Experimental investigation of edge-to-center density ratio in E-H mode transition of an inductively coupled plasma

Abstract

The edge-to-center density ratio is investigated in an inductively coupled plasma which has two discharge modes depending on the rf power: the E-and H-mode. The power dependence of the edge-to-center density ratio is obtained from the ion flux at the wall and the electron flux at the center. The transitions of the density ratio of edge-to-center are observed during the E-H mode transition at various pressures, which has different trends depending on the pressure. These can be understood by the changes in the plasma characteristics due to the heating mode transition and electron kinetics by pressures. The theoretical edge-to-center density ratio is similar to the measured ratio at low pressures where the electrons are in non-local kinetics. However, at high pressures where the electrons are in local kinetics, the theoretical edge-to-center density ratio has a large discrepancy with the measured value in the E-mode due to local heating of electrons near the antenna. The density ratio of edge-to-center measured in the E-mode is larger than the theoretical ratio because the electron flux at the center is lower than that near the antenna. When the E-H mode transition occurs, the electron flux at the center is increased by the skin depth, which causes the decreased edge-to-center density ratio.