Preparation method of silicon dioxide sol without small particles

Abstract

The invention relates to a preparation method of silicon dioxide sol without small particles. The method comprises the following steps: dropwise adding an alkoxy silane solution into an alkaline base solution at a variable adding speed at a certain temperature, and adding an alkaline solution into the base solution during the period to control the generation of small particles; and finally, adding water for dilution, and preparing a silicon dioxide aqueous solution which has the mass fraction of 15-20% and does not contain small particles by adopting a reduced pressure distillation mode. The invention innovatively provides the preparation method of the silicon dioxide sol without small particles, and the silicon dioxide sol can be suitable for the chemical mechanical polishing process of semiconductor silicon wafers or electronic devices and has the advantages of few particle residues on the polished surface and the like.

Description

Technical Field

[0001] This invention relates to a method for preparing a silica sol without small particles for chemical mechanical polishing, belonging to the field of nanomaterial preparation. Background Technology

[0002] Silica sol, composed of nanoscale silica, is a major consumable in the chemical mechanical polishing (CMP) process of semiconductor manufacturing.

[0003] The presence of residual particles on the polished surface is a key indicator for evaluating the performance of silica sol applications. Particle residue can lead to problems such as silicon wafer surface contamination, longer cleaning cycles, and uneven photoresist coating, resulting in decreased semiconductor manufacturing yield. Silica sol typically contains particles smaller than the main particles, and the presence of these small particles can cause residue issues on the polished surface.

[0004] To control small particles in silica sol, CN 119774625 A proposes a method of adding a precipitant during the reaction process. JP7505130B1 removes small particles from silica sol by heating it at a specific pH for 11-35 hours. JP7516763B2 uses ultrafiltration to remove small particles from the silica sol generated during the reaction.

[0005] While adding precipitants can remove small particles, the process becomes complex due to the selection of precipitants and the steps involved in their addition. Similarly, post-treatment methods such as heating and filtration, while effective in removing small particles from silica sol, increase process complexity and lengthen production cycles. Furthermore, prolonged heat treatment can degrade the stability of silica sol, causing particle aggregation. Filtration, on the other hand, can easily lead to gelation of the silica sol as it passes through membrane pores, affecting product properties.

[0006] This problem can be effectively solved if the operating parameters can be controlled during the synthesis of silica sol to suppress the formation of small particles. Summary of the Invention

[0007] To address the above issues, this invention innovatively proposes a method for preparing silica sol free of small particles. This invention involves adding alkoxysilanes to an alkaline substrate at a decreasing rate gradient, while simultaneously adding an alkaline solution to the substrate, thereby preparing a silica sol free of small particles, satisfying the requirement that the ratio of particles with a circular equivalent diameter ≤15 nm under TEM view to the total number of particles is less than 5%.

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

[0009] A method for preparing silica sol without small particles includes the following steps:

[0010] (1) Preparation of solution A: Mix organic solvent, water and alkaline catalyst evenly in a certain proportion;

[0011] (2) Preparation of solution B: Mix alkoxysilane with an optional organic solvent until homogeneous;

[0012] (3) Preparation of liquid C: Mix the alkaline catalyst, optional organic solvent, and optional water in a certain proportion until homogeneous;

[0013] (4) Particle preparation: Liquid B is gradually added to liquid A at a decreasing rate, and during the addition of liquid B, a certain amount of liquid C is added to liquid A to obtain the initial silica sol;

[0014] (5) Vacuum distillation: Dilute the initial silica sol with water to remove organic solvents and alkaline catalysts to obtain concentrated silica sol.

[0015] In this invention, in steps (1), (2), and (3), the organic solvent is one or more of methanol, ethanol, n-propanol, isopropanol, acetonitrile, acetone, methyl ethyl ketone, diethyl ether, ethyl propyl ether, and cyclohexane; preferably, the organic solvents in liquid A, liquid B, and liquid C are the same.

