It was recalled that in ultralow-k dielectric systems, the porous dielectrics were normally sealed using a SiC film before the deposition of a Ta diffusion barrier layer. However, the Ta barrier effects were negated when the SiC films were fabricated by plasma-enhanced chemical vapor deposition. Through large scale ab initio molecular dynamics simulations, the authors found that the barrier degradation was due to H atoms introduced during plasma-enhanced chemical vapor deposition. The H impurities diffused into and transformed an otherwise dense Ta layer into a loose amorphous phase which was ineffective as a diffusion barrier.

Large Scale ab initio Molecular Dynamics Simulations of Hydrogen-Induced Degradation of Ta Diffusion Barriers in Ultralow-K Dielectric Systems. Dai, L., Tan, V.B.C., Yang, S.W., Wu, P., Chen, X.T.: Applied Physics Letters, 2007, 90[3], 032906