A method for preparing long-term stable ultra-high purity silica sol

Abstract

This invention discloses a method for preparing long-term stable ultra-high purity silica sol. The method involves preparing silica sol using an alkoxide method, followed by forced cyclic desolvation. By adding conjugate acid-base ionic dispersants, the pH and thermal stability of the silica sol are maintained. The prepared silica sol is then modified and subjected to high-pressure aging to ultimately obtain an ultra-high purity silica sol with a mass fraction of over 20%, a primary particle size between 30-150 nm, a secondary particle size between 50-350 nm, and an association degree between 1.7-2.3. The silica sol has a metal ion content of less than 1 ppm, a loss of less than 5% during preparation, and exhibits excellent polishing performance.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation, specifically relating to a method for preparing long-term stable ultra-high purity silica sol using the sol-gel method and its application in semiconductor CMP polishing. Background Technology

[0002] Silica sol is a dispersion of nano-sized silica particles in water or a solvent. Because the SiO2 in silica sol contains a large amount of water and hydroxyl groups, silica sol can also be described as mSiO2·nH2O. There are different methods for preparing silica sol, the most common being ion exchange, one-step hydrolysis of silica powder, and the sol-gel method.

[0003] The ion exchange method involves ion-exchanging sodium silicate to create active silicic acid, which is then added to an aqueous solution containing seed particles (previously pH-adjusted with NaOH) under heating conditions to promote particle growth. This method yields particles with a relatively dense structure, but it introduces a large number of metal ions during preparation, making it unsuitable for use as an abrasive or polishing agent for semiconductors. The elemental silicon hydrolysis method involves hydrolyzing silicon under alkaline conditions to generate silicon dioxide. This method can produce high-purity, dense silicon dioxide, but silicon residue remains during preparation, easily causing scratches on the wafer surface during polishing, thus making it unsuitable for use as an abrasive or polishing agent for semiconductors. The sol-gel method is currently a relatively mature process for producing ultra-high purity silica sol. Under the action of an alkaline catalyst, alkoxysilanes react with water to generate silicon dioxide and alcohols. Considering the impact of organic solvents on subsequent wafer production, water is needed to displace the organic solvents. Furthermore, considering transportation and storage factors, the silica sol also needs to be concentrated to obtain a high-concentration aqueous silica sol. The purity of silica sol prepared by the sol-gel method is directly related to the purity of the raw materials and production equipment.

[0004] Throughout the silica sol concentration and replacement process, dispersants are required to reduce silica sol loss. Commonly used dispersants include alkali metal salt dispersants. For example, Japanese Patent Application Publication No. 37-9961 discloses a method for adding a monovalent cation-soluble metal salt (alkali metal salt) as a dispersant to obtain a silica sol with a high concentration of 30% or more. According to this method, the low viscosity of the silica sol can be maintained and the concentration can be increased. However, since the silica sol contains metal impurities derived from alkali metal salts, it is impossible to produce high-purity silica sol. Other dispersants include organic acids such as malic acid, citric acid, oxalic acid, and benzoic acid, and organic acid salts such as ammonium benzoate, triammonium citrate, and ammonium adipate. For example, patent CN101495409A discloses a method using citric acid, triammonium citrate, diammonium citrate, ammonium benzoate, and tetramethylammonium citrate as dispersants, and Japanese patent JPA1008015943 discloses a method using citric acid, ammonium citrate, and tetramethylammonium citrate as dispersants. According to these methods, the high purity of the silica sol can be maintained. However, due to the ionization of organic acids or organic acid salts, the pH of the silica sol changes after long-term storage, and the charge distribution on the silica sol surface changes, causing surface attraction to exceed repulsion. This leads to the aggregation of silica sol nanoparticles, forming a gel. Furthermore, during the later preparation of the polishing solution, a sudden change in the system pH can occur, resulting in silica sol flocculation and ultimately affecting the polishing quality. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for preparing long-term stable ultra-high purity silica sol. This invention innovatively proposes using two organic acids and organic salts that can form conjugate acid-base pairs as dispersants to maintain the stability of the silica sol during concentration and displacement processes; furthermore, epoxy modification and high-pressure aging improve the surface quality of the silica sol particles, thereby enhancing the polishing effect. The silica sol prepared by this method also exhibits minimal scale-up effect and good batch-to-batch stability of particle morphology.

