Global model for high pressure electronegative radio-frequency discharges

Abstract

We develop a global model for high pressure (0.1–1 Torr) electronegative rf discharges and apply it to model a capacitively driven plasma etcher. The molecular gases considered consist of either pure chlorine species or a mixture of chlorine and helium species. The charged and neutral heavy particle densities together with the electron density and electron temperature are calculated by using the equations of particle balance and power balance for the input discharge parameters rf power or rf current, inlet pressure, gas flow rates, reactor diameter, and gap spacing. The power is deposited in the electrons via ohmic heating and in those ions accelerated across the dc sheath potential. The voltage across the sheath is calculated self-consistently with the densities and the electron temperature by using a collisional Child law sheath model. Analytic scaling laws for the dependence of charged and neutral particle densities, electron temperature, rf voltage and current, sheath width, and plasma impedance on pressure and absorbed rf power are presented and used to explain the numerical results obtained from the global model. The model results are compared to recent experimental measurements in a chlorine discharge over a range of absorbed power Pabs=20–180 W at an inlet pressure pin=0.4 Torr and a range of pressure 0.1–1.6 Torr with a fixed input power of 100 W. We obtain reasonable agreement for Pabs<200 W and for 0.2 Torr<pin<1 Torr.