Influence of hydrogen sulfide addition on the alumina deposition by plasma CVD

Hard alumina (Al2O3) coatings are usually deposited by chemical vapour deposition (CVD) at temperatures of about 1000 °C. However, the required temperature can be decreased by activating the process gas by a plasma. The coatings deposited so far by plasma-assisted chemical vapour deposition (plasma CVD) show an admixture of α- and γ-alumina, whereby the α-alumina content in the coating increases with increasing temperature as well as plasma power. present study the effect of hydrogen sulfide (H2S) addition to the process gas on alumina deposition was investigated. Alumina was deposited on titanium nitride (TiN) coated boron doped silicon (100) substrates. The coatings were analysed by X-ray diffraction (XRD) for phase composition, by micro-indentation for hardness, by scanning electron microscopy (SEM) for morphology and by X-ray photoelectron spectroscopy (XPS) for chemical composition. It turned out that the coating thickness decreased strongly with the distance from the central gas inlet as in the case without H2S additions. At higher temperatures (800 °C) H2S additions favoured the formation of γ-alumina, whereby at lower temperatures (600 °C) H2S promotes α-alumina formation. No sulphur was found in the alumina coatings.