Eliminating Voids at Al 2 O 3 –Cu Interface During Direct Bonding

Direct bonding copper technique employs a eutectic liquid from C u– O system to bond copper to alumina. Many semispherical voids are found at the A l 2 O 3 – C u interface after bonding. Both the amount and the size of voids increase with the increase of oxygen content in copper. The void formation is resulted from the reduction of C u 2 O precipitates during bonding. Based on this observation, an approach to prevent the formation of voids is proposed. The approach introduces a sacrificial coating onto A l 2 O 3 substrate before bonding. The coating consumes the oxygen from the reduction, and the amount of voids is then reduced significantly.