Influence of surface conditions on plasma dynamics and electron heating in a radio-frequency driven capacitively coupled oxygen plasma

Abstract

The impact of changing surface condition on plasma dynamics and electron heating is investigated by means of numerical simulations, based on a semi-kinetic fluid model approach, and compared with measurements of the nanosecond electron dynamics in the plasma-surface interface region using phase resolved optical emission spectroscopy (PROES). The simulations are conducted in a one-dimensional domain and account for a geometrical asymmetry comparable to the experimental setup of a radio-frequency driven capacitively coupled plasma in a gaseous electronics conference reference cell. A simple reaction scheme is considered, including electrons, positive ions, negative ions and metastable singlet delta oxygen (SDO) as individual species. The role of surface loss and effective lifetime of SDO is discussed. To simulate different surface conditions, the SDO surface loss probability and the secondary electron emission coefficient were varied in the model. It is found that a change in surface condition significantly influences the metastable concentration, electronegativity, spatial particle distributions and densities as well as the ionization and electron heating dynamics. The excitation dynamics obtained from simulations are compared with PROES measurements. This allows to determine experimentally relevant SDO surface loss probabilities and secondary electron emission coefficient values in-situ and is demonstrated for two different surface materials, namely aluminum and Teflon.