CORROSION PROPERTIES OF THIN MOLYBDENUM SILICIDE FILMS

The corrosion properties of sputtered molybdenum and molybdenum silici de films in hydrochloric acid (HCl) have been studied by means of pote ntiodynamic measurements. Contributions from the substrate to the corr osion behaviour was avoided by depositing the films on inert aluminium oxide (Al2O3). The compositions studied were Mo, MoSi0.58, MoSi1.04, MoSi1.4 and MoSi1.9-2.1. Characterisation of the samples was made by X -ray diffraction (XRD) and scanning electron microscopy (SEM) before a nd after corrosion. X-ray photoelectron spectroscopy(XPS) and Auger el ectron spectroscopy (AES) were used to analyse the polarised films. Co rrosion of Mo3Si was found in the molybdenum-rich samples (MoSi0.58) c ontaining the two phases Mo,Si and Mo5Si3. Polarisation curves for the se films showed one passivation peak at 228 mV vs. the saturated calom el electrode (SCE). The MoSi1.9-2.1 films had the best corrosion prope rties of the films studied. This composition had three passivation pea ks, at about 154, 305 and 1850 mV(SCE), respectively. In the silicon-r ich samples, containing the phases MoSi2 and Mo5Si3, preferential corr osion of Mo5Si3 was found. All the samples containing the disilicide p hase showed at least two passivation peaks. XPS and AES studies on the passive films formed on the samples at the two first passivation peak s indicate that both peaks are due to oxidation of silicon-and molybde num-containing species. The amount of molybdenum in the outermost laye r is increased after the second peak. (C) 1997 Elsevier Science S.A.