A Channeling Study of Defect-Boron Complexes in Si

Abstract

ABSTRACTSi crystals were doped with 0.1–0.2 at% 11B in the near surface region by ion implantation followed by thermal diffusion at 1373 K or by ruby laser annealing. The position of the B atoms in the Si lattice was determined by channeling measurements, utilizing both the yield of H+ ions (of incident energy 0.7 MeV) backscattered from Si atoms and the yield of alpha particles from the 11B(p,α)8Be nuclear reaction. Initially, 95–99% of the B atoms were substitutional. Irradiation at 35 K or 293 K with 0.7 MeV H+ displaced B atoms from lattice sites. The displacement rate was greater at 293 K than at 35 K, and was greater for diffused samples than for laser annealed samples. Following 35 K irradiations, a large increase in the fraction fdB of displaced B atoms occurred during annealing near 240 K. At higher annealing temperatures, fdB decreased over a broad temperature range from 425–825 K. Angular scans through <110> channels for the laser annealed samples after 293 K irradiation or after 35 K irradiation plus 293 K annealing showed a pronounced narrowing of the dip in 11B(p,α)8Be yields compared with the dip in yields from Si, whereas no narrowing was observed for <100> channels. These results indicate that B atoms were displaced into specific lattice sites by the migration of an interstitial B defect (the EPR G28 defect) near 240 K.