MODELING THE KINETICS OF NEUTRAL PARTICLES IN LOW-PRESSURE CHEMICALLYACTIVE PLANAR MICROWAVE PLASMAS

Low-pressure planar microwave plasmas exhibit a pronounced spatial str ucture. If the discharge vessels are wide enough, they have a thin, pl ane homogeneous excitation region adjacent to a microwave coupling win dow, and they strongly decay in the direction normal to the window. Th e decay length of plasma parameters and activated neutrals differ by a bout one order of magnitude. This suggests a two-region approach for m odeling of neutral particle kinetics assuming spatial homogeneity insi de these two regions. The gaseous reactor volume is subdivided by a vi rtual interface on which mass exchange by directed gas flow, local mic roconvective mixing or diffusion, and exchange of enthalpy between the two different regions can be balanced. The main differences between t he two regions are that electron-induced generation of activated neutr als is restricted to the excitation region (1) and that basic loss pro cesses for activated neutrals due to the substrate surface and volume reactions are considered to occur in the second, chemical reaction reg ion (2). Processes of loss of active neutral atoms by recombination at inert surfaces of the vessel are considered in both regions. Effectiv ely, the model represents a system of two-coupled continuous flow stir red tank reactors given by a set of differential equations including u nsteady-state Bernoulli equations. For the case of an example process concerning an oxygen plasma surface treatment, numerical solutions for initial values at the startup of the reactor are computed. The result s for the dynamical behavior and the steady states of the concentratio ns, the temperatures, and the mass loss are in qualitative agreement w ith the experimental behavior of a real reactor arrangement. (C) 1998 American Institute of Physics. [S0021-8979(98)03820-1].