| This thesis describes an investigation into the electromigration behavior of copper interconnects fabricated using chemical mechanical polishing, (CMP). It focuses on the identification and characterization of copper electromigration damage mechanisms. The goal of this thesis is to provide a fundamental understanding of the processes through which the damage mechanisms operate.; The electromigration test structures were single copper lines and twenty copper line arrays, both on a tantalum adhesion layer. The tantalum layer also served as a polish stop for the CMP process used in patterning the wafers. The test structures were fabricated by a Damascene inlaid process where the tantalum and copper were deposited into 6000 A deep trenches etched into 12,000 A of SiO{dollar}sb2{dollar}. Chips were diced and mounted on standard packages for electromigration stress testing under argon.; The electromigration test was conducted under constant voltage providing control of the current density along with the test temperature and atmosphere. The resulting specimen current versus time data was analyzed to determine mean time to failure and mean test temperature. The results were used to calculate the electromigration failure activation energy and the current density exponent used to project mean time to failure.; A model was developed to determine the amount of Joule heating that occurs with this type of high current test. The electromigration specimens were examined by optical microscopy, SEM, EDS, AFM, XPS, XRD, and RBS to characterize damage caused by the electromigration testing. Damage structures thus identified were correlated with the electromigration stress test results to determine mechanisms and conditions for the structure's nucleation and growth.; Copper metallization, with Ta as the adhesion layer, was found to be more resistive to electromigration failure than aluminum. Many damage mechanisms were found but were deemed controllable to an extent that would result in longer lifetimes under electromigration conditions. Further studies, both theoretical and experimental, are suggested to follow on. They would develop the relationship between observed failure modes and the causes that lead to such failures. They would also isolate the contribution of each failure mode to the total failure. |
