With EUV attenuated phase shift absorbers rapidly approaching maturity, actinic metrology soon will be required to ensure phase accuracy, uniformity, and stability. The target phase shift for these absorbers is carefully optimized to a value typically around 1.2pi for optimal printing. The additional 0.2pi is necessary due to mask 3D effects (M3D), which increasingly distort the near-field scattering and phase as the feature size is reduced. Therefore, EUV attenuated phase shift masks require phase metrology not only for large-area multilayer and absorber, but also for feature-dependent in-pattern phase. We demonstrate in-pattern phase measurement using spectroscopic variable angle scatterometry with the commercially available EUV Tech ENK (EUV n/k tool). We describe experiments validating the accuracy and precision of actinic scatterometry-based pattern phase measurements conducted on the ENK platform through direct comparison to synchrotron reference scattering measurements.
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