SYNTHESIS AND PROPERTIES OF TANTALUM NITRIDE FILMS FORMED BY ION-BEAM-ASSISTED DEPOSITION

Tantalum nitride films TaNx were deposited onto 316L austenitic stainl ess steel and silicon wafer substrates by evaporation of tantalum unde r simultaneous nitrogen ion irradiation, applying an acceleration volt age of 2 kV. In order to study the influence of the nitrogen content, the atom-to-ion transport ratio ([Ta]/[N]) was varied. The composition al and structural characterization of the films was carried out using Auger electron spectroscopy, X-ray photoelectron spectroscopy, scannin g electron microscopy, and X-ray diffraction. It was observed that the surface morphology depends on the deposition conditions. X-ray diffra ction patterns show the crystal structure of the films changing from T a3N5, TaN, Ta2N and Ta-N solid solution when the transport ratio is in creased from 0.7 to 10. The crystal structure of the film deposited at [Ta]/[N]=6 has the feature of a b.c.c. phase plus an amorphous phase containing 30 at.% nitrogen. The chemical bonding state of tantalum at oms observed by X-ray photoelectron spectroscopy changes with increasi ng transport ratio [Ta]/[N], whereas the bonding state of nitrogen ato ms is independent of the transport ratio. The sheet resistivity and th e temperature coefficient of resistance (TCR) of the films were measur ed by the four-point probe method. The TCR values of all observed TaNx films were negative, showing a minimum value at the lowest observed v alue of [Ta]/[N]=0.7. The corrosion behavior was evaluated in an oxyge n saturated aqueous solution of sulfuric acid, using multisweep cyclic voltammetry measurements. The best corrosion protection was observed for the Ta-N solid solution film prepared at [Ta]/[N]=6. All other fil ms, existing in the compound state, show less resistivity.