Device and method for growing silicon carbide coating based on PVT method

Abstract

The invention relates to a device and a method for growing a silicon carbide coating based on a PVT method. The device comprises a sealed chamber, an induction coil heater, a heat preservation felt, a graphite barrel, a graphite crucible, a weight sensor and a rotary carrying table, the induction coil heater and the graphite barrel are respectively arranged on the outer side and the inner side of the insulation felt; the graphite crucible is arranged on the lower portion in the graphite barrel, the induction coil heater correspondingly surrounds the end, provided with the graphite crucible, of the graphite barrel, and the rotary carrying table is arranged above the graphite crucible and spaced by a height distance. The rotary carrying table can rotate and move up and down at a set speed; an exhaust system is arranged at the top of the sealed chamber; the gas inlet is connected with an argon input system; the graphite barrel, the graphite crucible and the rotary carrying table are arranged in the sealed chamber; a weight sensor is arranged at the bottom of the graphite crucible. The invention provides a growth device and method of a silicon carbide coating based on a PVT method, which can accurately control the thickness and uniformity of a silicon carbide film and solve the problems that impurities are easily introduced or harmful substances are generated or the uniformity of the coating is difficult to control and the like in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor material preparation, and in particular to a PVT-based silicon carbide coating growth device and method. Background Art

[0002] With the rapid development of electronic technology, the demand for semiconductor materials is also increasing. As the third-generation wide bandgap semiconductor material, SiC has the advantages of high thermal conductivity and low loss, and has become one of the key materials for the new generation of power devices. At present, there are three main methods for preparing SiC thin films: magnetron sputtering, chemical vapor deposition (CVD) and physical vapor deposition (PVD). Among them, magnetron sputtering is widely used due to its simple process and low cost. However, this method also has certain defects, mainly including: (1) the need to use expensive target materials; (2) different targets must be replaced for the growth of SiC film layers of different thicknesses; (3) X-rays generated during sputtering will pose a potential health threat to operators. CVD is also one of the most commonly used growth methods. It introduces a gaseous precursor containing the elements that constitute the thin film onto a heated substrate, undergoes a chemical reaction at an appropriate temperature, generates a solid product and deposits it on the substrate surface to form a thin film. This method requires the selection of a suitable precursor. Generally, the corresponding gaseous precursor is selected according to the type of silicon carbide to be deposited (such as 3C-SiC, 4H-SiC, etc.). Common precursors include silane (SiH4), methane (CH4), propane (C3H8), etc. The CVD method usually requires a higher temperature to prepare silicon carbide, which leads to problems such as cracks on the surface of the SiC film; and due to the presence of organic matter, impurity elements such as oxygen and nitrogen will be present in the SiC film, resulting in impurities in the SiC; some gases used, such as silane, may be toxic and flammable, requiring special safety measures; in addition, the CVD process takes a long time and has limited output.

[0003] The PVD method uses a vacuum coating machine to grow SiC thin films. PVD technology can produce high-purity, high-density, low-defect silicon carbide coatings with good mechanical properties and chemical stability. The PVD process is relatively environmentally friendly and produces almost no harmful byproducts. However, the PVD method has high technical requirements and it is difficult to accurately control the film thickness and uniformity. These factors severely limit the application of the PVD method in actual production. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a growth device and method for a silicon carbide coating based on the PVT method, which can accurately control the thickness and uniformity of the silicon carbide coating film on the surface of the substrate material, and solves the technical problems existing in the prior art of the magnetron sputtering method, such as expensive target materials, X-rays affecting the health of operators, impurities in the coating of the CVD method, and difficulty in controlling the coating thickness and uniformity of the PVD method.

[0006] (II) Technical solution

[0007] In a first aspect, the present invention provides a growth device for a silicon carbide coating based on a PVT method, comprising: a sealed chamber, an induction coil heater, a heat preservation felt, a graphite barrel, a graphite crucible, a weight sensor, and a rotating stage;

[0008] The induction coil heater is arranged on the outside of the insulation felt, and the graphite barrel is arranged on the inside of the insulation felt; the graphite crucible is arranged inside the graphite barrel and at the lower part, the induction coil heater surrounds one end of the graphite barrel where the graphite crucible is arranged, and the rotating platform is arranged above the graphite crucible and spaced at a certain height distance; the rotating platform can rotate and move up and down at a set speed; an air inlet is arranged at the bottom of the sealed chamber, and the top is connected to the exhaust system; the air inlet is connected to the argon input system; the graphite barrel, the graphite crucible and the rotating platform are arranged in the sealed chamber; a weight sensor is arranged at the bottom of the graphite crucible; the graphite crucible is used to hold silicon carbide powder; the rotating platform is used to fix the workpiece and drive the workpiece to rotate and / or move up and down; the graphite barrel is used to evenly distribute heat in the annular direction; the insulation felt is used to maintain the heat inside the graphite barrel; the induction coil heater is used to heat up and pyrolyze the silicon carbide powder in the graphite crucible.

