A detailed chemical reaction mechanism is reported that describes the CA and CHF3 plasma etching of silicon dioxide, which is widely used in the fabrication of microelectronic devices. The gas-phase part of the C2F6 mechanism involves 28 species and 132 reactions, while the surface part involves 2 materials, 6 species, and 85 reactions. Rate parameters are generally taken from independent studies in the literature, or estimated from rates measured for related species. Zero-dimensional simulations using these mechanisms compare well with a large body of etch rate and diagnostic measurements in three different high-density plasma reactors. The diagnostic measurements include electron and negative ion absolute densities, CF, CF2, and SiF densities, gas temperatures, and ion current densities. An analysis of the dominant reaction paths shows the importance of gas-phase electron impact reactions and the need to include reactions of the etch-product species. On the surface, the etching reactions are dominated by ion-assisted processes; spontaneous etching by F atoms is relatively unimportant.