Abstract
From the background information supplied by the inventors, news correspondents o btained the following quote: “Image-based overlay metrology may typically includ e determining relative offsets between two or more layers on a sample based on r elative imaged positions of features of an overlay target in the different layer s of interest. The accuracy of the overlay measurement may thus be sensitive to image quality associated with imaged features on each sample layer, which may va ry based on factors such as a depth of field or location of the plane (e.g., foc al position) with respect to the sample. Accordingly, overlay metrology procedur es typically include tradeoffs between image quality at particular sample layers and throughput. For example, it may be the case that overlay measurements based on separate images of each sample layer may provide the highest quality images of overlay target features. However, capturing multiple images per target may re duce throughput. By way of another example, overlay measurements based on a sing le image capturing features on multiple layers may provide relatively higher thr oughput, but may require reference measurements based on external tools or full- wafer measurements to provide a desired measurement accuracy. Therefore, it woul d be desirable to provide a system and method for curing defects such as those identified above.”
NETL
NSTL