Hyper-NA EUV lithography: challenges and opportunities for advanced interconnect patterning

Abstract

BackgroundContinued device scaling beyond high numerical aperture (NA) EUV (NA=0.55) resolution motivates the exploration of “hyper-NA” EUV lithography systems (NA≥0.75), which promise improved contrast and resolution but introduce stronger mask 3D effects, increased polarization sensitivity, and reduced depth of focus (DoF).AimWe assess whether 0.75 NA EUV can provide manufacturable imaging for post-2030 logic interconnect patterning and identify the principal ecosystem constraints on masks, depth of focus, and photoresists.ApproachWe analyze the consequences of NA scaling on the EUV scanner architecture, including mask-side angle distributions, and we model multilayer and absorber effects. Imaging performance is quantified through rigorous simulations with source mask optimization (SMO), comparing 0.55 and 0.75 NA under unpolarized illumination and central-obscuration constraints. Two representative use cases are studied: (i) a CFET Metal0 (M0) layer with 16-nm pitch lines/spaces and line-end structures, and (ii) 2D interconnect blocks down to 16-nm pitch. Photoresist effects are included via a simplified blur and absorption model, and local EPE tail behavior is assessed using ±20% dose contours with NA-scaled defocus.ResultsModest multilayer period adjustments are sufficient to support the larger mask-side angles at 0.75 NA with limited average reflectivity impact, while low-n/high-k mask absorbers improve contrast and reduce mask-3D penalties relative to standard Ta-based absorbers. Hyper NA consistently increases the image log slope (ILS)—with the largest gains observed for dark-field masks on the most critical CFET interconnect features—and reduces local EPE extremes compared with 0.55 NA in the evaluated patterns. The Rayleigh DoF at 0.75 NA decreases to ∼20 nm, indicating the need for thinner resist films and improved focus/wafer topography control.ConclusionsUnder the modeled assumptions, 0.75 NA hyper-NA EUV offers significant contrast and EPE-tail improvements for CFET-relevant interconnect layers without revealing fundamental imaging limitations, provided that mask multilayer/absorber optimization, scanner focus control, and thin-film resist performance advance in a coordinated manner.