Dry etching process of GaAs in capacitively coupled BCl 3-based plasmas

Abstract

Dry etching of GaAs was investigated in BCl 3, BCl 3/N 2 and BCl 3/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 BCl 3-based plasma during etching. Pure BCl 3 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 BCl 3 helped increase the etch rates of GaAs. For example, the GaAs etch rate was doubled with 20% N 2 composition in the BCl 3/N 2 plasma compared to the pure BCl 3 discharge at 150 W CCP power and 150 mTorr chamber pressure. The GaAs etch rate was ∼ 0.21 µm/min in the 20 sccm BCl 3 plasma. The BCl 3/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 BCl 3/N 2 and BCl 3/Ar plasma, respectively. Optical emission spectra showed that there was a broad BCl 3-related molecular peak at 450–700 nm wavelength in the pure BCl 3 plasma. When more than 50% N 2 was added to the BCl 3 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 BCl 3-based plasma.