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×${10}^{16}$ to 1×${10}^{18}$ ions/${\mathrm{cm}}^2$. In the Co-implanted system, ${\mathrm{CoSi}}_2$ forms with doses as low as 1×${10}^{16}$ Co/${\mathrm{cm}}^2$ and up to 3×${10}^{17}$ Co/${\mathrm{cm}}^2$, where the CoSi phase starts to form. At higher doses (8×${10}^{17}$ Co/${\mathrm{cm}}^2$), 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)×${10}^{17}$ Fe/${\mathrm{cm}}^2$ range as in the tetragonal ${\mathrm{FeSi}}_2$. However, the ${\mathrm{FeSi}}_2$ phase forms only at around 5×${10}^{17}$ Fe/${\mathrm{cm}}^2$. 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-${\mathrm{FeSi}}_2$ 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.