Vapor phase deposition of WO and WC
Abstract: WO3 and WC are two compounds that are widely used for a number of different thin film applications. In this thesis, these compounds have been deposited using two different deposition methods: atomic layer epitaxy (ALE) and chemical vapor deposition (CVD). In particular, the chemical interactions between the precursors and the substrates have been studied.The etching and adsorption. behaviors in ALE of WO3 were studied for three different metal precursors: WF6, in situ generated subfluorides (WFx) and in situ generatedoxyfluorides (WOxFy). The result suggests that WOxFy can be used as precursors in ALE whereas the other compounds are unsuitable due to etching and/or adsorption problems.Thin films of WO3 were also deposited by CVD using WF6 and H2O as reactants. It was found that epitaxial WO3 films could easily be deposited on sapphire substrates at temperatures down to 200 °C with this method. Moreover, at a higher total pressure, it was possible to synthesize nanocrystalline WO3 particles by homogenous gas phase nucleation. By collecting the particles on a substrate, porous films could be deposited with a very large surface area. The influence of experimental conditions on the particle size distribution was studied.CVD was also used to deposit thin tungsten carbide films. By using a C3H8/WF6/H2 precursor mixture, single phase, hexagonal WC could be deposited. It was found that a low pressure and a high linear gas flow velocity increased the zone for WC deposition. The influence of the substrate material was also studied. It was found that the reactivity of the substrate materials was an important factor during the initial stages of growth. Finally, depositions on SiC showed that WC is a potential candidate for metallization of high-temperature semiconductors.
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