Comments by "kazedcat" (@kazedcat) on "The Extreme Engineering of ASML’s EUV Light Source" video.

13.5nm needs vacuum chamber because air is opaque to the wavelength so immersion lithography where they use ultra pure water as focusing lens is not possible with EUV. But multi patterning is possible with EUV and it is part of the roadmap for future improvement.
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E-beam is to slow. There are research for multibeam E-beam but it becomes complicated very quickly.
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The previous technology called DUV (Deep Ultra Violet) is 193nm. So yes they are already using UV but not extreme UV which is 13.5nm
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@lystfiskerlars It would cost more to develop an intermediate step instead of going for a step change. I don't know why it is 15x but they need the new technology to be at least 10x the previous technology to justify the cost of developing it. For intermediate improvement they can rely on multipaterning. Also immersion lithography gives 2x higher resolution so the improvement of EUV over immersion is just around 7x.
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In addition to this they are manipulating the shape of the light. They need a dipole light source for increase resolution.
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@tylerdurden3722 They use a mirror to focus the light into a circular beam. A second mirror to convert a circular beam into an annular beam. Then a third mirror to convert annular beam into a dipole beam. This is before the beam hit the mask . Then after reflecting from the mask there are a set of mirrors for magnification and aberrations correction.
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