Inert gas effects on the deposition rate of TiO2 during reactive HiPIMS

Deposition rates have been measured during the reactive HiPIMS of Ti in the presence of oxygen and different inert gases (i.e. mixtures of X/O2 where X = Ne, Ar, Kr or Xe) by means of a quartz crystal microbalance (QCM). The QCM was positioned above the erosion racetrack directly facing the target surface at two different axial distances (50 and 100 mm). The HiPIMS discharge was operated with a pulse on-time τ = 100 μs, a pulse frequency f = 100 Hz and a constant average discharge power Pavg = 100 W (50 W for Xe/O2). The oxygen partial pressure, pO2, was maintained at a constant 0.2pt where pt is the total pressure and was maintained at a constant 0.4 Pa. Using these conditions, the discharge was operated in the so-called 'poisoned' mode. In contrast to the trends predicted by SRIM as well as those measured in DCMS, the power-normalized static deposition rates in reactive HiPIMS of titanium measured in gas mixtures of oxygen were observed to increase with the mass of the inert gas. The observed trend was attributed to a decreased return effect as a result of an increased average absolute target potential during the pulse on-phase when employing heavier inert gases as the buffer gas. For the case of Kr/O2, the normalized deposition rate measured in HiPIMS was found to be 87% of that measured in equivalent DCMS operation.