SELECTIVE REACTIVE ION ETCHING IN SICL4/SIF4 PLASMAS FOR GATE RECESS IN GAAS/ALGAAS MODULATION-DOPED FIELD-EFFECT TRANSISTORS

Various issues concerning the utilization of SiCl4/SiF4 selective reactive ion etching (SRIE) for gate recess in the fabrication of GaAs/AlGaAs modulation-doped field effect transistors (MODFETs) have been studied. Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy, and Schottky diode measurements were performed to determine the effects of SRIE and post-SRIE processing on the surface conditions of GaAs and A]GaAs layers. Hall measurements were conducted at 300 and 77 K to characterize the degradation of the two-dimensional electron gas properties of GaAs/Al0.3Ga0.7As heterostructures due to ion bombardment during SRIE. Finally, direct-current and high-frequency measurements were performed on dry-etched GaAs/Al0.3Ga0.7As MODFETs to determine the effects of SRIE on device performance. It is shown that extensive overetching at low plasma voltages (< 90 V) during gate recessing results in an increase in the device threshold voltage, but has little effect on the gate-to-drain breakdown voltage, maximum transconductance, and unity current gain frequency of the devices.