AVS 61st International Symposium & Exhibition
    Thin Film Friday Sessions
       Session TF+AS-FrM

Paper TF+AS-FrM1
Stability of Platinum Silicide Thin Films above 1000°C

Friday, November 14, 2014, 8:20 am, Room 307

Session: Thin Film Characterization
Presenter: Robert Fryer, University of Maine
Authors: R.T. Fryer, University of Maine
R.W. Meulenberg, University of Maine
G.P. Bernhardt, University of Maine
R.J. Lad, University of Maine
Correspondent: Click to Email
Stable, electrically conductive thin films are needed as components for sensors and actuators operating in harsh environments at temperatures above 1000°C, such as those found in turbine engines, power plants, and high temperature materials manufacturing. The Pt-Si thin film system has been extensively studied in the microelectronics industry but the focus has been on film characteristics below 800°C. In this work, Pt-Si films were grown at varying compositions and deposition temperatures on sapphire and fused silica substrates by electron-beam evaporation of Pt and Si sources in ultra-high vacuum (<10-9 Torr); the chemical and thermal stability of the Pt-Si films, both in air and in vacuum, at temperatures between 1000–1200°C were studied. X-ray diffraction (XRD) of as-deposited films indicates the formation of a polycrystalline tetragonal-Pt2Si phase for Pt-rich film compositions, an orthorhombic-PtSi phase near the Pt50Si50 composition, and an amorphous film for Si-rich film compositions. The electrical conductivities of these films, measured by a 4-point probe, are in the range of 1x106 to 5x104 S/m, with the conductivity decreasing at higher Si content. Annealing in vacuum at 1000°C causes grain growth and a marked increase in film conductivities. During annealing in air at 1000°C, film oxidation occurs leading to the formation of Pt-oxide phases coinciding with the Pt-Si phases, but only a ~3-fold decrease in film conductivities. After four hours at 1200°C in air, the Pt-Si films become insulating due to morphological roughening and formation of highly faceted Pt (111) and (200) nanocrystallites coexisting in a SiO2 matrix. Scanning electron microscopy (SEM) revealed that the use of a 50 nm capping layer of amorphous Al2O3, grown by atomic layer deposition (ALD) on top of the Pt-Si films, helps retard oxidation thereby preserving film conductivities in the 106-104 S/m range and leading to greater film stability as a function of annealing time at 1000°C in air.