Preparation method of non-spherical silica sol

Abstract

The invention discloses a preparation method of non-spherical silica sol, and belongs to the technical field of silicon material preparation. In order to solve the problem that the colloidal particle form is difficult to regulate and control in the existing silica sol preparation method, the technical means of controlling the adding proportion of ammonia water and the aging time is mainly adopted, small-particle-size spherical colloidal particles are formed through a base catalysis hydrolysis reaction, and the colloidal particles are promoted to collide with one another and be covalently connected in the aging process and then further grow into non-spherical colloidal particles. Aging modes comprise room-temperature stirring, heating reaction, pH value down-regulation and reactant concentration, form regulation and control are flexible, and operation is easy and convenient. The method can be used for preparing strip-shaped, peanut-shaped, nearly spherical and other non-spherical silica sol, has the advantages of uniform form, controllable particle size and high process stability, and is suitable for various silica sol application scenes.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon material preparation, and in particular relates to a method for preparing non-spherical silica sol. Background Art

[0002] Chemical mechanical polishing (CMP) is currently recognized in the IC industry as the best global planarization technology for silicon wafers, and silica sol is the only abrasive available in silicon wafer CMP polishing liquid. The silicon wafer CMP process is divided into edge polishing, rough polishing, medium polishing and fine polishing. Among them, the fine polishing process has extremely high requirements for the metal impurity content of silica sol abrasive. Usually, the sum of the common metal contents such as sodium, potassium, calcium, magnesium, iron, and aluminum cannot exceed 1ppm. The orthosilicate hydrolysis process, that is, The process is the only technological solution that can meet this requirement and is also the method commonly used in the industry.

[0003] Conventional orthosilicate hydrolysis processes can usually only produce spherical silica sols. This is because under the same volume, the surface area of ​​the sphere is the smallest, so the surface energy of spherical particles is lower and they are more stable in thermodynamics. However, in the CMP process, sometimes non-spherical particles are desired, because non-spherical particles slide on the surface of the silicon wafer during polishing, while spherical particles are prone to rolling. The friction coefficient of the former is much larger, so the polishing effect is often better.

[0004] There are currently documents on the preparation of non-spherical colloid particles by hydrolysis of orthosilicate. However, the single document method usually requires the addition of metal ions to the silica sol for colloid coupling, which will undoubtedly increase the content of metal impurities in the product and fail to meet the requirements for fine polishing of silicon wafers. Summary of the invention

[0005] The purpose of the present invention is to propose a method for preparing non-spherical silica sol, aiming to break through the limitations of traditional preparation methods and prepare the required non-spherical silica sol by precisely controlling the morphology and particle size of the colloidal particles.

[0006] The technical solution adopted by the present invention to achieve its purpose is as follows:

[0007] A method for preparing a non-spherical silica sol comprises the following steps:

[0008] 1) adding anhydrous ethanol, water and tetraethyl orthosilicate into a flask, mixing and stirring, placing in a water bath and controlling the water bath temperature; at the same time, preparing ammonia water by mixing concentrated ammonia water and water;

[0009] 2) Slowly add ammonia water into the flask to react, and pause when the amount reaches 20% to 80%, to obtain small-diameter spherical particles;

[0010] 3) Aging the small-size spherical colloid particles, wherein the aging method is selected from room temperature stirring aging, heating aging, pH reduction aging, and concentration aging;

[0011] 4) Continue to add ammonia water to the reaction system of step 3) and continue stirring to finally form a non-spherical silica sol.

[0012] Furthermore, in step 1), the volume ratio of anhydrous ethanol, water and tetraethyl orthosilicate is (10-40):(1-5):(0.8-8).

[0013] Furthermore, in step 1), the water bath temperature is 10-40°C.

[0014] Furthermore, in step 1), the volume ratio of concentrated ammonia water to water required for preparing ammonia water is (2-8):(5-20), and the mass fraction of concentrated ammonia water is 25%.

[0015] Furthermore, in step 2), the rate of adding aqueous ammonia is 1 to 10 mL / min.

[0016] Furthermore, the conditions of the aging method in step 3) include:

[0017] Room temperature stirring aging: Stir at room temperature of 20-30℃ for more than 24 hours;

[0018] Heat aging: heat the reaction system to boiling for 10 to 100 minutes;

[0019] pH down aging: adjust the pH to 5-7.5 by adding acidic substances and stir for 5-30 minutes;

[0020] Concentration aging: Concentrate the reaction system to 20%-50% of the original volume, then stir for 30-180 minutes, restore the original volume, and continue the reaction.

[0021] Furthermore, in step 3), during the pH lowering aging, the acidic substance selected includes one of formic acid, acetic acid, oxalic acid, sulfuric acid, hydrochloric acid, and nitric acid, or carbon dioxide is introduced to form carbonic acid.

