Exploiting STI stress for performance

Starting at the 65 nm node, stress engineering to improve performance of transistors has been a major industry focus. An intrinsic stress source -shallow trench isolation -has not been fully utilized up to now for circuit performance improvement. In this paper, we present a new methodology that combines detailed placement and active-layer fill insertion to exploit STI stress for performance improvement. We perform process simulation of a production 65 nm STI technology to generate mobility and delay impact models for STI stress. Based on these models, we are able to perform STI stress-aware delay analysis of critical paths using SPICE. We then present our timing-driven optimization of STI stress in standard cell designs, using detailed placement perturbation to optimize PMOS performance and active-layer fill insertion to optimize NMOS performance. We assess our optimization on small designs implemented with a 65 nm production cell library and a standard synthesis, place and route flow. Our timing-driven optimization of STI stress impacts can improve clock frequency by between 7% to 11%. The frequency improvement through exploitation of STI stress comes at practically zero cost in terms of design area and wirelength.