This paper discusses the use of simulation tools for semiconductor manufacturing applications. The simulation technique, based on the Direct Simulation Monte Carlo method, is designed for low pressure flow (less than 1.5 Torr), where traditional continuum methods are inapplicable. Calculations are presented for a parametric study using several flow configurations of industrial relevance, with operating pressures of 13.3 Pa (100 mTorr) and 2.66 Pa (20 mTorr). Results show that changing the locations of gas injection and exhaust, and heating on different portions of the reactor, can have significant effects on the flow profile above the wafer. These in turn may affect the uniformity of etching or deposition steps, and therefore the yield of a manufacturing process.