Fundamental study of atomic layer deposition in and on porous low-k films

Atomic layer deposition is a promising technique to deposit conformal, nm-thin metal barriers in high aspect ratio trenches. However, exactly because of its excellent conformality, the deposition can also occur inside the nanopores of the most advanced low-k materials. In this work, the mechanisms of atomic layer deposition on and in low-k, porous dielectric films were studied, using HfO₂ as a test material. Exhaustive analyses showed firstly that the HfCl₄ precursor penetrated uniformly in the pores throughout a 44 nm low-k film. Secondly it is shown that the pores were sealed as function of precursor size, i.e. there are conditions where the pores became inaccessible for HfCl₄, while the - smaller - H₂O molecules could still penetrate the pores. From these analyses a deposition model was proposed.