A comparative study on the hardness, stress and surface free energy of HfN films grown by HIPIMS and direct-current magnetron sputtering

HfN films with rocksalt structure have been grown by high-power impulse magnetron sputtering (HIPIMS) with various duty cycles, in a comparison with direct-current magnetron sputtering (dcMS) process. Such two sputtering processes yield the quite close compositions. Increasing the duty cycle from 7.5 % to 9 % and 11 % in HIPIMS process, a compressive stress rises up from 1.5 to 1.9 and 2.1 GPa, which is much smaller than the value of 3.8 GPa from dcMS. The hardness of such low-stressed HfN films has been identified to be 25.5-25.9 GPa, which agrees well with the theoretical one of 22.5 GPa by the density functional theory without the consideration of stress. In addition, the surface free energy of 26.3-29.0 mJ/m2 has been determined in HfN films grown by HIPIMS, much lower than that of 31.5 mJ/m2 of the films grown by dcMS.