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 mu m long, 205 Mt 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/O-2 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.