Low k dielectric films are of interest to the semiconductor industry as a part of the overall solution to minimize RC time delays in the ever-shrinking critical dimensions in modern semiconductor products. We have examined the etching characteristics of several representative porous silica surfaces in an industrially relevant high-density, low-pressure fluorocarbon plasma environment. These characteristics include etch rate, selectivity to Si and photoresist, etch isotropy, and etch stop. We determined that the bias power strongly influences etch rate and selectivity. It was found that the surface-plasma interaction has a strong effect on the growth of the thin fluorocarbon film which is known to mechanistically to control the etch process under optimal conditions of high etch rate and good selectivity to other materials. Furthermore, the porous nature, and modified chemical structure of the silica film has unique interactions with the etching plasma. We determined that porous silica films, where hydroxyl groups terminate surface sites, require higher bias in order to etch in comparison to similar porous silica films, which have been fluorinated. The hydroxylated surface scavenges fluorine creating a carbon rich polymer film which leads to premature etch stop and increased aspect ratio dependence etching (ARDE). FTIR and IRLAS were used to illuminate key differences in the modified surface and gas phase species in the plasma, as compared to conventional dense silica.