Convergence during feedback controlled reactive magnetron sputtering: Mechanisms and classification

During feedback control of reactive magnetron sputtering, process parameters often exhibit a complex timedependent behavior. This behavior hinders process stabilization and can lead to a modification of the desired film properties. This study investigates the processes behind this behavior by performing time-resolved measurements during reactive sputtering of aluminum in argon/oxygen mixtures. Two distinct groups of physical processes were identified. The first group exhibits a relatively fast time-dependent behavior, leading to process stabilization within 5 to 8 min. This group includes processes related to reactive gas introduction, its interaction with deposited material, and the feedback loop characteristics. The second group causes a continuous drift of the process for more than 45 min, primarily due to oxide deposition on the chamber walls and target erosion. These two groups have a different impact on the process curves known as hysteresis curves. For the first group, the impact is minimal while for the second group the hysteresis curve becomes distorted, potentially leading to misinterpretation or incorrect selection of deposition conditions. The utilization of the difference between the discharge voltage and floating potential as the feedback input signal eliminates the impact of oxide deposition and mitigates this problem.