Effect of Ti-capping thickness on the formation of an oxide-interlayer-mediated-epitaxial CoSi2 film by ex situ annealing

Abstract

A modified oxide mediated epitaxy process using a single deposition and ex situ annealing by Ti capping has been suggested in this study. It has been shown that in the case of pure Co on ${\mathrm{SiO}}_x$ -covered Si, the reaction between Co and Si did not occur up to $\text{800\hspace{0.05em}°}\mathrm{C}$ during ex situ annealing. However, Co silicidation occurred in the case of Ti-capped Co on ${\mathrm{SiO}}_x$ -covered Si. The crystalline nature of ${\mathrm{CoSi}}_{\mathrm{2}}$ formed in this case strongly depends on the Ti capping thickness. When a thin Ti capping layer of thickness less than 5 nm was used, Ti oxidation occurred nonuniformly, and the morphology of the surface Ti oxide layer was very rough. This caused an exposure of Co to the oxygen in the ambient, resulting in the formation of polycrystalline ${\mathrm{CoSi}}_{\mathrm{2}}$ due to the suppressed Co diffusion towards the Si substrate. In the case of Ti capping thickness being more than 10 nm, however, a uniform Ti oxide surface layer, which blocks the incoming oxygen retarding Co diffusion, was formed, and it led to uniform Co diffusion into the Si substrate, resulting in epitaxial ${\mathrm{CoSi}}_{\mathrm{2}}$ .