Temperature dependence of reactive ion etching of GaAs with CCl2F2:O2

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Abstract
The etch rate of GaAs during reactive ion etching (RIE) in a CCl2F2:O2 discharge (4 mTorr, 0.56 W cm−2) shows a strong temperature dependence, increasing from ∼500 Å min−1 at 50 °C to 2800 Å min−1 at 400 °C. Arrhenius plots of the etch rate show two activation energies (0.17 eV from 50 to 150 °C and 0.11 eV from 150 to 400 °C). There is no significant plasma power density dependence of the etch rate at elevated temperatures (≥100 °C) in contrast to the strong dependence at 50 °C. The surface morphology undergoes smooth‐to‐rough‐to‐smooth‐to‐rough transitions at ∼150, 250, and 400 °C, respectively, although TiPtAu Schottky diodes exhibit near‐ideal behavior on GaAs etched at 150 °C. The As‐to‐Ga ratio in the first 100 Å from the surface increases with increasing RIE temperature, with chloride residues absent above 150 °C. Fluorocarbon residues were present on all samples, but were limited to the first 10–15 Å. As determined by x‐ray photoelectron spectroscopy, fluorine was present almost exclusively as metallic gallium fluorides, while oxygen was present as both Ga and As oxides. Ion channeling detected lattice disorder to depths of ∼200 Å for etch temperatures from 50 to 250 °C, while there was less damage for etching at 400 °C. No new RIE‐induced deep levels were observed by capacitance transient spectroscopy in any of our samples, although the concentration of the midgap donor EL2 increased with increasing temperature during the RIE process.

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