Temperature-Dependent HfO2/Si Interface Structural Evolution and its Mechanism

In this work, hafnium oxide (HfO2) thin films are deposited on p-type Si substrates by remote plasma atomic layer deposition on p-type Si at 250 degrees C, followed by a rapid thermal annealing in nitrogen. Effect of post-annealing temperature on the crystallization of HfO2 films and HfO2/Si interfaces is investigated. The crystallization of the HfO2 films and HfO2/Si interface is studied by field emission transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscopy. The experimental results show that during annealing, the oxygen diffuse from HfO2 to Si interface. For annealing temperature below 400 degrees C, the HfO2 film and interfacial layer are amorphous, and the latter consists of HfO2 and silicon dioxide (SiO2). At annealing temperature of 450-550 degrees C, the HfO2 film become multiphase polycrystalline, and a crystalline SiO2 is found at the interface. Finally, at annealing temperature beyond 550 degrees C, the HfO2 film is dominated by single-phase polycrystalline, and the interfacial layer is completely transformed to crystalline SiO2.