N. Nakano et al., SIMULATIONS OF RF GLOW-DISCHARGES IN SF6 BY THE RELAXATION CONTINUUM MODEL - PHYSICAL STRUCTURE AND FUNCTION OF THE NARROW-GAP REACTIVE-IONETCHER, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 49(5), 1994, pp. 4455-4465
A capacitively-coupled reactive ion etcher (RIE) can operate, even und
er high pressure conditions, for dry etching. Most of the etching gase
s are known to be strongly electronegative. The spatiotemporal structu
re of an ideal narrow-gap RIE with parallel plate geometry in an SF6 d
ischarge is investigated over the pressure range of 0.05-0.5 Torr at 1
3.56 MHz, using numerical simulations based on the relaxation continuu
m model. The rf plasma consists of a majority of positive and negative
ions and a minority of more mobile electrons. The functionality of th
e narrow-gap RIE under typical operating conditions is due to the appe
arance of a double layer in front of the instantaneous anode. The doub
le layer serves as the source of beamlike ions and virgin radicals imm
ediately in front of the electrode surface. A narrower sheath width is
realized compared with that found in electropositive gases. The maint
enance of the rf discharge is accomplished by ionization at the double
layer, while detached electrons from the negative ions have no signif
icant influence on the function or the structure of the SF6 discharge.