Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – Fluid growth from gaseous state combined with subsequent...
Patent
1997-12-18
2000-08-22
Bowers, Charles
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
Fluid growth from gaseous state combined with subsequent...
438779, 438767, 438796, 438931, H01R 3108
Patent
active
061071684
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a method for passivating a silicon carbide (SiC) surface against oxygen.
A plurality of semiconductor structures based on silicon carbide (SiC) as the semiconductor material are known. In the manufacture of such SiC semiconductor structures, the surfaces of SiC single crystals, which in some cases are already preprocessed, must often be exposed to an oxygen-containing atmosphere, for example during interim storage of the SiC single crystal or transport from one process location to another. In an oxygen-containing atmosphere, however, a natural oxide coating consisting of SiO.sub.2 forms on the surface of the SiC single crystal. The thickness of this oxide coating after one week in air, for example, is already 2 nm. This natural oxide coating is generally undesirable, and must therefore be removed, by sputtering or with hydrofluoric acid (HF), before a subsequent process step.
It is known, from the publication Thin Solid Films 241 (1994), pp. 305-309, to treat silicon carbide surfaces with a hydrogen (H.sub.2) plasma and saturate the free bonds at the SiC surface by deposition of H.sub.2 ions. A general passivation is achieved thereby.
SUMMARY OF THE INVENTION
It is the object of the invention to passivate a SiC surface against oxygen in order to prevent an oxide coating from forming on said SiC surface in an oxygen-containing atmosphere.
This object is achieved, according to the invention, with the features of claim 1 or claim 12.
The invention is based on the conception of using a carbon coating to passivate the SiC surface. In contrast to an exposed SiC surface, no oxide coating forms on the carbon layer because of the low chemical affinity of carbon for oxygen. The SiC surface equipped with this carbon passivation can therefore be stored or transported for practically any length of time in an oxygen-containing atmosphere such as, for example, air.
The method is particularly advantageous in the manufacture of a semiconductor structure in which the surface of a SiC single crystal must be exposed to an oxygen-containing atmosphere between a first and a second process step. Before the SiC single crystal comes into contact with the oxygen-containing gas mixture, a carbon coating which is substantially chemically inert with respect to oxygen is generated on at least a part of its SiC surface. The carbon coating can then be removed again immediately before the second process step, or processed further in said second process step.
Advantageous embodiments and developments of the passivation method according to the invention are evident from the claims which depend upon claim 1.
DETAILED DESCRIPTION OF THE INVENTION
In a particularly advantageous embodiment, the carbon coating is produced by evaporating (subliming) silicon atoms off from the SiC surface. For this purpose, the SiC surface is preferably brought, in a vacuum or in an inert gas atmosphere, to a temperature of at least approximately 1000.degree. C. The carbon coating can, however, also be produced by chemical vapor deposition (CVD) or molecular beam epitaxy (MBE). Preferably a carbon coating having a crystal structure at least similar to the structure of graphite is produced. In a preferred embodiment, the thickness of the carbon coating is established at less than 1 nm. The carbon coating then comprises only a few atomic layers, or even only one layer of carbon atoms.
In a further embodiment, bound oxygen is removed from the SiC surface before the carbon coating is produced, at temperatures of at least 500.degree. C. in a hydrogen atmosphere.
The invention will now be explained with reference to exemplifying embodiments.
In a first exemplifying embodiment of the method for protecting a SiC surface from oxidation, carbon is delivered to the SiC surface in elemental form (C), for example by sputtering, or in the form of a chemical carbon compound, for example by CVD or MBE. From the delivered carbon, a carbon coating is deposited on the SiC surface. In a CVD or MBE process, a hydrocarbon gas su
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Bowers Charles
Siemens Aktiengesellschaft
Whipple Matthew
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