Microstructure, optical, electrical properties, and leakage current transport mechanism of sol-gel-processed high-k HfO2 gate dielectrics

Deposition of high-k HfO2 gate dielectric films on n-type Si and quartz substrates by sol-gel spin-on coating technique has been performed and the structural, optical and electrical characteristics as a function of annealing temperature have been investigated. The structural and optical properties of HfO2 thin films related to annealing temperature are investigated by X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis), and spectroscopic ellipsometry (SE). Results indicate that the monoclinic form of HfO2 appears when temperature rises through and above 500 °C. The reduction in band gap is observed with the increase of annealing temperature. Moreover, the increase of refractive index (n) and density and the decrease of the extinction coefficient with the increase of annealing temperature are obtained by SE measurements. Additionally, the electrical properties based on Al/Si/HfO2/Al capacitor are analyzed by means of the high frequency capacitance-voltage (C-V) and the leakage current density-voltage (J-V) characteristics. And the leakage current conduction mechanisms as functions of annealing temperatures are also discussed.