General Shot Refinement Technique On Fracturing Of Curvilinear Shape For Vsb Mask Writer

The increasing complexity of RET solutions has increased the shot count for advanced photomasks. In particular, the introduction of the inverse lithography technique (ILT) brings a significant increase in mask complexity and conventional fracturing algorithms generate many more shots because they are not optimized for curvilinear shapes.Several methods have been proposed to reduce shot count for ILT photomasks. One of the stronger approaches is model-based fracturing, which utilizes precise dose control, shot overlaps and many other techniques. However, it requires much more computation resources and upgrades to the EB mask writer to support user-level dose modulation and shot overlaps.We proposed an efficient algorithm to fracture curvy shapes into VSB shots(5) which was based on geometry processing. The algorithm achieved better EPE and reasonable process time compared with a conventional fracturing algorithm but its fracturing quality can be degraded for the pattern which has relatively rough contour though it is curvy ILT pattern.In this paper, we present a couple of general techniques to refine a set of VSB shots to reduce edge placement error (EPE) to an original curvy contour with their experimental results.