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

[0007] Another object of the present invention is to provide the application of such ultra-high purity silica sol in CMP.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a long-term stable ultra-high purity silica sol includes the following steps:

[0010] 1) Preparation of solution A: Mix the organic solvent, ultrapure water and alkaline catalyst in a certain proportion until homogeneous;

[0011] 2) Preparation of solution B: Mix the organic solvent and alkoxysilane thoroughly;

[0012] 3) Initial silica sol preparation: At a certain temperature, solution B is added to solution A, and the mixture is stirred and reacted to obtain the initial silica sol;

[0013] 4) Silica sol modification: A certain amount of epoxy-containing substances are introduced into the obtained initial silica sol to modify the silica sol;

[0014] 5) The silica sol is subjected to alcohol removal treatment to obtain silica sol with a silica solid content of 20%-30%;

[0015] 6) Silica sol aging: The de-alcoholized silica sol is subjected to high-temperature aging treatment in an autoclave;

[0016] 7) Filtration: The aged silica sol is filtered to remove large particles, resulting in ultra-high purity silica sol.

[0017] In one specific implementation, the organic solvent mentioned in steps 1) and 2) is one or more of methanol, ethanol, propanol, isopropanol, acetonitrile, acetone, methyl ethyl ketone, diethyl ether, ethyl propyl ether, etc.; the organic solvent is preferably methanol;

[0018] In one specific embodiment, the alkaline catalyst in step 1) is selected from at least one of alkali metal hydroxides, ammonia, organic amines, or guanidine compounds; preferably, the alkali metal hydroxide is selected from at least one of potassium hydroxide, sodium hydroxide, and lithium hydroxide; the organic amine is selected from at least one of ethylenediamine, triethanolamine, and tetramethylamine hydroxide; and the guanidine compound is selected from at least one of tetramethylguanidine, trimethylguanidine, and guanidine carbonate; more preferably, the alkaline catalyst is ammonia (preferably with an ammonia concentration of 25%).

[0019] In one specific implementation, in step 1), the contents of the three substances in solution A are as follows: 50%-80% by mass of organic solvent, 18%-49% by mass of ultrapure water, and 1%-2% by mass of alkaline catalyst.

[0020] In one specific implementation, in step 2), the alkoxysilane is one or more of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, preferably tetramethoxysilane. The volume ratio of the organic solvent to the alkoxysilane is 1:3-3:1, preferably between 1:3 and 1:1.

[0021] In one specific implementation, in step 3), the molar ratio of alkoxysilane to water is less than 1, preferably, the molar ratio of alkoxysilane to water is between 1:4 and 1:10;

[0022] In one specific implementation, in step 3), the initial silica sol is prepared by the following steps: the dropping rate of liquid B to liquid A is 1 ml / min-5 ml / min, preferably 1 ml / min-2 ml / min; the stirring speed is 200 r / min-1000 r / min; the reaction temperature is between 5-50℃, for example, including but not limited to 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, and 50℃, preferably 5-30℃; and the reaction time is 0.5 h-3 h, preferably 2 h. The initial silica sol is prepared by this step.

[0023] In one specific implementation, the modification of the silica sol in step 4) involves epoxy-containing substances including one or more of 1,4-epoxybutane, propylene oxide, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, hydrogenated bisphenol A type epoxy resin, hydroxymethyl bisphenol A type epoxy resin, 3-glycidyl etheroxypropyltrimethoxysilane, and 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, preferably 3-glycidyl etheroxypropyltrimethoxysilane and / or 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, more preferably 3-glycidyl etheroxypropyltrimethoxysilane; the addition amount is 10 to 5000 ppm of the mass of silica, preferably 500 to 1000 ppm.

