Reactive ion etching of GaAs with CCl2F2:O2: Etch rates, surface chemistry, and residual damage

Abstract

The reactive ion etching of GaAs with a CCl2F2:O2 discharge was investigated as a function of gas flow rate (10–60 sccm), total pressure (2–50 mTorr), power density (0.25–1.31 W cm−2), gas composition (0%–70% O2), and etch time (1–64 min). The etch rate decreases with increasing gas flow rate, increases with increasing power density, and goes through a maximum at a gas composition of 75:25 CCl2F2:O2 under our conditions. After etching at low-power densities (0.56 W cm−2) and for high CCl2F2 ratios (19:1 to O2), carbon and chlorine could be detected in the GaAs to a depth of less than 15 Å by x-ray photoelectron spectroscopy. Under these conditions there was a Ga deficiency to a depth of ∼100 Å, which we ascribe to surface roughening and the preferential vaporization of As2O3 over Ga2O3. At high-power densities (1.31 W cm−2) a polymeric layer several hundred angstroms thick containing CCl and CF bonds was observed on the GaAs surface. Etching under O2-rich conditions did not lead to any additional creation of surface oxides. Both ion channeling and electron microscopy detected a thin disordered layer on the GaAs after etching. Small (<100 Å diam) dislocation loops were present at a depth varying from ∼400 Å for 0.56 W cm−2 (380-V self-bias) plasma power density to ∼2200 Å for 1.31 W cm−2 (680-V self-bias). The disorder was stable against a 500 °C annealing treatment.