Date of Graduation
Eberly College of Arts and Sciences
Physics and Astronomy
In this work, experimental measurements and analysis of numerical simulations are performed for capacitively coupled plasmas driven by tailored voltage waveforms under conditions which examine complicating factors present in industrial processes, including the influence of resonance effects, electronegative gases or gas mixtures, and plasma-surface interactions at a changing plasma-surface interface. Furthermore, the influence of different tailored voltage waveforms on the spatio-temporal electron power absorption, the generation of a DC self-bias, and on process relevant plasma parameters like ion energy distribution functions is investigated to provide a more complete understanding of the underlying fundamental plasma physics responsible for sustaining the discharge. It is found that these complicating factors can dramatically alter the operation of discharges under conditions that are highly relevant to many industrial processes. First, it is demonstrated that tailored voltage waveforms provide improved control over the charged particle dynamics and process-relevant plasma parameters of electropositive argon discharges. The self-excitation of the plasma series resonance and its subsequent influence on the charged particle dynamics is then analyzed using numerical simulations of geometrically symmetric but electrically asymmetric argon discharges. The influence of negative ions and electronegativity on the charged particle dynamics produced by various tailored voltage waveforms is investigated for tetrafluoromethane discharges and argon-tetrafluoromethane gas mixtures. It is found that the discharge electronegativity and the presence of the drift-ambipolar heating mode dramatically alter the operation of the discharge. Lastly, the dependence of secondary electron emission on the surface characteristics (surface roughness, film thickness) of aluminum and aluminum oxide surfaces is demonstrated to be non-negligible and hypotheses for the underlying physical mechanisms behind these dependencies are presented. Thus, several important factors frequently used in industrial processing which are usually omitted from fundamental studies of capacitively coupled plasmas are shown to significantly modify the associated spatio-temporal charged particle dynamics and should not be neglected in future research.
Brandt, Steven W., "Control of charged particle dynamics and electron power absorption dynamics utilizing voltage waveform tailoring in capacitively driven radio-frequency plasmas" (2020). Graduate Theses, Dissertations, and Problem Reports. 7576.