Fe and Cu in Si: Lattice sites and trapping at implantation-related defects

We have used the emission channeling technique in order to study the lattice sites of radioactive 59Fe and 67Cu following 60 keV ion implantation into Si single crystals at fluences around 1012–1014 cm−2. We find that in the room temperature as-implanted state in high-resistivity Si both Fe and Cu occupy mainly lattice sites displaced around 0.05 nm (0.5 Å) from substitutional positions. Both are released from these positions during annealing at temperatures between 300 °C and 600 °C. Fe is then found mainly on near-tetrahedral interstitial sites and further annealing causes it to be increasingly incorporated on ideal substitutional sites, on which it is stable to around 800 °C. We have strong indications that during annealing around 600 °C, along with the dominance of interstitial Fe, a redistribution towards the surface takes place, suggesting that the subsequent formation of ideal substitutional Fe may be related to the trapping of Fe at Rp/2, half of its implanted depth. Possible Rp/2 trapping might also have taken place in our Cu experiments but appears to be less efficient since Cu tended to escape to the bulk of the samples.