Fabrication of two-dimensional photonic crystal waveguides for 1.5 mm in silicon by deep anisotropic dry etching

Fabrication process for sharp waveguide bends in a two-dimensional photonic band gap structure in silicon is developed. The waveguide bend is defined by removing a row of pillars in a two-dimensional photonic crystal of 5 µm long, 205 nm diameter pillars placed on a square lattice with a pitch of 570 nm. To meet the severe nanotolerance requirements in such a device the SF₆/O₂ electron cyclotron resonance plasma process at reduced temperature is tailored to extreme profile control. The impact of main plasma parameters-i.e., temperature, oxygen/fluorine content, and ion energy-on the sidewall passivation process is unraveled in detail. Crystallographic orientation preference in the etch rate is observed.