[0009] Among them, the induction coil heater, insulation felt and weight sensor can be arranged inside or outside the sealed chamber, while the graphite barrel, graphite crucible and rotating stage must be arranged inside the sealed chamber to accurately control the growth conditions of the silicon carbide thin film coating, including temperature, pressure and atmosphere conditions.

[0010] According to a preferred embodiment of the present invention, a pressure sensor is provided in the sealed chamber, and a temperature sensor is provided inside or beside the graphite crucible for monitoring the temperature inside the graphite crucible.

[0011] According to a preferred embodiment of the present invention, the rotating platform is provided with a driving mechanism, and the driving mechanism drives the rotating platform to rotate and / or move up and down at a set speed.

[0012] According to a preferred embodiment of the present invention, the growth device also includes a host computer control unit, which is communicatively connected with the temperature sensor, the pressure sensor, the argon gas input system, the exhaust system, the induction coil heater, the weight sensor at the bottom of the graphite crucible, and the driving mechanism of the rotating platform respectively; the host computer control unit controls the operating parameters of the induction coil heater, the argon gas input system, the exhaust system and the driving mechanism of the rotating platform according to the real-time data collected by the temperature sensor, the pressure sensor and the weight sensor.

[0013] According to a preferred embodiment of the present invention, the bottom of the graphite crucible is also provided with a uniform speed rotation mechanism to support the uniform speed rotation of the graphite crucible.

[0014] According to a preferred embodiment of the present invention, the workpiece is a graphite workpiece.

[0015] According to a preferred embodiment of the present invention, the induction coil heater, the insulation felt, and the graphite barrel are coaxially arranged, and the line connecting the center of the rotating platform and the center of the graphite crucible is the central axis.

[0016] In a second aspect, the present invention provides a method for growing a silicon carbide coating based on a PVT method, which uses the above-mentioned growth device to grow the silicon carbide coating and comprises the following steps:

[0017] S1. Place silicon carbide powder in a graphite crucible from bottom to top according to the particle size of the powder particles from small to large, and the particle size of silicon carbide powder in the same layer is within ±20% of the center value;

[0018] S2. Start the exhaust system to evacuate the sealed chamber to a vacuum state, and check whether the sealing of the sealed chamber is qualified by monitoring the pressure change in the sealed chamber over a period of time; after the test is qualified, the argon gas input system inputs protective gas from the bottom of the sealed chamber, and keeps the argon gas input system and the exhaust system working continuously to keep the pressure in the sealed chamber at 300Pa-1000Pa;

[0019] S3, start the induction coil heater to make the temperature in the graphite crucible reach 2000-2200°C, monitor the data of the weight sensor at the bottom of the graphite crucible, and perform the following control according to the data sensed by the weight sensor:

[0020] A. When the weight reduction of the silicon carbide powder monitored by the weight sensor reaches 10%, the rotating stage is controlled to rotate at a constant speed of 0.1rpm-10rpm;

[0021] B. When the weight reduction of the silicon carbide powder monitored by the weight sensor reaches 40%, the rotating stage is controlled to rotate at a constant speed of 0.1rpm-10rpm and descend at a constant speed of 20mm / hr-60mm / hr;

[0022] C. When the weight reduction of the silicon carbide powder monitored by the weight sensor reaches 70%, the rotating stage is controlled to stop descending, maintained at the stopped height position and rotated at a constant speed of 0.1rpm-10rpm; the working power of the induction coil heater is increased to heat and sublimate the remaining raw materials in the graphite crucible;

[0023] D. When the weight reduction of silicon carbide powder monitored by the weight sensor reaches 85%, the induction coil heater is controlled to stop heating and enter the cooling final stage. When the temperature in the graphite crucible drops to 1500℃-1000℃, the argon input flow rate is increased to increase the pressure of the sealed chamber to improve the cooling effect; when it cools to the ambient temperature, the argon input is stopped, and the sealed chamber is opened to take out the workpiece.

