High resolution optical lithography system using oblique incidence illumination

The authors propose a novel optical lithography system that has a resolving power more than 1.6 times higher than the resolving power of conventional projection systems. This system offers the superior practical advantage of using conventional masks without phase shifters. The authors explain the principle of the system and present its experimental confirmation. Possible applications to advanced processes are also mentioned. The combination of the optical system with an i-line and KrF excimer laser source will most probably be the lithography method used for 64 M and 245 M DRAM (dynamic RAM) processes.<>