A novel slurry for chemical mechanical polishing of single crystal diamond

Abstract

Single crystal diamond (SCD) has extremely high hardness and wear resistance. However, this hampers the development of surfaces with ultra-low surface roughness and ultra-thin damage layer. It is particularly challenging to achieve the chemical mechanical polishing (CMP) of SCD with a surface roughness less than 0.5 nm and a damage layer thickness <1 nm. In this study, the influence of the CMP slurries with different pH values and oxidants on the quality of polished SCD surface was investigated. The optimal slurry consisted of silica, ferrous sulfate, hydrogen peroxide, nitrilotriacetic acid, and deionized water achieved the lowest surface roughness of SCD. The average surface roughness Ra was 0.754 ± 0.062 nm over eight areas of 868 μm × 868 μm. The Ra value of 0.35 nm was obtained over a scanning area of 70 μm × 50 μm, while the thickness of the damage layer was 0.7 nm. The CMP mechanism was elucidated by X-ray photoelectron spectroscopy and infrared spectroscopy. Hydroxyl radicals and hydrogen ions were adsorbed on the surface, oxidation of the surface and generated C-H, C-O, and C = O groups, and they are eventually removed by silica abrasive, yielding an ultra-smooth SCD surface.