Al₂O₃ Passivation Effect in HfO₂·Al₂O₃ Laminate Structures Grown on InP Substrates

The passivation effect of an Al₂O₃ layer on the electrical properties was investigated in HfO₂–Al₂O₃ laminate structures grown on indium phosphide (InP) substrate by atomic-layer deposition. The chemical state obtained using high-resolution X-ray photoelectron spectroscopy showed that interfacial reactions were dependent on the presence of the Al₂O₃ passivation layer and its sequence in the HfO₂–Al₂O₃ laminate structures. Because of the interfacial reaction, the Al₂O₃/HfO₂/Al₂O₃ structure showed the best electrical characteristics. The top Al₂O₃ layer suppressed the interdiffusion of oxidizing species into the HfO₂ films, whereas the bottom Al₂O₃ layer blocked the outdiffusion of In and P atoms. As a result, the formation of In–O bonds was more effectively suppressed in the Al₂O₃/HfO₂/Al₂O₃/InP structure than that in the HfO₂-on-InP system. Moreover, conductance data revealed that the Al₂O₃ layer on InP reduces the midgap traps to 2.6 × 10¹² eV^–1 cm^–2 (compared to that of HfO₂/InP, that is, 5.4 × 10¹² eV^–1 cm^–2). The suppression of gap states caused by the outdiffusion of In atoms significantly controls the degradation of capacitors caused by leakage current through the stacked oxide layers

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