Effect of deposition temperature and sputtering ambient on in situ cobalt silicide formation

An investigation of in situ cobalt self-aligned silicide (salicide) formation has been carried out with emphasis on the effect of the deposition temperature and the role of nitrogen atoms in the sputtering ambient. The cobalt (Co) layer was deposited at between 300 and 500 degrees C in a mixed atmosphere of nitrogen and argon; the nitrogen volume percent [N-2 volume percent (v/o)] was,varied from 0 to 10%. The addition of nitrogen atoms to the sputtering ambient resulted in a poly morphic change of the Co layer which was deposited on the SiO2 substrate; from alpha-Co to beta-Co. At the same time, it limited the surface mobility of the sputtered atoms, resulting in a decrease of grain size. Specifically, during Co deposition on a Si substrate at temperatures as high as 500 degrees C, insitu cobalt silicide (CoSi) was formed. In that process, nitrogen atoms limited the available Co atoms involved in the reaction with the Si substrate, yielding the bilayer formation of beta-Co/CoSi. As the N-2 v/o increased, the thickness of the overlying beta-Co increased and that of the underlying CoSi decreased with improvement in the uniformity of the silicide film. It shows good selectivity with no overgrowth on the sidewall oxide, but also extremely uniform salicide on both the silicon and the polysilicon substrate. As a result, satisfactory electrical characteristics were obtained because of thin and uniform CoSi2 salicide.