Deep Reactive Ion Etching

Abstract

Reactive ion etching (RIE) (which we will use as a synonym for plasma etching) opens up many possibilities which cannot be done by wet etching. Practically any size and shape can be made by RIE. All sorts of mechanical devices, like springs, beams and plates, are fabricated by plasma etching, as are vertical capacitors and mirrors, in-plane and out-of-plane microneedles and nozzles, and fluidic filters and separation devices.DRIE is an extension of RIE for deep etching, but depth is very different from application to application. For example, in SOI MEMS there is a need to etch the SOI device layer, which can be 5-50 μm, but in many cases also the handle wafer needs to be etched, that is 300-500 μm. While typical RIE rates are on the order of 0.1-1 μm/min, DRIE rates are 2-20 μm/min. Even higher rates have been reported, but then other criteria have been sacrificed: sidewall profile control is poor and high rates are only available for designs which have small etchable area.This chapter concentrates on silicon DRIE processes, with some basic structures discussed. Comparison is often made to anisotropic wet etching because sometimes DRIE and KOH can both be used, and selection has to be reasoned. More advanced device examples will be found in Chapter 30 on MEMS integration. Introduction to Microfabrication, Second E ditionSami Franssila