2, Helmholtz-Zentrum Berlin, Berlin, , Germany
Leading-edge CMOS technology nodes use transistors with down-scaled dimensions, and simultaneously, challenge design and materials integration of on-chip interconnect stacks. Particularly insulating ultra low-k (ULK) materials with low Young’s modulus and fracture toughness weaken the mechanical behavior of the backend-of-line (BEoL) stack. Chip-package interaction (CPI) and the related thermomechanical stress increase the risk of failure caused by delamination along Cu/dielectrics interfaces (adhesive failure) and fracture in dielectrics (cohesive failure). In order to avoid mechanical chip damage, so-called crack-stop structures are integrated . Transmission X-ray microscopy (TXM) with sub-100nm resolution and nano X-ray computed tomography (nano-XCT) are a unique techniques to image crack propagation in interconnect stacks. We demonstrate in-situ crack propagation studies in BEoL structures. Based on 3D data sets, weak interfaces in the BEoL stack are identified and the effectiveness of crack stop structures is evaluated. The study of the crack evolution was performed in a laboratory-based X-ray microscope (Xradia) using a micro double cantilever beam (micro-DCB) test  and using synchrotron radiation (BESSY II Berlin) using an indenter manipulation . Conclusions will be discussed in the frame of fracture mechanics.
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 S. Niese, “Lab-based in-situ X-ray microscopy – Methodical developments and applications in materials science and microelectronics“, PhD thesis, BTU Cottbus (2015)
 K. Kutukova, J. Gluch, Y. Standke, E. Zschech, “Crack evolution in Cu/low-k stacks and crack stop evaluation using in-situ micro-DCB in a nano-XCT tool“, FCMN conference, March 2017, Monterey/CA (2017)