Instant Cu-to-Cu direct bonding enabled by 〈111〉-oriented nanotwinned Cu bumps

Cu-to-Cu direct bonding was successfully achieved in 10 s with 〈111〉-oriented nanotwinned Cu (nt-Cu) bumps in ambient N2. The bonding temperature and pressure were 300 °C and 90 MPa, respectively. A nearly void-free interface and a low bump resistance of 4.9 mΩ can be observed after a short-time bonding process. Besides, longer bonding times of 60 s and 30 s were employed, but the resistances of the Cu joints did not decrease significantly when the bonding time increased to 60 s. However, the nt-Cu columnar grains started to recrystallize during the 60 s bonding and started detwinning in 10 s bonding. Yet, the bonding interface remained under such a short bonding time.