New Emissive Probe Measurements of Electron Temperature in Two Modes of Radio-Frequency Plasmas

A new method which has recently been reported to measure electron temperature by an emissive probe is applied to radio-frequency (RF) plasmas. In particular the electron temperature measurements are made, focussed on the condition in which the mode transition from the capacitive to the inductive is occurred at the frequency of 13.56 MHz. The method is based on measurement of the functional relationship between the floating potential and the heating voltage of emissive probe. The measured data of the floating potential change as a function of the heating voltage behave quite differently, depending on the plasma mode. It is found that in the inductive mode, the floating potential change is consistent with the theory based on Maxwellian plasma, enabling to determine the electron temperature, while in the capacitive mode, the behavior of floating potential change is fairly complicated, hence non-Maxwellian plasma. With a great advantage of the present method the electron energy probability function (EEPF) is calculated with the energy resolution of 2.5kTe/e, and the EEPF thus obtained reveals a bi-Maxwellian in the capacitive mode while it becomes Maxwellian in the inductive mode after the transition. (C) 2009 The Japan Society of Applied Physics