Morphological, structural and mechanical properties of NbN thin films deposited by reactive magnetron sputtering

Hexagonal beta-Nb2N, cubic delta-NbN and hexagonal delta'-NbN films were deposited by reactive magnetron sputtering from a Nb metal target in Ar+N-2 atmosphere at various nitrogen partial pressures. Structural and mechanical properties of these films were investigated by X-ray diffraction, Electron Probe Microanalysis, Transmission Electron Microscopy, Rutherford Backscattering Spectroscopy, residual stress and nanoindentation measurements. TEM studies reveal that the films have a columnar morphology. The hardness of the films depends on the film phase: the hardness reaches 35 GPa and 40 GPa for hexagonal beta and delta' phases, respectively, and 25 GPa for the cubic 6 phase. The delta' phase films show a compressive residual stress of about 3.5 GPa, whereas no residual stress can be measured in 8 and phase films. The relative density (compared with the bulk value) of films depends on the film phase: 0.8 for delta, 0.86 for delta' and 0.96 for beta is remarkable that the hardness of the hexagonal delta' phase films is significantly higher than the hardness of the p phase films, in contrast with generally accepted morphological trends. (c) 2005 Elsevier B.V. All rights reserved.