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'''Deep Reactive Ion Etching''' or '''DRIE''' is a highly [[anisotropic]] [[etching|etch]] process developed in the [[semiconductor]] industry and used to create deep and high [[aspect ratio]] channels in materials such as [[silicon]]. Widely used for [[MEMS]] and high value integrated [[capacitor]]s, channels with vertical sides and having [[aspect ratio]]s greater than 20:1 can be produced.
There are three primary processes which are brought together to achieve the results in DRIE. First a highly reactive gas is used to perform an [[isotropic]] etch of the [[substrate]]. After a brief period the etching is stopped and the process switches over to deposition of a layer of [[passivation]] over the whole surface. This protects the substrate from further chemical attack and prevents further etching. The process now returns to etching, which is where the third process comes into play. Within the chamber there is an energetic [[Plasma (physics)|plasma]] which produces a [[collimated]] stream of [[ion]]s that bombard the substrate. By a process of [[sputtering]] these ions remove the passivation from the bottom of the previous etch step, but not from the sides. The etchant chemicals can then erode only the bottom of the channels.
The process is repeated many times over resulting in a large number of very small [[isotropic]] etch steps taking place only at the bottom of the etched pits. It is this selectivity that leads to the overall anisotropy of the process and the creation of high aspect ratio channels with vertical sidewalls.
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