Self-terminated etching of GaN with a high selectivity over AlGaN under inductively coupled Cl₂/N₂/O₂ plasma with a low-energy ion bombardment

Highlights: • A highly selective dry etching technique of GaN in Cl₂/N₂/O₂ plasma has been successfully developed for the micro-fabrication of GaN/AlGaN heterostructures with a self-termination at the surface of AlGaN layer. • Element distribution of the as-etched structure has been examined in detail by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS), showing a result of self-consistency. • According to the experimental results, a model is proposed about the etching self-termination. Formation of (Al,Ga)O_x film at the outmost, together with oxygen penetration into the AlGaN layer, leads to the self-termination when the O-containing ICP etching reaches the AlGaN layer. • The as-developed selective etching technique has enabled a uniform and reproducible process for the fabrication of III-nitride enhancement mode power electronic devices. - Abstract: Etching of GaN/AlGaN heterostructure by O-containing inductively coupled Cl₂/N₂ plasma with a low-energy ion bombardment can be self-terminated at the surface of the AlGaN layer. The estimated etching rates of GaN and AlGaN were 42 and 0.6 nm/min, respectively, giving a selective etching ratio of 70:1. To study the mechanism of the etching self-termination, detailed characterization and analyses were carried out, including X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). It was found that in the presence of oxygen, the top surface of the AlGaN layer was converted into a thin film of (Al,Ga)O_x with a high bonding energy, which effectively prevented the underlying atoms from a further etching, resulting in a nearly self-terminated etching. This technique enables a uniform and reproducible fabrication process for enhancement-mode high electron mobility transistors with a p-GaN gate.