Ion Implantation - Semiconductor Device Fabrication

Ion Implantation is another method of introducing dopants into silicon besides chemical deposition by solid state diffusion.
It involves introduction of ionized projectile atoms into targets. Such atoms are given enough energy to penetrate beyond surface regions. The depth of implantation which is proportional to the ion energy can be selected to meet any particular application.

The two key parameters that define the final implant profile are:

1.   Dose
2.   Energy

The dose is related to the beam current, I where Q = It / q_iA

Where:
t   =   Implantation Time
A   =   Beam Area
q_i   =   Charge per ion

The major advantage of ion implantation is the ability of precisely controlling the number of dopant atoms and the depth of penetration.
It has a setback which is the slight destruction of the surface of the slice which is corrected by thermal annealing (heating to a very high temperature, 500°C - 1000°C).

In comparison with chemical deposition, ion implantation is clean and dry because it is performed in a vacuum.
Another advantage of ion implantation is that masks can be made of any convenient material such as photoresist, oxides, nitrides etc.

Ion Implantation System
This consists of ion source where ions of desired elements are produced. An accelerator where electrons are electrically accelerated to a high energy and a target chamber where the ions impinge on a target which is the material to be implanted.

Each ion is a single atom and thus the actual amount of the material to be implanted ie the dose is the integral over time of the ion current.
The energy of the ions as well as the type of ion and the composition of target determine the depth of penetration of the ions in the solid.