Iterative actinometry: a new approach for tackling the deviations from a Maxwellian EEDF by using Boltzmann Solver

We propose a method to tackle the problem related to deviations of the actual electron energy distribution function (EEDF) from a Maxwellian distribution, as these deviations represent obstacles for the line-ratio methods, e.g. actinometry [1]. The method is based on the EEDF calculations in Boltzmann Solver with iterative determination of density of admixtures, reduced electric field and EEDF itself. The method also corrects the influence of dissociative excitation (which otherwise may lead to density overestimations), as basic chemistry is involved to the Solver.

The Lisbon Kinetics Boltzmann Solver (LoKI-B) [2], using the basic gas admixtures, the electric field and the kinetic gas parameters as input, is involved. The proposed procedure requires either the electric field or the mean electron energy as a basic input, in order to start the iterative calculations.

The method has been validated in radiofrequency discharges working at the pressure above 100 Pa in several gas mixtures (e.g. Ar, He, N₂, air, etc.). The local field approximation is elaborated so far (when electrons rapidly equilibrate their EEDF with the electric field, i.e. their equilibration length is much smaller than the electric field gradient), corresponding to relatively high pressures (> 100 Pa). The ultimate goal is to apply this approach also to low-pressure (< 10 Pa) plasmas, where the non-local field approximation becomes necessary (due to the slow equilibration of EEDF), such as etching plasmas working with CF₄+H₂ gas mixtures.