Scanning capacitance microscopy (SCM), a powerful technique to identify front-end defects, is also helpful in understanding failure mechanisms. This article discusses three front-end doping failure examples that were clearly identified by SCM analysis. The first example was NMOS leakage between drain and source. SCM images showed that N+ junction distortion resulted in effective channel length shortage. The second one was by-field SRAM failure with power leakage. From SCM images, it is clarified that P-well was directly short to P+ in bad die and slight P-well boundary shift to P+ was observed in good die. The third example was regarding low threshold voltage failure analysis. It illustrates that combination of plane-view and cross-sectional SCM analysis could help to diagnose the failure mechanism. The resolution and precision in SCM is better than that in chemical etching combined with SEM technique.
This paper discusses the failure analysis process of a DC failure using an in-FIB (Focused Ion Beam) nanoprobing technique with four probes and a scanning capacitance microscope (SCM) in advanced DRAM devices. Current-Voltage (I-V) curves measured by the nanoprobing technique indicate the curve of the failed device is different from that of the normal device. The failed device causes a high leakage current in the test. The cross-sectional 2-D doping profile of SCM verifies the region of the P-Well has shifted to create a leakage path that causes this failure.
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