Studies of Boron Segregation to {311} Defects in Silicon-Implanted Silicon

Czochralski Si wafers with a boron concentration of 2.7×1017 cm-3 were implanted with 50 keV or 150 keV Si+ with doses from 5×1012 cm-2 to 5×1015 cm-2, followed by annealing at 670°C, 720°C or 820°C in nitrogen ambient. During thermal annealing, boron pile-up in the {311} defect region was observed for the first time. In higher temperature annealing, the boron pile-up forms and dissolves more quickly, but has a lower peak value. The boron pile-up forms in the region where the self-interstitial concentration exceeds 3×1017 cm-3 regardless of implant energy and dose. The boron pile-up originates from the boron segregation to {311} defects. The process of boron segregation is limited by boron diffusion. The number of boron atoms segregated to {311} defects increases with annealing time, as t 1/2. After reaching its maximum, the number of segregated boron atoms falls exponentially with a characteristic decay time of 14 h at 670°C or 3 h at 720°C. Spreading resistance profiling reveals that boron atoms segregated to {311} defects are electrically inactive.