Differences in reliability effects for thick copper and thick aluminium metallizations

The use of a thick Copper layer on top of an AlCu-metallization stack instead of a common thick Aluminium layer triggers the need for a change in the reliability characterization, the test structure layouts and reliability test methods. The failure and degradation mechanisms of thick Copper and Aluminium are partly different for the material as well as for thick and thin metal layers. Electromigration and stressmigration are the main effects in thin metal layers. For thick metal layers the high thermal expansion leads to a change in the mechanical stress resulting in a different degradation behaviour and defect mechanisms. The paper describes the differences for reliability test structure layouts, test methods and reliability assessment strategies for thin and thick interconnect layer and thick Copper and Aluminium. Especially the requirements for a reliability test and assessment strategy for non-passivated Copper will be explained.