Local structural studies of TiSi₂ and ZrSi₂ thin films on Si(111) surfaces

This study explores the local structures of TiSi₂ and ZrSi₂ films on Si. The strain effect on the surface morphologies and phase stability of the films is investigated. Titanium silicide and zirconium silicide films were fabricated on atomically clean Si(111) substrates in UHV using electron gun evaporation followed by in situ annealing. A quantitative X-ray absorption spectroscopy analysis was performed to study the formation of epitaxial TiSi₂ and ZrSi₂ films on the Si surfaces, as well as the phase transition of TiSi₂ from the metastable C49 structure to the stable C54 structure. The surface morphologies and the surface roughness of the films were studied using atomic force microscopy (AFM). The strains of these films were determined by comparing the calculated bond lengths with the measured bond lengths using the extended X-ray absorption fine structure (EXAFS) technique. The final stable C54 structure of TiSi₂ has less strain than the initially formed metastable C49 phase. While the surface and interface free energies and the bulk free energy are critical to the structural formations and phase changes of the films, the energy associated with the lattice strain is another important factor.