Effect of Nanotwin Boundary on the Cu-Cu Bonding

Cu direct bonding has been achieved at 120 C by using (111)-oriented nanotwinned Cu because it has the fastest surface diffusivity. In this study, the effect of nanotwin boundary on the Cu bonding was investigated by using two types of (111)-oriented Cu films: sputtered 97% (111)-oriented Cu films and electroplated nano-twinned-Cu films. Artificial voids were introduced at bonded interfaces by bonding an etched-Cu sample to an unetched-Cu. The evolutions of interfacial voids were investigated at 150 C and 200 C. It was found that nanotwin boundary could enhance the transport of Cu atoms, thus enhance Cu-Cu direct bonding.