Damage in ion implanted silicon measured by x-ray diffraction

Abstract

The x-ray rocking curve analysis was used to investigate damage accumulation with increasing dose in silicon implanted with 50 keV and 1 MeV 11B+ ions, and 50 keV, 180 keV, and 0.7 MeV 28Si+ ions. The damage buildup was studied by following the maximum value of lattice strain normal to the surface (ε⊥) and the depth integral of ε⊥. The ε⊥ profiles were obtained with a dynamical diffraction formalism by using automated best fits to experimental x-ray rocking curves. It is shown that, for doses below the amorphization limit, the damage increases sublinearly with dose and not very differently for B and Si ions. The sublinearity results from intercascade recombination of point defects produced under bombardment. The small differences, if real, in the sublinearities observed for the two ions could be explained by the different forms of aggregation to which the surviving defects evolve when the dose approaches the amorphization threshold. However, the study of damage growth must stop at the upper dose at which a continuous buried amorphous layer begins to form. In fact, starting from this dose, a simple semikinematical diffraction model shows that the determination of a unique peak value of ε⊥ depth profile, and hence of its integral, is not possible. This is the consequence of the fact that the sample behaves as an x-ray interferometer when an embedded amorphous layer is present. The analysis reported here is compared with similar studies recently published in the literature.