Initial stages of cobalt-disilicide formation in mesotaxy

We present results on the formation of buried silicide layers at ion implantation doses in the range of 1-60% of the critical dose for formation of a uniform layer We emphasize observations for the low-dose range of 1-5% where the precipitate density is quite dilute. The Co redistribution during post-implant annealing is measured using Rutherford backscattering techniques and secondary ion mass spectrometry. Experimental observations during postimplantation annealing at 1000 degrees C involves (i) a contraction of the Co depth profile for all doses, (ii) shifting of the peak of the profile towards the hulk, and (iii) formation of a secondary Co peak near the surface. The secondary peak is only present in samples implanted to greater than 3% of the critical dose. The interpretation of the shift of the main peak and the occurrence of the secondary peak requires a model exceeding the standard ripening model used previously to describe mesotaxy. We suggest that more recent ripening-based concepts allow for a full description of these observations with a minimum of parameters, particularly not requiring interaction with the complex defect profiles formed initially during implantation. Essential for this model is a proper inclusion of precipitate-precipitate interactions and the role of diffusion screening.