Revealing Mechanisms of an Eco-Friendly GaN Electrochemical Mechanical Removal Process Modified with Green Fenton Reaction

Gallium Nitride (GaN), a leading third-generation semiconductor material, offers exceptional properties and broad application potential. However, its high hardness and chemical inertness make GaN wafers difficult to process, posing significant challenges in improving the polishing efficiency. During the electrochemical mechanical polishing (ECMP) process, the oxidation effect on the GaN surface critically affects the material removal rate (MRR). While various methods have been developed to enhance the concentration of hydroxyl radicals (OH*) to improve the process, their instability and rapid decomposition present further obstacles to maintaining concentration and stability. The present study proposed a novel approach using sodium tripolyphosphate (STPP) as an electrolyte additive for ECMP under a green Fenton reaction. Furthermore, the MRR and surface roughness (R_a) of GaN-ECMP were comprehensively evaluated. Atomic force microscopy (AFM) was used to observe the surface morphologies of GaN wafers after ECMP. Energy-dispersive spectrometry (EDS) and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the generated oxide layers. The nanoscratch tests were conducted to reveal the material removal mechanisms of GaN under the synergistic effect of STPP and Fe²⁺. The results indicated that an efficient GaN-ECMP process (MRR > 800 nm/h) with good surface quality (R_a < 0.33 nm) can be realized by employing STPP as electrolyte additives. This study breaks the limitation of iron precipitate formation in the ECMP slurries during the Fenton reaction. It extends the lifetime of the hydroxyl radicals (OH*) produced by the Fenton reaction, which presents a beneficial exploration of seeking an eco-friendly polishing slurry for GaN-ECMP.