Fine control of critical dimension for the fabrication of large bandgap high frequency photonic and phononic crystals

In this work artificial crystal structures designed to exhibit large and simultaneous photonic and phononic bandgaps, known as phoXonic crystals, are fabricated in silicon. Simulations have shown that honeycomb and square symmetry phoXonic crystals with high filling-fractions can produce large bandgaps in the photonic and phononic dispersion relations. To achieve this at hypersonic phononic frequencies and infrared (telecommunications) photonic frequencies, critical dimensions smaller than 100 nm are typically required. In this paper, dose variation for Electron Beam Lithography (EBL) combined with Reactive Ion Etching (RIE) and Thermal Oxidation (TO) are shown to be effective methods to carefully control these parameters.