STRUCTURE AND PROPERTIES OF NBN AND TAN FILMS PREPARED BY ION-BEAM-ASSISTED DEPOSITION

Niobium nitride NbNx and tantalum nitride TaNx films were deposited on 316L austenitic stainless steel and silicon wafer substrates by evapo ration of niobium and tantalum under simultaneous nitrogen ion irradia tion, applying an acceleration voltage between 2 and 20 kV, In order t o study the influence of the nitrogen content, the atom-to-ion transpo rt ratio Nb, Ta/N was varied. The compositional and structural charact erization of the films were carried out using Auger electron spectrosc opy, X-ray photoelectron spectroscopy, scanning electron microscopy, X -ray diffraction and transmission electron microscopy. It was observed that the surface morphology strongly depends on the deposition condit ions. X-ray diffraction patterns showed that the crystal structure of the films was changed from nitride to solid solution when the transpor t ratio was increased from 1 to 10, respectively. The crystal structur e of the films deposited at Nb, Ta/N = 6 and 10 had the feature of a n itrogen supersaturated bcc solid solution. Electron diffraction reveal ed the coexistence of an amorphous phase and a fine structured nitride phase in these films. The chemical bonding state of metal atoms obser ved by XPS changed with increasing the transport ratio, whereas the bo nding state of nitrogen atoms was independent of the transport ratio. The corrosion behavior was evaluated in an oxygen saturated 5% sulfuri c acid solution, using multisweep cyclic voltammetry measurements. The best corrosion protection was observed for the NbN film at an transpo rt ratio of Nb/N = 2 and for the Ta-N solid solution at Ta/N = 6.