SF6 and C4F8 global kinetic models coupled to sheath models

Abstract

Global kinetic models combined with Monte Carlo sheath models are developed for SF6 and C4F8 plasma discharges for silicon etching under the Bosch process. In SF6 plasma, the dominant positive ions are , , and F+ while in C4F8 the dominant positive ions are and . The simulation results show that the electrical parameters, such as the electron density and electron temperature, clearly affect the sheath dynamics and consequently the ion energy distribution function evolutions. In this context, we showed the effects of the operating conditions, such as the pressure and the radiofrequency power, on the electron density and electron temperature evolutions as well as the reactive particle fluxes (neutral and positive ions) involved in the plasma surface interactions for etching/deposition under the Bosch process. Ion energy distribution functions obtained from SF6 and C4F8 plasmas are compared with each other as regards the electrical properties of their associated plasmas. The simulation results show that the bimodal peaks of ion energy distribution functions are wider for SF6 plasma than for C4F8 plasma due to the high sheath thickness of SF6 compared to that of C4F8. This is explained by the low electron density due to the high electronegativity of SF6 in comparison to that of C4F8. The simulations also reveal that the bimodal peak of the ion energy distribution function is wider when the ion mass is low.