Reactively magnetron sputtered Hf-N films. I. Composition and structure

Thin films of Hf-N, covering the entire composition range from pure Hf to overstoichiometric HfN, have been prepared by reactive magnetron sputtering. The structure of the films has been investigated by x-ray diffraction, transmission electron microscopy, and scanning electron microscopy and the composition has been determined using Auger electron spectroscopy. A solubility of ≊30 at. % nitrogen is found in the α-Hf region. Above 30 at. % N a multiphase structure consisting of α-Hf, HfN, Hf3N2, and/or Hf4N3 is found, which is not in agreement with the equilibrium structure. In the mononitride region a lattice parameter of ≊4.53 Å is observed. This value is slightly higher than reported bulk values due to intrinsic stress in the films. Increasing the nitrogen content above 50 at. % causes a distortion of the cubic symmetry of the lattice. This is first observed as an increase in the (111) interplanar spacing while other spacings decrease. Also a splitting of some reflections occurs at higher nitrogen contents. This phase transition is suggested to be due to a successive change from a cubic to a rhombohedral structure.