Properties of ZrNx films with x > 1 deposited by reactive radiofrequency magnetron sputtering

Thin ZrNx films have been prepared by reactive radiofrequency magnetron sputtering varying the nitrogen partial pressure in the range 0–3.26 Pa. The films have been analyzed by X-ray photoelectron spectroscopy (XPS) and by optical characterization in the UV–Vis–IR range. The cross-section and surface morphology of the samples were examined by means of field emission gun–scanning electron microscopy. The effects of the nitrogen partial pressure on the ZrNx films stoichiometry have been studied correlating the N 1s photoelectron peaks with different bounding states for the zirconium nitride. The XPS depth profile analysis has revealed the presence of metastable phases (ZrN2, Zr3N4) that vanishes when lowering the nitrogen partial pressure. The optical analysis has permitted to distinguish two different behaviours of the deposited samples in the visible range: semi-transparent and absorbent. Drude–Lorentz model fitted the behaviour of absorbent films, while the O'Leary model was applied to the semi-transparent ones. The semi-transparent films had a band gap varying between 2.36 and 2.42 eV, typical values of N-rich zirconium nitride films. Morphological analysis showed a compact and dense columnar structure for all the samples. A simple growth model explains the presence of the different nitride phases considering implantation and re-sputtering effects.