Control of plasma properties in capacitively coupled oxygen discharges via the electrical asymmetry effect

Abstract

To cite this version:E Schüngel, Q-Z Zhang, S Iwashita, J Schulze, L-J Hou, et al.. Control of plasma properties in capacitively coupled oxygen discharges via the electrical asymmetry effect. Journal of Physics D: Applied Physics, IOP Publishing, 2011, 44 (28) Abstract. By using a combined experimental, numerical and analytical approach, we investigate the control of plasma properties via the Electrical Asymmetry Effect (EAE) in a capacitively coupled oxygen discharge. In particular, we present the first experimental investigation of the EAE in electronegative discharges. A dual-frequency voltage source of 13.56 MHz and 27.12 MHz is applied to the powered electrode and the discharge symmetry is controlled by adjusting the phase angle θ between the two harmonics. It is found that the bulk position and density profiles of positive ions, negative ions, and electrons have a clear dependence on θ, while the peak densities and the electronegativity stay rather constant, largely due to the fact that the time averaged power absorption by electrons is almost independent of θ. This indicates that the ion flux towards the powered electrode remains almost constant. Meanwhile, the dc self-bias and, consequently, the sheath widths and potential profile can be effectively tuned by varying θ. This enables a flexible control of the ion bombarding energy at the electrode. Therefore, our work proves the effectiveness of the EAE to realize separate control of ion flux and ion energy in electronegative discharges. At low pressure, the strength of resonance oscillations, which are found in the current of asymmetric discharges, can be controlled with θ.

Electron heating via self-excited plasma series resonance in geometrically symmetric multi-frequency capacitive plasmas

“…neglecting the voltage drop across the plasma bulk, have the same absolute value. This symmetry is due to the phase shift of about π/2 between (all the harmonics of) the current and the applied voltage [19,75,77,80,81,85]. The self-excitation of PSR oscillations can be observed in all multi-frequency cases (N ≥ 2 in figure 5), whereas the amplitude of these high-frequency oscillations becomes larger as a function of N. Moreover, the excitation strength found in the PIC/MCC simulations can only be reproduced in the model, if the temporal variation of the bulk parameter β(ϕ) is taken into account; using the RF period averaged value (2π) −1 2π 0 β(ϕ)dϕ leads to a strong underestimation of the PSR oscillation amplitude.…”

“…Although this approach has led to strong improvements, the control is not ideal due to the effects of frequency coupling and secondary electrons [70][71][72][73][74]. Since 2008, an alternative approach, called Electrical Asymmetry Effect (EAE) [42,50,70,[75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94], has been investigated. In contrast to the superposition of two frequencies separated by about one order of magnitude in the "classical" dual-frequency approach, here the discharge is operated at a combination of a fundamental frequency with one or more of its subsequent harmonics.…”

“…Thus, the EAE provides a convenient way of controlling the ion energy independently of the ion flux. This concept has been tested in dual-frequency experiments [19,[75][76][77][78][79][80][81][82] and simulations [42,50,75,[80][81][82][83][84][85][86] and has proven to be beneficial for surface processing applications of CCRF plasmas [62,78,79]. The control range of the EAE can be extended by using more than two frequencies [88,89], also called voltage waveform tailoring (VWT) [90][91][92][93][94].…”

Plasma Induced Hydrophilic Cellulose Wound Dressing

“…Similar observations are valid for capacitively coupled high-frequency discharges except that the electrons are accelerated in DC self-bias sheath next to the smaller (powered) electrode. The physics of such discharges has been studied to detail in [40][41][42]. The heating of electrons follows a different mechanism in inductively coupled discharges, especially those created in pure H-mode [43].…”

The influence of the secondary electron induced asymmetry on the Electrical Asymmetry Effect in capacitively coupled plasmas

“…The mean ion energy at the electrodes can be changed by a factor of about 2 at nearly constant Γ i by tuning a) Electronic mail: korolov.ihor@wigner.mta.hu θ 14,16,17 . Studies of the EAE have been performed for different gases 17,[20][21][22][23][24] , harmonics' amplitudes 25 , fundamental frequencies 26 , and numbers of consecutive driving harmonics 27,28 .…”