Influence of air gaps on the thermal-electrical-mechanical behavior of a copper metallization

Shrinking the IC dimensions the dielectric insulation between metal interconnects has become one of the major limits on increasing circuit speed. A lot of possible new low-k materials failed to meet specifications: too leaky, too soft, too unstable, and too expensive. Due to this air gaps beside the metallization are one solution. The reliability of ULSI multilevel copper metallizations under electro- and stress migration stress test conditions is investigated here with finite element analysis. A determination of the electrical and mechanical stress in a 3D copper metallization model based on the 45 nm technology node is carried out and the impact of a variation of the applied current density as well as geometrical parameters on the thermal-electrical and mechanical behavior is investigated. For a determination of the reliability the mass flux and mass flux divergence are separately calculated by a user routine. The influence of air gaps on single via structures and structures with a chain of four vias on the thermal-electrical-mechanical behavior is determined.