[0016] In this invention, in step (2), the alkoxysilane is one or more of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, methyltrimethoxysilane, and methyltriethoxysilane, preferably tetramethoxysilane;

[0017] In this invention, in steps (1) and (3), the alkaline catalyst is selected from at least one of alkali metal hydroxides, ammonia, or organic amine compounds; preferably, the alkaline catalyst is selected from one or more of ammonia, ethylenediamine, diethanolamine, triethanolamine, urea, tetramethylammonium hydroxide, or 3-ethoxypropylamine.

[0018] In step (1), the organic solvent in liquid A has a mass fraction of 60%-80%, the water has a mass fraction of 15%-36%, and the alkaline catalyst has a mass fraction of 0.5%-5%, preferably 3-4%.

[0019] In step (2), the mass fraction of alkoxysilane in solution B is 10%-100%, preferably 40%-85%.

[0020] In step (3), the organic solvent in liquid C has a mass fraction of 0%-30%, the water has a mass fraction of 0%-30%, and the alkaline catalyst has a mass fraction of 60%-100%.

[0021] In this invention, the mass ratio of the three solutions is: solution A: solution B = 2-6:1, preferably 3-5:1; solution B: solution C = 2-5:1, preferably 3-4:1.

[0022] In this invention, the reaction temperature in step (4) is 10-70℃, preferably 35-65℃.

[0023] Preferably, in step (4), the method of reducing the rate gradient is as follows: the B solution is divided into 3 parts, the first part accounts for 50% of the B solution, the second part and the third part each account for 25%, wherein the first part of the B solution is added dropwise over 0-40 minutes (it can be understood that "0 minutes" means adding at once), the second part of the B solution is added dropwise over 2-5 hours, and the third part of the B solution is added dropwise over 4-10 hours (the dropwise time of the second part is less than that of the third part); the 3 parts of the B solution are added sequentially (the next part is added as soon as the previous part is added), and each part is added dropwise at a uniform rate.

[0024] Preferably, in step (4), liquid C is added to liquid A between 20 minutes before and 20 minutes after the change in the dropping rate of liquid B. As described above, since liquid B is added in three portions with a decreasing rate gradient, there are two rate change points during the dropping process. The 20 minutes before and after these rate change points is the time for adding liquid C. Liquid C is added to liquid A at any time during this period, meaning liquid C is added in two portions (the first portion of liquid C preferably accounts for 45% to 80% of the total liquid C).

[0025] In this invention, in step (5), the initial silica sol is first diluted with water to a mass fraction of 2-5%, and then heated to boiling under vacuum conditions of 5kPa-40kPa to remove the organic solvent.

[0026] The beneficial effects of this invention are as follows:

[0027] Compared with existing technologies, this invention innovatively proposes a method for preparing silica sol without small particles. The resulting silica sol satisfies the requirement that the ratio of the number of particles with a circular equivalent diameter ≤15nm to the total number of particles under TEM view is less than 5%. It can be applied to the chemical mechanical polishing process of semiconductor silicon wafers or electronic devices, and has the advantages of less particle residue on the polished surface. Attached Figure Description

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

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

[0030] Figure 2This is a schematic diagram of the timing of adding liquid C in step (4) of the present invention. Detailed Implementation

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

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

[0033]

[0034]

[0035] Detection method:

[0036] The small particles of silica sol were observed using TEM characterization with images taken by a JEOL JEM2100plus.

[0037] Example 1

[0038] Mix 292.34g isopropanol, 170.77g water, and 18.12g ammonia water thoroughly to form solution A; mix 76.65g isopropanol and 53.06g tetramethoxysilane thoroughly to form solution B, and divide the solution into three portions, with the first portion accounting for 50%, and the second and third portions each accounting for 25%; mix 4.50g isopropanol, 13.16g water, and 26.70g ammonia water thoroughly to form solution C.

[0039] At 40°C, the first portion of solution B was added to solution A all at once, followed by the addition of 75% solution C to solution A all at once; the second portion of solution B was added to solution A over 2 hours, and 20 minutes before the end of the addition, 25% solution C was added to solution A all at once; the third portion of solution B was added to solution A over 7 hours, thus obtaining the initial silica sol.

[0040] After diluting the initial silica sol with water to a mass fraction of 2.32%, it was concentrated by vacuum heating at 10 kPa and 45°C to a concentration of about 20%, thus obtaining the concentrated silica sol.

