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Comment by londons_explore | Hacker News Reader

Why are people putting lots of effort into extreme UV generators when we could just use x-rays? We know plenty of ways to generate and focus x-rays...

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At sufficient photon energy the initial absorption kicks off secondary electrons which blurs the feature edges/limits effective resolution. This problem already exists to some extent with EUV but gets much worse at X-ray energy.

Just a guess as I am not in the industry but I would imagine has to do with the photoresists and masks - perhaps we don’t have ones that work with X-ray. Not much good using a wavelength that passes through or is unabsorbed by the resist material!

IIRC we don't even have masks that can really take EUV, the mask is destroyed after each exposure.

I think the masks can take it but their is a ton of difficulty in inspecting the masks themselves for defects. IIRC the leading candidate at the time I was in the industry was to actually expose wafers and then scan the wafers for defects which originated on the mask, hoping to not confuse these with other process defects. Not sure how they ended up solving that one.

Not just that but high throughput pellicles (prevents dust from ko-ing you) haven't hit production yet iirc

Do multiple exposures and see which defects come up more than once?

Yeah - typically print the entire wafer then compare dies within a field (usually there are multiple dies exposed in a single exposure) to see which defects are in the same place on each field. This won’t work if there is only one die per field, as could be the case for an exceptionally large server chip. In that case you probably need to predict what the image will look like based on design files and then compare with the actual image and look for differences. You could also e-beam scan the whole wafer but this can take a while (like 30 days when I was around), night damage the wafer, and bumps up against the reliability of E-beam components. It wasn’t being seriously considered.

That would ruin the economics of EUV. A mask set costs millions of dollars and for chip designers it is the generally the highest most expensive part of the manufacturing process and must be amortized over as many units as possible.

The machines that create the masks are also not very fast. A mask is created by firing an electron beam which is a sequential process.

If you were limited to one wafer per mask then not only would each chip cost tens of thousands of dollars you would also only be able to produce a single digit amount of wafers per year.

Issues like photoresist chemistry, stochastics, shot noise, etc.

These are already all problems for EUV and limit its lithographic resolution compared to the theoretical diffraction limited resolution.

> We know plenty of ways to generate and focus x-rays...

Generate, yes. Focus? Not so much.

Diffractive lenses exist for that (Fresnel zone plates are being used for that) - the problem is that they're absorptive diffractive lenses instead of phase masks and of course they have limited manufacturing precision. It's a contributing factor to the application of ptychographic methods (i.e. image synthesis from multiple diffraction patterns) to arrive at a high-resolution X-Ray image (e.g. in X-Ray microscopy).

Edit: Phase mask mirrors ('surface profile' fresnel zone plate) do exist though.

My initial idea would be a fluorescent lamp that takes x-rays and glows EUV but you would need to find the right substance for that

I heard somewhere that tin plasma can generate EUV.~

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