Editing Electromigration (section)

=== Wire material ===
Historically, aluminium has been used as conductor in integrated circuits, due to its good adherence to substrate, good conductivity, and ability to form [[ohmic contact]]s with silicon.<ref name="EM_book" /> However, pure aluminium is susceptible to electromigration. Research shows that adding 2-4% of copper to aluminium increases resistance to electromigration about 50 times. The effect is attributed to the grain boundary segregation of copper, which greatly inhibits the diffusion of aluminium atoms across grain boundaries.<ref name="contact_book">{{Cite book|author=M. Braunovic, N. K. Myshkin, V. V. Konchits|title=Electrical Contacts: Fundamentals, Applications and Technology|url=https://www.crcpress.com/Electrical-Contacts-Fundamentals-Applications-and-Technology/Braunovic-Myshkin-Konchits/p/book/9781574447279|publisher=CRC Press|date=2006|isbn=978-1-5744-47279}}</ref>

Pure copper wires can withstand approximately five times more current density than aluminum wires while maintaining similar reliability requirements.<ref name="Lienig" >J. Lienig: "Introduction to Electromigration-Aware Physical Design" [http://www.ifte.de/mitarbeiter/lienig/ispd06_emPaper_lienig.pdf (Download paper)], ''Proc. of the Int. Symposium on Physical Design (ISPD) 2006'', pp. 39–46, April 2006.</ref> This is mainly due to the higher electromigration activation energy levels of copper, caused by its superior electrical and thermal conductivity as well as its higher melting point. Further improvements can be achieved by alloying copper with about 1% [[palladium]] which inhibits diffusion of copper atoms along grain boundaries in the same way as the addition of copper to aluminium interconnect.