Enhancement of Existing Fault Isolation Techniques for CMOS VLSI Failure Analysis is important in keeping pace with device design and process technologies. Recently, we enhanced our photoemission microscopy capability by applying heat to the device during analysis1. This provided greater defect related light emission from nSRAM test structures and allowed identification of subtle failure modes not observable during room temperature inspection. In the present work, we investigate the theoretical dependencies of emission mechanisms and analyze experimental data to identify the dominant physical mechanisms involved with thermally assisted photoemission. We introduce a thermal factor to help quantify the effect from various light emitting structures. Experimentally, we find that emission mechanisms involving leaky and forward junctions are enhanced by temperature, and propose that the dominant factor for increased signal may be an increasing contribution from phonon absorption rather than phonon emission-based recombination. For emission mechanisms based on impact ionization; however, we find that the emission response is inversely proportional to temperature, and show that mobility degradation is the dominant limiting factor at higher temperatures.

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