SILICIDE FORMATION BY REACTION OF TA-TI THIN-FILMS AND A SI SINGLE-CRYSTAL

The formation of a ternary phase (TiTa)Si2 has been observed in a bulk system of Ti-Ta-Si which has been prepared by arc melting and annealing at high temperature for extended time. Before annealing, two separate phases were found by x-ray diffraction to coexist, TaSi2 and TiSi 2. This alloy served for comparison of the tendency to form the ternary compound in a binary Ti-Ta layer configuration also. This geometry was achieved by depositing individual Ta and Ti layers consecutively on Si single crystals. A trend to form the ternary silicide was observed at sufficiently high temperatures. This phase is isomorphous with TaSi2. The slow process of its formation, i.e., the high temperature needed for the formation of the ternary phase is explained on the basis of the different diffusion rates of Si through TaSi2 and the interdiffusion in the Ta-Ti system. It seems very probable that the effect of oxygen in slowing down the progress of the ternary formation, at least in our experiments, might be crucial.