Local racetrack plasma composition during reactive magnetron sputtering of ZnO:Al using rotatable Zn:Al target and influence on film properties

Reactive magnetron sputtering is a highly sensitive process because the working point depends on a large number of process parameters (power, pressure, reactive gas flow, pumping speed, magnetic field strength, resputtered material, …). Rotatable targets up to several meters long are used in large area coating tools due to their high productivity. Optimum film properties can only be obtained if the whole sputtered length of a tube target is operated in the same working point. Optical emission spectroscopy was used to monitor the local composition of species in the plasma during the deposition of ZnO:Al under standard deposition conditions. Differences in the plasma compositions and hence the working points of the two racetrack lines along the tube target were found. A special reactive gas channel set-up was used to influence the local racetrack plasma. The properties of the growing film can be much improved by balancing the plasma composition of the two racetrack lines.