[0024] In one specific implementation, step 5) of the silica sol de-alcoholization treatment employs forced circulation evaporation to concentrate and replace the initial alcohol-based silica sol with an aqueous silica sol containing 20-30% by mass. The forced circulation evaporation method can refer to existing technologies well-known to those skilled in the art, for example, a heating temperature of 80-100℃ and a vacuum degree of 10-100 kPa, preferably 10-20 kPa. During the concentration and replacement process, the stability of the silica sol deteriorates as the solid content increases. Therefore, some water needs to be added before replacement to increase the stability of the silica sol. The mass ratio of silica sol to added water is 1:10-3:1, preferably 1:1-1:5. Simultaneously, a dispersant is added to improve the yield and stability of the silica sol. The ultimate goal is to reduce the solvent content in the silica sol to below 200 ppm, preferably below 100 ppm, while the silica sol loss is less than 5%, preferably less than 2%. The dispersant is a combination of organic acid and organic acid salt that can form a conjugate acid-base pair. The organic acid is selected from one or more of citric acid, malic acid, oxalic acid, benzoic acid, maleic acid, tartaric acid, glutaric acid, salicylic acid, lactic acid, malonic acid, adipic acid, pimelic acid, succinic acid, phthalic acid, glyceric acid, and glycolic acid. The corresponding organic acid salt is one or more of ammonium citrate, ammonium malate, ammonium oxalate, ammonium benzoate, ammonium maleate, ammonium tartrate, ammonium glutarate, ammonium salicylate, ammonium lactate, ammonium malonate, ammonium adipic acid, ammonium pimelic acid, ammonium succinate, ammonium phthalate, ammonium glycerate, and ammonium glycolate. The amount of organic acid added is 10-3000 ppm by mass of silica, preferably 10-1000 ppm, and the amount of organic acid salt added is 10-3000 ppm, preferably 10-1000 ppm.

[0025] In one specific implementation, during step 6) of silica sol aging, an autoclave is used to age the silica sol. The aging temperature is set to 100-180℃, preferably 100-140℃; the aging time is set to 3-5h; and the stirring speed of the agitator is set to 300-800r / min, preferably 500r / min.

[0026] In one specific implementation, the filtration in step 7) adopts a two-stage filtration method, and the preferred material is PFA. The filtration accuracy of the first stage filter is 2-5µm, and the filtration accuracy of the second stage filter is 0.2-0.5µm.

[0027] In one specific implementation, the morphology of the obtained silica sol particles is mostly peanut-shaped, with a primary particle size between 30-150 nm, a secondary particle size between 50-350 nm, an association degree of 1.7-2.3, a total metal ion content of less than 1 ppm, and a SiO2 loss of less than 5% during the entire preparation process.

[0028] In another aspect, the present invention provides the application of the aforementioned ultra-high purity silica sol in chemical mechanical polishing (CMP).

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) This invention creatively proposes for the first time that by adding a conjugate acid-base pair during the preparation of silica sol by the alkoxide method, the silica sol can be made to have long-term stability, reduce silica sol loss and improve the transport and storage capacity of silica sol.

[0031] 2) Compared with the traditional alkoxide method, which uses acid or alkali dispersants and causes silica sol loss due to pH changes during later application or long-term storage, this invention adds conjugated acid and alkali ions to make the silica sol have long-term stability and a certain pH buffering capacity.

[0032] 3) This invention improves the surface properties of silica sol particles through epoxy modification and high-pressure aging, thereby increasing the polishing rate of silica sol on the wafer surface. Detailed Implementation

[0033] The preparation method of the present invention will be further explained and illustrated below through more specific embodiments, but these do not constitute any limitation.

[0034] Detection method:

[0035] The secondary particle size of the silica sol particles was measured using a Malvern Zetasizer Nano ZS90 particle size analyzer, and the primary particle size was determined using the BET surface area test method to obtain the specific surface area S. bet 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.

[0036] The concentration of metal ions was measured using an Agilent 7900 ICP-MS, and the results are shown in Table 2.

[0037] The solid content test method refers to HGT 2521-2008 Industrial Silica Sol. After the solid content test is completed, the solid content loss of silica sol is calculated by calculating the total mass of silica in the initial silica sol and the filtered silica sol. The results are shown in Table 1.

[0038] Stability of silica sol: The particle size and pH of silica sol were measured twice every 5 days by placing the silica sol in a 60℃ oven. The results are shown in Table 1.

[0039] Polishing slurry preparation: Silica sol is used as the abrasive. Before use, it is diluted with pure water to a solid content of 6%. Additives polypropylene glycol, glycerin, glycerol, and hydroxyethyl cellulose are added to improve the polishing rate. The addition amounts are 800, 300, 500, and 1000 ppm of the total solution mass, respectively. After preparation, a certain amount of KOH is used to adjust the pH of the solution (the final pH is between 10 and 11). See Table 3 for details.

