Polycrystalline silicon carbide rod, its preparation device and method, and polycrystalline silicon carbide powder

Abstract

The present invention belongs to the technical field of silicon carbide crystals, and particularly relates to a polycrystalline silicon carbide rod, its preparation device and method, and polycrystalline silicon carbide powder. The preparation device includes a reactor, which includes a bottom plate, a cover body, and a deposition carrier inside the cover body. A gas extraction hole is provided at the center of the bottom plate, an electrode connected to the deposition carrier is penetrated outside the gas extraction hole, and an air inlet hole is provided outside the electrode; an air inlet pipe extending into the reactor through the air inlet hole; a negative pressure assembly including an air extraction pipe, an air extraction part, an air extraction control part, and a negative pressure monitoring member. The first end of the air extraction pipe is connected to the inside of the reactor through the gas extraction hole, the end of the first end of the air extraction pipe is lower than the lower end of the deposition carrier, the second end of the air extraction pipe is connected to the air extraction part, the negative pressure monitoring member monitors whether the pressure in the reactor is within the range of 0.001 bar to 0.1 bar, and the air extraction control part is respectively connected to the negative pressure monitoring member and the air extraction part, which can improve the density of the silicon carbide rod and the purity of the powder.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon carbide crystals, and in particular relates to a polycrystalline silicon carbide rod and a preparation device and method thereof, as well as polycrystalline silicon carbide powder. Background Art

[0002] Silicon carbide single crystal substrate material is a wide bandgap semiconductor material with the advantages of high voltage resistance, high temperature resistance, high frequency, and low loss. It has been widely used in high-power power electronic devices and microwave radio frequency devices.

[0003] At present, the main method for industrial preparation of silicon carbide single crystal materials is physical vapor transport (PVT). Specifically, polycrystalline silicon carbide powder raw materials are placed in a closed cavity formed by a graphite crucible and a crucible cover, and a silicon carbide seed crystal is bonded to the inner wall of the crucible cover. In an inert atmosphere, the polycrystalline silicon carbide powder raw materials at the bottom of the graphite crucible are heated to sublime, and the sublimated gas grows and crystallizes on the silicon carbide seed crystal to obtain a silicon carbide single crystal.

[0004] In order to obtain polycrystalline silicon carbide powder raw materials, polycrystalline silicon carbide rods can be obtained by chemical vapor deposition of silicon source gas and carbon source gas on a carrier, and then the polycrystalline silicon carbide rods are crushed. However, the prepared polycrystalline silicon carbide rods are prone to have more pore structures, which are easy to absorb materials such as silicon source gas, carbon source gas, carrier gas, etc., and are easy to absorb dust and gas suspended in the air. After crushing, the purity of the polycrystalline silicon carbide powder is affected, and it is further used to grow silicon carbide single crystal materials, which affects the quality of the silicon carbide single crystal.

[0005] It should be noted that this part of the present invention only provides background technology related to the present invention and does not necessarily constitute prior art or known technology. Summary of the invention

[0006] The purpose of the present invention is to overcome the problem that a large number of pore structures are easily present on polycrystalline silicon carbide rods prepared by chemical vapor deposition reaction in the prior art, and the pore structures are easily adsorbed with impurities, thus affecting the purity of polycrystalline silicon carbide powder. A polycrystalline silicon carbide rod and a preparation device and method thereof, as well as polycrystalline silicon carbide powder are provided, which can improve the compactness of the polycrystalline silicon carbide rod, inhibit the rod from adsorbing impurities, and improve the purity of the polycrystalline silicon carbide powder.

[0007] In order to achieve the above-mentioned object, in a first aspect, the present invention provides a device for preparing high-density polycrystalline silicon carbide rods, comprising:

[0008] A reactor, which comprises a bottom plate, a cover body covering the bottom plate, and a vertical deposition carrier located inside the cover body. A gas extraction hole is provided at the center of the bottom plate, and a vertical electrode penetrates through the bottom plate. The electrode is located outside the gas extraction hole. The upper end of the electrode is connected to the lower end of the deposition carrier. An air inlet hole is provided on the bottom plate outside the electrode.

[0009] An air inlet pipe, one end of which extends into the reactor through the air inlet hole, and a nozzle is provided on the pipe section of the air inlet pipe located inside the reactor.

[0010] A negative pressure assembly, which comprises an air extraction pipe, an air extraction part, an air extraction control part, and a negative pressure monitoring member. The first end of the air extraction pipe is communicated with the inside of the reactor through the gas extraction hole. The end of the first end of the air extraction pipe is lower than the lower end of the deposition carrier. The second end of the air extraction pipe is communicated with the air extraction part. The negative pressure monitoring member monitors whether the pressure in the reactor is within the range of 0.001 bar to 0.1 bar. The air extraction control part is respectively connected to the negative pressure monitoring member and the air extraction part. One end of the air inlet pipe extends to the upper part of the deposition carrier through the air inlet hole. A plurality of nozzles are provided on the side of the pipe section of the air inlet pipe located inside the reactor close to the deposition carrier. The nozzles are arranged at intervals along the axial direction of the air inlet pipe. The uppermost nozzle is located above the deposition carrier, and the lowermost nozzle is located above the first end of the air extraction pipe and the vertical distance from the first end of the air extraction pipe is more than 50 cm.

[0011] In some preferred embodiments, the first end of the air extraction pipe extends into the reactor, and the pipe wall of the first end of the air extraction pipe extends obliquely outward and upward to form a flared structure.

[0012] Preferably, the included angle between the pipe wall of the first end of the air extraction pipe and the vertical direction is 30° to 60°.

