Hmm, that could perhaps do it. The ions are certainly not negative (at least, not many of them?), the energy levels are several times the electron affinity of anything on the Periodic Table. And with the energy levels being around 90eV as mentioned, it should really only take a few hundred to do that, or even thousands of volts, just because. Grids could even be hanging to enforce specific electric fields in the drift area, without sacrificing the optical path too much I think.
What's stopping them going to Xrays which are even shorter wavelength but relatively easy to generate?
X-rays tend to cause a lot of damage, both to the resist and the substrate. The beam resolution can be very good indeed (a few atoms, even), though the masks can't be magnified any, they have to be made at 1:1 scale (well, unless you want to take up many meters of beam length with grazing-incidence mirrors, which, eh, it could happen?). But the exposure resolution is limited by the movement of ionized (Auger) electrons in the substrate and resin, some 10-20nm depending. Electron beam writing, same idea, plus the added restriction that you can't really create a mask at all, so you have to scan vector or raster -- very slow indeed!
Tim