CHANNELING

• Depending on the crystal orientations, the ion can travel through the channels of the lattice  and stop much deeper in the wafer

• For angles smaller than: channeling occurs
• Effect: doping profile is much more spreaded than desired:
• Solutions:
  • Angle tilt of 7o used to avoid the tail in doping profile
  • Preamorphization can be used to avoid chanelling
    • a high dose of Si+ is implanted into the wafer to amorphise the Si wafer (B cannot cause amorphization because of small mass, in case of P and As, they can also be used instead of Si)
    • the desired does of impurities is implanted into amorphous Si without channeling effects

    • the wafer is annealed at 500-600oC to regrow the Si by SPE (solid-phase-epitaxy), using the substrate as a template; for higher tempereatures, nucleation takes place and the layer becomes poly-crystalline

    • the wafer is annealed at higher temperature after (900-1000oC) to activate dopants