[0041] Example 2

[0042] Mix 333.27g methanol, 143.08g water and 21.12g ammonia water evenly to form solution A; mix 17.63g methanol and 96.68g tetramethoxysilane evenly to form solution B, divide it into 3 portions, the first portion accounting for 50%, the second portion and the third portion each accounting for 25%; mix 7.91g methanol and 30.34g ammonia water evenly to form solution C.

[0043] At 60℃, the first portion of solution B was added dropwise to solution A within 20 minutes. After the addition was completed, 75% of solution C was added to solution A at once. The second portion of solution B was added to solution A within 3.8 hours. The third portion of solution B was added to solution A within 4 hours. 20 minutes after the addition started, 25% of solution C was added to solution A at once to obtain the initial silica sol.

[0044] After diluting the initial silica sol with water to a mass fraction of 4.89%, it was concentrated by vacuum heating at 10 kPa and 45°C to a concentration of about 20%, thus obtaining the concentrated silica sol.

[0045] Example 3

[0046] Mix 300.22g methanol, 62.18g acetone, 118.95g water and 15.94g ammonia water evenly to form solution A; mix 78.66g tetraethoxysilane and 18.45g methyltrimethoxysilane to form solution B, and divide it into 3 portions, with the first portion accounting for 50%, the second portion and the third portion each accounting for 25%; use 31.84g 3-ethoxypropylamine as solution C.

[0047] At 65℃, the first portion of solution B was added dropwise to solution A within 40 minutes. After the addition was completed, 75% of solution C was added to solution A at once. The second portion of solution B was added to solution A within 5 hours. After the addition was completed, 25% of solution C was added to solution A at once. The third portion of solution B was added to solution A within 10 hours to obtain the initial silica sol.

[0048] After diluting the initial silica sol with water to a mass fraction of 5%, it was concentrated by vacuum heating at 10 kPa and 45°C to a concentration of about 20%, thus obtaining the concentrated silica sol.

[0049] Example 4

[0050] Mix 357.79g methanol, 72.83g water and 18.15g ammonia water evenly to form solution A; mix 65.96g methanol and 87.53g tetraethoxysilane evenly to form solution B, divide it into 3 portions, the first portion accounting for 50%, the second portion and the third portion each accounting for 25%; mix 14.33g methanol, 4.65g water and 29.33g ethylenediamine evenly to form solution C.

[0051] At 35°C, the first portion of solution B was added dropwise to solution A within 25 minutes. After the addition was completed, 50% of solution C was added to solution A at once. The second portion of solution B was added to solution A within 3.5 hours. After the addition was completed, 50% of solution C was added to solution A at once. The third portion of solution B was added to solution A within 6 hours to obtain the initial silica sol.

[0052] After diluting the initial silica sol with water to a mass fraction of 3.21%, it was concentrated by vacuum heating at 10 kPa and 45°C to a concentration of about 20%, thus obtaining the concentrated silica sol.

[0053] Comparative Example 1

[0054] Mix 333.27g methanol, 143.08g water and 21.12g ammonia water evenly to form solution A; mix 17.63g methanol and 96.68g tetramethoxysilane evenly to form solution B; mix 7.91g methanol and 30.34g ammonia water evenly to form solution C.

[0055] At 60℃, solution B was added dropwise to solution A over 40 minutes. After the addition was complete, solution C was added to solution A in one go to obtain the initial silica sol.

[0056] The initial silica sol was diluted with water to a mass fraction of 4.89%, and then concentrated under reduced pressure at 10 kPa and 45°C to approximately 20%, yielding the concentrated silica sol. The resulting silica sol contained small particles.

[0057] Comparative Example 2

[0058] Mix 357.79g methanol, 72.83g water, and 18.15g ammonia thoroughly to form solution A; mix 65.96g methanol and 87.53g tetramethoxysilane thoroughly to form solution B, and divide the mixture into three portions, with the first portion accounting for 50%, the second portion and the third portion each accounting for 25%; mix 14.33g methanol, 4.65g water, and 29.33g ammonia thoroughly to form solution C.

