High-purity silicon carbide ceramic and preparation method thereof

Abstract

The invention belongs to the field of ceramics, and particularly relates to a high-purity silicon carbide ceramic and a preparation method thereof. Comprising the following steps: adding powder into a ball mill, adding deionized water, stirring, and carrying out ball milling to form water-based slurry; the powder is prepared from micron-scale alpha-silicon carbide powder, nano-scale alpha-silicon carbide powder, polyethylene glycol and polyvinyl alcohol which are different in particle size; carrying out spray granulation on the obtained water-based slurry; and adding the obtained granulated powder into a graphite mold in an oscillating hot-pressing sintering furnace, pre-pressing, heating and boosting to a set sintering temperature and a set sintering pressure, and performing oscillating hot-pressing sintering to obtain the high-purity silicon carbide ceramic. By adopting the method, the mechanical property of the high-purity silicon carbide ceramic can be remarkably improved.

Description

Technical Field

[0001] The invention belongs to the field of ceramics, and in particular relates to a high-purity silicon carbide ceramic and a preparation method thereof. Background Art

[0002] A wafer boat is a carrier device used to store, transport, react and process silicon wafers in the semiconductor manufacturing process and requires the use of high-purity silicon carbide ceramics.

[0003] In industry, silicon carbide ceramic materials are mainly prepared by reaction sintering and pressureless sintering. The former mainly generates silicon carbide materials through chemical reactions of carbon sources and silicon sources under high temperature conditions, and has a low density. Although the silicon carbide ceramics obtained are of high purity, there are often excess silicon residues inside and outside. Pressureless sintering is mainly due to the high sintering difficulty, and it is necessary to add certain sintering aids to the raw materials to promote the mass transfer process during the sintering process, which runs counter to the demand for high-purity silicon carbide ceramics. Therefore, the silicon carbide ceramic materials prepared by the two sintering technologies are greatly limited in the field of crystal boats.

[0004] With the continuous development of sintering technology, the sintering technology of silicon carbide ceramics has developed from reaction sintering and pressureless sintering to oscillating hot pressing sintering. Hot pressing sintering is a process in which the green body composed of silicon carbide powder is heated and sintered while applying external pressure that changes with a certain frequency to the green body through mechanical action along the axial direction, providing an additional driving force for the entire sintering process, so that the green body can quickly complete densification and achieve the simultaneous sintering and forming processes. Since the oscillating external pressure provides an additional sintering driving force, oscillating hot pressing sintering can greatly reduce the sintering difficulty of silicon carbide ceramics compared to pressureless sintering, thereby significantly reducing the amount of sintering aids required for ceramic densification sintering, thereby improving the purity of silicon carbide ceramics. Therefore, oscillating hot pressing sintering is an effective development direction for obtaining high-purity silicon carbide ceramic materials, which is of great significance to the application of silicon carbide ceramic materials in the field of crystal boats.

[0005] At present, there are relatively few reports on the preparation of high-purity silicon carbide ceramic materials by oscillating hot pressing and sintering. At present, the research on the preparation of high-purity silicon carbide ceramics is mainly focused on recrystallization sintering and reaction sintering. For example, the patent with publication number CN115466123B reported a high-purity silicon carbide prepared by two-step reaction sintering, which achieved a high density and purity, but in terms of mechanical properties, it has obvious defects due to the presence of elemental silicon inside. Another patent with publication number CN109678514A reported a high-purity silicon carbide ceramic prepared by recrystallization sintering, which also performed poorly in terms of mechanical properties. Therefore, there is a lot of room for development and research value in the preparation of high-performance and high-purity silicon carbide ceramic materials by oscillating hot pressing and sintering. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a high-purity silicon carbide ceramic and a preparation method thereof.

[0007] In order to solve the above technical problems, the present invention provides a method for preparing high-purity silicon carbide ceramics, comprising the following steps:

[0008] 1) Slurry preparation:

[0009] Add the powder into the ball mill, add deionized water, stir and ball mill to form a water-based slurry;

[0010] The powder material is composed of 20 to 30 parts of micron-grade α-silicon carbide powder I, 30 to 40 parts of micron-grade α-silicon carbide powder II, 10 to 20 parts of micron-grade α-silicon carbide powder III, 10 to 40 parts of nano-grade α-silicon carbide powder, 2±0.1 parts of polyethylene glycol (as a dispersant), and 1±0.1 parts of polyvinyl alcohol (as a binder);

