Process development of 10μm pitch Cu-Cu low temperature bonding for 3D IC stacking

Abstract

A low temperature <;200°C Cu-Cu bonding process is developed for 3D IC stacking application. To prepare and activate good copper surface, three planarization processes and two surface treatment methods are studied in details and compared. Best surface treatment method is identified. It is found that good Cu-Cu direct bonding with high shear strength is achieved by the developed process and verified by the cross sectional structure. Low temperature Cu-Cu bonding for 3D IC applications is demonstrated by a high density Cu bump array structure with 10 μm pitch and 5 μm diameter. Chip-to-chip bonding approach is used for 3D IC stack bonding. Final cross sectional and daisy chain electrical measurement showed good connectivity of micro bump joints.