Electron beam detection of cobalt trench embedded voids enabling improved process control for Middle-Of-Line at the 7nm node and beyond

Inline detection of embedded voids within Middle-Of-Line (MOL) cobalt metal lines is a major industry gap at 7nm technology node and below, for both developing the new metallization solutions, as well as for monitoring during ramp and production. We present a new non-destructive electron beam cobalt void detection method, leveraging an improved scanning electron microscope (SEM) imaging technique, which enable an accurate detection of voids embedded inside MOL metal trenches. After explaining the potential process mechanisms causing void formation, we introduce the e-beam technique, and demonstrate by simulation and experiments the correlation between the electron signal and the volume and depth of the voids. We conclude this paper by discussing how a defect inspection strategy using a massive metrology approach can lead to a faster and more efficient development of the Cobalt metallization.