Preparation method of silicon carbide single crystal

Abstract

The invention discloses a preparation method of a silicon carbide single crystal, which comprises the following steps: (1) arranging a spring in a graphite crucible, arranging a carrier for supporting silicon carbide powder on the spring, and enabling the silicon carbide powder to be opposite to a seed crystal at the top of the graphite crucible; (2) silicon carbide powder is placed on a carrier, then a graphite crucible is placed in an inductance furnace, at the moment, the uppermost portion of the silicon carbide powder is located in a high-temperature area of the inductance furnace, and heating is started after placing is completed; (3) in the heating process, the silicon carbide powder begins to sublimate to the surface of the seed crystal for crystal growth, the weight of the silicon carbide powder on the carrier is reduced, the compression amount of the spring begins to be reduced, the carrier rises, and at the moment, the residual silicon carbide powder on the carrier is located in a high-temperature area of the inductance furnace; and (4) continuously heating until the silicon carbide powder on the carrier is completely sublimated. The spring starts to rebound in the powder heating sublimation process, the undecomposed powder area is continuously pushed to the high-temperature area, and the powder decomposition rate and the raw material utilization rate are increased.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide materials, and in particular to a method for preparing a silicon carbide single crystal. Background Art

[0002] SiC material, with its unique large bandgap, high critical breakdown field strength, high electron mobility, high thermal conductivity and other characteristics, has become an ideal material for making high-temperature, high-frequency, high-power, radiation-resistant, short-wave luminescent and optoelectronic integrated devices. The unique physical properties of SiC material determine its application in important fields such as artificial satellites, rockets, radars, communications, fighter jets, non-interference electronic ignition devices, jet engine sensors, etc. Therefore, researchers in various countries have conducted relevant technical research on it.

[0003] In order to optimize the process of preparing silicon carbide single crystals from silicon carbide powder, the current induction furnace solution is to add a spiral lifting device to the support platform at the bottom of the crucible, and to lift the crucible position by a motor during the growth process to change the relative position of the powder and the high temperature zone, thereby improving the decomposition efficiency of the powder; or to add a high-temperature sensor and a motor lifting platform to the equipment to optimize the position of the powder in the high temperature zone in real time to improve the utilization rate of the powder. However, this method will cause the position of the front end of the seed crystal growth face and the high temperature zone to change when changing the relative position of the powder in the high temperature zone. When the position of the seed crystal and the high temperature zone is too high, the temperature decreases and the probability of growth defects increases. Chinese patent CN110055583B discloses a device for growing crystals, including a crucible, a charging part for loading raw materials and a seed crystal are arranged relatively in the crucible, the charging part can be reciprocated toward the seed crystal through an adjustment mechanism, a heating device heats the crucible by induction heating so that the sublimated raw materials flow out from the gas outlet and then are transferred to the surface of the seed crystal in the gas phase for crystal growth, the crystal growth device can accurately and automatically control the position of the charging part in the thermal field, the crystal growth environment is stable, the quality of the grown crystal is high, the crystal growth raw materials can be fully volatilized, and the utilization rate of the crystal growth raw materials is improved. However, it involves the use of weight sensors, high-temperature sensors and spiral motors, and the equipment cost is relatively high. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing silicon carbide single crystals to solve the problem that the process of preparing silicon carbide single crystals will cause the position of the front end of the seed crystal growth surface and the high temperature zone to change, resulting in an increase in growth defects and an increase in equipment costs. The spring in the present invention begins to rebound during the heating and sublimation of the powder, continuously pushing the undecomposed powder area to the high temperature zone, thereby improving the powder decomposition rate and raw material utilization rate.

[0005] To achieve the above object, the present invention provides a method for preparing a silicon carbide single crystal, comprising the following steps: (1) A spring is arranged in a graphite crucible, one end of the spring is connected to the bottom of the graphite crucible, and the other end of the spring is provided with a carrier for supporting silicon carbide powder, and the silicon carbide powder is opposite to the seed crystal at the top of the graphite crucible; (2) Place silicon carbide powder on a carrier, and then place the graphite crucible in an induction furnace. At this time, the top of the silicon carbide powder is located in the high temperature zone of the induction furnace. After the placement is completed, the induction furnace starts to heat; (3) During the heating process, the silicon carbide powder begins to sublimate to the surface of the seed crystal and grows. The weight of the silicon carbide powder on the carrier decreases, the compression of the spring begins to decrease, and the carrier rises. At this time, the remaining silicon carbide powder on the carrier is located in the high temperature zone of the induction furnace. (4) Continue heating until the silicon carbide powder on the carrier is completely sublimated.

