FLUID SIMULATIONS OF PARTICLE CONTAMINATION IN POSTPLASMA PROCESSES

Fluid flow and particle trajectories in postplasma processes are simul ated using a commercially available computational fluid dynamics code. Two parallel plate geometries are modeled. Recirculation eddies are o bserved and particles of 0.01 mu m diameter can be trapped in these zo nes. Gravity can be a dominant mechanism, resulting in particle deposi tion onto wafer and chamber surfaces. The collection efficiency of par ticles 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 e xample, 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 abov e the wafer, while at 20 seem and 100 mTorr (13.3 Pa), collection incr eases to 95%. Particle deposition as a function of initial particle po sition depends on chamber configuration. (C) 1995 American Vacuum Soci ety.