Broad-band UV absorption spectroscopy was used to determine radical de
nsities in reactive gas plasmas generated in a 13.56 MHz capacitively
coupled parallel plate reactor. Five radical species were detected: CF
2, CF, AIF, SiF2 and SP Absolute (line-integrated) CF2 densities were
determined in CF4 and C2F6 plasmas, as were the CF2 vibrational and ro
tational temperatures in the latter case. In CF4 plasmas the CF radica
l was also detected, along with the etch products AIF (from the Al pow
ered electrode) and SiF2 (when an Si substrate was present). The fract
ion that SiF2 comprises of the total etch products was estimated. Fina
lly, the S-2 dimer was detected in an SF6 plasma in the presence of an
Si substrate. This simple technique allows absolute concentrations of
many key reactive species to be determined in reactive plasmas, witho
ut the need to analyse the complex rotational spectra of these polyato
mic molecules.