Microstructure control of copper films by the addition of molybdenum in an advanced metallization process

The effect of annealing on the resistivity, morphology, microstructure, and diffusion characteristics of Cu(Mo)/SiO2/Si and Ti/Cu(Mo)/SiO2/Si multilayer films has been investigated in order to deterine the role of Mo. In the case of a Cu(Mo)/SiO2/Si multilayer, most of the Mo diffused out to the free surface to form MoO3 at temperatures up to 500 C, and complete dissociation of Mo occurred at higher temperatures. The segregation of Mo to the external surface leads to Mo-free Cu films with extensive grain growth up to 20 times the original grain size and strong (111) texture. In the case of a Ti/Cu(Mo)/SiO2/Si multilayer, a thin Ti film prohibits Cu agglomeration, out-diffusion of Mo, and diffusion of Cu into SiO2 at temperatures up to 750 C. Cu(Mo) grain growth was less extensive, but (111) fiber texturing was much stronger than in the case of Cu(Mo)/SiO2/Si. In the current study, significant changes in microstructure, such as a strong (111) texture and abnormal grain growth, have been obtained by adding Mo to Cu films when the films are annealed.