Wet Etching vs Dry Etching and Importance of Anisotropy

Parameter	Wet Etching	Dry Etching
Medium	Liquid chemical etchant	Plasma/reactive gas or ions
Nature	Often isotropic; some crystal-dependent etchants are anisotropic	Can be controlled for anisotropic profiles
Equipment	Relatively simple	More complex vacuum/plasma equipment
Selectivity	Often high	Can be engineered through plasma chemistry
Feature control	Lateral undercut may occur	Better control of vertical sidewalls is possible
Waste/safety	Chemical waste and handling issues	Gas/plasma safety requirements

Anisotropic etching

Anisotropic etching removes material preferentially in one direction, producing steep or well-defined sidewalls rather than equal lateral and vertical removal.

It is important in MEMS because it enables:

• high-aspect-ratio structures,
• accurate microchannels and cavities,
• vertical sidewalls,
• precise dimensions and better device performance.

Example: DRIE can produce deep silicon structures with nearly vertical sidewalls.