Electromigration results have provided clear evidence of a short or “Blech” length effect in dual- damascene, Cu/oxide, multilinked interconnects. The test structure incorporates a repeated chain of Blech-type line elements and is amenable to failure analysis tools such as focused ion beam imaging. This large interconnect ensemble provides a statistical representation of electromigrationinduced damage in the regime where steady-state interconnect stress is manifest. Statistical analysis yields a critical length of 90 μm for interconnects with line width 0.5 μm at j=1.0×106 A/cm2 and T=325 °C.

For copper/low-dielectric constant ͑low-k͒ interconnects, delamination at the dielectric-barrier metal interface has been studied. In particular, the role of deposited etch polymers used for sidewall passivation on the integrity of this interface has been examined. We found that etch polymers were deposited on the flat ͑horizontal͒ surfaces used as low-k masks. Fluorinated polymeric etch residues of approximately 10-20 Å in thickness were detected using time-of-flight secondary ion mass spectroscopy and Auger electron spectroscopy. Although these etch residues resulted primarily from the etch sidewall passivation process, no detectable residue was found on the sidewalls themselves. The presence of the polymeric residue was found to compromise the integrity of the dielectric-barrier metal interface. Removal of the residue could be accomplished through either sputtering or by a concluding O 2 plasma flash step during etch. Using these techniques, significant improvement in dielectric-barrier metal interfacial integrity could be obtained.

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