Fracture mechanics life-time modeling of low temperature Si fusion bonded interfaces used for 3D MEMS device integration

In addition to through silicon vias (TSV), wafer bonding became one of the key process steps within 3D integration technologies that allows stacking image or MEMS sensor chips on top of ASIC. Depending on the package, the wafer bonded interface can be loaded by built-in residual stresses and the risk of defect generation and propagation - caused by stress corrosion of the highly loaded siloxane - can lead to bond delamination and failure of the TSV interconnects. In this paper, the basic processes affecting the long-term strength properties in Si bonded interfaces are discussed and summarized on a specific demonstrator. Using finite-element simulation, it is shown that if low temperature Si fusion bonded components are mechanically stressed for extended times a subcritical crack growth of pre-existing micro-defects can occur. Fracture mechanics approaches were applied to predict the time-dependent strength reduction of initial defects, analyzed by Scanning-Acoustic-Microscopy. In addition, the paper presents a general framework of how the life-time properties of loaded low temperature fusion bonded interfaces can be simulated and how the needed material parameters can be determined. Using this method it is possible to consider the life-time properties already during the design stage, thus, reducing the risk of reliability issues during field use.