Anisotropic reactive ion etching of deep Si structures (≥8 μm), planarization of deeply stepped topographies, and multilayer resist processes have been developed for fabrication of silicon IR binary optics devices. The effect of adding O2and C2F6to the SF6feed gas on sidewall profile and etch selectivity (Si:photoresist) has been determined. Vertical profiles, without mask undercutting or surface texturing, and high etch selectivity (≥5:1) have been obtained with a 74% SF6–26% O2mixture. We have successfully fabricated 8‐μm deep Si optics with 16 phase levels and eight‐level structures with a total depth of 14 μm in Si.