Formation of epitaxial CoSi2 films on (001) silicon using Ti-Co alloy and bimetal source materials

Abstract

Using coevaporated Ti‐Co alloy and sequentially evaporated Ti‐Co bimetallic layer source materials, CoSi₂ films have been grown on (001) Si. The film resistivity and resistance thermal stability are excellent. The CoSi₂ are epitaxial single‐crystal films containing antiphase domains in the Ti‐Co bimetallic layer cases and are polycrystalline films containing a substantial portion of epitaxial grains in the Ti‐Co alloy cases. The epitaxial or substantially epitaxial nature of these CoSi₂ films is the reason for the excellence in the film resistivity and resistance thermal stability. We believe that the epitaxial nature of the CoSi₂ films results from two roles played by Ti. In the first, Ti served as a getterer for removing the native oxide layer on the Si wafer surfaces, which causes the nucleation of CoSi₂ grains with random orientations. In the second, Ti silicides formed in the early stage of the annealing process served as Co diffusion barriers preventing Co₂Si and CoSi formation, which would also lead to the formation of randomly oriented CoSi₂ grains. Models of the interfacial structure of the epitaxial CoSi₂ film and Si substrate have been constructed for [001] and [111] orientations. These models revealed that antiphase boundaries serve the role of relieving the lattice mismatch between the epitaxial CoSi₂ film and Si substrate.