[0013] In a second aspect, the present invention provides a method for preparing a high-density polycrystalline silicon carbide rod, which is prepared by the preparation device described in the first aspect. The negative pressure monitoring member monitors the pressure in the reactor, the air extraction control part adjusts the air extraction speed of the air extraction part according to the pressure in the reactor, the air extraction part extracts air from the reactor through the air extraction pipe, so that the pressure in the reactor is maintained at 0.001 bar to 0.1 bar, and the deposition gas source is introduced into the reactor through the nozzles on the air inlet pipe, and a deposition reaction occurs on the surface of the deposition carrier to generate polycrystalline silicon carbide and hydrogen chloride gas.

[0014] In some preferred embodiments, when the pressure in the reactor is normal pressure, the total flow rate of the introduced deposition gas source and carrier gas is Q, when the pressure in the reactor is maintained at 0.001 bar to 0.1 bar, the total flow rate of the deposition gas source and the carrier gas introduced is 0.08 Q ~0.15 Q。

[0015] In some preferred embodiments, an electric current is passed through the deposition carrier via an electrode to keep the surface temperature of the deposition carrier at a preset temperature, and the preset temperature is 1200 °C to 1600 °C.

[0016] In some preferred embodiments, the pressure in the reactor is maintained at 0.01 bar to 0.03 bar.

[0017] In a third aspect, the present invention provides a highly dense polycrystalline silicon carbide rod prepared by using the preparation method described in the second aspect, and the density is above 72%.

[0018] In a fourth aspect, the present invention provides a high-purity polycrystalline silicon carbide powder, and the polycrystalline silicon carbide powder is obtained by crushing the highly dense polycrystalline silicon carbide rod described in the third aspect.

[0019] For the preparation device of the present invention, the first end of the suction pipe is connected to the inside of the reactor through a suction hole, the end of the first end of the suction pipe is lower than the lower end of the deposition carrier, the second end of the suction pipe is connected to the suction part, the suction control part is respectively connected to the negative pressure monitoring part and the suction part. When the negative pressure monitoring part monitors that the pressure in the reactor is not within the range of 0.001 bar to 0.1 bar, the suction control part adjusts the suction speed of the suction part to adjust the pressure in the reactor to 0.001 to 0.1 bar. Since the pressure in the reactor can be maintained at 0.001 bar to 0.1 bar, for the deposition process in which the deposition gas source undergoes a deposition reaction to generate polycrystalline silicon carbide and hydrogen chloride gas, the gas flow rate can be increased, the gas flow rate on the surface of the silicon carbide rod can be increased, the separation of the reaction product hydrogen chloride from the surface of the silicon carbide rod can be accelerated, the concentration of hydrogen chloride gas in the reactor can be reduced, and the concentration of hydrogen chloride gas on the surface of the polycrystalline silicon carbide rod can be reduced. Thus, on the one hand, the corrosion of the polycrystalline silicon carbide rod by hydrogen chloride gas can be inhibited, the appearance of holes and coral-like structures on the silicon carbide rod caused by corrosion can be avoided, the density of the polycrystalline silicon carbide rod can be increased, the adsorption of inclusion impurities by the rod body can be inhibited, and the purity of the silicon carbide polycrystalline powder obtained by crushing the polycrystalline silicon carbide rod can be improved. On the other hand, the deposition process in which the deposition gas source undergoes a deposition reaction to generate polycrystalline silicon carbide and hydrogen chloride gas can be promoted, and the conversion rate of the deposition gas source can be increased. The present invention improves the density of the polycrystalline silicon carbide rod by inhibiting the corrosion of the polycrystalline silicon carbide rod by hydrogen chloride gas, and the polycrystalline silicon carbide rod with high density can further inhibit the corrosion of hydrogen chloride gas.

[0020] The reactor of the preparation device of the present invention has an air extraction hole in the center of the bottom plate. A vertical electrode penetrates through the bottom plate, and the electrode is located outside the air extraction hole. The upper end of the electrode is connected to a vertical deposition carrier. An air inlet hole is provided on the bottom plate outside the electrode. One end of the air inlet pipe extends into the reactor through the air inlet hole. A nozzle is provided on the pipe section of the air inlet pipe located inside the reactor. When the pressure in the reactor is negative pressure, specifically 0.001 bar to 0.1 bar, it can prevent the deposition gas source entering from the air inlet pipe from being sucked out due to negative pressure extraction before it reaches the surface of the carrier for deposition reaction. Compared with the situation where the air inlet pipe does not extend into the reactor, in the present invention, with the air inlet pipe extending into the reactor, under the dual action of the nozzle of the air inlet pipe extending into the reactor and the negative pressure, the air flow is smoother and more stable, making the gas attached to various parts of the axial and radial directions of the deposition carrier or the polycrystalline silicon carbide deposited on the deposition carrier more uniform, and the deposited silicon carbide more dense. The heat of the deposition carrier of the present invention can be evenly conducted to the outermost layer along the dense silicon carbide layer that has been deposited. Cooperating with the uniform air flow, the temperature of the outermost layer is more uniform, further ensuring the density of the polycrystalline silicon carbide rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can be obtained based on these drawings.

[0022] Figure 1 It is a schematic structural diagram of the preparation device of Embodiment 1 of the present invention.

[0023] DESCRIPTION OF THE REFERENCE NUMERALS

[0024] 1 - Reactor; 11 - Bottom plate; 111 - Air extraction hole; 112 - Air inlet hole; 12 - Cover; 13 - Deposition carrier; 14 - Electrode; 2 - Air inlet pipe; 21 - Nozzle; 3 - Air extraction pipe; 31 - Flared structure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] In the ranges disclosed herein, the endpoints and any value are not limited to the exact range or value. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0026] In this text, unless otherwise stated, the orientation terms such as "upper" and "lower" generally refer to the orientation understood in combination with the drawings and in practical applications, and "inner" and "outer" refer to the inner and outer of the contour of the component.

