Electronic and thermal properties of stoichiometric Pt₃Si films grown by co-evaporation

A stoichiometric Pt₃Si thin-film phase has been stabilized by electron beam (e-beam) co-evaporation of controlled Pt and Si fluxes onto several different substrates. This Pt₃Si phase has high electrical conductivity (≥ 10⁶ S/m) and is inaccessible via the more conventional solid-state thermal reaction of a Pt film/Si substrate diffusion couple, a method that is ubiquitous for forming Pt-silicide films (PtSi and Pt₂Si) in the semiconductor industry. The Pt₃Si films exhibit finely grained columnar morphologies when grown at ambient temperature but develop a larger granular morphology at deposition temperatures exceeding 200 °C and have an electrical conductivity of ~ 1 × 10⁶ S/m independent of substrate type and film thickness. For films deposited above 400 °C, film agglomeration and grain boundary grooving during fabrication leads to a decrease in overall film conductivity. Pt₃Si films are less conductive than Pt₂Si films, yet have a higher DOS population near the Fermi level as measured by valence band photoemission spectra in agreement with DOS calculations, which suggests a lower electron mobility in the Pt₃Si phase. In situ high-temperature X-ray diffraction (XRD) studies indicate that a polymorphic phase transition between a monoclinic-Pt₃Si and an orthorhombic-Pt₃Si phase occurs ca. 225 °C. Also, the melting temperature of Pt₃Si films was measured by in situ XRD to be ca. 920 °C; after cooling from melt, a small subset of Pt₃Si grains resolidify with a crystallographic texture strongly oriented in the direction of the film normal.