Dopant Contamination refers to unintended introduction of electrically active impurities during semiconductor processing that alter device characteristics.
## What Is Dopant Contamination?
- Sources: Cross-contamination from diffusion, ion implant, or handling
- Common Contaminants: Boron, phosphorus, arsenic from prior wafers
- Effect: Shifts threshold voltage, increases leakage, device failure
- Detection: SIMS, spreading resistance, electrical test
## Why Dopant Contamination Matters
At sub-20nm nodes, even 10¹⁰ atoms/cm² of unwanted dopant significantly affects transistor characteristics, causing parametric failures.
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Dopant Contamination Pathway:
Process Chamber Wall:
┌─────────────────────┐
│ ████ Prior wafer │
│ ████ residue │ ← B, P, As deposits
│ │
│ New wafer │ ← Contamination transfers
│ ●●●●●●●●● │
└─────────────────────┘
Even ppb-level contamination affects Vt
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Prevention Methods:
| Method | Application |
|--------|-------------|
| Dedicated equipment | P-type vs N-type separation |
| Barrier wafers | Dummy runs after contaminating process |
| Chamber cleaning | Periodic in-situ plasma clean |
| Wafer cleaning | Pre-process SC1/SC2/HF sequences |