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. Process development studies have shown that high aspect ratio contact holes can be open in thick dielectric layers with a good selectivity to the underlying silicon. Minimization of reactive ion etching lag is obtained by using high bias power conditions, which on the other hand induce a degradation of the photoresist, described as a graphitization of the resist. The degradation induces considerable roughness at the edges of the resist structures which leads to the creation of striations in the silicon dioxide as the pattern transfer in the SiO2 proceeds. X-ray photoelectron spectroscopy (XPS) studies have allowed analysis of high aspect ratio SiO2 contact holes. Using appropriate flood gun conditions, a complete separation of the XPS peaks originating from the resist mask and from the fluorocarbon polymer deposited on the bottom of the contact holes is possible. The XPS analyses show, in particular, that the fluorination of the polymers on the bottom of the contact holes strongly increases with the aspect ratio of the contact hole, and that the fluorination of the polymers deposited on the contact hole sidewalls Is even greater.