freeze drying
**Freeze Drying (Lyophilization)** in semiconductor processing uses sublimation to dry delicate structures, avoiding surface tension damage from liquid evaporation.
## What Is Freeze Drying?
- **Process**: Freeze liquid → Sublimate ice directly to vapor
- **Advantage**: Eliminates liquid-gas interface that causes stiction
- **Applications**: MEMS release, porous materials, delicate structures
- **Equipment**: Vacuum chamber with cold trap
## Why Freeze Drying Matters
Surface tension during conventional drying collapses fine structures like MEMS cantilevers. Sublimation bypasses the liquid phase entirely.
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**Freeze Drying Process**:
1. Rinse with water or t-butanol
2. Freeze below solvent melting point (-40°C typical)
3. Apply vacuum (<1 mbar)
4. Sublimate ice over hours
5. Warm to room temperature under vacuum
Alternative: Supercritical CO₂ drying (faster, no freezing damage)