Treatment of dust particles in an RF plasma monitored by Mie scattering rotating compensator ellipsometry

Micrometer size particles can be processed by trapping them in a low pressure radio-frequency (RF) plasma. Their size can be influenced by etching or deposition. Mie scattering ellipsometry has been applied to monitor the particle properties during the plasma processing. Using this diagnostic, in which the polarization of light is modulated by means of a rotating compensator, the size and the size distribution of a cloud of particles are measured. The 5 µm particles, made of melamine-formaldehyde (MF) have been etched in an oxygen plasma. The experimental data have been fitted with a numerical model. The results indicate that the average size of the particles decreases and that the etching rate is 1.1 Ås-1. At the same time, the dispersion of the particle size increases.