Plasma passivation of etch-induced surface damage on GaAs

Abstract

Various plasma passivation techniques for removal of etch-induced damage on GaAs have been studied. It was found that a Cl2 plasma generated with an electron cyclotron resonance source can efficiently remove dry etch-induced damage with minimal etching of the GaAs. Complete recovery of the electrical characteristics of both the Schottky diodes and unalloyed transmission lines was found with a 30 s Cl2 plasma passivation at 25 °C. The chlorine reactive species used for passivation were generated with 50 W microwave power at 2 mTorr without any rf power applied at the stage. The Cl2 passivated surface was thermally stable up to 450 °C. Similar recovery was also observed for diodes passivated with a N2 plasma. Compared to Cl2, however, N2 plasma passivation requires a higher temperature (350 °C) and higher microwave power (500 W). Capacitance–voltage measurements show that the presence of H2 in the plasma during passivation results in dopant depletion near the surface, but the dopants can be reactivated after annealing at temperature ≥450 °C for 3 min. Plasma passivation with H2S was found to result in a partial recovery of the electrical characteristics for the etched diodes and transmission lines. Annealing at 300 °C is also required after H2S plasma passivation to desorb the excess S on the GaAs surface. Changes in the defect density as a function of the conditions used for passivation have been correlated to Schottky diode characteristics.