Temporal evolution of a capacitively coupled argon discharge due to the sputtering of an oxide layer on an aluminum electrode

• Published in: Plasma sources science & technology Vol. 28; no. 6; pp. 65011 - 65025
• Main Authors: Qiu, Jie, Li, Jiang-Tao, Chen, Wen-Cong, Wang, Zhen-Bin, Liu, Fei-Xiang, Pu, Yi-Kang
• Format: Journal Article
• Language: English
• Published: IOP Publishing 24.06.2019
• Subjects: aluminum oxide; discharge impedance; plasma-surface interaction; rf sheath; secondary electron; sputtering
• ISSN: 0963-0252; 1361-6595; 1361-6595
• DOI: 10.1088/1361-6595/ab2184

In a 20 mTorr capacitively coupled argon discharge, when an oxide layer on the aluminum power electrode is sputtered away, the discharge characteristics change with time. One of the changing parameters is the sheath width near the power electrode. In addition, the measured electrical characteristics of the discharge and the emission intensities of argon and aluminum atoms also change with time. An integrated model is developed to investigate this phenomenon. This model incorporates the sputtering process and its effect on the secondary electron yield, the energy and current conservation in the discharge as well as the power coupling with the external rf driving circuit. The model predictions of the temporal evolution of the discharge parameters are in reasonable quantitative agreement with the observed ones. With this model, it is found that the root cause of the discharge evolution is the change of secondary electron yield due to the sputter removal of the oxide layer on the electrode surface. During the sputtering process, the decreasing secondary electron yield results in increasing discharge impedance. As a result, the sheath voltage and hence the sheath width increase, enhancing the discharge impedance further. This nonlinear discharge characteristic forms a positive feedback loop that greatly enhances the effect of changing the secondary electron yield.