Electromigration Reliability of Passivated Gold Interconnects for GaAs Devices

The electromigration lifetimes of a very large quantity of passivated electroplated Au interconnects were measured utilizing high resolution in-situ resistance monitoring equipment. Application of moderate accelerated stress conditions with current density limited to 2 MA/cm(2) and oven temperatures in the range of 300 degrees C to 375 degrees C avoided large Joule-heated temperature gradients and electrical overstress failures. A maximum Joule-heated Au film temperature of 12 degrees C was determined from measured temperature coefficients of resistance (TCRs). All Au interconnect lifetime distributions followed log-normal statistics. An activation energy of 0.80 +/- 0.05 eV was measured from constant-current electromigration tests at multiple temperatures. A current density exponent of 1.91 +/- 0.03 was extracted from multiple current densities at a single constant temperature. These electromigration model parameters correlate with the observed Au interconnect failure mechanism.