[0024] According to a preferred embodiment of the present invention, in S1, the particle size of silicon carbide powder is 20 mesh-500 mesh; the amount of silicon carbide powder added is calculated according to the thickness of the silicon carbide coating of the workpiece to be coated, and the mass of the silicon carbide powder raw material is obtained by the calculated value / (75%-80%).

[0025] Placing silicon carbide powder from bottom to top in the graphite crucible according to the particle size from small to large is conducive to the subsequent sublimation operation. Large-particle silicon carbide powder sublimates slowly. Placing it near the surface of the graphite crucible can absorb heat earlier and sublimate at a slower speed, matching the temperature rise rate of the surface of the graphite workpiece to be coated, which is conducive to improving the uniformity and density of the bottom layer of the silicon carbide coating film, and providing better bottom film conditions for further growth of the coating thickness.

[0026] According to a preferred embodiment of the present invention, in the control program C in S3, the working power of the induction coil heater is increased by: increasing the working power of the induction coil heater to 1.01-1.1 times of the previous working power. Here, the working power of the induction coil heater only needs to be higher than the previous working power, that is, several kW to more than ten kW, and there is no strict restriction. Usually, the working power of the induction coil heater is 70-200 kW. In the control program C, the working power of the induction coil heater can be increased to 1.01-1.1 times of the previous working power to basically meet the requirements.

[0027] According to a preferred embodiment of the present invention, in the control program D in S3, the argon input flow rate is increased to increase the pressure of the sealed chamber to 1.1-2 times of the previous pressure. At this time, the argon input flow rate is increased, but the exhaust speed of the exhaust system remains unchanged, so that the absolute pressure in the sealed chamber is increased. The main purpose is to ensure the cooling effect and cooling speed. The absolute pressure is increased to 1.1-2 times of the previous pressure to meet the requirements.

[0028] (III) Beneficial effects

[0029] Different from the coating growth method of the prior art, the present invention is a silicon carbide coating growth device and method based on the PVT method (Physical Vapor Transport), which heats the silicon carbide source material in a sealed chamber to make it sublime (directly change from solid to gas), and by accurately controlling the temperature, pressure, workpiece rotation speed, distance between the workpiece and the source material and other conditions in the reactor, the vapor is re-condensed at the colder end to form crystals, so as to obtain a high-purity, dense, low-defect silicon carbide coating film, and the film thickness and uniformity can be accurately controlled. The PVT method avoids the pollution problems that may be caused by the use of flux or organic matter or the problem of introducing impurities such as nitrogen and oxygen into the film, and can grow large-size, high-purity and low-defect single-crystal films. In addition, the PVT method does not require the use of expensive or scarce materials, can achieve continuous production, improve production capacity, and avoid the generation of harmful substances. The present invention is particularly suitable for coating and preparing workpieces with high-purity semiconductor materials (such as silicon carbide), and can achieve uniform and controllable coating of single crystal and polycrystalline samples to obtain high-quality silicon carbide films / coatings.

[0030] The growth device of the silicon carbide coating of the present invention has a simple structure and relatively simple process control. The coating film prepared by the growth method of the present invention has complete crystallization and is mainly composed of large-particle 4H-SiC. Compared with 3C-SiC coatings (CVD coatings are all 3C-SiC), the large-particle 4H-SiC coatings have higher durability, oxidation resistance and corrosion resistance. By controlling the process conditions, the preparation of coating films with a wider thickness range (100-1000 microns) can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the structure of the growth device of silicon carbide coating based on PVT method of the present invention.

[0032] Figure 2 This is a SEM image of the silicon carbide coating film on the surface of the graphite workpiece in Example 1. DETAILED DESCRIPTION

