PI Controller for Electron Density Control in Low Pressure Plasma ?

This paper reports a PID control application for real-time feedback control of electron density, ne, in a low pressure, capacitively coupled plasma chamber. Experimental results are presented which demonstrate that a PI controller enables effective control of electron density when radio frequency power is used as an actuator. A hairpin resonator probe is used to measure the electron density, when the resonator is placed in plasma, its characteristic resonance frequency in vacuum shifts to a higher value. From the frequency shifts, electron density can be easily determined. Actuation and data acquisition are briefly outlined.