Enhanced diffusion phenomena during rapid thermal annealing of preamorphized boron-implanted silicon

The diffusion of boron implanted in preamorphized silicon and rapid thermal annealed with an electron beam is analyzed. For an implanted dose of 5× 1015 B+/cm2 an enhanced diffusion in the early phase of the annealing is clearly observed. The enhancementof the diffusivity is of about a factor 30 at t  0 and exponentially decreases with a constant time of 0.5 s at the temperature of 1100 °C. For lower implanted dose (1 × 1015 B+/cm2) the phenomenon is less remarkable and no conclusive evidence on the existence of enhanced diffusion can be drawn. It is also observed that a recrystallization preannealing step at 550 °C for 1 h does notavoid enhanced diffusion during the rapid thermal annealing. The mechanismswhich could give rise to these effects are reported and discussed.