STUDY OF CO SILICIDE FORMATION BY MULTIPLE IMPLANTATION

The annealing behavior of [111] Si implanted with cobalt to doses betw een 2.5 X 10(16) and 2 X 10(17) cm-2 at energies between 30 and 250 ke V has been investigated. The silicide formation during postannealing h as been found to proceed in two phases characterized by activation ene rgies of 0.8 +/- 0.3 and 2.9 +/- 0.3 eV. During the first phase a fast Co redistribution and pronounced nucleation and growth of the CoSi2 p recipitates at defects has been observed. The investigation of the dos e dependence proved that the amount of Co redistributed during this ph ase depends on the initial Co and defect concentration. However, the p rocesses contributing to this fast Co redistribution require further i nvestigation. The second step is well characterized by Ostwald ripenin g. Multiple implantations of Co at different energies have been applie d to modify the Co concentration profile. In this way, it is possible to form Si/COSi2/Si/CoSi2-layer systems on Si substrate with different layer thicknesses. All Si layers and the deeper lying CoSi2 layer are A type, whereas the crystalline orientation of the near surface layer depends on the procedure of formation. If the dose of the second impl antation is too high CoSi nucleates during implantation. The CoSi prec ipitates are dissolved during annealing and a COSi2 surface layer of t ype A is formed. Additional Si implantations offer the possibility to modify the defect profile without changing the Co distribution. During the subsequent annealing a redistribution of Co into the region of th e additional defects was observed. Thus, implantation defects act as s inks for the metal atoms and play an important role during the first p hase of the annealing process.