Measurement of time varying RF impedance of a pulsed inductively coupled plasma

Abstract

Summary form only given. Pulsed high density plasmas have been widely employed to enhance process results in advanced semiconductor fabrication, such as reducing the notch effect and increase the selectivity in the etch process and improving the properties of plasma deposited films. A RF plasma impedance meter has been developed to measure the time varying impedance during the power on the period of an inductively-coupled pulsed plasma, where a shape adjustable coil and conventional 13.56 MHz RF power were used. A capacitive voltage divider and a Rogowski coil were used to sense the RF voltage and current on the transmission line connected to the ICP coil, respectively. After passing through a low pass filter to eliminate high order harmonics, the voltage and current signals were sent into an analog electronic circuitry to extract their RMS values and relative phase. The circuitry was cold tested using a function generator to show that, for the 13.56 MHz signal frequency, little distortion was observed for modulation frequency up to 50 kHz. A digital oscilloscope was used to record the temporal behavior of the RMS values of RF voltage and current, as well as phase and the data was passed to a personal computer through a GPIP interface for further analysis to deduce the complex impedance observed into the ICP coil and the net input RF power.