METHODS AND SYSTEMS FOR DETERMINING OVERLAY ERROR BASED ON TARGET IMAGE SYMMETRY

In systems and methods measure overlay error in semiconductor device manufacturing based on target image asymmetry. As a result, the advantages of using very small in-chip targets can be achieved, while their disadvantages are reduced or eliminated. Methods for determining overlay error based on measured asymmetry can be used with existing measurement tools and systems. These methods allow for improved manufacturing of semiconductor devices and similar devices formed from layers.