A high pressure, high throughout, single wafer semiconductor processing reactor is disclosed which is capable of thermal CVD, plasma-enhanced CVD, plasma-assisted etchback, plasma self-cleaning and deposition topography modification by sputtering, either separately or as part of in-situ multiple step processing. The reactor provides uniform processing over a wide range of pressures including very high pressures. A low temperature process for forming a highly conformal layer of silicon dioxide from a plasma of TEOS, oxygen and ozone is also disclosed. This layer can be planarized using an etchback process. Silicon oxide deposition and etchback can be carried out sequentially in the reactor.