channeling

Channeling occurs during ion implantation when ions travel deeper into the crystal than expected by following open channels between atoms in the crystal lattice. Silicon's diamond cubic structure has <110> channels that allow ions to penetrate with minimal collisions, creating deep tails in the doping profile that degrade junction abruptness and increase leakage. Channeling is most severe when the ion beam is aligned with major crystal axes. To prevent channeling, wafers are tilted 7° from normal incidence and rotated to avoid alignment with any major crystal direction. Pre-amorphization implants (PAI) using heavy ions like germanium or silicon create an amorphous surface layer that eliminates crystal channels, ensuring predictable shallow profiles. Channeling effects are more pronounced for light ions (boron, phosphorus) and low implant energies. Screen oxides can also reduce channeling by scattering ions before they enter the silicon. Proper tilt and rotation angles are critical for achieving designed junction profiles and device performance.