Mechanistic insights into high-efficiency polishing of AlN single crystals: synergistic effects of abrasives and oxidants

Chemical mechanical polishing (CMP) of aluminum nitride (AlN) requires a balance between high material removal rates (MRR) and atomic-level surface quality. This study systematically investigates the synergistic effects of abrasives (CeO 2 , Al 2 O 3 ) and oxidants (K 2 S 2 O 8 , KMnO 4 , H 2 O 2 ) on AlN polishing efficiency and interfacial mechanisms. Experimental results show that the combination of Al 2 O 3 abrasive and K 2 S 2 O 8 oxidant at pH 2.0 achieves an optimal MRR of 2.1 μm/h, outperforming KMnO 4 by 153%. Zeta potential and oxidation–reduction potential (ORP) analysis reveal strong specific electrostatic adsorption between negatively charged persulfate ions (S 2 O 8 2 ⁻) and positively charged Al 2 O 3 surfaces. Density functional theory (DFT) calculations further confirm that S 2 O 8 2 ⁻ exhibits the highest adsorption energy on Al 2 O 3 (−9.5 eV/molecule) and AlN (001) surfaces (−9.87 eV/molecule), promoting the formation of Al-O bonds. X-ray photoelectron spectroscopy (XPS) and differential charge density analyses demonstrate that K 2 S 2 O 8 treatment maximizes Al-O bonding (21.03%), facilitating oxidative removal. This work provides fundamental insights into abrasive-oxidant interactions for AlN CMP, enabling ultra-smooth AlN surface finishing (Sq < 0.18 nm, Ra < 0.05 nm) and thereby laying a theoretical foundation for high-efficiency AlN surface machining.