[0040] The polishing performance of the silica sol was tested under the following conditions: an EBAR polishing machine was used, an IC1000 polishing pad was selected, the polishing pressure was 5 Psi, a tetraethyl orthosilicate (TEOS) silica substrate (hereinafter referred to as "TEOS substrate"; manufacturer: Silicon Valley Microelectronic, Inc.; film thickness: 10000 Å) was used for polishing, the polishing time was 2 minutes, the upper plate rotation speed was 100 r / min, the lower plate rotation speed was 120 r / min, and the flow rate was 300 ml / min. The silica thickness on the wafer surface after polishing was measured using an OLYNPUS U-P4RE film thickness gauge, and the polishing rate was calculated as follows: Polishing rate = {(thickness before polishing) - (thickness after polishing)} / (processing time), where the unit of thickness is Å. o The processing time is measured in minutes, and the removal rate is measured in (A). o / minute). It should be noted that 1A o =0.1nm. Polishing performance results are shown in Table 3.

[0041] Example 1

[0042] 321.3 g of methanol, 133.11 g of water, and 4.69 g of 25% ammonia solution were mixed thoroughly to form solution A. 225.15 ml of tetramethoxysilane and 78.2 ml of methanol were mixed thoroughly to form solution B. Solution B was added to solution A using a peristaltic pump at a feed rate of 1 ml / min. After feeding, the mixture was reacted at 20 °C and 300 r / min for 3 h to obtain the initial silica sol.

[0043] Next, 500 ppm of KH-560 (diluted to a 1% methanol solution using methanol to facilitate dispersion) equivalent to the mass of silica in the silica sol was added. Citric acid and ammonium citrate (200 ppm relative to the mass of silica) were added as dispersants to the silica sol, and 2256.56 g of pure water was added to the silica sol at a ratio of approximately 1:3 (silica sol mass: water mass). The mixture was stirred at 500 rpm for ten minutes, followed by vacuum heating and concentration at 10 kPa and 100 °C until the silica sol solid content was approximately 20%. The resulting silica sol was then placed in a high-pressure reactor for high-temperature aging at 100 °C, with a stirring speed of 500 rpm for 5 hours. Finally, large particles were filtered out using 5 μm and 0.3 μm filter cartridges for secondary filtration. At this point, an ultra-high purity silica sol with a mass concentration of 20%, a primary particle size of 43 nm, a secondary particle size of 86 nm, an association degree of 2.0, and a total metal ion content of less than 1 ppm was obtained. The stability test results are shown in Table 1, and the content of some metal impurities is shown in Table 2. The obtained silica sol was used for CMP; the polishing conditions and polishing results are shown in Table 3.

[0044] Example 2

[0045] Solution A was prepared by mixing 78.5 g of isopropanol, 75.39 g of water, and 3.14 g of 25% ammonia solution until homogeneous. Solution B was prepared by mixing 62.32 ml of tetramethoxysilane with 60 ml of isopropanol until homogeneous. Solution B was added to solution A using a peristaltic pump at a feed rate of 1.5 ml / min. The reaction was carried out at 25 °C and 300 r / min for 3 h to obtain the initial silica sol. Then, 500 ppm of KH-560 (diluted to a 1% isopropanol solution with isopropanol to facilitate dispersion) was added to the silica sol. Then, malic acid and ammonium malate (200 ppm relative to silica mass) were added to the silica sol as dispersants. 2681.8 g of pure water was added to the silica sol at a silica sol:water mass ratio of approximately 1:10. The mixture was stirred at 500 rpm for ten minutes, followed by vacuum heating and concentration at 10 kPa and 100 °C until the silica sol solid content was approximately 20%. The resulting silica sol was then placed in a high-pressure reactor for high-temperature aging at 100 °C, with a stirring speed of 500 rpm and an aging time of 5 hours. Large particles were then removed by two-stage filtration using 5 μm and 0.3 μm filter cartridges. This yielded an ultra-high purity silica sol with a mass concentration of 20%, a primary particle size of 42 nm, a secondary particle size of 85 nm, an association degree of 2.02, and a total metal ion content of less than 1 ppm. The stability test results are shown in Table 1, and the content of some metal impurities is shown in Table 2. The obtained silica sol was used for CMP. The polishing conditions and polishing results are shown in Table 3.

