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

Abstract

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 \ifmmode^\circ\else\textdegree\fi{}C, to doses ranging from 1\ifmmode\times\else\texttimes\fi{}${10}^{16}$ to 1\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ions/${\mathrm{cm}}^{2}$. In the Co-implanted system, ${\mathrm{CoSi}}_{2}$ forms with doses as low as 1\ifmmode\times\else\texttimes\fi{}${10}^{16}$ Co/${\mathrm{cm}}^{2}$ and up to 3\ifmmode\times\else\texttimes\fi{}${10}^{17}$ Co/${\mathrm{cm}}^{2}$, where the CoSi phase starts to form. At higher doses (8\ifmmode\times\else\texttimes\fi{}${10}^{17}$ 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)\ifmmode\times\else\texttimes\fi{}${10}^{17}$ Fe/${\mathrm{cm}}^{2}$ range as in the tetragonal ${\mathrm{FeSi}}_{2}$. However, the ${\mathrm{FeSi}}_{2}$ phase forms only at around 5\ifmmode\times\else\texttimes\fi{}${10}^{17}$ 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 \ifmmode^\circ\else\textdegree\fi{}C, semiconducting \ensuremath{\beta}-${\mathrm{FeSi}}_{2}$ 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.