Wet thermal annealing effect on TaN/HfO₂/Ge metal–oxide–semiconductor capacitors with and without a GeO₂ passivation layer

Wet thermal annealing effects on the properties of TaN/HfO₂/Ge metal-oxide-semiconductor (MOS) structures with and without a GeO₂ passivation layer are investigated. The physical and the electrical properties are characterized by X-ray photoemission spectroscopy, high-resolution transmission electron microscopy, capacitance-voltage (C-V) and current-voltage characteristics. It is demonstrated that the wet thermal annealing at relatively higher temperature such as 550 ℃ can lead to Ge incorporation in HfO₂ and the partial crystallization of HfO₂, which should be responsible for the serious degradation of the electrical characteristics of the TaN/HfO₂/Ge MOS capacitors. However, the wet thermal annealing at 400 ℃ can decrease the GeO_x interlayer thickness at the HfO₂/Ge interface, resulting in a significant reduction of the interface states and a smaller effective oxide thickness, along with the introduction of positive charge in the dielectrics due to the hydrolyzable property of GeO_x in the wet ambient. The pre-growth of a thin GeO₂ passivation layer can effectively suppress the interface states and improve the C-V characteristics for the as-prepared HfO₂ gated Ge MOS capacitors, but it also dissembles the benefits of the wet thermal annealing to a certain extent.