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Comment by naasking | Hacker News Reader

Crazy they have physical masks with features as small as 7nm. I assume those are movable somehow but that seems like incredibly delicate work.

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> Crazy they have physical masks with features as small as 7nm.

Everything about this is crazy complex, and the state of the art in any given year is also secret to TSMC and other tiny-feature-size fabs.

But in addition to gradually upping the narrow-bandwidth/phase-coherent illumination frequency every year (which has many problems but continues to see continual progress), they've also long been using techniques to work around the diffraction limit/resolution barrier [1], such as subwavelength metamaterial "hyperlenses" / "superlenses" (previously widely thought to be impossible even in theory) [2][3] and "assist features" and other non-traditional masking elements to pre-compensate for imaging distortions [4]. Plus they fiddle a lot with the chip process to tune it in weird ways to assist with or compensate for the previous issues.

[1] https://en.wikipedia.org/wiki/Diffraction-limited_system

[2] https://en.wikipedia.org/wiki/Superlens#Theory

[3] "Subwavelength-Grating Metamaterial Structures for Silicon Photonic Devices" https://ieeexplore.ieee.org/document/8424820

[4] https://en.wikipedia.org/wiki/Extreme_ultraviolet_lithograph...

You can use lenses and curved mirrors to make a larger mask focus the light onto a smaller area.

That still seems pretty delicate. The lenses and mirrors would have to be aberration-free to an extreme degree so as to not introduce too many artifacts, and moving the mask further from the surface would increase risk of diffraction artifacts, no?

It is, but that's how modern semiconductor lithography is done. Massive lenses and mirrors (both made of different materials that normal, since they need to have optical properties at wavelengths much smaller than human vision) are manufactured at great cost to ensure that it is free of aberrations. The extremely limited supply of these is actually one of the many factors that restricts the ability to move to newer processes and scale production capability of newer lithographies.

For good telescope optics, we look for something like 1/4 - 1/6 wavelength tolerance, minimum. That's for optical wavelengths, but photolithography is in the UV range, so that's already stricter tolerance in absolute terms because of the shorter wavelength, but how does the tolerance in relative terms compare? Thanks for the info!

Read up on the Zeiss optics that go into the ASML EUV machines. (or at least what is publicly available knowledge). It's truly insane

They go pretty hardcore on the optics. Have a look at their light path:

https://www.asml.com/-/media/asml/images/technology/43679-in...

One youtube video[1] I watched had someone state that if you scaled up one of the curved mirrors to the size of the Earth, the largest imperfection would be the width of a hair.

[1] https://www.youtube.com/watch?v=en7hhFJBrAI around 7:30

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