The copper diffusion barrier properties of amorphous boron carbo-nitride (BCxNy) films were studied. The BCxNy films were deposited by chemical vapor deposition at 360 °C and 1 Torr using dimethylamine borane with no reaction gas (BC0.37N0.15), with NH3(BC0.19N0.44), or with C2H4(BC0.90N0.08); their dielectric constants were 4.1, 4.4, and 3.9, respectively. A SiC0.76N0.44 film was used to benchmark the study. Barrier films were deposited on 7 nm thermal oxide/n-type Si substrates. The leakage current for BC0.90N0.08, 1.1×10-8 A/cm2 at 0.5 MV/cm, is the lowest of the three but it is larger than that of the benchmark SiC0.76N0.44 film, 5.5×10-9 A/cm2. Time dependent dielectric breakdown is used to test barrier time-to-failure of Cu-gate capacitors at 150 °C and +2 to 5 MV/cm. BC0.90N0.80 displayed barrier performance comparable to SiC0.76N0.44 and was noticeably better than BC0.37N0.15 and BC0.19N0.44. Overall, BCxNy barriers are promising and are improved with lower boron content, fewer B–B bonds, and increased B–C bonds.