Electron bounce-cyclotron resonance in capacitive discharges at low magnetic fields

Abstract

We report the existence of an enhanced operating regime for a high-frequency, low-pressure capacitively coupled plasma (CCP) discharge in the presence of a weak magnetic field applied parallel to the electrodes. Our particle-in-cell simulations show that the discharge operates at significantly higher plasma density and ion flux when the electron-cyclotron frequency equals half the applied RF frequency at a given voltage. The physical mechanism responsible for this behavior is a resonance between the oscillatory motion of the sheath edge and the electron bounce in the cyclotron motion, which is half of the cyclotron period. Hence we call this resonance the electron bounce cyclotron resonance. In each collision with the sheath the electrons gain a substantial amount of energy eventually sufficient to produce higher ionization near the sheath leading to increase in the ion flux. The effect is observed at a relatively weak magnetic field, about 10G at 60 MHz. The proposed effect can be used for enhancing the operational performance of CCP devices in industrial applications.