This work demonstrates the capability of E-beam probing, combined with optical techniques, to effectively monitor the activity of the IC structures and extract the signals from a 16nm technology device through the silicon backside. We conducted optical probing to localize the area of interest on the device, where we aimed the E-beam probing to gather the signal. Once the target was located, a trench down to the STI level was opened on the device. This enables the use of E-beam probing, which has a much higher resolution than the optical methods.

Contactless probing methods through the chip backside have been demonstrated to be powerful attack techniques in the field of electronic security. However, these attacks typically require the adversary to run the circuit under specific conditions, such as enforcing the switching of gates or registers with certain frequencies or repeating measurements over multiple executions to achieve an acceptable signal-to-noise ratio (SNR). Fulfilling such requirements may not always be feasible due to challenges such as low-frequency switching or inaccessibility of the control signals. In this work, we assess these requirements for contactless electron- and photon-based probing attacks by performing extensive experiments. Our findings demonstrate that E-beam probing, in particular, has the potential to outperform optical methods in scenarios involving static or low-frequency circuit activities.

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.