Optical, electrical, and structural properties of ultrathin zirconium-oxide films

Zirconium oxide (ZrO2) is one of the candidate materials for the high-k dielectrics used in Dynamic random access memory (DRAM) devices. ZrO2 films in device structures are extremely thin, and their physical properties are highly sensitive to the preparation conditions. Thus, it is very important to monitor the properties of ZrO2 films during device fabrication. We investigated the optical, electrical and structural properties of ultrathin ZrO2 films with different thicknesses by various techniques, including vacuum UV spectroscopic ellipsometry. Particularly, the effects of annealing were studied in detail. The optical and the structural properties of thin (<4 nm) ZrO2 film did not show any significant change upon annealing. Meanwhile, thicker films (>4 nm) were crystallized, and the threshold temperature for crystallization depended on thickness. That is, thicker films crystallized at lower temperatures.