Layer Thickness Effect on Lifetime of Copper Oxide Passivated Plasma Etched Copper Line

Abstract

Previously, authors reported that copper oxide could be a good passivation material for the copper line because it prevented copper diffusion to adjacent layer at the high temperature. In this paper, the copper oxide thickness effect on the electromigration failure mechanism is studied. The copper oxide passivation layer was formed by exposing the copper line to the oxygen plasma in a parallel-plate plasma etcher. The copper oxide passivation layer has a smooth surface and a crystalline structure. The copper line with a very thin copper oxide passivation layer has an electromigration lifetime similar to that of the unpassivated copper line. However, the lifetime deteriorates with the increase of the copper oxide thickness due to the enlargement of the mechanical and thermal stress mismatches between the bulk copper film and the passivation layer. Therefore, the thickness of the copper oxide is critical to the effectiveness of its passivation function.