Interconnect Failure Dependence on Crystallographic Structure

A wealth of literature has arisen in the past couple of decades regarding the phenomenon of electromigration. In addition, stress voiding has received considerable attention from the research community. Some of the work on the structural character of these phenomena has focussed on the roles of crystallographic texture and grain boundary structure. It is an experimental fact that the strength of the (111) fiber texture is an indication of interconnect reliability, the stronger the texture, the more reliable the interconnect. It is also presumed that grain boundary diffusivity is a controlling factor in electromigration behavior of polycrystalline lines. Undesirable grain boundary structure is likely a cause of failure in lines with a bamboo structure as well because they are often sites of stress concentration and local incompatibilities. The present study focuses upon electromigration failures in test structures of Al-Cu lines and stress voiding in Cu lines. Texture and grain boundary structure were measured directly on the specimens using electron back-scatter diffraction and orientation imaging. It is observed that a correlation exists between grain boundary structure and void formation in strongly textured polycrystalline lines. Results indicate that secondary orientation (not just the (111) fiber), and boundary structure may be of primary importance in optimizing interconnect microstructure.