Observation of heat-induced particle resuspension and transport in a plasma chemical vapor deposition chamber

The influences of gas viscous force, thermal stress, and plasma electrostatic force on heat-induced particle resuspension and transport in a plasma chemical vapor deposition (CVD) chamber were studied experimentally. Using an in situ particle measurement system in a plasma CVD chamber based on a laser light scattering method, it was observed that silica particles with a diameter of 600 nm dispersed on a wafer were resuspended when the wafer was heated. At a wafer temperature of 573 K, when the pressure in the chamber was being changed, the removal ratio of particles from the wafer exhibited a weak dependence on pressure in the range from 13.3 Pa (0.1 Torr) to 1.33kPa (10Torr). A theoretical calculation based on thermophoresis that considers a temperature jump could explain the trend of the experimental results. Since the removal ratio of particles from the wafer is greater with larger difference in the linear coefficients of thermal expansion between the wafer and the particles, it is considered that the particles are separated from the wafer due to thermal stress and are scattered towards the upper electrode by the force of thermophoresis. It has also been revealed that, when plasma discharge is applied, the removal ratio of particles is reduced due to the electrostatic force of charged particles.