Influence of the nonequilibrium vacancies on the diffusion of phosphorus into silicon

Using Fair and Tsai’s model, a numerical solution is obtained for the coupled phosphorus and vacancy diffusion equations. It is shown that the supersaturation of vacancies, which enhances the phosphorus diffusion in the tail region, also causes an important backwards contribution to the total phosphorus flux in the surface region. It is thus proved that the diffusion via E centers alone cannot explain the plateau region in the phosphorus profiles, and that another mechanism is needed to describe the diffusion of phosphorus in silicon in the high concentration range.