Resonance induced striations in electronegative capacitively coupled radio-frequency plasmas*

The eigenfrequency of capacitively coupled radio-frequency plasmas in electronegative gases may locally match the frequency of the applied voltage. Such a resonance leads to a spatial modulation of the electric field, the densities of positive and negative ions, the energy gain of electrons, and the optical emission intensity in the plasma bulk region. Accordingly, self-organized striation patterns emerge. We investigate these striations and the physical mechanisms behind them in capacitive discharges in CF{\$}\textunderscore 4{\$} by a combination of Phase Resolved Optical Emission Spectroscopy measurements and outcomes of PIC/MCC simulations for various neutral gas pressures, electrode gaps, and applied voltage frequencies and amplitudes. The distance between the striations is found to decrease as a function of pressure. Furthermore, the discharge modes and mode transitions depending on the global control parameters are mapped in a phase diagram.