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

Abstract

The invention relates to a preparation method of high-purity short-chain silicon dioxide sol with a controllable particle size. The preparation method comprises the following steps: firstly, preparing long-chain silica sol seed crystal particles by using active silicic acid under an acidic condition; adjusting the liquid environment of a seed crystal system and adjusting the pH value to be alkaline, and adding alkoxy silane to grow particles; and finally, adding water for dilution, and preparing a high-purity short-chain silicon dioxide sol aqueous solution with the mass fraction of 5-20% by adopting a reduced pressure distillation mode. According to the method, the high-purity short-chain silicon dioxide sol particles with controllable particle sizes can be effectively prepared by adjusting the pH of the seed crystal preparation and seed crystal growth stages, and the method is high in repeatability and strong in controllability.

Description

Technical Field

[0001] The invention relates to a method for preparing a high-purity short-chain silicon dioxide sol with controllable particle size for chemical mechanical polishing, and belongs to the field of nano material preparation. Background Art

[0002] Silica sol composed of nano-scale silicon dioxide particles is an important production raw material and end product. Due to its unique properties, it is widely used in rubber, plastic, coating and semiconductor processing. At present, chemical mechanical polishing (CMP) is the most advanced technology for planarization in semiconductor processing. Silica sol, as the main consumable, has an important influence on the final effect of planarization.

[0003] Particle shape is an important factor affecting polishing performance. During the polishing process, spherical silica particles will roll, resulting in a small friction coefficient and a low polishing rate. At the same time, the high specific surface area of ​​spherical particles brings a high amount of silanols, which makes it easier for the particles to adhere to the equipment, thus causing scratches.

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

[0005] CN102390837A adopts the seed growth process to generate and grow seeds under alkaline conditions to prepare non-spherical particles with a particle size of 30 to 50 nm, but the obtained particle size variation range is narrow, which limits its applicable polishing scenarios. CN101402829A and CN101626979A add calcium salts and magnesium salts to the active silicate solution to prepare potato-shaped and elongated particles to increase the particle chain length, but CMP has extremely strict requirements on metal impurities. Metal impurities will diffuse into silicon wafers or electronic devices, eventually causing short circuits and seriously affecting the product yield. Improving the purity of silica sol is a common concern in the industry. Summary of the invention

[0006] In view of the above problems, the present invention innovatively proposes a method for preparing high-purity short-chain silica sol with controllable particle size. First, long-chain silica sol seed particles are prepared under acidic conditions, and then the liquid environment of the system is adjusted and the pH is adjusted to alkaline, and alkoxysilane is added to make the particles grow, thereby preparing high-purity short-chain silica sol with controllable particle size of 30-165nm.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solution:

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

[0009] (1) Preparation of active polysilicic acid: dilute water glass with deionized water to a mass fraction of 3-8% SiO2, then treat the aqueous solution with cationic resin exchange, and control the pH value at 2-4 to obtain active silicate. After that, the active silicate is alternately passed through anion and cation exchange resins to obtain active polysilicic acid with a lower ion content;

[0010] (2) Seed preparation: stirring the active polysilicic acid obtained in step (1) for a period of time at a certain temperature to obtain silica sol seed particles;

[0011] (3) Preparation of initial silica sol: Take the seed crystals obtained in step (2), mix them with a certain proportion of organic solvent, use an alkali catalyst to adjust the system pH to 9.5-11, and obtain a seed crystal growth base solution. Then, add a certain amount of seed crystal growth solution mixed with an organic solvent and alkoxysilane to the seed crystal growth base solution, and add an alkali catalyst to maintain the system pH stable, and react to obtain the initial silica sol;

[0012] (4) Vacuum distillation: The initial silica sol is diluted with water, and the organic solvent and the alkali catalyst are distilled off under reduced pressure to obtain a concentrated silica sol with a mass fraction of 5-20%.

