Effect of UV/ozone plasma treatment on sol-gel-derived HfO2 thin films

This study reports on the fabrication and characterization of sol-gel-derived HfO2 thin films on indium tin oxide (ITO) substrates. The films were dried in air and ultraviolet (UV)/ozone plasma environments and finally annealed at various temperatures ranging from 300 to 500 °C. Crystallization of the films was observed to occur even at low annealing temperature of 300 °C. Scanning electron microscopy results indicate that the films dried in the air environment were not uniform, and the grains were observed to be separated from each other. In contrast, the UV/ozone plasma-treated thin films exhibited smooth and uniform surfaces. The reduction of leakage current density of more than 3 orders of magnitude was observed with the UV/ozone plasma treated films. High transmittance of nearly 99% was observed for the films dried in both the air and UV/ozone plasma environments. Nanoindentation results of the air-dried films revealed pop-in events in the load-displacement curve at specific depths of 12.74 and 19.68 nm; in contrast, smooth and regular curves without any discontinuities along either the loading or unloading sections were observed for the UV/ozone plasma-treated films. The obtained results demonstrated that UV/ozone plasma-treatment is proved to be a promising technique in improving the quality of HfO2 on ITO substrates.