Peanut-shaped ultra-high-purity silica sol as well as preparation method and application thereof

Abstract

The invention introduces peanut-shaped ultra-high-purity silica sol as well as a preparation method and application thereof, and the silica sol which is controllable in morphology, high in purity and uniform in particle size distribution is successfully prepared by finely regulating and controlling the addition amount of a cationic surface active agent in the preparation process of an alkoxide method. The silica sol has a wide application prospect in the fields of chemical mechanical polishing (CMP) and the like.

Description

Technical Field

[0001] The invention belongs to the field of high-purity nano material preparation, and specifically relates to a peanut-shaped ultra-high-purity silica sol and a preparation method and application thereof. Background Art

[0002] Silica sol is a colloid formed by nano-scale silica particles in water. It is odorless, non-toxic, milky white, and the silica colloid particles are fine (10-20nm); it has a high specific surface area, and the particles themselves are colorless and transparent, which does not affect the original color of the covered object. When mixed with other substances, the dispersibility and permeability are very good. In recent years, high-purity silica sol has been widely used in the polishing of silicon wafers and the chemical mechanical polishing (CMP) step of semiconductor devices. At present, there are three main types of abrasives used in CMP, namely silica, cerium dioxide and aluminum oxide. Aluminum oxide has a large particle size and a high Mohs hardness. It often scratches the surface of the processed device and is difficult to clean after polishing. Cerium dioxide has a moderate hardness, but its resources are limited, making it difficult to achieve industrial polishing. Silica sol abrasives have moderate hardness, low viscosity, easy cleaning, no pollution to the environment, and silica sol is heat-resistant, wear-resistant, chemically stable and highly adsorbable.

[0003] At present, the commonly used methods for preparing silica sol include alkoxide method, elemental silicon hydrolysis method, ion exchange method, etc. However, the only methods that can effectively prepare high-purity silica sol are elemental silicon hydrolysis method and alkoxide method. The silica sol prepared by elemental silicon method has a high hardness and will cause scratches during the polishing process, which is not suitable for subsequent fine polishing.

[0004] The alkoxide method is a relatively mature process for producing ultra-high purity silica sol. Under the action of an alkaline catalyst, alkoxysilane reacts with water to produce silicon dioxide and alcohol. Finally, the solvent is replaced by water from alcohol to obtain aqueous silica sol.

[0005] CN101495409A uses TMOS and methanol as raw material solutions, mixes methanol, water and ammonia water as reaction solvents, and reacts at 20°C to obtain silica sol with a primary particle size of 32.1nm and a secondary particle size of 74.8nm. According to the patent, silica sols with different association degrees can be prepared by strictly controlling various experimental conditions, but the entire process strictly controls the experimental parameters, is difficult to scale up, and has poor repeatability. Especially in industrial production, there is a significant scale-up effect that is not conducive to further expansion of production and cost control. Summary of the invention

[0006] In view of the above problems, the present invention innovatively proposes to prepare silica sol by a new alkoxide method, and the morphology of the silica sol is controlled by adding a certain amount of cationic surfactant in the reaction stage, and then a series of steps such as sol-gel, concentration, water replacement, and filtration are performed to obtain ultra-high purity silica sol with a mass fraction of more than 20%, a primary particle size of 30-150nm, and an association degree of 1.8-2.2, and the total metal ion content of the silica sol is less than 1ppm. The present invention solves the problem of difficulty in controlling the morphology of silica sol prepared by the traditional alkoxide method, and has good batch stability.

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

[0008] Another object of the present invention is to provide application of the ultra-high purity silica sol in CMP.

[0009] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solution:

[0010] A method for preparing peanut-shaped ultra-high purity silica sol comprises the following steps:

[0011] 1) Preparation of liquid A: Mix the organic solvent, ultrapure water, alkaline catalyst and cationic surfactant in a certain proportion;

[0012] 2) Preparation of liquid B: Mix the organic solvent and alkoxysilane evenly;

[0013] 3) Preparation of initial silica sol: at a certain temperature, liquid B is added to liquid A, and stirred and reacted to obtain initial silica sol;

[0014] 4) Concentration: Concentrating the initial silica sol to a concentrated silica sol with a mass fraction of 10-20%;

[0015] 5) Solvent replacement: The organic solvent in the concentrated silica sol is replaced with ultrapure water and concentrated to a mass fraction of 20% or more;

[0016] 6) Filtration: The concentrated silica sol is filtered to remove large particles to obtain the peanut-shaped ultra-high purity silica sol.

