Modeling and simulation of CF₄/O₂ microwave plasma afterglows Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/w3763b89n

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  • A gas phase kinetic model for the CF₄/O₂ microwave discharge plasma and afterglow of our laboratory has been developed. A reaction pathway identifying the major chemical reactions is proposed. The rate coefficients of the electron impact dissociation reactions are determined at three different plasma powers using both published electron molecule collision cross section data and plug flow analysis of data collected in our system. Agreement between calculated and experimental rate coefficients is better than 20%. Fluid simulations of a two-dimensional mathematical model were performed using computational fluid dynamics. It is found that the model reproduced qualitatively the general trends of the experimental data. The effects of plasma power, feed gas composition, residence time and pressure on the product distribution of the system are studied. CF₄ conversion increases with power and residence time. The variation of CF₄ conversion and carbon containing species distribution falls into two regimes. In the oxygen rich regime (below 25 mole % CF₄ in the feed), CO₂ is found to be the major product of CF₄ decomposition; homogeneous recombination reactions between atomic oxygen and the free radicals are found to be the dominant mechanism in the afterglow region resulting in high CF₄ conversions. Homogeneous reactions convert CO to CO₂. In the CF₄ rich regime (above 50 mole % CF₄), COF₂ is found to be the major product of CF₄ decomposition. Recombination reactions of CF₃ with atomic fluorine dominate in the afterglow region and limit conversion. Lowering pressures result in increased conversion of CF₄ and increased concentration of the carbon containing species.
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