One-dimensional Ar-SF6 hydromodel at low-pressure in e-beam generated plasmas

Abstract

A one-dimensional steady-state hydrodynamic model of electron beam generated plasmas produced in Ar-SF6 mixtures at low pressure in a constant magnetic field was developed. Simulations were performed for a range of SF6 partial pressures at constant 30 mTorr total gas pressure to determine the spatial distribution of species densities and fluxes. With the addition of small amount of SF6 (∼1%), the confining electrostatic field sharply decreases with respect to the pure argon case. This effect is due to the applied magnetic field inhibiting electron diffusion. The hallmark of electronegative discharge plasmas, positive ion—negative ion core and positive ion—electron edge, was not observed. Instead, a plasma with large electronegativity (∼100) is formed throughout the volume, and only a small fraction (≈30%) of the parent SF6 molecules were dissociated to F2, SF2, and SF4. Importantly, F radical densities were found to be very low, on the order of the ion density. Model predictions for the electron density, ion density, and plasma electronegativity are in good agreement with experimental data over the entire range of SF6 concentrations investigated.