A high-purity silicon carbide ceramic and its preparation method

Abstract

The present invention belongs to the field of ceramics, and in particular to a kind of high-purity silicon carbide ceramics and preparation method thereof; comprising the following steps: adding powder into a ball mill, stirring and ball milling after adding deionized water to form a water-based slurry; the powder is composed of micron-sized α-silicon carbide powder, nano-sized α-silicon carbide powder, polyethylene glycol, and polyvinyl alcohol of 3 different particle sizes; the obtained water-based slurry is spray granulated; the obtained granulated powder is added into a graphite mold in an oscillating hot pressing sintering furnace, first pre-pressed, and then heated and pressurized to a set sintering temperature and a set sintering pressure, and oscillated hot pressing and sintering are performed to obtain high-purity silicon carbide ceramics. The method of the present invention can significantly improve the mechanical properties of high-purity silicon carbide ceramics.

Description

Technical Field

[0001] The present 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] Industrially, silicon carbide ceramics are primarily produced through reaction sintering and pressureless sintering. The former, which primarily generates silicon carbide through a chemical reaction between a carbon source and a silicon source at high temperature, has a lower density. While the resulting silicon carbide ceramics are highly pure, they often contain excess silicon residues inside and outside. Pressureless sintering, on the other hand, is more difficult to sinter, requiring the addition of sintering aids to the raw materials to promote mass transfer during sintering, which runs counter to the demand for high-purity silicon carbide ceramics. Therefore, the silicon carbide ceramics produced by both sintering techniques are subject to significant limitations in the crystal boat field.

[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 varies 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 realize the simultaneous sintering and forming processes. Because 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, and 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. The current 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 had 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 great 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 5-10 μm, the particle size of micron-grade α-silicon carbide powder II is 1-4 μm, the particle size of micron-grade α-silicon carbide powder III is 0.4-0.6 μm, and the particle size of nano-grade α-silicon carbide powder is 38-42 nm.

[0012] 2) Spray granulation:

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

[0014] 3) Oscillation hot pressing sintering:

[0015] The granulated powder obtained in step 2) is added to 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 the temperature and pressure are increased to the set sintering temperature and the set sintering pressure, and oscillating hot pressing 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 to the preparation method of the high-purity silicon carbide ceramic of the present invention: the oscillation hot pressing sintering in step 3) is as follows:

[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 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 in step 3) is 1 Hz and the amplitude is 10 MPa.

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

[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 to the preparation method of the high-purity silicon carbide ceramics of the present invention: the mass ratio of powder: deionized water = 1: (1.5±0.1).

[0024] As a further improvement to 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℃, outlet temperature 90℃, centrifugal atomizer frequency modulation 48Hz;

[0026] Step 3): The sintering temperature is set to 2000-2100° C., the initial pressure is 5-10 MPa, the sintering pressure (oscillation pressure during the holding stage) is set to 40±5 MPa, the sintering time is 60 min, and the oscillation frequency is 1 Hz.

[0027] As a further improvement to 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 to the preparation method of the high-purity silicon carbide ceramic of the present invention: the powder material is composed of 20-25 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, 15-20 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 and sintering technology using any of the above methods, which can be used to prepare a wafer boat.

[0032] This invention successfully produces a high-purity silicon carbide ceramic material using an oscillating hot-pressing sintering method without the use of sintering aids. Mechanical pressure applied during the sintering process provides additional sintering driving force, reducing the difficulty of the silicon carbide ceramic sintering process. This allows the ceramic powder to be densified at a lower holding temperature than recrystallization sintering, demonstrating its high practical value in specialty ceramic applications 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 present invention provides a method for preparing high-purity silicon carbide ceramics by oscillating hot pressing and sintering, which can produce high-purity and high-density silicon carbide ceramics with basically only high-purity silicon carbide powder as raw material. It can significantly improve the mechanical properties (including flexural 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 embodiments 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 with reference to 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 was added to a ball mill barrel, and deionized water was added in an amount 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 were set as follows: hot air inlet temperature of 285°C, outlet temperature of 90°C, and frequency modulation of the centrifugal atomizer of 48 Hz. Then, the feed pump was turned on and the water-based slurry obtained in step 1) was introduced into the granulation tower at a flow rate of 30 mL / min to obtain ceramic granulation powder with uniform particle size (particle size of about 20 to 40 μm).

