Role of a cyclopentadienyl ligand in Hf precursors using H₂O or O₃ as oxidant in atomic layer deposition

Reducing the gate dielectric thickness in semiconductor devices leads to an increase in leakage current due to tunneling. High-k materials, such as HfO₂, are essential in countering this and ensure an adequate equivalent oxide thickness at reduced physical thicknesses. This study investigated atomic layer deposition (ALD) of HfO₂ films using the heteroleptic precursor CpHf(NMe₂)₃ with two different oxidants, H₂O and O₃, to understand their effects on the growth characteristics, chemical compositional properties, structural properties, and electrical properties. Growth per cycle (GPC) analysis shows that O₃ achieved a saturated GPC of 0.85 Å/cycle, whereas H₂O exhibits a lower GPC of 0.6 Å/cycle owing to steric hindrance from incomplete Cp ligand removal, leading to higher carbon impurity. X-ray photoelectron spectroscopy revealed an increase in carbon impurity in the H₂O-deposited films, supporting these findings. Density functional theory calculations indicated more efficient Cp ligand removal when O₃ was used as the oxidant. Furthermore, x-ray diffraction analysis shows that the O₃-deposited films had a dominant monoclinic phase after postannealing, whereas the H₂O-deposited films exhibited an increase in orthorhombic/tetragonal phases owing to greater carbon concentrations and oxygen vacancy. Electrical characterization of metal-oxide-semiconductor capacitors revealed higher N_ot values and increased leakage current densities in the H₂O-deposited films. These differences are attributed to the higher levels of impurity and oxygen vacancy, which create additional charge-trapping sites and leakage paths. This study underscores the importance of selecting appropriate reactants for ALD to optimize the HfO₂ film properties in advanced semiconductor applications.