Brittle fracture and damage in bond pad stacks: Novel approaches for simulation-based risk assessment

We have presented an advanced FEM simulation model that is able to map the scenario of indentation of a diamond tip into a thin brittle SiN_x:H film deposited on a Si substrate. Our 2D axisymmetric and 3D quarter and half models are able to reproduce all failure modes observed in preceding indentation experiments. On the one hand, brittle fracture in both film and surface were successfully modelled via the XFEM approach implemented in ABAQUS™ Standard, using the VCCT method. This includes circumferential cracks on top of the silicon nitride film with directional crack initiation. On the other hand, we have replicated interface delamination by means of an energy-based Cohesive Zone approach. Simplified 2D models already enable appreciable insight into the nature of underlying failure mechanisms, i.e., over-critical mechanical stress. A complete 3D model comprising all relevant failure mechanisms and modes will be content of a future work. The mutual dependence of fracture onset, delamination, and elastic-plastic deformation will require further refinement and even higher exactitude of the embedded material models. All in all, the volume of information gathered in the scope of this work will be of paramount importance as to sophisticated FE models. In particular, top metallisation layers will add complexity in models describing the indentation process into BEOL bond pad stacks.