THERMOPHORETIC EFFECT OF PARTICLE DEPOSITION ON A FREE STANDING SEMICONDUCTOR WAFER IN A CLEAN ROOM

The thermophoretic effect of particle deposition on a free standing wafer was studied experimentally and numerically. The experimental study consisted of generating a monodisperse polystyrene latex (PSL) aerosol, transporting the aerosol to a vertical test chamber, depositing the monodisperse aerosol on a wafer surface heated to a desired temperature, and analysing the deposited particles with a wafer inspection system. Experimental data of particle deposition velocity to a free standing wafer at 30 cms-1 of free stream velocity were obtained for a temperature difference between the wafer surface and the airflow of 10-40-degrees-C, and a particle diameter range of 0.6-5-mu-m. The data were then compared with a numerical model which took into account deposition mechanisms due to convection, diffusion, sedimentation and thermophoresis. The comparison shows good agreement between the measured particle deposition velocity and the numerical results.