Optimized process for fabrication of free-standing silicon nanophotonic devices

A detailed procedure is presented for fabrication of free-standing silicon photonic devices that accurately reproduces design dimensions while minimizing surface roughness. By reducing charging effects during inductively coupled-plasma reactive ion etching, undercutting in small, high-aspect ratio openings is reduced. Slot structures with a width as small as 40 nm and an aspect ratio of 5.5:1 can be produced with a nearly straight, vertical sidewall profile. Subsequent removal of an underlying sacrificial silicon dioxide layer by wet-etching to create free-standing devices is performed under conditions which suppress attack of the silicon. Slotted one-dimensional photonic crystal cavities are used as sensitive test structures to demonstrate that performance specifications can be reached without iteratively adapting design dimensions; optical resonance frequencies are within 1% of the simulated values and quality factors on the order of 10⁵ are routinely attained.