Effects of microstructural control on the failure kinetics and the reliability improvement of Al and Al-alloy interconnects
- Univ. of California, Berkeley, CA (United States)
The reliability of microelectronic systems is often limited by electromigration failure in Al-based thin-film conducting lines which interconnect devices to form an integrated circuit. Under an applied electric field Al atoms migrate with the electron flow, causing a counterflow of vacancies that accumulate into voids, eventually leading to an open circuit failure. The work reported here is concerned with clarifying the microstructural mechanism of electromigration failure, and with developing a metallurgical method to improve the electromigration resistance of Al-based interconnects. Pure Al, Al-2Cu, and Al-2Cu-1Si lines with quasi-bamboo microstructures are explored as a function of heat treatment conditions and current density. The "weakest" microstructural unit that causes failure is identified by electron microscopy; with rare exceptions, failure occurs at the upstream end of the longest polygranular segment in a given line. This microstructural characteristic of electromigration failure is even observed in lines whose maximum segment lengths are less than a few microns. The time to failure appears to increase exponentially with decreasing longest polygranular segment length. A simple constitutive equation is reported to describe the failure kinetics as a function of the polygranular segment length that leads to failure. Given correct values of the kinetic constants included in the equation, this microstructure-based constitutive relation will provide a way to assess interconnect reliability. An effective metallurgical method that can eliminate relatively long polygranular segments is post-pattern annealing. This heat treatment particularly narrows the distribution of the longest polygranular segment lengths over a large set of lines. As a consequence, the time-to-failure distribution narrows as well, so that the time to first failure increases more substantially than the median time to failure.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 469118
- Report Number(s):
- LBNL-39719; ON: DE97005934; TRN: 97:003009
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: Dec 1996
- Country of Publication:
- United States
- Language:
- English
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