A study of plasma treatments limiting metal barrier diffusion into porous low-k materials

In this paper, different plasma sequences (NH3 followed by CH4/Ar and conversely) are compared to these chemistries alone in terms of limitation of metal precursor diffusion. Based on RBS analyses, it is shown that plasma sequences have a similar behavior than the CH4 and NH3 plasma alone. Complementary XPS analyses demonstrate a major difference between the two sequences: a carbon-rich layer (99%) is formed during the NH3+CH4/Ar sequence while we detect a SiON layer (with small amount of carbon 2%) after the CH4/Ar+NH3 sequence. A mixed CH4/Ar/N-2 chemistry is also investigated. This mixed chemistry is close to the CH4/Ar one but less efficient in terms of metal precursor diffusion than the sequences. Thus, it seems that using plasma sequences or the mixed chemistry does not lead to less metal diffusion compared to single chemistries and especially the ammonia-based. But FTIR measurements tend to indicate a lower film modification before metallization for the CH4/Ar+NH3 sequence compared to the other sequence and the single NH3 plasma. Therefore, this sequence leads to a better trade-off between metal precursor diffusion and dielectric modification.