The end of AI is the lithography machine, and the end of lithography machines is the lens

--- Why are EUV lithography lenses so difficult?
EUV and high-end DUV optics are the ultimate convergence of the ultra-precision industrial system. They depend on materials, coatings, metrology, assembly and adjustment, thermal control, vibration control, algorithms, error modeling, and long-term experience accumulation. The real bottleneck to expanding production is often not a single component, but the entire “precision closed loop.”
The core of this loop is: you cannot manufacture something more precise than your measurement capability.
The 13.5nm wavelength of EUV is almost entirely absorbed by all materials, so EUV cannot use traditional lenses and must rely on multilayer mirrors. Zeiss’s EUV mirror surface is essentially an atomic-level reflection system. Surface error requirements are typically in the tens of picometers.
1 pm = 10−12 meters
The atomic diameter is about 100 pm, meaning many permissible errors on EUV mirror surfaces are already close to half an atomic layer.
What’s even more difficult than making such a mirror is how to stabilize the measurement of these errors. How to perform measurements under thermal drift, air disturbances, and vibrations. How to maintain consistency on large-sized mirrors. How to achieve long-term stable industrial repeatability. Because at this point, what’s being measured is no longer just length, but the phase of the light wave itself.
EUV measurement systems are themselves ultra-high-end industrial chains. They include laser interferometers, ultra-stable laser sources, reference optics, ultra-low thermal expansion materials, active vibration isolation systems, ultra-precise displacement stages, wavefront sensors, vacuum systems, and long-term drift compensation algorithms. Many core suppliers are likely only 1-3 companies worldwide.
And these metrology systems also require even higher-grade measurement systems to manufacture. This creates a recursive (vicious cycle): advanced measurement equipment requires even more advanced measurement equipment.
Taking one of the bottlenecks as an example, the reference optics.
Reference mirrors are not ordinary mirrors. They are essentially the “primordial” objects in the optical world, representing the pinnacle of the entire industrial precision hierarchy. To measure EUV mirrors, you must first have a reference mirror more precise than the EUV mirror itself. This creates a terrifying question: who manufactures the most precise mirrors in the world?
Manufacturing reference optics is essentially an infinite approach to perfect surface quality. It first relies on ultra-low thermal expansion materials, such as SCHOTT’s Zerodur or ULE-type materials. These materials require not only extremely low thermal expansion but also internal uniformity, very low internal stress, long-term stability, and large-size consistency. Many materials need months of annealing.
Next comes ultra-precision shaping. This is no longer ordinary polishing but involves MRF (Magnetic Resonance Finishing), CCOS (Computer-Controlled Optical Surfacing), Ion Beam Figuring, etc. Ion beam figuring is especially critical because mechanical polishing is no longer sufficient; atomic-level material removal is necessary. The real challenge is that removing even a tiny amount of material causes the entire surface shape to change. So the entire manufacturing process becomes: measurement → correction → re-measurement → re-correction, possibly cycling hundreds of times.
The most difficult part is knowing whether the error originates from the mirror itself or from the measurement system. Industry uses three-mirror methods, multi-mirror cross-measurement, cross-calibration, and national laboratory standards. Often, there is no absolute correctness—only continuous reduction of uncertainty.
When precision reaches tens of picometers, the entire environment begins to become an adversary. Earthquakes, building vibrations, airflow, temperature fluctuations, human footsteps—all can affect the results. Therefore, many top metrology laboratories maintain temperature control to 0.001°C, use active vibration isolation, deep foundations, vacuum environments, and sometimes only measure at night, because daytime ground vibrations are greater.
Thus, the real difficulty of EUV and high-end DUV is never a single component but the entire ultra-precision industrial civilization’s collaborative capability. Zeiss’s true irreplaceability is not just the lens itself but the decades of optical design, error compensation, system-level algorithms, reference optics, assembly experience, ultra-precision metrology, process databases, and talent systems built over time. These elements together form the “precision infrastructure” of modern lithography industry.