Hybrid Plasma Modeling of Capacitively-Coupled O2 Plasma at Intermediate Pressures and Comparison with Experiments

Intermediate pressure (~a few Torr) plasmas are used for advanced plasma processing in the semiconductor industry. Plasma modeling at such pressures validated with experiments provides a better understanding of plasma behavior as well as equips us with modeling tools suitable for designing plasma products. Plasma modeling is performed for oxygen RF capacitively coupled discharges at intermediate pressures. The model considers a detailed chemistry for the oxygen plasma including O^- ions, which make the O₂ plasma significantly electronegative. Our hybrid plasma model includes continuity equations for charged and neutral species, drift-diffusion approximation for electron flux, the momentum conservation equation for ions coupled with the Poisson’s equation for electric potential. The secondary electrons emitted from the surface are treated kinetically to model the acceleration these electrons experience when going through the sheath. This kinetic secondary electron model is coupled with the fluid bulk plasma model so that the ionization caused by these secondary electrons is captured in the physics of simulations. The plasma modeling is performed over a range of pressures and powers as in the experiments. The electrode potential, electrode current, and the phase difference between potential and current are compared with the experimental data. In addition, electron density, O density, O^- density and gas temperature in the plasma chamber are used for model validation. Our simulation results show that secondary electron emission coefficient, gas temperature, surface recombination of O atom and the assumption of electron energy distribution function play important roles in achieving good agreement of computed O₂ plasma behavior with the experimental data.