Reduction of the phase transition temperature of TiSi ₂ on Si(111) using a Ta interlayer

The effect of a thin Ta interlayer on the C49 to C54 phase transition of TiSi ₂ on Si(111) was examined. The Ta interlayered samples were prepared by depositing Ta and Ti films sequentially on Si(111) substrates in a UHV system. As control samples, 100Å Ti films were deposited directly on clean Si(111) substrates. The deposited substrates were annealed for 10 min, in-situ, at temperatures between 500°C and 750°C using 50°C increments. The TiSi ₂, which formed in this UHV process, was analyzed with XRD, AES, SEM, TEM, and four-point probe measurements. The control samples exhibited the C49 to C54 transition at a temperature of 750°C. However, the TiSi ₂ samples with 5Å and 10Å Ta interlayers displayed a significant reduction of the phase transition temperature. The XRD analysis indicated that the C49 to C54 transition temperature of TiSi ₂ was lowered by ∼200°C. The sheet resistance measurement showed a low resistivity characteristic of C54. The SEM and TEM micrographs showed that the Ta interlayer also suppressed the surface agglomeration of the C54 TiSi ₂ film. The AES analysis data indicated that the composition of the titanium silicide showed the expected Ti:Si stoichiometry of 1:2.