Dry etching process of GaAs in capacitively coupled BCl3-based plasmas

Dry etching of GaAs was investigated in BCl3, BCl3/N2 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 N2 or Ar to the BCl3 helped increase the etch rates of GaAs. For example, the GaAs etch rate was doubled with 20% N2 composition in the BCl3/N2 plasma compared to the pure BCl3 discharge at 150 W CCP power and 150 mTorr chamber pressure. The GaAs etch rate was ∼ 0.21 µm/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 N2 and Ar in the BCl3/N2 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% N2 was added to the BCl3 plasma, an atomic N peak (367.05 nm) and molecular N2 peaks (550–800 nm) were detected. Etch selectivity of GaAs to photoresist decreased with the increase of % N2 and Ar in the BCl3-based plasma.