CEMS investigations of Fe-silicide phases formed by the method of concentration controlled phase selection

Conversion electron Mossbauer spectroscopy (CEMS) measurements have been made on Fe-silcide samples formed using the method of concentration controlled phase selection. To prepare the samples a 10 nm layer of Fe30M70 (M=Cr, Ni) was evaporated onto Si(100) surfaces, followed by evaporation of a 60 nm Fe layer. Diffusion of the Fe into the Si substrate and the formation of different Fe–Si phases was achieved by subjecting the evaporated samples to a series of heating stages, which consisted of (a) a 10 min anneal at 800°C plus etch of the residual surface layer, (b) a further 3 hr anneal at 800°C, (c) a 60 mJ excimer laser anneal to an energy density of 0.8 J/cm2, and (d) a final 3 hr anneal at 800°C. CEMS measurements were used to track the Fe-silicide phases formed. The CEMS spectra consisted of doublets which, based on established hyperfine parameters, could be assigned to α- or β-FeSi2 or cubic FeSi. The spectra showed that β-FeSi2 had formed already at the first annealing stage. Excimer laser annealing resulted in the formation of a phase with hyperfine parameters consistent with those of α-FeSi2. A further 3 hr anneal at 800°C resulted in complete reversal to the semiconducting β-FeSi2 phase.