RADIOFREQUENCY GLOW-DISCHARGES IN METHANE GAS - MODELING OF THE GAS-PHASE PHYSICS AND CHEMISTRY

A methane discharge fluid model is developed, and subsequently combine d with a simple gas-phase chemical kinetics model. The aim is to provi de better understanding of the charged species dynamics, and their int eraction with the gas-phase kinetics in a CH4 plasma. Swarm data are u sed as input in the fluid model, which predicts the ion and electron d ensities, electric fields and ionization rates as a function of space and time in the radio-frequency period. Results show that, due to deta chment, the negative ion density in CH4 is of order 10(-2) that of ele ctrons; a capacitive discharge behaviour is observed analogous to that of an electropositive gas. The effects of electrode spacing (2-6 cm), gas pressure (80 mTorr to 1 Torr) and radio-frequency current (2.2-3. 4 mA cm-2, 0.6-0.15 W cm-2) are studied and compared successfully with experimental data. The time-averaged, spatially-resolved electron den sity and energy, the set of cross sections for CH2 and CH3 dissociatio n, together with an assumption about the form of the electron energy d istribution function, are subsequently used as input in a simplified o ne-dimensional gas-phase kinetic model. The model predicts the CH2 and CH3 spatial profiles, which compare well with experimental data.