Effects of side reservoirs on the electromigration lifetime of copper interconnects

A new side reservoir test structure is shown to have improved electromigration reliability over conventional end-of-line reservoir structures. This is believed to be due to the ability of the side reservoir to “trap” migrating pre-existing voids before they reach the cathode end. The ability of the side reservoir to `trap´ pre-existing voids is believed to be associated with local differences in back-stresses and with the differing adhesion strength of Cu atoms with the Ta/Cu and SiN-SiCN/Cu interfaces.