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Progress in Plasma Processing of Materials, 2001

ISBN:
1-56700-165-3 (Print)

COMPARATIVE STUDY BETWEEN KINETIC AND THERMODYNAMIC CALCULATION OF COMPOSITION IN SF6 PLASMAS

V. Rat
PCTS -CNRS UMR 6638, University of Limoges, 123 av. A. Thomas, 87060 Limoges cedex, France

P. Andre
Laboratoire Arc Electrique et Plasmas Thermiques CNRS FRE 3120, Phys. Bât. 5 - Université Blaise Pascal, Aubière Cedex, France; and P.R.E.S. Clermont Université, Clermont-Ferrand Cedex 1, France

Jacque Aubreton
SPCTS University of Limoges, 123 av. A. Thomas, 87060 Limoges cedex, France

M. F. Elchinger
SPCTS University of Limoges, 123 av. A. Thomas, 87060 Limoges cedex, France

Pierre Fauchais
Laboratoire Sciences des Procedes Ceramiques et de Traitements de Surface UMR CNRS 6638 University of Limoges 123 avenue Albert Thomas, 87060 LIMOGES - France

A. Lefort
Laboratoire Arc Electrique et Plasmas Thermiques, Université Blaise Pascal, CNRS UMR 6069, 24 avenue des Landais, F63177 Aubiére Cedex, France

Abstract

For an SF6 plasma at atmospheric pressure the compositions calculated in chemical equilibrium, in the multi-temperature model and using kinetics (33 reactions involving 18 species) are compared. The ratio of the electron temperature Te to that of heavy species Th was calculated as a function of electron density and an intermediate temperature T* between Te and Th was introduced to cope with the relationship kf(T*) / kr(T*) = Kx(T*) where kf and kr are the reaction rate coefficients (forward and reverse) and Kx the equilibrium constant. The main difference between equilibrium and kinetic calculations lies in the densities of S+, S2+, SF+, F and S species between 2000 and 6000 K. The multi-temperature method gives results very different from those of the kinetic calculations even when neglecting the charge loss reactions. This is in contrast to what happens with H2 or N2.