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BEoL Damage Evaluation Utilizing Sub-Critical Cu-Pillar Shear Tests, Acoustic Emission, nXCT, and SEM/FIB Analysis

: Silomon, Jendrik; Gluch, Jürgen; Posseckardt, Juliane; Clausner, André; Paul, Jens; Breuer, Dirk; Zschech, Ehrenfried


Institute of Electrical and Electronics Engineers -IEEE-; IEEE Electron Devices Society; Japan Society of Applied Physics -JSAP-:
IEEE International Interconnect Technology Conference, IITC 2021 : Virtual Conference, July 6-9, 2021
Piscataway, NJ: IEEE, 2021
ISBN: 978-1-7281-7633-8
ISBN: 978-1-7281-7632-1
3 S.
International Interconnect Technology Conference (IITC) <24, 2021, Online>
Fraunhofer IKTS ()
mechanical BEoL reliability; Cu-pillar sheat test; acoustic emission (AE); nano x-ray computed tomography (nXCT); chip-package interaction (CPI)

In previous works, the resulting damages in the back end of line (BEoL) stack triggered by Copper pillar (Cu-pillar) shear-off events were evaluated and classified [1]. It was determined, especially by utilizing acoustic emission (AE) measurements, that damage events consist of multiple extremely fast sub-processes. The objective of this work is the development of an approach to enable the identification of the areas of damage initiation and comprehend the damage propagation in a BEoL stack under mechanical load by triggering only the initial sub-processes. Mechanical stress was induced into the BEoL stack utilizing a displacement-controlled sub-critical Cu-pillar loading approach with the approximate parametrization determined in previous experiments [1]. During mechanical loading, AE signals were constantly measured. As soon as significant acoustic events were detected, the experiment was aborted. The occurring damages were analyzed utilizing a customized nano X-ray computed tomography (nXCT) setup and focused ion beam (FIB) milling as well as scanning electron microscopy (SEM) imaging. In this work, a methodology could be developed to enable the evaluation of BEoL damages in an early, sub-critical stage. These results provide a better understanding of the damage formation and propagation in the BEoL stack and enable a design optimization procedure for the most damage prone areas.