Plasma Impedance Characteristics of Radio Frequency and Very High-Frequency Magnetron Discharges

Abstract

The impedance characteristics of radio frequency (RF) (13.56 and 27.12 MHz) and very high-frequency (60 MHz) magnetron discharges were investigated by the voltage–current probe technology. The discharge impedances $Z$ were found to decrease with the increase of discharge current at the frequency of 13.56 MHz, then change from a decreasing trend to an increasing trend at the frequency of 27.12 MHz, and further increase at the frequency of 60 MHz. This evolution was mainly related to the transition of the imaginary part $X$ from the capacitance to the reactance. Because of the low-electron density at the frequencies of 27.12 and 60 MHz and the enhanced electron Lorentz gyration at high voltages in the magnetron discharge, the electron inertia effect was enhanced. As a result, the plasma body reactance increased. The compensation of the plasma reactance to the sheath capacitance led to the transition of impedance $Z$ . Therefore, for the 27.12- and 60-MHz magnetron discharges, the electron inertia had a significant influence on the discharge impedance.