Trapping of ion-implanted Co-57 to cavities in c-Si: A qualitative study

We observe a pronounced dose dependence in the trapping of Co to the internal surface of nanosized cavities in c-Si. Mossbauer spectroscopy shows that cavity trapping is most explicit for low Co contamination levels (< 5 x 10(13) at/cm(2)). For high quantities (> 5 x 10(14) at/cm(2)), silicide formation becomes predominant at first and then subsequently partially dissolves upon prolonged annealing at temperatures exceeding 750 degrees C. In the intermediate region, a clear starting situation is only reached after several annealing steps. Again Co gets trapped at the cavities, reaching essentially an identical level as for the low dose case. For the low and intermediate dose case, the onset of cavity trapping is followed in detail, showing that a large initial fraction of weakly surface bound Co depopulates in favor of the formation of small CoSi2 precipitates in the vicinity of the voids, Subsequently, this CoSi2 phase then partially dissolves in favor of strongly surface bound Co.