A Robust in situ TEM Experiment for Characterizing the Fracture Toughness of the Interface in Nanoscale Multilayers

Abstract

A novel in situ transmission electron microscopy (TEM) bending method using a nano-cantilever specimen that includes a naturally sharp pre-crack at the interface between a 500 nm-thick SiN layer and a 200 nm-thick Cu layer on a Si substrate is developed in order to precisely characterize the fracture toughness of the interface in nanoscale multilayers. By fabricating a perpendicular nanoscale notch in the SiN layer close to the horizontal Cu/SiN interface, a sharp pre-crack is successfully introduced at the Cu/SiN interface. In addition, by changing the relative position of the notch with respect to the fixed end of the specimen, both the instant and continuous interface crack propagation behaviors could be in situ observed using TEM. Finite element analysis shows that the crack propagation from the sharp pre-crack is dominated by a singular stress field within a region 100 nm from the crack tip under a mixed-mode state in all specimens. On the other hand, the fracture toughness represented by the critical energy release rate for the start of crack propagation along the Cu/SiN interface in all specimens is determined through a compliance method and shows good agreement with an average value of 7.1 J/m2. This indicates the robust reliability and high precision for characterizing the fracture toughness of the interface in nanoscale multilayers.