Overlay registration target design for wafer-induced shift characterization

A novel overlay registration target design was developed for the purposes of characterizing pre- and post- etch wafer-induced shift (offset) on metal layers. The new target enables the measurement of metal overlay offset during the same measurement ran. The combination target was studied on production wafers and compared with the traditional two step pre- and post- etch characterization methodology. Wafer induced shift data measured by both methods showed good agreement in magnitude and direction across the wafer. The new target design was incorporated into an experiment to determine the effects of chemical-mechanical polishing, metal deposition thickness, and their interaction on the offset. Within the target process windows for both CMP and deposition, no significant dependencies of offset were observed. Analysis of this data indicated strong wafer level rotation and scale signatures, confirming offset arises from CMP and metal deposition processes. For the metal process conditions of the experiment, the offset is stable and reliable with respect to fluctuations in overpolish and deposition thickness.