What's stopping them from using hard x-rays? Those are really easy to emit. (Genuine question; not trying to suggest that they're all idiots who just never considered using hard x-rays.)
Interaction with the mask material, I imagine. With hard x-rays, most of the photons generated will just sail right through, not interacting at all, or (worse) ionize the material being exposed.
Personally, I'm surprised that there aren't ways to generate this energy by nonlinear mixing of light from two lasers that are separated by the desired frequency.
Lasers are an Electro-Magnetic emission of which the output is a synchronized at a specific and regular frequency.
If you have two lasers at about 700nm and 1000nm, and they 'start' at a synchronized point, then 7mm (7000nm) of emission later they'd have a repeat of the cycle begin again.
During that cycle the interference pattern would probably have an interesting shape, but I very much doubt it'd be useful for semiconductor production. Maybe a math or physics graduate could elaborate on if there's a name for this kind of pattern and if there are any uses I'm not aware of.
That’s a linear mixing, non-linear allows for the absorption of two photons followed by the emission of one with twice the energy. That allows for a laser pumped frequency doubler.
Actually most consumer oriented lasers (for example green lasers) work like this, but I don’t know if it works for frequencies as high as soft x-rays.
