Enhanced Nanotwinned Copper Bonding through Epoxy-Induced Copper Surface Modification

Abstract

For decades, Moore’s Law has neared its limits, posing significant challenges to further scaling it down. A promising avenue for extending Moore’s Law lies in three-dimensional integrated circuits (3D ICs), wherein multiple interconnected device layers are vertically bonded using Cu–Cu bonding. The primary bonding mechanism involves Cu solid diffusion bonding. However, the atomic diffusion rate is notably low at temperatures below 300 °C, maintaining a clear and distinct weak bonding interface, which, in turn, gives rise to reliability issues. In this study, a new method of surface modification using epoxy resin to form fine grains on a nanotwinned Cu film was proposed. When bonded at 250 °C, the interfacial grains grew significantly into both sides of the Cu film. When bonded at 300 °C, the interfacial grains extended extensively, eventually eliminating the original bonding interface.

Keywords

• Cu–Cu direct bonding
• surface modification
• grain refinement
• abnormal grain growth
• nanotwinned Cu