Silicon carbide manufacturing apparatus and method

Abstract

An apparatus for producing silicon carbide is disclosed, the apparatus comprising a heatable reactor (1), the reactor having an inlet (4) on an upper side for continuously supplying a precursor (7), an outlet (5) on a lower side for continuously discharging silicon carbide (10) formed from the precursor in the reactor (1), and an internal space (3) between the inlet (4) and the outlet (5), the inlet, the outlet and the internal space being arranged such that the precursor and silicon carbide pass through the internal space (3) and fall from the inlet (4) to the outlet (5).

Description

[Technical field]

[0001] The present invention relates to an apparatus and method for the production of silicon carbide, and in particular for the production of silicon carbide powder. [Background technology]

[0002] Silicon carbide is an attractive material for many applications due to its high hardness, its thermal conductivity and its special semiconducting properties. However, many of these properties are impaired by impurities. High purity silicon carbide is required for processes, especially in the semiconductor industry.

[0003] Silicon carbide is usually produced by carbothermal reaction in a high temperature reactor (furnace) from precursors containing Si and C. Examples of precursors include SiO 2 and powders or granules of a carbon-containing component.

[0004] A well-known method for producing silicon carbide is the Acheson process, in which silicon carbide is obtained in batches from silicon dioxide in the form of quartz sand and carbon in the form of coke in an air resistance furnace at temperatures above 2000°C.

[0005] EP 0 476 422 A1 discloses a method for producing silicon carbide from silicon dioxide powder and carbon black at temperatures of 1200 to 2000° C. under argon in a crucible or rotary kiln for one hour.

[0006] These methods are batch processes that produce SiC in batches from amounts of precursors preloaded into the reactor. However, batch processes are insufficient for industrial production of SiC due to the limited amount of material in one batch. Reloading of precursors is time consuming and involves energy losses due to cooling and reheating of the reactor, making it difficult to precisely control the process parameters over the entire production time. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] European Patent Application Publication No. 0476422 Summary of the Invention [Problem to be solved by the invention]

[0008] Furthermore, silicon carbide produced by known methods is not sufficiently pure for many applications, such as in the manufacture of electronic devices or semiconductors, and must be costly cleaned before further processing.

[0009] It is therefore an object of the present invention to provide a more efficient apparatus and method for producing silicon carbide than those of the prior art. [Means for solving the problem]

[0010] This object is achieved by an apparatus and a method for producing silicon carbide as set forth in the appended claims.

[0011] The present invention allows for the continuous production of silicon carbide in a reactor where the precursor is converted to silicon carbide as it falls through the reactor. The precursor and silicon carbide have little contact with the walls of the reactor. As a result, the silicon carbide produced in the reactor is substantially uncontaminated. The relatively short residence time between falls through the reactor also limits the absorption of foreign matter by the precursor and the silicon carbide produced. The present invention is ideally suited for the efficient production of high purity silicon carbide.

[0012] The transit or residence time during the drop through the reactor is well suited to convert the nanoscale or microscale precursor into nanocrystalline or microcrystalline silicon carbide powder, where nanoscale or microscale refers to the size of the primary particles in the precursor, i.e., particle size in the range of 5 to 1000 nm, typically in the range of about 20 to 200 or up to 1000 nm, or particle size in the range of 1 to 1000 μm, typically in the range of about 1 or 20 to 200 μm.

[0013] The properties according to the invention cannot be achieved in a horizontal rotary kiln as in the prior art. To avoid the introduction of other substances into the product and achieve the purity required for the production of high quality silicon carbide, the rotary kiln must be made of high purity silicon carbide. This is expensive and technically almost impossible to achieve. Furthermore, to produce high purity silicon carbide, the furnace chamber must be filled with inert gas and sealed from the outside atmosphere. However, in a rotary kiln, it is difficult to seal the moving parts even at temperatures of the order of 1800°C to 2000°C. It is technically almost impossible to seal the moving parts and still be able to feed and discharge the precursor. Moreover, the time that the precursor passes through a conventional rotary kiln for the production of silicon carbide is too long. These problems do not occur in the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 shows an apparatus for producing silicon carbide according to this embodiment.

