Asymmetric plasma potential fluctuation in an inductive plasma source

Time-averaged plasma potential in an inductive source with a ground wall has been measured by using an emissive probe. The inflection point method in the limit of zero emission is employed to determine the plasma potential. In this source, capacitive coupling results in a fluctuating plasma potential. The peak-to-peak value of the radiofrequency (RF) fluctuations, which is approximately given by the separation of the two peaks in the derivative of an I-V characteristic curve, has been reduced by introducing a gap between the antenna and the quartz window and by various electrostatic screens. Experimental data show that the lower potential peak, representing the lowest plasma potential, was approximately constant as the RF fluctuation level was reduced, while the higher potential peak, indicating the more positive plasma potential, changed and approached the lower potential peak. For very low fluctuation level, the lower potential peak becomes the de plasma potential and only the higher potential peak responds to the RF fluctuation.