RF PLASMAS IN METHANE - PREDICTION OF PLASMA PROPERTIES AND NEUTRAL RADICAL DENSITIES WITH COMBINED GAS-PHASE PHYSICS AND CHEMISTRY MODEL

A combined plasma physics and chemistry simulator is presented and applied for rf methane discharge in the 100 mTorr pressure range. The simulator consists of a self-consistent fluid model for charged species physics, a public-domain Boltzmann equation solver for de field calculation of the electron energy distribution function (EEDF), and a generalized one-dimensional gas-phase chemistry model. The methane discharge shows an electropositive and capacitive behavior analogous to that of noble gases, with negative ion densities one order of magnitude less than those of electrons. Electron densities and energies compare favorably with literature values of probe measurements. The high-energy tail of the EEDF in methane has fewer electrons than the Druyvensteyn or Maxwell distribution. The chemistry model was applied for four species, namely, CH4, CH3, CH2, and H, and the densities predicted are on the order of 10(15), 10(12), 10(10), 10(13) atoms/cm(3) respectively, at 140 mTorr. Their density profiles compare favorably with literature experimental data. Detailed analysis of the contribution of each reaction, and sensitivity analysis reveals the major creation and loss pathways for each chemical species.