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Anisotropic etching of SiO2 films is reported in low frequency (∼100 kHz), moderate-pressure (0.35 Torr) CF4/O2 and NF3/Ar plasmas. Rates up to 2000 Å/min were achieved with high selectivity over GaAs and InP substrates. The etching mechanism was studied with optical spectroscopy and downstream chemical titrations. Anisotropy is attributed to ion-enhanced reactivity of fluorine atoms with SiO2 at rates up to two hundred times larger than purely chemical etching by fluorine atoms. Damage and product sputter desorption models of this process were evaluated. These two models are nearly mathematically equivalent at steady state, and show that the effectiveness of ions in etching by enhanced reaction is roughly 15 times that in physical sputtering under these conditions.

Hydrogen plasma exposure of n-type GaAs(Si) at 250 °C results in a decrease of the free-carrier concentration by several orders of magnitude. This neutralization effect has been demonstrated in silicon-doped layers grown by molecular beam epitaxy or formed by annealed implants as well as in bulk material. The same effect is produced electrochemically (H3PO4 electrolyte), whereas helium plasma exposure has no effect, thus confirming the role of hydrogen insertion. The hydrogen penetration depth into GaAs(Si) is inversely dependent on the Si concentration. Recovery of the electrical activity follows first order dissociation kinetics with a dissociation energy of 2.1 eV. Complete restoration of free-carrier concentration occurs by heating at 420 °C for less than 3 min. Extrapolated to low temperatures, these results imply many years of stability at 150 °C or below.

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