Enhancement of Low-Temperature Cu-Cu Bonding by Metal Alloy Passivation in Ambient Atmosphere

This study proposes a chip-level integration scheme that uses Cu-Cu passivation bonding of metal alloys passivation with a low thermal budget (120 degree celsius) and short bonding duration (60 s) in an ambient atmosphere. This is achieved by employing an Ag-based alloy passivation bonding structure with three different thicknesses of passivation layer structures (3 nm, 30 nm, and 50 nm). The Ag-based alloy mitigates the abnormal grain growth of pure Ag, thus attaining superior grain morphology. With the Ag-based alloy passivation layer, better bonding quality, shorter bonding duration, and more stable electrical properties can be achieved. Furthermore, the enhancement of the Cu-Cu bonding with a thicker Ag-based alloy passivation layer was successfully verified. Consequently, the Ag-based alloy passivation structure offers a low thermal budget and a high throughput bonding process, making it suitable for chip-to-wafer integration.