Anomalous first-phase formation in rapidly thermal annealed, thin-layered Si/Ni/Si films

Abstract

The initial stages of silicide formation in very thin-layered Si/Ni/Si films reacted by rapid (pulsed) annealings were investigated using the rapid thermal annealing/transmission electron microscopy technique. At least four phases, NiSi, δNi2Si, θNi2Si, and Ni31Si12, are shown to form first after 1 s annealings in the 175-300 °C temperature regime; the actual phase and its nucleation kinetics depend on the Si:Ni ratio and on substrate deposition temperature. An amorphous (Ni+Si) mixture is shown to exist as a precursor to θNi2Si and NiSi. The multiplicity of ‘‘first’’ phases and the dependence on the Si:Ni ratio contradict various ‘‘first-phase’’ rules and steady-state annealing data obtained on thicker films and in metal-Si wafer reactions. A simple model that accounts for the stoichiometry and substrate-temperature dependences is suggested.