Solid state reactions in cobalt/amorphous-silicon multilayer thin films

Solid state reactions in Co/amorphous-Si multilayer thin films were investigated using differential scanning calorimetry and X-ray diffraction. The results are compared with the predictions of effective driving force (EDF) and effective heat of formation (EHF) models. Amorphous silicide growth does not occur in Co/amorphous-Si multilayer thin films; this is consistent with the predictions of the EDF model. The first crystalline phase formed by solid state reaction is found to be CoSi, rather than Co₂Si which is predicted by the EHF model to form first. The difference in the experimental and predicted first crystalline silicide is discussed. For Co:Si atomic concentration ratios of 2:1 and 1:2, the phase sequences are CoSi → Co₂Si and CoSi → Co₂Si → CoSi → CoSi₂ respectively. These reactions are analyzed using the EHF diagram. The formation of CoSi and CoSi₂ is controlled by nucleation and the activation energies for the formation of CoSi, Co₂Si, and CoSi₂ are 1.71, 2.34, and 2.79 eV respectively.