Layout design methodologies for sub-wavelength manufacturing

In this paper, we describe new types of layout design constraints needed to effectively leverage advanced optical wafer lithography techniques. Most of these constraints are dictated by the physics of advanced lithography processes, while other constraints are imposed by new photomask techniques. Among the methods discussed are (1) phase shift mask (PSM) lithography in which phase information is placed on the photomask in combination with conventional clear and dark information; (2) optical proximity correction (OPC) where predictable distortions in feature geometry are corrected by putting an inverse distortion on the mask; (3) off-axis illumination optics that improve resolution of some configurations at the expense of others; and (4) use of non-resolving assist features that improve neighboring structures.