add an alkoxy silane solution into the system in the step (2), supplementing an organic base catalyst to maintain the pH value of the system to be higher than 7 in the feeding process of the alkoxy silane solution, and ending the reaction after the feeding of the alkoxy silane solution is completed, so as to prepare initial silica sol; and 4) curing the initial silica sol to obtain the ultra-pure silica sol. The prepared ultra-pure silicon dioxide sol product has the advantages of high purity, excellent monodispersity, ideal morphology and accurate regulation and control of surface silicon hydroxyl.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor material preparation technology, specifically relating to an ultra-high purity silica sol with tunable surface silanol groups, its preparation method, and its application. Background Technology

[0002] In semiconductor chip manufacturing processes, chemical mechanical polishing (CMP) is a crucial step in achieving global planarization of the wafer surface, and its performance directly affects device performance and chip yield. As the core abrasive in CMP polishing slurries, the physicochemical properties of silica sol, such as particle size, morphology, particle size distribution, and surface chemical state, have a decisive impact on polishing rate, surface roughness, and defect control. Especially at advanced process nodes, the multilayering and increasing structural complexity of wafer surface materials place more refined and diverse demands on polishing processes.

[0003] In CMP (Chemical Polishing), a balance must be struck between efficient material removal and low damage in terms of abrasive particle size and morphology. Studies have shown that increasing the primary particle size or constructing a chain-like structure helps improve material removal rates and reduces particle agglomeration due to the decrease in specific surface area, facilitating subsequent cleaning. However, excessively large sizes or excessively long chain-like structures can easily introduce surface scratches and microscopic defects. Therefore, an ideal abrasive should maintain a certain structural length while possessing controllable unit size and a narrow particle size distribution to achieve a balance between high polishing efficiency and high surface quality.

[0004] Furthermore, the surface properties of silica sol, especially the density of surface silanol groups (Si-OH), significantly affect polishing performance. Silanol groups directly influence the dispersion stability of particles in the polishing slurry, the interaction mechanism with the wafer surface, and the extent of polishing chemical reactions. Excessively high silanol density may lead to increased agglomeration or excessive chemical reactivity, introducing surface contamination and defects; while insufficient density may weaken the polishing rate and surface modification capabilities. Therefore, achieving precise control of the surface silanol content has become an urgent goal to meet the diverse requirements of CMP processes.

[0005] Currently, traditional methods for preparing silica sol (such as...) The traditional method (e.g., the first step) lacks flexibility in controlling particle size and morphology, and the product uniformity is poor. While the multi-step growth method can increase the size, the process is complex and prone to secondary nucleation and agglomeration, affecting monodispersity. More importantly, existing processes have limited means to actively control the surface silanol groups, often relying on surface modification or additives. This is not only cumbersome but also prone to introducing impurities such as metals, affecting product purity and process stability, making it difficult to meet the stringent requirements of semiconductor-grade ultra-high purity materials.

[0006] Therefore, developing a method for preparing silica sol that can simultaneously achieve high purity, excellent monodispersity, ideal morphology, and precise controllability of surface silanol groups has become crucial for advancing high-end semiconductor CMP technology. This invention aims to address the aforementioned technical bottlenecks by proposing an innovative synthesis strategy to achieve synergistic control over the structure and surface properties of silica sol. Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to provide a method for preparing ultra-high purity silica sol. This method uses an organic base as a catalyst and, through solvent ratio control and a silanol activation-directional polycondensation process, prepares an ultra-high purity silica sol rich in surface silanol hydroxyl content. The initial silica sol is then aged to produce an ultra-high purity silica sol with precisely controllable surface silanol hydroxyl content.

[0008] Another objective of this invention is to provide an ultra-high purity silica sol product prepared by the aforementioned method, which can simultaneously achieve high purity, excellent monodispersity, ideal morphology, and precise controllability of surface silanol groups.

[0009] Another object of the present invention is to provide an application of the ultra-high purity silica sol product prepared by the aforementioned method in polishing slurry.

