On Lithography Aware Metal-Fill Insertion

Vikram Suresh,  Priyamvada Vijayakumar,  Sandip Kundu
University of Massachusetts, Amherst


Manufacturability and lithographic printability are growing concerns with advancing technology nodes. The two most important parameters which influence the printability of a design are lithographic process corner and pattern density of the design. Dummy metal-fills are used to improve post-chemical mechanical polishing surface planarity. Conventional metal-fills do not consider impact of fill on lithographic printability or critical area – this is the focus of our paper. Although systematic yield due to lithographic distortions is gaining prominence, particulate defects still remain a significant source of yield loss. Increasing design density in conjunction with growing manufacturability issues necessitates lithography aware particulate limited yield loss analysis. In this work, we propose a novel lithography aware metal-fill insertion technique taking both statistical lithographic variations and critical area into consideration. Specifically, the main contributions of this work are a) analyzing the influence of metal-fills on line width variation and critical area, b) synthesis of statistical lithography-aware metal-fill to improve design yield. The solution methodology has been built on existing commercial tools. Experiments on ISCAS’85 benchmark circuits show that on 45nm technology, metal-fills increase the linewidth variation of more than 30% of the nets by as much as 15% as compared to variation without metal-fill. Lithography aware metal-fill reduces linewidth variation by ~25% and critical area by ~35% compared to conventional metal-fill solutions without sacrificing density, planarity and performance targets.