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

Abstract

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.