The behavior of recrystallization and grain growth was examined in Cu-Cu joints during electromigration at 150 °C. Recrystallization and grain growth were observed in all the joints after electromigration for 9000 h. Voiding was formed in Cu current-feeding lines and in bonding interfaces, and resistance increased with time due to the void formation. However, instead of rising abruptly, the resistance of certain Cu joints dropped after 7000 h. Microstructural analysis revealed that a large grain growth occurred in these joints at 150 °C, and the bonding interface was eliminated. Therefore, the electromigration lifetime can be prolonged for these joints.
Keywords: Cu-Cu direct bonding; advanced packaging; electromigration; elimination of bonding interface; recrystallization and grain growth.