[0015] In the following, references to directions and orientations, such as "up" and "down," refer to the orientation of the apparatus when used as intended in a method for producing silicon carbide.

[0016] The silicon carbide manufacturing apparatus shown in FIG. 1 comprises a furnace, which is a heatable reactor 1. The reactor 1 comprises a jacket 2 surrounding an internal space 3, which is provided with a feed inlet 4 at the upper end of the internal space 3 at the top or apex of the reactor 1 and a discharge outlet 5 at the lower end of the internal space 3 at the lower or bottom of the reactor 1. In this embodiment, the jacket 2 is formed as an essentially vertical tube. The feed inlet 4 and the discharge outlet 5 are essentially located vertically one above the other. The internal space 3 is preferably filled with an inert gas, for example argon.

[0017] Above the feed inlet 4 is arranged a feeder 6 which feeds precursor 7 into the interior space 3 via the feed inlet 4. In this arrangement, the precursor flows down from the feed inlet 4 into the interior space 3 by gravity. The feed inlet 4 is provided with a partition 8 which divides the supplied stream of precursor 7 into several parallel streams which are distributed over a large part of the cross-sectional area of ​​the interior space 3, but which does not unnecessarily direct the precursor 7 towards the jacket 2.

[0018] The precursor 7 contains Si and C and is generally a powder or granule, e.g., SiO 2 with a carbon-containing component such as graphite or carbon black. 2 It is provided as a powder. Nanoscale or microscale precursors are preferred, i.e. precursors comprising nanoscale particles with a primary particle size in the range of 5 to 1000 nm, typically about 20 to 200 or up to 1000 nm, or precursors having microscale particles with a primary particle size in the range of 1 to 1000 μm, typically about 1 or 20 to 200 μm. The precursor should have a purity corresponding to the required purity of the silicon carbide to be produced.

[0019] Below the outlet 5 there is arranged a collector 9 for silicon carbide 10 produced in the reactor 1 from the precursor 7 and leaving the interior space 3 by gravity through the outlet 5. The collector 9 can be a container or a discharge designed as an inclined plane or a conveyor belt for the silicon carbide 10.

[0020] Since the reactor 1 is stationary, the interior space 3 filled with inert gas can be sealed in a simple manner to prevent outside atmosphere from entering, for example by a seal between the inlet 4 and the feeder 6 and between the outlet 5 and the collector 9, or by a casing (not shown) around the reactor 1.

[0021] The reactor 1 is heated and the jacket 2 is provided with one or more heating devices 11, 12 for this purpose. Preferably, an upper first heating device 11 is provided for heating a first heating zone 13 at the top of the inner space 3 to a first temperature and a lower second heating device 12 is provided for heating a second heating zone 14 at the bottom of the inner space 3 to a second temperature. In operation, the first temperature is in the range of about 1600 to 1900°C, preferably about 1800°C, and the second temperature is lower than the first temperature, preferably in the range of about 1500 to 1700°C.

[0022] Thus, the precursor descending through the interior space from the feed inlet 4 is first exposed to a first temperature in the first heating zone 13, which initiates a carbothermal reaction to form an intermediate product, which reacts at a second temperature in the second heating zone 14 to form silicon carbide 10, which exits through the outlet 5. In this way, the particles of precursor 7 are transformed into nano- or microcrystalline particles of silicon carbide 10. The silicon carbide 10 is collected as a powder by the recovery device 9.

[0023] The precursor 7 and silicon carbide 10 particles are transported essentially by free fall under gravity from the inlet 4 through the interior space 3 to the outlet 5. The precursor particle size and the vertical lengths of the first 13 and second 14 zones are selected such that, depending on the rate at which the particles fall, the residence time or heating time in the first heating zone 13 is about 100 to 200 ms, preferably about 150 ms, and the total residence time in both heating zones 13, 14 or the entire interior space 3 is about 300 to 1000 ms, preferably about 400 ms.

