Shape Effect Study of Copper Redistribution Layer in Electromigration Tests under Humidity

The miniaturization of integrated circuits has intensified the requirements for reliable Copper RDLs capable of withstanding extreme environmental conditions. Although electromigration (EM)-induced degradation of Copper RDLs has been extensively documented under controlled electrothermal stresses, the synergistic effects of thermal-humidity-electrical coupling on failure mechanisms remain insufficiently explored. In this work, an accelerated EM test was conducted on four 135°-bent and three straight electroplated Copper RDLs under combined 95°C, 35% RH conditions with currents of 1.35A and 2.25A. In-situ resistance monitoring revealed lifetime distribution characteristics: under high current density, bent interconnects exhibited approximately 50% shorter lifetimes compared to straight counterparts. This disparity diminished significantly at lower current density, where both configurations demonstrated comparable lifetimes. Advanced characterization through SEM, EDS, and FIB revealed that geometric discontinuities in bent structures can amplify current crowding effects, resulting in localized Joule heating. The thermal-humid-electrical synergy accelerates void nucleation and facilitates stress-corrosion cracking along grain boundaries. Contrastingly, failure sites displayed stochastic spatial localization under low current, with EDS mapping confirming moisture-assisted oxide-induced interface delamination between the copper seed layer and Si wafer as the corresponding predominant failure. While the XRD result confirms the formation of various copper oxidation products during electromigration test.