ISMP 2024

Abstract

• Technologies for heterogeneous integration of ICs and chiplet architectures face significant challenges to ensure the requested mechanical robustness of microelectronic products, particularly for use cases that require lifetimes much longer than in the past and for safety-critical applications. Microcracks in backend-of-line stacks, introduced e.g. during dicing of the wafer, are serious reliability concerns since they can grow and ultimately cause catastrophic failures in chiplets. Advanced packaging technologies and the integration of materials with different coefficients of thermal expansion (CTE) cause thermomechanical stress in packaged systems and in each chiplet, both during manufacturing and during operation of microelectronic products, that accelerates degradation processes such as microcrack propagation in backend-of-line stacks.
  For the understanding of reliability-limiting degradation and failure mechanisms in 3D-stacked ICs and for package failure analysis, new analytical techniques are needed. In this talk, the inherent advantages of high-resolution transmission X-ray microscopy (TXM) and nano X-ray computed tomography (XCT) for the nondestructive imaging of kinetic processes such as microcracks evolution in chiplets is demonstrated – as opposed to destructive failure analysis methods. We will show how the combination of a micromechanical test and high-resolution X-ray imaging allows to perform in-situ studies of crack propagation in backend-of-line stacks. A miniaturized Double Cantilever Beam (micro-DCB) test was designed and built, to grow microcracks in on-chip interconnect structures by applying a precisely controlled mechanical load and by monitoring force and displacements in the materials at the micro- and nanoscale. The methodology described allows a controlled steering of microcracks, e.g. generated during the wafer dicing process, into regions with relatively high fracture toughness. Based on nano-XCT studies, the effectiveness of guard rings, i.e. metallic structures at the rim of the chiplets, to stop microcracks was shown and input for the design of guard ring structures could be provided.
  
  Keywords: X-ray microscopy, failure mechanisms, microchip robustness, interconnect reliability, crack propagation

Biography

• Dr. rer. nat. Kristina Kutukova, received PhD from the Brandenburg University of Technology Cottbus-Senftenberg, Germany, in 2023. Her doctoral work, focusing on an "In-situ study of crack propagation in patterned structures of microchips using X-ray microscopy" earned her the DGM Young Scientist Award in 2023. Kristina Kutukova was a research associate in the Department of Microelectronic Materials and Nano-scale Analysis at Fraunhofer Institute for Ceramic Technologies and Systems Dresden, Germany, for more than 5 years. In the previous two years, she was acting as Head of the Development and Application Lab at deepXscan GmbH, a start-up company in Dresden, with the main tasks to the develop customized solutions for high-resolution 3D imaging and to coordinate development projects. Since June 2024 she works at Fraunhofer Institute for Reliability and Microintegration, All Silicon System Integration Dresden as a Scientific Advisor.

Abstract

• The rapid evolution of advanced packaging technologies, including hybrid bonding, presents significant challenges for metrology, defect inspection and physical failure analysis (PFA). To address these challenges, innovation in microscopy techniques and related workflows are required. The development of next-generation analytical tools that can tackle technologies for heterogeneous integration of ICs and chiplet architectures is a challenge to engineers at universities, research institutes and equipment manufacturers. With respect to nondestructive imaging, a balance between acquisition speed and achievable resolution is always a consideration for engineers [1]. Scanning acoustic microscopy (SAM) continues to be the tool of choice for inspecting interfacial integrity (e.g. delamination), and detecting defects (e.g. voids, cracks) in bonded wafers [2]. However, conventional SAM techniques reach limits for 3D-stacked dies since highly penetrating low frequency acoustic waves are unable to provide high resolution imaging of high-density submicron interconnects, and because of requirements to spatial resolution of 500 nm and below. In addition, the convolution of signals from various die interfaces makes it difficult to select the correct signal for rendering the right image from the interface of interest. Several beyond state-of-the-art approaches are addressing these challenges. We will demonstrate the detection of voids in through-silicon-vias (TSVs) applying the new GHz-SAM technology [3]. SAM interferometry, where the defocused sound field induces surface-acoustic-waves, provides unique interference patterns associated with the quality of each TSV. Finally, a fully automated high-efficient End-to-End Convolutional Neural Network model classifies thousands of TSVs and provides statistical information [4]. X-ray microscopy and high-resolution X-ray computed tomography (XCT) are well-known FA techniques that have been applied to visualize defects in metal interconnects and package structures such as TSVs, Copper pillars and solder microbumps [5,6]. However, usually a compromise had to be made between image quality and scan throughput, and state-or-the-art laboratory nano-XCT requires a destructive workflow. High-resolution imaging of voids in Cu-TSVs and AgSn microbumps will be shown, using conventional nano-XCT after thinning the Si down to about 50 m. To image defects with sub-500nm and sub-100nm size, respectively, further development of micro-XCT and nano-XCT techniques are needed. To ensure a highly reliable inspection method, the time for image acquisition must be reduced significantly without sacrificing the resolution of the X-ray images. Ways for a drastic throughput increase are high-brilliance laboratory X-ray sources and the application of AI algorithms for imaging of objects with large form factors (dies, wafers) and high-speed data processing. In addition, we will demonstrate for solid–liquid interdiffusion (SLID) bonded Cu/Cu6Sn5/Cu interconnects that in the hard X-ray regime, i.e. at photon energies > 10 keV, destructive sample preparation steps for nano-XCT are not needed [7]. An outlook for a seamless workflow for advanced package FA and defect inspection, that combines acoustic and X-ray techniques to auto-detect and auto-classify defects, with the goal to improve throughput and defect detectability, will be presented.
  
  [1] EDFAS Electronic Device Failure Analysis Technology Roadmap, ASM International (2023)
  [2] S. Brand et al., Microsystem Technologies 21, 1385–1394 (2015)
  [3] A. Phommahaxay et al., Proc. 63rd IEEE ECTC 2013, Las Vegas/NV, pp. 227 - 231 (2013)
  [4] P. Paulachan et al., Scientific Reports 13, 9376 (2023)
  [5] Y. Sylvester et al., Proc. ASMC, Saratoga Springs/NY, pp. 249–255 (2013)
  [6] E. Zschech et al., Proc. 20th PanPacific Microelectronics Symposium, Kolao/HI (2015)
  [7] B. Lechowski et al., Nanomaterials 14, 233 (2024)

Biography

• Ehrenfried Zschech is a consultant with hands-on experience in the fields of advanced materials, nanotechnology and microelectronics as well as process control and quality assessment. He holds honorary professorships for Nanomaterials at Brandenburg University of Technology Cottbus-Senftenberg and for Nanoanalysis at Dresden University of Technology. His activities include high-resolution X-ray imaging and the development of customized solutions for a broad range of applications including package failure analysis, metrology and inspection in microelectronics. Ehrenfried Zschech received his Dr. rer. nat. degree from Dresden University of Technology. He had several management positions at Airbus, at Advanced Micro Devices, at Fraunhofer and at the start-up deepXscan. Ehrenfried Zschech is Member of the European Academy of Science (EurASc) and Member of the of the German National Academy of Science and Engineering (ACATECH). In 2019, he was awarded with the FEMS European Materials Gold Medal.