[0027] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0028] In the present invention, unless otherwise clearly specified and defined, terms such as "connection" and "fixation" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature can be that the first feature is directly above or obliquely above the second feature, or simply means that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature can be that the first feature is directly below or obliquely below the second feature, or simply means that the first feature has a lower horizontal height than the second feature.

[0030] The inventors of the present invention have found through research that when preparing polycrystalline silicon carbide rods by chemical vapor deposition of a silicon source gas and a carbon source gas on a carrier, there are likely to be many pore structures on the polycrystalline silicon carbide rods. The pore structures are likely to adsorb and entrap impurities, which will affect the purity of the polycrystalline silicon carbide powder after crushing.

[0031] In view of this, on the one hand, the present invention provides a preparation device for a high-density polycrystalline silicon carbide rod, comprising:

[0032] Reactor 1, wherein the reactor 1 includes a bottom plate 11, a cover body 12 covering the bottom plate 11, and a vertical deposition carrier 13 located inside the cover body 12. A gas extraction hole 111 is provided at the center of the bottom plate 11. A vertical electrode 14 penetrates through the bottom plate 11. The electrode 14 is located outside the gas extraction hole 111. The upper end of the electrode 14 is connected to the lower end of the deposition carrier 13. An air inlet hole 112 is provided on the bottom plate 11 outside the electrode 14.

[0033] An intake pipe 2, one end of the intake pipe 2 extends into the reactor 1 through the air inlet hole 112, and a nozzle 21 is provided on the pipe section of the intake pipe 2 located inside the reactor 1.

[0034] A negative pressure assembly, the negative pressure assembly includes an extraction pipe 3, an extraction part, an extraction control part, and a negative pressure monitoring member. The first end of the extraction pipe 3 is connected to the inside of the reactor 1 through the gas extraction hole 111. The end of the first end of the extraction pipe 3 is lower than the lower end of the deposition carrier 13. The second end of the extraction pipe 3 is connected to the extraction part. The negative pressure monitoring member monitors whether the pressure in the reactor 1 is within the range of 0.001 bar - 0.1 bar. The extraction control part is respectively connected to the negative pressure monitoring member and the extraction part.

[0035] One end of the intake pipe 2 extends to the upper part of the deposition carrier 13 through the air inlet hole 112. A plurality of nozzles 21 are provided on the side of the pipe section of the intake pipe 2 located inside the reactor 1 close to the deposition carrier 13. The nozzles 21 are arranged at intervals along the axial direction of the intake pipe 2. The uppermost nozzle 21 is located above the deposition carrier 13. The lowermost nozzle 21 is located above the first end of the extraction pipe 3 and the vertical distance from the first end of the extraction pipe 3 is more than 50 cm.

[0036] In the preparation device of the present invention, one end of the air inlet pipe 2 extends to the interior of the reactor 1 through the air inlet hole 112, so that the carrier gas and the deposition gas source can be introduced into the reactor 1. A vertical electrode 14 is provided on the bottom plate 11 of the reactor 1. The upper end of the electrode 14 is connected to the lower end of the vertical deposition carrier 13, so that the deposition carrier 13 can be electrified through the electrode 14. After the deposition carrier 13 is electrified, resistance heat is generated due to its own resistance effect. The deposition gas source flows through the surface of the deposition carrier 13 or the carbon deposited on the deposition carrier 13. The surface of the silicon carbide polycrystal is deposited and grown into a polycrystalline silicon carbide rod by a deposition reaction. The deposition reaction will produce tail gas such as hydrogen chloride while generating silicon carbide polycrystals. The negative pressure component includes an exhaust pipe 3, an exhaust unit, an exhaust control unit and a negative pressure monitoring unit. The first end of the exhaust pipe 3 is connected to the inside of the reactor 1 through an exhaust hole 111, and the second end of the exhaust pipe 3 is connected to the exhaust unit. The exhaust control unit is connected to the negative pressure monitoring unit and the exhaust unit for monitoring whether the pressure in the reactor is within the range of 0.001 bar to 0.1 bar, respectively. When the negative pressure monitoring device monitors that the pressure in the reactor 1 is not within the range of 0.001 bar to 0.1 bar, the exhaust control unit adjusts the exhaust speed of the exhaust unit to quickly adjust the pressure in the reactor 1 to 0.001 bar to 0.1 bar. Since the pressure of the reactor 1 is maintained at 0.001 bar to 0.1 bar by exhausting, the gas flow rate on the surface of the polycrystalline silicon carbide rod can be increased, and the separation of hydrogen chloride from the surface of the polycrystalline silicon carbide rod body can be promoted. The concentration of hydrogen chloride gas in the reactor 1 can be reduced, and the concentration of hydrogen chloride gas on the surface of the polycrystalline silicon carbide rod can be reduced. Therefore, on the one hand, the corrosion of the polycrystalline silicon carbide rod by hydrogen chloride gas can be suppressed, and holes and coral-like structures on the silicon carbide rod caused by corrosion can be avoided, the compactness of the polycrystalline silicon carbide rod can be improved, the adsorption of impurities by the rod body can be suppressed, and the purity of the polycrystalline silicon carbide powder obtained after the polycrystalline silicon carbide rod is crushed can be improved. On the other hand, the deposition gas source can be promoted to undergo a deposition reaction to generate a deposition process of polycrystalline silicon carbide and hydrogen chloride gas, thereby improving the conversion rate of the deposition gas source. The present invention improves the density of the polycrystalline silicon carbide rod by inhibiting the corrosion of the polycrystalline silicon carbide rod by hydrogen chloride gas, and the polycrystalline silicon carbide rod with high density can also further inhibit the corrosion of the hydrogen chloride gas.

