A study of defects induced in GaAs by plasma etching

The effect of plasma dry etching on GaAs has been studied by photoreflectance (PR) and deep-level transient spectroscopy (DLTS). GaAs samples were etched by CF₄ plasma under different conditions to study the influence of sputtering chamber pressure and power on surface properties. Rapid thermal annealing (RTA) was conducted to remove plasma-induced damage. Schottky diodes were fabricated on the plasma etched wafers for electrical characterization. A 10 mTorr/50 W plasma etched sample showed two new peaks with energies lower than the bandgap energy which may imply defect introduction. Plasma processing at 50 mTorr/100 W and 100 mTorr/150 W also showed damage with a reduced PR signal and one lower energy peak. Franz-Keldysh oscillation (FKO) was observed in most samples. The FKO period was used to characterize sample surface quality. DLTS measurement showed plasma-induced deep levels on every plasma etched sample. The higher chamber pressure and power gave increased activation energy. Activation energies of 0.38, 0.57 and 0.67 eV were found for 10, 50 and 100 mTorr chamber pressure etching conditions, respectively. The 450°C/10 s RTA showed very good recovery on all plasma-induced damage.