Analysis of Electromigmtion-Induced Failures in Multilavered Interconnects

Electromigration-induced failure in multilayered interconnects with overlayered TiN has been studied in con- junction with the overlayered-TiN/Al heterointerface evalua- tion. The electrical contact resistance between AI and TIN changes with its fabrication processes. The contact between AI and underlayered TiN shows almost the same resistance as AI/AI direct contact. On the other hand, the contact between overlayered TIN and AI shows higher resistance compared with that of AI/AI direct contact, and its value varies with the de- position processes. That is, overlayered-TiN/Al structure suc- cessively deposited without breaking vacuum shows one order of magnitude higher contact resistance, while overlayered- TiN/AI structure deposited after the AI was exposed to air shows two orders of magnitude higher contact resistance com- pared with AI/AI direct contact. These contact resistances have a strong influence on layered metal line lifetime in terms of cur- rent bypass effect. The high contact resistance between over- layered TIN and AI suppresses the current bypass flow even when it is one order of magnitude higher compared with that of AI/AI direct contact. The simple multilayered structure of overlayered TiN/Ti/AI that has low resistance between TiN and AI, if the AI and Ti were deposited successively without breaking vacuum, has been found to be a metal line of high reliability for submicrometer-level interconnects.