A comparison of the oxidation behavior of CrN films deposited using continuous dc, pulsed dc and modulated pulsed power magnetron sputtering

Abstract

The study is aimed at comparing the oxidation behavior of the stoichiometric CrN films deposited by continuous dc magnetron sputtering (dcMS), mid-frequency pulsed dc magnetron sputtering (PMS), and modulated pulsed power (MPP) magnetron sputtering techniques in a closed field unbalanced magnetron sputtering system. These as-deposited CrN films exhibited a cubic structure and similar stoichiometric compositions, but with different microstructures and residual stresses. After annealing in the ambient air from 600 to 1000°C, the changes in the crystal phase, microstructure, and hardness of the films were characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy line scan, and nanoindentation. The oxidation activation energies of the films were calculated using Arrhenius equation. It was found that the MPP CrN film exhibited superior oxidation resistance than dcMS and PMS CrN films. After annealing at 900°C, the MPP CrN film exhibited an extremely dense structure and the cubic phase was well maintained. On the other hand, the dcMS and PMS CrN films were severely oxidized into a porous structure with the development of β-Cr2N and Cr2O3 phases and a rapid degradation of the cubic phase after 700 and 800°C, respectively. The results indicate that all films showed a parabolic oxidation rate below 900°C. The oxidation activation energies for the dcMS, PMS and MPP CrN films are 116kJ/mol, 141kJ/mol, and 195kJ/mol, respectively. The better oxidation resistance of the MPP CrN film is attributed to its dense microstructure and low residual stress.