[0011] The particle size of micron-grade α-silicon carbide powder I is 5 to 10 μm, the particle size of micron-grade α-silicon carbide powder II is 1 to 4 μm, the particle size of micron-grade α-silicon carbide powder III is 0.4 to 0.6 μm, and the particle size of nano-grade α-silicon carbide powder is 38 to 42 nm;

[0012] 2) Spray granulation:

[0013] The water-based slurry obtained in step 1) is subjected to spray granulation to prepare spherical granulated powder;

[0014] 3) Oscillating hot pressing sintering:

[0015] The granulated powder obtained in step 2) is added into a graphite mold in an oscillating hot pressing sintering furnace, pre-pressed at a pressure of 35-45 MPa (preferably 40 MPa) for 4-6 minutes, and then heated and pressurized to a set sintering temperature and a set sintering pressure, and oscillated hot pressing sintering is performed to obtain high-purity silicon carbide ceramics.

[0016] As an improvement to the preparation method of high-purity silicon carbide ceramics of the present invention: the spray drying granulation in step 2) is as follows: the water-based slurry feed rate is 30-60 mL / min, the hot air inlet temperature is 250-300°C, the outlet temperature is 70-90°C, and the centrifugal atomizer is 40-70 Hz.

[0017] As a further improvement of the preparation method of the high-purity silicon carbide ceramic of the present invention: the oscillation hot pressing sintering in step 3) is:

[0018] First, the temperature is raised to the set sintering temperature at a heating rate of 5-10°C / min; during the heating process, the external pressure is evenly increased from the initial pressure to the set sintering pressure; then, the oscillation hot pressing sintering is performed at the set sintering temperature and the set sintering pressure for 50-70 minutes;

[0019] The set sintering temperature is 1900-2200° C., the initial pressure is 5-10 MPa, and the set sintering pressure is (20±5)-(40±5) MPa.

[0020] As a further improvement to the method for preparing high-purity silicon carbide ceramics of the present invention: the oscillation frequency of step 3) is 1 Hz and the amplitude is 10 MPa.

[0021] As a further improvement of the preparation method of the high-purity silicon carbide ceramic of the present invention: the oscillation hot pressing sintering in step 3) is:

[0022] The heating rate is divided into two stages. In the first stage, when the temperature is raised to 1800±50°C, the heating rate is 10±1°C / min. In the second stage, when the temperature is raised from 1800±50°C to the set sintering temperature, the heating rate is 5±0.5°C / min.

[0023] As a further improvement of the preparation method of the high-purity silicon carbide ceramic of the present invention: the mass ratio of powder: deionized water = 1: (1.5±0.1).

[0024] As a further improvement of the preparation method of the high-purity silicon carbide ceramic of the present invention:

[0025] Step 2): slurry feed rate 30mL / min, hot air inlet temperature 285°C, outlet temperature 90°C, centrifugal atomizer frequency modulation 48Hz;

[0026] Step 3): the sintering temperature is set at 2000-2100°C, the initial pressure is 5-10Mpa, the sintering pressure (oscillation pressure in the insulation stage) is set at 40±5Mpa, the sintering time is 60min, and the oscillation frequency is 1Hz.

[0027] As a further improvement of the preparation method of the high-purity silicon carbide ceramic of the present invention: the purity of micron-grade α-silicon carbide powder I, micron-grade α-silicon carbide powder II, and micron-grade α-silicon carbide powder III is ≥99.99%;

[0028] The purity of nano-scale α-silicon carbide powder is ≥99.9%.

[0029] As a further improvement of the preparation method of the high-purity silicon carbide ceramic of the present invention: the powder material is composed of 20 to 25 parts of micron-grade α-silicon carbide powder I, 40 parts of micron-grade α-silicon carbide powder II, 20 parts of micron-grade α-silicon carbide powder III, 15 to 20 parts of nano-grade α-silicon carbide powder, 2 parts of polyethylene glycol, and 1 part of polyvinyl alcohol;

[0030] Sintering temperature 2000℃-2100℃.

[0031] The present invention also provides high-purity silicon carbide ceramics obtained by oscillating hot pressing sintering technology according to any of the above methods, which can be used to prepare a wafer boat.

[0032] The present invention adopts an oscillating hot pressing sintering method and successfully prepares a high-purity silicon carbide ceramic material without using a sintering aid. In the sintering process, the external pressure is applied by mechanical action to provide an additional sintering driving force, which reduces the difficulty of the silicon carbide ceramic sintering process and enables the ceramic powder to be sintered and dense at a lower insulation temperature than recrystallization sintering, which has a high practical value in the application field of special ceramics such as crystal boats.

