Stress Aware Layout Optimization Leveraging Active Area Dependent Mobility Enhancement

Starting from the 90 nm technology node, process induced stress has played a key role in the design of high-performance devices. The emergence of source/drain silicon germanium (S/D SiGe) technique as the most important stressing mechanism for p-channel metal-oxide-semiconductor field-effect transistor devices has opened up various optimization possibilities at circuit and physical design stage. In this paper, we exploit the active area dependence of the performance improvement achievable using S/D SiGe technology for late stage engineering change order (ECO) timing optimization. An active area sizing aware cell-level delay model is derived which forms the basis of linear program based optimization of a design for achieving maximum performance or target performance under a timing budget. To control the magnitude of layout perturbation and ensure predictable timing improvement, a set of physical constraints for active area sizing is proposed. Further, an efficient minimum movement legalization algorithm is proposed to remove the overlaps caused by active area sizing of timing critical cells. Results on a wide variety of benchmarks show consistent reduction in the cycle time by up to 6.3%. Predictability of the performance improvement achievable as well as resultant minuscule layout changes make our technique very attractive for late stage ECO optimization and design closure.