AVS 59th Annual International Symposium and Exhibition
    Energy Frontiers Focus Topic Wednesday Sessions
       Session EN+PS-WeM

Paper EN+PS-WeM12
Two-dimensional Simulations of Hydrogen and Hydrogen/Silane Capacitively Coupled Dual Frequency Discharges

Wednesday, October 31, 2012, 11:40 am, Room 15

Session: Plasmas for Photovoltaics and Energy Applications
Presenter: S. Mohr, Ruhr University Bochum, Germany
Authors: S. Mohr, Ruhr University Bochum, Germany
E. Schuengel, Ruhr University Bochum, Germany
J. Schulze, Ruhr University Bochum, Germany
U. Czarnetzki, Ruhr University Bochum, Germany
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Capacitively coupled radio-frequency (CCRF) discharges are commonly used in surface processing applications, for example the deposition of thin films. One of the most important challenges in optimizing CCRF discharges for this usage is achieving the ample and independent control of flux and energy of ions and reactive species at the surfaces, as these properties determine the quality and deposition rate of the films. This independent control can be attained by using electrically asymmetric discharges which use two consecutive harmonics to excite the plasma; the ion energy can be controlled by the phase between the two frequencies while the flux stays constant. The feasibility of this method has been demonstrated by both experiments and simulations in various gas mixtures [1-3], although limitations have been observed, for example in highly electronegative discharges.

Hydrogen is part of many gas mixtures used in industrial applications such as hydrogen/silane mixtures in the production of solar cells. Two traits, which distinguish hydrogen discharges from the already investigated gas mixtures, are the high ion mobility and the regular occurrence of field reversals during the sheath collapse. Additionally, deposition processes are usually carried out at quite high pressures of several 100 Pa. We conduct two-dimensional simulations of such discharges covering a wide range of discharge conditions (pressure: 20 Pa – 500 Pa, pure hydrogen discharges and hydrogen/silane mixtures) using the simulation tool Hybrid Plasma Equipment Model (HPEM) by Mark Kushner [4]. The focus of our investigations lies on the influence of high pressures, field reversals, and high ion mobilities on the separate control of ion energy and ion flux. For example, we observe a significant reduction of the ion energy control range, if field reversals are the main ionization source of the discharge. The physical mechanisms behind this effect and others occurring in hydrogen and hydrogen/silane - discharges will be discussed.

Funded by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (0325210B).

[1] U. Czarnetzki et al. 2011 PSST20 024010

[2] E. Schüngel et al. 2011 J. Phys. D.44 285205

[3] J. Schulze et al. 2011 PSST20 045008

[4] M. Kushner 2009 J. Phys. D42 194013