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

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: CF2, CF, AIF, SiF2 and SP Absolute (line-integrated) CF2 densities were determined in CF4 and C2F6 plasmas, as were the CF2 vibrational and rotational temperatures in the latter case. In CF4 plasmas the CF radical was also detected, along with the etch products AIF (from the Al powered electrode) and SiF2 (when an Si substrate was present). The fraction that SiF2 comprises of the total etch products was estimated. Finally, 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, without the need to analyse the complex rotational spectra of these polyatomic molecules.