Evolution of discharge parameters and sputtered species ionization in reactive HiPIMS with oxygen, nitrogen and acetylene

Reactive high power impulse magnetron sputtering offers a great opportunity for high quality coating production, thus understanding the processes accompanying deposition is of great importance. In this paper, the evolution of numerous discharge parameters such as total pressure, discharge current and sputtered species number densities are studied in argon with oxygen, nitrogen or acetylene admixture. The experiments are compared to the reactive direct current magnetron sputtering where the deposition process usually exhibits hysteresis behavior and the ionization fraction of sputtered species is significantly lower. The decrease in the titanium atom and ion number densities with the increasing degree of target poisoning is detected for all the studied admixtures. However, while the sputtered species number densities decrease the sputtered species ionization fraction increases. Depending on the reactive gas admixture, the ionization fraction of the sputtered species increases from 75% achieved in pure argon discharge up to 90% attained in the poisoned mode of the reactive sputtering. This increase was the most pronounced for oxygen and nitrogen admixtures. Mutual comparison of the reactive sputtering with nitrogen, oxygen and acetylene indicated multiple causes for the observed increase. (paper)