Editing Ion implantation (section)

==Problems with ion implantation==
===Crystallographic damage===
Each individual ion produces many [[crystallographic defect|point defects]] in the target crystal on impact such as vacancies and interstitials. Vacancies are crystal lattice points unoccupied by an atom: in this case the ion collides with a target atom, resulting in transfer of a significant amount of energy to the target atom such that it leaves its crystal site. This target atom then itself becomes a projectile in the solid, and can cause [[collision cascade|successive collision events]].
Interstitials result when such atoms (or the original ion itself) come to rest in the solid, but find no vacant space in the lattice to reside. These point defects can migrate and cluster with each other, resulting in [[dislocation]] loops and other defects.

===Damage recovery===
Because ion implantation causes damage to the crystal structure of the target which is often unwanted, ion implantation processing is often followed by a thermal annealing. This can be referred to as damage recovery.

===Amorphization===
The amount of crystallographic damage can be enough to completely amorphize the surface of the target: i.e. it can become an [[amorphous solid]] (such a solid produced from a melt is called a [[glass]]). In some cases, complete amorphization of a target is preferable to a highly defective crystal: An amorphized film can be regrown at a lower temperature than required to anneal a highly damaged crystal. Amorphisation of the substrate can occur as a result of the beam damage. For example, yttrium ion implantation into sapphire at an ion beam energy of 150 keV to a fluence of 5*10<sup>16</sup> Y<sup>+</sup>/cm<sup>2</sup> produces an amorphous glassy layer approximately 110&nbsp;nm in thickness, measured from the outer surface. [Hunt, 1999]

===Sputtering===
Some of the collision events result in atoms being ejected ([[sputtering|sputtered]]) from the surface, and thus ion implantation will slowly etch away a surface. The effect is only appreciable for very large doses.

===Ion channelling===
[[Image:Diamond structure.png|thumb|right|300 px|A diamond cubic crystal viewed from the [[Crystallography#Notation|<110>]] direction, showing hexagonal ion channels.]]

If there is a crystallographic structure to the target, and especially in semiconductor substrates where the crystal structure is more open, particular crystallographic directions offer much lower stopping than other directions. The result is that the range of an ion can be much longer if the ion travels exactly along a particular direction, for example the <110> direction in [[silicon]] and other [[diamond cubic]] materials.<ref>{{Cite book|title=Materials science of thin films : deposition and structure|author=Ohring, Milton|date=2002|publisher=Academic Press|isbn=9780125249751|edition=2nd|location=San Diego, CA|oclc=162575935}}</ref> This effect is called ''ion channelling'', and, like all the [[Channelling (physics)|channelling]] effects, is highly nonlinear, with small variations from perfect orientation resulting in extreme differences in implantation depth.  For this reason, most implantation is carried out a few degrees off-axis, where tiny alignment errors will have more predictable effects.

Ion channelling can be used directly in [[Rutherford backscattering]] and related techniques as an analytical method to determine the amount and depth profile of damage in crystalline thin film materials.