[0022] Furthermore, in the concentration and aging in step 3), vacuum distillation or ultrafiltration is used, and the reaction temperature must not exceed 40° C. during the vacuum distillation process.

[0023] Furthermore, in step 4), the reaction system is controlled at 10-40° C. and stirring is continued for not less than 24 hours.

[0024] The beneficial effects achieved by the present invention are as follows:

[0025] 1. The present invention can accurately adjust the morphology of silica sol particles by controlling the addition ratio of ammonia water and the aging time, and realize the preparation of various non-spherical particles such as strips, peanuts and nearly spherical particles.

[0026] 2. The present invention provides a variety of aging methods, including room temperature stirring, heating reaction, lowering the pH value and reactant concentration, which can be flexibly selected according to actual needs, and are easy to operate and highly adaptable.

[0027] 3. The present invention effectively promotes the polymerization and morphology control of the colloid particles by suspending the addition of ammonia water for aging, thus avoiding the limitation of single spherical colloid particles, and has high preparation efficiency and good morphology uniformity.

[0028] 4. The present invention can optimize the particle size and polymerization degree of the colloidal particles by adjusting the aging time and conditions, so that the prepared silica sol exhibits excellent performance in specific applications, such as enhanced dispersibility or special structural functions.

[0029] 5. The present invention adopts mild reaction conditions, such as controlling the temperature at 10-40°C, which reduces energy consumption, is safe to operate and is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the preparation principle of non-spherical silica sol.

[0031] Figure 2 This is a schematic diagram of the effect of aging time on product morphology.

[0032] Figure 3 This is an electron microscope photo of the product of Example 1.

[0033] Figure 4 This is an electron microscope photo of the product of Example 2.

[0034] Figure 5 This is an electron microscope photo of the product of Example 3.

[0035] Figure 6 This is an electron microscope photo of the comparative product. DETAILED DESCRIPTION

[0036] In order to make the various technical features and advantages or technical effects in the above technical solutions of the present invention more obvious and easy to understand, they are described in detail below in conjunction with embodiments.

[0037] The present invention proposes a method for preparing a non-spherical silica sol. The preparation principle is as follows: Figure 1 As shown, the specific preparation steps are as follows:

[0038] (1) Preparation of reactants

[0039] Add 1.0-4.0L of anhydrous ethanol, 100-500mL of water and 80-800mL of ethyl orthosilicate to a large flask, start magnetic stirring and set a high and low temperature water bath to keep the temperature of the reaction system at 10-40°C. At the same time, add 200-800mL of concentrated ammonia (mass fraction 25%) and 500-2000mL of water to a beaker, stir thoroughly and seal with plastic wrap.

[0040] (2) Formation of small-size spherical particles

[0041] The ammonia water in the beaker is slowly added to the flask through a peristaltic pump, and the adding rate is controlled at 1-10 mL / min. When the amount of ammonia water added reaches 20%-80%, the addition is stopped to form small-diameter spherical particles.

[0042] (3) Aging

[0043] You can choose one of the following options for aging treatment:

[0044] a. Aging under stirring at room temperature: Stir the reactants at room temperature of 20-30°C for more than 24 hours to ensure that the small-sized spherical particles have enough time to collide and covalently connect to form non-spherical particles.

[0045] b. Heating aging: Heat the reactants to boiling for 10 to 100 minutes. During the heating process, the thermal motion of the particles is accelerated and the collision frequency is increased, which is conducive to the covalent connection between the particles.

[0046] c. Lowering pH: Adjust the pH value to 5-7.5 by adding acidic substances, and continue stirring for 5-30 minutes. When the pH value is lowered, the negative charge on the surface of the colloid particles decreases, and the Coulomb repulsion between the colloid particles decreases, which is conducive to the collision and covalent connection between the colloid particles. Acidic substances that can be used to lower pH include formic acid, acetic acid, oxalic acid, sulfuric acid, hydrochloric acid, nitric acid, etc., or it can be achieved by passing carbon dioxide gas.

[0047] d. Concentration: Concentrate the reaction system to 20% to 50% of the original volume. Continue stirring for 30 to 180 minutes after concentration, then mix the solvent separated during the concentration process with the reactants, restore the volume before concentration, and continue the reaction. During the concentration process, the average distance between the colloid particles decreases, the collision frequency increases, and it is helpful to covalently connect the colloid particles. The concentration method can be vacuum distillation or ultrafiltration. During vacuum distillation, the heating temperature and vacuum degree must be controlled to ensure that the temperature of the reactants does not exceed 40°C.

[0048] (4) Growth of aging particles

[0049] Adjust the high and low temperature water bath to 10-40°C, and continue to add all the remaining ammonia water into the reaction system. Continue stirring for no less than 24 hours after adding, and finally obtain the silica sol product.

