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

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.