Plasma wave after HIPIMS pulse: time-resolved diagnostic of HIPIMS copper plasma using a homemade Langmuir probe

A homemade Langmuir probe was constructed to investigate the plasma characteristics of high power impulse magnetron sputtering (HIPIMS) for copper deposition. Five sets of HIPIMS power delivery parameters were selected for use in a constant-current mode with different pulse widths ( T on ) and discharge frequencies ( f ) at a working argon pressure of 0.16 Pa. Waveforms of the HIPIMS cathode current remained constant during the pulse. The time-resolved plasma properties were examined to explore HIPIMS physics. At the end of the HIPIMS pulse, the plasma density increased and built to a second peak. Double peaks were observed in the ion and electron densities for all tested HIPIMS parameters. We discuss the mechanism responsible for the generation of the second peak, which is based on the collisions of highly energetic electrons and metastable atoms that have long lifetimes. Lifetime of the electron and ion densities after the second peak are estimated in terms of exponential decay. The lifetimes range between 30 and 40 μ s.