Study of dry etched N-polar (Al)GaN surfaces obtained by inductively coupled plasma etching

Abstract

We report the Cl-based inductively coupled plasma etching of N-polar Al(Ga)N layers obtained from layer transfer. It is found that debris appeared on the etched N-polar surface after exposing in air for a short period whereas the etched Al-/Ga-polar surface was clean and smooth. The debris can be completely self-vanished on the N-polar Al0.4Ga0.6N surface after exposing in air for a few hours but still remained on the N-polar GaN surface even after over 1 month. The surface chemical analysis results suggested that the debris is the result of Cl-related byproduct generated during the etching process. Byproducts like Al(Ga)Clx and its derivatives are believed to cover on the N-polar surface after the inductively coupled plasma etching and increase the etched surface roughness significantly. The formation and disappearance of debris are attributed to the formation of Al(Ga)Clx⋅ 6H2O crystals when Al(Ga)Clx absorbs moisture in the air and its spontaneous decomposition on the N-polar surface, respectively. Adding O2/SF6 in the process helps remove Al(Ga)Clx byproducts but at the cost of roughened surface/reduced etch rate. With an additional cleaning process after etching, an uniform and smooth N-polar GaN surface with a low root-mean-square surface roughness of 0.5–0.6 nm has been successfully obtained at a reasonable etch rate (∼150 nm/min). The results can provide valuable guidance for the fabrication of high-performance N-polar GaN devices.

High-Performance N-Polar GaN/AlGaN Metal–Insulator–Semiconductor High-Electron-Mobility Transistors with Low Surface Roughness Enabled by Chemical–Mechanical-Polishing-Incorporated Layer Transfer Technology

“…As counted in Table 1, a significant Ga deficiency was evident after ICP treatment compared to the CMP sample, and the ICP sample had higher oxygen content (4.51%) and carbon content (15.6%) than those (1.27% and 8.09%) of the CMP sample, along with chlorine content (0.51%) on its surface. Byproducts like Al(Ga)Cl x cannot be easily removed from the N-polar surface during ICP etching [18]. The presence of ion bombardment appears to degrade the electrical characteristics through ion-related chemical changes [19].…”