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AIMS™ Die-to-Die (D2D) is widely used in checking the wafer printability of mask defects for DUV lithography. Two AIMS images, a reference and a defect image, are captured and compared with differences larger than certain tolerances identified as real defects. Since two AIMS images are needed, and since AIMS system time is precious, it is desirable to save image search and capture time by simulating reference images from the OPC mask pattern and AIMS optics. This approach is called Die-to-Database (D2DB). Another reason that D2DB is desirable is in single die mask, where the reference image from another die does not exist.This paper presents our approach to simulate AIMS optics and mask 3D effects. Unlike OPC model, whose major concern is predicting printed CD, AIMS D2DB model must produce simulated images that match measured images across the image field. This requires a careful modeling of all effects that impact the final image quality. We present a vector-diffraction theory that is based on solid theoretical foundations and a general formulation of mask model that are applicable to both rigorous Maxwell solver and empirical model that can capture the mask 3D-effects. We demonstrated the validity of our approach by comparing our simulated image with AIMS machine measured images. We also briefly discuss the necessary changes needed to model EUV optics. Simulation is particularly useful while the industry waits for an actinic EUV-AIMS tool.

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A wafer's printed CD error can be impacted by unaccounted mask making process variation. Unaccounted mask CD and/or corner rounding alters the intended drawn mask pattern contributing to a wafer's printed CD error. During OPC wafer calibration, average mask bias and corner rounding are accounted for in the OPC model, but random local mask making process variations or mask-to-mask variations can be difficult to account in such model calibration. Thus when a wafer's CD has error, it can be difficult to determine if the general root cause was due to mask or wafer or both. An in-line monitoring application has been developed to extract accurate mask CD and rendered mask polygon from collected mask CD-SEM images. Technical information will be presented on the challenges of accurately extracting information from SEM images. In particular, discussions include SEM image calibration, contour extraction, inverse pattern rendering, and general image processing to account for mask SEM aberrations (translation, rotation, & dilation), tool-to-tool variation, vendor-to-vendor variation, run-to-run variation, and dark/bright field pattern-to-pattern variation. After accurate mask SEM contours are obtained, lithographic simulations are performed on extracted polygon contours to determine the impact of mask variation on wafer CD. This paper will present detail information about the Inverse Pattern Rendering (IPR) capabilities developed for a virtual Wafer CD (WCD) application and its results, which is proven to achieved 0.5 nm accuracy across multiple critical layers from 28 nm to 40 nm nodes on multiple CD-SEM tools over multiple mask shop locations.