[0050] The basic principle of this preparation method is:

[0051] Ammonia water is slowly added to a mixed solution of ethanol-ethyl orthosilicate-water through a base-catalyzed hydrolysis reaction. During the hydrolysis process, ethyl orthosilicate is first hydrolyzed into orthosilicic acid, which polymerizes with each other to form seed crystals. Subsequently, the orthosilicic acid continues to condense on the surface of the seed crystals, increasing the seed crystal particle size and eventually forming a silica sol product. In order to prepare non-spherical silica sol, the addition of ammonia water is suspended after adding part of the ammonia water, and different aging methods (such as room temperature stirring, heating reaction, lowering the pH value or concentrating the reactants) are used to cause the colloid particles to collide with each other and covalently connect to form polymers. During the aging process, the morphology and particle size of the colloid particles will change, and the degree of deviation of the colloid particles from the spherical shape can be controlled by adjusting the aging time. When aging is performed in advance, the particle size of the colloid particles is small, the reaction activity is high, the degree of polymerization is large, and the final colloid particles are usually strip-shaped; while when aging is delayed, the particle size of the spherical colloid particles is large, the polymerization activity is low, and the final colloid particles are slightly deviated from the spherical shape. During the formation of the particles, stopping the feed at the right time and heating and aging the newly formed small-size particles can promote the collision and covalent connection of the particles to form aggregates. Subsequently, in the further growth process, the aggregates will develop into spherical, peanut-shaped or strip-shaped particles; if no aging treatment is performed, spherical particles will eventually be obtained.

[0052] Figure 2 The influence of aging time on product morphology is shown as follows:

[0053] 1. Aging when ammonia water is added to 30%: Aging is performed when ammonia water is added to 30% of the mixed solution. At this time, the primary particle size is small, the surface energy is high, and the degree of aggregation between particles is large during the aging process. Due to the high activity and strong aggregation of the particles, strip-shaped particles are eventually formed.

[0054] 2. Aging when ammonia water is added to 60%: Aging is carried out when ammonia water is added to 60% of the mixed solution. At this time, the primary particle size and surface energy are at a medium level. During the aging process, the particles undergo moderate micro-aggregation to form peanut-shaped particles. The degree of aggregation of the particles at this stage is between strips and nearly spherical.

[0055] 3. Aging when ammonia water is added to 80%: Aging is performed when ammonia water is added to 80% of the mixed solution. At this time, the primary particle size is larger, the surface energy is lower, and the aggregation between particles is weaker. The aggregation phenomenon is not significant during the aging process, and nearly spherical colloid particles are finally formed.

[0056] In summary, by adjusting the dosage ratio of ammonia water and the aging time, the morphology of the colloidal particles gradually changes from strips to peanuts and then to nearly spherical shapes. The differences in particle surface energy and polymerization activity corresponding to different aging times significantly affect the morphology and structure of the colloidal particles. This process reflects the key role of aging control in regulating the morphology of non-spherical silica sols.

[0057] Specific embodiments are listed below:

[0058] Example 1: Preparation of Strip Silica Sol (Heating Aging)

[0059] Add 1L of anhydrous ethanol, 100mL of water and 80mL of tetraethyl orthosilicate to the flask, add 200mL of concentrated ammonia water and 500mL of water to the beaker, and seal it with plastic wrap. Place the flask in a high and low temperature water bath, maintain the temperature at 40±1°C, then add ammonia water to the flask at a rate of 1mL / min. When the volume of ammonia water added reaches 300mL, stop feeding ammonia water, and heat the reactants in the flask to a slight boil, maintain this state for 1h, and then cool to 40±1°C. Continue to add ammonia water at a rate of 1mL / min, then stir for 36h to obtain the finished silica sol. See the electron microscope photo. Figure 3 .

[0060] Example 2: Preparation of Peanut-Shaped Silica Sol (Stirring and Aging at Room Temperature)

[0061] Add 3L of anhydrous ethanol, 300mL of water and 450mL of ethyl orthosilicate to the flask, add 600mL of concentrated ammonia water and 1000mL of water to the beaker, and seal it with plastic wrap. Place the flask in a high and low temperature water bath, maintain the temperature at 10±1℃, then add ammonia water to the flask at a rate of 4mL / min. When the volume of ammonia water added reaches 1700mL, stop feeding ammonia water, adjust the water bath temperature to 20℃, stir and age at room temperature for 48h, then continue to add ammonia water at a rate of 4mL / min, and then stir for 24h to obtain the finished silica sol. See the electron microscope photo. Figure 4 .

