Silicide formation and structural evolution in Fe-, Co-, and Ni-implanted silicon

Silicide formation and structural evolution in Fe-, Co-, and Ni-implanted silicon have been studied with use of extended x-ray-absorption fine-structure, x-ray-diffraction, and Rutherford backscattering spectrometry. Si(100) wafers were implanted at elevated temperatures, typically 350 °C, to doses ranging from 1×1016 to 1×1018 ions/cm2. In the Co-implanted system, CoSi2 forms with doses as low as 1×1016 Co/cm2 and up to 3×1017 Co/cm2, where the CoSi phase starts to form. At higher doses (8×1017 Co/cm2), ordered CoSi and a CoSi-like short-range-ordered phase coexist. The silicide formation observed in the Ni-implanted system is similar to that in the cobalt-implanted system. In the case of iron implantation, Fe is coordinated with about eight Si atoms in the (1-3)×1017 Fe/cm2 range as in the tetragonal FeSi2. However, the FeSi2 phase forms only at around 5×1017 Fe/cm2. At even higher doses, a substantial amount of iron is in disordered states in addition to the ordered FeSi phase. Upon annealing at 900 °C, semiconducting β-FeSi2 forms in all the Fe-implanted samples independent of the dose. Mechanisms for silicide formation in these ion-implanted systems are discussed with respect to crystal structure, diffusion, and implantation damage.