[0033] The beneficial effects of the present invention are mainly reflected in:

[0034] Silicon carbide powder with reasonable particle size distribution is used to produce high-purity (purity> 99.96%) silicon carbide ceramics through oscillating hot pressing with the assistance of oscillating pressure of a certain frequency without adding sintering aids.

[0035] In summary, the method for preparing high-purity silicon carbide ceramics by oscillating hot pressing and sintering provided by the present invention can produce high-purity and high-density silicon carbide ceramics on the premise that basically only high-purity silicon carbide powder is used as raw material, and can significantly improve the mechanical properties (including bending strength, hardness, etc.) of high-purity silicon carbide ceramics, overcome the problems of insufficient purity and poor performance faced by traditional silicon carbide ceramic preparation methods when applied in the semiconductor field, and has great application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0037] Figure 1 From left to right are cross-sectional scanning electron microscope images of Example 1-2, Example 2-2, and Example 3-2. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0039] In the present invention:

[0040] The purity of micron-grade α-silicon carbide powder I, micron-grade α-silicon carbide powder II, and micron-grade α-silicon carbide powder III is ≥ 99.99%;

[0041] The purity of nano-scale α-silicon carbide powder is ≥99.9%.

[0042] Example 1-1: A method for preparing high-purity silicon carbide ceramics, comprising the following steps in sequence:

[0043] 1) Slurry preparation:

[0044] The powder raw material is composed of the following components: 30 parts of micron-grade α-silicon carbide powder I (particle size 5-10 μm, preferably 7-9 μm), 40 parts of micron-grade α-silicon carbide powder II (particle size 1-4 μm, preferably 2-4 μm), 20 parts of micron-grade α-silicon carbide powder III (particle size 0.4-0.6 μm), 10 parts of nano-grade α-silicon carbide powder (particle size 39-41 nm), 2 parts of polyethylene glycol, and 1 part of polyvinyl alcohol;

[0045] The weighed powder raw material is added into a ball mill barrel, and deionized water is added in an amount of 1.5 times the weight of the powder raw material, and stirred and ball-milled for about 180 minutes to prepare a water-based slurry;

[0046] 2) Prepare spherical granulated powder by spray granulation of water-based slurry;

[0047] The parameters of the spray granulation tower are set as follows: hot air inlet temperature 285°C, outlet temperature 90°C, centrifugal atomizer modulation frequency 48Hz, and then the feed pump is turned on to introduce the water-based slurry obtained in step 1) into the granulation tower at a flow rate of 30mL / min, and finally ceramic granulation powder with uniform particle size (particle size is about 20-40μm) is obtained;

[0048] 3) Add the ceramic granulated powder obtained in step 2) into the graphite mold of the oscillating hot pressing sintering furnace and apply pressure by mechanical action. First, pre-press at a pressure of 40 MPa for 5 minutes, and then start the heating and pressurizing process.

[0049] First, the temperature was raised from room temperature to 1800°C at a heating rate of 10°C / min, and then raised to the sintering temperature of 1900°C at a heating rate of 5°C / min; during the heating process, the initial external pressure was raised uniformly from 5Mpa to 40±5Mpa; then, the hot pressing sintering was carried out at a sintering temperature of 1900°C for 60 minutes with a pressure range of 40±5Mpa and a frequency of 1Hz;

[0050] That is, an oscillating pressure is applied during the heat preservation stage with an amplitude of 10 MPa.

[0051] After 60 minutes of heat preservation and oscillation hot pressing sintering, the mixture was naturally cooled in the furnace and then demolded to obtain high-purity silicon carbide ceramics, which were named high-purity silicon carbide ceramics 1-1.

[0052] Then, according to actual needs, high-purity silicon carbide ceramic materials of various sizes can be obtained through precision processing.

[0053] The high-purity silicon carbide ceramic obtained in Example 1-1 has a low degree of compactness due to the low sintering temperature, and its density and mechanical properties are relatively poor.

[0054] Example 1-2: With respect to Example 1-1, the following changes are made:

[0055] Step 3) The sintering temperature was changed to 2000° C.; the rest was the same as Example 1-1.

[0056] The final sample was named high-purity silicon carbide ceramic 1-2.

[0057] As the sintering temperature increases, although the silicon carbide ceramics obtained in Example 1-2 are not completely sintered to be dense, their density and mechanical properties are improved to a certain extent compared with those in Example 1-1.

[0058] Example 2-1: With respect to Example 1-1, the following changes are made:

[0059] The powder raw material composition was modified to: 25 parts of micron-grade α-silicon carbide powder I, 40 parts of micron-grade α-silicon carbide powder II, 20 parts of micron-grade α-silicon carbide powder III, 15 parts of nano-grade α-silicon carbide powder, 2 parts of polyethylene glycol, and 1 part of polyvinyl alcohol.

