Device and method for the production of silicon carbide

Abstract

The invention relates to a device for the production of silicon carbide, said device comprising a heatable reactor (1) which comprises, on its upper side, a feed opening (4) for continuous feeding with a precursor (7), an outlet opening (5) on its underside for the continuous discharge of silicon carbide (10) formed in the reactor (1) from the precursor, and an interior space (1) between the feed opening (4) and the outlet opening (5), which are arranged in such a way that the precursor and the silicon carbide respectively fill the interior space (1). the silicon carbide can pass through the interior space (1) falling from the feed opening (4) to the outlet opening (5).

Description

[0001] Apparatus and method for producing silicon carbide

[0002] The invention relates to a device and a method for producing silicon carbide, in particular for producing silicon carbide powder.

[0003] Silicon carbide is an attractive material for many applications due to its high hardness, thermal conductivity, and special semiconductor properties. However, many of these properties are impaired by impurities. High-purity silicon carbide is particularly required for further processing in the semiconductor industry.

[0004] Silicon carbide is typically produced by carbothermal reactions in a reactor (furnace) at high temperatures from a precursor containing Si and C. Examples of the precursor are powders or granules of SiO2 and carbonaceous components.

[0005] A well-known process for producing silicon carbide is the Acheson process, in which the silicon carbide is obtained batchwise from silicon dioxide in the form of quartz sand and from carbon in the form of coke in an electric resistance furnace at temperatures of more than 2000 °C.

[0006] EP 0476422 A1 discloses a process for producing silicon carbide from silicon dioxide powder and soot under argon in a crucible or rotary kiln at temperatures of 1200 to 2000°C for a period of one hour. These processes are batch processes in which the SiC is produced batchwise from a quantity of precursor previously charged into the reactor. However, batch processes are unsatisfactory for the industrial production of SiC because the quantity in a batch is limited. Recharging the precursor is time-consuming and, due to the cooling and reheating of the reactor, involves energy loss, and makes precise control of the process parameters over the entire production time difficult.

[0007] In addition, silicon carbide produced in the known manner is not pure enough for many applications, for example in electronics or semiconductor production, and must be cleaned at great expense before further processing.

[0008] The invention is therefore based on the object of creating an apparatus and a method for producing silicon carbide which are more efficient than the prior art.

[0009] This object is achieved by a device and a method for producing silicon carbide according to the enclosed patent claims.

[0010] The invention allows for the continuous production of silicon carbide in a reactor in which the precursor is transformed into silicon carbide as it falls through the reactor. The precursor and silicon carbide barely come into contact with the reactor wall. Therefore, there is virtually no contamination of the produced silicon carbide in the reactor. The relatively short residence time during the fall through the reactor also limits the absorption of foreign substances by the precursor and the produced silicon carbide. The invention is ideally suited for the efficient production of high-purity silicon carbide.

[0011] The residence time during fall through the reactor is well suited for transforming nano- or microscale precursor into nano- or microcrystalline silicon carbide powder. Nanoscale or microscale refers here to the size of the primary particles in the precursor, i.e., a particle size in the range of 5 to 1000 nm, typically about 20 to 200 or up to 1000 nm, or a particle size in the range of 1 to 1000 pm, typically about 1 or 20 to 200 pm.

[0012] The properties of the invention cannot be achieved with horizontal rotary kilns as in the prior art. The purity required for high-quality silicon carbide would require a rotary kiln made of high-purity silicon carbide to avoid the absorption of other materials into the product, which would be technically difficult to achieve and expensive. When producing high-purity silicon carbide, the furnace chamber should be filled with inert gas and sealed off from the outside atmosphere. However, in rotary kilns, it is difficult to seal the moving parts, even at temperatures of approximately 1800°C to 2000°C. Sealing the moving parts while still allowing the precursor to flow in and out would be technically almost impossible. In addition, the precursor flow times through conventional rotary kilns are too long for silicon carbide production. All of these problems are eliminated with the invention. Preferred embodiments of the invention are described in

[0013] The following is explained using the drawing. It shows:

[0014] Figure 1 shows an apparatus for producing silicon carbide according to the embodiments.

