Effects of nitrogen partial pressure in Ta-N films grown by the cathodic vacuum arc technique

Ta-N films were prepared by the cathodic vacuum arc technique in Ar + N-2 atmosphere with various nitrogen partial pressures (f(N2) = 0-100%). The crystal structure, chemical composition, surface morphology and cross-section morphology of the Ta-N films were investigated by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy. The influence of nitrogen partial pressure on the material characteristics of the Ta-N film was systematically studied. Our results suggest that the structural and morphological properties of the Ta-N films have a strong dependence on the nitrogen partial pressure. With increasing nitrogen partial pressure from 0% to 100%, the phase composition of the films evolves from single tetragonal Ta to cubic TaN and then to multi-phase cubic TaN + monoclinic Ta3N5. And the crystallographic orientation of the main phase component, cubic TaN, develops from (1 1 1) preferred orientation to (2 0 0) preferred orientation. The N/Ta ratio of the films does not increase linearly with nitrogen partial pressure, and nearly reaches 1 : 1 at a nitrogen partial pressure of 65%. The deposition rate is found to decrease almost linearly with increasing nitrogen partial pressure. Macroparticles can be observed without using a magnetic filter, the amount of which can be significantly reduced by increasing the nitrogen partial pressure. And the smooth surface of the films is composed of nano-crystallites, while the grain size seems to increase as a function of the nitrogen partial pressure.