Channeling

In Implantation, since you are shooting at a crystal typically with a standard pattern, you can accidentally thread the needle with the ion being implanted

The critical angle for chanelling to happen is ${\alpha }_c$ , These ions will eventually hit an atom as the forces that act on them cause them to rock further and further. This does however affect the distribtuion.

Avoiding Channeling

A few things can be done to avoid channeling happen in the first place.

• Covering the surface with a non-crystal layer (e.g $\text{ce}SiO2$ ) taht will randomise the direction.
• Misorientate the substrate by a certain angle (around $7-10^o$ )
• Amorphise the surface with an inert element implanted (such as $\text{ce}N$ )

Fixing Channeling

You can anneal (to about $1000^{o}C$ ) to diffuse out the channelled ions, but this affects the ions that you wanted in the area targetted. The solution is to anneal and cool really quickly. Using something like a pulsed laser.