[0059] At 35°C, the first portion of solution B was added to solution A over 25 minutes; the second portion of solution B was added to solution A over 3.5 hours; the third portion of solution B was added to solution A over 6 hours. After the addition was completed, solution C was added to solution A all at once to obtain the initial silica sol.

[0060] The initial silica sol was diluted with water to a mass fraction of 3.21%, and then concentrated under reduced pressure at 10 kPa and 45°C to approximately 20%, yielding the concentrated silica sol. The resulting silica sol contained small particles.

[0061] Table 1 shows the presence of small particles (particles with a circular equivalent diameter ≤15nm under TEM view) in each embodiment and comparative example.

[0062] Table 1. Proportion of small particles in the total number of particles for each silica sol.

[0063] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Small particles <0.2％ 0％ 0％ <0.5％ >80％ >85％

[0064] Figure 1 TEM images of Embodiment 2 and Comparative Example 1 of the present invention are given, respectively corresponding to Figure 1 a and b in the example.

[0065] 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 process for the preparation of a colloidal silica sol free of small particles, characterized in that, The method comprises the following steps: (1) Preparation of A liquid: mixing organic solvent, water and base catalyst in a certain proportion; (2) Preparation of B liquid: mixing alkoxysilane and optional organic solvent uniformly; (3) Preparation of C liquid: mixing base catalyst and optional organic solvent, optional water in a certain proportion uniformly; (4) Preparation of particles: gradually adding B liquid into A liquid in a manner of decreasing adding speed gradient, and adding a certain amount of C liquid into A liquid during the adding of B liquid to obtain initial silica sol; preferably, the reaction temperature is 10-70℃, preferably 35-65℃; (5) Reducing pressure distillation: diluting the initial silica sol with water to remove organic solvent and base catalyst to obtain concentrated silica sol.

2. The production method according to claim 1, characterized by, The organic solvent in steps (1), (2) and (3) is one or more of methanol, ethanol, n-propanol, isopropanol, acetonitrile, acetone, methyl ethyl ketone, diethyl ether, ethyl propyl ether and cyclohexane; preferably, the organic solvent in steps (1), (2) and (3) is the same.

3. The preparation method according to claim 1, characterized in that, The alkoxysilane in step (2) is one or more of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, methyltrimethoxysilane and methyltriethoxysilane, preferably tetramethoxysilane; The mass fraction of alkoxysilane in B liquid is 10%-100%, preferably 40%-85%.

4. The production method according to claim 1 or 2, characterized by, The base catalyst in steps (1) and (3) is at least one of alkali metal hydroxide, aqueous ammonia or organic amine compound; preferably, the base catalyst is one or more of aqueous ammonia, ethylenediamine, diethanolamine, triethanolamine, urea, tetramethylammonium hydroxide or 3-ethoxypropylamine.

5. The method of any one of claims 1-4, wherein, In step (1), the mass fraction of organic solvent in A liquid is 60%-80%, the mass fraction of water is 15%-36% and the mass fraction of base catalyst is 0.5%-5%.

6. The method of any one of claims 1-5, wherein, In step (3), the mass fraction of organic solvent in C liquid is 0%-30%, the mass fraction of water is 0%-30% and the mass fraction of base catalyst is 60%-100%.

7. The method of any one of claims 1-6, wherein, The mass ratio of the three solutions is A liquid:B liquid=2-6:1, preferably 3-5:1; B liquid:C liquid=2-5:1, preferably 3-4:

1.

8. The method of any one of claims 1-7, wherein, In step (4), the manner of decreasing adding speed gradient is that B liquid is divided into three parts, the first part accounts for 50% of B liquid, the second and third parts each account for 25%, the first part of B liquid is added dropwise for 0-40 min, then the second part of B liquid is added dropwise for 2-5 h, and finally the third part of B liquid is added dropwise for 4-10 h.

9. The method of any one of claims 1-8, wherein, In step (4), C liquid is added into A liquid between 20 min before the change of adding speed of B liquid and 20 min after the change; Preferably, the first added C liquid accounts for 45%-80% of C liquid.

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

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