Electron and Negative Ion Analysis in Oxygen Capacitively Coupled Radio Frequency Plasma

Low pressure capacitively coupled radio frequency plasmas (cc-rf plasmas) were investigated by minimalinvasive 160 GHz Gaussian beam microwave interferometry. The interferometer is a frequency stabilized (PLL) heterodyne system which immediately provides the line integrated electron density at spatial (axial) resolution of about 10 mm and temporal resolution of 200 ns. The line integrated electron density was measured in dependence on the processing parameters rf power (10 … 100 W) and total pressure (10 … 100 Pa) in comparison between argon and oxygen. Thereby, the changed distance between the fixed microwave beam axis as well as the sheath edge is taken into consideration using an analytical collision-dominated sheath model and results from optical emission spectroscopy. Microwave, interferometry and simultaneous laser photodetachment in oxygen plasma additionally permits the measurement of the negative atomic oxygen ion density. Dynamic and transient phenomena in oxygen plasmas are discussed such as mode transitions, afterglow behaviour in pulsed rf plasma, and electron density fluctuations due to attachment-induced ionization instabilities (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)