Electrical properties and thermal stability in stack structure of HfO₂/Al₂O₃/InSb by atomic layer deposition

Changes in the electrical properties and thermal stability of HfO₂ grown on Al₂O₃-passivated InSb by atomic layer deposition (ALD) were investigated. The deposited HfO₂ on InSb at a temperature of 200 °C was in an amorphous phase with low interfacial defect states. During post-deposition annealing (PDA) at 400 °C, In-Sb bonding was dissociated and diffusion through HfO₂ occurred. The diffusion of indium atoms from the InSb substrate into the HfO₂ increased during PDA at 400 °C. Most of the diffused atoms reacted with oxygen in the overall HfO₂ layer, which degraded the capacitance equivalent thickness (CET). However, since a 1-nm-thick Al₂O₃ passivation layer on the InSb substrate effectively reduced the diffusion of indium atoms, we could significantly improve the thermal stability of the capacitor. In addition, we could dramatically reduce the gate leakage current by the Al₂O₃ passivation layer. Even if the border traps measured by C-V data were slightly larger than those of the as-grown sample without the passivation layer, the interface trap density was reduced by the Al₂O₃ passivation layer. As a result, the passivation layer effectively improved the thermal stability of the capacitor and reduced the interface trap density, compared with the sample without the passivation layer.