Using finite element analysis, we calculate the temperature range and the resulting cyclic Von Mises strain resulting from Joule heating, generated by the application of alternating current, applied to specimens representative of commercial copper damascene interconnect structures. Constraining the top surface of the lines with dielectric increased the cyclic temperature range required to produce a given strain range, relative to uncovered lines. Much narrower lines required much higher temperatures to reach this same range of strain. Scanning electron microscope images of the lines after testing showed that the uncovered lines exhibited significant topographic features that have been associated in previous reports with mechanical fatigue. None of the covered lines, including those cycled at ranges of total strain similar to uncovered lines, exhibited these features. We interpret these observations to indicate that the total strain approach to the prediction of fatigue deformation is not sufficient to describe the behavior of these micro- and nanoscale structures. Present and previously reported observations suggest that crystallography, dislocation behavior, and void formation should be considered in modeling the behavior of small-scale constrained structures subjected to thermal cycling.
Citation: Journal of Strain Analysis for Engineering Design
Pub Type: Journals
Fatigue, strain, stress, temperature