EFFECT OF ION-BEAM MIXING TEMPERATURE ON COBALT SILICIDE FORMATION

In this study, the influence of ion-beam mixing temperature on CoSi2 formation during subsequent annealing was investigated. For mixing of cobalt layers on silicon, germanium ions were implanted at various substrate temperatures ranging from 25 to 500-degrees-C. RBS and TEM investigations showed that only in the case of mixing temperatures at or above 400-degrees-C, silicide phases like Co2Si, CoSi, and CoSi2 were formed during mixing. Annealing at 700-degrees-C resulted in a complete conversion into CoSi2 for samples mixed at 400 and 500-degrees-C whereas no reaction could be observed for all other samples. A second annealing step at 1000-degrees-C was necessary to achieve complete silicidation also for these samples. However, only ion-beam mixing at 400 and 500-degrees-C led to uniform CoSi2 layers with abrupt silicide-silicon interfaces. It can be concluded that radiation enhanced reaction takes place when performing ion-beam mixing above a critical temperature. In this case, a sufficient metal amount could be mixed into the silicon surface resulting in uniform silicide growth.