Segmented box-in-box for improving back end overlay measurement

摘要

An improvement in the box-in-box overlay measurement method has been achieved by forming the outer box from a segmented trench comprised of a number of concentric ridges that project upwards from the floor of the trench. When the segmented trench has been overfilled with tungsten (or similar metal) the excess metal is removed using either etch-back or chem. mech. polishing as the planarizing technique. Because of the presence of the ridges, the trench (i.e. the outer box) becomes reproducibly easy to see when the inner box (which will be etched from a second layer deposited on the first one) is being positioned inside it. Furthermore, the tendency for the outer box to be broken in critical places (often seen in the prior art) is now largely eliminated.