Copper direct bonding for 3D integration

In 3D integration circuits, metal bonding is a key stage for stacking wafers. In this contribution, the direct Cu/Cu bonding at atmospheric pressure is investigated. At room temperature, a 2.8 J/m
²
bonding toughness is achieved without copper oxide at the interface. The vertical current of this bonding and the possibility to grind the top silicon down to 10 μm have been demonstrated.