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.
Highlights
Coupled plasma (CCP) discharges are widely used in industry for plasma processing applications, e.g., etching and deposition
We report a significant enhancement in the performance of low-pressure Capacitively coupled plasma (CCP) discharges at much lower magnetic-field strengths (∼ 10 G)
The enhancement in performance is caused by resonance between the oscillatory motion of the sheath edge and the motion of electrons bouncing off the sheath edge, subsequently gyrating, and returning to the sheath after half a cyclotron period
Summary
Coupled plasma (CCP) discharges are widely used in industry for plasma processing applications, e.g., etching and deposition. B, e, and me are the external magnetic field, electronic charge, and mass, respectively) is equal to half the applied RF frequency ( fr f ) This resonance condition corresponds to quite low strengths of the magnetic field The bounce-cyclotron resonance leads to a more effective energy gain by the electrons compared to that in the absence of a magnetic field, leading to a greater ionization of the neutral background gas and a resultant increase in the ion flux. This effect of a weak magnetic field on the discharge is distinct from the effects of much higher magnetic fields on the discharge [32,34–36]. We discuss the simulation results, the resonance mechanism, and the conditions for the existence of such a resonance
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