The ion implantation process selects ions of a desired dopant,
accelerates them using an electric field to form a beam of ions, and scans them across a wafer to obtain a uniform predeposition dopant profile inside
the crystal. The energy imparted to the dopant ion determines the ion
implantation depth. Using this technique, a controlled dose of dopant
impurities can be introduced deep inside the semiconductor. This is in
contrast to diffusion, where the dose of dopant is introduced only at the
wafer surface. In addition, like diffusion, it is possible to conduct the ion
implantation in only certain well-defined areas of the wafer by using an
appropriate mask. This method yields reproducible and controlled dopant
concentration for semiconductor devices.