A reliability study of barrier-metal-clad copper interconnects with self-aligned metallic caps

An advanced interconnection technology was studied by evaluating the performance of copper (Cu) interconnections capped with a barrier metal. Good selectivity of self-aligned tungsten (W) caps grown by chemical vapor deposition was obtained, and the isolation resistance and leakage current between adjacent Cu interconnects capped with W were similar to those between conventional Cu interconnects. There were also no significant wiring resistance or via resistance differences of between W-capped Cu interconnects and conventional Cu interconnects. When two-level Cu interconnects were fabricated to check the effects of the undulation of the interlayer dielectric deposited on W-capped Metal-1 lines, good isolation of fine-pitch Metal-2 lines was obtained. The reliability of metal-capped structures was evaluated by measuring time-dependent dielectric breakdown (TDDB), electromigration, and stressmigration. The TDDB lifetime of adjacent W-capped Cu interconnects 0.15 μm apart was found to be at least as long as that of conventional Cu interconnects with the same spacing, and the electromigration lifetime of W-capped Cu interconnects was found to be superior to that of conventional Cu interconnects. Furthermore, self-aligned caps of W or cobalt tungsten boron were found to suppress the stress-induced voiding of Cu interconnects.