VLSI failure analysis: A review

Abstract

EBP (electron beam probing) and FIB (focused ion beam) applications to VLSI failure analysis are reviewed. The EBP system is segregated into three generations from a testing automation viewpoint. The first generation is a simple modification to SEM: SEM + beam blanking equipment for pulse beam generation, a simple pulse generator to stimulate the DUT (device under test), etc. The second generation is a more practical system, which includes a pulse generator to stimulate a more complex DUT, image processor, etc. The third one is an automatic or semi-automatic system, which combines with an LSI design database. FIB applications were segregated into microscopic cross-sectioning and in situ observation, preparation for further failure analysis, and aluminum grain observation. Three VLSI failure analysis examples concerning microscopic cross-sectioning and in situ observations are shown. One is a cross section of a VLSI memory, which failed during a high temperature life test. Another example is the cross section of a gate array, which failed in wafer sorting test because of a short circuit caused by a pinhole at the SiO 2 layer between the metal layer and the substrate. The other example is that of a VLSI gate array, which failed in the wafer sorting test because of an open circuit caused by process anomalies. As a preparation tool for further failure analysis, FIB has been mainly utilized for cutting and connecting metal lines when changing a circuit, making holes at an insulation layer for EBP, probing pad formation for mechanical probing and EBP, microscopic cross-sectioning for SEM observation, and marking for TEM (transmission electron microscope) observation. As an aluminum microstructure observation tool, FIB as SIM (scanning ion microscope) is shown to be useful, not only for qualitative aluminum grain observation, but also for quantitative aluminum grain orientation measurement. Individual failure analysis examples is shown, using photographs.