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Electromigration tests at temperatures between 340 and 400 °C and current densities between 1.0 and 3.0 MA/cm2 have been performed to determine the temperature dependence of the critical length effect in 0.5-μm-wide Cu/oxide dual-damascene interconnects with 0.1 μm silicon nitride (SiNx) passivation. A focused-ion-beam-induced contrast imaging technique is used to locate failure sites of critical length test structures. Statistical analysis [E. T. Ogawa et al., Appl. Phys. Lett. 78, 18 (2001)] yields a threshold-length product (jL)c, of 3700 A/cm, and a temperature dependence is not observed within the temperature range 340–400 °C.

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.

Electromigration (EM) reliability was investigated for Cu/porous low k interconnects. The porous low k dielectric was a methylsilsesquioxane (MSQ) based spin-on organosilicate material with k of 2.2. The activation energy for EM failure was found to be about 0.9 eV for Cu/porous MSQ between 208 and 367 °C, which is commonly associated with mass transport at the Cu/SiNx cap-layer interface. The threshold product of current density and line length (jL)c for Cu/porous MSQ was found to be 2500–3000 A/cm. The reduction in EM lifetime compared with Cu/oxide interconnect can be attributed to smaller back stress, due to less thermomechanical confinement of Cu/low k interconnects. Most interconnects failed by voiding at the cathode. Some lateral Cu extrusion followed by interfacial breakdown was also observed near the anode.

The shrinking line-to-line spacing in interconnect systems for advanced integrated circuit technology and the use of lower dielectric constant materials create the need for tools to evaluate the interconnect dielectric reliability. A multi-temperature, dual-ramp-rate voltage-ramp-to-breakdown methodology is presented and used here to extract important dielectric-breakdown parameters accurately for minimum-spaced metal lines. It is demonstrated that correction for the true minimum line-to-line spacing distributions become critically important and that the minimum spacing can be extracted electrically and compares favorably to electron microscopy cross sections. The spacing-corrected breakdown field distributions, at various temperatures, for the organosilicate material tested, indicated a very low apparent zero-field activation energy ͑0.14± 0.02 eV͒ and an apparent field-acceleration parameter ␥ = 4.1± 0.3 cm/ MV that has little or no temperature dependence. Constant-voltage time-dependent-dielectric-breakdown measurements were found to agree well with these observations.

An electromigration study has determined the lifetime characteristics and failure mode of dual-damascene Cu/oxide interconnects at temperatures ranging between 200 and 325 °C at a current density of 1.0 MA/cm2. A novel test structure design is used which incorporates a repeated chain of “Blech-type” line elements. The large interconnect ensemble permits a statistical approach to addressing interconnect reliability issues using typical failure analysis tools such as focused ion beam imaging. The larger sample size of the test structure thus enables efficient identification of “early failure” or extrinsic modes of interconnect failure associated with process development. The analysis so far indicates that two major damage modes are observable: (1) via-voiding and (2) voiding within the damascene trench.