Reducing shot count through Optimization based fracture
The increasing complexity of RET solutions with each new process node has increased the shot count of advanced photomasks. In particular, the introduction of inverse lithography masks represents a significant increase in mask complexity. Although shot count reduction can be achieved through careful management of the upstream OPC strategy and improvement of fracture algorithms, it is also important to consider more dramatic departures from traditional fracture techniques. Optimization based fracture allows for overlapping shots to be placed in a manner that allows the mask intent to be realized while achieving significant savings in shot count relative to traditional fracture based methods. This paper investigates the application of optimization based fracture to reduce the shot count of inverse lithography masks, provide an assessment of the potential shot count savings, and assess its impact on lithography process window performance.
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