Temperature-Dependent HfO/Si Interface Structural Evolution and its Mechanism.

In this work, hafnium oxide (HfO) thin films are deposited on p-type Si substrates by remote plasma atomic layer deposition on p-type Si at 250 °C, followed by a rapid thermal annealing in nitrogen. Effect of post-annealing temperature on the crystallization of HfO films and HfO/Si interfaces is investigated. The crystallization of the HfO films and HfO/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 HfO to Si interface. For annealing temperature below 400 °C, the HfO film and interfacial layer are amorphous, and the latter consists of HfO and silicon dioxide (SiO). At annealing temperature of 450-550 °C, the HfO film become multiphase polycrystalline, and a crystalline SiO is found at the interface. Finally, at annealing temperature beyond 550 °C, the HfO film is dominated by single-phase polycrystalline, and the interfacial layer is completely transformed to crystalline SiO.