Dysprosium Incorporation for Phase Stabilization of Atomic-Layer-Deposited HfO₂ Thin Films

The relatively low thermal stability of HfO2 films severely affects the performance of semiconductor devices. For instance, the low crystallization temperature of HfO2 (∼500 °C) leads to the formation of grain boundaries, which increases the leakage current. In this study, Dy incorporation leads to the phase transformation of HfO2 films from various directional planes to a main m(−111) plane by the crystallographic stabilization of HfO2 films, increasing the size of grains. Dy-doped HfO2 thin films with modulated doping content, prepared by plasma-enhanced atomic layer deposition (PE-ALD), are characterized by analysis of their chemical composition combined with electron microscopy and synchrotron X-ray techniques. The transformation from m(110), m(−111), m(111), m(020), and m(120) to a main m(−111) plane is observed through X-ray diffraction, which indicates that Dy plays a role for the phase stabilization of HfO2 films. The atomic-scale images of the cross section and top view obtained using an electron microscope demonstrate that the in-plane average grain size is increased by approximately 4 times due to Dy incorporation compared with that of single HfO2 films. The reduction in the area of the grain boundary of HfO2 due to Dy incorporation decreases the leakage current density of HfO2 by 1000 times and increased the breakdown strength. This result can aid future electronics by determining the effect of a dopant on the crystallographic structure of host thin-film materials.