The influence of transverse magnetic field on the properties of a 13.56 MHz cylindrical CCRF device

Magnetic field transverse to the sheath electric field is frequently used in capacitively coupled RF devices, in low-pressure, low-temperature regimes for a variety of applications. The magnetic field parallel to the electrode surface has been primarily investigated for parallel plate arrangement. This configuration results in an inhomogeneity in plasma density over the discharge plates due to inherent EXB drifts in the system, which results in non-uniform surface modification of the substrate. To address this issue, a cylindrical CCRF device with a pair of grounded annular rings having an axisymmetric magnetic field is proposed. Experiments conducted for a set of discharge pressure and applied RF power finds that the plasma density tends to increase with magnetic field strength while the electron temperature increases towards the edge. However, at a fixed applied RF power, the plasma density is found to fall beyond a critical value of magnetic field. This observation has been attributed due to strong confinement of ionizing electrons in the peripheral region, as the electron Larmor radius becomes comparable with the sheath width, with a corresponding fall in electron temperature in the central region. A qualitative discussion has been presented which explains the radial potential, plasma density and electron temperature variation in this system.