Structural and Electrical Properties of EOT HfO₂ (<1 nm) Grown on InAs by Atomic Layer Deposition and Its Thermal Stability

We report on changes in the structural, interfacial, and electrical characteristics of sub-1 nm equivalent oxide thickness (EOT) HfO₂ grown on InAs by atomic layer deposition. When the HfO₂ film was deposited on an InAs substrate at a temperature of 300°C, the HfO₂ was in an amorphous phase with an sharp interface, an EOT of 0.9 nm, and low preexisting interfacial defect states. During post deposition annealing (PDA) at 600°C, the HfO₂ was transformed from an amorphous to a single crystalline orthorhombic phase, which minimizes the interfacial lattice mismatch below 0.8%. Accordingly, the HfO₂ dielectric after the PDA had a dielectric constant of ∼24 because of the permittivity of the well-ordered orthorhombic HfO₂ structure. Moreover, border traps were reduced by half than the as-grown sample due to a reduction in bulk defects in HfO₂ dielectric during the PDA. However, in terms of other electrical properties, the characteristics of the PDA-treated sample were degraded compared to the as-grown sample, with EOT values of 1.0 nm and larger interfacial defect states (D_it) above 1 × 10¹⁴ cm^-2 eV^-1. X-ray photoelectron spectroscopy data indicated that the diffusion of In atoms from the InAs substrate into the HfO₂ dielectric during the PDA at 600°C resulted in the development of substantial midgap states.