Effect of residual nanotwin on electromigration in copper lines with bamboo-like structures

Electromigration (EM) poses significant reliability challenges, especially as the line/space (L/S) of Cu redistribution lines (RDLs) continues to scale down. This study investigates the EM lifetime reliability of bamboo-like (BL) structure Cu lines with and without nanotwins. EM tests were conducted under a high current density (1.0 × 10 6 A/cm 2 ) at a low temperature (150 °C) in ambient air. The results show that BL nanotwinned Cu (BL-NT-Cu) lines exhibited densely packed twin boundaries (twin spacing = 108 nm), a high fraction of (111)-oriented grains (64 %), and a lower oxidation rate (0.04 nm/h) compared to BL-Cu lines, which contributed to enhanced EM resistance. It was found that BL-NT-Cu lines had a significantly longer EM lifetime (T 50 = 3551 h) than BL-Cu lines (T 50 = 779 h). The study highlights the potential of the BL-NT-Cu structural design in improving the EM reliability of fine L/S Cu-RDLs, offering a viable strategy for developing high-density, high-performance advanced packaging applications.