This paper describes the role of the temperature of the silicon wafer in controlling a deep trench etch sidewall angle and also the etch rate. In addition, we discuss the role of pressure in controlling etch rate and selectivity. This work was performed in a Tegal 1500 Test Bench. The temperature of the wafer could be held fixed as a function of time at any temperature between 20° and 200°C. Our chemistry is chloroform, with and as additives. We have found that the sidewall angle of the trench (the angle that the sidewall makes with a normal to the wafer surface) could be varied continuously from about 32° at 40°C to 7° at 190°C. The sidewalls are typically planar and relatively smooth. The bottom of the etch becomes increasingly planar as sidewall angle decreases. In order for the above processes to occur, there must be a small flow of through the chamber, e.g., 3–5 sccm. Results from the simulation code SAMPLE suggest that the rate of deposition of a material on the etch surface can control sidewall angle. We theorize that a chlorinated hydrocarbon polymer is being deposited, and that the wafer temperature is controlling the rate of deposition of the polymer. In addition to sidewall angle, for zero , increasing wafer temperature over the range stated above can cause the etch rate to increase with increasing temperature by 1800 Å/min at a nominal etch rate of 4000 Å/min. By adding to the gas mixture, the etch rate becomes insensitive to temperature. By increasing the total gas pressure to 1.2 torr, an etch rate of 8000 Å/min has been obtained, with an attendant selectivity in excess of 15.