Role of defects in the dopant diffusion in Si

Silicon technology is based on doping with atoms from the groups III and V of the periodic system, which provide free holes or electrons, respectively. During processes at elevated temperature, these dopants may diffuse in the crystal. The basic mechanisms suggested for the diffusion of dopants in literature are reviewed. The most successful ones assume that dopants form mobile pairs with vacancies and self-interstitials. This assumption leads within the methodology of diffusion-reaction equations directly to a system of coupled continuity equations, which is shown to explain a variety of diffusion phenomena. Some of these diffusion phenomena are intrinsic to dopant diffusion particularly at high concentrations. Others are related to nonequilibrium phenomena associated typically to chemical reactions at the surface or in the bulk. At high concentrations, a variety of mechanisms may lead to the deactivation of the dopants. Besides precipitates and small complexes, particularly, the segregation at interfaces is discussed.