TABLE OF CONTENTS Rupesh S. Shelar and Prashant Saxena
A design is said to exhibit routing congestion if the demand for the routing resources in some region within its layout exceeds their supply. Congestion is undesirable because it can degrade the performance and the yield of a design, and can add uncertainty to its convergence. With wire delays no longer being insignificant in modern process technologies, an unexpected increase in the delay of a net that lies on a critical path can cause a design to miss its frequency target. The routing of a net passing through a congested region may be detoured significantly, or forced to use the more resistive metal layers. Consequently, the delay estimates for nets that pass through congested regions are often erroneous. These estimates may mislead the design optimization trajectory by failing to correctly identify the truly critical paths, thus aggravating the design convergence problem. A densely congested design is also likely to result in a lower manufacturing yield than a similar uncongested design. Congestion typically results in an increased number of vias in the routes, which can affect the yield. Additionally, congested layouts tend to have larger critical areas for the creation of shorts and opens because of random defects.
Furthermore, it can be shown using first-order scaling models that the congestion problem is likely to worsen...