[0010] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a method for preparing ultra-high purity silica sol, comprising the following steps:

[0012] 1) Mix water, organic solvent, and organic base catalyst to obtain mother liquor;

[0013] 2) While stirring, continuously add alkoxysilane solution to the mother liquor from step 1) to carry out the reaction. Stop adding the material when the pH of the system is lower than 7. Then add an organic base catalyst to the system to make the pH higher than 7.

[0014] 3) Continue to add alkoxysilane solution to the system in step 2). During the addition of alkoxysilane solution, simultaneously add organic base catalyst to maintain the pH value of the system above 7. After the addition of alkoxysilane solution is completed, the reaction is ended to obtain the initial silica sol.

[0015] 4) Initially, the silica sol is aged to obtain ultra-high purity silica sol.

[0016] In one specific implementation, the mass ratio of water to organic solvent in step 1) is 0.5 to 1.5:1, for example including but not limited to 0.5:1, 0.7:1, 0.9:1, 1.1:1, 1.3:1, 1.5:1, preferably 0.9 to 1.1:1.

[0017] In one specific implementation, the organic solvent in step 1) is one or more of methanol, ethanol, isopropanol, glycerol, acetone, diethyl ether, tetrahydrofuran, methyl ethyl ketone, N,N-dimethylformamide, etc., preferably methanol or ethanol.

[0018] In one specific implementation, the organic base catalyst in step 1) is an organic amine, selected from one or more of methylamine, dimethylamine, ethylenediamine, aniline, triethylamine, diethanolamine, triethanolamine, tetramethylammonium hydroxide, tetramethylguanidine, etc., preferably one or more of diethanolamine, triethanolamine, and tetramethylguanidine, more preferably diethanolamine.

[0019] In one specific implementation, the pH of the mother liquor in step 1) is 9 to 12, for example, including but not limited to 9, 10, 11, and 12, preferably 10 to 11;

[0020] Optionally, the pH of the mother liquor can be adjusted by the amount of organic base catalyst added.

[0021] In one specific implementation, the alkoxysilane in step 2) is one or more of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, preferably tetramethoxysilane.

[0022] In one specific implementation, the alkoxysilane solution in step 2) is a mixed solution of alkoxysilane and an organic solvent, wherein the mass ratio of the alkoxysilane to the organic solvent is 1 to 5:1, for example, including but not limited to 1:1, 2:1, 3:1, 4:1, and 5:1. The range of selectable organic solvents refers to that described in step 1), and the two can be the same or different.

[0023] Optionally, the alkoxysilane solution is fed continuously, preferably by dropwise addition.

[0024] In one specific implementation, the stirring speed in step 2) is 200 to 400 r / min, for example, including but not limited to 200 r / min, 250 r / min, 300 r / min, 350 r / min, and 400 r / min, preferably 250 to 300 r / min.

[0025] In one specific implementation, the reaction in step 2) is carried out at a temperature of 25 to 70°C, for example, including but not limited to 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, and 70°C, preferably 40 to 60°C.

[0026] In one specific implementation, the addition of the alkoxysilane solution in step 2) is stopped when the pH of the system is below 7, preferably with a pH below 7 and above 6, such as including but not limited to 6.3, 6.6, and 6.9.

[0027] In one specific implementation, step 2) involves adding an organic base catalyst to the system to make the pH higher than 7, preferably 8 to 12, for example including but not limited to 8, 9, 10, 11, and 12, preferably 10 to 11.

[0028] In one specific implementation, during step 3) of feeding the alkoxysilane solution, an organic base catalyst is simultaneously added to maintain the pH value of the system above 7, preferably 8 to 12, such as including but not limited to 8, 9, 10, 11, and 12, preferably 10 to 11.

