Physical phenomena underlying failure due to electromigration and stress-induced voiding in fine AI and AI-alloy thin-film conducting lines are examined in the context of accelerated testing methods and structures. Aspects examined include effects due to line isolation (the absence of reservoirs at conductor ends), solute and precipitate phenomena, conductor critical (Blech) length, microstructure, film deposition conditions, and thermal processing subsequent to film deposition. Emphasis is on the isolated, submicron-wide, AI(Cu)-based thin-film interconnection lines of IBM VLSI logic and memory chips. "Copyright 1995 by International Business Machines Corporation. Copying in printed form for private use is permitted without payment of royalty provided that (1) each reproduction is done without alteration and (2) the Journal reference and IBM copyright notice are included on the first page. The title and abstract, but no other portions, of this paper may be copied or distributed royalty free without further permission by computer-based and other information-service systems. Permission to republish any other portion of this paper must be obtained from the Editor.

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Electromigrationinduced failure in passivated aluminumbased metallizations−The dependence on temperature and current density Mechanisms of thermal stress relaxation and stressinduced voiding in narrow aluminumbased metallizations Evaporated metallizations composed of aluminum alloys and titanium underlayers were patterned, passivated with plasma enhanced chemical vapor deposited SiN, and aged for 1000 h at 150°C in order to observe stress-induced void formation. Metal films were analyzed using scanning electron microscopy, transmission electron microscopy, and secondary ion mass spectrometry. The addition of copper to aluminum results in fewer voids than in comparable noncopper metallizations. For AI-Cu films, fewer voids were observed in 1.5 pm lines compared to 5 pm lines, apparently due to the presence of greater stress gradients in the wide line case. Silicon appears to promote void formation by rapid grain boundary diffusion to precipitates. Oxygen incorporation in aluminum produces small grained films, thereby generating many void nucleation sites. High oxygen concentrations produce films with a few long, channel-like voids and many small voids. Titanium underlayers decrease the percent of metal volume voided for Al and AlSi films, while for AICu films, the percentage void area and the average void size are increased. Volume reduction associated with interfacial TiAll formation may be responsible for the increase in void size associated with titanium underlayers.

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