EEDF analysis of CCP plasmas using regularized reconstruction analysis of IV characteristics from an RF compensated Langmuir probe

Abstract

Electron energy distribution function (EEDF) extraction from Langmuir probe data is an ill-posed problem due to the integral relationship between electron current and EEDF with respect to probe voltage. Curve fitting solutions to extract this EEDF assume a specific type of distribution. Point by point extraction of the second derivative relationship uses a small fraction of the integrated data to extract the EEDF. Recently EEDF extraction techniques have been evaluated using regularized solutions to the integral problem for the collisionless, thin sheath condition. 1,2 These techniques do not assume any mathematical representation of the EEDF and solve the integral problem for any function that best represents the EEDF. Additionally, the regularized extraction of the EEDF from electron current data provides a mechanism for addressing the noise amplification effects of the reconstruction without smoothing or fitting of experimental data.In this study, this regularized extraction of the EEDF is used to study the evolution of the electron energy distribution in SF 6 and BCl 3 plasmas due to the addition of N 2 . Previous work in this regime has shown significant influence on ion density and electron energy distribution, as well as in the interaction of these discharges with GaAs in plasma etch applications. 3 This paper will present EEDF analysis of this process regime using a regularized reconstruction of Langmuir Probe VI characteristics, as well as a comparison of the regularized solution to current best known methods for both calculated electron currents and electron currents obtained from experiment.