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.

This paper compares the three major semi-invasive optical approaches, Photon Emission (PE), Thermal Laser Stimulation (TLS) and Electro-Optical Frequency Mapping (EOFM) for contactless static random access memory (SRAM) content read-out on a commercial microcontroller. Advantages and disadvantages of these techniques are evaluated by applying those techniques on a 1 KB SRAM in an MSP430 microcontroller. It is demonstrated that successful read out depends strongly on the core voltage parameters for each technique. For PE, better SNR and shorter integration time are to be achieved by using the highest nominal core voltage. In TLS measurements, the core voltage needs to be externally applied via a current amplifier with a bias voltage slightly above nominal. EOFM can use nominal core voltages again; however, a modulation needs to be applied. The amplitude of the modulated supply voltage signal has a strong effect on the quality of the signal. Semi-invasive read out of the memory content is necessary in order to remotely understand the organization of memory, which finds applications in hardware and software security evaluation, reverse engineering, defect localization, failure analysis, chip testing and debugging.

The scope of this work is to investigate the timing characteristics of a state of the art fully functional IC through continuous wave (CW) and pulsed laser stimulation. The propagation delay of a gate depends on the drain current of nMOS and pMOS transistors, load capacitance and supply voltage. Localized photocurrent induced by laser beam alters some of these electrical characteristics, resulting in a change in the switching time of the gate. In addition to the desired local timing influence, a global effect on the timing throughout the full scanning period occurs as secondary phenomenon that - if not taken into account properly, may mask the local signal. This effect is strong under CW laser operation and can be drastically reduced in pulsed laser condition.