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

The silicide structure in high-dose [(18)×1017 Co/cm2] 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 CoSi2 at a dose of 1×1017 Co/cm2, to long-range-ordered CoSi2 and CoSi at 3×1017 Co/cm2, and to a short-range-ordered and highly defective CoSi-like structure at 8×1017 Co/cm2. We propose a model in which Co atoms preferentially occupy the interstitial site, first in silicon then in CoSi2, 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 CoSi2 and CoSi structures and the proposed model. Single-phase and strongly oriented CoSi2 are obtained in samples annealed at 700°C.