Area-Selective Electroless Deposition of Cu for Hybrid Bonding

This letter describes the use of area-selective electroless Cu deposition for topography control of Cu-SiCN hybrid bonding pads. The electroless deposition of Cu allows one to obtain protrusions on hybrid bonding Cu pads without further polishing optimization. A recessed Cu pad after chemical mechanical polishing becomes a protrusion after electroless deposition. This indicates that the electroless Cu film was selectively deposited on Cu, without deposition on the SiCN surface. A void-free Cu-Cu bonding interface was observed after annealing at 350 °C with an electroless Cu layer at the interface. 100% electrical connection was obtained at 1.4- μm pitch where the deposition thickness was on target.