In Situ Doped Epitaxy
In-Situ Doped Epitaxy is the process of incorporating dopant atoms into an epitaxial film during growth — simultaneously controlling crystal composition, strain, and doping concentration in a single deposition step, used for source/drain engineering, well formation, and channel doping in advanced CMOS transistors.
How In-Situ Doping Works
- During epitaxial growth (CVD/RPCVD), dopant precursor gas is added to the growth chemistry.
- Dopant atoms incorporate substitutionally into the crystal lattice — electrically active without requiring an additional implant/anneal step.
- Key advantage: No implant damage, no amorphization, no need for high-temperature dopant activation anneal.
Dopant Precursors
| Dopant | Type | Precursor Gas | Application |
|---|---|---|---|
| Boron (B) | p-type | B2H6 (diborane), BCl3 | PMOS S/D, SiGe channel |
| Phosphorus (P) | n-type | PH3 (phosphine) | NMOS S/D, Si channel |
| Arsenic (As) | n-type | AsH3 (arsine) | NMOS S/D (heavy doping) |
| Carbon (C) | n/a (SiC) | SiH3CH3 (MMS) | NMOS S/D stressor |
Applications in Advanced CMOS
PMOS Embedded SiGe Source/Drain:
- SiGe with heavy boron doping (> 2×10²⁰ cm⁻³) grown in recessed S/D regions.
- SiGe provides compressive channel strain + boron provides p-type contact.
- Ge content: 25-40% for 14nm-class, up to 50-60% at 3nm.
NMOS Si:P Source/Drain:
- Silicon epitaxy with phosphorus doping (> 3×10²⁰ cm⁻³) for low contact resistance.
- Si:P provides tensile strain (P is smaller than Si) — enhances NMOS mobility.
- Challenge: P clustering at high concentrations → reduced activation → metastable doping.
Nanosheet Channel:
- Si channels grown with precise background doping levels.
- In-situ doping during superlattice growth sets channel doping profile.
Process Control
- Doping Concentration: Controlled by dopant precursor flow rate relative to Si/SiGe precursor.
- Uniformity: ± 5% concentration uniformity across 300mm wafer.
- Abrupt Junctions: Gas switching creates sharp doping transitions (< 2 nm/decade).
- Dopant Segregation: Some dopants (B in SiGe) preferentially segregate during growth — must be managed.
In-situ doped epitaxy is the precision doping method of choice for advanced transistor engineering — eliminating the damage and thermal budget of ion implantation while delivering abrupt, highly activated doping profiles that optimize both contact resistance and channel strain simultaneously.