Absolute radical densities in etching plasmas determined by broad-band UV absorption spectroscopy

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Broad-band UV absorption spectroscopy was used to determine radical densities in reactive gas plasmas generated in a 13.56 MHz capacitively coupled parallel plate reactor. Five radical species were detected: , CF, AlF, and . Absolute (line-integrated) densities were determined in and plasmas, as were the vibrational and rotational temperatures in the latter case. In plasmas the CF radical was also detected, along with the etch products AlF (from the Al powered electrode) and (when an Si substrate was present). The fraction that comprises of the total etch products was estimated. Finally, the dimer was detected in an 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, without the need to analyse the complex rotational spectra of these polyatomic molecules.