The limiting factor is the size of pattern that can be created on the photoresist layer. Higher transistor densities require finer mask patterns and shorter light wavelengths. Here's the pressing issue: current photolithography uses ultraviolet light with a 193nm wavelength, but at some point in the near future, probably around the 10nm process, a switch to extreme UV (EUV) with a 13.5nm wavelength will be required.
In the late 1990s and early 2000s, there was confidence within the semiconductor industry that EUV equipment was coming soon. It has failed to materialize, however, due to the technical difficulties that EUV imposes. Optically, EUV is harder to work with. It precludes the use of lenses, as most optical materials strongly absorb EUV light. Instead only mirrors can be used...
Extreme UV progress to save Moore's Law
Posted on Thursday, Aug 08 2013 @ 12:21 CEST by Thomas De Maesschalck
ARS Technica reports new improvements in photolithography could pave the way to extend Moore's Law into the second half of this decade and beyond. As the industry moves towards smaller and smaller processes, physics gets in the way and threatens to put an halt to the process of doubling the number of transistors roughly every 18 to 24 months, but now ASML claims it could have production-ready extreme UV (EUV) equipment by 2015, suitable for producing chips with 10nm features.