Soft-template-assisted bottom-up fabrication of tunable porosity monolithic copper film for interconnection in microelectronics

Background:: Third-generation devices offer superior attributes, necessitating advanced packaging materials for harsh operating environments. Incorporating 3D porous architectures to increase the reaction area further enhances the reaction rate, making transient liquid phase bonding an ideal interconnection process. Methods:: Fabrication of monolithic porous Cu films using a bicontinuous microemulsion (BME) as a dynamic soft template is reported. The BME phase consists of interconnected three-dimensional networks of aqueous and oil phases, separated by surfactants and cosurfactants. This unique structure enables the selective electrodeposition of Cu exclusively within the aqueous region, preventing any unwanted reactions in the oil phase. Tunable porosity in the monolithic Cu film is achieved by adjusting the water to oil phase ratio in the BME. Significant findings:: The Sn-plated porous Cu films exhibit low-temperature reflow capability while still maintaining high service temperatures. The utilization of the BME soft template offers a promising approach for fabricating monolithic Cu films with tunable porosity, providing flexibility in controlling the compositions and performance of interconnections. The compatibility of the BME with existing wafer deposition techniques makes it a viable and scalable solution for mass production. The electrodeposition of monolithic Cu arrays on Cu pillars demonstrates its potential applicability in advanced packaging technologies.