Linear growth kinetics of nanometric silicides in Co/amorphous-Si and Co/CoSi/amorphous-Si thin films.

Evolution of the reaction zone on the nanoscale has been studied in bi- and multilayered Co/a-Si as well as in trilayered Co/a-CoSi/a-Si and Co/CoSi/a-Si thin film diffusion couples. The kinetics of the phase boundary movement during solid state reaction has been followed with special interest of the initial stage of the diffusion, i.e. effects happening on the nanoscale (short time, short distance). The interfacial reactions have been investigated in situ by synchrotron radiation. The formed phases were also characterized by transmission electron microscopy and resistance measurements. The effect of phase nucleation and shift of phase boundaries have been separated in order to determine the “pure” growth kinetics of the crystalline CoSi and Co2Si product phases at the very early stages. Deviations have been found from the traditional diffusion controlled parabolic phase growth. Computer simulations based on a kinetic mean field model illustrated that the diffusion asymmetry (large difference in diffusion coefficients of the materials in contact) may offer a plausible explanations for this. [ABSTRACT FROM AUTHOR]