Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With decomposition of a precursor
Reexamination Certificate
1997-01-30
2001-10-09
Bueker, Richard (Department: 1763)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With decomposition of a precursor
C117S098000, C117S951000, C118S715000, C118S719000, C118S725000, C427S249150
Reexamination Certificate
active
06299683
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for the production of silicon carbide by means of chemical deposition from the gas phase, i.e. chemical vapor deposition (CVD).
2. Description of Related Art
In a CVD process for the production of silicon carbide (SiC), a gas stream consisting of working gases to provide silicon and carbon, and a carrier gas (generally hydrogen) is passed to a substrate, and SiC is deposited on the substrate from the gas mixture, by means of chemical reactions. From “Technical Digest of International Conference on SiC and Related Materials, Kyoto, Japan, 1995, page
609
” a CVD method for the production of monocrystalline SiC is known, in which the substrate temperatures are adjusted to be between 1800° C. and 2300° C. This results in high growth rates, without any negative influence on the crystal quality. The growth rates for this known method amount to as much as 0.5 mm/h. However, with the known method, only crystals with a maximum length of 2 mm can be grown.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method and an apparatus for the production of silicon carbide by means of CVD, in which greater utilization of the process gases is achieved than is achieved with the prior art.
The invention is directed to a method for the production of silicon carbide which includes directing a first gas stream at a substrate. The first gas stream includes at least one working gas to provide silicon (Si) and carbon (C) and at least one carrier gas. From this first gas stream, silicon carbide grows on the substrate by means of chemical gas phase deposition, i.e. chemical vapor deposition (CVD). Additionally, a second gas stream is generated which practically surrounds the first gas stream completely, parallel to its direction of flow.
The invention is also directed to an apparatus for the production of silicon carbide (SiC) which includes a reactor, at least one substrate arranged in the reactor, means to generate a first gas stream directed at the substrate, with at least one working gas to provide silicon (Si) and carbon (C) and with at least one carrier gas, where silicon carbide grows on the substrate by means of chemical vapor deposition (CVD), and means to generate a second gas stream which substantially surrounds the first gas stream, parallel to its direction of flow.
The invention is based on the recognition that the divergence of the first gas stream can be reduced by the second gas stream, which surrounds the first gas stream, and that a high level of stability of the concentration of the process gases in the first gas stream is achieved in this way. This results in greater utilization of the working gases introduced into the process. With the same growth temperatures on the substrate, and with the same total gas flows of the process gases, the growth rate of the silicon carbide growing on the substrate therefore increases. With the second gas stream according to the invention, it was possible to achieve a working gas yield more than ten times higher than without the second gas stream.
Preferred embodiments and further developments of the method and apparatus will become apparent from the detailed description of the invention which follows. In a first embodiment, the flow velocity of the first gas stream is adjusted to be greater than the flow velocity of the second gas stream, by means of a corresponding form of the means to generate the two gas streams. Because of the higher flow velocity of the first gas stream, the loss of process gases from the first gas stream into the second gas stream due to interdiffusion of gas particles of the process gases and the carrier gas, is kept low.
The means to generate the first gas stream which is directed at the substrate preferably contains at least a nozzle with an outlet facing the substrate, and means for supplying at least one working gas and at least one carrier gas to the nozzle. The means to generate the second gas stream can then have a diffusor which generates an essentially homogeneous second gas stream and surrounds the nozzle of the means to generate the first gas stream.
In a further embodiment, a gas or gas mixture with a lesser viscosity than the first gas stream is provided for the second gas stream. This prevents mixture of the two gas streams due to eddy formation.
Preferred gases for the second gas stream are gases which do not chemically attack graphite, such as inert gases or inert gas mixtures. This makes it possible to use graphite parts in the reactor, even at high temperatures. If there are no graphite parts, particularly if there are no graphite parts in the reactor, hydrogen is also suitable for the second gas stream.
The growth temperature on the substrate is preferably adjusted to be between approximately 800° C. and approximately 2500° C.
In a particularly advantageous embodiment, monocrystalline silicon carbide is produced, which is particularly useful for semiconductor components.
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Nishino et al., Chemical Vapor Deposition of Single Crystalline B-SiC Films on Silicon Substrate with Sputtered SiC Intermediate Layer, J. Electrochem. Soc. 127 (1980) , No. 12, pp. 2674-2680.
Kordina et al., High Temperature Chemical Vapor Deposition, Technical Digest of Int'l Conf. on SiC and Related Materials, 1995, p. 609.
Rupp Roland
Voelkl Johannes
Bueker Richard
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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