[0015] Directional and orientational terms such as "top" and "bottom" used below refer to the orientation of the device when used as intended using the process for producing silicon carbide.

[0016] The device for producing silicon carbide shown in Figure 1 comprises a furnace as a heatable reactor 1. The reactor 1 comprises a jacket 2 which surrounds an interior space 3 and has a feed opening 4 at the upper end of the interior space 3 on the top side of the reactor 1 and an outlet opening 5 at the lower end of the interior space 3 on the underside of the reactor 1. In the present example, the jacket 2 is designed essentially as a vertical tube. Feed opening 4 and outlet opening 5 lie essentially vertically one above the other. The interior space 3 is preferably filled with an inert gas, for example argon.

[0017] Above the feed opening 4, a feed device 6 is arranged for feeding a precursor 7 through the feed opening 4 into the interior space 3. In this arrangement, the precursor trickles through the feed opening 4 into the interior space 3 due to gravity. The feed opening 4 is provided with a divider 8 for dividing the flow of the supplied precursor 7 into several parallel flows and thus for distributing it over a large part of the cross-sectional area of ​​the interior space 3, without, however, unnecessarily directing the precursor 7 against the casing 2. The precursor 7 contains Si and C and is typically provided as a powder or granulate, for example as SiCp powder with carbon-containing components such as graphite or soot.A nano- or microscale precursor is suitable, i.e., a precursor with nanoscale particles with a primary particle size in the range of 5 to 1000 nm, typically approximately 20 to 200 or up to 1000 nm, or with microscale particles with a primary particle size in the range of 1 to 1000 pm, typically approximately 1 or 20 to 200 pm. The precursor should have a purity corresponding to the required purity of the silicon carbide to be produced.

[0018] Below the outlet opening 5, a collecting device 9 is arranged for silicon carbide 10 produced in the reactor 1 from the precursor 7, which exits the interior 3 through the outlet opening 5 due to gravity. The collecting device 9 can be a container or a discharge device for the silicon carbide 10 designed as a ramp or conveyor belt.

[0019] Since the reactor 1 is static, it can be sealed in a simple manner so that the outside atmosphere does not penetrate into the inert gas-filled interior 3, for example by a seal between the feed opening 4 and the feed device 6 and between the outlet opening 5 and the collecting device 9 or by a shell around the reactor 1 (not shown).

[0020] The reactor 1 is heated, and for this purpose, the jacket 2 has one or more heating devices 11, 12. Preferably, an upper first heating device 11 is provided for heating an upper first heating zone 13 of the interior 3 to a first temperature, and a lower second heating device 12 is provided for heating a lower second heating zone 14 of the interior 3 to a second temperature. During operation, the first temperature is in the range of approximately 1600 to 1900°C, preferably approximately 1800°C, and the second temperature is lower than the first and is preferably in the range of approximately 1500 to 1700°C.

[0021] Thus, the precursor descending from the feed opening 4 through the interior is first exposed to the first temperature in the first heating zone 13, which initiates the carbothermal reactions and forms intermediate products that react at the second temperature in the second heating zone 14 to form silicon carbide 10, which exits from the outlet opening 5. The particles of the precursor 7 are thus transformed into nano- or microcrystalline particles of silicon carbide 10. The silicon carbide 10 is collected as a powder by the collecting device 9.

[0022] The transport of the particles of the precursor 7 and the silicon carbide 10 from the feed opening 4 through the interior space 3 to the outlet opening 5 occurs essentially in free fall under gravity. The particle size of the precursor and the lengths of the first zone 13 and the second zone 14 in the vertical direction are selected such that the sinking speed of the particles ensures a residence time, i.e., heating time, of approximately 100 to 200 ms, preferably approximately 150 ms, in the first heating zone 13 and a total residence time of approximately 300 to 1000 ms, preferably approximately 400 ms, in both heating zones 13, 14 or the entire interior space 3.

