Dopant redistribution:  The doped silicon is oxidized in some places, as part of the process sequence. The dopants which are present on the surface would be incorporated in the oxide, as expected. However, because of the formation of oxide, the dopants may re-distribute. If we consider two immiscible liquids, with a common solute, then the solute will preferentially move to one phase. This principle is used in liquid-liquid extraction in chemical industries. Here, we have two solid phases, viz. silicon dioxide and silicon. The solubility of the dopant in these two phases is different and hence redistribution occurs.

The diffusivity of the dopant in these phases will also be different. Thus, the concentration profile, after oxidation, can vary in different ways, as shown below.

Figure 6.7. Qualitative plots showing dopant redistribution under various solubility and diffusivity conditions

Thus, the final profile of dopant in the transistor will change depending on the processes such as oxidation that occur after doping.