Raman spectroscopic studies of the formation processes of cobalt silicide thin films

A confocal Raman system combined with a high-temperature furnace cell has been established to monitor the formation of cobalt silicides. This system enables the quasi in situ study of the influence of temperature, annealing duration, and oxygen impurities on phase transformation. The experimental data indicate that the Co2Si phase tends to form at low temperatures and emits only extremely weak signal. The CoSi phase is stable at temperatures lower than 500 °C but transforms to the CoSi2 phase at 550 °C. Two kinds of mechanisms were proposed: one is the diffusion-limited formation occurring at low temperatures (<550 °C), the other is nucleation-limited formation occurring at high temperatures (>650 °C), where phase transformation is so fast that the CoSi phase is practically impossible to be observed with Raman. Lastly, the formation of cobalt silicides in an oxygen-containing annealing ambient and for an oxidized cobalt film in an oxygen-free ambient was studied.