Growth Behavior and Orientation Evolution of Cu6Sn5 Grains in Micro Interconnect During Isothermal Reflow

At present, three-dimensional (3D) packaging technology is one of the effective methods to extend Moore's law. In 3D stacking, micro interconnects (below 30 μm) have been widely used. As for Cu/Sn/Cu micro interconnect, after repeated or long-term reflow, the micro interconnect will be mainly composed by Cu-Sn intermetallic compounds (IMCs) because of the small bonding gap and fast IMC growth rate under size effect. In the present research, a Cu/Sn(12.5 μm)/Cu micro interconnect was reflowed at 260 °C. Laminar scallop-like Cu
₆
Sn
₅
IMC was the dominant produce at both interfaces. The total thickness of the two Cu
₆
Sn
₅
layers and the consumption of the bottom Cu layer both showed a parabolic law with reflow time, and their logarithmic format followed a good linear relationship. It is also found that as the reaction time extended, the number of the Cu
₆
Sn
₅
grains decreased and the grain orientation tended to gathering towards certain directions, resulting in texture structure. The angle between the <;0001> direction of the Cu
₆
Sn
₅
grains and the growth direction of IMC (perpendicular to the interface) was analyzed to characterize the grain orientation evolution. The anisotropic growth of the Cu
₆
Sn
₅
grains along the <;0001> direction was discussed to reveal the mechanism of orientation evolution.