An investigation was made of the annealing behavior of <111> Si which had been implanted with Co, to doses of between 2.5 x 1016 and 2 x 1017/cm2, using energies of between 30 and 250keV. The formation of silicide during post-annealing was found to proceed via 2 stages which were characterized by activation energies of 0.8 and 2.9eV. During the first stage, fast Co redistribution and pronounced nucleation and growth of

CoSi2 precipitates at defects were observed. An investigation of the dose dependence proved that the degree of Co redistribution during this stage depended upon the initial Co and defect concentrations. However, the processes which contributed to this fast Co redistribution required further investigation. The second stage was characterized by Ostwald ripening. Multiple implantations of Co with various energies were used to modify the Co concentration profile. In this way, it was possible to form Si/CoSi2/Si/ CoSi2 layer systems, on Si substrates, with various layer thicknesses. All of the Si layers, and the deeper-lying CoSi2 layer, were A-type whereas the crystalline orientation of the near-surface layer depended upon the formation process. If the dose of the second implantation was too high, CoSi nucleated during implantation. The CoSi precipitates dissolved during annealing, and a CoSi2 surface layer of type-A was formed. Additional Si implantation offered the possibility of modifying the defect profile without changing the Co distribution. During subsequent annealing, Co redistribution into the region of the additional defects was observed. It was concluded that implantation defects acted as sinks for metal atoms, and played an important role during the first stage of annealing.

A.Witzmann, S.Schippel, A.Zentgraf, P.I.Gajduk: Journal of Applied Physics, 1993, 73[11], 7250-60