[0029] Optionally, both the alkoxysilane solution and the organic base catalyst are fed continuously, preferably dropwise. For example, the alkoxysilane solution is added dropwise while maintaining the pH value using an alkaline catalyst. In a specific embodiment, the ripening in step 4) is Ostwald ripening, with an operating temperature of 90°C to 250°C, including but not limited to 90°C, 130°C, 170°C, 210°C, and 250°C, preferably 120°C to 160°C; an operating pressure of 0.5 to 3 MPa, including but not limited to 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, and 3 MPa, preferably 1.5 to 2 MPa; and a ripening time of 2 to 4 hours, including but not limited to 2 hours, 2.5 hours, 3 hours, 3.5 hours, and 4 hours.

[0030] Secondly, the present invention provides an ultra-high purity silica sol.

[0031] The ultra-high purity silica sol described in this invention is prepared by the aforementioned preparation method.

[0032] The ultra-high purity silica sol has a solid content of 4.5–10.5 wt%.

[0033] The density of silanol hydroxyl groups on the surface of the ultra-high purity silica sol is 2-6 per nm. 2 .

[0034] The secondary particle size (nm) of the ultra-high purity silica sol ranges from approximately 50 to 125 nm.

[0035] The particle size distribution (PDI) of the ultra-high purity silica sol ranges from 0.01 to 0.12.

[0036] The total metal impurity content of the ultra-high purity silica sol is <1 ppm.

[0037] Due to factors such as raw material purity, production equipment and environment, and process flow, small amounts of metal impurities are inevitably present in current silica sols. These impurities typically include Na, K, Li, Fe, Cu, Ni, Cr, Zn, Al, Ca, and Mg. Semiconductor-grade silica sols need to reach electronic grade, which has strict requirements on the content of metal impurities. For example, the general industry standard is that the total metal impurity content in high-purity silica sols is less than 100 ppm, and the total metal impurity content in ultra-high-purity silica sols is less than 1 ppm. This invention meets the standard for ultra-high-purity silica sols.

[0038] Thirdly, the present invention also provides an application of the ultra-high purity silica sol prepared by the aforementioned preparation method in a polishing slurry.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1) Using weakly alkaline, low-volatility organic bases (such as amines) as catalysts overcomes the disadvantages of poor operating environment and high volatility of traditional ammonia catalysts, making the pH of the reaction system more stable and significantly improving the uniformity and distribution control of particle size.

[0041] 2) By adjusting the solvent ratio and using a silanol activation-directional polycondensation process, ultra-high purity silica sol with abundant surface silanol content is obtained. Then, under certain conditions, it is matured, causing the surface silanol content to condense and decrease. The surface silanol content is precisely controlled within a certain range (2-6 silanols / nm). 2 This allows the prepared silica abrasive to balance polishing rate and surface quality defects, meeting the needs of different polishing application scenarios. Attached Figure Description

[0042] Figure 1 The image shows a TEM image of the silica sol particles prepared in Example 1.

[0043] Figure 2 TEM image of silica sol particles prepared for Comparative Example 1. Detailed Implementation

[0044] To better understand the technical solution of the present invention, the preparation method of the present invention will be further described below through more specific embodiments, but these do not constitute any limitation.

[0045] It should be noted that the endpoints and any values ​​of the ranges disclosed in this specification are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0046] This application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0048] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0049] The main raw materials used in the following examples and comparative examples are shown in Table 1 below:

[0050] Table 1

[0051]

[0052]

[0053] The main detection methods used in the following examples and comparative examples are as follows:

[0054] The primary particle size of silica sol particles is determined by formula 2727 / S. bet The calculation yields S. bet The specific surface area is obtained by the BET specific surface area method; the secondary particle size of the silica sol particles was obtained by the Malvern particle size analyzer Zetasizer Nano ZS90.

[0055] The surface silanol content was characterized by titration: using an automatic titration potentiometer, standard alkali solution was used for titration, and the amount of alkali consumed to titrate the suspension from pH 4 to 9 was measured to calculate the hydroxyl content. The formula for calculating the surface silanol density is [(V1-V0)*C*N]. A ] / (m*S BET *1018 ), where V1 and V0 are the volumes of NaOH consumed by the sample and blank, respectively, C is the concentration of the NaOH standard solution, and N A Let m be Avogadro's constant, and m be the mass of the sample.

