Fabrication of 3D silicon photonic crystal structures using conventional micromachining technology

In this paper, we present a novel method for the fabrication of three-dimensional (3D) photonic crystal structures using conventional planar silicon micromachining technology. It overcomes the disadvantages of the methods hitherto. reported in the literature for the fabrication of 3D photonic crystal devices, which include high complexity of multi-step processes, tight alignment tolerances, long turnaround times, and incompatibility with an integrated photonics platform. The method utilizes a single planar etch mask coupled with time multiplexed sidewall passivating deep anisotropic reactive ion etching along-with isotropic etch process to create three-dimensional photonic crystal devices. In the process, anisotropic etching is followed by isotropic etching leading to the formation of sphere like voids. This step is followed by sidewall polymer deposition and local removal of the polymer from the bottom of the spheres that allows the etch process to be repeated and produce many layers. For the etch mask initially patterned with a square lattice, the etch sequence methodology explained above yields a 3D structure with simple cubic symmetry. Theoretical calculations predict that this structure should possess a complete photonic band gap. Optimization of the photonic band gap can be achieved by using different lattices (square, triangular, hexagonal) as the etch mask to produce photonic crystals with different crystalline structures. Further, by utilizing this fabrication scheme, photonic crystals over a wide range of the electromagnetic spectrum (<3Thz to >300Thz) can be fabricated by scaling the etch times and the mask dimensions.