Transition-metal silicides formed by ion mixing and by thermal annealing: Which species moves?

The moving species during the formation of Pt2Si, Ni2Si, and CrSi2 by both ion mixing with 300–600 keV Xe ions and thermal annealing is identified with inert markers using backscattering spectrometry. Samples of metal-on-silicon and silicon-on-metal have been used, evaporated on SiO2 substrates with two very thin markers (Mo for Pt2Si, W for Ni2Si and CrSi2) placed at the metal–silicon interface, and at the bottom interface with the SiO2 substrate. Monitoring the separation of the two markers as a function of the amount of silicide formed determines the ratio of atomic transport through the growing silicide layer. The results establish that the dominant moving species in both silicide formation processes is the same for the refractory metal-silicide CrSi2, e.g., Si, whereas different atomic transport ratios are found in the case of the near-noble metal silicides Pt2Si and Ni2Si. This outcome is discussed in terms of high-temperature effects during thermal formation of transition-metal silicides