We present and discuss results obtained in studies of the mechanisms underlying Various feature size dependencies of SiO2 etching in inductively coupled fluorocarbon plasmas. The Variation of the fluorocarbon deposition rate and the SiO2 etch rate with both feature size and rf bias power has been measured in a variety of constant aspect ratio features for both an etch stop (C3F6 /H-2) and a nonetch stop ( CHF3) feedgas chemistry.