ON THE FORMATION AND LOSS OF S-2 MOLECULES IN A REACTIVE ION ETCHING REACTOR OPERATING WITH SF6

Laser-induced-fluorescence (LIF) spectroscopy was used to study, with spatial and temporal resolution, the processes by which diatomic sulfu r S-2 is formed and lost in SF6 plasmas. We present results concerning the relative S-2 number density in steady-state or pulsed discharges in a reactive ion etching (RIE) reactor operated at different SF6 gas pressures and RF powers, in the presence or absence of a silicon wafer . It is found that S-2 is formed mainly on surfaces under conditions w hen the F-atom density is high, but that volume formation can also occ ur when the F-atom population is depleted (namely, when Si is present) . It is also shown that loss of S-2 is mainly due to diffusion out of the inter-electrode space to the main reactor volume, excluding electr on-impact dissociation processes. It is apparent that, in a RIE reacto r, the only electron process pertinent to the balance of S-2 density i s the formation of its precursors (probably S atoms and SF molecules) by fragmentation of the SF6 gas. The remaining reactions controlling t he density of S-2 are neutral-neutral interactions in the volume and o n surfaces. (C) 1995 American Institute of Physics.