[0013] In step (1), the cationic resin may be 001×4, 001×7 and 001×8 resins, and the anionic resin may be 201×4, 201×7 and 201×8 resins;

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

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

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

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

[0018] The mass fraction of SiO2 in the seed crystal growth bottom solution is 1%-3%, the mass fraction of the organic solvent is 60%-80%, and the mass fraction of water is 15%-35%;

[0019] In the seed crystal growth solution, the mass fraction of the organic solvent is 0%-80%;

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

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

[0022] Preparation of initial silica sol, reaction temperature is 5-60°C, preferably 10-40°C; and / or, the seed growth solution is added dropwise to the seed growth base solution, the adding time is 0.1min-70min; stirring speed is 200r / min-1000r / min;

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

[0024] The beneficial effects of the present invention are:

[0025] In the process of preparing high-purity short-chain silica sol in the present invention, first, silica sol seed particles are prepared under acidic conditions. The polysilicic acid solution flowing out from the anion exchange column has a small particle size and poor stability, so it must be heated under acidic conditions to generate seed crystals, otherwise the polysilicic acid solution is very easy to gel. The active silica is limited to polymerize under acidic conditions (limited polymerization speed and limited polymerization direction), which is conducive to the generation of chain-like crystal nuclei, thereby determining the initial form of silica sol particles. Then, the seed crystals with a determined form are mixed with an organic solvent and the liquid environment for seed crystal growth is changed by adjusting the pH value of the system to alkaline, so that the seed crystal particles are effectively grown, thereby obtaining a short-chain silica sol. Directly adding a silicon source for seed crystal growth without adjusting the liquid environment for seed crystal growth is likely to cause system abnormalities.

[0026] Compared with the prior art, the present invention innovatively proposes a method for preparing silica sol, which can obtain short-chain silica sol with controllable particle size and high purity. It can be applied to the chemical mechanical polishing process of semiconductor silicon wafers or electronic device crystals, and has the advantages of large friction coefficient, high polishing rate, and low polishing pollution. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

[0031] In order to better understand the technical solution of the present invention, the preparation method of the present invention is further explained below through more specific examples, but it does not constitute any limitation.

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

[0033]

[0034]

[0035] Detection method:

[0036] The apparent morphology and particle size statistics of silica sol were characterized by TEM images taken by JEM2100plus of JEOL Ltd.

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

[0038] Example 1

[0039] Take 16.51g of sodium water glass with a SiO2 mass fraction of 28%, add 41.26g of deionized water to dilute to obtain an aqueous sodium silicate solution with a SiO2 concentration of 8%. Pass the solution through a cation exchange column filled with 001×7 resin at a flow rate of 3mL / min to obtain an active silicic acid solution with a pH of 2.5. Pass the active silicic acid solution through an anion exchange column filled with 201×7 resin and a cation exchange column filled with 001×7 resin at a flow rate of 8mL / min, and circulate 3 times to obtain an active polysilicic acid solution A.

[0040] Take 55.02 g of solution A, stir and react at 50°C for 8 hours, then cool to room temperature, add 88.72 g of isopropanol to the solution, add ammonia water to adjust the pH to 10.0 and mix well to obtain a seed growth base solution.

[0041] At 20°C, use a peristaltic pump to drop 13.42g of isopropanol and 8.84g of tetramethoxysilane that are evenly mixed into the seed growth base solution. The addition is completed in 70 minutes. 0.5g of ammonia water is added every 15 minutes. The mixture is reacted at 20°C and 800r / min for 3 hours to obtain the initial silica sol.

[0042] After adding water to dilute the initial silica sol to a mass fraction of 3.9%, the silica sol was concentrated by heating under reduced pressure at 10 kPa and 43°C to about 20%, thereby obtaining a concentrated silica sol. At this time, a short-chain silica sol with a mass concentration of 20% was obtained.

[0043] Example 2

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

[0045] Take 39.63 g of solution A, stir and react at 60°C for 1 hour, then cool to room temperature, add 36.69 g of methanol and 68.14 g of acetonitrile to the solution, add ammonia water to adjust the pH to 9.5 and mix well to obtain a seed growth base solution.

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

[0047] After adding water to dilute the initial silica sol to a mass fraction of 4.4%, it was concentrated by heating under reduced pressure at 10 kPa and 43°C to about 20%, thereby obtaining a concentrated silica sol. At this time, a short-chain silica sol with a mass concentration of 20% was obtained.

