Microstructure and growth of Cu hillock on redistribution line under electromigration

The formation of hillock at the anode side of a circuit under electromigration is detrimental to electrical performance and electronic reliability. The study presented a detailed investigation of the microstructure of Cu hillock formed on 2 μm x 3 μm Cu redistribution line under high electrical current density 1.44 × 10⁷ A/cm². The electron backscatter diffraction analysis revealed that the microstructure of the Cu redistribution line remain intact after 162 min current stressing. High-resolution transmission electron microscope analysis showed that the dome shape Cu hillock formed is polycrystalline with amorphous inclusion and twin structure. A mechanism considering radial surface diffusion of Cu atoms was proposed to illustrate the growth of dome shape Cu hillock under electromigration.