An increased interest to stitching for High NA EUVL is observed; this is driven by expected higher demand of larger size chips for various applications. In the past a recommendation was published [1] to have 1-5 um band where no critical structures of a High NA layer would be allowed. In [2], we have introduced new insights on at-resolution stitching. In this publication, we present new experimental results obtained on NXE:3400B scanner. In the past we showed NXE feasibility results of vertical lines and contact holes stitching at relaxed resolution (40-48 nm pitch) in a single wafer location. In this study we evaluate stitching behavior through slit at more aggressive resolutions (P36 and P24 lines / spaces). We provide an overview of interactions in the stitching area such as aerial image interactions, absorber reflection, absorber to black border transition, black border vicinity impact and show corresponding experimental and simulations results. We formulate initial requirements for black border edge placement control and show performance of new masks. For stitching with low-n masks, we discuss using sub-resolution gratings to suppress the elevated mask reflectivity. We show rigorous simulations of stitched images, its sensitivity to overlay errors and propose mitigation mechanisms for OPC. Finally, an overview of stitching enablers will be described: from improved reticle black border position accuracy and absorber reflectivity control to mask resolution and OPC requirements.
Three methods to minimize the impact of alignment mark asymmetry on overlay variation are demonstrated. These methods are measurement based optimal color weighting (OCW), simulation based optimal color weighting, and wafer alignment model mapping (WAMM). Combination of WAMM and OCW methods delivers the highest reduction in overlay variation of 1.3nm (X direction) and 1.2nm (Y direction) as compared to best single color recipe. Simulation based OCW produces a similar reduction in overlay variation as compared to measurement based OCW, and simulation based OCW has the advantage that the scanner alignment recipe with optimize weights can be determined before the mark asymmetry excursion has occurred. Finally, WAMM is capable of reducing the contribution of mark asymmetry on overlay by using a more optimal high order wafer alignment recipe. Capabilities of WAMM can also be combined with OCW solutions.
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