Modelling of removal characteristics and surface morphology formation in capacitively coupled atmospheric pressure plasma processing of fused silica optics

Abstract

Capacitively coupled atmospheric pressure plasma processing (CCAPPP) has been developed as a sub-aperture figuring tool for high precision fused silica optics, due to deterministic high rate material removal, small tool spot and no induced subsurface damage. In order to carry out an in-depth understanding on the removal and surface morphology formation mechanism of CCAPPP, this study aims to model the plasma discharge process and surface chemical reaction using the multi-physics simulation. The discharge characteristics such as electron density, electron temperature and particle density in the plasma are firstly obtained. Reaction gas components (CF4 and O2) are also added, and the main chemical reactions are analyzed by zero-dimensional modelling. Then the distribution of active atoms (active F atoms, O atoms and CFx molecules) related to the removal process is simulated in the full CCAPPP model. Finally, experiments are carried out to verify the simulation results, indicating that the distribution of active F atoms on the workpiece surface determines the Gaussian removal profile and the ratio of O/CFx is the key factor affecting the surface morphology formation of CCAPPP.