Fluid flow and particle trajectories in postplasma processes are simulated using a commercially available computational fluid dynamics code. Two parallel plate geometries are modeled. Recirculation eddies are observed and particles of 0.01 mu m diameter can be trapped in these zones. Gravity can be a dominant mechanism, resulting in particle deposition onto wafer and chamber surfaces. The collection efficiency of particles on the wafer is near unity for particles 0.1 mu m or greater in diameter, and efficiency increases with pressure and flow rate. For example, for gas conditions of 20 seem and 15 mTorr (2 Pa) 35% of 0.01-mu m-diam particles are collected on the wafer when released 2 cm above the wafer, while at 20 seem and 100 mTorr (13.3 Pa), collection increases to 95%. Particle deposition as a function of initial particle position depends on chamber configuration.