Boron Accumulation in the {311} Defect Region Induced by Self-Implantation into Silicon Substrate

Boron pile-up in the {311} defect region during thermal annealing was observed for the first time. Czochralski Si wafers with a boron concentration of 2.7×1017 cm-3 were implanted with 50 keV Si+ at a dose of 5×1013 cm-2, followed by annealing at 670°C or 720°C in nitrogen ambient. During annealing, boron atoms accumulate in the region between R p and 2R p , which leads to a B-depleted region extending from 2R p to 0.4 µm. During lower temperature annealing, the number of boron atoms accumulated in the pile-up region reaches its maximum more slowly and has a greater peak value. After reaching its maximum, the number of boron atoms falls exponentially with a characteristic decay time of 14 h at 670°C or 3 h at 720°C. The correlation between the annealing time dependence of the boron pile-up and the evolution of interstitials contained in {311} defects suggests that the boron pile-up is due to the boron segregation to {311} defects.