Standard Cell and Custom Circuit Optimization using Dummy Diffusions through STI Width Stress Effect Utilization

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 enables the exploitation of STI stress for performance improvement of standard cells and custom integrated circuits. We start with process simulation of a 65 nm STI technology, and generate mobility models for STI stress based on these simulations. Based on these models, we are able to perform STI stress-aware modeling and simulation using SPICE. We then present our optimization of STI stress in standard-cell and custom designs using active-layer (dummy) fill insertion to alter the STI widths. Circuit level experimental results are based on a miscellaneous ring oscillator, which is known to correlate well to silicon. Using a generic 65 nm cell library, we show that the STI-optimized designs provide up to 8% improvement in clock frequency. The frequency improvement through exploitation of STI stress comes at practically zero cost with respect to area and wire length.