The Study of Activation Energy of Electromigration at Different Temperature

In this paper, electromigration (EM) activation energy versus temperature in advanced damascene copper lines has been studied. EM experiments have been carried out on fully back-end processed samples under the condition of different temperatures and current densities. The metal line test structures used have the four-terminal Kelvin configuration and the lines length is 800µm with the minimum design rule width. The specific location of failure was observed by scanning electron microscope (SEM) and the failure mechanism was analyzed. The mechanical stress of the test structure was measured by Raman spectroscopy and the effect of mechanical stress on the reliability of metal electromigration was studied. It is found that the activation energy decreases slowly with the decrease of the test temperature. When the activation energy acquired under high temperature environment was extrapolated to operation condition by quadratic polynomial fitting, the activation energy under the environment temperature of 300°C is different from the value under the operation condition. Meanwhile, when predicting the EM lifetime, the results is that the EM lifetime under the operation condition decreased to 18% compared to that under the environment temperature of 300°C.