The need and opportunities of electromigration-aware integrated circuit design

Abstract

Electromigration (EM) is becoming a progressively severe reliability challenge due to increased interconnect current densities. A shift from traditional (post-layout) EM veri cation to robust (pro-active) EM-aware design-where the circuit layout is designed with individual EM-robust solutions-is urgently needed. This tutorial will give an overview of EM and its e ects on the reliability of present and future integrated circuits (ICs). We introduce the physical EM process and present its speci c characteristics that can be a ected during physical design. Examples of EM countermeasures which are applied in today's commercial design ows are presented. We show how to improve the EM-robustness of metallization patterns and we also consider mission pro les to obtain application-oriented current-density limits. The increasing interaction of EM with thermal migration is investigated as well. We conclude with a discussion of application examples to shift from the current post-layout EM veri cation towards an EM-aware physical design process. Its methodologies, such as EM-aware routing, increase the EM-robustness of the layout with the overall goal of reducing the negative impact of EM on the circuit's reliability.

Visualizing the Electron Wind Force in the Elastic Regime

“…This system is somewhat like an elastic rod, supported above and below, in a gravitational field (Figure S7), but here the applied force scales like 1/A as a function of the rod's cross sectional area A; as the wire widens into the contacts, the (wind) force decreases with the current density J, whereas the nanowire's effective (1D) stiffness increases ∝ A. This spatial dependence P(x) ∝ xJ(x) for the plastic stress has been anticipated for decades, 5,9,26 and the elastic stress's profile would be expected to be similar. Assuming electrons are the charge carriers, fitting the observed P(x) to eq 2 gives a value Z* = −4 for the effective ionic charge.…”

“…Simultaneously, because of the increasing total length of interconnect, robustness to electromigration must increase simply to maintain the current levels of IC reliability. The resulting squeeze creates a technological horizon only a few years out, beyond which manufacturable solutions are not known. , …”

“…To minimize the electromigration constraints on circuit performance, IC designers consider all aspects of interconnect geometry and nanostructure, from the wire material to its routing, cladding, capping, curvature, and grain structure. , Importantly, they increasingly rely on the short-length (or Blech) effect, , namely that, at a given current density and temperature, electromigration is self-limiting in wires shorter than the threshold “Blech length”. This short-length effect arises because the atomic motion produced by electromigration leads to a back-stress gradient (i.e., an opposing stress migration) such that the net migration eventually comes to a halt .…”

“…The resulting squeeze creates a technological horizon only a few years out, beyond which manufacturable solutions are not known. 2,5 To minimize the electromigration constraints on circuit performance, IC designers consider all aspects of interconnect geometry and nanostructure, from the wire material to its routing, cladding, capping, curvature, and grain structure. 5,6 Importantly, they increasingly rely on the short-length (or Blech) effect, 7,8 namely that, at a given current density and temperature, electromigration is self-limiting in wires shorter than the threshold "Blech length".…”

Photocontrollable liquid-crystalline block copolymers: design, photo-directed self-assembly and applications

“…With the development of miniaturization and intelligence of modern electronic equipment, the manufacture of integrated circuits (ICs) has undergone rapid changes, 1–5 which has profoundly influenced scientific and technological progress. In addition, IC manufacturing technology has made great advances over the past few decades obeying the famous Moore's Law, 6–8 i.e.…”