Deep Reactive Ion Etching

This chapter concentrates on silicon deep reactive ion etching (DRIE) processes, with some basic structures. Comparison is often made to anisotropic wet etching because sometimes DRIE and KOH can both be used, and selection has to be reasoned. Fluorine, chlorine and bromine etch silicon. Fluorine is chosen for MEMS DRIE because of its etch rate: etch rates an order of magnitude higher are possible with SF6 than with Cl2 or HBr. Anisotropic etching is the special case and isotropic profile is the default profile. The high rate offered by DRIE is beneficial also in isotropic etching. The combination of anisotropic and isotropic etching steps can be used to make free-standing single crystal silicon structures with vertical walls. In-plane microneedles can be made very long because silicon is strong. There are various ways of making nozzles with the through-wafer fluidic channel. Controlled Vocabulary Terms micromechanical devices; sputter etching