An alumina powder for polishing and a preparation method thereof

Abstract

The present invention provides an alumina powder for polishing and a preparation method thereof. The method includes: selecting an aluminum hydroxide raw material, adding it to hot pure water, and adding a growth agent to prepare a first slurry; adding a pH regulator to the first slurry, adjusting it to an acidic state, and grinding to obtain an aluminum hydroxide mother liquor; washing the aluminum hydroxide mother liquor with a ceramic membrane and concentrating it to obtain a second slurry; performing hydrothermal crystallization treatment on the second slurry, washing it with a ceramic membrane after treatment, and drying to obtain an alumina precursor; calcining the alumina precursor to obtain an alumina powder. This method has simple processes, is easy to control, and the obtained alumina powder has a flat plate-like structure, regular shape, few edges and corners, a flat surface, appropriate particle size and thickness dimensions, and is suitable for use as a fine polishing material for semiconductor wafers.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic materials, and particularly relates to alumina powder for polishing and a preparation method thereof. Background Art

[0002] With the rapid rise of semiconductor chip manufacturing, the demand for wafer fine polishing is increasing. Currently, SiO2 abrasive polishing slurries are commonly used for fine polishing. However, SiO2 has a relatively low hardness and a relatively slow polishing rate, requiring further improvement in both polishing accuracy and efficiency. Alumina particles are currently used as an abrasive for wafer fine polishing. Due to their greater hardness and uniform particle size distribution, alumina increases friction with the product, significantly improving grinding speed, shortening grinding time, and reducing grinding costs. However, existing nano-sized alumina particles, due to their irregular and angular morphology, are prone to scratching wafers, hindering their practical application in wafer polishing. Summary of the Invention

[0003] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide an alumina powder for polishing and a preparation method thereof. The alumina powder prepared by this method has a flat structure, regular shape, smooth surface, appropriate particle size and thickness, and is suitable for use as a precision polishing material for semiconductor wafers.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A method for preparing alumina powder for polishing, comprising the following steps:

[0006] Step S1, selecting aluminum hydroxide raw material, adding it to hot pure water, and adding a growth agent to prepare a first slurry;

[0007] Step S2, adding a pH regulator to the first slurry to adjust to acidic pH, grinding, and obtaining an aluminum hydroxide mother liquor;

[0008] Step S3, washing the aluminum hydroxide mother liquor with a ceramic membrane and concentrating it to obtain a second slurry;

[0009] Step S4, subjecting the second slurry to a hydrothermal crystallization treatment, washing with a ceramic membrane after the treatment, and drying to obtain an alumina precursor;

[0010] Step S5: calcining the alumina precursor to obtain alumina powder.

[0011] In one embodiment of the present application, in step S1, the temperature of the hot pure water is 50-80° C., and the solid content of aluminum hydroxide in the first slurry is 40% or more.

[0012] In one embodiment of the present application, the growth agent is one or more of titanium dioxide, potassium sulfate, sodium sulfate, aluminum fluoride, ammonium fluoride, titanium trifluoride, and aluminum sulfate; the addition amount of the growth agent is 0.3-0.8% of the mass of the aluminum hydroxide raw material by mass;

[0013] and / or, the pH regulator is one or more of sulfuric acid, acetic acid, polyacrylic acid, lactic acid, and oxalic acid.

[0014] In one embodiment of the present application, in step S2, a pH regulator is added to the first slurry to adjust its pH to within the range of 2.0-6.0;

[0015] and / or, in step S2, the grinding time is 0.5-5 h, and the particle size of the solid content in the aluminum hydroxide mother liquor is ≤200 nm.

[0016] In one embodiment of the present application, in step S3, the number of times of washing the aluminum hydroxide mother liquor through a ceramic membrane and the concentration ratio are controlled so that the solid content of the obtained second slurry is about 40%, and the conductivity of the second slurry is ≤50 us / cm.

[0017] In one embodiment of the present application, in step S4, the hydrothermal crystallization temperature is 160-300 °C, and the hydrothermal crystallization treatment time is 2-24 h.

[0018] In one embodiment of the present application, in step S4, after hydrothermal crystallization treatment, it is washed multiple times through a ceramic membrane. When the solid content of the washed slurry is about 40%, the conductivity is within the range of 10-50 us / cm.

[0019] In one embodiment of the present application, in step S4, spray drying is used, and the particle size of the obtained alumina precursor is ≤500 nm.

[0020] In one embodiment of the present application, in step S5, the calcination temperature is 1000-1050 °C, and the calcination time is 3-10 h.

