Structural devices
Structural devices

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Structural devices

8 Etching

8.1 Introduction

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.


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