Low Temperature Cu-to-Cu Bonding in Non-vacuum Atmosphere with Thin Gold Capping on Highly (111) Oriented Nanotwinned Copper

Abstract

Cu-to-Cu bonding has drawn a lot of attention as it not only has excellent electrical and thermal properties but also excellent electromigration resistance. It is believed to be a next-generation technology of IC packaging and it will help keep Moore's law effective. According to previous studies, copper direct bonding using nanotwinned copper can reduce the bonding temperature to 150 degrees C but still requires a vacuum atmosphere. This study employed an E-gun to plate a gold layer on nanotwinned copper thin films in order to prevent oxidation. With the aid of the thin gold layer, we can prevent the oxidation of Cu surfaces and reduce the surface roughness. In this way, we achieved bonding at 200 degrees C in N-2 and 250 degrees C in ambient pressure with a low bonding pressure of 0.78 MPa.