A model for damage release in ion-implanted silicon

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Abstract
A model to describe the amorphization in ion-implanted silicon is presented, based on the idea that a transferred energy threshold (around 5 keV) is necessary to produce a sufficiently branched and energetic cascade. This amorphizing cascade is seen first as energetic two body collisions, then as the branching of the primary skeleton and, at the final stages, as a hot cloud in which the primary energy is equipartitioned, and remains adiabatically confined before cloud quenching. This view allows some quantitative estimations: the dimension of the cloud, the threshold energy for their formation, and the number of the involved atoms. Original experimental evidence is presented to support this framework. In principle, the behavior of boron implanted in (100) silicon, at a constant fluence (9×1015 cm−2) and at a variable impinging energy (in the range 20–45 keV), puts in evidence the possibility to amorphize only above a critical threshold. The position of the amorphized regions also suggests that amorphization can take place only where sufficiently energetic recoils are produced. The existence of point defects out of the amorphized regions and their progressive involvement causes superlinear amorphization effects. This mechanism is viewed, in the framework of this model, as a decreasing of the amorphization threshold energy, because of the releasing of the residual energy by the involved point defects. The predictions of the model are compared with the experimental data referring to N+ implanted into (111) silicon at 40 keV, and the resulting agreement is quite satisfactory.

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