Time-resolved perturbations near a self-biased, planar probe

Abstract

Summary form only given. Modulated discharges are of interest to today's plasma processing technology as a means of manipulating plasma properties. Furthermore, a modulated perturbation of a discharge can be used for diagnostic purposes. Experiments reported here have been performed in a GEC reference reactor. Time resolved experiments were carried out on the plasma disturbance caused by the transient biassing of a surface-mounted, planar probe. This particular probe utilizes the nonlinearity of the plasma sheath to derive a bias potential from the rectification of an imposed RF signal. Following the onset of a burst of RF excitation, a self-bias develops over a period of several tens of microseconds. The time scale of this phase is determined by external capacitance. During the early stages, before the self bias has begun to build up, the surface potential can be swept above that of the local plasma. As a consequence, on a time scale typically of several microseconds, the plasma potential, the electron temperature and the ion and electron densities are perturbed during this early phase. A Langmuir probe, an emissive probe and a retarding field energy analyzer have been used to follow the perturbation in time. Argon, neon and hydrogen plasmas have been studied. The time-resolved measurements show that the bulk plasma is perturbed even though the area of the perturbing surface is small compared to the discharge electrodes it. This observation confirms associated work with time-resolved optical emission, which first identified the extent of plasma disturbance. The electron density and temperature are most affected. Data are presented and the physical mechanisms behind the effects are investigated. This work is relevant both to plasma diagnostics and plasma processing schemes involving pulse-modulated excitation.