Corrosion properties of thin molybdenum silicide films

Abstract

The corrosion properties of sputtered molybdenum and molybdenum silicide films in hydrochloric acid (HCl) have been studied by means of potentiodynamic measurements. Contributions from the substrate to the corrosion behaviour was avoided by depositing the films on inert aluminium oxide (Al 2O 3). The compositions studied were Mo, MoSi 0.58, MoSi 1.04, MoSi 1.4 and MoSi 1.9–2.1. Characterisation of the sampies was made by X-ray diffraction (XRD) and scanning electron microscopy (SEM) before and after corrosion. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were used to analyse the polarised films. Corrosion of M 3Si was found in the molybdenum-rich samples (MoSi 0.58) containing the two phases Mo 3Si and Mo 5Si 3. Polarisation curves for these films showed one passivation peak at 228 mV vs. the saturated calomel electrode (SCE). The MoSi 1.9–2.1 films had the best corrosion properties of the films studied. This composition had three passivation peaks, at about 154, 305 and 1850 mV SCE, respectively. In the silicon-rich samples, containing the phases MoSi 2 and Mo 5Si 3, preferentiai corrosion of Mo 5Si 3 was found. All the samples containing the disilicide phase showed at least two passivation peaks. XPS and AES studies on the passive films formed on the samples at the two first passivation peaks indicate that both peaks are due to oxidation of silicon- and molybdenum-containing species. The amount of molybdenum in the outermost layer is increased after the second peak.