[0037] In the preparation device of the present invention, an exhaust hole 111 is provided at the center of the bottom plate 11 of the reactor 1, and the first end of the exhaust pipe 3 is connected to the inside of the reactor 1 through the exhaust hole 111. The end of the first end of the exhaust pipe 3 is lower than the lower end of the deposition carrier 13. A vertical electrode 14 is penetrated on the outside of the exhaust hole 111 on the bottom plate 11, and the upper end of the electrode 14 is connected to the lower end of the vertical deposition carrier 13. An air inlet 112 is provided on the outside of the electrode 14 of the bottom plate 11. One end of the air inlet pipe 2 extends to the inside of the reactor 1 through the air inlet hole 112. A nozzle 21 is provided on the pipe section of the air inlet pipe 2 located inside the reactor 1. The exhaust hole 111 is located at the bottom of the reactor 1. On the inner side of the polycrystalline silicon carbide rod, the end of the first end of the exhaust pipe 3 is lower than the lower end of the deposition carrier 13, and the air inlet 112 is located on the periphery of the polycrystalline silicon carbide rod. The deposition gas source and the carrier gas are sprayed into the reactor 1 from the periphery of the polycrystalline silicon carbide rod, and the deposition gas source and the carrier gas flow through the surface of the rod body, bringing the deposition gas source and taking away the tail gas such as hydrogen chloride. The exhaust pipe 3 located at the lower inner side of the polycrystalline silicon carbide rod extracts the carrier gas and the tail gas such as hydrogen chloride. Under the premise that the pressure in the reactor 1 is negative pressure, specifically 0.001bar~0.1bar, it can be avoided that the deposition gas source coming in from the air inlet pipe 2 is not yet drawn out due to the negative pressure exhaust before reaching the carrier surface for deposition reaction. At the same time, compared with the case where the air inlet pipe 2 of the present invention extends to the interior of the reactor 1, the airflow is smoother and more stable under the dual guidance of the nozzle 21 of the air inlet pipe 2 extending to the interior of the reactor 1 and the negative pressure, so that the gas attached to the deposition carrier 13 or the silicon carbide polycrystalline deposited on the deposition carrier 13 in the axial and radial directions is more uniform, and the silicon carbide deposited on the surface is more dense. The dense silicon carbide can also make the heat of the deposition carrier 13 uniformly transferred. The heat of the deposition carrier 13 of the present invention can be uniformly conducted to the outermost layer along the already deposited dense silicon carbide layer, and cooperate with the uniform airflow to make the temperature of the surface more uniform, further ensuring the density of the polycrystalline silicon carbide rod.

[0038] The heat of the deposition carrier 13 will be transferred to the surface of the silicon carbide rod unevenly as holes or coral-like silicon carbide are formed, further leading to uneven temperature at various locations on the surface of the silicon carbide rod. Places with relatively low temperatures will cause silicon carbide to fail to deposit well, thereby forming larger holes or coral-like shapes there. In severe cases, this will limit the further growth of the rod and thus limit the growth diameter of the rod. The present invention can also increase the growth diameter of the rod by maintaining the pressure of the reactor 1 at 0.001 bar to 0.1 bar and extending the air inlet pipe 2 to the inside of the reactor 1 to form dense silicon carbide.

[0039] The intake pipe 2 extends to the upper part of the deposition carrier 13. The intake pipe 2 has nozzles 21 near the side of the deposition carrier 13. The uppermost nozzle 21 is located above the deposition carrier 13. The deposition gas source is sprayed horizontally towards the deposition carrier 13. Along the height direction of the deposition carrier 13, multiple nozzles 21 are distributed. When the pressure in the reactor 1 is negative pressure, specifically in the range of 0.001 bar to 0.1 bar, it is more conducive to avoiding the situation that the deposition gas source entering from the intake pipe 2 is sucked out due to negative pressure pumping before it reaches the surface of the deposition carrier 13 for deposition reaction. It is also more conducive to smooth and stable air flow, enabling the deposition gas source to be evenly deposited on the deposition carrier 13, improving the deposition uniformity and the density of the polycrystalline silicon carbide rod. The vertical distance between the lowermost nozzle 21 and the first end of the exhaust pipe 3 is more than 50 cm, which is more conducive to avoiding the deposition gas source sprayed from the lowermost nozzle 21 being sucked out due to negative pressure pumping before it reaches the surface of the deposition carrier 13 for deposition reaction.

[0040] It can be understood that the intake holes 112 of the present invention are preferably evenly arranged along the circumferential direction of the bottom plate 11.

[0041] In some preferred embodiments, the first end of the exhaust pipe 3 extends into the reactor 1, and the pipe wall of the first end of the exhaust pipe 3 extends obliquely outward and upward to form a trumpet-shaped structure 31. On the one hand, it is necessary for the deposition gas source to circulate fully in the reactor 1 for sufficient deposition. On the other hand, it is necessary to quickly discharge gases such as hydrogen chloride to inhibit corrosion. However, the rapid discharge of gases such as hydrogen chloride through the exhaust pipe 3 will also bring about the discharge of the deposition gas source. In this preferred scheme, the first end of the exhaust pipe 3 is in the shape of a trumpet-shaped structure 31, which can effectively collect the tail gas containing a higher concentration of hydrogen chloride components in the central area, promote the rapid and stable extraction of gases such as hydrogen chloride from the reactor 1, and is more conducive to balancing the two effects of sufficient deposition of the deposition gas source and rapid discharge of gases such as hydrogen chloride to inhibit corrosion. It can control the corrosion of the polycrystalline silicon carbide rod by hydrogen chloride while maintaining good utilization rate of the deposition gas, making the silicon carbide rod have good density. In addition, the first end of the exhaust pipe 3 of the present invention being in the shape of a trumpet-shaped structure 31 is also more conducive to the air flow inside the reactor 1 tending to be in a steady flow, reducing air flow jitter and interference, and enabling the deposition gas source to be evenly deposited on the deposition carrier 13, thereby improving the density of the polycrystalline silicon carbide rod.

