Characterization of Ultra-Thin Hafnium Oxide Films Grown on Silicon by Atomic Layer Deposition Using Tetrakis(ethylmethyl-amino) Hafnium and Water Precursors

Abstract

The role and effectiveness of chemical pre-functionalization of silicon surfaces (with hydrogen, chlorine, and nitride) to minimize interfacial SiO2 formation during atomic layer deposition growth has been investigated using in situ transmission infrared spectroscopy, ex situ Rutherford backscattering spectroscopy, and ex situ medium energy ion scattering spectroscopy. No measurable SiO2 was formed during growth at low temperatures (∼100 °C) with tetrakis(ethylmethylamino) hafnium and heavy water as precursors on H-, Cl-, and nitride-passivated silicon surfaces. Interfacial SiO2 appeared after postdeposition annealing, at the point when the initially amorphous HfO2 film crystallized, as reflected by the appearance of a monoclinic HfO2 phonon peak at ∼780 cm-1 and by a periodic arrangement of atoms observed in high-resolution transmission electron microscopic images. Electrical characterization of as-deposited HfO2 films showed that, while the interfacial defect density was reasonably low at growth temperatures when interfacial hydrogen was still present (∼100 °C), the leakage current was significantly increased after postdeposition annealing (∼700 °C in nitrogen).