Compensation for EUV multilayer defects within arbitrary layouts by absorber pattern modification

According to the ITRS roadmap, mask defects are among the top technical challenges to introduction of extreme ultraviolet (EUV) lithography into production. Making a multilayer defect-free extreme ultraviolet (EUV) blank is not possible today, and is unlikely to happen in the next few years. This means that EUV must work with multilayer defects present on the mask. The method proposed by Luminescent is to compensate effects of multilayer defects on images by modifying the absorber patterns. The effect of a multilayer defect is to distort the images of adjacent absorber patterns. Although the defect cannot be repaired, the images may be restored to their desired targets by changing the absorber patterns. This method was introduced in our paper at BACUS 2010, which described a simple pixel-based compensation algorithm using a fast multilayer model. The fast model made it possible to complete the compensation calculations in seconds, instead of days or weeks required for rigorous Finite Domain Time Difference (FDTD) simulations. In this paper the method is extended from one-dimensional to two-dimensional patterns by formulating the problem with level-set methods. Since only the top layer profile is measurable a multi-layer growth model is applied to infer the location of the defect and how it distorts the multi-layer reflector. The fast image model is applied to determine how these assumptions influence accuracy of the compensation method.