[0056] The solid content test method refers to HG / T 2521-2008 Industrial Silica Sol.

[0057] The morphology of the silica sol particles was characterized using a JEM-F200 TEM from Nippon Electron.

[0058] Metallic impurities were characterized using an Agilent 7900 ICP-MS, with the test method conforming to GB / T 30903-2014.

[0059] Example 1

[0060] Mix 180g of deionized water and 180g of methanol evenly to obtain a mixed solution. Add a certain amount of diethanolamine to make the pH 10.5 to obtain the mother liquor.

[0061] Mix 200g of tetramethoxysilane and 200g of methanol, stir well, and use as a base solution. At 40℃, slowly add the base solution dropwise to the mother liquor to carry out the reaction, while turning on the top stirrer at a speed of 200r / min. Add the solution dropwise until the pH reaches 6.5, and then add a certain amount of diethanolamine to make the pH 10. Then, add the base solution dropwise while maintaining the pH at 10 to obtain the initial silica sol.

[0062] Then, Ostwald curing was carried out at an operating temperature of 120℃ and an operating pressure of 2MPa for 2 hours to prepare an ultra-high purity silica sol with a surface silanol density of 5.29 hydroxyl groups / nm. 2 Total metal impurities are less than 1 ppm.

[0063] Example 2

[0064] Mix 90g of deionized water and 180g of ethanol evenly to obtain a mixed solution. Add a certain amount of triethanolamine to make the pH 10 to obtain the mother liquor.

[0065] Mix 200g of tetramethoxysilane and 100g of ethanol and stir well to obtain a base solution. At 25°C, slowly add the base solution to the mother liquor to carry out the reaction while turning on the top stirrer at a speed of 250r / min. Add the solution until the pH reaches 6.5, and then add a certain amount of triethanolamine to make the pH 11. Then, add the base solution while adding triethanolamine dropwise to maintain the pH at 11, thus obtaining the initial silica sol.

[0066] Then, Ostwald curing was carried out at an operating temperature of 140℃ and an operating pressure of 1.5MPa for 2.5 hours to prepare ultra-high purity silica sol with a surface silanol density of 5.07 hydroxyl groups / nm. 2 Total metal impurities are less than 1 ppm.

[0067] Example 3

[0068] Mix 135g of deionized water and 180g of isopropanol evenly to obtain a mixed solution. Add a certain amount of tetramethylammonium hydroxide to make the pH 11 to obtain the mother liquor.

[0069] Mix 200g of tetraethoxysilane and 66g of isopropanol, stir well and use as a base solution. At 40℃, slowly add the base solution dropwise to the mother liquor to carry out the reaction, while turning on the top stirrer at a speed of 300r / min. Add the solution dropwise until the pH reaches 6.5, and then add a certain amount of tetramethylammonium hydroxide to make the pH 12. Then, while adding the base solution, add tetramethylammonium hydroxide dropwise to maintain the pH at 12, and obtain the initial silica sol.

[0070] Then, Ostwald curing was carried out at an operating temperature of 160℃ and an operating pressure of 1.2MPa for 3 hours to prepare ultra-high purity silica sol with a surface silanol density of 4.32 hydroxyl groups / nm. 2 Total metal impurities are less than 1 ppm.

[0071] Example 4

[0072] Mix 225g of deionized water and 180g of isopropanol evenly to obtain a mixed solution. Add a certain amount of ethylenediamine to make the pH 12 to obtain the mother liquor.

[0073] Mix 200g of tetrapropoxysilane and 50g of isopropanol, stir well and use as a base solution. At 55℃, slowly add the base solution dropwise to the mother liquor to carry out the reaction, while turning on the top stirrer at a speed of 350r / min. Add the solution dropwise until the pH reaches 6.5, and then add a certain amount of ethylenediamine to make the pH 9. Then, add the base solution dropwise while maintaining the pH at 9 to obtain the initial silica sol.

