Phase Formation and Morphology of Nickel Silicide Thin Films Synthesized by Catalyzed Chemical Vapor Reaction of Nickel with Silane

The synthesis of nickel silicide thin films via a vapor-solid reaction has been studied by exposing thin (10 nm) Ni films to silane (SiH4). The crystalline phases, the Ni/Si stoichiometric ratios, as well as the surface and interface properties of the resulting silicide films were investigated as a function of the growth parameters such as the SiH4 partial pressure, the reaction temperature, and the exposure time. At low temperature (300 degrees C), SiH4 exposure led to the self-limiting deposition of Si on Ni by catalytic decomposition of SiH4 but not to silicate formation. Between 350 and 400 degrees C, phase pure orthorhombic NiSi films were obtained that were formed directly without any apparent intermediate Ni-rich silicide phases. A transformation to NiSi2 occurred at 450 degrees C and above, and at 500 degrees C phase pure NiSi2 was obtained. Here, the transient formation of NiSi was observed that transformed into NiSi2 for prolonged SiH4 exposure. The results indicate that the Si solubility governs the phase formation sequence whereas kinetics are determined by Ni diffusion and the reaction rate. Resistivity values of 21 and 36 mu Omega cm were found for the NiSi and NiSi2 thin films, respectively, corresponding to the values reported for films obtained by solid-state reactions.