Floating potential probes for process control during reactive magnetron sputtering

Abstract

Long term deposition of aluminum oxide by reactive magnetron sputtering results in a drift of the discharge voltage. A similar drift of the floating potential is observed. The latter observation is further investigated and it is shown that the change of the floating potential can be linked to a change of the electric properties of the vacuum chamber walls. Optimization of the floating potential probe is performed to use the difference between the discharge voltage and the floating potential as a parameter for process control. The best results were obtained with a planar probe sufficiently far positioned opposite to the magnetron, and close enough to the chamber wall facing the magnetron. This choice can be understood in terms of the ability of the probe to sense the discharge while being protected from deposition. The usage of the aforementioned difference to control the process is demonstrated with the measurement of process curves, more specifically IV-characteristics and hysteresis experiments. The shown reproducibility of these measurements opens a pathway for more precise quantification of reactive sputter deposition simulations and enhanced process control.