One class of devices that requires high aspect ratio structures is photonic crystals. Photonic crystals are formed by a periodic variance of a high and low refractive index materials, such as a periodic arrangement of nanopores etched in silicon. The scale of the periodicity needs to be on the length scale of the wavelength of light for which a band gap is desired, for example the near infrared, which is of interest for telecommunications. The diameter of the nanopores is chosen to obtain a low silicon to air ratio to maximize the photonic strength of the crystal. Tuning the nanopore diameter and pitch of the pores allows one to control the position and width of the photonic band gap, comparable to how doping changes the electronic band gap in semiconductors. For the fabrication of both 2D and 3D silicon photonic crystals, it is important to have good control over the shape, diameter, length and roughness of the side wall of the nanopores. For certain classes of photonic crystals, the etched structures must be as close to a perfect cylinder of a precise diameter as possible, that is, little to no tapering, minimal scalloping and no under etch. Previously, Woldering et al. explored the effects or deviations in diameter, tapering and pore misalignment, among others. They found that the photonic band gap is greatly affected by relatively small changes, so consistency and control in the manufacturing process is a must. To achieve such nanopores, an etching technique with a high degree of directionality and control must be used such as the Bosch process.