Plasma Passivation of Etch-Induced Surface Damage on GaAs

摘要

Various plasma passivation techniques for removal of etch-induced damage on GaAshave 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 deg 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 deg 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 deg 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 deg 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 deg 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.