Abstract

Modern integrated circuits (ICs) are in permanent risk of hardware attacks on sensitive data. But, proper and affordable protection of the IC backside against Focused Ion Beam (FIB) and optical fault injection attacks is missing. In this work, we investigate a patent [1] that uses p-n junctions as light emitters (forward bias) and detectors. We improved the backside detection mechanism presented in the patent by developing a test structure and adding an optically active layer on the backside as protective element to detect an attacked backside with electrical signals in the IC. The angle dependent reflection provided by the layer acts as the protective function. We demonstrate how the light emission and detection concept is quantitatively working and how the active layer produces a backside layer integrity related signal in the IC which can act as attack indicator. We also show that, due to the weak light emission intensity of silicon and the high excitation current, influences such as multi-angle reflection and stray current are reducing the angle-dependent effect on the signal and have to be taken into account in practical use.

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