Hot-Carrier Photoemission in Scaled CMOS Technologies: A Challenge for Emission Based Testing and Diagnostics

Optical testing of advanced CMOS circuits successfully exploits the near-infrared photon emission by hot-carriers in transistor channels (see EMMI (Ng et al., 1999) and PICA (Kash and Tsang, 1997) (Song et al., 2005) techniques). However, due to the continuous scaling of features size and supply voltage, spontaneous emission is becoming fainter and optical circuit diagnostics becomes more challenging. Here we present the experimental characterization of hot-carrier luminescence emitted by transistors in four CMOS technologies from two different manufacturers. Aim of the research is to gain a better perspective on emission trends and dependences on technological parameters. In particular, we identify luminescence changes due to short-channel effects (SCE) and we ascertain that, for each technology node, there are two operating regions, for short- and long-channels. We highlight the emission reduction of p-FETs compared to n-FETs, due to a "red-shift" (lower energy) of the hot-carrier distribution. Eventually, we give perspectives about emission trends in actual and future technology nodes, showing that luminescence dramatically decreases with voltage, but it recovers strength when moving from older to more advanced technology generations. Such results extend the applicability of optical testing techniques, based on present single-photon detectors, to future low-voltage chips