Measurement of plasma potential fluctuations by emissive probes in CF4 radio-frequency plasma

Plasma potential fluctuations are measured with an emissive probe in low-pressure CF4 plasma produced by a 13.56 MHz rf source. The inflection point method in the limit of zero emission is employed to determine the plasma potential. The maximum and minimum values of the plasma potential are observed. The values of the potential fluctuations depend on the rf source power, the amplitude of the applied voltage and the plasma density. The variations in the plasma potential fluctuations with the source power show the plasma mode changes from a capacitively coupled to an inductively coupled and then to a helicon mode. Electron density, temperature and ion saturation currents measured with a double probe also exhibit the transition. A Langmuir probe is employed to measure the floating potential and its fluctuation and the result verifies the same transition.