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° („reentrant“) or 92° („retrograde“).
Another mechanism is sidewall passivation: SiOxFy 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.
|ICP 13.56 MHz plasma source 3 000 W|
|RF substrate biasing|
|sample size up to 6’’|
|Bosch or cryo process|
|substrate temperature –150 to 400 °C (LN2)|
|gases:||SF6, C4F8, O2, Ar|
|standard materials for etching||Si,SiO2, SiN|