New model for damage accumulation in Si during self-ion irradiation

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Abstract
The dependence of the damage produced by self-ion implantation in Si on dose is determined and is shown to exhibit two distinct behaviors: an initial sublinear increase of damage with dose, followed by a period of greatly accelerated growth. Ion backscattering analysis using both single- and double-alignment channeling measurements is used to determine the distribution of damage in the samples. The nature of the damage is determined from its thermal annealing behavior and differences in the spectra recorded in the two channeling configurations. Damage is found to consist predominantly of two components: simple defects, such as divacancies, and regions of amorphous Si. The behavior of these components is shown to be divergent at the fluence which separates the two different growth regimes. A model is proposed which considers the amorphization process in Si as a critical-point phenomenon, one in which the onset of amorphization leads to a cooperative behavior among the various types of damage resulting in a greatly accelerated transition.