Semiconductor Fabs III: Ion Implantation
a month ago
- #doping
- #semiconductor
- #ion-implantation
- Ion implantation is used in semiconductor manufacturing to alter silicon's properties by introducing dopants.
- Dopants create n-type (donor impurities) or p-type (acceptor impurities) semiconductors by affecting the Fermi energy level.
- Dose (ions/cm²) and concentration (ions/cm³) are key metrics, with dose calculated via beam current and time.
- Implant profiles are approximated using Gaussian functions, with skewness and kurtosis affecting distribution.
- Junction depth (xj) is where impurity concentration equals substrate concentration, critical for p-n junctions.
- Ions stop via nuclear stopping (collisions with nuclei) and electronic stopping (interaction with electrons).
- Activation anneal repairs lattice damage post-implantation, integrating dopants into the silicon lattice.
- Common dopants include boron, phosphorus, and arsenic, ionized using gases like BF₃, PH₃, and AsH₃.
- Mass analyzers (magnetic sector or RF quadrupole) filter ions by mass to ensure purity of the implant beam.
- Scanning methods (mechanical or electrostatic) ensure uniform implantation across the wafer.
- Masks (e.g., SiO₂, photoresist) block specific areas from implantation, with material choice critical for stopping power.
- Channeling (ions traveling deep due to crystal alignment) is mitigated by tilting the wafer or amorphizing the surface.
- Alternatives to ion implantation include diffusion doping (furnace-based) and spin-on doping (liquid-based).