Towards atomic-scale smooth surface manufacturing of β-Ga₂O₃ via highly efficient atmospheric plasma etching

Abstract The highly efficient manufacturing of atomic-scale smooth β-Ga₂O₃ surface is fairly challenging because β-Ga₂O₃ is a typical difficult-to-machine material. In this study, a novel plasma dry etching method named plasma-based atom-selective etching (PASE) is proposed to achieve the highly efficient, atomic-scale, and damage-free polishing of β-Ga₂O₃. The plasma is excited through the inductive coupling principle and carbon tetrafluoride is utilized as the main reaction gas to etch β-Ga₂O₃. The core of PASE polishing of β-Ga₂O₃ is the remarkable lateral etching effect, which is ensured by both the intrinsic property of the surface and the extrinsic temperature condition. As revealed by density functional theory-based calculations, the intrinsic difference in the etching energy barrier of atoms at the step edge (2.36 eV) and in the terrace plane (4.37 eV) determines their difference in the etching rate, and their etching rate difference can be greatly enlarged by increasing the extrinsic temperature. The polishing of β-Ga₂O₃ based on the lateral etching effect is further verified in the etching experiments. The Sa roughness of β-Ga₂O₃ (001) substrate is reduced from 14.8 nm to 0.057 nm within 120 s, and the corresponding material removal rate reaches up to 20.96 μm·min⁻¹. The polished β-Ga₂O₃ displays significantly improved crystalline quality and photoluminescence intensity, and the polishing effect of PASE is independent of the crystal face of β-Ga₂O₃. In addition, the competition between chemical etching and physical reconstruction, which is determined by temperature and greatly affects the surface state of β-Ga₂O₃, is deeply studied for the first time. These findings not only demonstrate the high-efficiency and high-quality polishing of β-Ga₂O₃ via atmospheric plasma etching but also hold significant implications for guiding future plasma-based surface manufacturing of β-Ga₂O₃.