[0048] Example 3

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

[0050] Take 53.75 g of solution A, stir and react at 70°C for 4 hours, then cool to room temperature, add 100.42 g of isopropanol to the solution, add ammonia water to adjust the pH to 11.0 and mix well to obtain a seed growth base solution.

[0051] At 40°C, use a peristaltic pump to drop 6.85g of isopropanol and 15.84g of tetramethoxysilane that are evenly mixed into the seed growth base solution. The addition is completed in 20 minutes. 0.5g of ammonia water is added every 5 minutes. The mixture is stirred at 40°C and 200r / min for 3 hours to obtain the initial silica sol.

[0052] After adding water to dilute the initial silica sol to a mass fraction of 3.68%, the silica sol was concentrated by heating under reduced pressure at 10 kPa and 43°C to about 20%, thereby obtaining a concentrated silica sol. At this time, a short-chain silica sol with a mass concentration of 20% was obtained.

[0053] Example 4

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

[0055] Take 27.98 g of liquid A, stir and react at 90°C for 5 hours, then cool to room temperature, add 41.56 g of methanol and 77.19 g of acetonitrile to the solution, add ammonia water to adjust the pH to 10.9 and mix well to obtain a seed growth base solution.

[0056] At 60°C, use a peristaltic pump to drop a uniformly mixed 9.42g of organic solvent (a mixture with the same ratio as the organic solvent in liquid A) and 12.17g of tetramethoxysilane into the seed growth base solution. The addition is completed in 5 minutes. 0.5g of ammonia water is added every 1 minute. The mixture is reacted at 60°C and 1000r / min for 1.5 hours to obtain the initial silica sol.

[0057] After adding water to dilute the initial silica sol to a mass fraction of 2.79%, the silica sol was concentrated by heating under reduced pressure at 10 kPa and 43°C to about 20%, thereby obtaining a concentrated silica sol. At this time, a short-chain silica sol with a mass concentration of 20% was obtained.

[0058] Comparative Example 1

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

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

[0061] At 40°C, use a peristaltic pump to drop 6.85g of isopropanol and 15.84g of tetramethoxysilane that are evenly mixed into the seed growth base solution. The addition is completed in 20 minutes. 0.5g of ammonia water is added every 5 minutes. The mixture is stirred at 40°C and 200r / min for 3 hours to obtain the initial silica sol.

[0062] The silica sol obtained was agglomerated, and micron-sized particles were visible to the naked eye adhering to the wall of the beaker or deposited on the bottom of the beaker.

[0063] Comparative Example 2

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

[0065] Take 53.75g of liquid A, stir and react at 70℃ for 4h, then cool to room temperature, add 100.42g of isopropanol to the solution to obtain a seed growth base solution. At 40℃, use a peristaltic pump to drop 6.85g of isopropanol and 15.84g of tetramethoxysilane into the seed growth base solution, add it in 20min, add 0.5g of ammonia water every 5min, stir at 40℃ and 200r / min for 3h, and obtain the initial silica sol. The obtained silica sol undergoes gelation.

[0066] Comparative Example 3

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

[0068] Comparative Example 4

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

[0070] Table 1 shows the particle size information of each embodiment and comparative example. Due to the abnormal phenomena in the systems of comparative examples 1 and 2, the particle size data cannot be shown. As shown in Table 1, by adjusting the conditions for preparing seed crystals under acidity, the present invention can adjust the particle size within the range of 30-165nm to achieve the purpose of controllable particle size, while the particle size of the particles obtained in the comparative example is small and the range of variation is relatively narrow.

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

[0072]

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

[0074] According to Comparative Example 3 prepared by patent CN102390837A, potassium carbonate is used to adjust the pH of the system during the preparation process, and active silicate is used to grow the particles, resulting in a high content of potassium ions and sodium ions in the final product. According to Comparative Example 4 prepared by patent CN101402829A, calcium chloride is used to adjust the particle morphology, and sodium hydroxide is used to adjust the pH value of the system, resulting in a high content of calcium ions and sodium ions in the final product, which affects the purity of the final product and limits its application in semiconductor CMP.