[0042] Preferably, the included angle between the pipe wall of the first end of the exhaust pipe 3 and the vertical direction is 30° to 60°. In this preferred scheme, it is more conducive to balancing the two effects of sufficient deposition of the deposition gas source and rapid discharge of gases such as hydrogen chloride to inhibit corrosion.

[0043] In some preferred embodiments, the negative pressure monitoring device monitors whether the pressure in the reactor 1 is within the range of 0.01 bar to 0.03 bar, which is more conducive to inhibiting the corrosion of the polycrystalline silicon carbide rod by the hydrogen chloride gas, improving the compactness of the polycrystalline silicon carbide rod, improving the purity of the polycrystalline silicon carbide powder, and improving the conversion rate of the deposition gas source.

[0044] In the second aspect, the present invention provides a method for preparing a high-density polycrystalline silicon carbide rod, which is prepared by the preparation device described in the first aspect, so that the negative pressure monitoring device monitors the pressure in the reactor 1, and the exhaust control unit adjusts the exhaust speed of the exhaust unit according to the pressure in the reactor 1, so that the exhaust unit exhausts gas from the reactor 1 through the exhaust pipe 3, so that the pressure in the reactor 1 is maintained at 0.001bar~0.1bar, and the deposition gas source is introduced into the reactor 1 through the nozzle 21 on the air inlet pipe 2, and a deposition reaction occurs on the surface of the deposition carrier 13 to generate polycrystalline silicon carbide and hydrogen chloride gas.

[0045] In the preparation method of the present invention, the negative pressure monitoring part monitors the pressure in the reactor 1, and the exhaust control part adjusts the exhaust speed of the exhaust part according to the pressure in the reactor 1. The exhaust part exhausts gas from the reactor 1, so that the pressure in the reactor 1 is maintained at 0.001 bar~0.1 bar, which can increase the gas flow rate on the surface of the polycrystalline silicon carbide rod, promote the separation of hydrogen chloride from the surface of the polycrystalline silicon carbide rod, reduce the concentration of hydrogen chloride gas in the reactor 1, reduce the concentration of hydrogen chloride gas on the surface of the polycrystalline silicon carbide rod, and further inhibit the corrosion of the polycrystalline silicon carbide rod by hydrogen chloride gas, avoid the corrosion causing holes and coral-like structures on the silicon carbide rod, improve the compactness of the polycrystalline silicon carbide rod, inhibit the rod from absorbing impurities, and improve the purity of the polycrystalline silicon carbide powder obtained after the polycrystalline silicon carbide rod is crushed. The pressure in the reactor 1 of the present invention is maintained at 0.001 bar~0.1 bar, which can also inhibit the generation of particulate matter in the atmosphere in the reactor 1, improve the utilization rate of the raw gas, and prevent the gas entering the exhaust pipe 3 from carrying particulate matter and causing pipeline blockage.

[0046] If the pressure in the reactor 1 is lower than 0.001 bar, the growth rate of the polycrystalline silicon carbide is likely to be too slow, and the growth rate can only reach the level of micrometers per hour. For example, it is difficult to grow a silicon carbide film into a silicon carbide rod. The growth rate of the present invention can reach the level of millimeters per hour. If it is greater than 0.1 bar, hydrogen chloride is likely to accumulate on the surface of the polycrystalline silicon carbide rod and corrode the polycrystalline silicon carbide rod.

[0047] The present invention does not limit the deposition gas source, and the deposition gas source can be SiCH 3 Cl 3 , CH 4 and SiCl 4 Mixed gas and SiH4 and CCl 4 At least one of the mixed gas. The type of the carrier gas is not limited, and the carrier gas can be at least one of hydrogen and argon. The pressure in the reactor of the present invention is maintained at 0.001 bar to 0.1 bar, which can promote the detachment of hydrogen chloride from the surface of the polycrystalline silicon carbide rod, reduce the concentration of hydrogen chloride gas on the surface of the polycrystalline silicon carbide rod, and can inhibit the corrosion of the silicon carbide rod by hydrogen chloride when the carrier gas is hydrogen.

[0048] The pressure in the reactor 1 of the present invention can be maintained, for example, at 0.001 bar, 0.003 bar, 0.005 bar, 0.008 bar, 0.01 bar, 0.03 bar, 0.05 bar, 0.07 bar, 0.09 bar and 0.1 bar.

[0049] In some preferred embodiments, when the pressure in the reactor 1 is normal pressure, the total flow rate of the deposition gas source and the carrier gas is Q , when the pressure in the reactor 1 is maintained at 0.001 bar to 0.1 bar, the total flow rate of the deposition gas source and the carrier gas is 0.08 Q ~0.15 Q。 Under this preferred scheme, the total flow rate of the deposition gas source and the carrier gas is 8% to 15% of the total flow rate at normal pressure, which can prevent the deposition gas source concentration on the rod surface from being too high, resulting in too fast deposition speed, and is more conducive to inhibiting the appearance of holes and coral-like structures on the silicon carbide rod, improving the density of the polycrystalline silicon carbide rod, and inhibiting the rod from adsorbing and incorporating impurities. Since the pressure in the reactor 1 is maintained at 0.001 bar to 0.1 bar, it can promote the deposition process of the deposition gas source to generate polycrystalline silicon carbide and hydrogen chloride gas, improve the conversion rate of the deposition gas source, and still maintain a good deposition speed and stable deposition when the total flow rate of the deposition gas source and the carrier gas is 8% to 15% of the total flow rate at normal pressure. Q When the pressure in the reactor 1 is normal pressure, to achieve the same material flow rate on the surface of the silicon carbide rod, the total flow rate of the deposition gas source and the carrier gas can be obtained by means such as historical data and theoretical calculation. Preferably, when the pressure in the reactor 1 is maintained at 0.001 bar to 0.1 bar, the total flow rate of the deposition gas source and the carrier gas is 0.12 Q ~0.15 Q .

