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'''Deep reactive-ion etching''' ('''DRIE''') is a highly [[anisotropy|anisotropic]] [[etching (microfab)|etch]] process used to create deep penetration, steep-sided holes and trenches in [[wafer (semiconductor)|wafer]]s/substrates, typically with high [[aspect ratio (image)|aspect ratio]]s. It was developed for [[microelectromechanical systems]] (MEMS), which require these features, but is also used to excavate trenches for high-density [[capacitor]]s for [[dynamic random access memory|DRAM]] and more recently for creating through silicon vias ([[Through-silicon via|TSVs]]) in advanced 3D wafer level packaging technology. In DRIE, the substrate is placed inside a reactor, and several gases are introduced. A plasma is struck in the gas mixture which breaks the gas molecules into ions. The ions accelerated towards, and react with the surface of the material being etched, forming another gaseous element. This is known as the chemical part of the reactive ion etching. There is also a physical part, if ions have enough energy, they can knock atoms out of the material to be etched without chemical reaction.
DRIE is a special subclass of reactive-ion etching (RIE).
There are two main technologies for high-rate DRIE: cryogenic and Bosch, although the Bosch process is the only recognised production technique. Both Bosch and cryo processes can fabricate 90° (truly vertical) walls, but often the walls are slightly tapered, e.g. 88° ("reentrant") or 92° ("retrograde").
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