A groundbreaking advancement in semiconductor manufacturing technology has been unveiled through the proposal of an all-reflective two-mirror projection system designed for extreme ultraviolet (EUV) lithography. Published on September 10, 2026, by researcher Vasiliy A. Es’kin, the study details a revolutionary optical architecture capable of operating at wavelengths of 13.5 nm and 11.2 nm. This system achieves a numerical aperture (NA) of approximately 0.993, a figure that nears the theoretical limit for air-based or vacuum-based lithography. By significantly reducing the number of reflections required to project circuit patterns onto silicon wafers, the design promises to quadruple optical throughput compared to current industry standards, potentially paving the way for the next generation of sub-2-nanometer chip production.
The Evolution of Lithographic Resolution
For decades, the semiconductor industry has followed Moore’s Law, doubling the number of transistors on a microchip roughly every two years. This progress is primarily driven by photolithography—the process of using light to etch circuit patterns onto silicon. The resolution of these patterns is governed by the Rayleigh criterion, which states that the minimum feature size is proportional to the wavelength of light used and inversely proportional to the numerical aperture of the projection system.
The industry’s transition to EUV lithography, utilizing a 13.5 nm wavelength, marked a pivotal shift in the 2010s. However, as chipmakers push toward even smaller nodes, the limitations of current EUV systems have become apparent. Standard EUV projection objectives typically employ six to ten aspheric mirrors. Because EUV light is absorbed by almost all materials, these mirrors must be coated with specialized multilayer stacks to reflect light. Even with high-quality coatings, each reflection results in a power loss of roughly 30% to 40%. In a 10-mirror system, the cumulative loss is staggering, often leaving less than 15% of the original light to reach the wafer.
The proposed two-mirror system addresses this fundamental bottleneck by streamlining the optical path and maximizing the energy that reaches the photoresist.
Architectural Innovation: The Faceted Mirror Design
The core innovation of the proposed system lies in its departure from traditional aspheric mirror geometries. Conventional systems use a series of large, complex curved mirrors to focus and demagnify the image of the mask. In contrast, the design presented by Es’kin utilizes a dedicated pair of planar mirror facets for each accepted discrete spatial diffraction order scattered by the mask.
By fixing the number of reflections at exactly two for all accepted orders, the system retains between 50% and 60% of the power leaving the mask. This represents a nearly fourfold increase in efficiency over contemporary High-NA EUV systems. The architecture utilizes a fourfold ($4times$) demagnification of the periodic mask pattern, ensuring that the intricate designs on the reticle are accurately scaled down to the nanometric dimensions required on the wafer.
To maintain image integrity, the researchers derived a complex spatial geometry that provides rigorous optical path length equalization across all diffraction orders. This mathematical achievement is critical because it removes order-dependent propagation phase shifts, which would otherwise cause blurring or distortion in the final aerial image.
Advanced Materials and Wavelength Versatility
The study explores two primary operating environments for the projection system:
- 13.5 nm Wavelength: Utilizing Molybdenum/Silicon (Mo/Si) multilayer coatings, which is the current industry standard for EUV.
- 11.2 nm Wavelength: Utilizing Ruthenium/Beryllium (Ru/Be) coatings. This shorter wavelength allows for even finer resolution but requires more sophisticated material science to manage heat and reflectivity.
To optimize these mirrors, the researchers employed the transfer matrix method combined with global evolutionary optimization algorithms. This allowed them to design individually optimized 30-bilayer Bragg multilayer coatings for each specific facet. These coatings are engineered to handle the specific angles of incidence and phases of the light as it travels through the two-reflection system.
The transition to 11.2 nm is particularly significant for the industry’s roadmap toward "Hyper-NA" lithography. As the numerical aperture approaches 1.0, the physics of the light-matter interaction changes, necessitating the 3D vector formulation and differentiable electromagnetic modal waveguide solvers used in this study to accurately predict how light will behave at such extreme scales.
