Shallow junctions--Modeling the dominance of point defect charge states during transient diffusion
Ion implantation damage produces point defects during annealing which can significantly enhance dopant diffusion. This diffusion at low temperatures was studied for P, As, and B implants in Si. Enhanced diffusion was observed below certain doping concentrations which depend only on temperature. For As, this concentration corresponds to As solid stability. For P, enhanced diffusion occurs below ni for temperatures below 850°C. A model is presented which correlates the self-interstitial donor level position in the Si bandgap with the dominance of B diffusion via neutral self-interstitials. It is shown that when self-interstitials are externally generated the resulting changes in the free energy of self-interstitial formation force the B diffusion via Ix (neutral self-interstitial) to be 10-100 times greater than B diffusion via I+ (donor self-interstitial).