Tribo-electrochemical characterization of copper with patterned geometry

Abstract

Non-uniformity of chemical mechanical polishing (CMP) induced by diverse pattern geometry in copper damascene structures has to be solved to increase the process yield. In the current research, we investigated the mechanisms of a step height reduction of copper during CMP. The tribological approach combined with an electrochemical study was applied. The surface modification controlled by potential altered the tribological behavior in terms of a friction coefficient and a surface morphology. Anodic CMP resulted in more step height reduction than cathodic CMP. The contact pressure increased exponentially with the decrease of pattern width and thus the more step height reduction was obtained for the smaller pattern. The rate of step height reduction varied with the contact pressure even among the patterns with same pattern densities. The mechanical factor such as the contact pressure and the pattern density was not the only factor but the metal-ion-concentration-cell established between each different pattern could also be the factor for the step height reduction. Analysis was based on the electrochemical behavior among the patterns and the Hertzian contact theory. Based on these results, we proposed two combinatorial mechanisms of the step height reduction for the better understanding and optimization of the CMP process.