Dual N/Pb ion-implanted Si: Temperature dependence of the novel shift of the Pb peak under electron beam annealing

(1 0 0) Si was dual ion-implanted with 24 keV N and 7 keV Pb to peak concentrations ∼10 at.%. Implanted samples were then electron beam annealed (EBA) at a peak temperature T for 30 s with T ranging from 100 °C to 900 °C and for 15 s at 1000 °C. Pb profiles were measured using RBS and surfaces characterised by AFM. For T up to 500 °C there was no shift in the profile from the implanted depth ∼10 nm. For higher values of T a striking feature was the large movement of the Pb profile away from the surface without a significant change in width or Pb content. The profile depths were: ∼40 nm for 600 °C, ∼68 nm for 700-900 °C and ∼80 nm for 1000 °C. The response to EBA was found to be strongly dependent on both ion implantation order and Si starting structure. For (1 0 0) Si nanowhiskers formed on the treated surfaces for T = 900 °C and 1000 °C. A model is developed based on the restructuring of the amorphous implanted layer under EBA. It is proposed that a compaction starting at the surface sweeps the Pb before it via a stress interaction as it advances into the Si.

Research highlights▶ Novel movement of lead under electron beam annealing of silicon shallowly dual implanted with nitrogen and lead has been discovered. ▶ The results are in stark contrast to those expected from conventional diffusion. ▶ The lead atoms, retaining a narrow profile, are swept into the depth via stress interactions.