Reduction of the transition temperature of C54 TiSi ₂ through a Ta interlayer

We examined the phase transition of TiSi ₂ from C49 to C54 by introducing a thin Ta interlayer between Ti film and Si(111) substrate. The Ta interlayered samples were prepared by depositing 5 Å Ta and 100 Å Ti films sequentially on Si(111) substrates in the UHV system. As control samples, 100 Å Ti films were deposited on Si(111) substrates. The deposited substrates were annealed insitu at temperatures between 500-750°C with 50°C increments for 10 min. The TiSi ₂ formed in UHV system was analyzed by using XRD, AES, SEM and a four-point probe. The control samples exhibited the transition temperature of 750°C from C49 to C54. However, the TiSi ₂ samples with 5 Å of Ta interlayer showed significant reduction of the phase transition temperature of C54 TiSi ₂. The XRD pattern analysis indicated that the transition temperature of TiSi ₂ from the C49 to C54 phase was lowered by about 200°C with the addition of 5 ÅTa interlayer. The sheet resistance measurement showed lower resistivity of Ta interlayered samples of TiSi ₂ due to the reduction in the formation temperature of C54 phase. The SEM micrographs showed that the TiSi ₂ with 5 Å Ta interlayer suppressed the surface agglomeration, significantly. The AES analysis data indicated that the titanium suicide formed at high temperature (>500°C) showed a 1:2 stoichiometry of Ti:Si and small amounts of impurities in the suicide film and the interface between suicide and Si substrate.