Abstract
In this thesis, we use the atomic-layer-deposition (ALD) technique with remote-plasma system to prepare high-κ dielectrics on Ge substrate. In Chapter 3, the HfO2/La2O3/p-Ge and n-Ge stacks were deposited as gate dielectric to discuss the effect on material and electrical properties of different La2O3 ratio in fixed thickness. It shows that insertion of a La2O3 layer at the HfO2/Ge interface improves the interfacial and electrical properties of HfO2/Ge MOS devices. Moreover, we fabricated thin HfO2/La2O3/Ge devices for scaling down the EOT. The lowest EOT we achieved is down to 1.08 nm while thickness reduces to about 4 nm. In Chapter 4, in-situ N2/H2/Ar plasma surface-nitridation treatment on p-type Ge (100) with HfO2/La2O3 high-κ gate oxide was investigated by remote rf plasma on radical-assisted atomic layer deposition (RAALD). The interfacial LaGeOxNy formation and Ge outdiffusion were also investigated by X-ray Photoelectron Spectroscopy (XPS) and transmission electron microscopy (TEM). The high-κ MOS device with an ultrathin LaGeOxNy interlayer shows good electrical characteristics, including larger κ value, smaller equivalent oxide thickness, lower leakage current density, smaller C-V hysteresis, and lower interface-state density. The involved mechanism lies in that the LaGeOxNy interlayer can effectively block the diffusion of Ge, thus improving the high-κ films/Ge interface quality. In Chapter 5, we fabricated 8 nm thick TiO2-Al2O3-La2O3 stack structure with different arrangement to investigate the oxide location effect the Ge MOSCAPs properties. The location of high-κ layers were accurately controlled by atomic layer deposition (ALD). From the results, we found that the La2O3 be the contact layer with Ge substrate, Al2O3 be the blocking layer to suppress the Ge outdiffusion and TiO2 be the higher-κ layer on the top to reduce the EOT. In this arrangement, we could take all advantages of high-κ oxides and get the best electrical properties. Finally, in Chapter 6, we fabricate cyclic D2O plasma treatments on HfO2 films and surface D2O plasma treatment on p- Ge (100) substrate by radical-assisted atomic layer deposition (RAALD). The samples with cyclic and surface D2O plasma treatments show better electrical properties than the sample without treatment, because of higher quality of HfO2 films and better surface quality. It shows higher capacitance density, lower equivalent oxide thickness (EOT) and lower leakage current density, respectively. The mechanism lies in that D2O radical pre-treatment remove native oxide and D2O chemisorption sites to form better surface quality. On the other hand, in-situ cyclic D2O radical anneal could form purer and denser HfO2 to suppress Ge diffusion through HfO2 films.