Silicide structural evolution in high-dose cobalt-implanted Si(100) crystals

The silicide structure in high-dose [(1–8)×${10}^{17}$ Co/${\mathrm{cm}}^2$] cobalt-implanted Si(100) crystals is studied by extended x-ray-absorption fine structure, x-ray diffraction, and Rutherford backscattering spectrometry. As the implant dose increases we observe silicide structural evolution from a locally ordered ${\mathrm{CoSi}}_2$ at a dose of 1×${10}^{17}$ Co/${\mathrm{cm}}^2$, to long-range-ordered ${\mathrm{CoSi}}_2$ and CoSi at 3×${10}^{17}$ Co/${\mathrm{cm}}^2$, and to a short-range-ordered and highly defective CoSi-like structure at 8×${10}^{17}$ Co/${\mathrm{cm}}^2$. We propose a model in which Co atoms preferentially occupy the interstitial site, first in silicon then in ${\mathrm{CoSi}}_2$, to understand the silicide-formation mechanism in the implanted system. The short-range-ordered silicides, observed for the first time, and the structural evolution are discussed in terms of both the ${\mathrm{CoSi}}_2$ and CoSi structures and the proposed model. Single-phase and strongly oriented ${\mathrm{CoSi}}_2$ are obtained in samples annealed at 700 °C.