Abstract
In this work, we analyze the creation of the discharge asymmetry and the concomitant formation of the DC self-bias voltage in capacitively coupled radio frequency plasmas driven by multi-frequency waveforms as a function of the electrode surface characteristics. For the latter, we consider and vary the coefficients that characterize the elastic reflection of electrons from the surfaces and the ion-induced secondary electron yield. Our investigations are based on particle-in-cell/Monte Carlo collision simulations of the plasma and on a model that aids the understanding of the computational results. Electron reflection from the electrodes is found to slightly affect the discharge asymmetry in the presence of multi-frequency excitation, whereas secondary electrons cause distinct changes to the asymmetry of the plasma as a function of the phase angle between the harmonics of the driving voltage waveform and as a function the number of these harmonics.
Highlights
Coupled plasma sources (CCPs) driven by radiofrequency (RF) waveforms have been aiding the plasma processing industry for decades
We have examined the establishment of a discharge asymmetry and the concomitant formation of a DC selfbias voltage in capacitively coupled RF discharges driven by multifrequency voltage waveforms
We have shown that this model, in its more complete form when it includes the charge dynamics, is able to successfully reproduce and explain the behavior of the DC self-bias voltage as a function of the phase angle between the harmonics of the driving voltage waveform
Summary
Coupled plasma sources (CCPs) driven by radiofrequency (RF) waveforms have been aiding the plasma processing industry for decades. Studies of the EAE were extended to a higher number of harmonics (N > 2), and various special waveforms, such as peakand valley-waveforms as well as sawtooth-waveforms, have been introduced and investigated both experimentally and computationally These waveforms, known as “Tailored Voltage Waveforms” (TVW), have been shown to provide large flexibility for controlling charged particle dynamics, the spatiotemporal distribution of the rates of elementary processes (e.g., ionization and excitation), the electron energy distribution function, and the ion properties. The DC self-bias voltage (η) has a direct effect on the ion flux-energy distribution (IFED) at the electrodes This makes such discharges attractive for surface processing applications.. Note that most plasma reactors used in industrial applications are geometrically asymmetric When such a discharge is driven by a multi-frequency waveform and has different electrode materials, three types of asymmetry effects are present simultaneously.
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