Mentor Graphics

As the IC Industry moves towards 32nm technology node and below, it becomes important to study the impact of process window variations on yield. PVBands is a technique to express process parameter variations such as dose, focus, mask size, etc. However, PVBands width and area ratio alone are insufficient as a quantitative measure for judging the PVBand performance, as it does not take into consideration how far away the contours are from the target. In this paper, a novel mathematical formulation is developed to better judge the PVBands performance. It expresses the PVBand width and symmetry with respect to the target through a single score. This score can be used in OPC (Optical Proximity Correction) iterations instead of working with the nominal EPE (Edge Placement Error). Not only does this approach provide a better measure of the PVBands performance through the value of the score, but it also presents a straightforward method for PWOPC optimization by using the PV Score directly in the iterations.