Fabrication of large scale optical components in silicon by reactive ion etching

An improved procedure for etching silicon utilizes reactive ion etching in an SF6 plasma. The etch rate of single-crystal 〈111〉 silicon was measured as a function of power density and gas pressure. Etch rates of 3.5 μm/min were obtained at a pressure of ∼25 Pa and a power density of 0.25 W/cm2. Silicon-to-aluminum and silicon-to-photoresist etch rate ratios of better than 300:1 and 30:1, respectively, were achieved. The operation at high gas pressure resulted in improved etching uniformity and reduced surface pitting. A similar result was observed when a low concentration (5%) of oxygen was introduced into the SF6 plasma.