Comparison of PVD, PECVD & PEALD Ru(-C) films as Cu diffusion barriers by means of bias temperature stress measurements

The diffusion barrier properties of PVD Ru and PECVD / PEALD Ru-C films, deposited by RuEtcp(2) precursor and N-2/H-2 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 degrees C, +5 MV/cm was 7 s for PVD Ru samples, approximate to 500 s for PECVD Ru-C, approximate to 800 s for PEALD Ru-C and > 3600 s for PVD TaN. Triangular voltage sweep measurements at 300 degrees 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. (C) 2010 Elsevier B.V. All rights reserved.