[0048] 3) The ceramic granulated powder obtained in step 2) is added to a graphite mold of an oscillating hot pressing sintering furnace and pressurized by mechanical action. First, pre-pressing is performed at a pressure of 40 MPa for 5 minutes, and then the heating and pressurizing process is started.

[0049] The temperature was first 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 external pressure was uniformly increased from an initial pressure of 5 MPa to 40±5 MPa. The sintering was then carried out at a sintering temperature of 1900°C with a holding oscillation hot pressing process for 60 minutes, with a pressure range of 40±5 MPa and a frequency of 1 Hz.

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

[0051] After 60 minutes of heat preservation and oscillation hot pressing sintering, the product was naturally cooled in the furnace and then demolded to obtain a high-purity silicon carbide ceramic, designated as high-purity silicon carbide ceramic 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 ceramics obtained in Example 1-1 have a low degree of density and relatively poor density and mechanical properties due to the low sintering temperature.

[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 in 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 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 remaining conditions were the same as those in Example 1-1. The resulting sample was designated high-purity silicon carbide ceramic 2-1. As the proportion of nano-sized α-silicon carbide powder in the raw material mix increased, the difficulty of sintering and densifying the silicon carbide ceramic was significantly reduced. Therefore, compared to Example 1-1, the silicon carbide ceramic obtained in Example 2-1 exhibited significant improvements in all aspects of performance.

[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, the 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 holding temperature further increased, the performance of the silicon carbide ceramics obtained in Example 2-4 decreased again compared with Example 2-3, once again confirming 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 is 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 densification sintering under the promotion of 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: With respect to 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 resulting sample was named Comparative Example 1. Even with the addition of a significantly larger proportion of nano-sized α-silicon carbide powder, the performance of the silicon carbide ceramic obtained in Comparative Example 1 actually declined to a certain extent, demonstrating that nano-sized silicon carbide powder needs to be added in an appropriate amount, and that improper powder particle size distribution can 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 was modified as shown in Table 2 below, and the sintering temperature remained at 2000°C; the rest was 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 2 to 4 decreased to varying degrees compared with that of Example 3-2 of the present invention; and the purity of the product had no significant difference compared with that of Example 3-2.

[0093] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples and is subject to numerous variations. All variations that can be directly derived or conceived by a person of ordinary skill in the art from the disclosure of the present invention are considered to be within the scope of protection 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 20-30 parts of micron-grade α-silicon carbide powder I, 30-40 parts of micron-grade α-silicon carbide powder II, 10-20 parts of micron-grade α-silicon carbide powder III, 20-40 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 5~10μm, the particle size of micron-grade α-silicon carbide powder II is 1~4μm, the particle size of micron-grade α-silicon carbide powder III is 0.4~0.6μm, and the particle size of nano-grade α-silicon carbide powder is 38~42 nm; 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%; 2) Spray granulation: The water-based slurry obtained in step 1) is spray-granulated to prepare spherical granulated powder; 3) Oscillation hot pressing sintering: The granulated powder obtained in step 2) is added to 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 is performed to obtain high-purity silicon carbide ceramics; The oscillation hot pressing sintering 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 uniformly increased from the initial pressure to the set sintering pressure. Then, the oscillating hot pressing is performed at the set sintering temperature and the set sintering pressure for 50-70 minutes. The set sintering temperature is 1900° C. to 2200° C., the initial pressure is 5 to 10 MPa, and the set sintering pressure is (20±5) to (40±5) MPa.

2. The method for preparing high-purity silicon carbide ceramics according to claim 1, wherein: 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 frequency of the centrifugal atomizer is 40-70 Hz.

3. The method for preparing high-purity silicon carbide ceramics according to claim 2, wherein: The oscillation frequency of step 3) is 1 Hz and the amplitude is 10 MPa.

4. The method for preparing high-purity silicon carbide ceramics according to claim 2 or 3, 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.

5. The method for preparing high-purity silicon carbide ceramics according to claim 4, wherein: The mass ratio of powder: deionized water = 1: (1.5 ± 0.1).

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

7. The method for preparing high-purity silicon carbide ceramics according to claim 6, wherein: The powder material is composed of 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; Sintering temperature is 2000℃~2100℃.

8. The high-purity silicon carbide ceramic obtained by the method according to any one of claims 1 to 7.

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