Experimental measurements of spatial plasma potentials and electron energy distributions in inductively coupled plasma under weakly collisional and nonlocal electron kinetic regimes

Spatial profiles of the plasma potential and electron energy distribution function (EEDF) were measured in inductively coupled plasma (ICP) under weakly collisional and electron nonlocal kinetic regimes. The measured EEDF at the discharge center was a bi-Maxwellain distribution with low (T-1) and high (T-2) electron temperature groups, while the EEDF at the radial boundary was closely Maxwellian distribution due to cutting of the low energy electrons by relatively large ambipolar potential in this discharge regime. The ambipolar potential in the entire radial region was in the scale of T-eff - 1.5 T-eff, where T-eff is the effective electron temperature. At the boundary region with the ion mean free path scale, the ambipolar potential increased abruptly and was about T-eff,T-edge/2, where the T-eff,T-edge is the effective electron temperature at the boundary, which corresponds to the presheath scale. These results of the ICP, which are contrary to the ambipolar potential of capacitively coupled plasma in a nearly free-fall regime, are caused by relatively high T-1 and a small portion of low energy electron group density to total electron density in the ICP under the weakly collisional and nonlocal electron kinetic regimes. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3692768]