CITRIC-ACID ETCHING OF GAAS1-XSBX, AL0.5GA0.5SB, AND INAS FOR HETEROSTRUCTURE DEVICE FABRICATION

Citric acid/hydrogen peroxide (C6H8O7:H2O2) at volume ratios from 0.2: 1 to 20:1 was found to provide selective etching between GaAs1-xSbx (x =0.15 to 1.0), Al0.5Ga0.5Sb, InAs, and various III-V semiconductor mat erials for use in new GaAs and InP based heterostructure transistors a nd optoelectronic devices. By choosing different concentration volume ratios of citric acid to hydrogen peroxide (chi C6H8O7:1H(2)O(2)), hig hly selective as well as uniform (nonselective) etching regions were f ound to exist in these material systems. Etchant selectivities greater than 50 were found for most combinations of the III-V semiconductor m aterials under investigation, with selectivities of over 100 measured for GaAs/GaSb and InAs/GaSb material combinations, and with selectivit ies of over 3850 calculated for InAs/Al0.5Ga0.5Sb to 13,650 for GaAs/A l0.5Ga0.5Sb. The highest overall etch rates were measured for InAs and the lowest etch rates were found for Al0.5Ga0.5Sb. The etch rate for the GaAs1-xSbx materials systematically decreased from the highest etc h rate for the smallest Sb mole fraction examined of GaAs0.85Sb0.15 to the lowest etch rate for GaSb. The dramatic change in etch rate with citric acid/hydrogen peroxide volume ratio previously observed for the GaAs/AlGaAs material system was also observed for GaAs0.85Sb0.15, but this effect was not seen in higher Sb mole fraction alloys of GaAs1-x Sbx examined. Al0.5Ga0.5Sb and GaSb were found to have very low etch r ates with this etchant system at all volume ratios, making both materi als suitable as an etch stop layer for simplified processing in device fabrication. Finally, citric acid/hydrogen peroxide can be used to pr eferentially etch these materials through a photoresist mask, since it does not erode photoresist at any volume ratio.