The use of PH3 as the P source in the growth of amorphous ruthenium-phosphorus (Ru(P)) alloy films by dual-source chemical vapor deposition (CVD) with Ru-3(CO)(12) to produce thin (similar to 3 nm) Cu diffusion barriers is examined. Comparisons are made to films grown using P(CH3)(3). Carbon contamination of 10 at.% carbon or less was observed in PH3-produced Ru(P) films, compared to greater than 30 atomic % carbon in films using P(CH3)(3), and lower resistivity was also observed. PH3 was found to be much more reactive than previously-used P precursors, requiring the use of very low PH3 partial pressures (similar to 0.13 mPa) and a sequenced addition process that allowed accumulated P to diffuse into the Ru(P) film during growth. X-ray reflectivity and atomic force microscopy indicate that films of good continuity and smoothness can be grown by CVD in the 3 nm thickness range. X-ray diffraction shows the amorphous phase to be stable for annealing at 400 degrees C for 3 h. Electric field stress tests to failure for Cu/Ru(P)/SiO2/Si stacks indicate that low-carbon Ru(P) barrier films function at least as well as their higher-carbon counterparts as Cu barriers and better than Ta/TaN stacks of similar thickness grown for comparison purposes. (C) 2014 Elsevier B.V. All rights reserved.