K. B. Chung

Thermal evolution and electrical correlation of defect states in Hf-based high-κ dielectrics on n-type Ge (100): Local atomic bonding symmetry

The crystal field splittings and Jahn–Teller (J-T) distortions in Hf-based high-κ dielectric oxides on n-type Ge (100) substrates were investigated through the examination of O K1 edge spectra, obtained via x-ray absorption spectroscopy. Second derivative analysis of these O K1 edge spectra provided unambiguous evidence of J-T d-state degeneracy removal, resulting from the symmetry of the local atomic bonding environment. Additionally, two distinct defect states were found below the conduction band edge. The conduction band’s molecular orbital energy structure, including defect states, was determined based on the results of these investigations. Moreover, the thermal evolution of the defect states was found to be dependent on both postdeposition annealing temperature and Hf-based high-κ dielectric oxides. These subband-edge defect states were determined to be electrically active, and their density and the local atomic bonding symmetry were found to be correlated with the effective electron charge trapping...

Thickness dependence on crystalline structure and interfacial reactions in HfO2 films on InP (001) grown by atomic layer deposition

The crystalline structure and interfacial reactions in HfO2 films grown on InP (001) substrates was investigated as a function of film thickness. High resolution transmission electron microscopy and x-ray diffraction measurements were used to investigate changes in the crystalline structure of the HfO2 films. As the thickness of the HfO2 increased, the crystal structure was transformed from monoclinic to tetragonal, and the interfacial layer between the HfO2 film and the InP substrate disappeared. High resolution x-ray photoelectron spectroscopy was also applied to confirm the existence of an interfacial chemical reaction in HfO2/InP. An interfacial self-cleaning effect occurred during the atomic layer deposition process, resulting in a clear interface with no indication of an interfacial layer between the HfO2 film and the InP surface. Finally, the crystallization process in the HfO2 films was found to be significantly affected by the interfacial energy.

Interfacial reaction of atomic-layer-deposited HfO2 film as a function of the surface state of an n-GaAs (100) substrate

The characteristics of interfacial reactions and the valence band offset of HfO2 films grown on GaAs by atomic layer deposition were investigated by combining high-resolution x-ray photoelectron spectroscopy and high-resolution electron transmission microscopy. The interfacial characteristics are significantly dependent on the surface state of the GaAs substrate. Polycrystalline HfO2 film on a clean GaAs surface was changed to a well-ordered crystalline film as the annealing temperature increased, and a clean interface with no interfacial layer formed at temperatures above 600°C. The valence band offset of the film grown on the oxidized GaAs surface gradually increased with the stoichiometric change in the interfacial layer.

Phase separation and electronic structure of Hf-silicate film as a function of composition

Thermal stability and electronic structure of xHfO2∙(100−x)SiO2 (HfSiO) (x=25%, 50%, and 75%) grown by atomic layer deposition were investigated by various measurement tools. The quantity of incorporated SiO2 content changes the binding energy of HfO2 as the charging effect in the silicate is enhanced with the quantity SiO2. When the annealing temperature is increased over 800 °C, phase separation between SiO2 and HfO2 is observed in the films with 50% and 75% HfO2, while it does not occur in a Hf-silicate film with a high mole fraction of SiO2. The phase separation begins in the surface region via the segregation of SiO2. After the annealing treatment, the quantity of SiO2 supplied to the film surface due to interfacial interactions influences the phase separation process, resulting in no phase separation being observed, even at a high annealing treatment of 900 °C.

Change in band alignment of HfO2 films with annealing treatments

Energy band alignment of a nitrided HfO2 film and dependence of the band gap (Eg) on annealing treatments with nitrogen plasma and ambient gases (N2 and O2) were studied by reflection electron energy loss spectra and x-ray photoelectron spectroscopy. We also investigated the nitrogen content in the film and its influence on the band alignment using medium energy ion scattering. The nitrogen incorporated into the HfO2 film by directed nitrogen plasma treatment significantly decreased the band gap and band offsets, i.e., the incorporated N in the film decreased both conduction and valance band offsets. The nitrogen content in depth direction was dependent on the postannealing conditions using O2 or N2.

