APPARATUS FOR MEASURING OVERLAY ERRORS

A metrology system for determining overlay is disclosed. The system includes an optical assembly for capturing images of an overlay mark and a computer for analyzing the captured images to determine whether there is an overlay error. The mark comprises first and second regions that each include at least two separately generated working zones, juxtaposed relative to one another, configured to provide overlay information in a first direction, and include a periodic structure having coarsely segmented elements. The mark comprises third and fourth regions that each include at least two separately generated working zones, juxtaposed relative to one another, configured to provide overlay information in a second direction, and include a periodic structure having coarsely segmented elements. Working zones of the first and second regions are diagonally opposed and spatially offset relative to one another, and the working zones of the third and fourth regions are diagonally opposed and spatially offset relative to one another.