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 + N2 atmosphere with various nitrogen partial pressures (fN2 = 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. (paper)