Film Conformality and Extracted Recombination Probabilities of O Atoms during Plasma-Assisted Atomic Layer Deposition of SiO₂, TiO₂, Al₂O₃, and HfO₂

Surface recombination of plasma radicals is generally considered to limit film conformality during plasma-assisted atomic layer deposition (ALD). Here, we experimentally studied film penetration into high-aspect-ratio structures and demonstrated that it can give direct information on the recombination probability r of plasma radicals on the growth surface. This is shown for recombination of oxygen (O) atoms on SiO₂, TiO₂, Al₂O₃, and HfO₂ where a strong material dependence has been observed. Using extended plasma exposures, films of SiO₂ and TiO₂ penetrated extremely deep up to an aspect ratio (AR) of â900, and similar surface recombination probabilities of r = (6 ± 2) × 10^-5 and (7 ± 4) × 10^-5 were determined for these processes. Growth of Al₂O₃ and HfO₂ was conformal up to depths corresponding to ARs of â80 and â40, with r estimated at (1-10) × 10^-3 and (0.1-10) × 10^-2, respectively. Such quantitative insight into surface recombination, as provided by our method, is essential for modeling radical-surface interaction and understanding for which materials and conditions conformal film growth is feasible by plasma-assisted ALD.