High numerical aperture (NA) scanners allow continued extension of Moore’s law at 13.5 nm wavelength and come with various technical and economic challenges. In this special section, we review the current and future challenges of high NA scanners, at 2 nm node and beyond, in 11 papers covering a broad range of technical aspects. We have one lead paper on the conception design and integration of the high NA exposure tool. Two papers cover the defectivity and (future) multi-layer aspects of the EUV masks. Sub-resolution enhancement features have come a long way in EUV lithography and provide a powerful way to tune the aerial imaging properties. This topic is also covered by two papers. The high NA exposure tool comes with a reduced size exposure field, and for a chip size that is larger than the reduced exposure field, stitching of two exposures is needed. Two papers in our special section cover the stitching requirements both from a process control requirement and from a mask performance requirement.

The high NA exposure tool also has different magnification in x- and in y-direction. This poses some challenges in the calculation of aerial imaging for rotated lines and spaces.

Multiple patterning is also applied in EUV lithography and one paper discusses the achieved tip-to-tip resolution using pitch splitting with a spacer process.

Last but not least we have two papers discussing the extension of high NA EUV lithography by using an advanced resolution enhancement technique, or what is needed to achieve finest resolution in the future.

Van Schoot et al. provide a comprehensive overview of the high NA EUV system and update the status of the imaging and overlay performance of this exposure tool at high NA lab in Veldhoven.

Liang et al. present a general discussion of the need for actinic inspections and then a detailed description of actinic pattern mask inspection (APMI) and actinic blank inspection (ABI), two critical capabilities for the EUV mask infrastructure.

The multilayer is a crucial aspect of an EUV mask, as it acts as a Bragg reflector and needs to accommodate multiple angles. Maguire and Smith discuss the options for further optimization of the multilayer, e.g. using an aperiodic multilayer.

Dhagat et al. investigate the benefit of sub-resolution assist features (SRAF) in improving the performance of potential depth of focus (DOF)-limited logic-like layers in 0.55 numerical aperture (NA) lithography.

Lee et al. look into the impact of sub-resolution grating, especially on the mask-induced best focus errors, and into the diffraction properties, showing ways to minimize the M3D induced phase errors.

Van Meerten, Pistor, and de Winter discuss fast computation methods for 1D features in an anamorphic system by rotating the features to avoid the extensive computation times typically needed for 2D simulations.

When stitching is applied, there is a delay between exposing the first image and the second image. In that case the condition of the wafer in the time between can have an impact on the critical dimensions observed finally. San Roman et al. discuss the mechanisms behind it and explain different ways to mitigate CD differences between image 1 and image 2.

Wiaux et al. discuss the need for die stitching to create a die larger than the high NA full field in the high NA scanner. Their paper presents results from stitching experiments at NA 0.33 scanner, focusing on mitigating higher reflectivity using sub-resolution gratings and quantifying the imaging impact of the transition between the absorber and the black border in the stitching region.

Grzeskowiak et al. explore anti-spacer technology, which facilitates self-aligned pitch splitting and high throughput via a single-pass track-based process. Their work shows improvements in unbiased space width roughness and pitch-walking.

Erdmann et al. examine the lithographic imaging performance for high NA scanners using dual monopole or split pupil exposures (SPs) on dense arrays of contacts on both dark field and light field masks with various mask absorber options. They conclude that SPs are promising for resolution enhancement in low k1 high-NA lithography using low-n/low-k absorber materials.

Levinson discusses various aspects that need to be considered when pushing EUV lithography to very fine resolution below 10 nm lines and spaces. This comprises multiple aspects of the infrastructure eco-system: mask, scanner and resist.

All these papers highlight the technical progress that has been made in EUV lithography and especially in the upcoming era of the high NA exposure tool. This opens the door to an exciting next decade of EUV lithography. We hope this gives JM3 readers a good overview by addressing the specific topics covered in this section. Enjoy reading.