Structural evolution in ZrNxOy thin films as a function of temperature

Single-layered zirconium oxynitride (ZrNx.Oy) thin films have been deposited on steel substrates, at a constant temperature of 300 deg C, by radiofrequency (rf) reactive magnetron sputtering of a pure Zr target in an argon-oxygen-nitrogen atmosphere. The variation of the flow rate of the reactive gases enabled changes in the composition and structure of the films. X-ray diffraction (XRD) and glancing incidence X-ray diffraction (GIXRD) were used to study the as-deposited films and their structural changes during or after heat treatment, from 400 to 900 deg C, in controlled atmosphere and in vacuum. The as-deposited films revealed the occurrence of a face-centred cubic (fcc) phase (Zr-N type), but a Zr-N oxygen-doped phase (Zr-N-0) may be also present depending on the oxygen content in the films. Heat treatment above 600 deg C reveals the appearance of a tetragonal phase of zirconium oxide. The results are discussed as a function of the chemical composition of the films, annealing temperature, and type of the annealing process.