[0006] The high temperature zone of the induction furnace in the present invention mainly refers to the position of the induction coil of the induction furnace.

[0007] Preferably, the material of the spring in step (1) is a carbon-carbon composite material.

[0008] The carbon-carbon composite material used in the present invention has excellent properties, such as light specific gravity, high modulus, high specific strength, low thermal expansion coefficient, high temperature resistance, heat shock resistance, corrosion resistance, good vibration absorption, good friction, etc. It is a multifunctional, designable, new material with both structure and function. For example, Chinese patent CN107285796A discloses a carbon-based composite coil spring, which can withstand temperatures up to 2800, and there is no need to worry about the introduction of impurities such as other metals except carbon elements.

[0009] Preferably, the elastic coefficient of the spring in step (1) is 0.01-50 N / mm.

[0010] Preferably, in step (1), the carrier is one of a graphite sheet, an upper open graphite barrel, and a porous graphite cylinder.

[0011] The carrier in the present invention is not limited to the above three types, as long as it is a graphite hollow carrier.

[0012] Preferably, the mass of the silicon carbide powder in step (2) is 2-8 kg.

[0013] Preferably, the heating temperature of the induction furnace in step (2) is 2200-2500°C.

[0014] Preferably, the decomposition rate of silicon carbide powder in step (2) is 1-100 g / h.

[0015] Therefore, the present invention adopts a method for preparing a silicon carbide single crystal with the above structure, which has the following beneficial effects: (1) The present invention introduces a spring made of carbon-carbon composite material at the bottom of the powder material. After the powder material is partially sublimated, the weight is reduced, the expansion and contraction of the spring is increased, and the lower area of ​​the powder material is raised to the high temperature zone, thereby continuing to maintain the decomposition rate of the powder material, thereby ensuring that the crystal growth rate will not be reduced due to the decrease in the decomposition efficiency of the powder material.

[0016] (2) The present invention adjusts the relative position of the powder in the high temperature zone of the induction furnace by the expansion and contraction amount of the carbon-carbon composite material spring. Compared with the equipment achieving the same process effect, the complexity of the equipment lifting machinery manufacturing and the subsequent maintenance cost can be avoided.

[0017] (3) The present invention can ensure that the powder is in a high temperature zone throughout the entire growth process, thereby ensuring the decomposition rate of the powder during the growth cycle and improving the utilization rate of the powder.

[0018] (4) The crystal growth rate of the present invention fluctuates less in the later stage of crystal growth, thereby improving the crystal growth efficiency.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a graphite crucible structure diagram; Figure 2 This is a simulation diagram of the temperature field of silicon carbide powder before heating; Figure 3 This is a temperature field simulation diagram after silicon carbide powder is heated and grown for 50 hours; Figure 4 is an appearance picture of the silicon carbide crystal prepared in Example 7; Figure 5 is an appearance picture of the silicon carbide crystal prepared in Example 8; Figure 6 is an appearance picture of the silicon carbide crystal prepared in Example 4; In the figure: 1. Graphite crucible; 2. Spring; 3. Carrier; 4. Silicon carbide powder; 5. Seed crystal. DETAILED DESCRIPTION

[0021] The present invention will be further described below. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and a specific operation process, but the present invention is not limited to this embodiment. Example 1

[0022] This embodiment provides a method for preparing a silicon carbide single crystal, comprising the following steps: (1) If Figure 1As shown, a spring of carbon-carbon composite material is arranged in a graphite crucible, the elastic coefficient of the spring is 5N / mm, one end of the spring is connected to the bottom of the graphite crucible, and the other end of the spring is provided with a carrier graphite sheet for supporting silicon carbide powder, and the silicon carbide powder is opposite to the seed crystal at the top of the graphite crucible; (2) 5 kg of silicon carbide powder was placed on the carrier, the compression amount of the spring was 10 mm, and then the graphite crucible was placed in the induction furnace. At this time, the top of the silicon carbide powder was located in the high temperature zone of the induction furnace. After the placement was completed, the induction furnace began to heat up, and the heating temperature was 2200 ° C; the decomposition rate of silicon carbide powder was 80 g / h; During initial heating, the relative positions of the high temperature zone and silicon carbide powder are shown in Figure 2 .

