Crack identification and evaluation in BEoL stacks of two different samples utilizing acoustic emission testing and nano X-ray computed tomography

• Published in: Microelectronics and reliability Vol. 121; p. 114137
• Main Authors: Silomon, Jendrik, Gluch, Jürgen, Clausner, André, Paul, Jens, Zschech, Ehrenfried
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-06-2021
• Subjects: Acoustic emission; Back end of line; Chip package interaction; Microcrack; X-ray computed tomography; Acoustic emission; Back end of line; Microcrack; X-ray computed tomography; Chip package interaction
• ISSN: 0026-2714; 1872-941X
• DOI: 10.1016/j.microrel.2021.114137

A novel approach is presented to evaluate the mechanical stability of back end of line (BEoL) stacks. A SRAM test vehicle manufactured in 28 nm technology with copper pillar bumps is used. In a second step, the validity of the approach is also shown for a second sample manufactured in 22 nm technology and the experimental results are compared. To inflict damage to the BEoL stack of the respective semiconductor device, external forces are applied to the copper pillars (Cu-pillars) by shear loading using a tribo-indenter system. An acoustic emission (AE) detection sensor is attached to the sample to measure acoustic waves during the shear experiment as an indication for damage. The damage progression in the BEoL stack is extremely fast, hence details can't be resolved anymore with the piezo sensors of the tribo-indenter. However, due to the much higher temporal resolution, AE measurements give a more precise insight into the damage process. The resulting damages are imaged using nano X-ray computed tomography (nXCT) as well as scanning electron microscopy (SEM). The results provide a better understanding of the origin and the propagation of damages in the BEoL stack.
•Novel workflow to evaluate the mechanical stability of the back end of line stack•Triggering of different failure modes utilizing copper pillar shear-off•Damage evaluation and categorization utilizing acoustic emission signals•Detection of sub-surface damages utilizing nano X-ray computed tomography•In-situ copper pillar shear-off in nano X-ray computed tomography tool