Etching is central to all forms of micro-device production, from microelectronics and memory through to microsystems technology. Although materials, geometries and feature sizes vary widely, etch processes have a few common features and requirements:
Etching acts by converting solid material into a gas or a liquid that can be pumped or flushed away.
It is usually restricted to the openings in a lithographically defined mask, and since this mask must survive for the duration of the process the etch must be selective.
The cross-sectional shape (profile) of the etched hole is usually important; the most common requirement, both for microelectronics and MEMS, is for near-vertical walls without undercutting of the mask.
The roughness of the etched surface and any electrical or mechanical damage to the device must be controlled.
A consistent result is needed both across a wafer (uniformity) and between wafers (repeatability), since this determines the proportion of working devices (the yield); it may be necessary to monitor the etch to detect when the process is finished (endpoint).
Etch rate is always important, since time is money.