Many reactive species of interest in technological plasmas absorb light in
the UV spectral region (200-300 nm). Measurement of these weak absorbances
(typically 10(-2)-10(-4) for a single pass) allows us to determine their ab
solute concentration. Low-resolution absorption spectra of these systems ha
ve previously been obtained by broad-band absorption spectroscopy. Here we
present spectra obtained using laser cavity ring-down spectroscopy, which h
as much higher spectral resolution, and potentially higher sensitivity. Spe
ctra were obtained for CF, CF2, AlF and SiF2 radicals in capacitively-coupl
ed radio-frequency plasmas in fluorocarbon gases. This technique offers the
possibility of real-time (1 s) absolute concentration measurements during
wafer processing. (C) 2000 Elsevier Science B.V. All rights reserved.