Performance Results: Breaking the 10-nanometer Barrier
The effectiveness of the two-mirror system was validated through simulated aerial images of sub-10-nm features. Utilizing inverse lithography technology (ILT) and Fourier parameterization, the research team solved the synthesis problem for binary absorber masks, specifically focusing on Lanthanum (La) absorbers on a Ru/Be/Sr multilayer mirror.
The simulation results were highly promising:
- Isolated Peaks: The system produced isolated peaks with a full width at half maximum (FWHM) of approximately 5.4 nm.
- Line Pairs: The system successfully resolved line pairs with a critical dimension (CD) of 6 nm.
- Depth of Focus: One of the most significant challenges in high-NA lithography is the shrinking depth of focus. The researchers found that the two peaks remained clearly resolved even with wafer defocus values ranging from 0 to 5 nm along the z-axis.
These results suggest that the system could reliably produce features necessary for the "1nm" and "sub-1nm" process nodes, which are expected to become the industry focus in the late 2020s and early 2030s.
Chronology of EUV Development and Future Milestones
The development of this two-mirror system occurs at a critical juncture in semiconductor history.
- 2019-2021: Mass production using 0.33 NA EUV systems begins at TSMC and Samsung for 7nm and 5nm nodes.
- 2023-2024: ASML ships the first High-NA (0.55 NA) EUV "Twinscan EXE" machines to Intel, marking the beginning of the 2nm era.
- 2025-2026: Research shifts toward "Hyper-NA" (NA > 0.7). The publication of the all-reflective two-mirror system (Sept 2026) provides a theoretical and design framework for reaching NA 0.993.
- 2027 and Beyond: The industry is expected to evaluate the feasibility of Ru/Be based 11.2 nm systems. The higher throughput of the two-mirror design could potentially reduce the "cost-per-wafer" which has been skyrocketing due to the immense power requirements of current EUV light sources.
Industrial Implications and Economic Impact
The implications of a 60% throughput EUV system are profound for the global economy. Currently, EUV lithography machines are among the most expensive pieces of equipment on Earth, costing upwards of $350 million per unit. A significant portion of this cost is driven by the need for massive power supplies to generate enough EUV light to compensate for the losses within the 10-mirror optical column.
If the industry can transition to a two-mirror architecture, several benefits emerge:
- Lower Power Consumption: With four times the throughput, chipmakers could achieve the same wafer output with significantly less raw power, or dramatically increase the number of wafers processed per hour.
- Simplified Maintenance: Fewer mirrors mean fewer surfaces that can degrade over time due to carbon contamination or thermal stress, potentially increasing the "up-time" of the machines.
- Extended Scaling: By reaching an NA of 0.993, this technology could extend the life of optical lithography for another decade, delaying the need for more exotic (and unproven) technologies like nano-imprint or directed self-assembly.
However, the transition to such a system is not without challenges. The "faceted" approach requires extreme precision in the alignment of individual planar segments. Furthermore, the use of Beryllium in the 11.2 nm coatings presents toxicity concerns that would need to be strictly managed in a high-volume manufacturing environment.
Analysis of Theoretical Feasibility
While the simulation results are rigorous, industry analysts note that moving from a differentiable electromagnetic modal waveguide solver to a physical prototype is a monumental task. The "all-reflective" nature of the system is essential because no known lens material is transparent to EUV light. However, the requirement for "path length equalization" means that the manufacturing tolerances for these facets will be measured in picometers.
The use of inverse lithography technology (ILT) in the design process indicates that the masks used for such a system would be incredibly complex. ILT uses mathematical optimization to determine the mask shape that will produce the desired pattern on the wafer, often resulting in "curvy" or non-intuitive mask designs. This would require a parallel advancement in multi-beam electron-beam mask writing technology.
Conclusion
The proposal of an all-reflective two-mirror projection system represents a bold step toward the limits of what is physically possible in semiconductor fabrication. By achieving a numerical aperture of 0.993 and boosting throughput to 60%, this design addresses the two most critical hurdles in the path to sub-nanometer electronics: resolution and cost-efficiency. As the global demand for high-performance computing, artificial intelligence, and mobile technology continues to surge, the innovations detailed in the September 2026 report may provide the essential roadmap for the silicon industry’s future.
