Fabrication of three-dimensional photonic structures with submicrometer resolution by x-ray lithography

We report on the fabrication of diamond-like photonic structures in PMMA resist and their use as porous templates for transferring three-dimensional patterns to metals or dielectrics. Following the original “three drilling holes” approach first proposed by Yablonovitch, we used three consecutive exposures of PMMA resist to an x-ray beam through a triangular lattice of holes. A submicronic patterning was thus obtained in thick PMMA layers (>6 μm). Optical characterizations of 1.3 μm period templates showed a well-defined photonic gap in the midinfrared. The pattern transfers from the PMMA templates to a metal (copper) and a high refractive index dielectric (titania) were achieved by the electrodeposition and sol–gel filling techniques, respectively. Three-dimensional metallic structures of 1.3 μm lattice constant were obtained with extreme regularity over a thickness of ∼6 μm, thereby providing a way to build submicrometer photonic band gap materials for optical wavelengths.