A study was made of the phase transition of Co/Ni thin films on amorphous Si by using an approach which was based upon in situ sheet resistance analyses made during isothermal annealing. As compared with conventional Co/Si systems, the Co/Ni/Si reaction produced a double peak in the resistance curve versus time. This behavior was extensively studied by using Rutherford back-scattering spectroscopy, X-ray diffraction, energy filtered transmission electron microscopy and selected-area diffraction analyses. It was found that kinetic evolution of the Co/Ni/Si structure occurred via 2 consecutive transition stages which were strictly related to each of the resistance peaks. In the beginning, the Co atoms remained confined at the surface while Ni reacted with Si; thus producing the first resistance peak. The second peak was instead related to Co atoms diffusing through the grain boundaries of the underlying Ni2Si layer; converting Ni2Si into a continuous CoSi film and forming pipe through the underlying NiSi, down to the substrate. As a result, a ternary compound nucleated in contact with the Si. The final structure at the plateau of the resistance curve was a multi-layer of CoSi/NiSi/Co(Ni)Si2; different from the case of Co/Ni thick-layer reactions.

High-Resolution Investigation of Atomic Interdiffusion during Co/Ni/Si Phase Transition. A.Alberti, C.Bongiorno, F.La Via, C.Spinella: Journal of Applied Physics, 2003, 94[1], 231-7