Effects of Cl-Based Ligand Structures on Atomic Layer Deposited HfO₂

Atomic layer deposition (ALD) of HfO₂ is a key technology for the application of high dielectric constant gate dielectrics ranging from conventional Si devices to novel nanodevices. The effects of the precursor on the growth characteristics and film properties of ALD HfO₂ were investigated by using hafnium tetrachloride (HfCl₄) and bis(ethylcyclopentadienyl)hafnium dichloride (Hf(EtCp)₂Cl_2, Hf(C₂H₅C₅H₄)₂Cl₂) with O₂ plasma reactant. The growth characteristics were significantly affected even by simply changing the precursor. Theoretical calculations utilizing geometrical information on the precursor and density functional theory revealed that the steric demands of the precursor ligands have a dominant effect on the different growth characteristics rather than the reaction probability of the precursor on the surface. The chemical compositional analysis results showed that the Cl residue in the HfO₂ films was reduced by using Hf(EtCp)₂Cl₂ due to the lower number of Cl atoms in each Hf precursor molecule and the relieved bridge formation of Hf-Cl-Hf bridge on the surface compared to HfCl₄. The electrical property measurement results showed significantly improved insulating properties in HfO₂ using Hf(EtCp)₂Cl₂ compared to HfCl₄ due to the low concentration of Cl residue in the film. These results provide broad insights to researchers who are interested in the fabrication of high quality dielectric layers to achieve better device performance and overcome physical limitations in the nanoscale regime.