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 wet thermal annealing at relatively higher temperature such as 550 degrees C 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, wet thermal annealing at 400 degrees C can decrease the GeOx 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 a positive charge in the dielectrics due to the hydrolyzable property of GeOx 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 wet thermal annealing to a certain extent.