Toward Unidirectional Routing Closure in Advanced Technology Nodes

In advanced technology nodes, unidirectional layout is strongly preferred for high-density metal layers for better manufacturability. The lithography printing of unidirectional layout can be tightly controlled with illumination source optimization and resolution enhancement techniques. Meanwhile, with the unidirectional layout, self-aligned double and quadruple patterning can be applied to achieve finer pitches beyond the resolutions limits of 193 nm lithography tools. However, unidirectional layout style introduces significant impacts on the physical design flow. Notably, unidirectional routing limits the standard cell pin accessibility, which makes manual cell layout design and optimization more and more challenging under modern standard cell architecture. In the routing phase, routing densities and resource competitions on lower metal layers are becoming increasingly high, where intelligent approaches are needed to resolve routing resource competitions for unidirectional routing closure. Moreover, post-routing optimization is inevitable to avoid significant engineering-changing-efforts for unidirectional routing under advanced manufacturing constraints. In this paper, we present a holistic approach, including standard pin access evaluation/optimization, pin access and routing co-optimization and post-routing optimization, to enable unidirectional routing closure in advanced technology nodes.