[0075] Table 2 Some metal impurity contents of various silica sols (ppm)

[0076] Na K Cr Cu Fe Ca Mg Example 1 5 <1 <1 <1 <1 <1 <1 Example 2 4 <1 <1 <1 <1 <1 <1 Example 3 5 <1 <1 <1 <1 <1 <1 Example 4 2 <1 <1 <1 <1 <1 <1 Comparative Example 3 124 633 2 <1 3 8 11 Comparative Example 4 550 30 10 7 14 1350 22

[0077] Figure 1 The TEM images of Example 1, Example 2, Example 3 and Example 4 of the present invention are given, corresponding to Figure 1 a, b, c, d in. As can be seen from the figure, all the particles in the embodiment are in the shape of short chains, but they show different particle sizes. The difference between Comparative Example 1 and the embodiment is whether the active polysilicic acid is heated and stirred under acidic conditions to prepare seed crystals after obtaining the active polysilicic acid. There is no step of preparing seed crystals under acidic conditions. After adjusting the pH to alkaline, the active silicic acid with too high concentration will explode into nuclei, and then particle agglomeration will occur. The difference between Comparative Example 2 and the embodiment is whether a catalyst is added to adjust the pH to alkaline after obtaining the seed crystals under acidic conditions. Directly adding a silicon source under acidic conditions will cause gelation.

[0078] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as limiting the present invention. Those skilled in the art will appreciate that, under the guidance of this specification, some modifications or adjustments may be made to the present invention. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing a high-purity short-chain silica sol with controllable particle size, characterized in that: The following steps are included: (1) Preparation of active polysilicic acid: diluting water glass with deionized water, and then exchanging it with a cationic resin to control the pH value to be acidic to obtain active silicate; then, purifying the active silicate to obtain active polysilicic acid with a low ion content; (2) Seed preparation: stirring the active polysilicic acid obtained in step (1) for a period of time to obtain silica sol seed particles; (3) Preparation of initial silica sol: taking the seed crystals obtained in step (2), mixing them with an organic solvent, adding an alkali catalyst to adjust the pH of the system to 9.5-11, and obtaining a seed crystal growth base solution; then, adding a seed crystal growth base solution mixed with an organic solvent and alkoxysilane dropwise to the seed crystal growth base solution, and adding an alkali catalyst to maintain the pH of the system stable, and reacting to obtain an initial silica sol; (4) Vacuum distillation: The initial silica sol is diluted with water to remove the organic solvent and the alkali catalyst to obtain concentrated silica sol.

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

3. The preparation method according to claim 1, characterized in that: In the step (2), the reaction temperature is 50-90°C, preferably 60-70°C; and the stirring time is 1-8h.

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

5. The preparation method according to any one of claims 1 to 4, characterized in that: In step (3), the base catalyst is selected from at least one of alkali metal hydroxides, ammonia water or organic amine compounds; preferably, the base catalyst is selected from at least one of sodium hydroxide, potassium hydroxide, ammonia water, triethanolamine or tetramethylammonium hydroxide.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In step (3), the mass fraction of SiO2 in the seed crystal growth base solution is 1%-3%, the mass fraction of the organic solvent is 60%-80%, and the mass fraction of water is 15%-35%.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The mass fraction of the organic solvent in the seed crystal growth solution in step (3) is 0%-80%.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The alkoxysilane described in step (3) is one or more of tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane, preferably tetramethoxysilane.

9. The preparation method according to any one of claims 1 to 8, characterized in that: In step (3), the initial silica sol is prepared at a reaction temperature of 5-60° C.; and / or the seed growth solution is added dropwise to the seed growth base solution for a dropwise addition time of 0.1 min-70 min.

10. The preparation method according to any one of claims 1 to 9, characterized in that: In step (4), the initial silica sol is first diluted with water to a mass fraction of 2-5%, and then the organic solvent is removed under a vacuum condition of 5 kPa-40 kPa.

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