Layout-Aware Compact Model of MOSFET Characteristics Variations Induced by STI Stress

Abstract

A compact model is proposed for accurately incorporating effects of STI (shallow trench isolation) stress into post-layout simulation by making layout-dependent corrections to SPICE model parameters. The model takes in-plane (longitudinal and transverse) and normal components of the layout-dependent stress into account, and model formulas are devised from physical considerations. Not only can the model handle the shape of the active-area of any MOSFET conforming to design rules, but also considers distances to neighboring active-areas. Extraction of geometrical parameters from the layout can be performed by standard LVS (layout versus schematic) tools, and the corrections can subsequently be back-annotated into the netlist. The paper spells out the complete formulation by presenting expressions for the mobility and the threshold voltage explicitly by way of example. The model is amply validated by comparisons with experimental data from 90 nm- and 65 nm-CMOS technologies having the channel orientations of, respectively, (110) and (100), both on a (100) surface. The worst-case standard errors turn out to be as small as 1.7% for the saturation current and 8 mV for the threshold voltage, as opposed to ∼20% and ∼50 mV without the model. Since device characteristics variations due to STI stress constitute a significant part of what have conventionally been treated as random variations, use of the proposed model could enable one to greatly narrow the guardbands required to guarantee a desired yield, thereby facilitating design closure.