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I was curious that they claim that lithography is done with ultraviolet, and I looked up the wavelengths involved. Sure enough, "typical" UV is still hundreds o

I was curious that they claim that lithography is done with ultraviolet, and I looked up the wavelengths involved. Sure enough, "typical" UV is still hundreds of nanometers long, like visible light. This would be too coarse for small features since you'd get diffraction at the edges of the stencil. I looked up UV in wikipedia and apparently they have defined "extreme UV" to be down to 10nm - which I would have called X-rays. Indeed, if 10nm is extreme UV, perhaps we can also call 10nm light "underachieving X-rays". https://en.wikipedia.org/wiki/Ultraviolet https://en.wikipedia.org/wiki/Ultraviolet

whatshisface 3y ago
Well, I would have called infrared microwaves because the wavelengths are in micrometers, but I believe that ship sailed over a century ago. (P.S. they're using them to cause chemical reactions, not ionize atoms or scatter off electrons, which is definitely more of a UV thing than an X-ray thing.)
- marcosdumay 3y ago
  > they're using them to cause chemical reactions, not ionize atoms or scatter off electrons Those three are approximately the same thing. The distinguishing characteristic of X-rays is that they remove electrons from other layers than the last one. And the most relevant feature of UV is that it ionizes atoms. (Even though what distinguishes it is that we can't see it.) For completeness, the thing that differentiates IR from microwaves is that IR creates molecular compression while microwaves can only make matter vibrate. The IR name is about 3 centuries old, and it's because it often comes from light sources. While microwaves are the smaller version of the short waves; from the short, medium, and long waves used on radio. Anyway, the dividing between those is always fuzzy.
starspangled 3y ago
> I was curious that they claim that lithography is done with ultraviolet, and I looked up the wavelengths involved. Sure enough, "typical" UV is still hundreds of nanometers long, like visible light. This would be too coarse for small features since you'd get diffraction at the edges of the stencil. 173nm DUV is used commercially to create features in the 20-30nm range, possibly smaller. > I looked up UV in wikipedia and apparently they have defined "extreme UV" to be down to 10nm - which I would have called X-rays. Indeed, if 10nm is extreme UV, perhaps we can term 100nm light "underachieving X-rays". What are you are trying to say? EUV light used in lithography (13.5nm) is close to soft x-ray light, but what does 100nm light have to do with it?
- simpaticoder 3y ago
  It was a typo, now corrected. I was suggesting, humorously, that 10nm light could be called both 'extreme uv' and 'underachieving xrays', since they overlap. The EM spectrum is continuous, so these distinctions and names are arbitrary, so why not have some fun?
kurthr 3y ago
Ok, so the answer is marketing, but there's a long story. There were so many failures of X-ray lithography that it was easier to name it EUV. Sorta like you don't have nuclear MRI for medicine. They choose to emphasize the 3D Imaging over the n-word. One can get quite small even with DUV (193nm ArF) by using high NA (water immersion) to get 1.3-1.4x better resolution (wavelength scales with index of refraction). That along with multi-patterning (which puts limits on the design layout, but allows 2-4x tighter pitch) can get you down to a pitch of about 65nm (single patterned) or 10-20nm (multi-patterned). However, the whole idea of pitch for the gate length falls apart around here and 40 is basically the same pitch as 65 with transistor packing tweaks, and 28 is the last "analog" node. By the time you're multi-patterned bellow 22nm, you're using fin-FETs and the scaling is totally broken (some would say made-up by marketing). That's how TSMC's 7nm was the same pitch as Intel's 10nm. Quad multi-patterning's poor yield finally broke the long dominance of 193nm, but it was cheaper than X-rays for about 20 years (and a lot of bankruptcies). The use of the name EUV with 13nm wavelength and now immersion EUV, which allows 2-3nm without multi-patterning is meant to evoke the extension of lithographic techniques rather than the revolution X-rays implied 20 years earlier. Note that it's still so expensive that only a few critical layers are patterned with EUV. Double patterning will double the costs (half as many layers patterned per stepper per hour) so all the old tricks will come out again. Transistors will evolve again with nano-sheets and GAA to reduce leakage at even closer spacings. We should get below "2nm", but you're not talking about gate or metal dimensions anymore, just peak transistor density is ~400x better than 40nm (1M/mm2 vs 400M/mm2). When you're selling $100M pieces of equipment in a field wit decades of history, names matter.
- metricspaces 3y ago
  fantastic info. thanks for sharing.
  - kurthr 3y ago
    Hah, I left actual silicon process engineering a long time ago, but I worked on the early 68020 at 2um and then early submicron in R&D. That was 40 years ago and the process now 1000x smaller (1 million more transistors). It's pretty amazing... even if it does seem like fab investment costs have grown so much that we're nearing the end of profitable scaling.