[0060] The rest is the same as Example 1-1. The final sample is named high-purity silicon carbide ceramic 2-1. As the proportion of nano-scale α-silicon carbide powder in the raw material ratio increases, the difficulty of sintering and densification of silicon carbide ceramics is significantly reduced. Therefore, compared with Example 1-1, the performance of the silicon carbide ceramics obtained in Example 2-1 is significantly improved in all aspects.

[0061] Example 2-2: With respect to Example 2-1, the following changes are made:

[0062] Step 3) The sintering temperature was changed to 2000°C.

[0063] The rest is the same as Example 2-1. The final sample is named high-purity silicon carbide ceramic 2-2.

[0064] As the sintering and holding temperature increases, compared with Example 2-1, various properties of the silicon carbide ceramics obtained in Example 2-2 are improved to a certain extent, and the density is significantly improved.

[0065] Example 2-3: With respect to Example 2-1, the following changes are made:

[0066] Step 3) The sintering temperature was changed to 2100°C.

[0067] The rest is the same as Example 2-1. The final sample is named high-purity silicon carbide ceramic 2-3.

[0068] As the sintering and holding temperature increases again, compared with Example 2-2, Example 2-3 has a higher degree of density. However, due to the excessively high sintering temperature, the grains are coarsened and the mechanical properties are reduced to a certain extent.

[0069] Example 2-4: With respect to Example 2-1, the following changes are made:

[0070] Step 3) The sintering temperature was changed to 2200°C.

[0071] The rest is the same as Example 2-1. The final sample is named high-purity silicon carbide ceramic 2-4.

[0072] As the sintering and holding temperature further increased, the performance of the silicon carbide ceramics obtained in Example 2-4 decreased again compared with Example 2-3, which once again confirmed that the silicon carbide ceramics were over-burned due to the high temperature.

[0073] Example 3-1: With respect to Example 1-1, the following changes are made:

[0074] The powder raw material composition was modified to: 20 parts of micron-grade α-silicon carbide powder I, 40 parts of micron-grade α-silicon carbide powder II, 20 parts of micron-grade α-silicon carbide powder III, 20 parts of nano-grade α-silicon carbide powder, 2 parts of polyethylene glycol, and 1 part of polyvinyl alcohol.

[0075] The rest is the same as Example 1-1.

[0076] The final sample was named high-purity silicon carbide ceramic 3-1. After adding a larger proportion of nano-sized α-silicon carbide powder, the silicon carbide ceramic obtained in Example 3-1 completed the densification sintering under the promotion of the nano-sized silicon carbide powder.

[0077] Example 3-2: With respect to Example 3-1, the following changes are made:

[0078] Step 3) The sintering temperature was changed to 2000°C.

[0079] The rest is the same as Example 3-1. The final sample is named high-purity silicon carbide ceramic 3-2.

[0080] The silicon carbide ceramic obtained in Example 3-2 has excellent density and mechanical properties and is a preferred embodiment of the present invention.

[0081] Comparative Example 1: Compared with Example 1-2, the following changes were made:

[0082] The powder raw material composition was modified to: 20 parts of micron-grade α-silicon carbide powder I, 30 parts of micron-grade α-silicon carbide powder II, 10 parts of micron-grade α-silicon carbide powder III, 40 parts of nano-grade α-silicon carbide powder, 2 parts of polyethylene glycol, and 1 part of polyvinyl alcohol.

[0083] The rest is the same as Example 1-2.

[0084] The final sample was named Comparative Example 1. After adding a significantly larger proportion of nano-sized α-silicon carbide powder, the performance of the silicon carbide ceramic obtained in Comparative Example 1 was reduced to a certain extent, indicating that nano-sized silicon carbide powder needs to be added in an appropriate amount, and unreasonable powder particle size distribution will lead to performance degradation.

[0085] Table 1 Mechanical properties of silicon carbide ceramic samples in various embodiments and comparative examples

[0086]

[0087] Note: The sample size for the above test is 3*4*40mm strip sample.

[0088] Comparative Example 2 series, relative to Example 3-2, the powder raw material composition is modified as shown in Table 2 below, the sintering temperature is still 2000°C; the rest is the same as Example 3-2. The obtained properties are shown in Table 2 below.

[0089] Table 2

[0090]

[0091]

[0092] The flexural strength of the above-mentioned comparative examples 2-1 to comparative examples 2 to 4 all decreased to varying degrees compared with that of the embodiment 3-2 of the present invention; and there was no significant difference in the purity of the product compared with that of the embodiment 3-2.

