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

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.