[0046] Example 3

[0047] 201.77 g of acetone, 127.79 g of water, and 6.73 g of 25% ammonia solution were mixed thoroughly to form solution A. 175.81 ml of tetramethoxysilane and 87.90 ml of acetone were mixed thoroughly to form solution B. Solution B was added to solution A using a peristaltic pump at a feed rate of 2 ml / min. The reaction was carried out at 20°C and 300 r / min for 2.5 h to obtain the initial silica sol. Then, 750 ppm of KH-560 (diluted to a 1% acetone solution using acetone for dispersion) was added to the silica sol. Then, benzoic acid and ammonium benzoate, at a mass ratio of 400 ppm relative to silica, were added to the silica sol as dispersants. 2342.28 g of pure water was added to the silica sol at a mass ratio of approximately 1:4 (silica sol mass: water mass). The mixture was stirred at 500 rpm for ten minutes, followed by vacuum heating and concentration at 10 kPa and 100 °C until the silica sol solid content was approximately 20%. The resulting silica sol was then placed in a high-pressure reactor for high-temperature aging at 120 °C, with a stirring speed of 500 rpm and an aging time of 4 hours. Large particles were then removed by two-stage filtration using 5 μm and 0.3 μm filter cartridges. This yielded an ultra-high purity silica sol with a mass concentration of 20%, a primary particle size of 40 nm, a secondary particle size of 81 nm, an association degree of 2.03, and a total metal ion content of less than 1 ppm. The stability test results are shown in Table 1, and the content of some metal impurities is shown in Table 2. The obtained silica sol was used for CMP. The polishing conditions and polishing results are shown in Table 3.

[0048] Example 4

[0049] 205.33 g of acetonitrile, 82.13 g of water, and 5.87 g of 25% ammonia solution were mixed and stirred until homogeneous to form solution A. 135.59 ml of tetramethoxysilane and 90.39 ml of acetonitrile were mixed until homogeneous to form solution B. Solution B was added to solution A using a peristaltic pump at a feed rate of 1 ml / min. The reaction was carried out at 20 °C and 300 rpm for 3 h to obtain the initial silica sol. Then, 750 ppm of KH-78 (diluted to a 1% acetonitrile solution using acetonitrile to facilitate dispersion) was added to the silica sol. Next, 400 ppm of oxalic acid and ammonium oxalate (relative to the mass of silica) were added to the silica sol as dispersants, and 1501.35 g of pure water was added to the silica sol at a ratio of approximately 1:3 (silica sol mass: water mass). The mixture was stirred at 500 rpm for ten minutes. The silica sol was then concentrated and replaced under reduced pressure at 10 kPa and 100 °C until the solid content was approximately 20%. The resulting silica sol was then placed in a high-pressure reactor for high-temperature aging at 140 °C, with a stirring speed of 500 r / min and an aging time of 3 hours. Large particles were then removed by two-stage filtration using 5 μm and 0.3 μm filter cartridges. This yielded an ultra-high purity silica sol with a mass concentration of 20%, a primary particle size of 41 nm, a secondary particle size of 81 nm, an association degree of 1.98, and a total metal ion content of less than 1 ppm. The stability test results are shown in Table 1, and the content of some metal impurities is shown in Table 2. The obtained silica sol was then used for CMP (Chemical Motion Processing), and the polishing conditions and results are shown in Table 3.

[0050] Comparative Example 1

[0051] In Comparative Example 1, based on Example 1, citric acid was used as the dispersant, and no epoxy modification or high-pressure aging was performed.

[0052] Solution A was prepared by mixing 321.3 g of methanol, 133.11 g of water, and 4.69 g of 25% ammonia solution. Solution B was prepared by mixing 225.15 ml of tetramethoxysilane and 78.2 ml of methanol. Solution B was added to solution A using a peristaltic pump at a feed rate of 1 ml / min. After feeding, the mixture was reacted at 20 °C and 300 rpm for 3 h to obtain the initial silica sol. Citric acid at 400 ppm (by mass of silica) was added to the silica sol as a dispersant. Then, 2256.56 g of pure water was added to the silica sol, and the mixture was stirred at 500 rpm for 10 minutes. Subsequently, the mixture was concentrated and replaced under reduced pressure at 10 kPa and 100 °C until the silica sol solid content was approximately 20%. Finally, the mixture was filtered through two filters (5 μm and 0.3 μm) to remove large particles. At this point, an ultra-high purity silica sol with a mass concentration of 20%, a primary particle size of 43 nm, a secondary particle size of 86 nm, an association degree of 2.0, and a total metal ion content of less than 1 ppm was obtained. The stability test results are shown in Table 1, and the content of some metal impurities is shown in Table 2. The obtained silica sol was used for CMP; the polishing conditions and polishing results are shown in Table 3.

