Discharge physics of high power impulse magnetron sputtering

High power impulse magnetron sputtering (HIPIMS) is pulsed sputtering where the peak power exceeds the time-averaged power by typically two orders of magnitude. The peak power density, averaged over the target area, can reach or exceed 107W/m2, leading to plasma conditions that make ionization of the sputtered atoms very likely. A brief review of HIPIMS operation is given in a tutorial manner, illustrated by some original data related to the self-sputtering of niobium in argon and krypton. Emphasis is put on the current–voltage–time relationships near the threshold of self-sputtering runaway. The great variety of current pulse shapes delivers clues on the very strong gas rarefaction, self-sputtering runaway conditions, and the stopping of runaway due to the evolution of atom ionization and ion return probabilities as the gas plasma is replaced by metal plasma. The discussions are completed by considering instabilities and the special case of “gasless” self-sputtering. ► Overview with review and tutorial character. ► High power impulse magnetron sputtering is defined and distinguished from other forms of sputtering. ► Roles of self-sputtering and rarefaction are emphasized. ► Self-sputtering may (or may not) run away. ► HIPIMS physics is illustrated using niobium target. ► HIPIMS offers new opportunities for selected coatings applications.