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

An apparently damage free and selective Reactive Ion Etching (RIE) pro cess has been developed using a mixture of SiCl4/SiF4 plasma for etchi ng 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 >50 00:1. No surface induced damage by this process can be detected. Raman scattering measurements made on a heavily doped GaAs layer showed tha t the etched surfaces improved on etching. Hall effect measurements on pseudomorphic HEMT material structure showed no detectable modificati on of the sheet carrier concentration even after 10 minute of continuo us bombardment of the active layer. This SRIE has been applied to the recessing of T-shaped gates and the lateral etching rate of these gate s could be suppressed to <10 nm/min, resulting in a precise control of the gate off-set and hence effective gate length.