[0074] Then, Ostwald curing was carried out at an operating temperature of 250℃ and an operating pressure of 0.5MPa for 3.5 hours to prepare ultra-high purity silica sol with a surface silanol density of 3.05 hydroxyl groups / nm. 2 Total metal impurities are less than 1 ppm.

[0075] Example 5

[0076] Mix 270g of deionized water and 180g of methanol evenly to obtain a mixed solution. Add a certain amount of tetramethylguanidine to make the pH 9 to obtain the mother liquor.

[0077] Mix 200g of tetrabutoxysilane and 50g of methanol, stir well and use as a base solution. At 70℃, slowly add the base solution dropwise to the mother liquor to carry out the reaction, while turning on the top stirrer at a speed of 400r / min. Add the solution dropwise until the pH reaches 6.5, and then add a certain amount of tetramethylguanidine to make the pH 8. Then, add the base solution dropwise while maintaining the pH at 8 to obtain the initial silica sol.

[0078] Then, Ostwald curing was carried out at an operating temperature of 100℃ and an operating pressure of 3MPa for 4 hours to prepare an ultra-high purity silica sol with a surface silanol density of 2.61 hydroxyl groups / nm. 2 Total metal impurities are less than 1 ppm.

[0079] Comparative Example 1

[0080] Silica sol was prepared according to the method in Example 1, except that ammonia was used as the catalyst, while other operations and conditions remained unchanged, resulting in an ultra-high purity silica sol with a surface silanol density of 3.86 hydroxyl groups / nm. 2 The total metal impurities are less than 1 ppm, and the size and size distribution of silica particles are uneven.

[0081] Comparative Example 2

[0082] Silica sol was prepared according to the method in Example 1, except that the initial silica sol was not subjected to Ostwald curing, while other operations and conditions remained unchanged, resulting in an ultra-high purity silica sol with a surface silanol density of 7.20 hydroxyl groups / nm. 2 Total metal impurities are less than 1 ppm.

[0083] The basic characteristic parameters of the silica sol prepared in the embodiments of the present invention are shown in Table 2 below:

[0084] Table 2

[0085] Secondary particle size (nm) Particle size distribution (PDI) Solid content (wt%) Example 1 115.5 0.016 10.4 Example 2 79.63 0.034 9.8 Example 3 72.55 0.021 9.3 Example 4 53.26 0.025 6.5 Example 5 89.42 0.043 4.9 Comparative Example 1 65.48 0.118 10.4 Comparative Example 2 122.70 0.022 10.4

[0086] The only difference between Comparative Example 1 and Example 1 is the preparation method; Comparative Example 1 uses ammonia as a catalyst instead of diethanolamine. Furthermore, the silica sol particles prepared in Example 1 and Comparative Example 1 were characterized by TEM, as shown below. Figure 1 and Figure 2As shown, the particles prepared in Example 1 are uniformly distributed and have good monodispersity, while the sample prepared in Comparative Example 1 has secondary small particles and uneven particle size distribution. Furthermore, the particles prepared in Examples 1-5 have a wide secondary particle size range, from a minimum of 53.26 nm to a maximum of 115.5 nm. Silica sol products with specific secondary particle sizes and PDI can be selected according to the specific technical requirements of different polishing applications.

[0087] The only difference between Comparative Example 2 and Example 1 is the preparation method; the silica sol prepared in Comparative Example 2 was not subjected to Ostwald curing. The comparison shows that Example 1, compared to Comparative Example 2, has a significantly lower surface silanol content. This indicates that Ostwald curing converts connected hydroxyl groups to isolated hydroxyl groups and promotes condensation between surface silanol groups, thereby significantly reducing the surface silanol density.

