Microstructures of HfO_x Films Prepared via Atomic Layer Deposition Using La(NO₃)₃·6H₂O Oxidants

Hafnium oxide (HfO_x) films have a wide range of applications in solid-state devices, including metal-oxide-semiconductor field-effect transistors (MOSFETs). The growth of HfO_x films from the metal precursor tetrakis(ethylmethylamino) hafnium with La(NO₃)₃·6H₂O solution (LNS) as an oxidant was investigated. The atomic layer deposition (ALD) conditions were optimized, and the chemical state, surface morphology, and microstructure of the prepared films were characterized. Furthermore, to better understand the effects of LNS on the deposition process, HfO_x films deposited using a conventional oxidant (H₂O) were also prepared. The ALD process using LNS was observed to be self-limiting, with an ALD temperature window of 200-350 °C and a growth rate of 1.6 Å per cycle, two times faster than that with H₂O. HfO_x films deposited using the LNS oxidant had smaller crystallites than those deposited using H₂O, as well as more suboxides or defects because of the higher number of grain boundaries. In addition, there was a difference in the preferred orientations of the HfO_x films deposited using LNS and H₂O, and consequently, a difference in surface energy. Finally, a film growth model based on the surface energy difference was proposed to explain the observed growth rate and crystallite size trends.