DAMAGE-FREE AND SELECTIVE RIE OF GAAS/ALGAAS IN SICL4/SIF4 PLASMA FOR MESFET AND PSEUDOMORPHIC HEMTS GATE RECESS ETCHING

An apparently damage free and selective Reactive Ion Etching (RIE) process has been developed using a mixture of SiCl4/SiF4 plasma for etching GaAs/AlGaAs. Using a rf power of 9-12 W and hence a low dc bias of less-than-or-equal-to 35 V, with a flow rate ratio of (2-3):9 sccm of SiCl4:SiF4, the selectivities we obtained are extraordinarily high >5000:1. No surface induced damage by this process can be detected. Raman scattering measurements made on a heavily doped GaAs layer showed that the etched surfaces improved on etching. Hall effect measurements on pseudomorphic HEMT material structure showed no detectable modification of the sheet carrier concentration even after 10 minute of continuous bombardment of the active layer. This SRIE has been applied to the recessing of T-shaped gates and the lateral etching rate of these gates could be suppressed to <10 nm/min, resulting in a precise control of the gate off-set and hence effective gate length.