Non-invasive VHF monitoring of atmospheric pressure plasma

摘要

This lecture presents details on how to perform non-invasive Very High Frequency (VHF) signal injection on the power line of atmospheric pressure plasma (APP). The purpose of this frequency injection is to interrogate in real-time the frequency reflection properties of plasma under varying gas and power conditions, and ultimately provide performance monitoring. The technique has evolved out of non-destructive analysis of plasma chambers and on-line analysis of semiconductor manufacturing plasma etching and axial DC magnetron sputtering systems [1]. For APP [2, 3] the measurement approach uses a sinusoidal signal that is stepped from a few MHz to a few 100 MHz with a specific resolution bandwidth. This signal is injected whilst the plasma is turned on, and travels both to the source impedance and the plasma-load. The return signal produces a superposition (vector summation) of the incident and reflected waves.