Core Viewpoint - The article discusses the advancements in high numerical aperture (NA) EUV lithography systems, particularly the transition from 0.33 NA to 0.55 NA, highlighting the implications for multi-patterning techniques and image quality [1][3]. Group 1: Numerical Aperture and Imaging - The increase in numerical aperture (NA) from 0.33 to 0.55 allows for the use of more diffraction orders, resulting in brighter and narrower peaks in imaging [1][3]. - Higher NILS (Normalized Image Log Slope) is achieved due to sharper peaks, which reduces the impact of random effects from photon absorption noise [3][11]. - Direct printing images at 0.33 NA are more prone to quality degradation compared to 0.55 NA, necessitating higher doses to maintain low noise levels [3][13]. Group 2: Multi-Patterning Techniques - The article illustrates that DUV (Deep Ultraviolet) double patterning can achieve similar results to EUV by splitting patterns into separate exposures, improving NILS due to increased spatial frequency range [5][9]. - It is anticipated that high NA EUV will require two patterning steps, while low NA EUV will require three, and DUV will require four [5][9]. Group 3: Depth of Focus and Resist Thickness - The article emphasizes that higher numerical apertures lead to a wider range of spatial frequencies, which can result in greater phase differences and loss of image contrast due to defocus [9][11]. - A depth of focus less than 30 nanometers for high NA systems implies that resist thickness must also be under 30 nanometers, potentially leading to significant resist loss [13][15]. - The article suggests that future hyper NA systems (at least 0.75) may exacerbate these issues, as they are unlikely to provide sufficient depth of focus for reasonable resist thickness [13].