[0053] Comparative Example 2

[0054] In Comparative Example 2, based on Example 1, the difference was that high-pressure aging was not performed. The stability test results of the obtained silica sol are shown in Table 1, and the content of some metal impurities is shown in Table 2. The obtained silica sol was used for CMP, and the polishing conditions and polishing results are shown in Table 3.

[0055] Comparative Example 3

[0056] In Comparative Example 3, based on Example 1, the difference was the absence of KH-560. The stability test results of the obtained silica sol are shown in Table 1, and the content of some metal impurities is shown in Table 2. The obtained silica sol was used for CMP; the polishing conditions and polishing results are shown in Table 3.

[0057] Table 1. Changes in particle size and pH of silica sol after storage in a 60℃ oven for a certain period of time.

[0058]

[0059] Table 2 shows the content (ppb) of some metal impurities in the silica sol prepared in each example.

[0060] Na K Cr Cu Fe Ni Ti Example 1 78 86 15 11 87 25 10 Example 2 75 79 13 14 88 17 12 Example 3 79 77 12 13 79 16 11 Example 4 80 81 11 11 83 19 9 Comparative Example 1 65 71 8 16 77 25 8 Comparative Example 2 66 68 12 12 84 17 9 Comparative Example 3 69 68 10 17 86 18 11

[0061] Table 3 Polishing conditions and polishing results

[0062]

[0063]

[0064] In Comparative Example 1, without the addition of a conjugate acid-base dispersant and only organic acid, the silica sol loss reached 9%. Furthermore, during storage in a 60°C oven, the particle size and pH of the silica sol increased continuously over time, with the particle size increasing by more than 10% after ten days of storage, indicating poor silica sol stability. In contrast, Examples 1-4, which incorporated a conjugate acid-base pair as a dispersant, showed a loss of no more than 5%, and no significant changes in particle size and pH after prolonged storage. Example 4, with 400 ppm of oxalic acid and ammonium oxalate as dispersants, demonstrated the best effect, with an overall loss of only 1.7%, and no significant change in particle size after 15 days of storage in a 60°C oven.

[0065] Referring to Table 3 for polishing conditions and results, from Examples 1-4, it can be seen that after epoxy modification and high-pressure aging treatment, the silica sol exhibited a high polishing rate on the TEOS wafer surface, at 500-600 Å. o The polishing rate was approximately 610 Å / min, with the silica sol synthesized using the method in Example 4 exhibiting the highest polishing rate of 610 Å / min. o / min. Therefore, the optimal amount and type of epoxy modifier added is 750 ppm of KH-78, and the optimal aging temperature is 140℃. In contrast, in Comparative Example 1, the polishing slurry prepared with any epoxy modifier and no aging treatment resulted in the lowest polishing rate, only 300A. o / min, the polishing rate of the polishing slurry prepared with only epoxy modification in Comparative Example 2 was 420A. o The polishing rate of the polishing slurry prepared with silica sol that underwent only high-pressure aging in Comparative Example 3 was 481A / min. o / min. Therefore, based on the polishing results of the comparative example, both epoxy modification and high-pressure aging can have a certain impact on the polishing rate of silica sol, with the presence or absence of high-pressure aging having a greater impact on the polishing rate of silica sol.

[0066] In summary, the silica sol prepared by the method of this invention has a metal ion content of less than 1 ppm, a mass fraction of more than 20%, and a silica sol loss of less than 5%, which reduces costs. It also has long-term stability and a certain pH buffering capacity, and exhibits excellent polishing performance.

[0067] 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 long-term stable ultra-high purity silica sol, comprising the following steps: 1) Preparation of solution A: Mix the organic solvent, ultrapure water and alkaline catalyst in a certain proportion until homogeneous; 2. Preparation of Solution B: Mix the organic solvent and alkoxysilane thoroughly; 3. Preparation of initial silica sol: At a certain temperature, solution B is added to solution A, and the mixture is stirred and reacted to obtain the initial silica sol; 4. Silica sol modification: A certain amount of epoxy-containing substances are introduced into the obtained initial silica sol to modify the silica sol; 5. The silica sol is subjected to a de-alcoholization treatment to obtain a silica sol with a silica solid content of 20%-30%; 6. Silica sol aging: The de-alcoholized silica sol is subjected to high-temperature aging treatment in an autoclave; 7. Filtration: The aged silica sol is filtered to remove large particles, resulting in ultra-high purity silica sol.

