Superhard tantalum-nitride films formed by inductively coupled plasma-assisted sputtering

The effect of inductively coupled plasma (ICP) power on the mechanical properties of tantalum-nitride films was investigated. TaN films were grown on an Si (001) substrate using ICP assisted magnetron sputter deposition in a mixed Ar/N2 discharges at 20 mTorr (2.67 Pa) and 350 °C. For the structural analysis, X-ray diffraction, auger electron scanning and atomic force microscopy were used and the hardness was measured using a micro indentation tester. The structure of the TaN films changed as the ICP power (100–400 W) and nitrogen fraction fN2(0.1–0.15) were varied. When the ICP RF power was increased from 100 to 400 W, hexagonal ε-TaN appeared in the existing compound of hexagonal γ-Ta2N (fN2 = 0.1) or cubic δ-TaN (fN2 = 0.125 and 0.15). When the ICP power was increased from 100 W to 400 W, the hardness also increased from 25–35 GPa to around 70 GPa. It is supposed that the significant increase in the hardness was contributed to by the dense microstructure with very small grains and also by the multi-phase structure of the film.