Current transport mechanism of hafnium oxide films prepared by direct sputtering
by Ng Kit Ling
M.Phil. Electrical and Electronic Engineering
xiii, 68 leaves : ill. (some col.) ; 30 cm
The downscaling of MOSFET devices to improve the packing density and device performance has faced a lot of challenges. Within a decade, an ultra-thin gate dielectric ( 22225232322...[ Read more ]
The downscaling of MOSFET devices to improve the packing density and device performance has faced a lot of challenges. Within a decade, an ultra-thin gate dielectric (<2.0 nm in thickness) is required. However, the downscaling is constrained by the physical limitation of the dielectric thickness. The tunneling leakage current for such an ultra-thin oxide will probably be unacceptable for mainstream ULSI applications. An alternative gate dielectric must be found to sustain the scaling trend.
Hafnium oxide thin film is one of the most promising materials to replace SiO2 to suit further downscaling requirements. Its dielectric constant is more than 4 times of that of SiO2. It exhibits a low leakage current compared with the SiO2 with same equivalent oxide thickness. Besides, it is thermally stable on Si substrate compared with Ta2O5, A12O3, Y2O3 and ZrO2.
In our research, HfO2 film deposited with a pure Hf metal target by direct sputtering in a mixture of oxygen and argon ambient is first introduced into HKUST. The deposition kinetics of hafnium oxide has been investigated. The leakage current of MOSFET is one of the most important parameters of the scaling limitations. The origin of leakage current of HfO2 as gate dielectric has been explored. The leakage current is transported by the Frenkel-Poole emission. The current flow is due to electrons jumping from one isolated trap site to another in the presence of electric field. This mechanism is temperature dependent. The electron transportation of HfO2 has been first described. Applying HfO2 as the gate dielectric in MOSFET devices, the amount of leakage from p-channel to the gate is expected to be smaller than that of n-channel to the gate.