At SPIE 2008, TSMC published a paper which talked about shot noise for the different lithography technologies and its impact on CD uniformity. EUV already had trouble in this area at 30 nm, so for the 20 nm size applications, it would have a prohibitive impact on minimum dose requirements, as that would drive up the source power requirement many times beyond the currently already difficult-to-reach target level.
The paper title is "Influence of Shot Noise on CDU with DUV, EUV, and E-Beam"
What about 193i (or nanoimprint as used in disk drives) to form parallel lines and e-beam to cut them and form vias? TSMC has a Mapper prototype system. David Lam is targeting Multibeam for this purpose, rather than rastering a mask, since it has much relaxed overlay/resolution/writing speed requirements compared to rastering the whole wafer.
157 died since it was a lot of investment for relatively little gain in process capability. EUV may start to be in that position, unless it can demonstrate significant capability improvement or cost reduction at the time it would be inserted.
Rick, the only viable option right now is multi-patterning solution. Ofcourse the cost will be very high and the challenges immense but some top level executive would want to make it a marketing sucess.
We should look beyound the lithography tool solutions. We should modify the design rule and make relatively simple chips. I think we have already missed the deadline on 7nm EUV with the current source power.