[0024] A baffle plate 15 may be optionally provided, which in the illustrated embodiment projects downward from the jacket 2 towards the first and / or second heating zones 13, 14 of the internal space 3 to interrupt the fall of the precursor 7 and / or silicon carbide 10 particles, thereby extending the residence time of the particles in the zones 13, 14 compared to continued free fall. The inclination angle of the baffle plate 15 may be adjustable to adjust the residence time. The residence time may also be adjusted by flowing the inert gas in the internal space 3 upwards to increase the residence time or downwards to decrease the residence time, for example by circulating the inert gas in a closed circuit through a return line (not shown) interconnecting the internal space 3 with the supply and exhaust ports 4, 5 outside the reactor 1.

[0025] Within the heating zones 13, 14, the precursor 7 and silicon carbide 10 are transported in free fall with little contact with the jacket 2 and therefore little contact except with the provided baffle plates 15. Thus, the precursor 7 and silicon carbide 10 do not absorb impurities and the silicon carbide 10 produced can be of high purity depending on the purity of the precursors used. The jacket 2 and any provided baffle plates 15 are preferably made of silicon carbide or coated with silicon carbide towards the interior space 3 so that foreign matter does not get into the silicon carbide 10 produced.

[0026] The device is very robust as it has few moving parts.

[0027] In operation, the apparatus allows for an efficient continuous method for the production of silicon carbide 10. In this method, precursor 7 is continuously and continuously fed by feed device 6 through feed inlet 4. The precursor falls through the heated interior space 3, i.e. in particular through the first and second heating zones 13, 14 as described above, where it is converted into silicon carbide 10. The silicon carbide falls through outlet 5 and is also continuously collected by recovery device 9.

Claims

1. 1. An apparatus for producing silicon carbide, comprising: An apparatus comprising a reactor (1), the reactor (1) having, on an upper side, a supply port (4) for continuously supplying a precursor (7), and, on a lower side, a discharge port (5) for continuously discharging silicon carbide (10) formed from the precursor in the reactor (1), and a heatable internal space (3) between the supply port (4) and the discharge port (5), the supply port, the discharge port, and the internal space being arranged such that the precursor and the silicon carbide each pass through the internal space (3) and fall from the supply port (4) to the discharge port (5).

2. 2. The apparatus of claim 1, The apparatus has a heating device (11, 12) for heating the interior space (3).

3. 3. The apparatus of claim 2, The heating device includes: a first heating device (11) for heating a first heating zone (13) of said interior space (3) to a first temperature; a second heating device (12) for heating a second heating zone (14) located below the first heating zone (13) of the internal space (3) to a second temperature lower than the first temperature; An apparatus comprising:

4. 4. An apparatus according to any one of claims 1 to 3, comprising: a supply device (6) for continuously supplying the precursor (7) to the supply port (4); and a partition (8) for distributing the flow of the precursor supplied from the supply port (4) into the interior space (3).

5. 5. An apparatus according to any one of claims 1 to 4, comprising: An apparatus comprising an inclined baffle plate (15) projecting into the flow of said precursor (7) or silicon carbide (10) falling through said internal space to control the time said precursor (7) or silicon carbide (10) remains in said internal space.

6. 6. The apparatus of claim 5, The device wherein the inclination angle of the baffle plate (15) is adjustable.

7. A method for producing silicon carbide by using an apparatus according to any one of claims 1 to 6, comprising the steps of: The precursor (7) is continuously fed into the reactor (1) via the feed port (4), The precursor (7) passes through the heated internal space (3) and falls to the outlet (5) where it is converted into silicon carbide (10); The silicon carbide (10) continuously exiting from the outlet (5) is recovered.

8. 8. The method of claim 7, further comprising: The process wherein the precursor (7) is provided in the form of a powder.

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

10. 10. The method according to any one of claims 7 to 9, comprising: The method comprises passing said precursor (7) and said silicon carbide (10) through said heated interior space (3) in substantially free fall.

Images