Electromigration testing using modulated reflectance imaging

A new nondestructive technique, the modulated reflectance or thermal wave imaging, was used to observe the formation of defects at the surface and under the surface of metal lines, after successive steps of conventional accelerated electromigration (EM) stress. The change in film morphology and the growth of subsurface defects was correlated with the EM stress data and with the ultimate time to failure of the lines. As the wafer was heated during the EM TEST a set of lines that were not electrically stressed were also imaged at each step, in order to separate the electrical and thermal stress components. Detection and analysis of the defect growth, at early stages in the stress process, using the modulated reflectance method, could be used towards the prediction of metalization lifetime and reliability, reducing considerably the duration of stress tests