Cohesive zone modeling on fatigue fracture of Cu/Si interface in nanoscale multilayers

This study investigates the fatigue delamination of the Cu/Si nanoscale interface using a cohesive zone model (CZM) informed by in situ Transmission Electron Microscope (TEM) experiments. CZM parameters including the cohesive strength, initial stiffness, final failure displacement, and damage scaling factor are determined through finite element analysis and validated by comparative verification. The plastic deformation behavior of the Cu layer during fatigue loading is analyzed, and the cumulative damage evolution leading to interface delamination is elucidated. The damage threshold, represented by the cohesive strength of the Cu/Si interface, is identified as 1.25 GPa, with plastic deformation in the Cu layer occurring exclusively during the first cycle, which accounts for the residual deflection observed in the load-displacement curve. The damage progression involves three stages: an initial stage with a damage variable of 0.47, a cumulative fatigue stage where the damage variable reaches 0.81, and eventual rapid failure, resulting in the instantaneous fracture observed experimentally. Interface failure, primarily governed by normal stress, is characterized by a damage zone extending 70 nm where the damage variable is nonzero, and a localized damage concentration zone of 12 nm in which the damage variable is close to 1. These findings provide valuable insights into the evolution of damage and the progression of failure of fatigue-induced delamination at nanoscale interfaces.