Molybdenum Capping Layer Effect on Electromigration Failure of Plasma Etched Copper Lines

Abstract

The electromigration failure phenomena of plasma etched copper lines with and without the molybdenum capping layer have been studied. Surface color change was observed during the constant current stress of the copper line. For the uncapped line, the color change is due to the copper surface oxidation from the Joule heating effect. For the capped line, it is probably due to the surface oxidation and copper diffusion to the capping layer. For the wide line, the color change near the broken point was obvious due to the local heating effect. The time dependent temperature change of the line was estimated from the resistance-to-time curve assuming that the heat dissipation to the glass substrate was negligible. The pattern of the surface color during the electromigration of the uncapped or capped copper line is a useful reference for the prediction of the line failure spot and time.