amorphization

Amorphization occurs when heavy-dose ion implantation displaces enough silicon atoms to destroy the crystalline lattice, creating an amorphous layer. **Mechanism**: Each implanted ion creates a cascade of displaced atoms. Above a critical damage density (~10% displaced), the crystalline structure collapses into amorphous silicon. **Threshold**: Depends on ion mass, energy, dose, and substrate temperature. Heavy ions (As, Ge, Si) amorphize more readily than light ions (B). **Pre-Amorphization Implant (PAI)**: Intentional amorphization using Ge or Si ions before dopant implant. Creates uniform amorphous layer for controlled recrystallization. **Benefits of PAI**: Eliminates channeling during subsequent dopant implant (amorphous material has no crystal channels). Enables sharper junction profiles. **Solid-Phase Epitaxial Regrowth (SPER)**: Amorphous layer recrystallizes from the crystalline substrate interface upward during anneal at 500-700 C. Fast, low-temperature activation mechanism. **End-of-range (EOR) defects**: Damage beyond the amorphous/crystalline interface forms dislocation loops that are difficult to anneal out. Can cause junction leakage. **Depth**: Amorphous layer depth depends on implant conditions. Must be controlled to stay above junction depth. **Temperature effect**: Implanting at elevated temperature allows dynamic annealing, reducing amorphization. Cryogenic implant maximizes amorphization. **Characterization**: TEM imaging shows amorphous/crystalline boundary. Ellipsometry for thickness measurement.