On the HiPIMS benefits of multi-pulse operating mode

High power impulse magnetron sputtering (HiPIMS) technology is particularly interesting for its high ionization efficiency of the sputtered target elements. However, one of its major drawbacks is the typically lower deposition rate, compared to direct current magnetron sputtering (DCMS), mainly due to the metal ion back-attraction. Using HiPIMS with very short pulses (less than 5 µs), it is possible to partially overcome the deposition rate limitation. In this contribution our focus is the optimization of the HiPIMS process with respect to DCMS, based on the physical understanding of the plasma state when using sequences of pulses, instead of general single high power pulse. Sequences of consecutive very short high-power pulses significantly increase the deposition rate compared to standard HiPIMS (s-HiPIMS), as proven by quartz crystal microbalance measurements and by scanning electron microscopy cross section images of the deposited films. Tailoring the sequences of multi-pulses (m-HiPIMS), experimental results undoubtedly show that tungsten deposition rate is at least 50% higher than in the s-HiPIMS, for the same average power. This finding is explained via tuneable diode laser absorption spectroscopy measurements of the sputtered W atoms correlated with electrostatic probe ion detection and time evolution of the plasma potential measured at the substrate position. Moreover, poly-crystalline thin film structure changes to a mainly preferential orientation (2 0 0) and film roughness is drastically reduced as provided by x-ray diffraction and atomic force microscopy, respectively. (paper)