Simulations of rf glow discharges in SF6 by the relaxation continuum model: Physical structure and function of the narrow-gap reactive-ion etcher

A capacitively coupled reactive ion etcher (RIE) can operate, even under high pressure conditions, for dry etching. Most of the etching gases are known to be strongly electronegative. The spatiotemporal structure of an ideal-narrow gap RIE with parallel plate geometry in an SF6 discharge is investigated over the pressure range of 0.05-0.5 Torr at 13.56 MHz,using numerical simulations based on the relaxation continuum model. The rf plasma consists of a majority of positive and negative ions and a minority of more mobile electrons. The functionality of the narrow-gap RIE under typical operating conditions is due to the appearance of a double layer in front of the instantaneous anode. The double layer serves as the source of beamlike ions and virgin radicals immediately in front of the electrode surface. A narrower sheath width is realized compared with that found in electropositive gases. The maintenance of the rf discharge is accomplished by ionization at the double layer, while detached electrons from the negative ions have no significant influence on the function or the structure of the SF6 discharge.