2. The method according to claim 1, wherein, In step 1), the contents of the three substances in solution A are as follows: organic solvent mass fraction is 50%-80%, ultrapure water mass fraction is 18%-49%, and alkaline catalyst mass fraction is 1%-2%.

3. The method according to claim 2, wherein, In step 1), the alkaline catalyst is selected from at least one of alkali metal hydroxide, ammonia, organic amines, or guanidine compounds; the alkali metal hydroxide is selected from at least one of potassium hydroxide, sodium hydroxide, and lithium hydroxide; the organic amine is selected from at least one of ethylenediamine, triethanolamine, and tetramethylamine hydroxide; and the guanidine compound is selected from at least one of tetramethylguanidine, trimethylguanidine, and guanidine carbonate.

4. The method according to claim 3, wherein, In step 1), the alkaline catalyst is ammonia water with a concentration of 25%.

5. The method according to claim 1, wherein, In step 2), the alkoxysilane is one or more of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane; The volume ratio of organic solvent to alkoxysilane is 1:3-3:

1.

6. The method according to claim 5, wherein, In step 2), the volume ratio of the organic solvent to the alkoxysilane is between 1:3 and 1:

1.

7. The method according to claim 1, wherein, In step 3), the molar ratio of alkoxysilane to water is less than 1.

8. The method according to claim 7, wherein, In step 3), the molar ratio of alkoxysilane to water is between 1:4 and 1:

10.

9. The method according to claim 7, wherein, In step 3), the stirring speed is 200 r / min-1000 r / min, the reaction temperature is between 5-50℃, and the reaction time is 0.5h-3h.

10. The method according to claim 1, wherein, In step 4), the substances containing epoxy groups include one or more of the following: 1,4-epoxybutane, propylene oxide, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, hydrogenated bisphenol A type epoxy resin, hydroxymethyl bisphenol A type epoxy resin, 3-glycidyl etheroxypropyltrimethoxysilane, and 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane. The amount added is 10 to 5000 ppm of the mass of silica.

11. The method according to claim 10, wherein, In step 4), the substance containing an epoxy group is 3-glycidyl etheroxypropyltrimethoxysilane and / or 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane; The amount added is 500 to 1000 ppm of silica by mass.

12. The method according to claim 1, wherein, In step 5), a dispersant is added during the silica sol de-alcoholization process. The dispersant is a combination of organic acids and organic acid salts that can form conjugate acid-base pairs. The organic acid is selected from one or more of citric acid, malic acid, oxalic acid, benzoic acid, maleic acid, tartaric acid, glutaric acid, salicylic acid, lactic acid, malonic acid, adipic acid, pimelic acid, succinic acid, phthalic acid, glyceric acid, and glycolic acid. The corresponding organic acid salt is one or more of ammonium citrate, ammonium malate, ammonium oxalate, ammonium benzoate, ammonium maleate, ammonium tartrate, ammonium glutarate, ammonium salicylate, ammonium lactate, ammonium malonate, ammonium adipic acid, ammonium pimelic acid, ammonium succinate, ammonium phthalate, ammonium glycerate, and ammonium glycolate. The amount of organic acid added is 10-3000 ppm of the mass of silica, and the amount of organic acid salt added is 10-3000 ppm of the mass of silica.

13. The method according to claim 12, wherein, In step 5), the amount of organic acid added is 10-1000 ppm of the mass of silica, and the amount of organic acid salt added is 10-1000 ppm of the mass of silica.

14. The method according to claim 1, wherein, Step 6) During the silica sol aging process, the aging temperature is 100-180℃; the aging time is 3-5h.

15. The method according to claim 14, wherein, Step 6) During the aging process of silica sol, the aging temperature is 100-140℃.

16. The method according to any one of claims 1-7, wherein, The filtration in step 7) adopts a two-stage filtration method, where the filtration accuracy of the first stage is 2-5um and the filtration accuracy of the second stage is 0.2-0.5um.

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