A surface chemistry model was developed to understand the mechanism of etching or deposition on silicon dioxide surfaces exposed to a high density C2F6 plasma. The surface chemistry model in combination with a gas phase plasma chemistry model was implemented in the Modular Plasma Reactor Simulator (MPRES) to study oxide etching and uniformity under typical processing conditions. Simulation results on etch rate and uniformity as a function of operating conditions were consistent with experimental data. The transition from polymerization to etching as the ion bombardment energy (bias power) was increased was also captured by the simulation. Under low pressure conditions (several mtorr) the ion flux peaked at the wafer center while the neutral flux peaked at the wafer edge. Under such conditions, the oxide etch rate was highest at the edge. This supports the conclusion that, at such low pressures, oxide etching is ion driven but neutral dominated.