Microstructure and electrical properties of thin HfO2 deposited by plasma-enhanced atomic layer deposition

The influence of annealing in the temperature range of 150–300 °C during plasma-enhanced atomic layer deposition of HfO2 and the conditions of the following thermal processing on microstructure and electrical properties have been studied. The microstructure was examined by transmission electron microscopy and electron diffraction. The as-deposited HfO2 film consists of monoclinic crystallites embedded in an amorphous matrix. It was found that the crystallite density grows with the increase in the deposition temperature; however, the size of the crystallites does not change. Subsequent annealing at 425 °C for 30 min or at 950 °C for 4 s led to complete crystallization through the lateral growth of the crystallites of samples formed at 250 and 300 °C. However, for the sample formed at 150 °C, subsequent annealing at 425 °C resulted in the formation of dendritic-like crystalline clusters embedded in an amorphous matrix. The leakage currents in polycrystalline and even amorphous HfO2 films after the annealing were drastically increased. That could be explained by crystallization after the annealing. However, the C impurity redistribution and the growth of an interfacial layer could also affect the leakage.