Introducing Process Variability Score for Process Window OPC Optimization
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.
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