Development of a Planarization Process for the Fabrication of Nanocrystalline Diamond Based Photonic Structures

A significant reduction of the intrinsic surface roughness of nanocrystalline diamond (NCD) layers (e.g., from 25-50 nm down to approximate to 2-6 nm) is accomplished together with an adjustment of the film thickness applying a two-step planarization process. Therefore, a spin-on-glass (SOG), consisting of the inorganic polymer perhydropolysilazane, is spin-coated on top of the NCD layer. After baking, a smooth silica-like layer covered the diamond crystallites. This planar surface is transferred to the NCD surface by a dry etching step, yielding a similar etch selectivity for the diamond and the SOG layer (etching rates of SOG:NCD approximate to 1) applying a mixture of sulfur hexafluoride and oxygen. The planarized surface of the NCD layer led to an enhancement of the uniformity of structures defined by electron beam lithography (EBL), e.g., nanopillars with various diameters as well as two-dimensional photonic crystal slabs.