Investigations of capacitively coupled neutral loop discharges (CCP-NLD) via PIC simulation

The neutral loop discharge (NLD) is an RF driven low pressure discharge with three magnetic coils placed coaxially outside the vacuum chamber, generating an axisymmetric magnetic field that vanishes at the so-called magnetic neutral loop (NL). In a capacitively coupled neutral loop discharge (CCP-NLD), the accelerating electrical field is generated by applying an RF potential to external electrodes; the corresponding electric field lines are co-planar to the magnetic field lines but perpendicular to the NL. This paper studies the plasma dynamics, particularly the electron heating mechanisms, in a CCP-NLD by means of spatially resolved particle-in-cell/Monte Carlo simulations. The behaviour of the electron density and the energy distribution for different neutral gas pressures, magnetic field strengths and radii of the NL is investigated. The results imply that a good time-averaged uniformity of the plasma can be achieved by a suitable control of the coil currents during process operation