Determination of Type and Concentration of Traps in Nanoscale-Thick HfO2 Films Applicable for Gate Dielectric Stacks

Nanoscale-thick films, including high-k dielectrics, are an essential element of modern electronic devices (e.g., transistors based on III–V semiconductors). In this regard, the development of techniques for studying the electronic properties of such nano-objects is an important task. In this work, we propose a technique that makes it possible to determine the presence of trap levels, their concentration, and the activation energy for films up to 40 nm thick. The mechanism of charge transport in high-k dielectrics, such as HfO2, is the subject of active study. We investigated thin hafnia films grown on the Si surface with TEMAH-H2O or Hf­(thd)4-O2 precursor systems. It was shown by X-ray photoemission spectroscopy that the TEMAH-H2O sample was grown with oxygen deficiency. On the Hf­(thd)4-O2 sample, the SiO2 sublayer between hafnia and substrate was formed, which was confirmed by Kelvin probe microscopy and X-ray reflectivity studies. This SiO2 sublayer significantly affects the charge dissipation. Diffusion in the lateral direction along the SiO2 sublayer has a higher diffusion coefficient than in the HfO2 layer, but the presence of the SiO2 sublayer reduces the level of charge leakage to the substrate. The activation energies for hole traps and electron traps were found to be E a ≈ 0.46 ± 0.03 and 0.37 ± 0.03 eV for the TEMAH-H2O sample and E a ≈ 0.22 ± 0.05 and 0.16 ± 0.04 eV for the Hf­(thd)4-O2 sample, respectively. It was also shown that the process of positive charge localization occurs faster than negative charge localization. Electron localization leads to a decrease of the intensity of the 2.65 eV CL band, associated with oxygen vacancies.