After the ions have been implanted they are lodged principally in interstitial positions in the silicon crystal structure, and the surface region into which the implantation has taken place will be heavily damaged by the impact of the high-energy ions.

The disarray of silicon atoms in the surface region is often to the extent that this region is no longer crystalline in structure, but rather amorphous.

To restore this surface region back to a well-ordered crystalline state and to allow the implanted ions to go into substitutional sites in the crystal structure, the wafer must be subjected to an annealing process.

The annealing process usually involves the heating of the wafers to some elevated temperature often in the range of 1000°C for a suitable length of time such as 30 minutes.

Laser beam and electron-beam annealing are also employed. In such annealing techniques only the surface region of the wafer is heated and re-crystallized.

Features of Annealing

1. Remove primary damage created by the implant and activate the dopants.
2. Point defect removal and activation.
3. Restore silicon lattice to its perfect crystalline state.
4. Restore the electron and hole mobility.
5. Do this without appreciable dopant redistribution.