Nano-scale zirconia and hafnia dielectrics grown by atomic layer deposition: Crystallinity, interface structures and electrical properties

With the continued scaling of transistors, leakage current densities across the SiO2 gate dielectric have increased enormously through direct tunneling. Presently, metal oxides having higher dielectric constants than SiO2 are being investigated to reduce the leakage current by increasing the physical thickness of the dielectric. Many possible techniques exist for depositing high-kappa gate dielectrics. Atomic layer deposition (ALD) has drawn attention as a method for preparing ultrathin metal oxide layers with excellent electrical characteristics and near-perfect film conformality due to the layer-by-layer nature of the deposition mechanism.; For this research, an ALD system using ZrCl4/HfCl4 and H2O was built and optimized. The microstructural and electrical properties of ALD-ZrO2 and HfO2 grown on SiO2/Si substrates were investigated and compared using various characterization tools. In particular, the crystallization kinetics of amorphous ALD-HfO2 films were studied using in-situ annealing experiments in a TEM. The effect of crystallization on the electrical properties of ALD-HfO 2 was also investigated using various in-situ and ex-situ post-deposition anneals. Our results revealed that crystallization had little effect on the magnitude of the gate leakage current or on the conduction mechanisms.; Building upon the results for each metal oxide separately, more advanced investigations were made. Several nanolaminate structures using ZrO2 and HfO2 with different sequences and layer thicknesses were characterized. The effects of the starting microstructure on the microstructural evolution of nanolaminate stacks were studied. Additionally, a promising new approach for engineering the thickness of the SiO2-based interface layer between the metal oxide and silicon substrate after deposition of the metal oxide layer was suggested. Through experimental measurements and thermodynamic analysis, it is shown that a Ti overlayer, which exhibits a high oxygen solubility, can effectively getter oxygen from the interface layer, thus decomposing SiO2 and reducing the interface layer thickness in a controllable fashion.; As one of several possible applications, ALD-ZrO2 and HfO 2 gate dielectric films were deposited on Ge (001) substrates with different surface passivations. After extensive characterization using various microstructural, electrical, and chemical analyses, excellent MOS electrical properties of high-kappa gate dielectrics on Ge were successfully demonstrated with optimized surface nitridation of the Ge substrates.