[0088] 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. It can be applied to various fields suitable for the present invention, and other modifications can be easily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A method for preparing ultra-high purity silica sol, characterized in that the steps include... include: 1) Mix water, organic solvent, and organic base catalyst to obtain mother liquor; 2) While stirring, continuously add alkoxysilane solution to the mother liquor from step 1) to carry out the reaction. Stop adding the material when the pH of the system is lower than 7. Then add an organic base catalyst to the system to make the pH higher than 7. 3) Continue to add alkoxysilane solution to the system in step 2). During the addition of alkoxysilane solution, simultaneously add organic base catalyst to maintain the pH value of the system above 7. After the addition of alkoxysilane solution is completed, the reaction is ended to obtain the initial silica sol. 4) Initially, the silica sol is aged to obtain ultra-high purity silica sol.

2. The preparation method according to claim 1, characterized in that, Step 1) The mass ratio of water to organic solvent is 0.5–1.5:1; and / or, The organic solvent in step 1) is one or more of methanol, ethanol, isopropanol, glycerol, acetone, diethyl ether, tetrahydrofuran, methyl ethyl ketone, and N,N-dimethylformamide, preferably methanol or ethanol.

3. The preparation method according to claim 1 or 2, characterized in that, Step 1) The organic base catalyst is an organic amine, selected from one or more of methylamine, dimethylamine, ethylenediamine, aniline, triethylamine, diethanolamine, triethanolamine, tetramethylammonium hydroxide, and tetramethylguanidine, preferably one or more of diethanolamine, triethanolamine, and tetramethylguanidine, more preferably diethanolamine; and / or, The pH of the mother liquor in step 1) is 9-12, preferably 10-11; Optionally, the pH of the mother liquor can be adjusted by the amount of organic base catalyst added.

4. The preparation method according to any one of claims 1-3, characterized in that, Step 2) The alkoxysilane is one or more of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, preferably tetramethoxysilane; and / or, Step 2) The alkoxysilane solution is a mixed solution of alkoxysilane and organic solvent, wherein the mass ratio of alkoxysilane to organic solvent is 1 to 5:1; Optionally, the alkoxysilane solution is fed continuously, preferably by dropwise addition.

5. The preparation method according to any one of claims 1-4, characterized in that, The stirring in step 2) is performed at a speed of 200–400 r / min, preferably 250–300 r / min; and / or, The reaction described in step 2) is carried out at a temperature of 25–70°C; and / or, Step 2) The addition of the alkoxysilane solution is stopped when the pH of the system is below 7, preferably below 7 and above 6; and / or, Step 2) involves adding an organic base catalyst to the system to make the pH higher than 7, preferably 8-12.

6. The preparation method according to any one of claims 1-5, characterized in that, Step 3) During the feeding of the alkoxysilane solution, an organic base catalyst is simultaneously added to maintain the pH value of the system above 7, preferably pH 8-12; Optionally, both the alkoxysilane solution and the organic base catalyst are fed continuously, preferably by dropwise addition.

7. The preparation method according to any one of claims 1-6, characterized in that, The curing process in step 4) involves an operating temperature of 90℃ to 250℃, preferably 120℃ to 160℃; an operating pressure of 0.5 to 3 MPa; and a curing time of 2 to 4 hours.

8. An ultra-high purity silica sol, prepared by the preparation method according to any one of claims 1-7; Optionally, the ultra-high purity silica sol has a solid content of 4.5–10.5 wt%. Optionally, the density of silanol groups on the surface of the ultra-high purity silica sol is 2 to 6 per nm. 2 ; Optionally, the secondary particle size of the ultra-high purity silica sol is 50–125 nm; Optionally, the particle size distribution of the ultra-high purity silica sol is 0.01 to 0.

12. Optionally, the total metal impurity content of the ultra-high purity silica sol is <1 ppm.

9. The ultra-high purity silica sol according to claim 8, characterized in that, The density of silanol hydroxyl groups on the surface of the ultra-high purity silica sol is 2-6 per nm. 2 ; and / or, The total metal impurity content of the ultra-high purity silica sol is <1 ppm.

10. The application of the ultra-high purity silica sol prepared by the preparation method according to any one of claims 1-7 or the ultra-high purity silica sol according to claim 8 or 9 in a polishing slurry.

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