Using a Free-Electron Laser as a Light Source for Extreme Ultraviolet Lithography

Just when you thought semiconductor manufacturing couldn’t go any further off the deep end after High Numerical Aperture Photolithography (posted here on 2023-08-27), along comes the idea of using a free-electron laser as the light source, allowing greater intensity than the current tin plasma zapping technique and tunable wavelength, permitting scaling to even smaller device feature sizes in the future.


Potential drawbacks (or “challenges”) in adopting this technology? Well, the linear accelerator required to boost the electrons to the relativistic velocity (800 MeV) needed and the “undulator” that magnetically accelerates the electrons back and forth to generate the light are both around 200 metres long, arranged in an oval racetrack 20 metres wide with bending magnets at both ends, and the whole apparatus is expected to cost around US$ 400 million, although a single light source may be shared by multiple photolithography machines.

The research paper discussing a proof of concept free-electron laser for extreme ultraviolet lithography is “High-power EUV free-electron laser for future lithography” (full text at link). Here is the abstract.

The development of a high-power EUV light source is very important in EUV lithography to overcome the stochastic effects for higher throughput and higher numerical aperture (NA) in the future. We have designed and studied a high-power EUV free-electron laser (FEL) based on energy-recovery linac (ERL) for future lithography. We show that the EUV-FEL light source has many advantages, such as extremely high EUV power without tin debris, upgradability to a Beyond EUV (BEUV) FEL, polarization controllability for high-NA lithography, low electricity consumption, and low construction and running costs per scanner, as compared to the laser-produced plasma source used for the present EUV lithography exposure tool. Furthermore, the demonstration of proof of concept (PoC) of the EUV-FEL is in progress using the IR-FEL in the Compact ERL (cERL) at the High Energy Accelerator Research Organization. In this paper, we present the EUV-FEL light source for future lithography and progress in the PoC of the EUV-FEL.

In 1987, I wrote a science fiction short-short story titled “Free Electrons”. Prophetic?—nope.


Equivalence between free-electron-laser oscillators and actively-mode-locked lasers: Detailed studies of temporal, spatiotemporal, and spectrotemporal dynamics
C. Bruni, T. Legrand, C. Szwaj, S. Bielawski, and M. E. Couprie
Phys. Rev. A 84, 063804 – Published 1 December 2011

We show experimentally and numerically that free-electron-laser (FEL) oscillators behave in a very similar way to conventional actively-mode-locked lasers. This stems from the similar structures of their underlying Haus equations. A comparative study of the temporal evolutions of the pulse train shapes and spatiotemporal regimes is performed on a Nd:YVO4 laser and a storage-ring free-electron laser. Furthermore, since direct observations of time-resolved pulse shapes and spectra are more accessible on free-electron lasers, the analogy also potentially enables one to investigate mode-locked laser dynamics using existing FEL facilities.

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Could this scale up for The Boring Company? Probably not, but…

…as Musk often asks his engineers: “Is there anything in the laws of physics that prohibits it?” (ROP: Rate of Penetration)


This was discussed in a comment on another post on 2023-01-29. The reaction was unenthusiastic, but perhaps that’s to be expected for innovative technological fixes to problems which it’s more acceptable to lament as insoluble.

Lancing the Earth with a beam weapon to let out deep strata’s heat from natural radioactive decay sounds like a nifty idea to me. And, with a big enough zapper, it works everywhere, not just near tectonic plate boundaries where the the hot stuff is close to the surface.


I’d missed that.

As far as The Boring Company is concerned (tunnels) the aforelinked paper’s Levelized Cost of Electricity estimate for an 8in bore, at $144/m would “scale up” for a 21ft diameter tunnel to almost $150k/m. That’s not going to fly without some pretty massive energy economies of scale for larger bore area.

Of course geothermal electric economics (ie: an 8in diameter bore) is entirely different.