[0023] (3) During the heating process, the silicon carbide powder begins to sublimate to the surface of the seed crystal and grows. The weight of the silicon carbide powder on the carrier decreases, the compression of the spring begins to decrease, and the carrier rises. At this time, the remaining silicon carbide powder on the carrier is located in the high temperature zone of the induction furnace. (4) Continue heating until the silicon carbide powder on the carrier is completely sublimated. The crystal growth time is 50 hours. At this time, the relative position of the high temperature zone and the silicon carbide powder is shown in the figure. Figure 3 The distance that silicon carbide powder moves upward during the growth process is 8mm, and the final utilization rate of the powder is 80%.

[0024] The difference between Example 2-6 and Example 1 is that the elastic coefficient of the spring is different. Specific parameters are shown in Table 1.

[0025] Table 1 Parameter settings of Examples 1-6 Group Silicon carbide powder mass kg Elastic constant N / mm Actual compression of spring (mm) The distance the powder moves upward during the growth process (mm) Example 1 5 5 10 8 Example 2 5 2.5 20 16 Example 3 5 1.67 30 24.1 Example 4 5 1.25 40 32 Example 5 5 1 50 40 Example 6 5 0.83 60 48 Note: The mass of the carrier is much smaller than the gravity of the powder and can be ignored. Example 7

[0026] The difference from Example 4 is: the utilization rate of silicon carbide powder. The utilization rate of silicon carbide powder in this example is controlled to be 40%, that is, the decomposed weight of the powder is 2 kg. Example 8

[0027] The difference from Example 4 is: the utilization rate of silicon carbide powder. The utilization rate of silicon carbide powder in this example is controlled to be 60%, that is, the decomposed weight of the powder is 2 kg.

[0028] The parameter settings of Example 4 and Examples 7-8 are shown in Table 2. The appearance of the prepared silicon carbide single crystal is shown in Figure 4-6 .

[0029] Table 2 Parameter settings of Example 4 and Examples 7-8 Group Powder decomposition weight kg Sublimation rate of silicon carbide raw material% Powder upward movement distance mm Example 7 2 40 16 Example 8 3 60 24 Example 4 4 80 32 Comparative Example 1 The difference from Example 1 is that the structure of the spring is different. In this comparative example, the spring is replaced by a fixed column made of a carbon-carbon composite material, one end of the fixed column is connected to the bottom of the graphite crucible, and the other end of the fixed column is provided with a carrier graphite sheet for supporting silicon carbide powder. The silicon carbide powder is opposite to the seed crystal at the top of the graphite crucible, and the position of the powder does not change during the sublimation of the silicon carbide powder. The final powder utilization rate in Comparative Example 1 is 45%.

[0030] Therefore, the present invention adopts a method for preparing a silicon carbide single crystal with the above structure. The spring in the present invention begins to rebound during the powder heating and sublimation process, continuously pushing the undecomposed powder area to the high temperature zone, thereby improving the powder decomposition rate and raw material utilization rate.

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a silicon carbide single crystal, characterized in that: The following steps are involved: (1) A spring is arranged in a graphite crucible, one end of the spring is connected to the bottom of the graphite crucible, and the other end of the spring is provided with a carrier for supporting silicon carbide powder, and the silicon carbide powder is opposite to the seed crystal at the top of the graphite crucible; (2) Place silicon carbide powder on a carrier, and then place the graphite crucible in an induction furnace. At this time, the top of the silicon carbide powder is located in the high temperature zone of the induction furnace. After the placement is completed, the induction furnace starts to heat; (3) During the heating process, the silicon carbide powder begins to sublimate to the surface of the seed crystal and grows. The weight of the silicon carbide powder on the carrier decreases, the compression of the spring begins to decrease, and the carrier rises. At this time, the remaining silicon carbide powder on the carrier is located in the high temperature zone of the induction furnace. (4) Continue heating until the silicon carbide powder on the carrier is completely sublimated.

2. The method for preparing a silicon carbide single crystal according to claim 1, characterized in that: The material of the spring in step (1) is a carbon-carbon composite material.

3. The method for preparing a silicon carbide single crystal according to claim 1, characterized in that: The elastic constant of the spring in step (1) is 0.01-50N / mm.

4. The method for preparing a silicon carbide single crystal according to claim 1, characterized in that: In step (1), the carrier is one of a graphite sheet, an upper open graphite barrel, and a porous graphite cylinder.

5. The method for preparing a silicon carbide single crystal according to claim 1, characterized in that: The mass of the silicon carbide powder in step (2) is 2-10 kg.

6. The method for preparing a silicon carbide single crystal according to claim 1, characterized in that: The heating temperature of the induction furnace in step (2) is 2200-2500°C.

7. The method for preparing a silicon carbide single crystal according to claim 1, characterized in that: The decomposition rate of silicon carbide powder in step (2) is 1-100 g / h.

Images