Stuttgart 2012 – scientific programme

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P: Fachverband Plasmaphysik

P 20: Poster: Diagnostik

P 20.11: Poster

Thursday, March 15, 2012, 16:30–19:00, Poster.III

Spatio-temporal diagnostics of instabilities in cc-rf oxygen plasma — •Christian Küllig, Thomas Wegner, Kristian Dittmann, and Jürgen Meichsner — Institute of Physics, University of Greifswald

Instabilities in low density oxygen cc-rf plasmas driven at 13.56 MHz appear in a wide range of processing parameters rf power and pressure. The instabilities can be observed by characteristic fluctuations of plasma parameters measured by microwave interferometry, Langmuir probe diagnostics or optical emission spectroscopy. At the total gas pressure higher than 70 Pa the investigated cc-rf plasma is completely unstable within the studied rf power range from 10 to 100 W. The measured peak to peak values of the line integrated electron density fluctuations by 160 GHz microwave interferometry are between 0.2×10¹⁵ and 3.5×10¹⁵ m⁻², which can be in the same order of magnitude as the time-averaged line integrated electron density. The fluctuations are characterized by periodical non-harmonic functions with frequencies from 0.1 to 3 kHz [1]. The instabilities are also observed in the variation of the floating potential, the ion and electron saturation current in Langmuir probe diagnostics. The spatio-temporal mapped plasma volume by Langmuir probe measurements reveals that the fluctuations may have the origin in the rf plasma sheath and they appear as an oscillation in contrast to wave phenomenon in similar investigation of the positive column of DC glow discharge in oxygen. // Funded by the DFG Collaborative Research Centre TRR24, project B5.
C. Küllig et al.; IEEE Trans. Plasma Science, 39 Part I, 2564 (2011)