Radiofrequency phase resolved electron density measurements with the hairpin resonator probe

A floating hairpin resonator probe is used to measure electron density within the radiofrequency cycle of a parallel plate capacitively coupled plasma at steady state. A time resolution capable of detecting electron density oscillations within the radiofrequency cycle is demonstrated. Electron density oscillations are observed at the drive frequency over a range of operating conditions including 10–250 mTorr (1.3–33 Pa) in argon driven at 13.56 or 27.12 MHz. Localized electron density oscillation amplitudes show moderate agreement with literature and fluid simulations near the powered electrode and disagreement in the plasma bulk. The technique is useful for studying electron heating mechanisms in radiofrequency discharges due to its high time resolution. (paper)