PLASMA PASSIVATION OF ETCH-INDUCED SURFACE DAMAGE ON GAAS

Various plasma passivation techniques for removal of etch-induced dama ge on GaAs have been studied. It was found that a Cl-2 plasma generate d with an electron cyclotron resonance source can efficiently remove d ry etch-induced damage with minimal etching of the GaAs. Complete reco very of the electrical characteristics of both the Schottky diodes and unalloyed transmission lines was found with a 30 s Cl-2 plasma passiv ation at 25 degrees C. The chlorine reactive species used for passivat ion were generated with 50 W microwave power at 2 mTorr without any rf power applied at the stage. The Cl-2 passivated surface was thermally stable up to 450 degrees C. Similar recovery was also observed for di odes passivated with a N-2 plasma. Compared to Cl-2, however, N-2 plas ma passivation requires a higher temperature (350 degrees C) and highe r microwave power (500 W). Capacitance-voltage measurements show that the presence of H-2 in the plasma during passivation results in dopant depletion near the surface, but the dopants can be reactivated after annealing at temperature greater than or equal to 450 degrees C for 3 min. Plasma passivation with H2S was found to result in a partial reco very of the electrical characteristics for the etched diodes and trans mission lines. Annealing at 300 degrees C is also required after H2S p lasma passivation to desert, the excess S on the GaAs surface. Changes in the defect density as a function of the conditions used for passiv ation have been correlated to Schottky diode characteristics. (C) 1995 American Vacuum Society.