Measurement of interfacial fracture energy in microelectronic multifilm applications

摘要

A testing method in the literature, the modified edge lift-off test (MELT), was evaluated as a potential candidate for determining the quality of interfaces. Delamination is induced through the release of strain energy stored in an elastic superlayer which results from a large mismatch in coefficients of thermal expansion (CTE) between the film and substrate. However, several experimental issues as well as the mechanics used to describe the problem need to be considered closely. In this work a critical examination of the energy release rate was considered. Experimental data suggest that the energy release rate is independent of starting flaw size for starter flaws greater than 5% of the epoxy film thickness. This is contrary to a conventional rule of thumb that suggests the energy release rate, G, only achieves steady state conditions after the crack length exceeds 10-20 times the film thickness. Numerical models confirm this observation for epoxy films on silicon substrates. Simulations of a chromium film were also performed to (a) confirm that the models were consistent with chromium simulations in the literature and (b) to evidence that the observed behavior of the epoxy/silicon system was due to the low modulus of the epoxy film relative to the substrate. The rule of thumb does not apply when Young's modulus of the film is much smaller than the substrate Young's modulus.