INTERFACIAL REACTIONS BETWEEN THIN-FILMS OF TI-TA AND SINGLE CRYSTALLINE SI

Interfacial reactions in a contact system comprising of thin films of two refractory metals, Ti and Ta, codeposited onto a single crystalline substrate of Si have been studied and compared with the behavior of each of these elements separately on Si. The work analyzed systematically the behavior of this alloy system, both in its "as deposited" state as well as in its interaction with Si, as a function of the alloy composition and the applied heat treatments. The analytical tools employed were Auger electron spectroscopy, transmission electron microscopy and x-ray diffraction. It has been found that only binary compounds, silicides of each of the metals, and their mutual solid solutions, and not any new ternary compounds, are formed. The reaction products at the early stages of the reaction are TaSi2 and the metastable (C49 structure) TiSi2. Extra diffraction lines were obtained, they possibly belong to Ta5Si3. The final stage of the reaction consists of a uniform intermixing of the disilicides, TiSi2 and TaSi2. Alloying causes a shift in the temperature of silicide formation to intermediate values between those for pure Ti and Ta (500 and 700-degrees-C, respectively), and this value increases with Ta content in the alloy film.