Mechanical integrity of nano-interconnects; the impact of metallization density

Abstract

In this study the impacts of two main design parameters, namely the metal and via densities on the mechanical integrity of nano-interconnects were investigated. To this aim, analytical modelling was used in order to derive the effective mechanical properties of nano-interconnect layers which were subsequently used as material properties in a layer-specific finite element model of nano-interconnects exposed to bump level mixed mode loading. The energy release rates for nano-interconnect cracks were used to determine the impact of metal and via density variations on the mechanical integrity of nano-interconnects. Using a parametric study, the key parameters that determine the mechanical integrity of nano-interconnects under chip package interaction (CPI) loads were identified to be the via densities in the intermediate layers with ultra low-k dielectric (ULK) and the via and metal densities of the top stiff group of layers often referred to as the “Z” group. Increasing the effective stiffness of the “Z” group by maximizing its via and metal density mitigated the energy release rate at the ULK pre-cracks in the intermediate via layers by means of elastic stress shielding. In addition, increasing the via density of the via layers integrated with ULK, increases the effective critical fracture energy of the via layer (i.e. the effective via layer adhesion), thereby improving the mechanical integrity. Keywords: Nano-interconnect, Mechanical integrity, Delamination, Chip package interaction (CPI), Metal density, Via density