edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 26 NO. 2 36 work involved using two 12.5 GHz oscilloscopes with conditional triggering schemes as displayed in Fig. 5. Similar to how SDL and LADA techniques are setup,[6] the device of interest is characterized across voltage and frequency as seen in Fig. 6. The test is then continuously executed in a looping fashion with the device biased at a pass/fail boundary in the shmoo plot. Two auxiliary tester channels are configured to serve as the conditional trigger signals that feed each scope as shown in Fig. 5 (Trigger A and Fail Flag). Trigger A asserts at the end of every test loop and Fail Flag is only asserted Fig. 5 Diagram of how pass and fail data are separated into different waveform channels using two scopes and conditional triggering. Fig. 6 Typical voltage versus clock period shmoo plot indicating the conditions of the pass/fail boundary used for dLVP. at the end of a test loop if the tester recorded a failure. The right side of Fig. 5 shows an overview of how the conditional triggering scheme works. Essentially, as the device under test randomly flickers between pass and fail states, all of the fail waveform data is collected by Oscilloscope 1 while only the passing waveform samples are collected by Oscilloscope 2. The two channels are then post processed to synchronize phase offset that may have been introduced from cabling or scope input impedance mismatches, as well as normalized to correct for differences in pass/fail rates. An example of a 5 nm FinFET dLVP waveform set collected from inside an 8-bit flip flop is shown in Fig. 7. A lot of crosstalk is observed from the 1064 nm probe and 3.3NA SIL, however, the yellow differential waveform indicates when a difference occurs between the two simultaneously collected data sets. Using this technique gives a tool that indicates if and when a NAND, NOR, XOR, FLOP, MUX or any other standard library cell is corrupted. Consider cases where there are no simulated waveforms or even a good understanding of how a circuit is supposed to work. The dLVP waveform result instantly identifies whether the probe site contains corrupted logic and when the corruption exists within the test pattern and clocking scheme. SUMMARY AND CLOSING THOUGHTS On most commercially available LVP systems, the oscilloscopes use fast acquisition modes to efficiently collect
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