[0021] A polishing alumina powder is prepared by using the preparation method described in any one of the above, and the alumina powder has a flat plate structure, an average particle size of 0.5-5 μm, and an average thickness of 20-200 nm.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] The preparation method of the present invention is as follows: aluminum hydroxide raw materials are added to hot pure water and a growth agent to prepare a slurry, and a pH regulator is added. Grinding is carried out in an acidic system. After grinding, an aluminum hydroxide mother liquor is obtained. After washing and concentration to remove impurities, hydrothermal crystallization is carried out. After hydrothermal crystallization, washing and drying are carried out to obtain an alumina precursor. The alumina precursor is calcined to obtain alumina powder. Grinding in an acidic system can effectively control the particle size and morphology of the solids content in the aluminum hydroxide mother liquor, providing a guarantee for obtaining products with uniform particle size, regular and flat morphology subsequently. Two washings are carried out to ensure obtaining an alumina precursor with high purity and dense structure, reducing the influence of impurities on subsequent calcination, and providing a guarantee for obtaining alumina powder with high hardness, regular structure and flat surface subsequently. This method has low requirements for the purity and morphology of aluminum hydroxide raw materials. The alumina powder obtained by this method has a flat plate structure, regular and uniform shape, flat surface, and dense structure. The average particle size is in the range of 0.5 - 5 μm, and the average thickness is in the range of 20 - 200 nm. It is suitable for use as a fine polishing material for semiconductor wafers because of its good flatness and high hardness, with high grinding accuracy and fast grinding speed during fine polishing processing. The preparation process flow of this method is simple, and each process is easy to control, which is suitable for popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 It is a process flow chart for the preparation of alumina powder for polishing according to the present invention.

[0026] Figure 2 It is a scanning electron microscope picture of the alumina powder prepared in Example 1 of the present invention.

[0027] Figure 3 It is a scanning electron microscope picture of the alumina powder prepared in Example 2 of the present invention.

[0028] Figure 4 It is a scanning electron microscope picture of the alumina powder prepared in Example 3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] In the following, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the drawings and the description are considered to be exemplary in nature rather than restrictive.

[0030] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0031] As Figure 1 , Figure 2 , Figure 3 and Figure 4 shown, the present invention provides an alumina powder for polishing and a preparation method thereof. The preparation method follows the process shown in Figure 1 . Using commercially available industrial aluminum hydroxide as the raw material, a growth agent is added and mixed with hot pure water to prepare a first slurry. The pH of the first slurry is adjusted to acidic, and the aluminum hydroxide mother liquor is obtained by grinding under acidic conditions. After being washed multiple times with a ceramic membrane and concentrated, a second slurry is obtained. The second slurry is subjected to hydrothermal crystallization treatment, washed again, and dried to obtain an alumina precursor, and finally calcined to obtain an alumina powder. The alumina powder obtained by this method has a flat plate-like structure, with regular and uniform shape, a flat surface, a compact structure, an average particle size in the range of 0.5 - 5 μm, and an average thickness in the range of 20 - 200 nm. Due to its good flatness, high hardness, and appropriate particle size and thickness dimensions, it is suitable for use as a fine polishing material for semiconductor wafers, and has high grinding accuracy and fast grinding speed during fine polishing.

[0032] Specifically, a preparation method of an alumina powder for polishing includes the following steps:

[0033] S1, Select industrial aluminum hydroxide prepared by methods such as the Bayer process, choline process, direct hydrolysis method, co-precipitation method, or alkoxide hydrolysis method as the raw material, add it to hot pure water at 50 - 80 °C, and add a certain proportion of a growth agent, and stir and mix well to prepare a first slurry with a solid content of 40% or more. Preferably, the solid content in the first slurry is 40 - 50%.

[0034] Using hot pure water at 50 - 80 °C for preparation can fully wet the aluminum hydroxide raw material, and uniformly mix and contact-react with the growth agent.

[0035] The growth agent can be one or more of titanium dioxide, potassium sulfate, sodium sulfate, aluminum fluoride, ammonium fluoride, titanium trifluoride, and aluminum sulfate. The addition amount of the growth agent should be controlled at 0.3 - 0.8% of the mass of the aluminum hydroxide raw material by mass.

[0036] Preferably, the aluminum hydroxide raw material is first added to hot pure water and stirred and wetted sufficiently, and the stirring time is controlled at 0.5 - 1 h; then the growth agent is added, and stirred and mixed well, and reacted for 0.5 - 3 h to prepare the first slurry.

