|AVS 54th International Symposium|
|Plasma Science and Technology||Thursday Sessions|
|Session:||Plasma Diagnostics I|
|Presenter:||H. Shindo, Tokai University, Japan|
|Authors:||H. Shindo, Tokai University, Japan
K. Kusaba, Tokai University, Japan
|Correspondent:||Click to Email|
A new method to measure electron energy by an emissive probe has been proposed. The method is based on measurement of the functional relationship of the floating potential and the heating voltage of emissive probe. From the measured data of the floating potential change as a function of the heating voltage, the curve of the probe collection current-voltage can be analytically obtained. The present method has several important advantages of the following: (1) it is even applicable to radio-frequency plasma in which the potentials are usually fluctuating, (2) also applicable to plasmas which are produced in non-conductive containers. One of key issues in the method is to achieve a perfect floating condition for radio-frequency. To ensure this condition, the probe circuit was optically connected into the measurement circuit. In the experiment, the emissive probe 30 micrometer diameter tungsten was heated by 40 kHz pulse voltage, and the floating potential at the heating voltage off period and the floating potential difference between the heating off and on period were measured by digital oscilloscope in argon plasma. The measurements were made in plasmas, produced by a variety of frequencies of 2 MHz to 60 MHz, and these plasmas are both the capacitively coupled and inductively coupled. It was shown that the plasma electron energy probability function could be obtained without any RF compensating circuit even in capacitively coupled plasmas. In particular at the frequency of 60 MHz, since the method is very sensitive near the plasma potential, the clear indication for the depletion of the low energy electron could be obtained. This low energy electron depletion is due to high plasma potential. Therefore, in the inductively coupled plasma at the frequencies below 27 MHz this low energy electron depletion was obtained near the induction antenna, but at the further positions from the antenna the energy distribution became Maxwellian. This change in the electron energy distribution found in ICP was very systematic with the frequency, the gas pressures and the distances from the antenna. Thus the present method is quite innovative in that it is applicable to the potential fluctuating RF plasma and measurements are all done in a floating condition of probe.