Studies on the lattice position of boron in silicon†

From a compilation of known literature, the substitutional fraction of boron in silicon is depicted in a diagram as a function of implantation dose and annealing temperature. Samples implanted at 1 1016 B/cm2 and annealed at 900, 1000 and 1100°C for 1 hour each are examined by the (n, α) method and compared to the RBS signal of the host atoms in various directions. Our results indicate a gradual transition from completely random positions after 900°C anneal to substitutional sites after 1100°C anneal.The observation of random positions for B in Si, annealed at 900°C, disagrees with earlier experiments after application of (p, α) reactions. We ascribe the differences to proton irradiation induced boron diffusion in those former accelerator experiments by other authors.Our results for the samples annealed above 900°C indicate lattice positions for the interstitial boron fraction which were not yet discussed in the literature.After 1100°C anneal, nearly all B atoms are found on positions slightly (approx. 7%) displaced from substitutional sites. This may result from the formation of small B2 or B3 clusters during the cooling period of the thermal annealing procedure.