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

Abstract

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.