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Recent developments in multi-beam mask writers (MBMW)1 enable the manufacturing of curvilinear masks. This promises higher patterning accuracy on wafer. The increased patterning flexibility takes us into new territories for mask manufacturing accuracy, precision and Mask Rule Check (MRC). MBMW allows Optical Proximity Correction (OPC) to venture into Inverse Lithography Technology (ILT) solutions, enabling accurate curvilinear masks. New challenges are also encountered when building OPC models that target ILT masks, such as on wafer metrology and pattern coverage. This exploration will be the focus of this study, in particular the MRC and mask characterization aspects, leveraging a new curvilinear reticle available at imec. As a result of its fully curvilinear nature, conventional mask metrology – solely based on cutline CDs – is no longer entirely adequate. Therefore, a new metrology flow must be developed to assess and quantify mask errors, relying on mask SEM image contour extraction and Mask Edge Placement Error (MEPE) evaluations. Our proposed flow has three steps: -Mask CDSEM images are loaded into a software, which enables an accurate contour extraction and alignment to the original design. The output of this exercise is a design file with open contours. - The output design file is converted into polygons (i.e., defining inside/outside polygons areas) by utilizing the original design as a guide. This allows for full compatibility with the next stage. -Lastly, a highly-sampled MEPE is determined for all polygons, both from the main and assisting features. The result is then analyzed offline. Ultimately, this curvilinear mask data analysis sequence was used on several subsets of the mask metrology dataset. In order to validate the approach, we reproduced the CD based metrology provided by the mask shop. We then expanded our scope to parametric curvilinear features, to find correlators (i.e. local design properties) to the observed mask error observed (e.g., polygon local curvature or density). Finally, ILT clips were used to verify the determined correlators.
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