[0037] S2, Add a pH regulator to the first slurry prepared above, mix well, adjust the pH to acidic, and then grind to obtain an aluminum hydroxide mother liquor.

[0038] Among them, the pH regulator can be selected from one or more of sulfuric acid, acetic acid, polyacrylic acid, lactic acid and oxalic acid; preferably, the pH value of the slurry is adjusted to be within the range of 2.0 - 6.0 for grinding.

[0039] The grinding can be carried out by a planetary ball mill, a sand mill, a vibration mill or a colloid mill; the grinding time should be controlled within the range of 0.5 - 5h, and the particle size of the solid content in the obtained aluminum hydroxide mother liquor should be controlled ≤200nm.

[0040] S3. Wash the above - obtained aluminum hydroxide mother liquor through a ceramic membrane for multiple times, and then concentrate it to obtain a second slurry.

[0041] Among them, the ceramic membrane can be selected from a ceramic flat membrane, a ceramic tubular membrane or a ceramic disc membrane for washing. By controlling the number of washing times and the concentration ratio, the solid content of the obtained second slurry is maintained at about 40%, and the conductivity of the second slurry is reduced to within 50 us / cm. This is beneficial to obtaining alumina products with fewer edges and corners, regular morphology, dense texture and appropriate size during the subsequent hydrothermal crystallization and calcination processes.

[0042] S4. Feed the above - obtained second slurry into a reaction kettle, carry out hydrothermal crystallization treatment at a temperature of 160 - 300°C for 2 - 24h. After the hydrothermal crystallization treatment, wash it through a ceramic membrane for multiple times, control the number of washing times, when the solid content of the washed slurry is about 40%, the conductivity of the slurry is within the range of 10 - 50 us / cm; then carry out spray drying to obtain an alumina precursor, and this alumina precursor is pseudo - boehmite and / or boehmite, and the particle size of this alumina precursor is ≤500nm.

[0043] S5. Feed the obtained alumina precursor into a kiln for calcination, control the calcination temperature within the range of 1000 - 1050°C, and the calcination time is 3 - 10h. Preferably, the calcination time is controlled within 5 - 8h to obtain alumina powder.

[0044] Calcining at a temperature of 1000 - 1050°C and controlling the calcination duration within 3 - 10h can make the surface of the obtained alumina powder smooth and flat, and it is not easy for the powders to adhere and connect to each other, and the morphology is more regular and uniform.

[0045] The alumina powder prepared by this method has a relatively thin flat - plate structure, with a relatively regular shape, mostly in structures such as rhombus, hexagon, quadrilateral, etc., having fewer edges and corners, a flat surface and a dense structure; the average particle size of this alumina powder is 0.5 - 5μm, and the average thickness is 20 - 200nm; it can contact with the crystal plane well, meet the fine polishing requirements of the semiconductor wafer without scratching the crystal plane; therefore, the alumina powder prepared by this method is suitable for use as a fine polishing material for semiconductor wafers.

[0046] Example 1

[0047] A preparation method of alumina powder for polishing, comprising the following steps:

[0048] S1, Select bayer process industrial seeded precipitation aluminum hydroxide raw material, add it into hot pure water at 50 °C, and add growth agent titanium dioxide, the addition amount of titanium dioxide is 0.3% of the mass of the aluminum hydroxide raw material; after adding, stir and mix fully to prepare a first slurry with a solid content of about 40%.

[0049] S2, Add pH regulator sulfuric acid to the prepared first slurry, mix well, adjust the pH of the slurry to about 3.5, then use a planetary ball mill for grinding, control the grinding time to be 1 h, the particle size of the discharge of the planetary ball mill is about 150 nm, and obtain aluminum hydroxide mother liquor after grinding; the particle size of the solid content in the aluminum hydroxide mother liquor is about 150 nm.

[0050] S3, Wash the obtained aluminum hydroxide mother liquor through a ceramic flat membrane for 3 times, and concentrate it to a solid content of about 40% after washing to obtain a second slurry, and measure the conductivity of the second slurry to be about 48 us / cm.

[0051] S4, Feed the obtained second slurry into a steam curing kettle, perform hydrothermal crystallization treatment at a temperature of 160 - 200 °C for 12 h, and wash it through a ceramic flat membrane after hydrothermal crystallization treatment for 3 times; when the solid content of the slurry after washing is about 40%, measure the conductivity of the slurry to be about 44 us / cm; then perform spray drying to obtain an alumina precursor, the alumina precursor is pseudo-boehmite and / or boehmite, and the average particle size of the alumina precursor is about 350 nm. After the process is determined, spray drying can be directly carried out after washing 3 times, or spray drying can be carried out after concentrating to an appropriate concentration after washing, without strictly controlling the concentration to a solid content of about 40%.

