Editing Electromigration (section)

== Practical implications of electromigration ==
[[File:In situ electromigration.gif|Top visualization of electromigration under scanning electron microscope of a nanoconstriction (60 nm width) on silicon oxide substrate.<ref>{{Cite journal|last1=Lombardo|first1=Joseph|last2=Baumans|first2=Xavier D. A.|last3=Željko|first3=Jelić L.|last4=Scheerder|first4=Jeroen E.|last5=Zharinov|first5=Vyacheslav S.|last6=Kramer|first6=Roman|last7=Van de Vondel|first7=Joris|last8=Silhanek|first8=Alejandro V.|date=2018-03-07|title=Healing effect of controlled anti-electromigration on conventional and high-Tc superconducting nanowires|hdl=2268/214980|journal=Small|language=en|volume=13|issue=26|pages=1700384|pmid=28544388|doi=10.1002/smll.201700384|url=http://orbi.ulg.ac.be/handle/2268/212130}}</ref>|thumb]]
[[File:leiterbahn ausfallort elektromigration.jpg|thumb|right|[[scanning electron microscope|SEM]] image of a failure caused by electromigration in a [[copper interconnect]]. The [[Passivation (chemistry)|passivation]] has been removed by [[reactive ion etching]] and [[hydrofluoric acid]]]]

Electromigration decreases the reliability of [[integrated circuits]] (ICs). It can cause the eventual loss of connections or failure of a circuit. Since reliability is critically important for [[Space exploration|space travel]], [[Armed force|military purposes]], [[anti-lock braking system]]s, medical equipment like [[Automated External Defibrillator]]s and is even important for personal computers or home entertainment systems, the reliability of chips [[integrated circuits|(ICs)]] is a major focus of research efforts.

Due to the difficulty of testing under real-world conditions, [[Black's equation]] is used to predict the life span of integrated circuits.
To use [[Black's equation]], the component is put through [[high temperature operating life]] (HTOL) testing. The component's expected life span under real conditions is [[Extrapolation|extrapolated]] from data gathered during this testing.<ref name="Black" />

Although damage from electromigration ultimately results in the failure of the affected IC, the first symptoms are intermittent glitches, which are quite challenging to diagnose. As some interconnects fail before others, the circuit exhibits seemingly random errors, which may be indistinguishable from other failure mechanisms (such as [[electrostatic discharge]] damage). In a laboratory setting, electromigration failure is readily imaged with an electron microscope, as interconnect erosion leaves telltale visual markers on the metal layers of the IC.

With increasing miniaturization, the probability of failure due to electromigration increases in [[Very-large-scale integration|VLSI]] and [[Ultra Large Scale Integration|ULSI]] circuits because both the power density and the current density increase.<ref name="EM_book">{{Cite book|author=J. Lienig, M. Thiele|title=Fundamentals of Electromigration-Aware Integrated Circuit Design|url=https://link.springer.com/book/10.1007/978-3-319-73558-0|pages=1–12|chapter=Introduction|chapter-url=https://link.springer.com/chapter/10.1007/978-3-319-73558-0_1|publisher=Springer|date=2018|isbn=978-3-319-73557-3|doi=10.1007/978-3-319-73558-0}}</ref> Specifically, line widths will continue to decrease over time, as will wire cross-sectional areas. Currents are also reduced due to lower supply voltages and shrinking gate capacitances.<ref name="EM_book" /> However, as current reduction is constrained by increasing frequencies, the more marked decrease in cross-sectional areas (compared to current reduction) will give rise to increased current densities  in ICs going forward.<ref name="Lienig2" >J. Lienig, M. Thiele: "The Pressing Need for Electromigration-Aware Physical Design  " [https://www.ifte.de/mitarbeiter/lienig/ispd_2018_pp144_151.pdf (Download paper)], ''Proc. of the Int. Symposium on Physical Design (ISPD) 2018'', pp. 144–151, March 2018</ref>

In advanced [[semiconductor manufacturing]] processes, [[Copper interconnects|copper]] has replaced [[Aluminum interconnects|aluminium]] as the [[Interconnects (integrated circuit)|interconnect]] material of choice. Despite its greater fragility in the fabrication process, copper is preferred for its superior conductivity. It is also intrinsically less susceptible to electromigration. However, electromigration (EM) continues to be an ever-present challenge to device fabrication, and therefore the EM research for copper interconnects is ongoing (though a relatively new field).<ref name="Lienig2" />

In modern consumer electronic devices, ICs rarely fail due to electromigration effects.  This is because proper semiconductor design practices incorporate the effects of electromigration into the IC's layout.<ref name="Lienig2" />  Nearly all IC design houses use automated [[Electronic design automation|EDA]] tools to check and correct electromigration problems at the transistor layout-level.  When operated within the manufacturer's specified temperature and voltage range, a properly designed IC device is more likely to fail from other (environmental) causes, such as cumulative damage from [[gamma ray|gamma-ray]] bombardment.

Nevertheless, there have been documented cases of product failures due to electromigration.  In the late 1980s, one line of [[Western Digital]]'s desktop drives suffered widespread, predictable failure after 12–18 months of field usage.  Using forensic analysis of the returned bad units, engineers identified improper design-rules in a third-party supplier's IC controller.  By replacing the bad component with that of a different supplier, WD was able to correct the flaw, but not before significant damage was done to the company's reputation.

Electromigration can be a cause of degradation in some [[power semiconductor device]]s such as low voltage [[power MOSFET]]s, in which the lateral current through the source contact metallisation (often aluminium) can reach the critical current densities during overload conditions.  The degradation of the aluminium layer causes an increase in on-state resistance, and can eventually lead to complete failure.