[0017] In a specific embodiment, the organic solvents described in step 1) and step 2) are independently selected from one or more of methanol, ethanol, propanol, isopropanol, acetonitrile, acetone, methyl ethyl ketone, diethyl ether, ethyl propyl ether, etc., preferably methanol; preferably, the organic solvent in liquid B is the same as the organic solvent in liquid A.

[0018] In a specific embodiment, the cationic surfactant in step 1) is selected from ammonium salt type cationic surfactants, quaternary ammonium salt type cationic surfactants, heterocyclic type cationic surfactants and pyrochlore type cationic surfactants, preferably quaternary ammonium salt type cationic surfactants; further, the quaternary ammonium salt type cationic surfactant is selected from one or more of dodecyldimethylbenzylammonium bromide, dodecyldimethyltertiary amine, didecyldimethylammonium chloride, tetradecyltrimethylammonium bromide and the like.

[0019] In a specific embodiment, the amount of the cationic surfactant added in step 1) accounts for 10 to 1000 ppm of the total mass of liquid A, for example including but not limited to 10, 100, 200, 300, 400, 500, 600, 700, 800, 900 and 1000 ppm, and the preferred addition amount is 100 to 300 ppm.

[0020] In a specific embodiment, the base catalyst in step 1) is selected from at least one of alkali metal hydroxide and ammonia water; preferably, the alkali metal hydroxide is selected from at least one of potassium hydroxide, sodium hydroxide and lithium hydroxide; more preferably, the base catalyst is ammonia water, and the concentration of ammonia water is 25wt% to 28wt%.

[0021] In a specific embodiment, in the liquid A of step 1), the mass fraction of the organic solvent is 50%-80%, the mass fraction of the ultrapure water is 19%-49%, and the mass fraction of the base catalyst is 0.5%-1.5%.

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

[0023] In a specific embodiment, the mass ratio of the organic solvent to the alkoxysilane in step 2) is 1:3 to 3:1.

[0024] In a specific embodiment, in the preparation of the initial silica sol in step 3), the reaction temperature is 5 to 80°C, for example, including but not limited to 5°C, 15°C, 25°C, 35°C, 40°C, 50°C, 60°C, 65°C, 70°C, 75°C and 80°C, preferably 40 to 70°C; the mass ratio of liquid A to liquid B is 1:1 to 1:2, and the dropwise addition time of liquid B to liquid A is controlled at 5 to 20h, for example, including but not limited to 5h, 7.5h, 10h, 12.5h, 15h, 17.5h and 20h, preferably 10 ~20h, the stirring speed is 200r / min~1000r / min, for example including but not limited to 200r / min, 300r / min, 400r / min, 500r / min, 600r / min, 700r / min, 800r / min, 900r / min, 1000r / min, preferably 300~500r / min, the reaction time after the completion of dropwise addition is 0.5h~3h, for example including but not limited to 0.5h, 1h, 1.5h, 2h, 2.5h, 3h.

[0025] In a specific embodiment, the concentration in step 4) is concentrated by vacuum heating concentration to concentrate the initial silica sol to a concentrated silica sol with a mass fraction of 10-20%. The vacuum heating concentration method can refer to the prior art and is well known to those skilled in the art. During the concentration process, as the solid content of the silica sol increases, the stability of the silica sol will deteriorate, so alkalis such as ammonia water, organic amines, organic acids such as citric acid, benzoic acid, polyacrylic acid, etc. or high molecular surfactants such as polyvinyl pyrrolidone, polyether P123, etc. are added to increase the stability of the silica sol, and dispersants are added to improve the yield and stability of the silica sol.

[0026] In a specific embodiment, the solvent replacement described in step 5) is specifically to add ultrapure water while heating, evaporate and remove the solvent in the water, so as to replace the organic solvent in the concentrated silica sol with ultrapure water; the inlet temperature of ultrapure water is 20-80°C, for example, including but not limited to 20°C, 30°C, 40°C, 50°C, 60°C, 70°C and 80°C, preferably 50-80°C, the absolute pressure is 10-20kPa, and the solvent in the water is evaporated and removed until the solvent content in the silica sol is reduced to less than 200ppm, preferably less than 100ppm, and the mass fraction of the silica sol is preferably concentrated to 20%-25%. The vacuum heating concentration described herein can refer to the common scraper evaporation, forced circulation evaporation or distillation in industry.

