Fabrication of Cu-Ag Interconnection Using Electrodeposition: The Mechanism of Superfilling and the Properties of Cu-Ag Film

The dimensions of Cu interconnections in electronic devices have been rapidly reduced to achieve high integration. The continual down scaling considerably increases both the electrical resistivity and the probability of electromigration failure. The addition of a secondary metal into Cu can improve the resistance against electromigration. However, the co-deposition of a secondary metal inevitably reduces the electrical conductivity. Thus, the main consideration in alloying with Cu is to find a secondary metal that shows the lowest resistivity. Ag has been known as the most appropriate. In this research, the superfilling of Cu-Ag and its mechanism are investigated. The area reduction at the surface with negative curvature induces the accumulation of adsorbed accelerators, finally resulting in local increment of the deposition rate of Cu-Ag at the bottom of a trench. Additionally, the microstructure of Cu-Ag film is investigated, and it is confirmed that Cu-Ag film exhibits superior oxidation resistance and mechanical strength without severe deterioration of the electrical conductivity compared to pure Cu.