期刊
PHOTOMASK TECHNOLOGY 2020
卷 11518, 期 -, 页码 -出版社
SPIE-INT SOC OPTICAL ENGINEERING
DOI: 10.1117/12.2573240
关键词
Extreme ultraviolet; defect inspection; lensless imaging; ptychography; actinic; photomask; mask review
资金
- Electronic Component Systems for European Leadership Joint Undertaking [783247-TAPES3]
- European Union's Horizon 2020 research and innovation program
- Swiss National Science Foundation [200021_172768]
- Swiss National Science Foundation (SNF) [200021_172768] Funding Source: Swiss National Science Foundation (SNF)
Actinic EUV mask metrology is essentially needed for EUV lithography in the semiconductor device manufacturing process. At PSI, we are developing RESCAN, a coherent diffractive imaging (CDI)-based platform that can meet current and future mask inspection resolution requirements. In CDI, the diffraction patterns obtained by illuminating the sample with coherent light are recorded by a pixel detector, and these are used to reconstruct the complex-amplitude image of an object through an iterative phase retrieval algorithm. While in a conventional optical system, aberrations can compromise the final image's resolution, the CDI approach is inherently aberration-free. Nevertheless, a careful preprocessing of the diffraction signal is necessary to avoid artifacts in the reconstructed image. In particular, since our system works in reflection mode with an angle of incidence of 6 degrees and uses a flat detector, it is necessary to correct the recorded diffraction patterns that are conically distorted due to the non-telecentricity. This paper discusses the impact of the diffraction data preprocessing on the reconstructed image quality and demonstrates the defect sensitivity improvement by applying an optimized data preprocessing pipeline in the RESCAN microscope. As a result, we achieve defect sensitivity down to 20 nm on the photomask and uniform image quality in a large field-of-view.
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