High-aspect-ratio sub-half-micron contacts were etched in SiO2 using a high-density C2F6 plasma generated by an inductively coupled, low-pressure reactor. As expected, oxide and resist etch rates increased with increasing bias. The aspect ratio (depth/width) dependence of the etch process was also shown to vary with bias power; at high bias power conditions, reactive ion etching (RIE) lag was observed, where high-aspect-ratio features etch slower than low-aspect-ratio features, and at low bias powers, inverse RIE lag was observed. Increasingly vertical sidewall angles and increasing microtrenching depth were also observed for higher rf bias conditions on contacts, trenches, and steps. Topography modeling shows that the microtrench profiles are consistent with specular ion reflection from sidewalls and the increase in their depths with rf bias is consistent with the energy-dependent etching yields in high-density, fluorocarbon plasma etch chemistries reported by Oehrlein et al. [J. Vac Sci. Technol. A 12, 323, 333 (1994)].