High TEC Copper to Connect Copper Bond Pads for Low Temperature Wafer Bonding

Abstract

Copper to copper wafer hybrid bonding is the most promising technology for three-dimensional (3D) integration. In the hybrid bonding process, two silicon wafers are aligned and contacted. At room temperature (RT), these aligned copper pads contain radial-shaped nanometer-sized hollows due to the dishing effect induced by chemical-mechanical polishing (CMP). These wafers are annealed for copper to expand and connect upper and lower pads. This copper expansion is key to eliminate the radial-shaped hollows and make copper pads contacted. Therefore, in this research, we investigated the new high thermal expansion coefficient (TEC) electrodeposited copper to eliminate the dishing hollows at lower temperature than that with conventional copper using the combination of new additive A and low TEC additives. The TEC of new electrodeposited copper is 25.2 × 10−6 °C−1, 46% higher than conventional copper and the calculated contact area of copper surface at 250 °C with 5 nm dishing depth is 100%.