[0050] In some preferred embodiments, an electric current is applied to the deposition carrier 13 through the electrode 14 to keep the surface temperature of the deposition carrier 13 at a preset temperature, and the preset temperature is 1200°C to 1600°C. Under this preferred scheme, the temperature on the surface of the deposition carrier 13 is 1200°C to 1600°C, and the temperature is relatively high, which can further improve the conversion rate of the deposition gas source. When the total flow rate of the deposition gas source and the carrier gas introduced is 8% to 15% of the normal pressure total flow rate, it is more conducive to maintaining a good deposition rate and stable deposition. Since the pressure in the reactor 1 is maintained at 0.001 bar to 0.1 bar, the detachment rate of the hydrogen chloride generated by the deposition reaction from the surface of the polycrystalline silicon carbide rod is fast, and the concentration of the hydrogen chloride gas on the surface of the polycrystalline silicon carbide rod is low. Even when a relatively high deposition temperature of 1200°C to 1600°C is adopted, the corrosion of the polycrystalline silicon carbide rod by the hydrogen chloride gas can be effectively controlled, and the denseness of the silicon carbide rod can be ensured. Preferably, the preset temperature is 1450°C to 1600°C.

[0051] In some preferred embodiments, keeping the pressure in the reactor 1 at 0.01 bar to 0.03 bar is more conducive to suppressing the corrosion of the polycrystalline silicon carbide rod by the hydrogen chloride gas, improving the denseness of the polycrystalline silicon carbide rod, increasing the purity of the polycrystalline silicon carbide powder, and improving the conversion rate of the deposition gas source.

[0052] In some preferred embodiments, the flow rate of the deposition gas source ejected from the nozzle 21 on the intake pipe 2 is 5 m / s to 50 m / s.

[0053] In some preferred embodiments, before introducing the deposition gas source into the interior of the reactor 1, a carrier gas is introduced into the interior of the reactor 1 to displace the atmosphere inside the reactor 1 and remove impurity atmospheres such as air and water vapor inside the reactor 1; the deposition gas source and the carrier gas are mixed and then introduced into the interior of the reactor 1 through the intake pipe 2; the gas extracted by the air extraction part is subjected to tail gas recovery, and the tail gas recovery includes pressurization, cooling, partial condensation, rectification, etc., and the purified deposition gas source and carrier gas are sent back into the reactor 1.

[0054] In a third aspect, the present invention provides a polycrystalline silicon carbide rod with high denseness prepared by using the preparation method described in the second aspect, and the denseness is above 72%.

[0055] In a fourth aspect, the present invention provides a polycrystalline silicon carbide powder with high purity, and the polycrystalline silicon carbide powder is obtained by crushing the polycrystalline silicon carbide rod with high denseness described in the third aspect.

[0056] The present invention will be further elaborated in detail below with reference to specific embodiments.

[0057] Example 1

[0058] A preparation device for a polycrystalline silicon carbide rod with high denseness, seeFigure 1 ( Figure 1 In the figure, the arrow lines indicate the flow directions of the deposition gas source and the carrier gas), and it includes a reactor 1, an inlet pipe 2, and a negative pressure assembly; the reactor 1 includes a bottom plate 11 and a cover body 12 covering the bottom plate 11. There is a vertical deposition carrier 13 inside the cover body 12. A suction hole 111 is provided at the center of the bottom plate 11. A vertical electrode 14 penetrates through the bottom plate 11. The electrode 14 is located outside the suction hole 111. The upper end of the electrode 14 is connected to the lower end of the deposition carrier 13. An air inlet hole 112 is provided on the bottom plate 11 outside the electrode 14; one end of the inlet pipe 2 extends to the upper part of the deposition carrier 13 through the air inlet hole 112. Nozzles 21 are arranged at intervals along the axial direction of the inlet pipe 2 on the side of the pipe section of the inlet pipe 2 inside the reactor 1 close to the deposition carrier 13. The uppermost nozzle 21 is located above the deposition carrier 13; the negative pressure assembly includes a suction pipe 3, a suction part (not shown in the figure), a suction control part (not shown in the figure), and a negative pressure monitoring part (not shown in the figure). The first end of the suction pipe 3 is connected to the inside of the reactor 1 through the suction hole 111 and extends into the reactor 1. The pipe wall of the first end of the suction pipe 3 extends obliquely upward and outward to form a horn-shaped structure 31. The included angle between the pipe wall of the first end of the suction pipe 3 and the vertical direction is 30°. The end of the first end of the suction pipe 3 is lower than the lower end of the deposition carrier 13. The second end of the suction pipe 3 is connected to the suction part. The suction control part is respectively connected to the negative pressure monitoring part for monitoring whether the pressure in the reactor 1 is within the range of 0.01 bar to 0.03 bar and the suction part; the lowermost nozzle 21 is located above the first end of the suction pipe 3 and the vertical distance from the first end of the suction pipe 3 is 60 cm.

