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Photonics
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Computational Imaging for Semiconductor Devices Metrology Applications
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Computational Imaging for Semiconductor Devices Metrology Applications

A special issue of Photonics (ISSN 2304-6732).

Deadline for manuscript submissions: 31 December 2025 | Viewed by 5152

Special Issue Editor

Dr. Iacopo Mochi

E-Mail Website
Guest Editor
Advanced Lithography and Metrology, Paul Scherrer Institute PSI, Forschungsstrasse 111, 5232 Villigen, Switzerland
Interests: EUV metrology; coherent diffraction imaging; soft X-ray scatterometry; image processing; EUV interference lithography

Special Issue Information

Dear Colleagues,

For decades, the fabrication of semiconductor devices has been driven by Moore’s law and has been powered by advancements in photolithography. The ecosystem of a modern semiconductor devices foundry includes metrology tools for every step of the fabrication process, from the control of the photomask and the EUV pellicle, to the characterization of every layer of the printed wafer. The constant scaling of the semiconductor devices requires the metrology infrastructure to be continuously upgraded and, with the introduction of EUV lithography, the necessity of providing actinic photomask inspection and high-resolution imaging of printed wafers dramatically increased the cost of ownership of the metrology tools.

In response to this challenge, in recent years there has been a renewed interest in lensless imaging technologies which could mitigate the fabrication costs of suitable metrology tools and simplify the scaling roadmap. Thanks to the increasing availability of computational power, lensless imaging is a growing field which has found many different applications. The application of this technology for the metrology of EUV photomasks and semiconductor devices however, presents some unique challenges due to the high resolution, the wavelength range and the structure and topology of the samples under investigation.

This special issue aims to investigate the opportunities and the possibilities offered by computational imaging in addressing the raising challenges in the metrology required by the semiconductor industry.

We invite submissions of original research, and case studies that demonstrate innovative applications of computational techniques to metrology solutions for the semiconductor industry.

Topics of interest include, but are not limited to:

  • Computational imaging techniques for EUV photomask and pellicle inspection
  • High-resolution lensless imaging for semiconductor wafers
  • New algorithms and methods for improving metrology accuracy
  • Applications of machine learning in semiconductor metrology
  • Cost-effective metrology tools for scaling semiconductor devices
  • Novel approaches to overcoming challenges in high-resolution semiconductor imaging

Dr. Iacopo Mochi
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Photonics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • extreme ultraviolet
  • actinic patterned mask inspection
  • coherent diffractive imaging
  • lensless imaging
  • ptychography
  • defect inspection, defect review, EUV mask metrology
  • wafer metrology
  • pellicle inspection

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Published Papers (3 papers)

