Quantitative evaluation of bonding energy for the interfaces in Cu metallization systems

The toughness of two different interfaces in Cu metallization systems (Cu/barrier metals and Cu/cap layer) was evaluated by developed techniques. To establish the measurement technique at first, the effect of Cu film thickness on the evaluated toughness of the interface between Cu and barrier metal was examined. A small-scale yielding condition was realized even with ductile thin-film systems, and the toughness obtained was almost independent of the film thickness. The difference in the interface toughness among different Cu deposition techniques (sputtered and vacuum evaporated) was also quantitatively discussed. The method was then expanded to the Cu films as thin as those in the commercial integrated circuit. Finally, the toughness of interfaces between nanometer-scale cap layer materials and Cu was also evaluated by using a modified configuration of the specimens.