[0093] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for preparing high-purity silicon carbide ceramics, characterized in that The following steps are involved: 1) Slurry preparation: Add the powder into the ball mill, add deionized water, stir and ball mill to form a water-based slurry; The powder material is composed of 20 to 30 parts of micron-grade α-silicon carbide powder I, 30 to 40 parts of micron-grade α-silicon carbide powder II, 10 to 20 parts of micron-grade α-silicon carbide powder III, 10 to 40 parts of nano-grade α-silicon carbide powder, 2±0.1 parts of polyethylene glycol, and 1±0.1 parts of polyvinyl alcohol; The particle size of micron-grade α-silicon carbide powder I is 5 to 10 μm, the particle size of micron-grade α-silicon carbide powder II is 1 to 4 μm, the particle size of micron-grade α-silicon carbide powder III is 0.4 to 0.6 μm, and the particle size of nano-grade α-silicon carbide powder is 38 to 42 nm; 2) Spray granulation: The water-based slurry obtained in step 1) is subjected to spray granulation to prepare spherical granulated powder; 3) Oscillating hot pressing sintering: The granulated powder obtained in step 2) is added into a graphite mold in an oscillating hot pressing sintering furnace, pre-pressed at a pressure of 35-45 MPa for 4-6 minutes, and then heated and pressurized to a set sintering temperature and a set sintering pressure, and oscillated hot pressing sintering is performed to obtain high-purity silicon carbide ceramics.

2. The method for preparing high-purity silicon carbide ceramics according to claim 1, characterized in that: The spray drying granulation in step 2) is as follows: the water-based slurry feed rate is 30-60 mL / min, the hot air inlet temperature is 250-300° C., the outlet temperature is 70-90° C., and the centrifugal atomizer is 40-70 Hz.

3. The method for preparing high-purity silicon carbide ceramics according to claim 1 or 2, characterized in that: The oscillation hot pressing sintering in step 3) is as follows: First, the temperature is raised to the set sintering temperature at a heating rate of 5-10°C / min; during the heating process, the external pressure is evenly increased from the initial pressure to the set sintering pressure; then, the oscillation hot pressing sintering is performed at the set sintering temperature and the set sintering pressure for 50-70 minutes; The set sintering temperature is 1900-2200° C., the initial pressure is 5-10 MPa, and the set sintering pressure is (20±5)-(40±5) MPa.

4. The method for preparing high-purity silicon carbide ceramics according to claim 3, characterized in that: The oscillation frequency of step 3) is 1 Hz and the amplitude is 10 MPa.

5. The method for preparing high-purity silicon carbide ceramics according to claim 3 or 4, characterized in that: The oscillation hot pressing sintering in step 3) is as follows: The heating rate is divided into two stages. In the first stage, when the temperature is raised to 1800±50°C, the heating rate is 10±1°C / min. In the second stage, when the temperature is raised from 1800±50°C to the set sintering temperature, the heating rate is 5±0.5°C / min.

6. The method for preparing high-purity silicon carbide ceramics according to any one of claims 1 to 5, characterized in that: The mass ratio of powder: deionized water = 1: (1.5 ± 0.1).

7. The method for preparing high-purity silicon carbide ceramics according to claim 6, characterized in that: Step 2): slurry feed rate 30mL / min, hot air inlet temperature 285°C, outlet temperature 90°C, centrifugal atomizer frequency modulation 48Hz; Step 3): the sintering temperature is set to 2000-2100° C., the initial pressure is 5-10 MPa, the sintering pressure is set to 40±5 MPa, the sintering time is 60 min, and the oscillation frequency is 1 Hz.

8. The method for preparing high-purity silicon carbide ceramics according to any one of claims 1 to 7, characterized in that The purity of micron-grade α-silicon carbide powder I, micron-grade α-silicon carbide powder II, and micron-grade α-silicon carbide powder III is ≥ 99.99%; The purity of nano-scale α-silicon carbide powder is ≥99.9%.

9. The method for preparing high-purity silicon carbide ceramics according to any one of claims 1 to 7, characterized in that: The powder material is composed of 20 to 25 parts of micron-grade α-silicon carbide powder I, 40 parts of micron-grade α-silicon carbide powder II, 20 parts of micron-grade α-silicon carbide powder III, 15 to 20 parts of nano-grade α-silicon carbide powder, 2 parts of polyethylene glycol, and 1 part of polyvinyl alcohol; Sintering temperature 2000℃-2100℃.

10. High-purity silicon carbide ceramics obtained by the method according to any one of claims 1 to 9.

Images