Nanocrystalline diamond films and e-beam patterning techniques have been used to fabricate visible to near-infrared photonic slab crystals (PhCs) with deep submicron feature sizes. Two methods of fabrication, both based on electron-beam lithography, have been explored and are detailed in this Communication. The first method uses direct patterning of flowable oxide as a hard mask for a subsequent highly anisotropic oxygen plasma reactive ion etching of the nanocrystalline diamond film. The second method involves image inversion and employs an organic-inorganic bilayer resist structure that planarizes the surface and provides for a well-controlled undercut. The subsequent metal evaporation and lift-off creates a metal mask with 100 nm features demonstrating fine control over edge roughness that is not compromised by the nanocrystalline roughness of the diamond film. Chromium etch mask and oxygen plasma were used to fabricate the diamond PhC. With the proper choice of metal mask and reactive ion etch, this technique can be applied to a wide range of nanocrystalline and polycrystalline films and will enable further scaling into the sub-100 nm regime. (c) 2006 American Vacuum Society.