Reactive processes in the high target utilization sputtering (HiTUS) W-C based coatings

Abstract

High Target Utilization Sputtering (HiTUS) is a novel technique with an independent plasma source, which offers higher plasma densities, possibilities for the increase of the level of ionization of the sputtered material and significant reduction of negative effects accompanying reactive sputtering related to target poisoning. The aim of the work was to investigate some details of the reactive sputtering behavior during HiTUS and the possibilities of this technology in the increase of the hardness of W-C coatings. It was found out that HiTUS plasma is similar to that in DCMS and hysteresis behavior of sputtering rates during reactive sputtering after modification of acetylene flow was suppressed. The reason seems to be related to higher sputtering rates due to high plasma density from the independent plasma source compared to target poisoning rates within limited acetylene addition range. The reactive HiTUS resulted in substoichiometric amorphous or nanocrystalline WC1−x/amorphous carbon coating containing at least 20% of free disordered carbon. The amount of carbon was proportional to the acetylene flow. Slight shifts of G peak of Raman spectra toward higher values at higher RF bias power were attributed to ordering of carbon structure. Moreover, hardness increased approximately linearly with biasing power within limited acetylene flow range. The highest nanohardness values of HiTUS W-C coatings of around 33GPa–35GPa were comparable to those obtained in the best magnetron sputtered coatings which emphasized the applicability of HiTUS technology in hard coatings.