Measurement of electron temperature and ion density using the self-bias effect in plasmas

Abstract

For novel plasma diagnostics, the rf floating probe was revisited. For inducing the self-bias effect, ac bias voltage (∼kilohertz) was applied through a dc blocking capacitor between a probe and a signal generator. The dc self-bias potential was changed not only with ac bias voltages but also with electron temperatures, and therefore, the electron temperature was derived from the variations in the self-bias potential with and without ac bias voltage. The harmonic component of the probe contains information about the ion flux, and using a fast Fourier transform analysis of the probe current, the ion density was derived from the first harmonic current of the probe. The experimental results were compared with a single Langmuir probe. The electron temperature and the ion density were in good agreement with those from the Langmuir probe. Because the amplitude of the ac bias voltage is very low (<3 V), local ionizations affected by a high bias-voltage can be neglected.