Optimization of reactive ion etching of Al0.48In0.52As in CH4/H2 by the experimental design method

Abstract

The use of methane/hydrogen for reactive ion etching (RIE) of III–V compounds offers several advantages when compared to other chemistries. It shows a widespread use for etching of InP, GaAs, and related compounds for fabrication of optoelectronic devices, transistors, and mesoscopic systems. In the present work the etching of Al0.48In0.52As lattice matched to InP has been optimized by an experimental design technique by measuring the etch rate, the dc self-bias, and the polymer formation as function of the following process parameters: total flow, methane content, pressure, and rf power. Results show that interactions between process parameters cannot be disregarded. The optimized process parameters are 90 sccm, 13.2% of CH4 in H2, 60 mTorr, and 100 W. At this setup the process is diffusion limited, showing a maximum etch rate at 60 mTorr and strong sputtering action. Atomic force microscopy (AFM) shows that the trench quality is better compared to wet phosphoric based chemistry [2.07 nm root mean square (rms) versus 4.65 nm rms]. X-ray photoelectron spectroscopy shows, when compared to a wet-etched reference, a strong surface depletion of arsenic ([As]ref/[As]etch=15) and an increase in the aluminum and indium concentration ([Al]ref/[Al]etch=0.2; [In]ref/[In]etch=0.3). Before etching the surface consists mainly of indium oxide, aluminum oxide, pure As, and a small amount of arsenic oxide. After etching aluminum oxide is still present but the other oxides are being replaced by InAs compounds.