Mechanical stability of Cu/low-k BEOL interconnects

Different approaches combining Finite Element Simulations and in-situ electrical measurement of stress sensors during a BABSI test are proven to be ideal combination to quantitatively compare the strength of BEOL layers. It is shown that detectable mechanical failures during a shear or BABSI test are insufficient to detect early opens of the metal interconnections. A good agreement was found between the applied loads to the BEOL stack, the response of stress sensors below the Cu pillar and finite element simulations. Next, the risk of cohesive and adhesive failures in the Cu/low-k layers is evaluated in function of stiffness of low-k and design of metal interconnections.