High resolution and aspect ratio two-dimensional photonic band-gap crystal

This paper reports the challenges resolved to realize high aspect ratio pillar-type two-dimensional photonic band-gap crystal (PhC), designed for application at the optical communication wavelengths. Specifically, the issue of a drastically reduced process window of deep UV lithography and deep reactive ion etching, for a super dense array of submicron size pillars with a diameter of 230 nm and a spacing of 340 nm is treated. A rigorous design of experiments yielded high-resolution PhCs with precise lattice dimensions even near regions of "defect structures" designed for device operations. At the same time, in the etching process, the stringent requirement of an etch angle needed for successful realization of such a super dense array of submicron size PhC lattice was also satisfied to yield sidewalls of high vertically, aspect ratios greater than 50, and scallop-depths of 12 nm.