ChipPackage Interaction and Crackstop Study for CuUltra lowk Interconnects

In this paper, the thermo-mechanical reliability of Cu/ultra low-k interconnects under chip to package interaction was investigated using finite element modeling and modified edge liftoff test (MELT). The crack propagation behavior in the low-k interconnect was simulated based on the crack tip opening displacement method (CTOD) and the maximum hoop stress criterion. In a six-level Cu/low-k interconnect model, the crack was found to grow from interconnect towards the Si substrate driven by shear stress and the calculated energy release rate (ERR) increases as crack grows. Structure reinforcement such as crackstops was demonstrated to be very effective in preserving the low-k interconnects integrity by reducing the crack driving force and increasing the fracture resistance if properly designed.