Crystallization behaviors of ultrathin Al-doped HfO2 amorphous films grown by atomic layer deposition**Project supported by the National High Technology Research and Development Program of China (Grant No. 2015AA016501) and the National Natural Science Foundation of China (Grant Nos. 61574168 and 61504163).

Abstract

In this work, ultrathin pure HfO2 and Al-doped HfO2 films (about 4-nm thick) are prepared by atomic layer deposition and the crystallinities of these films before and after annealing at temperatures ranging from 550 °C to 750 °C are analyzed by grazing incidence x-ray diffraction. The as-deposited pure HfO2 and Al-doped HfO2 films are both amorphous. After 550-°C annealing, a multiphase consisting of a few orthorhombic, monoclinic and tetragonal phases can be observed in the pure HfO2 film while the Al-doped HfO2 film remains amorphous. After annealing at 650 °C and above, a great number of HfO2 tetragonal phases, a high-temperature phase with higher dielectric constant, can be stabilized in the Al-doped HfO2 film. As a result, the dielectric constant is enhanced up to about 35. The physical mechanism of the phase transition behavior is discussed from the viewpoint of thermodynamics and kinetics.