Via Electromigration Characteristics in Aluminum Based Multilevel Interconnection

Takahisa YAMAHA  Masaru NAITO  Tadahiko HOTTA  

Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E77-A   No.1   pp.187-194
Publication Date: 1994/01/25
Online ISSN: 
DOI: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Reliability)
Category: Failure Physics and Failure Analysis
Keyword: 
reliability,  electromigration,  metallization,  via contact,  multilevel interconnection,  laminated interconnections,  aluminum,  

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Summary: 
Via electromigration (EM) performance of aluminum based metallization (AL) systems has been investigated for vias chains of 1500-4000 vias of 1.0 micron diameter. The results show that via EM lifetime can not be enhanced by a simple increase of M2 step coverage in AL/AL vias because the EM induced voids are formed at AL/AL via interface where electrons flow from Ml to M2 even in the case of very poor M2 step coverage. The voids are induced by the boundary layer in AL/AL vias, where a temperature gradient causes discontinuity of aluminum atoms flux. The failure location is not moved though via EM lifetime can be improved by controlling stress in passivation, sputter etch removal thickness and grain size of the first metal. Next, the effect of the boundary layer are eliminated by depositing titanium under the second aluminum or depositing WSi on the first aluminum. In the both cases, via EM lifetime are improved and the failure locations are changed. Especially WSi layer suppresses the voids formation rather than titanium. Models for the failure mechanism in each metallization system are further discussed.