Effects of metal stacks and patterned metal profiles on the electromigration characteristics in super-thin AlCu interconnects for sub-0.13 μm technology

The electromigration (EM) characteristics of super-thin aluminum-copper alloy (AlCu) interconnects for sub-0.13 μm complementary metal-oxide-semiconductor logic technology were investigated by varying the AlCu underlayers and etched sidewall profile of AlCu wire. Super-thin AlCu wire with a Ti/TiN underlayer and a smooth etched sidewall profile was confirmed to have the best EM resistance in terms of the mean-time-to-failure (MTTF) and the failure distribution. The Ti/TiN underlayer is believed to lead to a longer MTTF by dramatically reducing the effective current density at the super-thin AlCu film in the entire of EM test line with a smaller formation of TiAl3 at the TiN/AlCu interface. The smooth etched sidewall profile is considered to induce a steeper EM failure distribution by removing the early EM failure at the rough sidewall of aluminum. In terms of the location of EM-induced voids, the super-thin AlCu film inhibits the formation of EM-induced voids directly under the tungsten via by insignificant current crowding at the via–metal line corner.