The diffusion barrier properties of PVD Ru and PECVD / PEALD Ru-C films, deposited by RuEtcp₂ precursor and N₂/H₂ plasma, were compared on the basis of bias temperature stress measurements. An MIS test structure was used to distinguish between thermal diffusion induced by annealing and a Cu field drift due to applied electric fields. BTS-CV, TZDB and TDDB measurements revealed that the barrier performance is significantly better for PEALD and PECVD Ru-C films. This improvement is associated with carbon impurities in the Ru films with a concentration in the order of several percent according to ToF-SIMS and ERDA. The TDDB mean time to failure at 250 °C, +5 MV/cm was 7 s for PVD Ru samples, ≈500 s for PECVD Ru-C, ≈800 s for PEALD Ru-C and >3600 s for PVD TaN. Triangular voltage sweep measurements at 300 °C, 0.1 V/s confirmed the presence of Cu ions inside the SiO₂ for degraded dots, in contrast to the Al reference sample and to PVD TaN, which performed best among all the Cu barriers under test. XRD data suggests that PEALD and PECVD Ru-C films are only weakly crystalline.