Aachen PK 2003 – wissenschaftliches Programm
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P: Plasmaphysik
P 17: Poster III
P 17.24: Poster
Donnerstag, 20. März 2003, 17:30–19:15, Foyer
Studies of the EDF in reactive rf-discharges by means of absorption spectroscopy combined with a simple chemical model — •I. Möller, A. Serdioutchenko, and H. Soltwisch — Institut für Experimentalphysik, Ruhr-Universität Bochum, Germany
The chemical composition in a CH4/O2-plasma depends strongly on the external parameters (applied power, flow rate, mixing ratio) as well as on the internal parameters (electron density ne and energy distribution function EDF). A change in the EDF shifts the balance of the reactions, and the production/depletion of one species can be altered dramatically.
An absorption spectrometer with 5 tunable diode lasers has been set up to measure the densities of CH4, O2, CH3, CO and CO2 in dependence on the external parameters. The measurements have been performed in an inductively coupled plasma cell which exibits two coupling modes and provides a wide range of ne (108−109 cm−3 (E-mode), 1010−1011 cm−3 (H-mode), 0-500 W, 10 Pa). In addition, a capacitively coupled plasma cell was used (109-1010 cm−3, 0-60 W, 100 Pa) to investigate in more detail the influence of the coupling mechanism on the plasma parameters.
The EDF in reactive plasmas with low ne is often not directly accessible. Therefore we have made use of a simple chemical model as additional diagnostic tool. The EDF can be obtained from an implemented Boltzmann solver or loaded from an external data file and is used for the calculation of the rate coefficients for dissociation and ionization.
By fitting the chemical model to the experimental measurements, reasonable borders for possible electron distribution functions are obtained and main reaction paths are identified.