Silicide formation in cobalt/amorphous silicon, amorphous Co [sbnd]Si and bias-induced Co [sbnd]Si films

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The silicide formation in cobalt/amorphous silicon multilayer films, amorphous cobalt-silicon films, and bias-induced cobalt-silicon films has been examined by differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. For amorphous cobalt-silicon and bias-induced cobalt-silicon films, Co 2Si forms as a firstsilicide phase, followed by the formation of CoSi and CoSi 2. For a Co/a-Si multilayer film with the atomic concentration ratio of the cobalt to silicon layer being 1:2, CoSi is found to be formed as the first silicide phase. It is confirmed that CoSi, Co 2Si, CoSi, and CoSi 2 form sequentially as the scanning temperature increases. The observed phase sequence is analyzed by the effective heat of formation. A structure factor in addition to the effective heat of formation is used to explain the difference in the formation of the firstphase between cobalt/amorphous silicon multilayer films, amorphous cobalt-silicon alloy films, and bias-induced cobalt-silicon films. For the case of bias-induced cobalt-silicon films prepared at various substrate temperatures and bias conditions, the phase sequence and crystallinity of cobalt silicide have a stronger dependence on the substrate bias voltage than on the substrate temperature due to the effects of collisional cascade mixing, in-situ cleaning, and an increase in the number of nucleation sites by ion bombardment on the growing surface. Also, bias-induced epitaxial CoSi 2 layer is grown at 200 °C,a much lower temperature than molecular beam epitaxy. In order to quantitatively explain low-temperature epitaxial growth of the CoSi 2 layer, the Ar ion energy transferred to Co and Si atomsand the resputtering yield as a function of substrate bias voltage are calculated.