Electromigration and IC Interconnects

Abstract

A modern integrated circuit (IC) is composed of 10⁶ or more electronic devices. They are connected to form a circuit through the use of metallic films patterned into strips which function as wires to interconnect devices. These wires are usually simply referred to as interconnects. In an IC occupying the surface of a 1 cm² Si chip, there can be 10 m of total interconnect length. This length is in the form of more than 10⁶ line segments contacting pairs of devices and different segments of the circuit. This enormous number of wires is made possible by their small widths. Interconnect widths as small as 0.55 μm are currently used in commercial circuits, and circuits and processes leading to smaller and smaller widths are continuously in development.During operation of an IC, interconnects carry current densities as high as 4 × 10⁵ A/cm². This should be compared with a current density of 10² A/cm², the maximum allowed for house wiring. Thin-film conductors can carry these high current densities only because of the relatively good heat sinking provided by the Si substrate.