S. W. Whangbo

Epitaxial growth of Y2O3 films on Si(100) without an interfacial oxide layer

Heteroepitaxial Y2O3 films were grown on Si(100) substrates by the technique of reactive ionized cluster beam deposition. The crystallinity of the films was investigated with reflection high energy electron diffraction (RHEED), glancing angle x-ray diffraction (GXRD), and the interface was examined by high resolution transmission electron microscopy (HRTEM). Under the condition of 5 kV acceleration voltage at the substrate temperature of 800 °C, the Y2O3 film grows epitaxially on the Si(100) substrate. RHEED and GXRD results revealed that the epitaxial relationship between Y2O3 and Si(100) is Y2O3(110)//Si(100), and HRTEM observation showed a sharp interface without an amorphous layer.

Structural transition of crystalline Y2O3 film on Si(111) with substrate temperature

Abstract Crystalline Y 2 O 3 films on Si(111) were grown by ionized cluster beam (ICB) deposition in an ultra high vacuum (UHV). The crystallinity of the films deposited at several different temperatures was studied using X-ray diffraction (XRD) and reflection of high-energy electron diffraction (RHEED), and the chemical states of the films was investigated using X-ray photoelectron spectroscopy (XPS). The transformation from monoclinic to cubic structure was observed upon the increase of the substrate temperature from 100°C to 500°C. The single crystal cubic structure was obtained at substrate temperatures over 500°C. The stoichiometry and binding state in the films were gradually changed to a cubic Y 2 O 3 structure with the increase of the substrate temperature. The transformation of the film structure from a monoclinic structure to a cubic structure was also observed by post annealing treatment in an oxygen ambient.

GROWTH STAGE OF CRYSTALLINE Y2O3 FILM ON SI(100) GROWN BY AN IONIZED CLUSTER BEAM DEPOSITION

We investigated the initial and epitaxial growth stage of Y2O3/Si(100) grown by reactive ionized cluster beam deposition, using x-ray diffraction (XRD), atomic force microscope, and reflection high-energy electron diffraction. We also investigated the crystalline structure of the films using transmission electron microscopy and XRD. The preferred growth direction of Y2O3 grown by an ion beam changed completely from the 〈111〉 to the 〈110〉 orientation in order to minimize the overall energy of the film as the substrate temperature increased. In addition to the kinetic energy of the deposited atoms, oxygen partial pressure and the substrate surface state also bear a relationship to the change in the preferred growth direction. The crystalline growth of Y2O3 film depends on the state of the surface at the initial growth stage, whether the Si surface was first exposed to oxygen or yttrium. In particular, the silicon oxide layer which formed on the Si surface during the initial growth stage played an important ...

Titanium oxide films on Si(100) deposited by electron-beam evaporation at 250 °C

Titanium oxide films with a thickness of a 400 nm were deposited on p-type Si(100) at 250 °C by electron-beam evaporation where titanium dioxide was evaporated in oxygen environment at a pressure of 2×10−6–4×10−5 Torr. Effects of oxygen flow rate (FO2) between 0 and 40 sccm on properties such as crystallinity, surface roughness, and chemical states of the films have been investigated. Oxygen resonance backscattering spectroscopy shows that all films are oxygen rich, i.e., the ratio of oxygen to titanium of the films ranged from 2.25 to 2.3. X-ray diffraction patterns show that these films grown at 250 °C are polycrystalline of anatase TiO2. Ti K-edge x-ray absorption near-edge spectroscopy (XANES) spectra show that the films have mixed phases of anatase and rutile TiO2. More than 70% of the films is anatase TiO2 and its proportion of the films is decreased with increasing FO2. XANES spectra from the films grown at FO2=0 sccm are very similar to that of the powdered anatase TiO2. X-ray photoelectron spectr...

Temperature dependence of the properties of heteroepitaxial Y2O3 films grown on Si by ion assisted evaporation

Heteroepitaxial Y2O3 films were grown on an Si(111) substrate by ion assisted evaporation in an ultrahigh vacuum, and their properties such as crystallinity, film stress, and morphological change were investigated using the various measurement methods. The crystallinity was assessed by x-ray diffraction (XRD) and reflection high-energy electron diffraction. Interface crystallinity was also examined by Rutherford backscattering spectroscopy (RBS) channeling and transmission electron microscopy. The strain of the films was measured by RBS channeling and XRD. Surface and interface morphological characteristics were observed by atomic force microscopy and x-ray scattering method. By comparing the interface with the surface characteristics, we can conclude that many defects at the interface region were generated by interface interaction between the yttrium metal and Si substrate. Moreover, the film quality dominantly depended on the deposition temperature. The crystallinity was greatly improved and the surface...