High-pressure Gas Activation for Amorphous Indium-Gallium-Zinc-Oxide Thin-Film Transistors at 100 °C

We investigated the use of high-pressure gases as an activation energy source for amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistors (TFTs). High-pressure annealing (HPA) in nitrogen (N2) and oxygen (O2) gases was applied to activate a-IGZO TFTs at 100 °C at pressures in the range from 0.5 to 4 MPa. Activation of the a-IGZO TFTs during HPA is attributed to the effect of the high-pressure environment, so that the activation energy is supplied from the kinetic energy of the gas molecules. We reduced the activation temperature from 300 °C to 100 °C via the use of HPA. The electrical characteristics of a-IGZO TFTs annealed in O2 at 2 MPa were superior to those annealed in N2 at 4 MPa, despite the lower pressure. For O2 HPA under 2 MPa at 100 °C, the field effect mobility and the threshold voltage shift under positive bias stress were improved by 9.00 to 10.58 cm2/V.s and 3.89 to 2.64 V, respectively. This is attributed to not only the effects of the pressurizing effect but also the metal-oxide construction effect which assists to facilitate the formation of channel layer and reduces oxygen vacancies, served as electron trap sites.

Suppression of phase separation in Hf-silicate films using NH3 annealing treatment

The structural characteristics of Hf-silicate films and nitrogen incorporated Hf-silicate films, prepared using a NH3 annealing treatment, were investigated by various measurements. Hf-silicate films annealed in a N2 ambient at 900°C show the evidence of crystallization in local regions, resulting in the phase separation of HfO2 and SiO2. In addition, a SiO2 overlayer is formed on the Hf-silicate films, due to the diffusion of Si by postannealing in an ambient of N2 at 900°C. However, in nitrogen incorporated Hf-silicate films, prepared using a NH3 annealing treatment, phase separation is effectively suppressed and no SiO2 overlayer is present. The incorporated N is distributed into the film and interfacial layer, and obstructs the diffusion of Si from the substrate as well as the film. Structural changes in films affect electrical characteristics such as the dielectric constant and flatband voltage.

Facile fabrication of high-performance InGaZnO thin film transistor using hydrogen ion irradiation at room temperature

Device performance of InGaZnO (IGZO) thin film transistors (TFTs) are investigated as a function of hydrogen ion irradiation dose at room temperature. Field effect mobility is enhanced, and subthreshold gate swing is improved with the increase of hydrogen ion irradiation dose, and there is no thermal annealing. The electrical device performance is correlated with the electronic structure of IGZO films, such as chemical bonding states, features of the conduction band, and band edge states below the conduction band. The decrease of oxygen deficient bonding and the changes in electronic structure of the conduction band leads to the improvement of device performance in IGZO TFT with an increase of the hydrogen ion irradiation dose.

Thermal Annealing Effects on the Atomic Layer Deposited LaAlO3 Thin Films on Si Substrate

The changes in film structure of amorphous atomic layer deposited LaAlO 3 thin films after thermal annealing were examined by medium-energy ion-scattering measurements and angle-resolved X-ray photoelectron spectroscopy. Thermal annealing induces Si-rich LaSiO and Al-deficient LaAl x Si y O z layers on a few monolayers of SiO 2 . Al atoms do not participate in silicate formation during annealing. Instead, they migrate toward the film surface, which induces nonhomogeneity in the films along the vertical direction. The concentrations of Al and La on the film surface increase and decrease, respectively, as a result of Si diffusion from the substrate and silicate formation.

Suppression of defect states in HfSiON gate dielectric films on n-type Ge(100) substrates

Defect states in HfO2 and HfSiON films deposited on Ge(100) substrates were studied by spectroscopic ellipsometry (SE) and x-ray absorption spectroscopy (XAS). In addition, structural and compositional changes in these films were examined via medium energy ion scattering (MEIS). SE and XAS experiments revealed two distinct band edge defect states, located at 1.7±0.1eV and at 2.7±0.1 below the conduction band edges of these films. The number of defect states in HfO2 increased noticeably following postdeposition annealing (PDA), whereas in HfSiON, it showed only small increases following the same treatment. MEIS measurements showed that Ge diffusion into HfO2 films was enhanced significantly by PDA as well; however, this effect was less pronounced in the HfSiON films. The suppression of defect state enhancement in HfSiON films was correlated with lower levels of Ge diffusion and increased structural stability with respect to HfO2.