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Electron heating mode transition induced by the magnetic confinement of secondary electrons in capacitively coupled radio frequency discharges

Based on particle-in-cell and test-particle simulations, an α- to γ-mode transition of the electron power absorption dynamics is found to be induced as a function of an externally applied transverse magnetic field in low pressure capacitively coupled radio frequency discharges operated in argon. This transition is caused by the increased magnetic confinement of energetic ion-induced secondary electrons (γ-electrons) at higher magnetic fields. If a transverse magnetic field is applied, γ-electrons, that are accelerated to high energies by the sheath electric field, are confined in the vicinity of the sheath. Due to their gyromotions they are returned periodically to the adjacent sheath and interact repetitively with the sheath electric field. Such confined γ-electrons are, thus, effectively multiplied by ionization collisions in the vicinity of the sheath, thereby resulting in a significant enhancement of the local ionization rate and the plasma density. In such cases, the energy coupling efficiency of γ-electrons is greatly enhanced, implying that the discharge operates in a magnetized γ-mode. Moreover, the effects of the magnetic field on ion properties and ionization dynamics at different driving frequencies and operating pressures are studied.