Coupling-aware mixed dummy metal insertion for lithography

As integrated circuits manufacturing technology is advancing into 65nm and 45nm nodes, extensive resolution enhancement techniques (RET) are needed to correctly manufacture a chip design. The widely used RET called offaxis illumination (OAI) introduces forbidden pitches which lead to very complex design rules. It has been observed that imposing uniformity on layout designs can substantially improve printability under OAI. In this paper, two types of assist features for the metal layer are proposed to improve the uniformity, printable assist feature and segmented printable assist feature. They bring different costs on performance and manufacturing. Coupling and lithography costs from these assist features are discussed. Optimal insertion algorithm is proposed to use both types of dummy metals, considering trade-offs between coupling and lithography costs.