Simulation of crack penetration/deflection and interfacial toughness at a bimaterial interface for thin films on a substrate

The reliability of microelectronic devices, which are built by multi-layer film deposition, is a strong function of cohesive strength of the films and adhesive strength of bimaterial interfaces present. As technology progresses, the need for smaller and faster chips pushes the limit of traditional materials such as Aluminum and Silicon oxides. Low dielectric constant (low-k) materials are replacing silicon oxide. The integrity of the interfaces between the new materials and other films, among other factors, is dependent upon the intrinsic stresses in the films during deposition, and stresses due to the coefficient of thermal expansion mismatch in subsequent heating and cooling events.;A number of techniques have been developed to measure adhesion of a thin film to its substrate. Most of the techniques suffer from a common disadvantage, which is that it is difficult to distinguish between delamination energy and other energy dissipation processes due to excessive plastic deformation.;This work focuses on the four-point bend (4PB) test, which is an industry standard in assessment of adhesion in thin films. Obtaining crack propagation along the desired interface plays a critical role in the success of this test. Crack penetration and deflection at a bimaterial interface has been extensively studied in the past. It has been shown that previous results based on asymptotic analyses involving the interface between two semi-infinite media, cannot be directly used to understand the 4PB test, since the boundary conditions and finite size effects in actual test specimen geometry are not accounted for.;We also look at the role residual stresses play on the competition between deflection and penetration energy release rates of a bimaterial interface and the extent to which the previous assumption of two semi-infinite media can be accepted.