Properties of activated formic acid using for low- temperature all-copper interconnect assisted with nanoparticles paste

Currently, electronic packaging technology is towards miniaturisation and high interconnect density to meet the demands for high performance, high reliability and low cost electronic devices. As the pitch and size of the microbumps decreases, it becomes significantly more difficult to establish reliable interconnections on the chip due to the increased risk of bridging. To overcome the inherent limitations of solder-based interconnects and to meet the need for higher current densities, all-copper interconnects with high conductivity are a promising approach. However, the impact of Cu pillar surface flatness on the bonding interface remains a bottleneck in all-copper interconnect technology. In this paper, a Cu nanoparticle paste assisted sintering method in an activated formic acid atmosphere was presented to improve the low- temperature bonding performance for all-copper interconnects. The hydrogen radicals generated by the activated formic acid atmosphere effectively protect the Cu nanoparticles from oxidation resulting in the formation of a dense sintered layer even at 250°C for 10 min. And a shear strength of 32 MPa was obtained for 30 min. Moreover, the resistance and specific contact resistance of the bare Cu pillar was 2 mΩ and 10 Ω. µm
²
, respectively. In addition, the sintering mechanism assisted with Cu nanoparticles was explained. This method can effectively reduce the requirements of Cu pillar surface electroplating process during wafer fabrication, and has potential applications in all-copper interconnect technology.