Fig. 1. Historic overview of lithography exposure tools^[3], reprinted with permission, Copyright 2024 SPIE, permission conveyed through Copyright Clearance Center, Inc.

Fig. 2. Optical constants of different materials at the wavelength of 13.5 nm^[23]

Fig. 3. Absorption of EUV light. (a) Transmission of light at the wavelength of 13.5 nm through a 1 cm long path filled with gas at 10 Torr^[26]; (b) attenuation length at the wavelength of 13.5 nm for materials that can be used for EUV mask absorbers^[28]

Fig. 4. Reflective properties of multilayers^[32], reprinted with permission, Copyright 2016 SPIE. (a) EUV reflectivity versus wavelength and (b) EUV reflectivity versus angle of incidence for ideal Mo/Si (40 bilayers) and ideal Ru/Si (20 bilayers) multilayers (no intermixing at the interfaces)

Fig. 5. Schematic of the cross-section of an EUV mask

Fig. 6. Mo/Si and Ru/Si multilayers^[32], reprinted with permission, Copyright 2016 SPIE. (a) Plots of reflectivity at 13.5 nm wavelength and 6° angle of incidence versus the number of bilayers for ideal Mo/Si and ideal Ru/Si multilayers; (b) relative position of the effective reflection plane

Fig. 7. Estimation of effective reflection surface depth^[14], reprinted with permission, Copyright 2019 SPIE. (a) Reflectivity of multilayer as a function of the incident angle; (b) relationship between phase and incident angle

Fig. 8. Mask models^[39], reprinted with permission, Copyright 2021 SPIE. (a) Kirchhoff model of the DUV mask; (b) double diffraction model of the EUV mask

Fig. 9. Classification of EUV masks based on the reflectance of the absorber^[54], reprinted with permission, Copyright 2021 SPIE

Fig. 10. Schematic of the defects on an EUV mask

Fig. 11. DGL membrane acts as a physical outgassing barrier to protect POB^[102], reprinted with permission, Copyright 2017 SPIE

Fig. 12. Schematic of an EUV ptychography microscope^[18], reprinted with permission, © Optical Society of America [or Optica Publishing Group, as applicable]

Fig. 13. Origin of the M3D effects, M3D effects on mask or wafer impact, and mitigation strategies, as well as the lithography metrics^{[38, 80, 107]}

Fig. 14. Comparison of the M3D effects between the 0.33NA and the 0.55NA systems^[38], reprinted with permission, Copyright 2019 SPIE. (a) Relationship between NILS and k₁; (b) relationship between nTC and k₁

Fig. 15. A 10 nm horizontal dense LS-CD through focus and dose [center slit position in the field, other parameters: 0.55NA, standard small dipole Y illumination, metal-oxide resist (YAQY-9000), and a 60 nm TaBN mask]^[3], reprinted with permission, Copyright 2024 SPIE, permission conveyed through Copyright Clearance Center, Inc.

Fig. 16. Comparison of through-pitch imaging performance of reference TaBN absorber for horizontal L/S pattern using different illumination source shapes^[108],reprinted with permission, Copyright 2022 SPIE. (a) NILS; (b) best focus variation through pitch; (c) telecentricity error; (d) threshold-to-size; (e) throughput criterion; (f) mask bias

Fig. 17. Comparison of through-pitch imaging performance of TaCo alloy absorber for horizontal L/S pattern using different illumination source shapes^[108], reprinted with permission, Copyright 2022 SPIE. (a) NILS; (b) best focus variation through pitch; (c) telecentricity error; (d) threshold-to-size; (e) throughput criterion; (f) mask bias

Fig. 18. The M3D effects on wafer impact^[125], reprinted with permission, Copyright 2017 SPIE, permission conveyed through Copyright Clearance Center, Inc. (a) Experimentally measured BF shifts through pitch; (b) experimentally measured CD asymmetry through focus (36 nm horizontal two bar pitch), other parameters are 70 nm thick Ta based absorber mask, 0.33NA, and Quasar illumination

Fig. 19. Aerial image intensity through focus for a horizontal 36 nm two bar pitch of various absorber materials^[125], reprinted with permission, Copyright 2017 SPIE, permission conveyed through Copyright Clearance Center, Inc. (a) Ta based; (b) Ni based

Fig. 20. Mask shadowing effect^[134], reprinted with permission, Copyright 2013 SPIE. (a) Simplified illustration of mask shadowing; (b) shadowing effect is dependent on pattern placement along the illumination arc on scanner

Fig. 21. Schematic of the absorber shadowing^[135], reprinted with permission, Copyright 2012 SPIE

Fig. 22. Optimized multilayer by a structure design^[14], reprinted with permission, Copyright 2019 SPIE. (a)(b) Layer thickness for Si and Mo of a traditional and optimized multilayer; (c)(d) reflectivity versus angle and normalized spatial frequency

Fig. 23. Optimization flow of absorber thickness^[108], reprinted with permission, Copyright 2022 SPIE

Fig. 24. Relationship between M3D effects and material n & k. (a) Impact on the M3D effects accoring to material n & k region (reference TaBN)^{[80, 147]}; (b) simulated nearfield intensity (top) and phase (bottom) plots for the 70 nm Ta based reference absorber, the arrow indicates the direction of the EUV light and the black box represents the area where the absorber is^[125], reprinted with permission, Copyright 2017 SPIE, permission conveyed through Copyright Clearance Center, Inc.

Fig. 25. Optical constants for thin metal films and their alloys at the wavelength of 13.5 nm (shaded areas depict regions for different mask type applications)^[25], reprinted with permission, © Optical Society of America (or Optica Publishing Group, as applicable)

Fig. 26. Results of multi-objective optimization for 11 nm square contacts in 22 nm pitch on a dark field mask using different absorbers and exposure options^[15], reprinted with permission, Copyright 2024 SPIE

Fig. 27. NILS/focus performance for various combinations of masks and illumination sources^[4], reprinted with permission, Copyright 2024 SPIE, permission conveyed through Copyright Clearance Center, Inc.

Fig. 28. Schematics of various EUV mask structures. (a) Etched multilayer binary mask^[153]; (b) refilled multilayer binary mask^[155]; (c) etched multilayer APSM^[155]; (d) two-material embedded APSM^[43]; (e) AltPSM with a phase step^[158]; (f) double etched AltPSM^[43]; (g) AltPSM with an absorber stack^[160]; (h) refilled AltPSM^[160]

Fig. 29. Phase shift of PSM^[54], reprinted with permission, Copyright 2021 SPIE. (a) Phase of the reflected wave; (b) phase shift value at the absorber surface; (c) phase shift value of TaN

Fig. 30. Two types of models to describe light transmission through a binary optical mask^[165], reprinted with permission, Copyright 2014, Elsevier. (a) Kirchhoff approach; (b) rigorous EMF simulation

Fig. 31. Separate the light cones at the mask^[3], reprinted^{with permission, Copyright 2024 SPIE, permission conveyed through Copyright Clearance Center, Inc. (a) Using oblique illumination to separate the light cones from the illumination system and reflections; (b) just increasing NA will result in overlapping light cones; two ways to accommodate for increasing NA and to separate the light cones at the mask, namely (c) increase the CRAO or (d) increase the demagnification}

Fig. 32. Calculated reflectivity of a typical Mo/Si multilayer mirror as a function of angle of incidence^[40], reprinted with permission, Copyright 2023 SPIE