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Self-organized striated structures of the plasma emission have recently been observed in capacitive radiofrequency CF 4 plasmas by Phase Resolved Optical Emission Spectroscopy (PROES) and their formation was analyzed and understood by Particle in Cell / Monte Carlo Collision (PIC/MCC) simulations [Y.-X.Liu, et al. Phys. Rev. Lett. 116, 255002 (2016)]. The striations were found to result from the periodic generation of double layers due to the modulation of the densities of positive and negative ions responding to the externally applied RF potential. In this work, an in-depth analysis of the formation of striations is given, as well as the effect of the driving frequency on the plasma parameters, such as the spatially modulated charged species densities, the electric field, and the electron power absorption is studied by PROES measurements, PIC/MCC simulations, and an ion-ion plasma model. The measured spatiotemporal electronic excitation patterns at different driving frequencies show a high degree of consistency with the simulation results. The striation gap (i.e., the distance between two ion density maxima) is found to be inversely proportional to the driving frequency. In the presence of striations the minimum (CF 3 + , F − ) ion densities in the bulk region exhibit an approximately quadratic increase with the driving frequency. For these densities, the eigenfrequency of the ion-ion plasma is near the driving frequency, indicating that a resonance occurs between the positive and negative ions and the oscillating electric field inside the plasma bulk. The maximum ion densities in the plasma bulk are found not to exhibit a simple dependence on the driving frequency, since these ion densities are abnormally enhanced within a certain frequency range due to the ions being focused into the "striations" by the spatially modulated electric field inside the bulk region.2 / 31 Striations in electronegative capacitively coupled radio-frequency plasmas: analysis of the pattern formation and the effect of the driving frequency 2 / 31 deposition (PECVD) -often performed at relatively high pressures, low driving frequencies, and in electronegative gasessince the striations can drastically affect various process relevant plasma parameters, e.g., the flux-energy distribution functions of different charged species.One of the most well-known scenarios is the self-organized striated structure occurring in the positive column region of dc glow discharges, wherein ion-acoustic or ionization waves are generally considered to be responsible for their appearance [1,[11][12][13]. Over the past few years, several types of striated structures have been observed in different versions of atmospheric pressure plasma jets (APPJ). Depending on the discharge conditions, the plasma streamer ejected from the nozzle was found in [14,15] to be stratified into stationary bright and dark slender regions between the nozzle and the target plate. Very recently, a stratified filament occurring in the discharge tube of a RF argon APPJ was observed in num...

The influence of a uniform magnetic field parallel to the electrodes on radio frequency capacitively coupled oxygen discharges driven at 13.56 MHz at a pressure of 100 mTorr is investigated by one-dimensional Particle-in-Cell/Monte Carlo collision (1D PIC/MCC) simulations. Increasing the magnetic field from 0 to 200 G is found to result in a drastic enhancement of the electron and the O + 2 ion density due to the enhanced confinement of electrons by the magnetic field. The time and space averaged O − ion density, however, is found to remain almost constant, since both the dissociative electron attachment (production channel of O − ) and the associative electron detachment rate due to the collisions of negative ions with oxygen metastables (main loss channel of O − ) are enhanced simultaneously. This is understood based on a detailed analysis of the spatio-temporal electron dynamics.The nearly constant O − density in conjunction with the increased electron density causes a significant reduction of the electronegativity and a pronounced change of the electron power absorption dynamics as a function of the externally applied magnetic field. While at low magnetic fields the discharge is operated in the electronegative Drift-Ambipolar (DA) mode, a transition to the electropositive α-mode is induced by increasing the magnetic field. Meanwhile, a strong electric field reversal is generated near each electrode during the local sheath collapse at high magnetic fields, which locally enhances the electron power absorption. A model of the electric field generation reveals that the reversed electric field is caused by the reduction of the electron flux to the electrodes due to their trapping by the magnetic field.The consequent changes of the plasma properties are expected to affect the applications of such discharges in etching, deposition and other semiconductor processes.

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