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.