Epitaxy of metal silicides

Abstract Epitaxial growth of the silicon-rich metal silicides NiSi 2 , CoSi 2 and IrSi 3 is reviewed. Codeposition of metals and silicon at low substrate temperatures is shown to alleviate the main problem associated with solid phase epitaxy using metal deposition alone, i.e. the nucleation controlled reaction to the silicide in question. NiSi 2 is an exception since owing to an epitaxial precursor phase the interfacial energies are lowered sufficiently, so that for thin films nucleation is no longer a problem. The growth of high quality CoSi 2 /Si superlattices is shown to be feasible by combining the codeposition technique with silicon MBE. Excellent electrical properties of epitaxial CoSi 2 films is demonstrated, remaining metallic down to a thickness of 10 A. Surface scattering in Si/CoSi 2 /Si heterostructures is nearly eliminated, CoSi 2 thicker than 35 A showing bulk residual resistivities. Such heterostructures have been applied to the fabrication of the permeable base transistor (PBT), using low pressure vapour phase epitaxy for the last overgrowth step after patterning. Device performance is found to be superior to any overgrown silicon PBT reported to date.