RF discharge under the influence of a transverse magnetic field

Abstract

We examine the effects of an externally applied magnetic field (0–150 G) on an argon discharge generated capacitively at 13.56 MHz, in a Gaseous Electronics Conference reference cell. Dependence of the electrical characteristics of the discharge are measured as functions of applied magnetic field, rf power and argon pressure. At fixed power the rf voltage decreases with increasing magnetic field. Likewise, the impedance of the discharge is capacitive but becomes more resistive as the electron mobility becomes limited by the magnetic field. The impact of the magnetic field is found to diminish as the cyclotron frequency of the electron becomes smaller than that of the collision frequency of the electron. We also measure the impact the magnetic field has on the distribution of the plasma in vertical planes parallel and perpendicular to the magnetic field using Langmuir probes, optical emission and laser-induced fluorescence. It is found that the distribution of the plasma remains symmetric in the plane parallel to the magnetic field and becomes skewed in the plane perpendicular to the magnetic field. The degree of skew depends on the optical state probed. Finally, we examine the spatial distribution and the temporal evolution of the electric fields in the plasma. It is shown that with the presence of the magnetic field, the thickness of the sheath is reduced and that most of the voltage drop is contained within the sheath. Consistent with dc voltage trends, there was no significant sheath reversal observed at higher magnetic fields. Comparisons of the results presented here are made with trends predicted by models and simulations found in the literature.