The issue isn't in generating short wavelength light, it's in focusing it accurately enough to print a pattern with trillions of nanoscale features with few defects. We can't really use lenses since every material we could use is opaque to high energy photons so we need to use mirrors, which still absorb a lot of the light energy hitting them. Now this only explains why we need all the crazy stuff that asml puts in it's EUV machines to use near x-ray light, but not why they don't use x-ray or higher energy photons. I believe the answer to this is just that the mirrors they can use for EUV are unacceptably bad for anything higher, but I'm not sure
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replyThere is such a thing as X-ray lithography, but it comes with significant challenges that make it not really worth it compared to EUV.
replyI'd like to hear more about these challenges
replyStochastic effects become a bigger and bigger problem. At some point (EUV) a single photon has enough energy to ionize atoms, causing a cascade that causes effects to bloom outside of the illumination spot.
replyAs I understand it, primarly because due to the high energy level of x-rays, light x-ray interacts very differently with materials[1]. Primarily they get absorbed, so very difficult to make mirrors or lenses, which are crucial for litography to redirect and focus the light on a specific miniscule point on the wafer.
replyThe primary method is to rely grazing angle reflection, but that per definition only allows you a tiny deflection at a time, nothing like a parabolic mirror or whatnot.
All of these problems or equivalent still exist in EUV. Litho industry had to kind of rethink the source and scanner because it went from all lenses to all mirrors in EUV. This is also why low NA and high NA EUV scanners were different phases.
replyAs I hear it, the decision had large economic component related to Masks and even OPC.
100%. EUV barely works. XRay litho takes all the issues with EUV and cranks them up to 11. It will take comparable effort to EUV, if not more, to get XRay litho up and running, and I'm not aware of anyone approaching this to anywhere near the level of investment that ASML (and others) have pumped into developing EUV tech. We may get there eventually as a species, but we're a ways off.
replyIt really is the specific wavelength. Higher or lower is easier. But euv has tricky properties which make it feasible for Lithography (although just barely it you have a look at the optics) but hard to produce with high intensities.
replySpecifically, what makes x-rays easy to generate are these: https://en.wikipedia.org/wiki/Characteristic_X-ray In essence, smashing electrons into atoms allows you to ionize the inner shell of an atom and when an electron drops down from an outer shell, the excess energy is shed as high-energy photons. This constrains the energy range of X-ray tubes ("smash electron into metal") to wavelengths well below 13.5nm.
reply(These emission lines are also what is being used in x-ray spectroscopy to identify elements)
You can also generate broad spectrum bremsstrahlung radiation easily, this is widely used for medical X-rays.
replyAny source to this? I am hearing this for the first time.
replyITs easy to make X-rays, you just hit a metal target with electrons: https://en.wikipedia.org/wiki/X-ray_tube
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