Inductively coupled plasma reactive ion etching of rutile-structured Ge0.64Sn0.36O2 with BCl3/Ar plasmas

Rutile-phase GexSn1−xO2 (GTO) is a promising ultra-wide bandgap semiconductor for future high-power and RF electronics. In this study, we present an BCl3/Ar inductively coupled plasma reactive ion etch (ICP-RIE) for RF-sputtered, rutile-phase Ge0.64Sn0.36O2 films. Under optimized etch conditions, GTO was etched at a rate of 61.8 nm min−1 with a selectivity of 0.35 to the photoresist SPR220. The selectivity can be improved to 0.45 by lowering ICP coil power, which also reduces the GTO etch rate to 38.8 nm min−1. Sidewall redeposition or “fencing” occurred, likely due to Si-assisted polymer formation and was eliminated by blanket coating the Si carrier wafer with photoresist. Erosion of the photoresist mask’s sidewalls caused features to narrow and round. Atomic force microscopy scans showed smoothing of the plasma-exposed regions with an rms roughness, Rq, of 2.45 nm in exposed regions vs 5.53 nm in areas protected by resist. In summary, we have identified a BCl3/Ar ICP-RIE process window for patterning rutile GTO thin films for future high performance device fabrication.