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Research

25 pages, 5513 KB  
Article
Ptycho-LDM: A Hybrid Framework for Efficient Phase Retrieval of EUV Photomasks Using Conditional Latent Diffusion Models
by Suman Saha, Paolo Ansuinelli, Luis Barba, Iacopo Mochi and Benjamín Béjar Haro
Photonics 2025, 12(9), 900; https://doi.org/10.3390/photonics12090900 - 8 Sep 2025
Viewed by 704
Abstract
Extreme ultraviolet (EUV) photomask inspection is a critical step in semiconductor manufacturing, requiring high-resolution, high-throughput solutions to detect nanometer-scale defects. Traditional actinic imaging systems relying on complex optics have a high cost of ownership and require frequent upgrades. An alternative is lensless imaging [...] Read more.
Extreme ultraviolet (EUV) photomask inspection is a critical step in semiconductor manufacturing, requiring high-resolution, high-throughput solutions to detect nanometer-scale defects. Traditional actinic imaging systems relying on complex optics have a high cost of ownership and require frequent upgrades. An alternative is lensless imaging techniques based on ptychography, which offer high-fidelity reconstruction but suffer from slow throughput and high data demands. In particular, the ptychographic standard solver—the iterative Difference Map (DifMap) algorithm—requires many measurements and iterations to converge. We propose Ptycho-LDM, a hybrid framework integrating DifMap with a conditional Latent Diffusion Model for rapid and accurate phase retrieval. Ptycho-LDM alleviates high data acquisition demand by leveraging data-driven priors while offering improved computational efficiency. Our method performs coarse object retrieval using a resource-constrained reconstruction from DifMap and refines the result using a learned prior over photomask patterns. This prior enables high-fidelity reconstructions even in measurement-limited regimes where DifMap alone fails to converge. Experiments on actinic patterned mask inspection (APMI) show that Ptycho-LDM recovers fine structure and defect details with far fewer probe positions, surpassing the DifMap in accuracy and speed. Furthermore, evaluations on both noisy synthetic data and real APMI measurements confirm the robustness and effectiveness of Ptycho-LDM across practical scenarios. By combining generative modeling with physics-based constraints, Ptycho-LDM offers a promising scalable, high-throughput solution for next-generation photomask inspection. Full article
(This article belongs to the Special Issue Computational Imaging for Semiconductor Devices Metrology Applications)
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12 pages, 3310 KB  
Article
Resolution Enhancement in Extreme Ultraviolet Ptychography Using a Refined Illumination Probe and Small-Etendue Source
by Seungchan Moon, Junho Hong, Taeho Lee and Jinho Ahn
Photonics 2025, 12(8), 831; https://doi.org/10.3390/photonics12080831 - 21 Aug 2025
Viewed by 1466
Abstract
Extreme ultraviolet (EUV) ptychography is a promising actinic mask metrology technique capable of providing aberration-free images with subwavelength resolution. However, its performance is fundamentally constrained by the strong absorption of EUV light and the limited detection of high-frequency diffraction signals, which are critical [...] Read more.
Extreme ultraviolet (EUV) ptychography is a promising actinic mask metrology technique capable of providing aberration-free images with subwavelength resolution. However, its performance is fundamentally constrained by the strong absorption of EUV light and the limited detection of high-frequency diffraction signals, which are critical for resolving fine structural details. In this study, we demonstrate significant improvements in EUV ptychographic imaging by implementing an upgraded EUV source system with reduced source etendue and applying an illumination aperture to spatially refine the probe. This approach effectively enhances the photon flux and spatial coherence, resulting in an increased signal-to-noise ratio of the high-frequency diffraction components and an extended maximum detected spatial frequency. Simulations and experimental measurements using a Siemens star pattern confirmed that the refined probe enabled more robust phase retrieval and higher-resolution image reconstruction. Consequently, we achieved a half-pitch resolution of 46 nm, corresponding to a critical dimension of 11.5 nm at the wafer plane. These findings demonstrate the enhanced capability of EUV ptychography as a high-fidelity actinic metrology tool for next-generation EUV mask characterization. Full article
(This article belongs to the Special Issue Computational Imaging for Semiconductor Devices Metrology Applications)
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13 pages, 3806 KB  
Article
Impact of Sn Particle-Induced Mask Diffraction on EUV Lithography Performance Across Different Pattern Types
by Seungchan Moon, Dong Gi Lee, Jinhyuk Choi, Junho Hong, Taeho Lee, Yasin Ekinci and Jinho Ahn
Photonics 2025, 12(3), 266; https://doi.org/10.3390/photonics12030266 - 14 Mar 2025
Cited by 1 | Viewed by 2394
Abstract
This study investigates the differences in the lithographic impact of particles on the pellicle surface depending on the type of extreme ultraviolet (EUV) mask pattern. Using an EUV ptychography microscope, we analyzed how mask imaging performance is affected by locally obstructed mask diffraction [...] Read more.
This study investigates the differences in the lithographic impact of particles on the pellicle surface depending on the type of extreme ultraviolet (EUV) mask pattern. Using an EUV ptychography microscope, we analyzed how mask imaging performance is affected by locally obstructed mask diffraction caused by a 10 μm × 10 μm patterned tin particle intentionally fabricated on the pellicle surface. The resulting critical dimension variations were found to be approximately three times greater in line-and-space patterns than in contact hole patterns. Based on these findings, we recommend defining the critical size of particles according to the mask pattern type to optimize lithographic quality. Full article
(This article belongs to the Special Issue Computational Imaging for Semiconductor Devices Metrology Applications)
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