Tuneable Properties of Zirconium Oxynitride Thin Films

This chapter is related to the investigation of decorative zirconium oxynitride, ZrO_xN_y, films prepared by dc reactive magnetron sputtering, using a 17:3 nitrogen-to-oxygen-ratio gas mixture. The films changed appearance from metallic-like, very bright yellow-pale and golden yellow, for low gas mixture flows to red-brownish for intermediate gas flows. A significant decrease of brightness was associated with this colour change. With further increase of the reactive gas flow, the colour of the samples changed from red-brownish to dark blue. The films deposited with relatively high gas flows showed only apparent colorations due to interference effects. The variations in composition disclosed the existence of four different zones, which were correlated to different crystalline structures. X-ray diffraction analysis revealed significant changes in the films crystalline structure, which changed at relatively low gas flows from B1 NaCl face-centred cubic zirconium nitride-type phase to a poorly crystallized overstoichiometric nitride phase, which may be similar to that of Zr₃N₄. For higher flows, the texture changed from an oxynitride-type phase, similar to that of γ-Zr₂ON₂, to a ZrO₂ monoclinic-type structure. The composition/structure variations were consistent with the chemical bonding analysis carried out by X-ray Photoelectron Spectroscopy (XPS), which showed oxygen doping in both Zr₃N₄ and ZrN-type grown films. The electronic, optical and mechanical properties of the films exhibited significant changes from zone to zone, consistent with the different compositions, as well as wit the variations in the crystalline phases and bonding states.

Keywords: Reactive sputtering, zirconium oxynitride, decorative applications, thin films.