1.1.6 Ion Implantation

Ion implantation is the most widely used technique to introduce dopant impurities into semiconductors. A beam of ionized particles is accelerated through an electric field and aimed at a semiconductor target. The particles penetrate into the target until they come to rest due to interactions with the atoms of the target material. The penetration depth of the dopants depends on the kinetic energy of the ions, which can be controlled very accurately. But not only the penetration depth but also the absolute concentration of the dopants influences the electrical behavior. The concentration can be adjusted quite accurately by varying the implantation dose.

One drawback of the ion implantation technique is that the crystal structure of a semiconductor is damaged by the implanted particles, which impairs the electrical properties of the semiconductor. Additionally the implanted dopants are electrically inactive because they reside on interstitial sites after the implantation. To repair the crystal damage and to activate the dopants a thermal activation step is necessary after an ion implantation step.