Printing circuits with 4nm feature size: similarities and differences between EUV and optical lithographies

One of the main concerns about EUV lithography is whether or not it can be extended to very high numerical aperture. Recently, a waveguide effect in high-NA EUV lithography was observed. This effect serves to overcome the problem of shadowing in EUV lithography and allows EUV lithography to be extended to the 4-nm node. In this paper, an exact eigenmode analysis is presented to explain the observed effect. This waveguide effect is then applied to simulate the printing of 4-nm lines and spaces with excellent aerial-image contrast and peak intensity. The feasibility of EUV lithography for printing logic circuits containing general 2D patterns with 4-nm feature size is also demonstrated.