Resolution enhancement in EUV ptychography via optimized probe overlap ratio for diffraction diversity

초록

Extreme ultraviolet (EUV) ptychography is an imaging technique for high-resolution and aberration-free imaging under a simple optical configuration. However, its performance critically depends on the independent constraints for the phase retrieval algorithm. This constraint can be defined by the probe overlap ratio, which provides tunable data redundancy and diffraction diversity crucial for robust phase retrieval. This study experimentally demonstrates that optimizing the overlap ratio to maximize diffraction diversity enhances both phase retrieval accuracy and image resolution. A Fourier transform-based simulation was performed to explore the optimal ratio. We generated diffraction datasets for overlap ratios ranging from 60% to 80% in 4% increments and identified 72% as the optimal condition. This was experimentally validated using an EUV ptychography microscope with a Siemens star pattern, comparing the 72% overlap ratio against the 80% overlap ratio, the condition exhibiting the lowest diffraction diversity. The optimized condition improved phase retrieval accuracy by 17.95% and achieved a spatial resolution of 14 nm (at the wafer), representing an 11.6% enhancement compared to the 80% overlap condition, as determined by Fourier ring correlation (FRC) analysis. In conclusion, this study validates that an overlap ratio optimized for diffraction diversity under sufficient redundancy provides a more robust and effective constraint for the phase retrieval algorithm, enabling high-fidelity image reconstruction.

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