Simple Monitoring Method for RF Plasmas by the Insulated Pulse Probe Method

A simple technique using the insulated pulse probe method, which is basically reliable against any changes in the probe surface conditions due to contamination, is proposed and demonstrated for monitoring RF plasmas by analyzing the changes in both amplitude and phase of the fundamental RF component in the probe current signal by the application of a square pulse voltage to the probe. At the positive edge of the pulse, amplitude is enhanced and phase lags. These changes decay with a certain time constant and show the opposite sign at the negative edge. This is because the conduction current component changes in a different manner from the displacement current component on changing the voltage across the probe sheath. By this method, the essential parameters of RF plasma, such as electron temperature, plasma density, time-averaged sheath voltage, and the amplitude of the plasma potential oscillation, can be estimated.