XPS studies of the ALD-growth of TaN diffusion barriers: Impact of the dielectric surface chemistry on the growth mechanism
The introduction of SiOCH low-k dielectrics in the copper interconnections of sub-45nm node technologies is a challenge in terms of both material and process criteria. For instance, the deposition of a diffusion barrier between copper and dielectric is strongly dependent on the nature of the dielectric surface. In this study, we investigate the first steps of ALD TaN growth with respect to dielectric surface chemistry, using XPS measurements. Three different dielectrics have been tested: SiOCH, SiO2 or SiOCH capped by a thin SiO2 layer. We show that TaN can only grow over a monolayer-thick Ta2O5 formed at the early stages of deposition. A mechanism for the growth first steps is described, explaining the incubation delays observed for the appearing of TaO and TaN bonds. In addition, we show that a 3nm-thick SiO2 layer is able to hide the effect of SiOCH chemistry and obtain similar growth rates on SiOCH and SiO2.
low-k sioch dielectric tan ald deposition xps analysis