# A Two-Mirror Faceted Projection System for EUV Lithography

arXiv: https://arxiv.org/abs/2609.11299 · HTML: https://mlsanity.com/paper/2609.11299/

## Key facts

- No citing papers in the map yet (data through 14 Oct 2026).
- Builds on 3 of its 34 references that are in the map.
- First posted on arXiv 10 Sep 2026.

## Builds on (most cited first, 3 of 3)

- [Physics-informed neural networks and neural operators for a study of EUV electromagnetic wave diffraction from a lithography mask](https://mlsanity.com/paper/2507.04153/) (2025)
- [Physics-Informed Neural Systems for the Simulation of EUV Electromagnetic Wave Diffraction from a Lithography Mask](https://mlsanity.com/paper/2603.15584/) (2026)
- [Gradient-based inverse lithography for EUV masks via the waveguide method and a physics-informed neural operator](https://mlsanity.com/paper/2606.25753/) (2026)

## Abstract (arXiv)

We propose an all-reflective two-mirror projection system for extreme ultraviolet (EUV) lithography operating at exposure wavelengths of 13.5~nm (Mo/Si) and 11.2~nm (Ru/Be), delivering a fourfold (4×) demagnification of the periodic mask pattern at a numerical aperture approaching unity (NAmax ≈ 0.993). In contrast to conventional EUV projection objectives that incorporate 6--10 aspheric mirrors with an overall optical throughput of less than 15%, the proposed design redirects each accepted discrete spatial diffraction order scattered by the mask onto the wafer via a dedicated pair of planar mirror facets. The number of reflections is strictly fixed at two for all accepted orders, retaining 50--60% of the power leaving the mask in each accepted order. We derive a spatial geometry providing rigorous optical path length equalization across all diffraction orders, thereby removing order-dependent propagation phase shifts. Individually optimized 30-bilayer Bragg multilayer coatings are designed for each facet using the transfer matrix method combined with global evolutionary optimization algorithms. The architecture is generalized to a three-dimensional vector formulation with a two-dimensionally periodic mask. Utilizing inverse lithography technology, Fourier parameterization, and a differentiable electromagnetic modal waveguide solver, we solve the synthesis problem for binary absorber masks (La absorber on a Ru/Be/Sr multilayer mirror). We demonstrate simulated aerial images of sub-10-nm features on the wafer (isolated peaks with a full width at half maximum (FWHM) of approximately 5.4~nm and line pairs with a critical dimension of 6~nm) and find that the two peaks remain resolved for the tested wafer defocus values from 0 to 5~nm along the z-axis.