Characterization of GaAs/AlxGa1−xAs selective reactive ion etching in SiCl4/SiF4 plasmas

Abstract

Selective reactive ion etching of GaAs over AlxGa1−xAs using SiF4/SiCl4 gas mixtures is studied. Etch rates of GaAs and AlxGa1−xAs are measured versus pressure, etch gas ratio, and plasma self-bias voltage. A selectivity ratio of 500:1 has been obtained for GaAs over Al0.35Ga0.65As at a gas composition ratio of SiCl4/SiF4=0.25, a pressure of 60 mTorr, and a self-bias voltage of −60 V. The etch stop mechanism is studied using Auger electron spectroscopy. Auger surface scan spectra indicate a high concentration of fluorine at the surface of etched AlGaAs samples suggesting the formation of an AlF3 etch stop layer.1 It is also shown that the AlF3 layer is easily removed with a very short dip in HCl/H2O or NH4OH/H2O. Hall effect measurements at 300 and 77 K are made on etched GaAs/Al0.3Ga0.7As modulation doped heterostructures to determine the effect of low-power etching on two-dimensional electron gas (2-DEG) sheet concentrations and carrier mobility. Slight reduction in both 2-DEG sheet carrier concentration and mobility are observed after the RIE process. This may be an indication of ion-beam induced damage to the AlGaAs/GaAs heterostructure. Finally, the effects of extended etching on the dc and microwave device characteristics of short gate length GaAs/AlGaAs/InGaAs MODFETs are reported.