CrN thin films deposited by HiPIMS in DOMS mode

It is well known that increasing the energy of the bombardment species, whether by using a bias or an additional ion source in direct current magnetron sputtering (DCMS) or by optimizing the deposition conditions in mid-frequency bipolar magnetron sputtering, enables us to tailor the properties of the CrN thin films. In the last fifteen years, several magnetron sputtering deposition methods have been developed which have aimed to produce highly ionized fluxes of sputtered material, thus enabling increased control over the energy and impinging angle distributions of the bombarding species. In this study, CrN thin films were deposited by deep oscillation magnetron sputtering (DOMS), a variant of High-power Impulse Magnetron Sputtering (HiPIMS), in order to study the effect of the additional control of the energetic ion bombardment on the film properties. The structural properties of the CrN films (lattice parameter and preferred orientation) showed that an intense energetic bombardment is always present in the DOMS deposition irrespective of the deposition conditions. This energetic bombardment was attributed to energetic N neutrals which are reflected at the target surface upon impingement of N2+ ions. A change from a columnar growth mode to a featureless one was observed with an increasing peak power at both 0.3 and 0.7 Pa. At the same time, the hardness of the films increased from 21-22 GPa to 28-29 GPa. This transformation was attributed to the increasing fraction of ionized sputtered species with increasing peak power. The columnar growth is interrupted by preventing the shadowing effect, i.e., due to the higher ionization fraction at higher pressure and/or peak power, rather than by overcoming the shadowing effect by using more energetic bombardment.