Contact Resistivity of Submicron Hybrid Bonding Pads Down to 400 nm

Abstract

Three-dimensional (3D) stacking using hybrid bonding is the most scalable method for 3D integration. As the hybrid bonding pad width is reduced to adopt a higher number of interconnections, the ability to extract the contact resistivity at the bonding interface with high accuracy is critical. Using specific electrical test structures and a dedicated methodology, we extract the contact resistivity for hybrid bonding pad widths down to 400 nm for a Cu/SiO2 hybrid bonding integration. Very low values around 10−11 Ω cm2 were obtained for our reference process, close to the those of Cu grain boundaries. A comprehensive analysis of the experimental contact resistivity is performed to understand its increase with the Cu recess within the bonding pads. Based on thermomechanical simulations and experimental results, the influence of both the pad thickness and initial dishing on the interface closure is discussed, for bonding pad width down to 100 nm. These analyses enable us to propose process conditions to reach low contact resistivity with low sensitivity to wafer-to-wafer overlay for hybrid bonding stacking using bonding pad widths down to 100 nm.