Method for lowering resistance value of cobalt disilicide layer of semiconductor devices

In the invention, first a layer of metal cobalt is formed on silicon substrate. Next, two times of annealing treatment are carried out. First annealing treatment turns layer of metal cobalt to layer of cobalt silicide (CoSi). Then, a covering layer in thickness of 1000-3000 Angstrom is formed to cover the layer of metal cobalt in order to restrain regrowth of crystal grain of cobalt silicide in following procedure. Finally, second annealing treatment is carried out to turn the layer of cobalt silicide to layer of disilcobalt (CoSi2).