10.1.6 Doping

Dopants are introduced into the wafer by ion implantation or surface diffusion.

10.1.6.1 Ion Implantation

Ion implantation is the main method of introducing dopants into the wafer. The dopant atoms are accelerated and the wafer is bombarded so that the dopants enter the substrate and become part of the crystal near the surface. The advantage of this method is the accurate control of the concentration of the dopant atoms, but its disadvantage is the significant damage of the crystal. Therefore a subsequent diffusion step is often used to anneal the defects of the crystal lattice caused by the bombardment (RTA, rapid thermal annealing).

10.1.6.2 Diffusion

In semiconductor manufacturing diffusion refers to the migration of dopants into the wafer through its surface (pre-deposition) or inside the substrate. The temperature during the diffusion step as a function of time determines the final doping profile which of course governs the performance of the device. Consecutive diffusion steps alter the concentration of all dopants in the wafer. This additional migration has to be taken into account when simulating a whole process flow.