Diffusion of boron in heavily doped n- and p-type silicon

The diffusion of 10B in the presence of high-concentration 11B and As doping has been studied. Dopants were introduced by ion implantation and profiles after annealing were obtained by secondary ion mass spectrometry. Diffusion coefficients were derived by comparing experimental profiles with those from a computer simulation program and results confirmed that diffusion of boron is enhanced in p+ silicon and depressed in n+ silicon. These results have been analyzed using the widely accepted vacancy model for boron diffusion and have produced values of the parameter β, which is related to the ratio of diffusivity for charged and uncharged vacancies, of 0.25 to 3.0 for the p+ and 3.0 to 7.7 for the n+ conditions. This difference cannot be ascribed to experimental error and suggests that further refinement of the vacancy model is required.