Magnetically induced formation and disruption of striations in capacitively coupled radio-frequency CF 4 plasmas

Abstract The influence of externally applied homogeneous transverse magnetic fields of up to 200 G on self-organized striations in capacitively coupled radio-frequency (RF) CF 4 plasmas is investigated using kinetic simulations. The striations are known to originate from a resonance between the applied RF excitation and the eigenfrequency of the ion–ion plasma, the magnetic field is found to affect the striations indirectly through its impact on electron dynamics as ions do not get magnetized within the range of magnetic fields covered. Depending on the discharge conditions, increasing the magnetic field can either switch striations on or off and, in this way, strongly affect the spatial electron energy distribution function as well as the generation of process relevant charged and neutral species. We demonstrate that at some discharge conditions where striations form in the absence of a magnetic field, applying a moderate B-field can lead to the suppression of striations near the discharge center as a result of enhanced electron power absorption and a corresponding increase in electron density, enabling electrons to neutralize the space charge caused by the ion oscillations. We also illustrate the opposite effect that can occur at some other operating conditions, where the plasma operates close to the striation regime, but striations are absent due to insufficient ion densities, the magnetic field enhances the ion density and amplifies the local space charge formation, which can no longer be balanced by electrons. As a result, striations appear, inducing a transition from the drift ambipolar to a striation/magnetized drift ambipolar hybrid mode.