Selective etching of GaAs over Al0.2Ga0.8As semiconductor in pulsed DC BCl3/SF6 plasmas

Selective dry etching of GaAs over Al0.2Ga0.8As in pulsed DC BCl3/SF6 plasmas was studied. The process variable was the composition of SF6 gas flow rate (0–50% ) in the BCl3/SF6 plasmas. The total flow rate of the gases was 20sccm. The other plasma conditions were held constant at 13.33Pa chamber pressure, 500V pulsed DC voltage, 200kHz frequency and 0.7μs reverse time. Only a mechanical pump was used for the processing. Oscilloscope data showed that there was little variation of the input voltage and current on the chuck with the composition change. 10% mixing of SF6 in the BCl3/SF6 plasma produced the highest etch selectivity (48:1) of the GaAs over the Al0.2Ga0.8As. However, further addition of the SF6 gas to the plasma reduced the etch rate of GaAs and the selectivity. The GaAs and AlGaAs would not etch when the SF6 composition was ≥30% in the plasma. The root mean square surface roughness of the GaAs was 0.7–1.3nm after etching. The overall results indicated that the best selective etching was achieved at 10% SF6 composition in the pulsed DC BCl3/SF6 plasma.