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

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.