Structure and mechanical properties of hafnium nitride films deposited by direct current, mid-frequency, and high-power impulse magnetron sputtering

Highlights: • The mfMS- and HiPIMS-HfN films have a (111) preferred orientation. • The dcMS-HfN films exhibit a pronounced orientation along the (200) plane. • The mfMS-HfN films have the largest crystal sizes and lowest residual stresses. • HfN films with a N content of approximately 52 at.-% have the highest hardness. -- Abstract: The structural properties of hafnium nitride films are mainly influenced by the deposition conditions, which are affected by the sputtering technique. A suitable use of the different sputtering modes allows to control the structural development of the films and thus to adjust the profile of the properties. NaCl-type hafnium nitride films were deposited using direct current magnetron sputtering (dcMS), mid-frequency magnetron sputtering (mfMS), and high-power impulse magnetron sputtering (HiPIMS). dcMS produces films with a columnar microstructure, whereas a fully-dense morphology is achieved by mfMS and HiPIMS. X-ray diffraction patterns show that films sputtered in dcMS mode have a (200) orientation, whereas mfMS and HiPIMS favor an orientation with the (111) plane parallel to the samples' surface. mfMS leads to films with the largest crystal sizes and lowest stresses, which is ascribed to recrystallization mechanisms during the film growth. Hafnium films with an overstoichiometric composition show the highest hardness values. In this context, the dcMS-Hf_49.8N_50.2, mfMS-Hf_50.4N_49.6, and HiPIMS-Hf_49.0N_51.0 have a hardness of 28.2 ± 2.1, 32.4 ± 3.4, and 30.4 ± 3.1 GPa, respectively. In summary, the sputtering technique has a crucial role on the properties of the film and can be suitable used to adjust the structure and hardness of HfN films.