Real Time Optical Monitoring of III-V Semiconductor Wet Chemical Etching

摘要

Spectroscopic ellipsometry (SE) was used to study the effects of wet chemical etching and oxidation on GaAs and Al(0.3)Ga(0.7)As. Etch solutions were mixtures of citric acid, hydrogen peroxide, and water, with various volume ratios. Oxidation in both H2O2 and H2O was studied. Etch rates of GaAs and AlGaAs were determined from real time SE (RTSE) measurements during etching of heterostructures. The surface condition was also studied, with strong differences observed between fast-etch and slow-etch solutions. Use of RTSE as an etch-stop detector, either at the end of a layer or at a preselected depth within a layer, was demonstrated, with a precision of several rim during nonselective etching. Etch control was also demonstrated using focused-beam RTSE, in which the optical beam diameter was reduced from several mm to about 150 microns. Finally, application of RTSE to patterned surfaces yielded a surprising and useful interference effect which can be used to monitor etch depth into bulk material.