Junction leakage control is studied with electron beam (e-beam) defect inspection after tungsten chemical mechanical polishing (WCMP). Leakage-induced bright voltage contrast (BVC) defects are detected. For both wafer to wafer (WtW) and within wafer (WiW), e-beam inspection results strongly correlate with leakage results of wafer acceptance test (WAT). Failure analysis results showed that the junction leakage was caused by lateral diffusion of nickel silicide (NiSi) underneath the spacer. The extrusion length correlates with gray levels of the tungsten plug very well. In this study we found the optimized condition to suppress junction leakage and also confirmed that post WCMP e-beam inspection can be used to monitor and control junction leakage.

Dark voltage contrast (DVC) defects are detected on normally bright tungsten plugs (W-plugs) during the in-line e-beam inspection step. Cross-sectional scanning electron microscope (SEM) and transmission electron microscope (TEM) in a failure analysis (FA) lab verified that DVC defects with different gray level values (GLV) are caused by different resistances of the W-plugs. We found that DVC defects with lower GLV (GLV1) are W-plugs that are open or almost open. DVC defects with higher GLV GLV2 are caused by partially open W-plugs and in-plug voids. Wafer acceptance test (WAT) results correlated well with e-beam inspection results.