[0052] S5, Feed the obtained alumina precursor into a kiln for calcination, control the calcination temperature to be about 1050 °C, and the calcination time to be 5 h to obtain alumina powder.

[0053] The scanning electron microscope picture of the alumina powder is as Figure 2 shown, the average particle diameter of the powder is 0.72 μm, and the average thickness is 118 nm. According to Figure 2 it can be seen that the alumina powder is mainly in a rhombic or quasi-rhombic flat plate structure, with regular and uniform structure, flat surface, and tight structure.

[0054] Example 2

[0055] A preparation method of alumina powder for polishing, comprising the following steps:

[0056] S1. Select Bayer process industrial grade aluminum hydroxide raw material, add it to 70°C hot pure water, and add titanium dioxide as a growth agent. The amount of titanium dioxide added is 0.5% of the mass of the aluminum hydroxide raw material. After adding, stir and mix thoroughly to prepare a first slurry with a solid content of about 50%.

[0057] S2, adding acetic acid as a pH adjuster to the prepared first slurry, mixing thoroughly, adjusting the pH of the slurry to about 5.0, then grinding with a planetary ball mill, controlling the grinding time to be 4 hours, and the output particle size of the planetary ball mill to be about 200 nm, to obtain an aluminum hydroxide mother liquor after grinding; the particle size of the solid content in the aluminum hydroxide mother liquor is about 200 nm.

[0058] S3, washing the obtained aluminum hydroxide mother liquor through a ceramic flat membrane for 4 times, and concentrating it to a solid content of about 40% after washing to obtain a second slurry. The conductivity of the second slurry is measured to be about 27 us / cm.

[0059] S4, passing the obtained second slurry into a hydrothermal pressure autoclave, hydrothermally crystallizing it at a temperature of 220-260°C for 12 hours, and then washing it with a ceramic flat membrane for 4 times; then spray drying it to obtain an alumina precursor, which is pseudo-boehmite and / or boehmite, and has an average particle size of about 460nm.

[0060] S5, the obtained alumina precursor is introduced into a kiln for calcination, the calcination temperature is controlled at about 1000° C., the calcination time is 5 hours, and alumina powder is obtained.

[0061] The scanning electron microscope image of the alumina powder is as follows Figure 3 As shown in Figure 2, the average particle size of the powder is 1.12 μm and the average thickness is 33 nm. Figure 3 It can be seen that the alumina powder mainly presents a hexagonal or quasi-hexagonal flat plate structure with a regular and uniform structure, a smooth surface and a compact structure.

[0062] Example 3

[0063] A method for preparing alumina powder for polishing, comprising the following steps:

[0064] S1. Select Bayer process industrial grade aluminum hydroxide raw material, add it to 60°C hot pure water, and add titanium dioxide as a growth agent. The amount of titanium dioxide added is 0.8% of the mass of the aluminum hydroxide raw material. After adding, stir and mix thoroughly to prepare a first slurry with a solid content of about 42%.

[0065] S2. Add acetic acid, a pH regulator, to the prepared first slurry, mix well, and adjust the pH of the slurry to about 4.5. Then, grind it using a planetary ball mill, control the grinding time to be 4 h, and the particle size of the discharged material from the planetary ball mill to be about 200 nm to obtain an aluminum hydroxide mother liquor; the particle size of the solid content in the aluminum hydroxide mother liquor is about 200 nm.

[0066] S3. Wash the obtained aluminum hydroxide mother liquor through a ceramic flat membrane 5 times, and concentrate it after washing to a solid content of about 40% to obtain a second slurry. The measured conductivity of the second slurry is about 23 us / cm.

[0067] S4. Feed the obtained second slurry into a hydrothermal autoclave, perform hydrothermal crystallization treatment at a temperature of 220 - 260 °C for 12 h, and clean it through a ceramic flat membrane 5 times after the hydrothermal crystallization treatment; then perform spray drying to obtain an alumina precursor, which is pseudo-boehmite and / or boehmite, and the average particle size of the alumina precursor is about 480 nm.

[0068] S5. Feed the obtained alumina precursor into a kiln for calcination, control the calcination temperature to be about 1000 °C, and the calcination time to be 8 h to obtain an alumina powder.

