Characterization of vacancy-like defects in boron-implanted silicon with slow positrons

Vacancy-like defects in Si after boron implantation were studied by means of slow positrons. Ion implantation was carried out at 300 K subsequently with 3 energies to obtain a wide, homogeneously damaged layer. The width of the defect profiles increases with the ion dose and is in good agreement with Monte-Carlo simulations (TRIM-92), The defect production rate was similar to root N, where N is the boron fluence. This behavior is typical for defect formation via homogeneous nucleation. The divacancy concentration observed by infrared absorption was nearly constant after boron implantation, whereas the overall concentration of vacancy-like defects and the S-parameter in the implanted layer increase. This led to the conclusion that the divacancy is dominated by another defect of larger volume in highly boron-implanted Si. The samples were annealed in-situ up to 1150 K. The annealing behavior depends on the implantation dose and on the sample material (i.e. FZ- or Cz-Si). An annealing stage at 725 K was found in all samples. A decrease of the S-parameter below the value obtained for defect-foe Si was observed in Ct-Si only after annealing at 750 K. This must be attributed to the formation of oxygen-vacancy complexes. An increase of the S-parameter above the defect value at room temperature was observed in a region 100 nm below the surface for high boron fluences after annealing at 650 K.