Ion Implant Damage and Solid-Phase Epitaxial Regrowth (SPER) is the process by which high-dose ion implantation amorphizes the silicon crystal lattice, and subsequent annealing recrystallizes it through solid-phase epitaxial regrowth from the underlying crystalline silicon seed — a fundamental mechanism that governs dopant activation, junction depth, and transient enhanced diffusion (TED) behavior. Controlling implant damage and SPER is essential for forming the ultra-shallow junctions required at advanced CMOS nodes.
Implant Damage Mechanism
- Implanted ions collide with lattice atoms → displace them from crystal sites → create vacancy-interstitial (Frenkel) pairs.
- At low dose: isolated point defects (vacancies, interstitials) — crystal remains crystalline.
- At high dose (>10¹⁴ cm⁻²): Damage cascades overlap → amorphous zone forms — no long-range crystal order.
- Amorphization threshold: ~5×10¹³ cm⁻² for As, ~1×10¹⁴ cm⁻² for BF₂, ~1×10¹³ cm⁻² for Ge (pre-amorphization).
Pre-Amorphization Implant (PAI)
- Deliberately amorphize with Ge or Si implant before dopant implant.
- Benefit: Subsequent B or As implant goes into amorphous Si → no channeling → sharp junction.
- Also improves SPER quality → better dopant activation after anneal.
Solid-Phase Epitaxial Regrowth (SPER)
- Annealing (500–700°C) drives epitaxial recrystallization: amorphous/crystalline interface advances toward surface.
- Regrowth rate: ~1–10 nm/min at 600°C; exponential temperature dependence.
- Dopants trapped in amorphous Si become substitutionally incorporated during regrowth → high activation (>10²⁰ cm⁻³ for B).
- Result: Dopant activation far exceeding solid solubility possible transiently via SPER.
Transient Enhanced Diffusion (TED)
- Excess interstitials from implant damage diffuse during anneal → kick out substitutional dopants → greatly enhanced diffusion.
- B is most TED-susceptible: diffusivity can increase 100–1000× transiently.
- TED fades as interstitials annihilate at surface or form interstitial clusters (311 defects).
- Impact: If anneal temperature too high or too long, B junction diffuses deeper than target → fails USJ spec.
Extended Defects from Implant
| Defect | Formation | Anneal Behavior | Impact |
|--------|----------|----------------|--------|
| Point defects (V, I) | Direct implant damage | Annihilate at low T | TED source |
| {311} defects | Interstitial clusters | Dissolve at 750–850°C, release I | TED burst |
| Dislocation loops | High-dose damage | Stable above 900°C | Leakage if in junction |
| EOR damage (end-of-range) | Below amorphous/crystalline interface | Requires 1000°C+ to dissolve | Junction leakage |
EOR (End-of-Range) Damage
- Damage peak below the amorphous/crystalline interface (EOR region) — not recrystallized by SPER.
- EOR dislocation loops remain after anneal → carrier generation-recombination centers → junction leakage.
- Mitigation: Anneal temperature ≥1000°C (spike anneal) to dissolve loops, or design junction deeper than EOR.
Advanced Anneal for Implant Damage
- Spike Anneal (RTP): Fast ramp to 1000–1080°C → dissolves most EOR damage, activates dopants, minimal TED.
- Flash Lamp Anneal: Sub-millisecond pulse to >1200°C → ultra-fast activation, minimal diffusion.
- Laser Spike Anneal (LSA): CO₂ laser scan, 1–3 ms dwell at surface → activates B to 10²¹ cm⁻³, zero diffusion.
Process Control Metrics
- Rs (sheet resistance): Measures dopant activation — lower Rs = higher activation.
- SIMS (Secondary Ion Mass Spectroscopy): Measures dopant profile depth — verifies Xj within spec.
- TEM: Reveals residual EOR loops, SPER quality, amorphous/crystalline interface.
Managing ion implant damage and SPER is the foundational process challenge for ultra-shallow junction formation — the precise balance between amorphization, regrowth, TED control, and EOR defect annihilation determines whether a 3nm node transistor achieves its threshold voltage, leakage, and drive current targets or fails due to excessive junction depth or defect-induced leakage.