FORMATION OF EPITAXIAL COSI2 FILMS ON (001) SILICON USING TI-CO ALLOY AND BIMETAL SOURCE MATERIALS

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.