Determination of sputtered species densities in HIPIMS discharge by optical emission spectroscopy

Developing of magnetron sputtering process is aiming mainly to increase ionization of sputtered particles, to improve target yield or to enhance deposition rate. HIPIMS discharge yields higher number density of ionized sputtered species than DC case. However, it is difficult to estimate absolute number densities of the sputtered species (atoms and ions) in ground and metastable states from optical emission spectroscopy, because the ground and metastable levels do not directly produce any optical signal. There has been developed variety of indirect methods, however, mainly for rare gases to obtain information about number densities of metastable levels. Our research aim is to adapt these techniques such as self-absorption or effective branching fraction [1] on conditions of HIPIMS discharge. We ran experiments on magnetron with 20 cm titanium target. Lines of titanium neutrals and ions which originate at same higher level and fall to certain sub-level of neutral or ion ground state were carefully selected in our research. The population of these ground state sub-levels was assumed to follow Boltzmann distribution. Fitting theoretically calculated branching rations to experimentally measured ratios of the line intensities enable us to determine number densities of ground state sputtered species from optical emission spectroscopy in a HIPIMS discharge – see estimated evolution of Ti ion number-density together with the discharge current at Fig. 1. This research has been supported by the CZ.1.05/2.1.00/03.0086 and GACR P205/12/0407 projects.