ionimplantation

Ion implantation is a materials processing technique in which ions of dopant or other species are accelerated in an electric field and implanted into a solid substrate to modify its composition, structure, and properties. The method offers precise control over dopant concentration and depth versus lateral spread, with minimal unintended diffusion, making it central to semiconductor device fabrication and surface engineering.

Typical implanter equipment generates a beam of the chosen ion species, accelerates it to energies from a few keV to several MeV, and scans the beam across the substrate to achieve uniform coverage. The implanted dose is quoted as ions per square centimeter and commonly ranges from about 10^11 to 10^18 ions/cm^2, depending on the application. The depth profile depends on ion mass and energy and is influenced by channeling in crystalline substrates.

Implantation damages the lattice, creating vacancies and interstitials. Dopant atoms may occupy lattice sites (activation) or become interstitials. Activation generally requires thermal annealing to repair damage and place dopants on lattice sites. Diffusion during annealing shapes the final profile and junction depths.

Applications include doping of silicon and compound semiconductors (boron, phosphorus, arsenic, nitrogen), production of shallow junctions for MOS devices, isolation schemes, and modification of optical, mechanical, and magnetic properties of various materials. Ion implantation is used in surface hardening, wear resistance, and ion-beam-assisted deposition.

Advantages include precise control over depth profiles, compatibility with ultra-clean processing, and avoidance of high-temperature diffusion during processing. Limitations include lattice damage requiring annealing, possible channeling effects that complicate profiles, costs of ion implanters, and potential implantation-induced defects.