Numerical simulation of thermophoretic particle decontamination in clean rooms

Abstract

In order to develop strategies for minimizing deposition of contaminant particles of diameters ranging from 0.1 to 1.0 μm on a wafer, the effect of thermophoresis on a particle deposition velocity was numerically studied. The angle between wafer surface and direction of free-stream flow was introduced as a system parameter. Convection, diffusion, sedimentation, and thermophoresis were included as particle transport mechanisms. Similarity transform was applied to the model equations and obtained equations with dimensions reduced by one. The results suggest that it is possible to enhance the removal of particles of diameter ranging from 0.1 to 1.0 μm by heating with a temperature difference of 10–30°C between wafer surface and the air stream. If the filter of a clean room removes well around 0.1 μm sized particles, the free-slream velocity or flow angle should be increased for the effective removal of particle by thermophoresis, but, if the filter is efficient in removing particles around 1 μm, the free-stream velocity or flow angle should be decreased.