Fabrication of microscale and nanoscale silicon waveguide devices requires patterning silicon, but until recently, exploitation of the technology has been restricted by the difficulty of forming ever-small features with minimum linewidth fluctuation. A technique was developed for fabricating such devices achieving vertical sidewall profile, smooth sidewall roughness of less than 10 nm, and fine features of 40 nm. Subsequently, silicon microring resonator and silicon-grating coupler were realized using this technique.