Circuit Placement, Chip Optimization, and Wire Routing for IBM IC Technology

Abstract

Recent advances in integrated circuit technology have imposed new requirements on the chip physical design process. At the same time that performance requirements are increasing, the effects of wiring on delay are becoming more significant. Larger chips are also increasing the chip wiring demand, and the ability to efficiently process these large chips in reasonable time and space requires new capabilities from the physical design tools. Circuit placement is done using algorithms which have been used within IBM for many years, with enhancements as required to support additional technologies and larger data volumes. To meet timing requirements, placement may be run iteratively using successively refined timing-derived constraints. Chip optimization tools are used to physically optimize the clock trees and scan connections, both to improve clock skew and to improve wirability. These tools interchange sinks of equivalent nets, move and create parallel copies of clock buffers, add load circuits to balance clock net loads, and generate balanced clock tree routes. Routing is done using a grid-based, technology-independent router that has been used over the years to wire chips. There are numerous user controls for specifying router behavior in particular areas and on particular interconnection levels, as well as adjacency restrictions.