Silicon crystal growth on a Ni silicide seeding layer by dc magnetron sputtering

Direct current (d.c.) magnetron sputtering was applied to polycrystalline Si growth and yielded a uniform Si film at a deposition temperature below the glass softening point. The approach involved the deposition of a thin Ni film over SiO₂ prior to Si sputtering. The interaction of a fine-grained metallic Ni with an atomic Si provided by a sputtering gun resulted in the formation of Ni silicide at the Ni-Si interface immediately after the onset of Si deposition. The phase composition of the nickel silicide was controlled by the temperature of deposition and the Si-to-Ni concentration ratio. The silicide region exhibited a layered structure where the bottom layer consisted of the mixture of several Ni_XSi_Y phases and the top layer represented the pure NiSi₂ phase. This Ni disilicide layer provided the nucleation sites for the epitaxial Si crystal growth. As a result, the polycrystalline silicon film consisted of 0.1-0.5 μm grains with preferred (111) or (110) orientation without an indication of an amorphous phase. The carrier lifetime of 11 μs indicated good electrical properties which make the film potentially applicable to fabrication of thin film transistors and solar cells. The Ni prelayer thickness in the 5-100 nm range dramatically influenced the crystal size and preferential crystal orientation. Possible mechanisms responsible for the nickel silicide induced grain growth of silicon and the correlation between the Ni silicide and silicon microstructure is discussed.