[0033] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0034] like Figure 1The structure diagram of the growth device of silicon carbide coating based on the PVT method of the present invention is shown, which includes an induction coil heater 1, a heat preservation felt 2, a sealed chamber 3, a graphite barrel 4, a rotating stage 5, a graphite crucible 6 and a weight sensor 7. Among them, the weight sensor 7 is arranged at the bottom of the graphite crucible 6, and is used to sense the weight change of the silicon carbide powder raw material in the graphite crucible 6. The induction coil heater 1 is arranged on the outside of the heat preservation felt 2, and the graphite barrel 4 is arranged on the inside of the heat preservation felt 2. The graphite crucible 6 is arranged inside the graphite barrel 4 and close to the lower part. The induction coil heater 1 is correspondingly surrounded by one end of the graphite barrel 4 where the graphite crucible 6 is arranged. The rotating stage 5 is arranged above the graphite crucible 6 and is separated by a certain height distance (i.e., axial distance). The axial height of the induction coil heater 1 is lower than the graphite barrel 4, so that the induction coil heater 1 is not arranged outside the end of the graphite barrel 4 where the rotating stage 5 is arranged, so that the temperature of the lower part of the graphite barrel 4 is the highest and the temperature gradually decreases upward. The rotating stage 5 is driven by the driving mechanism of the device and can rotate and move up and down at a set speed. An air inlet 31 is provided at the bottom of the sealed chamber 3, and an exhaust port 32 is provided at the top, and the exhaust port 32 is connected to the exhaust system. The air inlet 31 is connected to the argon gas input system. Among them, the graphite barrel 4, the graphite crucible 6 and the rotating stage 5 are all arranged inside the sealed chamber 3. The graphite crucible 6 is used to hold the silicon carbide powder raw material 9, and the rotating stage 5 is provided with a fixture for fixing the workpiece 8 (such as a graphite workpiece) and driving the workpiece 8 to rotate and / or move up and down synchronously. Among them, the graphite barrel 4 is a heat-sensitive body with strong thermal conductivity, which is used to evenly distribute the heat in the annular direction (the meaning of evenly distributing the heat in the annular direction is: with the central axis of the graphite barrel as the center of the circle, the temperature of each point on the same circle on the same horizontal plane is equal, that is, the isothermal point connection line on the same horizontal plane constitutes a circle with the central axis of the graphite barrel as the center of the circle), and the insulation felt 3 is used to maintain the heat inside the graphite barrel 4. The induction coil heater 1 is used to heat and pyrolyze the silicon carbide powder in the graphite crucible 6. Among them, the induction coil heater 1, the insulation felt 2 and the weight sensor 7 can be arranged in the sealed chamber 3 or outside the sealed chamber 3, but the graphite barrel 4, the graphite crucible 6 and the rotating stage 5 must be arranged inside the sealed chamber 3 to accurately control the growth conditions of the silicon carbide thin film coating on the workpiece 8, including temperature, pressure and atmosphere conditions, and prevent the graphite barrel 4, the graphite crucible 6, the workpiece 8 from oxidation. In this embodiment, the graphite barrel 4, the graphite crucible 6 and the rotating stage 5 are arranged inside the sealed chamber 3, and the induction coil heater 1, the insulation felt 2 and the weight sensor 7 are arranged outside the sealed chamber 3. A plurality of pressure sensors 12 are also distributed inside the sealed chamber 3, and a temperature sensor 11 is arranged inside or beside the graphite crucible 6 to monitor the real-time temperature of the silicon carbide powder raw material in the graphite crucible 6. The rotating platform 5 is driven by a driving mechanism provided in the device to rotate or move up and down at a set speed inside the graphite barrel 4 .

[0035] Furthermore, the induction coil heater 1, the insulation felt 2, and the graphite barrel 4 are coaxially arranged, and the line connecting the center of the rotating stage 5 and the center of the graphite crucible 6 is the central axis. Preferably, the induction coil heater 1, the insulation felt 2, and the graphite barrel 4 are all cylindrical hollow tube structures, and they are arranged in concentric circles in a top view. The workpiece 8 is fixed at the center position of the rotating stage 5, and the graphite crucible 6 is a circular crucible. The above structure can effectively ensure that the graphite crucible 6 and the workpiece 8 in the graphite barrel 4 are heated (temperature) uniformly in the circumferential direction, that is, the heating degree of each point on the same circle of the same horizontal plane is the same.

[0036] Furthermore, a uniform speed rotating mechanism may be provided at the bottom of the graphite crucible 6 to support the uniform speed rotation of the graphite crucible 6 , thereby further improving the heating uniformity of the silicon carbide powder raw material 9 in the graphite crucible 6 .

[0037] In addition, the growth device also includes a host computer control unit, which is respectively connected to the temperature sensor 11, the pressure sensor 12, the argon gas input system, the exhaust system, the induction coil heater 1, the weight sensor 7 at the bottom of the graphite crucible 6, and the driving mechanism of the rotating stage 5. The host computer control unit accurately controls the working parameters of the induction coil heater 1, the argon gas input system, the exhaust system, and the driving mechanism of the rotating stage 5 according to the real-time data collected by the temperature sensor 11, the pressure sensor 12, and the weight sensor 7. Among them, for the induction coil heater, its working parameters include heating power and start and stop, such as the current size and on and off time of the induction coil heater. For the argon gas input system, its working parameters include the flow rate of the input argon gas, the input pressure, the start and stop time or the initial temperature of the argon gas; the working parameters of the exhaust system include the exhaust speed and the opening / closing time of the exhaust valve. The working parameters of the driving mechanism of the rotating stage include the rotation speed, lifting speed, rotation start and stop or lifting start and stop, etc.

