Dry etching of GaAs was investigated in BCl3, BCl3/N-2 and BCl3/Ar discharges with a mechanical pump-based capacitively coupled plasma system. Etched GaAs samples were characterized using scanning electron microscopy and surface profilometry. Optical emission spectroscopy was used to monitor the BCl3-based plasma during etching. Pure BCl3 plasma was found to be suitable for GaAs etching at >100 mTorr while producing a clean and smooth surface and vertical sidewall. Adding N-2 or Ar to the BCl3 helped increase the etch rates of GaAs. For example, the GaAs etch rate was doubled with 20% N-2 composition in the BCl3/N-2 plasma compared to the pure BCl3 discharge at 150 W CCP power and 150 mTorr chamber pressure. The GaAs etch rate was similar to 0.21 pm/min in the 20 sccm BCl3 plasma. The BCl3/Ar plasma also increased etch rates of GaAs with 20% of Ar in the discharge. However, the surface morphology of GaAs was strongly roughened with high percentage (>30%) of N-2 and Ar in the BCl3/N-2 and BCl3/Ar plasma, respectively. Optical emission spectra showed that there was a broad BCl3-related molecular peak at 450-700 nm wavelength in the pure BCl3 plasma. When more than 50% N-2 was added to the BCl3 plasma, an atomic N peak (367.05 nm) and molecular N-2 peaks (550-800 nm) were detected. Etch selectivity of GaAs to photoresist decreased with the increase of % N-2 and Ar in the BCl3-based plasma. (C) 2010 Elsevier B.V. All rights reserved.