The detection and investigation of Tungsten-plug voids by electron-beam inspection

The study aims at the inline detection of invisible defects of tungsten (W) plug voids. Those voids inside contact holes would directly lead to chip yield fail or, even worse, reliability issues. A dedicated electron-beam (E-beam) inspection (EBI) method with “penetration mode” was performed to detect W plug voids. Then experiments showed the failure model involved poor CT hole profiles, the accumulating polymers in the CT hole, incompatible ILB/W DEP processes; furthermore, the quantified impacted factors of void defects were also discussed, including the aspect ratio (AR) and shape of CT holes, CT etch polymer status, the thermal effect of ILB/W DEP processes, and even the FOUP materials. The corresponding improvement actions including changing new material FOUP, reducing CT hole AR by optimization of the ILD loop and CT loop process and optimizing the ILB/W DEP process were executed. The W plug void defects obviously trended low accordingly.