Highly selective GaAs/AlGaAs dry etching using HBr/SF6/He

Selective etching of GaAs is critical for many applications, including flat optical components and high electron mobility transistors. It is long-known that F-containing process gases produce a nonvolatile AlFx layer on AlGaAs. In this work, we present a selective GaAs etch using an inductively coupled plasma with an HBr/SF6/He etch chemistry. The optimized process exhibits >1μm/min etch rates, >200:1 GaAs:AlGaAs selectivity, >50:1 GaAs:photoresist selectivity, sub-nm surface roughness, and minimal undercut. The effect of aspect ratio is investigated, revealing limitations for deposition of an Si-rich passivation layer. Moreover, selectivity dramatically increases with an AlGaAs etch stop with high (90%) Al content. By characterizing an HBr-based selective GaAs etch, this work provides a possible alternative to the better established chlorine-based selective processes.