Titanium oxide films on Si(100) deposited by e-beam evaporation

Titanium oxide films with a thickness of a 400 nm were deposited on p-type Si(100) at room temperature by e-beam evaporation, and titanium dioxide was evaporated in oxygen environment at a pressure of 2×10−6–4×10−5 Torr. Effects of oxygen flow rate (FO2) on the properties of the films, such as surface roughness, composition, and chemical states, have been investigated. The root-mean-square surface roughness of the films increased with increasing FO2 up to 20 sccm, and then decreased over 20 sccm. X-ray diffraction patterns show that the titanium oxide films are amorphous. Oxygen resonance backscattering spectroscopy shows that all films are oxygen rich, i.e., relative atomic ratio (CO/CTi) of the films ranged from 2.05 to 2.25. But the x-ray photoelectron spectroscopy (XPS) analysis shows that the titanium oxide films were oxygen deficient. The ratio of oxygen to titanium (CO2/CTi) of the films calculated by XPS ranged from 1.82 to 1.93. XPS shows that there exist only Ti3+ and Ti4+ charge states in the f...

Characteristics of Y2O3 films on Si(111) grown by oxygen-ion beam-assisted deposition

Abstract We investigated the dependence of the crystallinity, strain, and morphological characteristics of epitaxial Y2O3 films grown on Si(111) by ion beam-assisted deposition. Various characterization tools, such as reflection high-energy electron diffraction, X-ray diffraction, high-resolution transmission electron and atomic force microscopy, were used to reveal the physical properties which depend on the assisted energy of the oxygen-ion beam. When the assisted energy of the oxygen-ion beam was applied to grow films, the growth temperature for epitaxy was lowered. The crystallinity was improved and the film was compressed as the assisted energy increased up to 45 eV, while the improvement of crystallinity and the strain increment was suppressed as the assisted energy increased further. Moreover, the morphological shape shows that island growth is induced when ion energy is supplied. That is, when the ion energy is increased, islands are expanded and the surfaces are flattened. The surface morphology yields information on film characteristics, such as crystallinity and strain, both of which depend on the assisted energy of the oxygen ion.

Growth of epitaxial γ-Al2O3(111) films using an oxidized Si(111) substrate

High-quality epitaxial γ-Al2O3(111) films were grown on a Si(111) substrate covered with a chemically formed 2 nm SiO2 layer using reactive ionized beam deposition. An epitaxial γ-Al2O3 layer was formed at above 800 °C, while the films showed polycrystalline below this temperature. Al2O3 films grown on an oxidized Si substrate showed a better crystalline quality, a more flat surface and a sharper interface than the films grown on a clean Si substrate. A thin SiO2 layer acts as a barrier to prevent a direct reaction of incident Al with Si substrate, the thin layer is consumed during the Al2O3 growth to yield an abrupt Al2O3/Si interface. The role of the thin oxide layer on the film growth and the chemical reactions at the interface during the initial growth of Al2O3 were investigated.

Effects of thermal annealing a glass surface in air

Abstract Glass slides were annealed at a temperature range of 300–600 °C for 30 min in air. We investigated the effects of thermal annealing treatments on the chemical composition, and surface roughness of the glass. Metallic sodium concentration at the glass surface was 2.2%, but sodium concentration at the annealed glass surface ranged from 4.3% to 5.5%. The sodium composition at the glass surface was greatly increased at an annealing temperature of 400 °C, but the sodium composition at the surface was gradually decreased at Ta⩾500 °C. This phenomenon may be due to the volatility of the sodium atoms at the glass surface. However, carbon concentration at the glass surface was reduced from 49% at room temperature to 22% at annealing temperature (Ta) of 600 °C. Surface morphology of the glass was changed with annealing temperature. The root-mean-square surface roughness of the bare glass was 0.6 nm, but the roughness of the glass annealed at a temperature of 300, 400, 500, and 600 °C in air for 30 min was 1.0, 1.8, 2.0, 3.0 nm, respectively.

Effect of oxidized Al prelayer for the growth of polycrystalline Al2O3 films on Si using ionized beam deposition

Abstract Polycrystalline Al2O3 thin films have been grown on Si substrates by ionized beam deposition using an aluminum solid source in O2 environments. To prevent the aluminum interdiffusion to Si at high substrate temperature (Ts>500°C), the oxidized Al prelayer with a thickness of 3 nm was deposited on the Si substrate at room temperature before Al2O3 deposition, and subsequently polycrystalline Al2O3 films were grown at 700°C. Although Al interdiffusion increased at the interface with increasing Ts, the oxidized Al prelayer was effective as a buffer layer on which to grow stoichiometric and crystalline Al2O3 films up to Ts=800°C.