[0062] Example 3: Preparation of Nearly Spherical Silica Sol

[0063] Add 4L of anhydrous ethanol, 500mL of water and 800mL of tetraethyl orthosilicate into the flask, add 800mL of concentrated ammonia water and 2000mL of water into the beaker, and seal it with plastic wrap. Place the flask in a high and low temperature water bath, maintain the temperature at 25±1°C, then add ammonia water into the flask at a rate of 10mL / min. When the volume of ammonia water added reaches 2300mL, suspend the ammonia feeding, then add 2mol / L of acetic acid into the flask at a rate of 5mL / min, and use a pH meter to monitor the pH value until the pH reaches 6. Stir for 30 minutes after the acetic acid is added. Then continue to add ammonia water at a rate of 10mL / min, and then stir for 24h to obtain the finished silica sol. See the electron microscope photo. Figure 5 .

[0064] Example 4: Preparation of Peanut-Shaped Silica Sol (Concentrated Aging)

[0065] Add 2.5L of anhydrous ethanol, 250mL of water and 400mL of tetraethyl orthosilicate to the flask, add 500mL of concentrated ammonia water and 800mL of water to the beaker, and seal it with plastic wrap. Place the flask in a high and low temperature water bath, maintain the temperature at 10±1℃, then add ammonia water to the flask at a rate of 4mL / min. When the volume of ammonia water added reaches 2000mL, suspend the ammonia water feeding, then install a vacuum distillation device on the reaction flask, control the liquid temperature in the flask to ≤40℃, concentrate until about half of the liquid is evaporated, and then stir at normal pressure for 180min. Then pour the distilled liquid back into the flask, continue to add ammonia water at a rate of 4mL / min, and then stir for 24h to obtain the finished silica sol. Electron microscope photos are supplemented later.

[0066] Comparative example: Spherical silica sol

[0067] The comparative example was carried out according to the parameters of Example 2, except that the heating aging process was removed.

[0068] Add 3L of anhydrous ethanol, 500mL of water and 450mL of ethyl orthosilicate into the flask, add 900mL of concentrated ammonia water and 2000mL of water into the beaker, and seal it with plastic wrap. Place the flask in a high and low temperature water bath, maintain the temperature at 20±1℃, then add ammonia water into the flask at a rate of 4mL / min until it is added, and then stir for 24h to obtain the finished silica sol. The electron microscope photo is shown in Figure 6 .

[0069] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Appropriate modifications or equivalent substitutions of the technical solutions of the present invention made by ordinary technicians in the field should all be included in the protection scope of the present invention. The protection scope of the present invention shall be based on what is defined in the claims.

Claims

1. A method for preparing a non-spherical silica sol, characterized in that: The following steps are involved: 1) adding anhydrous ethanol, water and tetraethyl orthosilicate into a flask, mixing and stirring, placing in a water bath and controlling the water bath temperature; at the same time, preparing ammonia water by mixing concentrated ammonia water and water; 2) Slowly add ammonia water into the flask to react, and pause when the amount reaches 20% to 80%, to obtain small-diameter spherical particles; 3) Aging the small-size spherical colloid particles, wherein the aging method is selected from room temperature stirring aging, heating aging, pH reduction aging, and concentration aging; 4) Continue to add ammonia water to the reaction system of step 3) and continue stirring to finally form a non-spherical silica sol.

2. The preparation method according to claim 1, characterized in that In step 1), the volume ratio of anhydrous ethanol, water and tetraethyl orthosilicate is (10-40):(1-5):(0.8-8).

3. The preparation method according to claim 1, characterized in that: In step 1), the water bath temperature is 10-40°C.

4. The preparation method according to claim 1, characterized in that: The volume ratio of concentrated ammonia water and water required for preparing ammonia water in step 1) is (2-8):(5-20), and the mass fraction of concentrated ammonia water is 25%.

5. The preparation method according to claim 1 or 4, characterized in that: In step 2), the rate of adding ammonia water is 1-10 mL / min.

6. The preparation method according to claim 1, characterized in that: The conditions of the aging method in step 3) include: Room temperature stirring aging: Stir at room temperature of 20-30℃ for more than 24 hours; Heat aging: heat the reaction system to boiling for 10 to 100 minutes; pH down aging: adjust the pH to 5-7.5 by adding acidic substances and stir for 5-30 minutes; Concentration aging: Concentrate the reaction system to 20%-50% of the original volume, then stir for 30-180 minutes, restore the original volume, and continue the reaction.

7. The preparation method according to claim 6, characterized in that: In step 3), in the pH lowering aging, the acidic substance selected includes one of formic acid, acetic acid, oxalic acid, sulfuric acid, hydrochloric acid, and nitric acid, or carbon dioxide is introduced to form carbonic acid.

8. The preparation method according to claim 6, characterized in that: In step 3), during the concentration and aging, vacuum distillation or ultrafiltration is used. During the vacuum distillation process, the reaction temperature must not exceed 40°C.

9. The preparation method according to claim 1, characterized in that: In step 4), the reaction system is controlled at 10-40° C. and stirring is continued for not less than 24 hours.

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