Study on the mechanism of chemical mechanical polishing on high-quality surface of single crystal diamond

Due to the ultra-high hardness and excellent chemical inertness of single crystal diamond (SCD), achieving a high-quality surface of SCD by chemical mechanical polishing (CMP) is challenging. To obtain a high-quality surface of SCD, we developed a novel slurry containing a mixed oxidant of hydrogen peroxide (H2O2) and potassium ferrate (K2FeO4). The surface micro-morphology, profile, roughness, and damage layer characteristics of SCD were characterized by a 3D surface optical profiler, atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscope (TEM). Simultaneously, the reasons for the formation of high-quality surface of SCD were investigated. The results demonstrated that the polished SCD surface was smooth and scratch-free with an average Ra of 0.681 ± 0.023 nm over six areas of 868 × 868 μm2 and a damage layer thickness of 0.6 nm. Furthermore, the state of the chemical bonds of elements on the SCD surface was surveyed by X-ray photoelectron spectroscopy (XPS), and the polishing mechanism was deduced as follows: hydroxyl radicals were adsorbed on the SCD surface to oxidize and formed COH and CO bonds, while the damage due to lattice distortion resulted in the breakage of the CC bond to achieve carbon atom removal.