13nm is hard enough. ASML seems to have settled on laser-driven tin plasma light source, which is miserably inefficient: https://en.wikipedia.org/wiki/Extreme_ultraviolet_lithograph

>The required utility resources are significantly larger for EUV compared to 193 nm immersion, even with two exposures using the latter. Hynix reported at the 2009 EUV Symposium that the wall plug efficiency was ~0.02% for EUV, i.e., to get 200-watts at intermediate focus for 100 wafers-per-hour, one would require 1-megawatt of input power

The optical train is also tough. 13nm is getting close to soft x-rays, and photons that hot don't like reflecting, and the optics are rapidly degraded by exposure light:

>EUV collector reflectivity degrades ~0.1-0.3% per billion 50kHz pulses (~10% in ~2 weeks), leading to loss of uptime and throughput [...] Due to the use of EUV mirrors which also absorb EUV light, only a small fraction of the source light is finally available at the wafer. There are 4 mirrors used for the illumination optics, and 6 mirrors for the projection optics. The EUV mask or reticle is itself an additional mirror. With 11 reflections, only ~ 2% of the EUV source light is available at the wafer.

The design of EUV lasers is already completely absurd. It's an awesome piece of engineering, but it's no easier to push the laser wavelength downwards than anything else.

13nm * 2 is 26nm.

Using a smaller wavelength is kind of useless for the optical lithography, as below this photons will make too many secondary electrons which will reduce the effective resolution. This is the reason X-ray lithography went nowhere.

This is why the ultimate limit of 157nm lithography was also not so far away from EUV. Also somewhere in between 25nm-30nm

This is also why some people suggest resurrecting 157nm — getting nearly same half pitch without maintenance, and expensive tooling of EUV.