Target placement Optimization

摘要

Lithography manufacturers may place specific structures known as 'marks' or 'targets' on their reticles to facilitate the measurement (and. optionally, correction) of performance parameters such as overlay, dose, and focus. Placing more targets will enable a more accurate measurement/correction, at the expense of physical space on the reticle ('real estate') and read-out time. It is thus of interest to optimize (he number and placement of the targets. The optimal placement depends on the model that will be applied to the data, the (systematic part of) the measurement values ('fingerprint') and the capability to deal with variation of the fingerprint over time.