Synergistic mechanism of multi-energy fields: achieving atomic-scale smooth GaN surfaces via ultrasonic vibration-assisted electrochemical mechanical polishing

As a prominent representative of third-generation semiconductor materials, gallium nitride (GaN) exhibits superior characteristics and extensive application prospects. However, the high hardness and chemical inertness of GaN wafers present substantial obstacles to enhancing the polishing efficiency. To address this issue, a novel approach of ultrasonic vibration-assisted electrochemical mechanical polishing (UV-ECMP) technique was proposed. Fluorescence intensity experiments, X-ray photoelectron spectroscopy (XPS), molecular dynamics (MD) simulations, nanoscratch experiments, and scanning electron microscopy (SEM) were employed to elucidate the atomic-scale material removal mechanism during UV-ECMP. It is demonstrated that ultrasonic vibration can enhance the electrochemical oxidation activity of the polishing slurry, thereby promoting the formation of the gallium oxide (Ga₂O₃) layer on the GaN surface. Furthermore, cavitation effects induced by ultrasonic vibration generate porous structures and extensive microcracks on the oxide layer, facilitating subsequent material removal. Meanwhile, ultrasonic vibration reduces the average normal force exerted on abrasives, minimizing subsurface damage and yielding a smooth surface. Finally, a material removal rate (MRR) of 1327 nm/h and a surface roughness R_aof 0.264 nm were achieved. This novel hybrid multi-energy field-assisted polishing technique provides significant insights into efficient GaN processing with superior surface quality while streamlining wafer manufacturing processes.