The time dependent dielectric breakdown (TDDB) in copper/ultra‐low‐k on‐chip interconnect stacks of integrated circuits has become one of the most critical reliability concerns in recent years. In this paper, a novel experimental in situ microscopy approach using transmission X‐ray microscopy (TXM) and scanning transmission electron microscopy (STEM) is proposed to study TDDB degradation and failure mechanisms. It combines electrical testing and imaging techniques. Low‐dose bright field (BF) STEM inserting a small condenser aperture is chosen to reduce the beam damage of the dielectric material, while the electron spectroscopic imaging technique is used for the chemical analysis to detect the migration path of Cu atoms. This new experimental approach will contribute to an improved understanding of the TDDB effect.
Laboratory transmission X-ray microscopy with a spatial resolution of about 100 nm was used to image 3D interconnect structures and failures in microchips during mechanical loading, applied by a microDouble Cantilever Beam (micro-DCB) test. High-resolution 3D image sequences based on nano X-ray computed tomography (nano-XCT) are used to visualize crack opening and propagation in fully integrated multilevel on-chip interconnect structures of integrated circuits. The nondestructive investigation of sub-micron cracks during the in-situ micro-DCB test allows one to identify the weakest layers and interfaces, to image delamination along Cu/dielectric interfaces (adhesive failure) and fracture in dielectrics (cohesive failure), as well as to evaluate the robustness of Backend-of-Line stacks against process-induced thermomechanical stress.
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