Growth mechanism of interfacial IMCs on (111) preferred orientation nanotwinned Cu UBM for 3D IC packaging

The interfacial reaction in the solder interconnects with (111)-oriented nt-Cu as UBMs during the liquid-solid soldering was investigated, and the grain orientation evolution of interfacial intermetallic compounds (IMCs) during the interfacial reaction was also characterized. Due to the specific crystal orientation and high-density twins structure of (111)-oriented nt-Cu UBM, in the as-soldered state, the thickness and orientation of interfacial Cu
₆
Sn
₅
grains were remarkably affected by the (111)-oriented nt-Cu substrate. The interfacial Cu
₆
Sn
₅
formed on (111)-oriented nt-Cu substrate is significantly thinner than that on common polycrystalline Cu substrate; the orientation of interfacial Cu
₆
Sn
₅
grains formed on (111)-oriented nt-Cu substrate exhibits <;11-20> texture while randomly distributed on common polycrystalline Cu substrate. With increasing reaction time, the (111)-oriented nt-Cu substrate significantly reduce the growth kinetics of interfacial IMCs (Cu
₆
Sn
₅
and Cu
₃
Sn) compared with the common polycrystalline Cu. The <;11-20> preferred orientation Cu
₆
Sn
₅
grains initially formed on (111)-oriented nt-Cu substrate gradually transformed into random distribution with prolonged reaction time. This study will provide a better understanding on the interfacial reaction and the orientation evolution of interfacial IMCs with (111)-oriented nt-Cu as UBMs in 3D packaging technology.