[0059] A preparation method of a high-density polycrystalline silicon carbide rod is prepared by using the aforementioned preparation device, and it includes:

[0060] Step 1: Disconnect the connection between the suction pipe 3 and the suction part. Hydrogen (carrier gas) and argon (carrier gas) are introduced into the reactor 1 through the inlet pipe 2. The atmosphere in the reactor 1 cavity is discharged from the suction pipe 3, so as to realize the replacement of the atmosphere in the reactor 1 cavity. After replacement, the pressure in the reactor 1 is normal pressure;

[0061] Step 2: Connect the suction pipe 3 and the suction part, and make the negative pressure monitoring part monitor the pressure in the reactor 1. The pressure in the reactor 1 is made to be 0.01 bar to 0.03 bar by pumping air through the suction part. The electrode 14 is energized to the deposition carrier 13. After the deposition carrier 13 is energized, resistance heat is generated due to its own resistance effect, and the surface temperature of the deposition carrier 13 is 1600 °C;

[0062] Step 3: Add SiCH 3 Cl 3The deposition gas source, hydrogen (carrier gas), and argon (carrier gas) are mixed and then introduced into the reactor 1 through the inlet pipe 2. They flow to the surface of the deposition carrier 13 to react and generate polycrystalline silicon carbide and hydrogen chloride gas. The total flow rate of the deposition gas source and the carrier gas introduced is 0.12 Q, Q When the pressure in the reactor 1 is at atmospheric pressure, the total flow rate of the deposition gas source and the carrier gas introduced ， During the gas introduction process, the negative pressure monitoring component monitors the pressure in the reactor 1. The air extraction control unit adjusts the air extraction speed of the air extraction unit according to the pressure in the reactor 1. The air extraction unit extracts gas from the reactor 1 through the extraction pipe 3 to keep the pressure in the reactor 1 at 0.01 bar to 0.03 bar. The gas extracted by the air extraction unit is subjected to tail gas recovery. After pressurization, cooling, partial condensation, rectification, etc., the purified SiCH 3 Cl 3 , hydrogen, and argon are returned for reuse.

[0063] Example 2

[0064] Referring to Example 1, the difference is that the angle between the tube wall at the first end of the extraction pipe 3 of the preparation device and the vertical direction is 15°.

[0065] Example 3

[0066] Referring to Example 1, the difference is that the first end of the extraction pipe 3 of the preparation device does not extend into the reactor 1. The first end of the extraction pipe 3 is flush with the bottom plate 11, and the first end of the extraction pipe 3 does not form a flared structure 31.

[0067] Example 4

[0068] Referring to Example 1, the difference is that in step 3 of the preparation method, the total flow rate of the deposition gas source and the carrier gas introduced is 0.5 Q。

[0069] Example 5

[0070] Referring to Example 1, the difference is that in step 2 of the preparation method, the negative pressure monitoring component monitors the pressure in the reactor 1, and the pressure in the reactor 1 is made to be 0.05 bar to 0.1 bar by extracting gas through the air extraction unit. In step 3, the pressure in the reactor 1 is kept at 0.05 bar to 0.1 bar, and the negative pressure monitoring component of the preparation device monitors whether the pressure in the reactor 1 is within the range of 0.05 bar to 0.1 bar.

[0071] Comparative Example 1

[0072] Referring to Example 1, the difference is that in step 2 of the preparation method, the negative pressure monitoring component monitors the pressure in the reactor 1, and the pressure in the reactor 1 is made to be 1.0 bar to 1.2 bar by pumping air through the air extraction part. In step 3, the pressure in the reactor 1 is maintained at 1.0 bar to 1.2 bar, and the negative pressure monitoring component of the preparation device monitors whether the pressure in the reactor 1 is within the range of 1.0 bar to 1.2 bar.

[0073] Test Example

[0074] Measure the density of the polycrystalline silicon carbide rods prepared by the preparation methods of Examples 1 to 5 and Comparative Example 1, as shown in Table 1. The polycrystalline silicon carbide rods are broken into small fragments with a particle size of 10 mm to 30 mm, the depth of the pits on the surface of the small fragments is measured, the small fragments with a pit depth of more than 5 mm and the small fragments with a pit depth of less than 5 mm are separated, and the proportion of the weight of the small fragments with a pit depth of less than 5 mm in the weight of the polycrystalline silicon carbide rod is calculated to obtain the density. The polycrystalline silicon carbide rods prepared by the preparation methods of Examples 1 to 5 and Comparative Example 1 are broken to obtain polycrystalline silicon carbide powder. Referring to GB / T 37254-2018 and GB / T 41153-2021, the glow discharge mass spectrometry (GDMS) and secondary ion mass spectrometry (SIMS) are used to measure the content of impurity elements in the polycrystalline silicon carbide powder, and the purity of the polycrystalline silicon carbide powder is obtained after removing the content of impurity elements, as shown in Table 1. In the table, purity > 7.5N means the purity is greater than 99.999995%, purity > 7N means the purity is greater than 99.99999%, and purity > 6N means the purity is greater than 99.9999%.

[0075] Table 1

[0076]

[0077] Comparing the examples and the comparative example, keeping the pressure in the reactor 1 at 0.001 bar to 0.1 bar can improve the density of the polycrystalline silicon carbide rod and the purity of the polycrystalline silicon carbide powder.

[0078] Comparing Examples 1 to 3, it can be seen that the first end of the air extraction pipe 3 extends into the reactor 1, and the pipe wall at the first end of the air extraction pipe 3 extends obliquely outward and upward to form a horn-shaped structure 31, which is more conducive to improving the density of the polycrystalline silicon carbide rod. The angle between the pipe wall at the first end of the air extraction pipe 3 and the vertical direction is 30° to 60°, which is more conducive to further improving the density of the polycrystalline silicon carbide rod. Comparing Example 1 and Example 4, the total flow rate of the deposition gas source and the carrier gas is 0.08 Q ~0.15 Q，It is more conducive to improving the density of the polycrystalline silicon carbide rod and increasing the purity of the polycrystalline silicon carbide powder. Comparing Example 1 and Example 5, keeping the pressure in the reactor 1 at 0.01 bar to 0.03 bar is more conducive to improving the density of the polycrystalline silicon carbide rod and increasing the purity of the polycrystalline silicon carbide powder.

