Hyper NA EUV: Ultra-Thin Resist Materials and Imaging in the Angstrom Era

This PhD project is a feasibility study of extending EUV lithography beyond the current high-NA limit of 0.55 NA toward so-called hyper-NA systems (NA ≥0.75). It combines two closely linked research pillars: (1) the development of ultra-thin resist and underlayer platforms, and (2) the optimization of hyper-NA imaging and patterning strategies. The work will be carried out within imec’s EUV lithography program in collaboration with its industrial and academic partners.
 

 

Previous research demonstrated the imaging feasibility of hyper-NA EUV but identified a major challenge: a depth of focus of only about 20 nm. Such a limited process window requires simultaneous optimization of both imaging conditions and the resist/underlayer stack. Ultra-thin photoresists, combined with suitable underlayers, will be needed to accommodate focus variations while maintaining resolution, roughness performance, stochastic robustness, mechanical stability, and pattern-transfer capability at sub-10 nm dimensions.
 

 

The first objective of the PhD is therefore to identify resist-underlayer combinations capable of printing and transferring extremely small features relevant to hyper-NA lithography. Candidate stacks will be experimentally evaluated using hyper-NA image emulation on imec’s high-NA scanner. Key performance metrics include printable pitch, dose-to-size, line-edge and line-width roughness (LER/LWR), stochastic defects, pattern collapse, scumming, and post-etch fidelity.
 

 

The second pillar focuses on imaging optimization. In particular, the project will investigate methods to improve depth of focus and mitigate polarization-related imaging limitations. While current designs are largely based on one-dimensional features at the smallest printable pitches, hyper-NA systems may benefit from more two-dimensional design styles. The PhD will study the imaging behavior of such 2D structures and explore enhancement techniques including source optimization, mask absorber tuning, and mask assist features.
 

 

The work will begin with simulation studies to understand and optimize 2D hyper-NA imaging and to define experimentally relevant material qualification criteria for resist-underlayer stacks. Subsequently, experimental validation will be performed using imec’s scanner-based hyper-NA emulation capabilities and complementary beamline exposures. By combining imaging and materials research, the project aims to establish a co-optimization framework linking imaging conditions and resist-stack design to reliable sub-10 nm patterning for future hyper-NA EUV lithography.