Electrical characteristics of self-aligned cobalt-tungsten-phosphide (CoWP) as a copper (Cu) drift barrier for advanced Cu interconnects were investigated using blanket Al/SiO2/CoWP/Cu metal-insulator-metal (MIM) structures. The time-dependent dielectric breakdown measurements of the MIM structure under the bias-temperature stress tests demonstrated that the median time-to-failure (MTF) of chemical-vapor-deposited SiO2 improves by more than 20 times by forming a 10 nm thick CoWP. The improved MTF is comparable to that measured with the reversed-bias stress in which no Cu-ion drift occurs. It is concluded that Cu-ion drift is suppressed by a 10 nm thick CoWP barrier. (c) 2007 The Electrochemical Society.