wet anisotropic etch
**Wet Anisotropic Etching** uses orientation-dependent etch rates in crystalline materials to create precisely shaped structures, commonly using KOH or TMAH on silicon.
## What Is Wet Anisotropic Etching?
- **Mechanism**: Different crystal planes etch at different rates
- **Etchants**: KOH (potassium hydroxide), TMAH (tetramethylammonium hydroxide)
- **Rate Ratio**: {100}:{111} can exceed 100:1
- **Applications**: MEMS cavities, V-grooves, sharp tips, through-wafer vias
## Why Anisotropic Wet Etching Matters
Etching self-terminates on slow-etching {111} planes, creating atomically smooth surfaces and precisely defined angles without expensive plasma equipment.
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**Etchant Comparison**:
| Property | KOH | TMAH |
|----------|-----|------|
| {100}/{111} ratio | ~400 | ~35 |
| CMOS compatible | No (K+ contaminant) | Yes |
| Cost | Low | Higher |
| Surface roughness | Better | Good |