whatshisface 3y ago

Well, I would have called infrared microwaves because the wavelengths are in micrometers, but I believe that ship sailed over a century ago. (P.S. they're using them to cause chemical reactions, not ionize atoms or scatter off electrons, which is definitely more of a UV thing than an X-ray thing.)

marcosdumay 3y ago
> they're using them to cause chemical reactions, not ionize atoms or scatter off electrons Those three are approximately the same thing. The distinguishing characteristic of X-rays is that they remove electrons from other layers than the last one. And the most relevant feature of UV is that it ionizes atoms. (Even though what distinguishes it is that we can't see it.) For completeness, the thing that differentiates IR from microwaves is that IR creates molecular compression while microwaves can only make matter vibrate. The IR name is about 3 centuries old, and it's because it often comes from light sources. While microwaves are the smaller version of the short waves; from the short, medium, and long waves used on radio. Anyway, the dividing between those is always fuzzy.

starspangled 3y ago

> I was curious that they claim that lithography is done with ultraviolet, and I looked up the wavelengths involved. Sure enough, "typical" UV is still hundreds of nanometers long, like visible light. This would be too coarse for small features since you'd get diffraction at the edges of the stencil. 173nm DUV is used commercially to create features in the 20-30nm range, possibly smaller. > I looked up UV in wikipedia and apparently they have defined "extreme UV" to be down to 10nm - which I would have called X-rays. Indeed, if 10nm is extreme UV, perhaps we can term 100nm light "underachieving X-rays". What are you are trying to say? EUV light used in lithography (13.5nm) is close to soft x-ray light, but what does 100nm light have to do with it?

simpaticoder 3y ago
It was a typo, now corrected. I was suggesting, humorously, that 10nm light could be called both 'extreme uv' and 'underachieving xrays', since they overlap. The EM spectrum is continuous, so these distinctions and names are arbitrary, so why not have some fun?

kurthr 3y ago

Ok, so the answer is marketing, but there's a long story. There were so many failures of X-ray lithography that it was easier to name it EUV. Sorta like you don't have nuclear MRI for medicine. They choose to emphasize the 3D Imaging over the n-word. One can get quite small even with DUV (193nm ArF) by using high NA (water immersion) to get 1.3-1.4x better resolution (wavelength scales with index of refraction). That along with multi-patterning (which puts limits on the design layout, but allows 2-4x tighter pitch) can get you down to a pitch of about 65nm (single patterned) or 10-20nm (multi-patterned). However, the whole idea of pitch for the gate length falls apart around here and 40 is basically the same pitch as 65 with transistor packing tweaks, and 28 is the last "analog" node. By the time you're multi-patterned bellow 22nm, you're using fin-FETs and the scaling is totally broken (some would say made-up by marketing). That's how TSMC's 7nm was the same pitch as Intel's 10nm. Quad multi-patterning's poor yield finally broke the long dominance of 193nm, but it was cheaper than X-rays for about 20 years (and a lot of bankruptcies). The use of the name EUV with 13nm wavelength and now immersion EUV, which allows 2-3nm without multi-patterning is meant to evoke the extension of lithographic techniques rather than the revolution X-rays implied 20 years earlier. Note that it's still so expensive that only a few critical layers are patterned with EUV. Double patterning will double the costs (half as many layers patterned per stepper per hour) so all the old tricks will come out again. Transistors will evolve again with nano-sheets and GAA to reduce leakage at even closer spacings. We should get below "2nm", but you're not talking about gate or metal dimensions anymore, just peak transistor density is ~400x better than 40nm (1M/mm2 vs 400M/mm2). When you're selling $100M pieces of equipment in a field wit decades of history, names matter.

metricspaces 3y ago
fantastic info. thanks for sharing.
- kurthr 3y ago
  Hah, I left actual silicon process engineering a long time ago, but I worked on the early 68020 at 2um and then early submicron in R&D. That was 40 years ago and the process now 1000x smaller (1 million more transistors). It's pretty amazing... even if it does seem like fab investment costs have grown so much that we're nearing the end of profitable scaling.