Novel planarization method of single-crystal diamond using 172 nm vacuum-ultraviolet light

We propose a novel planarization method for diamond substrates with 172 nm vacuum-ultraviolet (VUV) irradiation. To demonstrate the effectiveness of the proposed method, a polishing plate made of sapphire was used to polish diamond substrates with and without VUV irradiation under atmospheric conditions at room temperature. To interpret the planarization mechanism of the diamond substrate, the hydrophilic nature, cleanliness, and chemical-bonding state of the polishing plate before and after VUV irradiation were analyzed by a contact angle meter and X-ray photoelectron spectroscopy (XPS). The surface roughness and material removal rate were measured and evaluated by scanning white light interferometric microscopy and atomic force microscopy. The chemical-bonding state on the diamond surface before and after polishing were also analyzed by XPS. The experimental results show that VUV irradiation yields a hydrophilic and OH-terminated surface on the polishing plate, and give the effects in terms of the material removal rate and surface finish. The material removal rate with VUV irradiation (238.1 nm/h) was approximately seven times higher than that without VUV irradiation (33.3 nm/h). An atomically smooth diamond surface with a root-mean-square surface roughness below 0.1 nm can be prepared by polishing with VUV irradiation within 1.5 h.