Experimental benchmark of kinetic simulations of capacitively coupled plasmas in molecular gases

Z Donkó,E Johnson,J-P Booth,B Berger,T Gans,S Brandt,B Bruneau,D O’Connell,J Schulze,I Korolov,M Koepke,A R Gibson,A Derzsi,P Hartmann,T Lafleur

doi:10.1088/1361-6587/aa8378

Abstract

We discuss the origin of uncertainties in the results of numerical simulations of low-temperature plasma sources, focusing on capacitively coupled plasmas. These sources can be operated in various gases/gas mixtures, over a wide domain of excitation frequency, voltage, and gas pressure. At low pressures, the non-equilibrium character of the charged particle transport prevails and particle-based simulations become the primary tools for their numerical description. The particle-in-cell method, complemented with Monte Carlo type description of collision processes, is a well-established approach for this purpose. Codes based on this technique have been developed by several authors/groups, and have been benchmarked with each other in some cases. Such benchmarking demonstrates the correctness of the codes, but the underlying physical model remains unvalidated. This is a key point, as this model should ideally account for all important plasma chemical reactions as well as for the plasma-surface interaction via including specific surface reaction coefficients (electron yields, sticking coefficients, etc). In order to test the models rigorously, comparison with experimental ‘benchmark data’ is necessary. Examples will be given regarding the studies of electron power absorption modes in O2, and CF4–Ar discharges, as well as on the effect of modifications of the parameters of certain elementary processes on the computed discharge characteristics in O2 capacitively coupled plasmas.

Highlights

Introduction ce pte an usThe number of numerical modelling / simulation studies of low-temperature plasma sources has been rapidly growing during the last two decades, thanks to the fast advance of computational tools
Careful parametric investigations of plasma sources equipped with a variety of diagnostics tools can provide experimental benchmark data for this purpose
As an example of such a recent study, we quote measurements on low-pressure capacitively-coupled radio-frequency oxygen plasmas [9, 10] that were driven by singleand multi-frequency voltage waveforms [11, 12] with different peak-to-peak voltage amplitudes over a wide range of pressures. These experiments provided the dc self-bias voltage, the ion flux and the flux-energy distribution of positive ions at the grounded electrode, the power absorbed by the discharge and spatio-temporal maps of electron power deposition as obtained from Phase-Resolved Optical Emission Spectroscopy (PROES) [13]