Hannover 2010 – wissenschaftliches Programm
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P: Fachverband Plasmaphysik
P 6: Low Temperature Plasmas I
P 6.2: Vortrag
Dienstag, 9. März 2010, 14:40–14:55, B 305
Time resolved analyses of electron density and instabilities in oxygen rf plasma (CCP) with 160 GHz microwave interferometry — •Christian Küllig, Kristian Dittmann, and Jürgen Meichsner — University of Greifswald, Institute of Physics, Greifswald, Germany
The microwave interferometry compared with probe diagnostic represents a minimal-invasive diagnostics which affords a direct measurement of line integrated electron density by the phase shift of the microwave due to the change of electron density without any model assumptions. The microwave interferometer is a frequency stabilized (PLL) heterodyne system, operating at a frequency of 160.28 GHz (λ=1.87 mm). Consequently a quasi-optical setup was designed to guide the microwave with minimum beam radius of 5 mm in the plasma centre. Applying this diagnostics on oxygen rf plasma at 13.56 MHz, it is possible to measure a minimum phase shift of ΔΦ=0.016∘ and corresponding line integrated electron density down to 5.3·1013 m−2 with time resolution of 10 µs. Under these circumstances it is possible to study different temporal phenomena. Firstly, electron peaks were investigated in the afterglow of a pulsed oxygen rf plasma (10 Hz, duty cycle 50 %), which are connected with the detachment of negative ions as a possible production channel for electrons. Secondly, the observed electron density variation in the range of 0.2·1016 m−3 and 3.5·1016m−3 is analysed and is associated with the attachment induced ionization instabilities with frequencies in the range from 100 Hz to 3 kHz.