Electron population above 13.5 eV in the plasma through the C2F4/CF3I mixture, which is novel chemistry proposed for low-damaged, fine structure etching of SiO2, is studied by Ar emission analysis and Langmuir probe measurement. The integrated electron energy distribution function (eedf) above threshold energy for Ar 750.4 nm emission (13.5 eV) exhibits the weaker dependence on the gas composition for the C2F4/CF3I mixture than for the C4F8/Ar mixture which is conventional chemistry for SiO2 etching. In the practical etching conditions, the integrated eedf above 13.5 eV for the C2F4/CF3I mixture becomes smaller than one third of that for the C4F8/Ar mixture, regardless of the plasma sources used in this study (ultrahigh-frequency plasma and inductively coupled plasma sources). These results indicate that even lower charging damage of devices would be expected in SiO2 etching using the C2F4/CF3I chemistry than the C4F8/Ar chemistry. © 2000 American Vacuum Society.