A particle-in-cell/Monte Carlo simulation of a capacitively coupled chlorine discharge

Shuo Huang,J T Gudmundsson

doi:10.1109/plasma.2014.7012492

Abstract

We demonstrate the oopd1 (object oriented plasma device for one dimension) particle-in-cell/Monte Carlo simulation tool for the capacitively coupled chlorine discharge with a comprehensive reaction set [1]. We explore a typical capacitively coupled chlorine discharge operated at both single frequency [1] and dual frequency [2,3] using oopd1 and obtain key plasma parameters, including particle density, effective electron temperature, electron energy probability function and ion energy and angular distributions for both Cl + and Cl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + ions. The dependence of the plasma parameters on the discharge pressure, driving frequency, driving current density and secondary electron emission, is systematically investigated. As the pressure increases from 5 mTorr to 100 mTorr, the heating mechanism evolves from both stochastic and ohmic heating to predominantly ohmic heating and the electron heating outweighs the ion heating at high pressure. Also, the density profile for Cl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + and Cl − ions becomes flat in the bulk region and the electronegativity increases with increasing pressure. The creation of Cl + ions in the sheath region is mainly due to conversion from Cl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + ions to Cl+ ions through non-resonant charge exchange, while in the bulk region the creation of Cl + ions is mainly ascribed to electron impact ionization processes. As the low-frequency current density is increased the flux of Cl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + ions to the surface increases only slightly while the average energy of Cl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + ions to the surface increases almost linearly with increasing low-frequency current, which shows possible independent control of the flux and energy of Cl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + ions by varying the low-frequency current in a dual-frequency capacitively coupled chlorine discharge. However, the increase of the flux of Cl + ions with increasing low-frequency current, which is mainly due to the increased dissociation fraction of the background gas caused by extra power supplied by the low-frequency source, is undesirable.

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