DEFECTS PRODUCTION AND ANNEALING IN SELF-IMPLANTED SI

230-keV Si-28 ions were implantated into Si(100) at room temperature with doses from 10(14) to 10(15)/cm2. The samples were analyzed by x-ray double crystal diffractometry and 2--MeV He-4 ion channeling spectrometry. The implanted layer has a parallel lattice spacing equal to that of the unimplanted substrate. The perpendicular lattice spacing is larger than that of the unimplanted substrate and is proportional to the defect concentration extracted from the channeling measurement. Both the perpendicular lattice spacing and the defect concentration increase nonlinearly with ion dose. The defect concentration initially increases slowly with dose until a critical value (approximately 15%, at 4 x 10(14)/cm2), then rises rapidly, and finally a continuous amorphous layer forms. The initial sluggish increase of the damage is due to the considerable recombination of point defects at room temperature. The rapid growth of the defect concentration is attributed to the reduction of the threshold energy for atomic displacement in a predamaged crystal. The amorphization is envisioned as a cooperative process initiated by a spontaneous collapse of heavily damaged crystalline regions. The annealing behavior of the damaged layer reveals various stages of defect recovery, indicating that the damage consists of a hierarchy of various defect structures of vacancy and interstitial aggregates.