Planarization for three-dimensional photonic crystals and other multi-level nanoscale structures

We describe an approach for achieving local as well as global planarization in the fabrication of multi-level nanoscale structures. Using a 'pre-fill-in' technique, where trenches are filled with SiO(2) prior to the application of a planarizing liquid, we demonstrate that the global degree of planarization can be improved from a mere approximately 25% to over approximately 90%. The first layer of a woodpile photonic lattice with a period of approximately 0.5 microm and a minimum feature size of approximately 0.2 microm is used as an example structure to illustrate the issues involved in planarization. This method provides an attractive and simpler alternative to the traditional chemical mechanical polishing approach, which can be quite complicated at nanoscale features involving non-traditional materials.