Influence of co-reactants on surface passivation by nanoscale hafnium oxide layers grown by atomic layer deposition on silicon

Abstract

Hafnium oxide thin films have attracted considerable interest for passivation layers, protective barriers, and anti-reflection coatings. Atomic layer deposition offers a route to produce conformal films at the nanometre scale, but there is a lack of clarity over how the growth conditions affect the film properties. Here we present a study into the role of different atomic layer deposition co-reactants (O₂ plasma, O₃ and H₂O) in the growth of HfO_x on n-type silicon from a tetrakis(dimethylamido)hafnium (TDMAH) precursor followed by post-deposition annealing (up to 500 °C). Through X-ray diffraction and X-ray photoelectron spectroscopy, we demonstrate variations in film composition, stoichiometry and crystallinity with co-reactant. Depth profiling conducted with X-ray photoelectron spectroscopy reveals differences in composition between the HfO_x surface and the HfO_x/Si interface. We also determine differences in fixed charge density and chemical passivation through photoconductance decay measurements and Kelvin probe analysis. We find surface recombination velocities (SRVs) <10 cm s⁻¹ are possible for HfO_x films, with the best passivation achieved for H₂O-based HfO_x (SRVs as low as ∼5 cm s⁻¹). With TDMAH as a hafnium precursor, we show that neither co-reactant choice nor annealing environment influence the resulting charge polarity.