[0038] In a preferred embodiment of the present invention, the specification of the sealed chamber 3 is (diameter) 1000-1500mm, the inner diameter (diameter) of the graphite barrel 4 is 800-1200mm; the bearing range of the rotating stage 5 is 10-25kg; the specification range of the workpiece 8 to be coated is φ (φ represents diameter) 30-200mm; the size (diameter) of the graphite crucible 6 is 500-700mm; the starting height difference between the rotating stage 5 and the graphite crucible 6 is 400-1000mm. The working power range of the induction coil heater 1 is 70-200 kilowatts.

[0039] The starting height difference between the rotating stage 5 and the graphite crucible 6 matches the specifications of the sealed chamber 3 and the workpiece 8 to be coated, and the operating power range of the induction coil heater 1 matches the specifications of the sealed chamber 3 and the workpiece 8 to be coated. The load-bearing range of the rotating stage 5 matches the weight of the workpiece 8 to be coated, and the size of the graphite crucible 6 matches the workpiece 8 to be coated and the thickness of the silicon carbide coating.

[0040] The present invention uses the above-mentioned silicon carbide coating growth device to prepare a silicon carbide coating on a graphite workpiece, and the steps are as follows:

[0041] S1. Place silicon carbide powder in a graphite crucible from bottom to top according to the particle size of the powder particles from small to large, and the particle size of silicon carbide powder in the same layer is within ±20% of the center value;

[0042] S2. Start the exhaust system to evacuate the sealed chamber to a vacuum state, and check whether the sealing of the sealed chamber is qualified by monitoring the pressure change in the sealed chamber over a period of time; after the test is qualified, the argon gas input system inputs protective gas from the bottom of the sealed chamber, and keeps the argon gas input system and the exhaust system working continuously (using argon as the carrier gas for the sublimated silicon carbide molecules), so that the pressure in the sealed chamber is maintained at 300Pa-1000Pa;

[0043] S3, start the induction coil heater to make the temperature in the graphite crucible reach 2000-2200°C, monitor the data of the weight sensor at the bottom of the graphite crucible, and perform the following control according to the data sensed by the weight sensor:

[0044] A. When the weight reduction of the silicon carbide powder monitored by the weight sensor reaches 10%, the rotating stage is controlled to rotate at a constant speed of 0.1rpm-10rpm;

[0045] B. When the weight reduction of the silicon carbide powder monitored by the weight sensor reaches 40%, the rotating stage is controlled to rotate at a constant speed of 0.1rpm-10rpm and descend at a constant speed of 20mm / hr-60mm / hr;

[0046] C. When the weight reduction of the silicon carbide powder monitored by the weight sensor reaches 70%, the rotating stage is controlled to stop descending, maintained at the stopped height position and rotated at a constant speed of 0.1rpm-10rpm; the working power of the induction coil heater is increased to heat and sublimate the remaining raw materials in the graphite crucible;

[0047] D. When the weight reduction of silicon carbide powder monitored by the weight sensor reaches 85%, the induction coil heater is controlled to stop heating and enter the cooling final stage. When the temperature in the graphite crucible drops to 1500℃-1000℃, the argon input flow rate is increased to increase the pressure of the sealed chamber to improve the cooling effect; when it cools to the ambient temperature, the argon input is stopped, and the sealed chamber is opened to take out the workpiece.

[0048] The scheme and effects of the present invention are described below in conjunction with specific embodiments.

[0049] Example 1

[0050] This embodiment adopts Figure 1 The growth device shown grows a silicon carbide coating film on a graphite workpiece. The diameter of the sealed chamber 3 of the growth device is 1000 mm. The workpiece 8 to be coated is a graphite workpiece with a diameter of 50 mm. The preset thickness of the silicon carbide coating is 120 μm. The starting height distance from the rotating stage to the graphite crucible is 400 mm. The preparation process is as follows:

[0051] (1) Silicon carbide powder is placed in a graphite crucible 6 from bottom to top according to the particle size of the powder particles from small to large. The particle size of the silicon carbide powder in the same layer is within ±10% of the center value, and the particle size of the silicon carbide powder particles is distributed within 50 mesh-300 mesh.

