Control of the Local Critical Dimension Uniformity (LCDU) and the associated Edge Placement Error of contact holes (CHs) is important for the implementation of EUV lithography in high-volume production today and for future nodes 1 .The Systematic part of the LCDU is governed by the local CD variation on the mask, multiplied with a Mask Error Enhancement Factor (MEEF). Recent studies have shown that the relevant MEEF to predict the LCDU systematics is the Local MEEF, where not all CHs grow at the same time 2,3 . This stands in contrast to the more commonly used Global MEEF, that quantifies the wafer CD impact of all CHs growing simultaneously on mask.In this work, we experimentally study how the systematic LCDU, and the Local and Global MEEF depend on illumination condition and mask variability strengths and signatures. We expose a test mask with programmed local CD variability on an NXE:3400 exposure tool and perform anchored CD-SEM metrology on the mask and on wafer.Our results show that the illumination condition and the local mask CD fingerprint impact the Global and Local MEEF independently in a non-trivial way. Two pupils with similar Global MEEF show a 55% difference in Local MEEF and systematic LCDU component. Optimizing the pupil for Global MEEF therefore does not guarantee an optimum Local MEEF (or Systematic LCDU).

We perform experimental and theoretical studies of image placement error induced by aberrations of the projection lens. The goal is to experimentally determine the magnitude of the image placement errors, to compare experiments and simulations, and to screen possible correction strategies. The calculations and experiments are done for ArF lithography. Theoretically, we simulate image placement error using the projection lens aberration data and simulators such as Prolith or Solid-C. Features with low and high sensitivities to lens aberrations are identified, together with a reference feature that has low sensitivity for image placement error. Dedicated reticles are fabricated to print various features at different illumination conditions on the same substrate. The resulting patterns could be analyzed using top-down scanning electron microscopy ͑SEM͒, but also optically with the standard optical overlay tool KLA5200. For both techniques, the experimentally found image placement errors are in excellent agreement with simulations. In simulations, we calculate the dependency of the image placement error on pattern density, pattern orientation, and illumination conditions. These tendencies are experimentally reproduced. We conclude with a case study that demonstrates a possible correction strategy for image placement error.

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