Measurement of negative-ion density in high-density C4F8 plasma using a laser photodetachment technique combined with a millimeter-wave open resonator

Abstract

A technique for measuring negative-ion density in high-density plasmas used for materials processing has been developed; negative ions were detected by measuring the electron-density perturbation caused by laser photodetachment using a millimeter-wave open resonator. The measured negative-ion density for an inductively-coupled C4F8(5%–20%)/Ar plasma with electron densities around 1011 cm−3 at a pressure of 25 mTorr was comparable to the electron density. The results suggest that species produced via dissociation of C4F8 attaches electrons as effectively as C4F8.