Interfacial reaction depending on the stack structure of Al ₂O₃ and HfO₂ during film growth and postannealing

Interfacial reactions as a function of the stack structure of Al ₂O₃ and HfO₂ grown on Si by atomic-layer deposition were examined by various physical and electrical measurements. In the case of an Al₂O₃ film with a buffer layer of HfO ₂, reactions between the Al₂O₃ and Si layers were suppressed, while a HfO₂ film with an Al₂O ₃ buffer layer on the Si readily interacted with Si, forming a Hf-Al-Si-O compound. The thickness of the interfacial layer increased dramatically after an annealing treatment in which a buffer layer of Al ₂O₃ was used, while no change in thickness was observed in the film in which a HfO₂ buffer layer was used. Moreover, the stoichiometric change caused by a different reaction process altered the chemical state of the films, which affected charge trapping and the interfacial trap density.