Deposition rates, wet etch rates, and thickness uniformity experiments were performed using O3/TEOS thermal chemical‐vapor deposition. Our results for oxide deposition show optimum process window around 200 Torr for producing films of good quality (uniformity and material properties). This is in excellent agreement with the modeling predictions over a broad range of pressure (100–600 Torr) and temperature (370–470 °C). The model invokes both gas phase and surface reaction mechanisms. The former is needed to produce deposition precursors and leads to an observed increase‐maximum‐decrease dependence on the deposition pressure; this decrease is associated with a competing (parasitic) role of gas phase reactions. Our experiments identify particle formation at higher pressures which is consistent with the expected dual role of gas phase reaction in generating (1) required deposition precursors and (2) particulates in the gas phase under some conditions.