Nucleation-limited phase selection during reactions in nickel/amorphous-silicon multilayer thin films

Abstract

Isothermal and constant-heating-rate differential scanning calorimetry, cross-sectional transmission electron microscopy, thin-film x-ray diffraction, and thermodynamic and kinetic analyses have been used to investigate silicide phase selection in nickel/amorphous-silicon multilayer thin-film reactions. The atomic concentration ratio of the films was two Ni atoms to one Si atom and the layer thickness ratio was one to one. During deposition, a thin layer of amorphous nickel silicide formed between the nickel and amorphous-silicon layers. Upon heating, this amorphous nickel silicide thickened slightly, until crystalline Ni2Si formed at the nickel/amorphous-nickel-silicide interface. Further heating caused the simultaneous growth of both the amorphous nickel silicide and crystalline Ni2Si. Comparison of thermodynamic data to kinetic models for silicide formation and the analysis of calorimetry data suggests that nucleation barriers are responsible for the initial formation of the amorphous nickel silicide and limit subsequent formation of crystalline Ni2Si.