Anomalous low-temperature dopant diffusivity and defect structure in Sb-implanted and Sb/B-implanted annealed silicon samples

The diffusivity of antimony into silicon and its dependence on the Fermi-level position and on the structure of lattice defects has been investigated by high-dose ion implantation (2 and 5X10(16) atoms Sb cm(-2)). The donor concentration has been strongly increased by a subsequent pulsed laser annealing treatment. For comparison, laser annealing of samples coimplanted with the same doses of both Sb and B has been performed in order to obtain a strong electrical compensation. The heat treatment for diffusion experiments of both Sb- and Sb+B-implanted wafers have been performed at a rather low temperature (600 degrees C for 1 h). Contrary to the prediction of the extrapolated Fair's equation, a significant shift in the dopant concentration profiles, as well as the formation of Sb precipitates, Sb-vacancy, and/or Sb-B pairing have been observed. To explain this diffusivity, a diffusion coefficient D-Sb independent of the dopant concentration and seven orders of magnitude higher than that previously determined by Fair, must be assumed. This means that the increased Sb diffusivity is not related primarily to the Fermi-level position. The huge increase in D-Sb is related to defects (e.g., twins, dislocations, rodlike defects, precipitates, and dopant complexes) which have been characterized by extended x-ray-absorption fine-structure, Rutherford backscattering spectrometry and channeling, and TEM techniques analyses. Moreover, an anomalous high tensile strain of the samples indicates a large incorporation of vacancies. These defects are also responsible for the dopant backwards diffusion and outdiffusion, which is another surprising phenomenon which occurred during thermal annealing of most of the samples.