[0052] The amount of silicon carbide powder raw material 9 added is calculated according to the thickness of the silicon carbide coating of the workpiece 8 to be coated, and is calculated as calculated value / 80%, wherein the loss of part of the silicon carbide powder is taken into account, and the initial mass of the silicon carbide powder raw material is calculated.

[0053] (2) Start the exhaust system to evacuate the sealed chamber 3 to a vacuum state, and confirm that the sealing of the sealed chamber 3 is qualified by monitoring the pressure change in the sealed chamber 3 within 3 hours. The argon gas input system inputs protective gas from the bottom of the sealed chamber 3, and keeps the argon gas input system and the exhaust system working continuously to keep the pressure in the sealed chamber 3 at 500Pa-600Pa.

[0054] (3) Start the induction coil heater 1 to make the temperature of the silicon carbide powder raw material 9 in the graphite crucible 6 reach 2000-2200° C., monitor the data of the weight sensor 7 at the bottom of the graphite crucible 6, and perform the following control according to the data sensed by the weight sensor 7:

[0055] A. When the weight reduction of the silicon carbide powder monitored by the weight sensor 7 reaches 10%, the rotating stage is controlled to rotate at a constant speed of 3 rpm;

[0056] B. When the weight reduction of the silicon carbide powder monitored by the weight sensor 7 reaches 40%, the rotating stage is controlled to rotate at a constant speed of 3 rpm and descend at a constant speed of 35 mm / hr;

[0057] C. When the weight reduction of the silicon carbide powder monitored by the weight sensor 7 reaches 70%, the rotating stage 5 is controlled to stop descending, remain at the stopped height position and rotate at a constant speed of 3 rpm. At this time, the working power of the induction coil heater 1 is increased to 1.04 times the previous one, and the remaining raw materials in the graphite crucible 6 are heated and sublimated;

[0058] D. When the weight reduction of the silicon carbide powder monitored by the weight sensor 7 reaches 85%, the induction coil heater 1 is controlled to stop heating and enter the cooling end stage. In this stage, the rotating stage 5 still keeps a constant rotation speed of 3rpm. When the temperature in the graphite crucible 6 drops to 1500℃-1000℃, the argon input flow rate is increased to increase the pressure of the sealed chamber 3 to 800pa-900pa to increase the cooling speed. When the sealed chamber 3 is cooled to the ambient temperature, the argon input is stopped, and the sealed chamber 3 is opened to take out the workpiece that has completed the silicon carbide coating.

[0059] Example 2

[0060] This embodiment is based on the embodiment 1, and the rotating stage is controlled to rotate at a constant speed of 5 rpm, and the control program B of step (3) is used to descend at a constant speed of 40 mm / hr. The remaining conditions of this embodiment are exactly the same as those of the embodiment 1.

[0061] Example 3

[0062] This embodiment adopts Figure 1 The growth device shown grows a silicon carbide coating film on a graphite workpiece. The diameter of the sealed chamber 3 of the growth device is 1200 mm. The workpiece 8 to be coated is a graphite workpiece with a diameter of 100 mm. The preset thickness of the silicon carbide coating is 120 μm. The starting height distance from the rotating stage to the graphite crucible is 600 mm. The preparation process is as follows:

[0063] (1) Silicon carbide powder is placed in a graphite crucible 6 from bottom to top according to the particle size of the powder particles from small to large. The particle size of the silicon carbide powder in the same layer is within ±10% of the center value, and the particle size of the silicon carbide powder particles is distributed within 40 mesh-300 mesh.

[0064] The amount of silicon carbide powder raw material 9 added is calculated according to the thickness of the silicon carbide coating of the workpiece 8 to be coated, and is calculated as calculated value / 80%, wherein the loss of part of the silicon carbide powder is taken into account, and the initial weight of the silicon carbide powder raw material is calculated.

[0065] (2) Start the exhaust system to evacuate the sealed chamber 3 to a vacuum state, and confirm that the sealing of the sealed chamber is qualified by monitoring the pressure change in the sealed chamber 3 within 2 hours. The argon gas input system inputs protective gas from the bottom of the sealed chamber 3, and keeps the argon gas input system and the exhaust system working continuously to keep the pressure in the sealed chamber at 600Pa-800Pa.