[0027] In a specific embodiment, in step 6), the concentrated silica sol is filtered to remove large particles to obtain the peanut-shaped ultra-high purity silica sol, wherein the filtration can be performed using a filter element made of PP material with a filtration accuracy of 0.1 μm to 5 μm, and preferably two-stage, three-stage or multi-stage filtration is used.

[0028] Another aspect of the present invention provides an ultra-high purity silica sol prepared by the above method, wherein the silica sol particles are mostly peanut-shaped, with a primary particle size of 30 to 150 nm, an association degree of 1.7 to 2.3, and a total metal ion content of less than 1 ppm.

[0029] Another aspect of the present invention is the use of the aforementioned ultra-high purity silica sol in chemical mechanical polishing (CMP).

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1) The present invention creatively proposes for the first time to prepare peanut-shaped ultra-high purity silica sol by adding a certain amount of cationic surfactant in the silica sol reaction stage to control the morphology and association degree of the silica sol.

[0032] 2) The peanut-shaped ultra-high purity silica sol has significant advantages in the field of chemical mechanical polishing (CMP). Its unique morphology and excellent purity help improve polishing efficiency and surface quality, and reduce scratches and residues. In addition, the silica sol can also be used to prepare high-performance silicon-based composite materials, coatings and other fields, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 TEM image of the silica sol particles prepared in Example 1 of the present invention;

[0034] Figure 2 TEM image of silica sol particles prepared in Comparative Example 1 of the present invention;

[0035] Figure 3 This is a TEM image of the silica sol particles prepared in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0036] 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.

[0037] The main raw materials used in the following examples and comparative examples are as follows:

[0038] Table 1 Example / Comparative Example Raw Materials

[0039]

[0040]

[0041] Detection method:

[0042] The test method for solid content refers to HGT 2521-2008 industrial silica sol.

[0043] The secondary particle size of silica sol particles was measured by using a Malvern Zetasizer Nano ZS90 particle size analyzer, and the primary particle size was measured by using the BET specific surface area test method to obtain the specific surface area S bet , primary particle size is 2727 / S bet The degree of association is the ratio of the secondary particle size to the primary particle size.

[0044] The morphology of silica sol was characterized by TEM.

[0045] The residual methanol content was measured using an Agilent 8890GC.

[0046] The concentration of metal ions was measured using an Agilent 7900 ICP-MS.

[0047] Example 1

[0048] 1752.3g isopropanol, 761.8g water, 101.56g ammonia water (25wt%) and 0.592g dodecyl dimethyl tertiary amine were mixed and stirred evenly as liquid A, 2535.4g isopropanol and 845.13g tetramethoxysilane (TMOS) were mixed evenly as liquid B, and liquid B was added to liquid A with a peristaltic pump, and the addition was completed in 10 hours. The reaction was carried out at 50°C and 300r / min for 0.5h to obtain the initial silica sol. Then, the silica sol was concentrated to about 20% by heating under reduced pressure at 20Kpa and 100°C, and then concentrated to about 20%, and the concentrated silica sol was obtained. Then, ultrapure water was added while evaporating, and the inlet temperature of ultrapure water was 60°C and the absolute pressure was 20Kpa, until the content of organic matter in the silica sol dropped below 100ppm, and the concentration of the silica sol was controlled to about 20wt%, and then 5μm and 0.3μm filter elements were used for secondary filtration to filter out large particles. At this time, the mass concentration is 20%, the primary particle size is 40nm, the secondary particle size is 75nm, and the degree of association is 1.87. Figure 1 As shown, the ultra-high purity silica sol has a total metal ion content of less than 1 ppm, and the content of some metal impurities is shown in Table 2.

[0049] Example 2

[0050] 2025.16g methanol, 493.63g water, 50.64g ammonia water (25wt%) and 1.12g didecyl dimethyl ammonium chloride were mixed and stirred evenly as liquid A, 1576.32g methanol and 1469.52g tetramethoxysilane (TMOS) were mixed evenly as liquid B, and liquid B was added to liquid A using a peristaltic pump, and the addition was completed in 15h. React at 60℃ and 400r / min for 1h to obtain the initial silica sol. Then, the solution was concentrated by heating under reduced pressure at 10Kpa and 100℃ to about 20%, and the concentrated silica sol was obtained. Then, ultrapure water was added while evaporating, with an absolute pressure of 10Kpa and an inlet water temperature of 40℃, until the content of organic matter in the silica sol dropped below 100ppm, and the concentration of the silica sol was controlled to about 20wt%, and then 5μm and 1μm filter elements were used for secondary filtration to filter out large particles. At this time, an ultra-high purity silica sol with a mass concentration of 20%, a primary particle size of 100 nm, a secondary particle size of 190 nm, an association degree of 1.90, and a total metal ion content of less than 1 ppm was obtained. The content of some metal impurities is shown in Table 2.

