Electron energy distributions and anomalous skin depth effects in high-plasma-density inductively coupled discharges

Electron transport in low pressure (<10s mTorr), moderate frequency (<10s MHz) inductively coupled plasmas (ICPs) displays a variety of nonequilibrium characteristics due to their operation in a regime where the mean free paths of electrons are significant fractions of the cell dimensions and the skin depth is anomalous. Proper analysis of transport for these conditions requires a kinetic approach to resolve the dynamics of the electron energy distribution (EED) and its non-Maxwellian character. To facilitate such an investigation, a method was developed for modeling electron-electron collisions in a Monte Carlo simulation and the method was incorporated into a two-dimensional plasma equipment model. Electron temperatures, electron densities, and EEDs obtained using the model were compared with measurements for ICPs sustained in argon. It was found that EEDs were significantly depleted at low energies in regimes dominated by noncollisional heating, typically within the classical electromagnetic skin depth. Regions of positive and negative power deposition were observed for conditions where the absorption of the electric field was both monotonic and nonmonotonic.