[0066] (3) Start the induction coil heater 1 to make the temperature of the silicon carbide powder raw material 9 in the graphite crucible 6 reach 2000-2200° C., monitor the data of the weight sensor 7 at the bottom of the graphite crucible, and perform the following control according to the data sensed by the weight sensor 7:

[0067] A. When the weight reduction of the silicon carbide powder monitored by the weight sensor 7 reaches 10%, the rotating stage is controlled to rotate at a constant speed of 5 rpm;

[0068] B. When the weight reduction of the silicon carbide powder monitored by the weight sensor 7 reaches 40%, the rotating stage is controlled to rotate at a constant speed of 4 rpm and descend at a constant speed of 40 mm / hr;

[0069] C. When the weight reduction of the silicon carbide powder monitored by the weight sensor 7 reaches 70%, the rotating stage 5 is controlled to stop descending, remain at the stopped height position and rotate at a constant speed of 4 rpm. At this time, the working power of the induction coil heater 1 is increased to 1.06 times of the previous one, and the remaining raw materials in the graphite crucible 6 are heated and sublimated;

[0070] D. When the weight reduction of the silicon carbide powder monitored by the weight sensor 7 reaches 85%, the induction coil heater 1 is controlled to stop heating and enter the cooling end stage. In this stage, the rotating stage 5 still maintains a uniform rotation of 4rpm. When the temperature in the graphite crucible 6 drops to 1500℃-1000℃, the argon input flow rate is increased to increase the pressure of the sealed chamber 3 to 1000-1200pa to improve the cooling effect. When the sealed chamber 3 is cooled to the ambient temperature, the argon input is stopped, and the sealed chamber 3 is opened to take out the workpiece that has completed the silicon carbide coating.

[0071] Comparative Example 1

[0072] This comparative example is based on Example 1, and the prepared silicon carbide powder raw material is randomly piled in the graphite crucible 6. The remaining conditions of this comparative example are the same as those of Example 1.

[0073] Comparative Example 2

[0074] This comparative example is based on Example 1, and the rotating stage 5 does not move downward at a constant height position and always rotates at a constant speed of 3 rpm. The remaining conditions of this comparative example are the same as those of Example 1.

[0075] The silicon carbide coating on the surface of the graphite workpiece in Example 1 was tested by electron microscope. The test results are as follows: Figure 2 The SEM image of the surface of the graphite workpiece 8 is shown. As can be seen from the figure, the silicon carbide coating film is very dense and defect-free, and the thickness uniformity of the coating is good.

[0076] After the graphite workpieces 8 of Examples 1-3 and Comparative Examples 1-2 were taken out, the silicon carbide coatings on their surfaces were tested, including randomly testing the sidewalls (average film thickness of a single side in the vertical direction, n=3) and top surfaces (average film thickness of a single side in the horizontal direction, n=3) of the graphite workpieces 8 to compare the uniformity of the thickness of the silicon carbide coating films. The film thickness was tested using an imager, the purity of the silicon carbide coating films was measured using GDMS, and the grain type of the silicon carbide coating was tested using XRD. The measurement results are as follows:

[0077]

[0078] As can be seen from the above table, the silicon carbide coating films grown on the surface of the graphite workpiece 8 in Examples 1-3 have a more uniform thickness, the RSD is less than 5%, and the film thickness is very close to the preset thickness (120 μm). In addition, the purity of the silicon carbide film grown by the present invention is greater than 6N (the film purity is greater than 6N, which means that the purity of the film material exceeds 99.9999%, that is, its impurity content is less than 1 ppm), and all are large 4H-SiC grains, which have stronger oxidation resistance and corrosion resistance than the film prepared by CVD method.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A growth device for silicon carbide coating based on PVT method, characterized in that: include: Sealed chamber, induction coil heater, insulation felt, graphite barrel, graphite crucible, weight sensor and rotating stage; The induction coil heater is arranged on the outside of the insulation felt, and the graphite barrel is arranged on the inside of the insulation felt; the graphite crucible is arranged inside the graphite barrel and at the lower part, the induction coil heater surrounds one end of the graphite barrel where the graphite crucible is arranged, and the rotating platform is arranged above the graphite crucible and spaced at a certain height distance; the rotating platform can rotate and move up and down at a set speed; an air inlet is arranged at the bottom of the sealed chamber, and the top is connected to the exhaust system; the air inlet is connected to the argon input system; the graphite barrel, the graphite crucible and the rotating platform are arranged in the sealed chamber; a weight sensor is arranged at the bottom of the graphite crucible; the graphite crucible is used to hold silicon carbide powder; the rotating platform is used to fix the workpiece and drive the workpiece to rotate and / or move up and down; the graphite barrel is used to evenly distribute heat in the annular direction; the insulation felt is used to maintain the heat inside the graphite barrel; the induction coil heater is used to heat up and pyrolyze the silicon carbide powder in the graphite crucible.

