Mohammed Shihab

Ion energy distribution functions behind the sheaths of magnetized and non-magnetized radio frequency discharges

The effect of a magnetic field on the characteristics of capacitively coupled radio frequency discharges is investigated and found to be substantial. A one-dimensional particle-in-cell simulation shows that geometrically symmetric discharges can be asymmetrized by applying a spatially inhomogeneous magnetic field. This effect is similar to the recently discovered electrical asymmetry effect. Both effects act independently, they can work in the same direction or compensate each other. Also the ion energy distribution functions at the electrodes are strongly affected by the magnetic field, although only indirectly. The field influences not the dynamics of the sheath itself but rather its operating conditions, i.e., the ion flux through it and voltage drop across it. To support this interpretation, the particle-in-cell results are compared with the outcome of the recently proposed ensemble-in-spacetime algorithm. Although that scheme resolves only the sheath and neglects magnetization, it is able to reproduce the ion energy distribution functions with very good accuracy, regardless of whether the discharge is magnetized or not.

Kinetic simulation of the sheath dynamics in the intermediate radio frequency regime

The dynamics of temporally modulated plasma boundary sheaths is studied in the intermediate radio frequency regime where the applied radio frequency and the ion plasma frequency (or the reciprocal of the ion transit time) are comparable. Two fully kinetic simulation algorithms are employed and their results are compared. The first is a realization of the well-known particle-in-cell technique with Monte Carlo collisions and simulates the entire discharge, a planar radio frequency capacitively coupled plasma with an additional ionization source. The second code is based on the recently published scheme Ensemble-in-Spacetime (EST); it resolves only the sheath and requires the time-resolved voltage across and the ion flux into the sheath as input. Ion inertia causes a temporal asymmetry (hysteresis) of the charge‐voltage relation; other ion transit time effects are also found. The two algorithms are in good agreement, both with respect to the spatial and temporal dynamics of the sheath and with respect to the ion energy distributions at the electrodes. It is concluded that the EST scheme may serve as an efficient post-processor for fluid or global simulations and for measurements: it can rapidly and accurately calculate ion distribution functions even when no genuine kinetic information is available. (Some figures may appear in colour only in the online journal)

Ion energy distribution functions in magnetized capacitively coupled RF discharges

Summary form only given. The influence of a spatially inhomogeneous static magnetic field on the characteristics of capacitively coupled radio frequency discharges is investigated. In particular, the focus is placed on the sheath dynamics and the ion energy distribution functions (IEDFs) of ions impinging the electrodes. For this study we employ two different kinetic models. The first is the Particle-in-Cell (PIC) code yapic [1], which takes into account the entire discharge; the second code is the Ensemble-in-Spacetime (EST) model [2] which resolves the plasma boundary sheath only. We make a comparison of the two models by using the sheath voltage and the ion flux through the sheath calculated with PIC as input for EST. [3] We find excellent agreement of the IEDFs calculated with both methods. In addition, good qualitative agreement of the sheath dynamics is observed. However, a quantitative discrepancy between the models can be identified, caused by different collision processes implemented in both models. While it is found that electrons are strongly affected by the applied magnetic field, ions are only indirectly influenced in terms of the asymmetry of the discharge. In addition, we find that EST may be used as an efficient postprocessing tool to obtain the IEDFs even in magnetized cases, in particular if only simplified (i.e., global or fluid-dynamic) models are available.

Custom tailored ion energy distribution functions online for everybody

Summary form only given. Plasma processes, particularly plasma etching and plasma deposition processes are crucial for a large variety of industrial manufacturing processes. For these processes the knowledge of the ion energy distribution function plays a key role. Measurements of the ion energy distribution function (IEDF) are at least challenging and often impossible in industrial processes. An alternative to measurements of the IEDF are simulations.