High- resistance W-plug monitoring with an advance e- beam inspection system

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.