[0051] Example 3

[0052] 1677.32g methanol, 1044.89g water, 27.48g sodium hydroxide and 1.52g tetradecyl trimethyl ammonium bromide were mixed and stirred evenly as liquid A, 1595.32g ethanol and 1237.84g tetramethoxysilane (TMOS) were mixed evenly as liquid B, and liquid B was added to liquid A with a peristaltic pump, and the addition was completed in 20 hours. React at 80℃ and 500r / min for 1 hour to obtain the initial silica sol. Then, it was concentrated by heating under reduced pressure at 10Kpa and 100℃ to about 20%, and the concentrated silica sol was obtained. Then, ultrapure water was added while evaporating, with the water inlet temperature of 40℃ and the absolute pressure of 10Kpa, until the content of organic matter in the silica sol dropped below 100ppm, and the concentration of the silica sol was controlled at about 20wt%, and then 5μm and 0.1μm filter elements were used for secondary filtration to filter out large particles. At this time, an ultra-high purity silica sol with a mass concentration of 20%, a primary particle size of 98 nm, a secondary particle size of 208 nm, an association degree of 2.12, and a total metal ion content of less than 1 ppm was obtained. The content of some metal impurities is shown in Table 2.

[0053] Comparative Example 1

[0054] Comparative Example 1 Compared with Example 1, no cationic surfactant was added, and finally a spherical silica sol with a mass concentration of 20% and a particle size of 50 nm was obtained. Figure 2 As shown, the ultra-high purity silica sol has a total metal ion content of less than 1 ppm, and the content of some metal impurities is shown in Table 2.

[0055] Comparative Example 2

[0056] Comparative Example 2 Compared with Example 1, the amount of cationic surfactant tetradecyltrimethylammonium bromide added was 7.51 g. During the experiment, the silica sol gelled and the experiment was terminated.

[0057] Comparative Example 3

[0058] Comparative Example 3 Compared with Example 1, 1.52 g of anionic surfactant polyacrylamide was added. Finally, a spherical silica sol with a mass concentration of 20% and a particle size of 45 nm was obtained. Figure 3 As shown, the ultra-high purity silica sol has a total metal ion content of less than 1 ppm, and the content of some metal impurities is shown in Table 2.

[0059] Table 2 Partial metal impurity content (ppb) of silica sol prepared in various embodiments and comparative examples

[0060]

[0061]

[0062] In Examples 1-3, by changing the content of cationic surfactant added to solution A and controlling the addition amount to be within 10 to 1000 ppm, silica sols with peanut-shaped morphology can be prepared in different solvent systems, such as Figure 1 As shown; in Comparative Example 1, silica sol particles can be prepared without adding cationic surfactant, but the silica sol particles are spherical in shape, such as Figure 2 As shown in FIG. 2 , a peanut-shaped silica sol cannot be prepared; in Comparative Example 2, the cationic surfactant added exceeds 1000 ppm, the silica sol stability is extremely poor, and gelation occurs during the synthesis process. Therefore, the amount of cationic surfactant added needs to be controlled. In Comparative Example 3, silica sol particles can be prepared by adding anionic surfactants, but the silica sol particles are spherical in shape, as shown in FIG. Figure 3 As shown, peanut-shaped silica sol cannot be prepared

[0063] It can be seen that the high-purity silica sol prepared by the present invention has a peanut-shaped particle morphology, a particle association degree of 1.87-2.12, a metal ion content of less than 1ppm, and a mass fraction of more than 20%, and can be used for polishing large semiconductor silicon slices or wafers.

