SELECTIVE AND NONSELECTIVE RIE OF GAAS AND AL(X)GA(1-X)AS IN SICL4 PLASMA

An anisotropic Reactive Ion Etching (RIE) process has been developed using SiCl4 for etching GaAs/AlGaAs. Using a low rf power of less than or equal to 15 W and hence a low de bias of less than or equal to 70 V, a low flow rate of 6 seem, a pressure of 9 mtorr, we obtained an extraordinarily high selectivity > 10000:1 for etching GaAs/A1GaAs. A very thin Al0.3Ga0.7As layer (4 monolayers 1.1 nm thick) served to stop the etching, while maintaining very good anisotropy. It seems likely that etching is stopped by an involatile layer of A(l)2O(3) or ALN formed by residual oxygen, air or moisture in the chamber. At flow rates higher than 12 seem so a pressure > 14 mtorr and at 15 W rf power the selectivity rapidly deteriorates. A relative etch ratio of 1.35:1 for GaAs:AlGaAs was obtained using 12 seem, 15 mtorr and 15 W power. In this case, the etch profile of the AlGaAs layer is undercut. To improve the verticality of AlGaAs while using low powers and hence under low damage conditions, a system with a load lock is required.