Hot spot and process window monitoring

Metrology overlay targets are provided, as well as method of monitoring process shortcomings. Targets comprise periodic structures, at least one of which comprises repeating asymmetric elements alonga corresponding segmentation direction of the periodic structure. The asymmetry of the elements may be designed in different ways, for example as repeating asymmetric sub-elements along a direction perpendicular to the segmentation direction of the elements. The asymmetry of the sub-elements may be designed in different ways, according to the type of monitored process shortcomings, such as varioustypes of hot spots, line edge shortening, process windows parameters and so forth. Results of the measurements may be used to improve the process and/or increase the accuracy of the metrology measurements. 本发明提供计量叠加目标以及监测工艺缺点的方法。目标包括周期性结构，所述周期性结构中的至少者包括沿着所述周期性结构的对应分段方向的重复不对称元件。举例来说，可以不同方式将所述元件的不对称性设计为沿着垂直于所述元件的所述分段方向的方向重复的不对称子元件。可根据所监测工艺缺点的类型(例如各种类型的热点、线边缘缩短、工艺窗参数等等)来以不同方式设计所述子元件的不对称性。测量的结果可用于改进工艺及/或提高计量测量的精度。