Dry etching of GaAs in asymmetric bipolar pulsed dc BCl3 plasmas

Abstract

Dry etching of GaAs in asymmetric bipolar pulsed dc BCl3 plasmas using only mechanical pumping is reported. The mean pulsed dc voltage on the cathode was used as a process variable in the experiment. When the mean pulsed dc voltage changed from −350 to −550 V at the cathode electrode, the dependent mean current and power were increased from 0.22 to 0.33 A and from 100 to 220 W, respectively. The etch rate of GaAs increased from 0.01 to 0.55 μm/min, and etch selectivity over photoresist was also strongly increased from 0.2:1 to 2.2:1 with this voltage change. The threshold mean voltage for plasma ignition pulsed dc plasma was −350 V. Scanning electron microscopy micrographs showed that dry etching at −500 V provided excellent surface smoothness (rms roughness of ∼1 nm) and sidewall passivation. At a lower mean voltage of −400 V, there was a rough surface and some undercutting of GaAs after etching at −400 V. Degradation of the photoresist surface was negligible in both cases.