Crystallographic etching of GaAs with bromine and chlorine plasmas

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Abstract
We report results that show (100)GaAs can be crystallographically etched by a bromine or chlorine plasma. Specifically, {110}, {100}, and {111}A crystal facets develop under masked portions when the substrate is etched under ‘‘isotropic’’ or chemical plasma etching conditions (0.15–0.30 Torr, 0.1–14 MHz, ≲0.5 W cm−2). The etch rate of GaAs(100) is ∼20 to ∼70 μ/min in a pure Br2 discharge under these conditions. Absolute Br and Br2 concentrations were measured as a function of applied frequency by absorption spectroscopy. Relative optical emission from Br, Br+, and Br+2 was also recorded. The relationship between Br emission at 700.5 nm and Br concentration is quantitatively accounted for by an increase in the population of electrons above 13.5 eV with discharge frequency. The etch rate of GaAs(100) is directly proportional to Br concentration, and increases by a factor of 2.0 between 0.1 and 14 MHz.