[0064] 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 peanut-shaped ultra-high purity silica sol, characterized in that: The following steps are included: 1) Preparation of liquid A: Mix the organic solvent, ultrapure water, alkaline catalyst and cationic surfactant evenly; 2) Preparation of liquid B: Mix the organic solvent and alkoxysilane evenly; 3) Preparation of initial silica sol: Add liquid B to liquid A, stir and react to obtain initial silica sol; 4) Concentration: Concentrating the initial silica sol to a concentrated silica sol with a mass fraction of 10-20%; 5) Solvent replacement: The organic solvent in the concentrated silica sol is replaced with ultrapure water and concentrated to a mass fraction of 20% or more; 6) Filtration: The concentrated silica sol is filtered to remove large particles to obtain the peanut-shaped ultra-high purity silica sol.

2. The method for preparing peanut-shaped ultra-high purity silica sol according to claim 1, characterized in that: The organic solvents described in step 1) and step 2) are independently selected from one or more of methanol, ethanol, propanol, isopropanol, acetonitrile, acetone, methyl ethyl ketone, diethyl ether, and ethyl propyl ether; preferably, the organic solvent in liquid B is the same as the organic solvent in liquid A.

3. The method for preparing peanut-shaped ultra-high purity silica sol according to claim 1, characterized in that: In the step 1), the cationic surfactant is selected from one or more of ammonium salt type cationic surfactants, quaternary ammonium salt type cationic surfactants, heterocyclic type cationic surfactants and pyrochlore type cationic surfactants, preferably quaternary ammonium salt type cationic surfactants; more preferably, one or more of dodecyl dimethyl benzyl ammonium bromide, dodecyl dimethyl tertiary amine, didecyl dimethyl ammonium chloride, tetradecyl trimethyl ammonium bromide; preferably, the cationic surfactant is added in an amount of 10 to 1000 ppm, more preferably 100 to 300 ppm, based on the total mass of liquid A.

4. The method for preparing peanut-shaped ultra-high purity silica sol according to claim 1, characterized in that: In step 1), the base catalyst is selected from at least one of alkali metal hydroxide and ammonia water; preferably, the alkali metal hydroxide is selected from at least one of potassium hydroxide, sodium hydroxide and lithium hydroxide; more preferably, the base catalyst is ammonia water, and the mass fraction of ammonia water is preferably 25%-28%.

5. The method for preparing a peanut-shaped ultra-high purity silica sol according to any one of claims 1 to 4, characterized in that: In the step 1), the mass fraction of the organic solvent in liquid A is 50% to 80%, the mass fraction of the ultrapure water is 19% to 49%, and the mass fraction of the base catalyst is 0.5% to 1.5%; preferably, the mass ratio of liquid A to liquid B is 1:1 to 1:

2.

6. The method for preparing peanut-shaped ultra-high purity silica sol according to claim 1, characterized in that: The alkoxysilane in step 2) is one or more of tetramethoxysilane, tetraethoxysilane and tetrapropoxysilane, preferably tetramethoxysilane; preferably, the mass ratio of the organic solvent to the alkoxysilane is 1:3 to 3:

1.

7. The method for preparing peanut-shaped ultra-high purity silica sol according to claim 1, characterized in that: In the preparation of the initial silica sol in step 3), the reaction temperature is 5-80°C, preferably 40-70°C; the dropwise addition time of liquid B to liquid A is 5-20h, preferably 10-20h, the stirring speed is 200r / min-1000r / min, preferably 300-500r / min, and the reaction time after the dropwise addition is 0.5h-3h; preferably, the solvent replacement in step 5) is performed by heating and supplementing ultrapure water, the inlet temperature of the ultrapure water is 20-80°C, preferably 50-80°C, the absolute pressure is 10-20kpa, and the solvent in the water is evaporated to remove the solvent content in the silica sol until the solvent content in the silica sol is reduced to less than 200ppm, preferably less than 100ppm, and the mass fraction of the silica sol is concentrated to 20%-25%.

8. The method for preparing peanut-shaped ultra-high purity silica sol according to claim 1, characterized in that: The filtration in step 6) uses a filter element made of PP material with a filtration accuracy of 0.1 μm to 5 μm, and preferably two-stage or three-stage filtration is used.

9. A peanut-shaped ultra-high purity silica sol obtained by the preparation method according to any one of claims 1 to 8, characterized in that: The primary particle size of the silica sol particles is 30-150 nm, the degree of association is 1.8-2.2, and the total content of metal ions is less than 1 ppm.

10. Use of the peanut-shaped ultra-high purity silica sol obtained by the preparation method according to any one of claims 1 to 8 or the peanut-shaped ultra-high purity silica sol according to claim 9 in chemical mechanical polishing.

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