Laser-induced-fluorescence detection of SO and SO2 in SF6/O2 plasma-etching discharges

Laser-induced-fluorescence spectroscopy was used to detect SO and SO2 molecules in the active volume of 13.56-MHz discharges through mixtures of sulfur hexafluoride and oxygen. A KrF laser was used to excite the SO B3Σ state and the SO2B̃1B1 and C̃1B2 states. 235-nm light was used to directly monitor the ground-state densities of these molecules. For a 100-W discharge through a 12.5% oxygen mixture (42 sccm SF6, 6 sccm O2, 340-mTorr total pressure), the SO and SO2 densities were determined to be ∼2×1014/cm3 and ∼4×1013/cm3, respectively. For the same discharge conditions, the SO vibrational temperature was ∼880 K. The SO vibrational temperature was independent of oxygen content in our experiments.