The performances of a novel Ru/WHfN barrier against Cu diffusion are compared with those of Ru and Ru/WN barriers by sheet resistance, X-ray diffraction, elemental depth profiles, and leakage-current measurement of metal-oxide-silicon capacitors. For the Cu/barrier/Si samples, both Ru(10nm) and Ru(5nm) /WN(5nm) barriers fail after annealing at 500 and 750 degrees C, respectively. However, the Ru(5 nm)/WHfN(5nm) barrier can still maintain the perfect ability to prevent Cu penetration at the failure temperature of the Ru(5nm)/WN(5 nm) barrier. This could be attributed to the fact that the incorporation of Hf into WN greatly enhances the crystallization temperature of WHfN, whose amorphous texture can be maintained after 800 degrees C annealing. In contrast, the WN film begins to crystallize after 700 degrees C annealing, and many of the generated grain boundaries facilitate Cu diffusion through the barrier. (c) 2010 The Electrochemical Society. [DOI: 10.1149/1.3518522] All rights reserved.