[0023] Optionally, impact plates 15 may be provided which, as in the example shown, project downwardly from the shell 2 into the first and / or second heating zones 13, 14 of the interior 3 and interrupt the fall of the particles of the precursor 7 and / or the silicon carbide 10, thus extending the residence time of the particles in the zones 13, 14 compared to a continuous free fall. The angle of inclination of the impact plates 15 may be adjustable in order to set the residence time. The residence time can also be adjusted by allowing the inert gas in the interior 3 to flow upwards to extend the residence time and downwards to shorten the residence time, for example by circulating the inert gas in a closed circuit which leads through the interior 3 and a return line (not shown) connecting the feed and outlet openings 4, 5 outside the reactor 1.

[0024] Within the heating zones 13, 14, the precursor 7 and the silicon carbide 10 are transported in free fall, largely without contact with the casing 2 and therefore largely without contact, except for possible contact with any impact plates 15 provided. Therefore, the precursor 7 and the silicon carbide 10 do not absorb any impurities, and the produced silicon carbide 10 can be of high purity, depending on the purity of the precursor used. The casing 2 and any impact plates 15 provided are preferably made of silicon carbide or coated with silicon carbide towards the interior 3 in order to prevent any foreign substances from being introduced into the produced silicon carbide 10.

[0025] The device is very robust, as it has hardly any moving parts. During operation, the device allows for an efficient continuous production process for silicon carbide 10. Precursor 7 is continuously fed through the feed opening 4 by means of the feed device 6. As described, this precursor falls through the heated interior 3, i.e., in particular, the first and second heating zones 13, 14, and is thereby transformed into silicon carbide 10, which falls out through the outlet opening 5 and is also continuously collected by the collecting device 9.

Claims

Patent claims 1. Device for producing silicon carbide, comprising: a reactor (1) which has on its upper side a feed opening (4) for continuous feeding with a precursor (7), on its lower side an outlet opening (5) for continuous outlet of silicon carbide (10) formed in the reactor (1) from the precursor and between feed opening (4) and outlet opening (5) a heatable interior space (3) which are arranged such that the precursor or the silicon carbide can pass through the interior space (3) falling from the feed opening (4) to the outlet opening (5).

2. Device according to claim 1, comprising a heating device (11, 12) for heating the interior (3) .

3. Device according to claim 2, wherein the heating device comprises a first heating device (11) for heating a first heating zone (13) of the interior (3) to a first temperature and a second heating device (12) for heating a second heating zone (14) of the interior (3) located below the first heating zone (13) to a second temperature, and the second temperature is lower than the first temperature.

4. Device according to one of the preceding claims, comprising a feed device (6) for continuously feeding the precursor (7) to the feed opening (4) and a divider (8) for distributing the current of the precursor guided through the feed opening (4) into the interior (3).

5. Device according to one of the preceding claims, with an inclined baffle plate (15) which projects into the flow of the precursor (7) or silicon carbide (10) falling through the interior space in order to control its residence time in the interior space.

6. Device according to claim 5, wherein the inclination angle of the impact plate (15) is adjustable.

7. Method for producing silicon carbide using a device according to one of the preceding claims, wherein: the reactor (1) is continuously fed with precursor (7) through the feed opening (4), the precursor (7) falls through the heated interior (3) to the outlet opening (5) and is thereby transformed into silicon carbide (10), and the silicon carbide (10) continuously exiting from the outlet opening (5) is collected.

8. The method of claim 7, wherein the supplied precursor (7) is in powder form.

9. Method according to claim 7 or 8, wherein the silicon carbide (10) produced is in powder form.

10. Method according to any one of claims 7 to 9, wherein precursor (7) and silicon carbide (10) traverse the heated interior space (3) essentially in free fall.

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