IC camouflaging has been proposed as a promising countermeasure against reverse engineering. Camouflaged gates contain multiple functional device structures, but appear as a single layout under microscope imaging, thereby concealing circuit functionality. The recent covert gate camouflaging design comes with a significantly reduced overhead cost, allowing numerous camouflaged gates in circuits which improves resiliency against invasive and semi-invasive attacks. Dummy inputs are used in the design, but SEM imaging analysis has only been performed on simplified contact structures so far. In this study, we fabricated real and dummy contacts in different structures and performed a systematic SEM analysis to investigate contact charging and passive voltage contrast. Machine learning based pattern recognition was also employed to examine the possibility of differentiating real and dummy contacts. Based on our experimental results, we found that the difference between real and dummy contacts is insignificant, which effectively prevents SEM-based reverse engineering.

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