Backside Flip-Chip testing by means of high-bandwidth luminescence detection

We present the results of backside non-invasive optical testing of CMOS Flip-Chips. The exploited principle is the hot-carrier luminescence emitted by MOS transistors in saturation. The set-up is based on a solidstate single-photon avalanche diode with a time resolution better than 30ps. We discuss the methodology for backside investigation, the criteria for selecting the appropriate detector, and the sample thinning. Characterization of a ring oscillator and the debug of a failing circuit are developed. We show how optical investigation and SPICE simulations of the luminescence are valuable tools for defects identification in circuits.