Deep Reactive-ion Etching

Deep reactive-ion etching (DRIE) is a highly anisotropic etch process used to create deep penetration, steep-sided holes and trenches in wafers/substrates, typically with high aspect ratios . It was developed for microelectromechanical systems (MEMS), which require these features, but is also used to excavate trenches for high-density capacitors for DRAM and more recently for creating through silicon via's (TSV)'s in advanced 3D wafer level packaging technology .

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° or 92° ("retrograde").

Another mechanism is sidewall passivation: SiO_xF_y functional groups (which originate from sulphur hexafluoride and oxygen etch gases) condense on the sidewalls, and protect them from lateral etching. As a combination of these processes deep vertical structures can be made.