New Method for BEOL Overlay and Process Margin Characterization

This paper presents a new method, Design-for-inspection (DFI) to characterize overlay. Using design-assisted voltage contrast measurement, the method enables in-line test and monitoring of process induced OVL and CD variation of back-end-of line (BEOL) features with litho-etch-litho-etch (LELE) patterning. While only some of the features of multi-color patterning scheme are chosen to be aligned directly, other combination of metal line and via colors may have uncontrolled misalignment risking open or short failures. The paper shows how the complete metrology coverage of multi-color combination between dual patterned Via and dual patterned Metal Lines helps driving the improvement of overlay and process margins in 14nm technology. The enlarged process margin for Via Opens will drive yield improvement and better reliability.