Certain Hitherto Unpublished Data Concerning the Insane

121

151

Two fundamentally different types of dual-frequency (DF) capacitively coupled radio frequency discharges can be used for plasma processing applications to realize separate control of the ion mean energy, E i , and the ion flux, i , at the substrate surface: (i) classical discharges operated at substantially different frequencies, where the low-and high-frequency voltage amplitudes, φ lf and φ hf , are used to control E i and i , respectively; (ii) electrically asymmetric (EA) discharges operated at a fundamental frequency and its second harmonic with fixed, but adjustable phase shift between the driving frequencies, θ. In EA discharges the voltage amplitudes are used to control i and θ is used to control E i. Here, we report our systematic simulation studies of the effect of secondary electrons on the ionization dynamics and the quality of this separate control in both discharge types in argon at different gas pressures. We focus on the effect of the control parameter for E i on i for different secondary yields, γ. We find a dramatic effect of tuning φ lf in classical DF discharges, which is caused by a transition from α-to γ-mode induced by changing φ lf. In EA discharges we find that no such mode transition is induced by changing θ within the parameter range studied here and, consequently, i remains nearly constant as a function of θ. Thus, despite some limitations at high values of γ the quality of the separate control of ion energy and flux is generally better in EA discharges compared with classical DF discharges.

Section: Simulation Methodsmentioning

confidence: 99%

Secondary electrons in dual-frequency capacitive radio frequency discharges

Schulze

Donkó

Schüngel

et al. 2011

121

151

“…This procedure is continued until the bias reaches a converged value and the charged particle fluxes to each of the two electrodes balance. For the simulations in pure argon, the cross sections for electron-neutral and ion-neutral collisions are taken from Phelps and Petrović [78][79][80]. For the argon ions, elastic collisions with the neutral gas atoms are divided into an isotropic and a backward part.…”

Section: Simulation Methodsmentioning

confidence: 99%

Electron heating and the electrical asymmetry effect in dual-frequency capacitive CF₄discharges

Schulze

Derzsi

2011

The electron heating and the electrical asymmetry effect (EAE) in electronegative dual-frequency capacitive CF 4 discharges are investigated by particle-in-cell simulations and analytical modeling. One electrode is driven at 13.56 and 27.12 MHz with fixed but adjustable phase shift, θ , between the driving harmonics. First, the electron heating and ionization rates are studied, space and time resolved, for different phase shifts and pressures. The results are compared with those obtained for an electropositive gas (argon). In contrast to classical α-or γ-mode operation, we observe the electron heating and ionization rates to be high inside the bulk. This bulk heating mode is a consequence of the high electronegativity of CF 4 discharges, where the conductivity in the bulk is low due to the low density of electrons. Thus, a high electric field builds up to drive the RF current through the bulk causing a high electron mean energy and ionization rate in the discharge center. Second, we investigate the consequences of the bulk heating on the EAE. We focus on the electrical generation of a dc self-bias as a function of θ and the quality of the separate control of the ion mean energy and flux at the electrodes by tuning θ. Compared with argon discharges the high voltage drop across the plasma bulk and the specific ionization dynamics affect the bias generation and the separate control of ion properties. These effects are described and explained by an analytical model.

“…Displaying the trajectories up to given values of time, the temporal development of an electron avalanche can be visualized, as shown in figure 2. The collision cross sections have been taken from [12].…”

Section: Monte Carlo Simulation Of Electron Transportmentioning

confidence: 99%

“…The examples shown here relate to these two types of df discharges. The simulations are carried out for argon discharges, and the cross sections of the collision processes are taken from [12,42,73]. Figure 8 illustrates the results of a 1D PIC/MCC simulation of a dual-frequency rf discharge.…”

Section: Pic Simulation Of Radiofrequency Dischargesmentioning

confidence: 99%

Particle simulation methods for studies of low-pressure plasma sources

Donkó

2011

189

178

This paper illustrates the application of particle simulation methods for the description of low-pressure discharges: Townsend discharges, cathode fall dominated dc glows and capacitively coupled radiofrequency discharges. The spatially and/or temporally varying electric field and the presence of boundaries (e.g. electrodes) in these plasma sources induce a non-hydrodynamic (or non-equilibrium) transport of some types of charged species, particularly of electrons. Particle-based methods provide, even under non-equilibrium conditions, a correct method of mathematical description of the particle transport and the determination of the distribution functions, which are crucial quantities in discharge modeling.