XeF2 etcher
About
Process: This is a custom-built xenon difluoride (XeF₂) vapor-phase etcher that provides extremely fast, isotropic, and highly selective etching of silicon. XeF₂ reacts spontaneously with Si to form volatile SiF₄, enabling rapid Si removal without plasma, ions, or damage to non-Si materials.
Hardware: Vacuum chamber with XeF₂ crystal source sublimation. Controlled XeF₂ vapor delivery via pulse or continuous flow. No RF/plasma required (purely chemical etch). Substrate holder for up to 6" wafers. Temperature controlled at ~20°C (room temperature). Simple, low-damage design ideal for release etching or bulk Si removal.
Gases / Source:
- XeF₂ crystals (solid source – sublimes to vapor; no carrier gas needed)
- N₂ or Ar purge/backfill (if equipped; typically high vacuum or XeF₂-only atmosphere)
Etch Properties:
- Extremely high selectivity to Si (>1000:1 vs. SiO₂, Si₃N₄, photoresist, Al, Au, etc.)
- Completely isotropic (undercut, rounded features)
- Very high etch rate (often 1–10 µm/min depending on vapor pressure and exposure)
- No plasma damage, charging, or ion-induced defects
- Excellent for release of suspended structures or deep undercut
Applications:
- MEMS structural release (e.g., removing sacrificial Si in SOI devices)
- Bulk Si thinning or cavity formation
- Nanowire or freestanding structure fabrication
- Selective Si removal in hybrid devices
- Failure analysis or delayering (Si etch without attacking metals/oxides)
Usage: Load wafer (up to 6"), pump down chamber, introduce XeF₂ vapor (pulse or continuous), monitor etch progress (timed or visual), purge and vent. Use short pulses for controlled etching. Avoid over-etching due to high rate. Follow SOP for crystal loading and safety (XeF₂ is reactive).
Detailed Specifications
- Model: Custom XeF₂ etcher (built by Armani group)
- Location: Deposition bay 1
- Substrate size: Up to 6" wafers (pieces/smaller supported)
- Temperature: 20°C (room temperature operation)
- Etch source: Solid XeF₂ crystals (sublimation-based vapor delivery)
- Etch type: Purely chemical, isotropic, plasma-free
- Features: High Si etch rate, exceptional selectivity (>1000:1 to most masks/materials), simple operation, low damage
- Restrictions: Si only (no etching of oxides, nitrides, metals, polymers, etc.); avoid moisture/contamination in chamber
- Other: Fast and selective alternative to DRIE for isotropic Si removal
Documentation
- SOP – Standard Operating Procedure
- Quickstart Guide
- Training required – contact lab staff (Chandan Ramakrishnaiah or Shivakumar Bhaskaran)
Recipes & Data
- Standard Processes: Typical XeF₂ pulses for controlled Si undercut/release (e.g., 30–120 s pulses at varying pressure for 1–50 µm removal)
- Process Control: Measure etch depth via profilometer or SEM cross-section. Check selectivity on test patterns. Monitor chamber pressure and XeF₂ consumption.
- Notes: Etch rate depends on XeF₂ vapor pressure and substrate temperature. Use short pulses + purge cycles for precision. High selectivity makes it ideal for stopping on oxide/nitride layers.
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