[0079] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-density polycrystalline silicon carbide rod, characterized in that: The high-density polycrystalline silicon carbide rod is prepared by a preparation device, wherein a negative pressure monitoring component monitors the pressure in the reactor (1), and a gas extraction control unit adjusts the gas extraction speed of the gas extraction unit according to the pressure in the reactor (1), so that the gas extraction unit extracts gas from the reactor (1) through a gas extraction pipe (3), and the pressure in the reactor (1) is maintained at 0.001 bar to 0.1 bar. A deposition gas source is introduced into the reactor (1) through a nozzle (21) on an air inlet pipe (2), and a deposition reaction occurs on the surface of a deposition carrier (13) to generate polycrystalline silicon carbide and hydrogen chloride gas; The preparation device comprises: a reactor (1), the reactor (1) comprising a bottom plate (11), a cover body (12) covering the bottom plate (11), and a vertical deposition carrier (13) located inside the cover body (12); a gas extraction hole (111) is provided at the center of the bottom plate (11); a vertical electrode (14) is provided on the bottom plate (11); the electrode (14) is located outside the gas extraction hole (111); the upper end of the electrode (14) is connected to the lower end of the deposition carrier (13); and an air inlet hole (112) is provided on the bottom plate (11) outside the electrode (14); An air inlet pipe (2), one end of the air inlet pipe (2) extending into the interior of the reactor (1) through the air inlet hole (112), a nozzle (21) being provided on the pipe section of the air inlet pipe (2) located inside the reactor (1); A negative pressure component, the negative pressure component comprising an exhaust pipe (3), an exhaust unit, an exhaust control unit and a negative pressure monitoring unit, the first end of the exhaust pipe (3) being connected to the interior of the reactor (1) through the exhaust hole (111), the end of the first end of the exhaust pipe (3) being lower than the lower end of the deposition carrier (13), the second end of the exhaust pipe (3) being connected to the exhaust unit, the negative pressure monitoring unit monitoring whether the pressure in the reactor (1) is within the range of 0.001 bar to 0.1 bar, and the exhaust control unit being connected to the negative pressure monitoring unit and the exhaust unit respectively; One end of the air inlet pipe (2) extends through the air inlet hole (112) to the upper part of the deposition carrier (13); a plurality of nozzles (21) are provided on the side of the air inlet pipe (2) located inside the reactor (1) and close to the deposition carrier (13); the nozzles (21) are arranged at intervals along the axial direction of the air inlet pipe (2); the uppermost nozzle (21) is located above the deposition carrier (13); and the lowermost nozzle (21) is located above the first end of the air extraction pipe (3) and is at a vertical distance of more than 50 cm from the first end of the air extraction pipe (3); The first end of the air extraction pipe (3) extends into the interior of the reactor (1), and the pipe wall of the first end of the air extraction pipe (3) extends outwardly and upwardly to form a trumpet-shaped structure (31); The gas inlet (112) is located at the periphery of the polycrystalline silicon carbide rod. The deposition gas source and the carrier gas are injected from the periphery of the polycrystalline silicon carbide rod into the reactor (1). The deposition gas source and the carrier gas flow through the surface of the polycrystalline silicon carbide rod, bringing in the deposition gas source and taking away the tail gas including hydrogen chloride. The trumpet-shaped structure (31) of the exhaust pipe (3) is located at the inner lower part of the polycrystalline silicon carbide rod. The trumpet-shaped structure (31) of the exhaust pipe (3) collects the tail gas containing the hydrogen chloride component in the central area, thereby facilitating the exhaust gas to be extracted from the reactor (1).

2. The method for preparing a high-density polycrystalline silicon carbide rod according to claim 1, characterized in that: When the pressure in the reactor (1) is normal pressure, the total flow rate of the deposition gas source and the carrier gas is Q When the pressure in the reactor (1) is maintained at 0.001 bar to 0.1 bar, the total flow rate of the deposition gas source and the carrier gas is 0.08 Q ~0.15 Q。 3. The method for preparing a high-density polycrystalline silicon carbide rod according to claim 1 or 2, characterized in that: The deposition carrier (13) is energized through the electrode (14) so ​​that the surface temperature of the deposition carrier (13) is maintained at a preset temperature, wherein the preset temperature is 1200° C. to 1600° C.

4. The method for preparing a high-density polycrystalline silicon carbide rod according to claim 1, characterized in that: The pressure in the reactor (1) is maintained at 0.01 bar to 0.03 bar.

5. The method for preparing a high-density polycrystalline silicon carbide rod according to claim 1, characterized in that: The preparation device further comprises: the angle between the tube wall of the first end of the exhaust tube (3) and the vertical direction is 30° to 60°.

6. A high-density polycrystalline silicon carbide rod prepared by the method for preparing a high-density polycrystalline silicon carbide rod according to any one of claims 1 to 5, characterized in that: The density is 72% to 89%, and the purity is greater than 99.99999%. The density is calculated by breaking the polycrystalline silicon carbide rod into small pieces with a particle size of 10 mm to 30 mm, measuring the depth of the pits on the surface of the small pieces, separating the small pieces with a pit depth of more than 5 mm and the small pieces with a pit depth of less than 5 mm, and calculating the weight of the small pieces with a pit depth of less than 5 mm as a proportion of the weight of the polycrystalline silicon carbide rod to obtain the density.

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