Noninvasive electrical plasma monitoring method using reactor substrates as alternative current-sensing electrodes

Abstract

The authors propose a noninvasive electrical plasma monitoring method that uses two initially present metal reactor substrates, without the probe insertion. When a small sinusoidal voltage is applied between these two substrates, harmonic currents flow in a closed-loop circuit through the plasma. Assuming that the plasma exhibits nonlocal electron kinetics, the electron temperature and plasma density are determined based on an asymmetric double probe harmonic currents analysis. Experimental demonstrations were conducted in an inductively coupled plasma reactor, in which a grounded substrate and a bias electrode were used as the current-sensing electrodes. The electron temperature and plasma density measured with the proposed method agree well with measurements from a floating-type planar probe. This method can be applied to processing reactors that have no available port for electrical probe installation.