[0069] The scanning electron microscope image of the alumina powder is as Figure 4 shown. Its average particle diameter of the powder is 1.05 μm, and the average thickness is 35 nm. It can be seen from Figure 4 this that the alumina powder is mainly in the shape of a hexagonal or quasi-hexagonal flat plate structure, with a regular and uniform structure, a flat surface, and a dense structure.

[0070] In summary, for the preparation method of the present application, aluminum hydroxide raw materials are added to hot pure water and a growth agent to prepare a slurry, and a pH regulator is added. Grinding is carried out in an acidic system. After grinding, an aluminum hydroxide mother liquor is obtained. After washing and concentration to remove impurities, hydrothermal crystallization is carried out. After hydrothermal crystallization, washing and drying are carried out to obtain an alumina precursor. The alumina precursor is calcined to obtain alumina powder. The method carries out grinding in an acidic system, which can effectively control the particle size and morphology of the solids in the aluminum hydroxide mother liquor, providing a guarantee for obtaining products with uniform particle size, regular morphology, and flat surface in the subsequent process. Two washes are carried out to ensure obtaining an alumina precursor with high purity and dense structure, reducing the influence of impurities on the subsequent calcination, and providing a guarantee for obtaining alumina powder with high hardness, regular structure, few edges and corners, and flat surface in the subsequent process. The method has low requirements for the purity and morphology of aluminum hydroxide raw materials. The alumina powder obtained by this method has a flat plate structure, with regular and uniform shape, flat surface, and dense structure. The average particle size is in the range of 0.5 - 5 μm, and the average thickness is in the range of 20 - 200 nm. It is suitable for use as a fine polishing material for semiconductor wafers because of its good flatness and high hardness, and has high grinding accuracy and fast grinding speed during fine polishing. The preparation process flow of this method is simple, and each process is easy to control, which is suitable for popularization and application.

Claims

1. A method for preparing alumina powder for polishing, characterized in that It includes the following steps: Step S1: Select aluminum hydroxide raw materials, add them to hot pure water, and add a growth agent to prepare a first slurry; Step S2: Add a pH regulator to the first slurry, adjust it to acidic, and grind it in an acidic system to obtain an aluminum hydroxide mother liquor; Step S3: Wash and concentrate the aluminum hydroxide mother liquor through a ceramic membrane to obtain a second slurry; Step S4: Perform hydrothermal crystallization treatment on the second slurry, wash it through a ceramic membrane after treatment, and dry it to obtain an alumina precursor; Step S5: Calcinate the alumina precursor to obtain an alumina powder; Among them, in Step S1, the temperature of the hot pure water is 50 - 80 °C. The aluminum hydroxide raw materials are first added to the hot pure water and stirred sufficiently to be wetted, and then the growth agent is added and stirred and mixed sufficiently, and the reaction is carried out for 0.5 - 3 h. The solid content of aluminum hydroxide in the prepared first slurry is above 40%; The growth agent is one or more of titanium dioxide, potassium sulfate, sodium sulfate, aluminum fluoride, ammonium fluoride, titanium trifluoride, and aluminum sulfate; the addition amount of the growth agent is 0.3 - 0.8% by mass of the aluminum hydroxide raw materials; In Step S2, the grinding time is 0.5 - 5 h, and the particle size of the solid content of the aluminum hydroxide mother liquor is ≤200 nm; In Step S3, the solid content of the second slurry is 40%, and the conductivity of the second slurry is ≤50 μs / cm; In Step S4, after hydrothermal crystallization treatment, it is washed through a ceramic membrane multiple times, and the solid content of the washed slurry is controlled to be 40%, and the conductivity is in the range of 10 - 50 μs / cm; the particle size of the obtained alumina precursor is ≤500 nm.

2. The preparation method of the alumina powder for polishing according to claim 1, characterized in that, The pH regulator is one or more of sulfuric acid, acetic acid, polyacrylic acid, lactic acid, and oxalic acid.

3. The preparation method of the alumina powder for polishing according to claim 2, characterized in that, In Step S2, a pH regulator is added to the first slurry to adjust its pH to the range of 2.0 - 6.

0.

4. The preparation method of the alumina powder for polishing according to claim 1, characterized in that In Step S4, the temperature of hydrothermal crystallization is 160 - 300 °C, and the hydrothermal crystallization treatment time is 2 - 24 h.

5. The preparation method of the alumina powder for polishing according to claim 4, characterized in that, In Step S4, spray drying is adopted.

6. The preparation method of the alumina powder for polishing according to claim 1, characterized in that, In Step S5, the calcination temperature is 1000 - 1050 °C, and the calcination time is 3 - 10 h.

Images