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 concen tration of 2.7 x 10(17) cm(-3) were implanted with 50 keV Si+ at a dos e of 5 x 10(13) cm(-2), followed by annealing at 670 degrees C or 720 degrees C in nitrogen ambient. During annealing, boron atoms accumulat e in the region between R-p and 2R(p), which leads to a B-depleted reg ion extending from 2R(p) to 0.4 mu m. During lower temperature anneali ng, the number;of boron atoms accumulated in the pile-up region reache s its maximum more slowly and has a greater peak value. After reaching its maximum, the number of boron atoms falls exponentially with a cha racteristic decay time of 14 h at 670 degrees C or 3 h at 720 degrees 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 (31 1) defects.