Electrical properties of atomic layer deposited Al₂O₃ with anneal temperature for surface passivation

The electrical characteristics of Al₂O₃ layers prepared by the atomic layer deposition technique using O₃, H ₂O, and plasma O₂, as oxidants are investigated through capacitance-voltage measurements of metal-insulator-semiconductor capacitors. Particular emphasis is placed on the properties of thermal annealed Al ₂O₃ for surface passivation. Capacitance measurements at flatband voltage before and after the application of constant voltage stress in the inversion regime indicate that the charge trapping and hysteresis behavior of the capacitors are more dominant at low temperature annealing. Positive flatband voltage shifts due to negative charge tunneling are also observed under both negative and positive bias voltage polarities. The interface trap densities of O₃ and plasma O₂-based Al₂O ₃ samples at 450 °C decrease by an order of magnitude with increasing annealing temperature, approaching the interface trap density levels in the 10¹¹ eV^{- 1} cm^{- 2} range. However, H ₂O-based Al₂O₃ doesn't change considerably. The interface trap density distribution shows that H₂O-based Al ₂O₃/Si annealed over 400 °C has depassivated defects, similar to those observed in SiO₂/Si interfaces. A comparison of the emitter saturation current density and the interface defect density shows that the interface density at the midgap is not so useful in predicting interface recombination after corona charging.