2. The growth device of silicon carbide coating based on PVT method according to claim 1, characterized in that: A pressure sensor is arranged in the sealed chamber, and a temperature sensor is arranged inside or beside the graphite crucible.

3. The growth device of silicon carbide coating based on PVT method according to claim 1, characterized in that: The rotating platform is provided with a driving mechanism, and the driving mechanism drives the rotating platform to rotate and / or move up and down at a set speed.

4. The growth device of silicon carbide coating based on PVT method according to claim 1, characterized in that: The growth device also includes a host computer control unit, which is respectively communicatively connected with a temperature sensor, a pressure sensor, an argon gas input system, an exhaust system, an induction coil heater, a weight sensor at the bottom of a graphite crucible, and a driving mechanism of a rotating platform; the host computer control unit controls the operating parameters of the induction coil heater, the argon gas input system, the exhaust system, and the driving mechanism of the rotating platform according to real-time data collected by the temperature sensor, the pressure sensor, and the weight sensor.

5. The growth device of silicon carbide coating based on PVT method according to claim 1, characterized in that: The bottom of the graphite crucible is also provided with a uniform speed rotating mechanism.

6. The growth device of silicon carbide coating based on PVT method according to claim 1, characterized in that: The induction coil heater, the insulation felt and the graphite barrel are coaxially arranged, and the line connecting the center of the rotating platform and the center of the graphite crucible is the central axis.

7. A method for growing a silicon carbide coating based on a PVT method, characterized in that: The growth device according to any one of claims 1 to 6 is used to grow a silicon carbide coating, and comprises the following steps: S1. Place silicon carbide powder in a graphite crucible from bottom to top according to the particle size of the powder particles from small to large, and the particle size of silicon carbide powder in the same layer is within ±20% of the center value; S2. Start the exhaust system to evacuate the sealed chamber to a vacuum state, and check whether the sealing of the sealed chamber is qualified by monitoring the pressure change in the sealed chamber over a period of time; after the test is qualified, the argon gas input system inputs protective gas from the bottom of the sealed chamber, and keeps the argon gas input system and the exhaust system working continuously to keep the pressure in the sealed chamber at 300Pa-1000Pa; S3, start the induction coil heater to make the temperature in the graphite crucible reach 2000-2200°C, monitor the data of the weight sensor at the bottom of the graphite crucible, and perform the following control according to the data sensed by the weight sensor: A. When the weight reduction of the silicon carbide powder monitored by the weight sensor reaches 10%, the rotating stage is controlled to rotate at a constant speed of 0.1rpm-10rpm; B. When the weight reduction of the silicon carbide powder monitored by the weight sensor reaches 40%, the rotating stage is controlled to rotate at a constant speed of 0.1rpm-10rpm and descend at a constant speed of 20mm / hr-60mm / hr; C. When the weight reduction of the silicon carbide powder monitored by the weight sensor reaches 70%, the rotating stage is controlled to stop descending, maintained at the stopped height position and rotated at a constant speed of 0.1rpm-10rpm; the working power of the induction coil heater is increased to heat and sublimate the remaining raw materials in the graphite crucible; D. When the weight reduction of silicon carbide powder monitored by the weight sensor reaches 85%, the induction coil heater is controlled to stop heating and enter the cooling final stage. When the temperature in the graphite crucible drops to 1500℃-1000℃, the argon input flow rate is increased to increase the pressure of the sealed chamber to improve the cooling effect; when it cools to the ambient temperature, the argon input is stopped, and the sealed chamber is opened to take out the workpiece.

8. The growth method according to claim 7, characterized in that: In S1, the particle size of silicon carbide powder is 20-500 mesh; the amount of silicon carbide powder added is calculated according to the thickness of the silicon carbide coating of the workpiece to be coated, and the mass of the silicon carbide powder raw material is obtained by the calculated value / (75%-80%).

9. The growth method according to claim 7, characterized in that: In the control program C in S3, increasing the working power of the induction coil heater is: increasing the working power of the induction coil heater to 1.01-1.1 times of the previous power.

10. The growth method according to claim 7, characterized in that: In the control procedure D in S3, the argon gas input flow rate is increased to raise the pressure of the sealed chamber to 1.1-2 times of the previous pressure.

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