Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth with a subsequent step acting on the...
Patent
1997-12-19
2000-10-31
Utech, Benjamin L.
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth with a subsequent step acting on the...
117 88, C30B 3306, C30B 2500
Patent
active
061396249
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a method for producing an electrical contact on a silicon carbide surface.
Electrical contacts on silicon carbide (SiC) are generally produced by applying a metal, such as for example platinum, tungsten, titanium, nickel, or chromium, directly onto a SiC surface. Both ohmic contacts and Schottky contacts on SiC are known.
From Appl. Phys. Lett., Vol. 65, No. 16, Oct. 17, 1994, pp. 2075-2077, a method is known for producing an ohmic contact on n-type cubic .beta.-SiC in which a 150-nm thick coating of titanium carbide (TiC) is deposited chemically from the gas phase (chemical vapor deposition=CVD) epitactically onto a (111) surface of the .beta.-SiC. The process gases used for this CVD process are TiCl.sub.4 and C.sub.2 H.sub.4.
One problem with these known methods for producing an electrical contact on a SiC surface is represented by the natural oxide formed on any exposed SiC surface in an oxygen atmosphere. In the case of ohmic contacts, this natural oxide coating increases the contact resistance. In the case of Schottky contacts, the oxide coating leads to a decrease in the contact barrier, and thus to higher leakage currents when a blocking voltage is applied. The natural oxide coating must therefore generally be removed, by sputtering or with hydrofluoric acid (HF), before application of the metal or the TiC.
From the publication Novel Refractory Semiconductors Symposium, Anaheim (US), April 21-23, 1987, Proceedings pp. 265-270, a method is known for producing an electrical contact on a SiC surface in which a carbon coating is created on a silicon carbide surface by evaporating off silicon atoms, said coating is treated with argon ions in order to remove silicon oxides, and the carbon coating is then converted, with titanium as the carbide-forming material, to titanium carbide. This method is comparatively complex due to the argon sputtering, since a separate vacuum process step is necessary.
SUMMARY OF THE INVENTION
It is the object of the invention to indicate a particular method for producing an electrical contact on a SiC surface.
This object is achieved, according to the invention, with the features of claim 1. In a first process step a carbon coating is created on the SiC surface. In a subsequent second process step, the carbon coating is converted with at least one carbide-forming metal at least largely into the corresponding metal carbide.
It is essential in this connection that before creation of the carbon coating, the silicon carbide surface is exposed to a hydrogen atmosphere at temperatures of at least 500.degree. C. A procedure of this kind makes it possible to prevent oxides from occurring on the silicon carbide surface, which was preferably created by epitaxial growth. A separate vacuum process step is not necessary for this purpose, so that the entire method is substantially simplified.
It is known from the existing art, for example from U.S. Pat. No. 5,352,636, to remove oxide from a silicon wafer in hydrogen at 800 to 950.degree. C. GB A 1,112,016 furthermore shows that silicon carbide is compatible with a hydrogen atmosphere.
The invention is based on the conception that an oxide coating which degrades the contact properties does not form on the carbon coating, in contrast to an exposed SiC surface. The chemical reaction of the carbon (C) with the metal yields an almost oxygen-free metal carbide/silicon carbide interface for the electrical contact.
Advantageous embodiments and developments of the method in accordance with the invention are evident from the claims which depend on claim 1.
DETAILED DESCRIPTION OF THE INVENTION
The method is particularly advantageous for producing an electrical contact on a surface of a SiC single crystal, in particular of the cubic polytype (.beta.-SiC) or of a non-cubic polytype (.alpha.-SiC). The SiC surface used in this context is preferably the silicon basal plane or carbon basal plane of the SiC single crystal. The silicon plane corresponds in the case of an .alpha.-SiC to a (0 0 0 1) cry
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Anderson Matthew
Siemens Aktiengesellschaft
Utech Benjamin L.
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