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

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.