Characterization of defects produced during self-annealing implantation of As in silicon

Several electron microscopy techniques were used to investigate in detail the structure of the defects produced by implantation of Si with high current density As+ ion beam under self-annealing conditions (i.e., with simultaneous damage recovery activated by the transient beam heating). The defects, which display a basic octahedral shape, appear if the irradiation is prolonged after the time for which the transient beam heating has produced the complete crystallization of the previously amorphized surface layer. With increasing irradiation time and temperature they grow up to a maximum diameter of about 20 nm, and concentrate in a band located around the position of the maximum of nuclear energy loss of As+ ions, where a segregation peak of electrically inactive As is developed simultaneously. The results of different microstructural and microanalytical techniques used to investigate the defects (conventional and high resolution electron microscopy, electron holography, and energy dispersion x-ray microanalysis) give information which leads us to identify them as large vacancy aggregates, or voids, with As atoms segregated in proximity of the inner surfaces. The role of As atoms is likely to reduce the strain energy which a vacancy aggregate is expected to produce in the surrounding lattice.