Kiyoshi Ogata

Large-Area and High-Speed Deposition of Microcrystalline Silicon Film by Inductive Coupled Plasma using Internal Low-Inductance Antenna

A novel inductively-coupled RF plasma source with internal low-inductance antenna (LIA) units was developed to synthesize microcrystalline silicon (µc-Si) film on a large glass substrate. A film thickness profile on a 600×720 mm2 glass substrate was achieved with high plasma uniformity and a variation of less than ±5% without a standing-wave effect. Raman and transmission electron microscope (TEM) analysis revealed that highly crystallized µc-Si films, which were directly deposited on a glass substrate, were synthesized without an amorphous-phase incubation layer at the substrate interface. A bottom-gate thin-film transistor (BG-TFT) was fabricated employing an optimized µc-Si layer and exhibited a field-effect mobility of 3 cm2/(Vs), which is one order higher than that of a typical amorphous silicon TFT.

Effects of Antenna Size and Configurations in Large-Area RF Plasma Production with Internal Low-Inductance Antenna Units

Recent trends of liquid crystal display (LCD) fabrication toward a significant enlargement of glass substrates require large-area plasma sources with a scale length exceeding 1 m. To meet this requirement, large-area plasma sources with internal low-inductance antenna (LIA) units have been developed for uniform processes, in which design principles for selecting antenna size and configurations in the multiple installation of the LIA units are established. In this study, the effects of antenna size were examined in terms of plasma production characteristics indicating small increase in plasma density with a decrease in antenna size (or antenna impedance). Furthermore, plasma density distributions with the LIA units were investigated to understand the nature of plasma diffusion, which can be utilized for designing plasma profiles with multiple LIA units. First, it was shown that the plasma density distributions followed exponential decay as a function of distance from the antenna. Secondly, the measured plasma density profiles with multiple LIA units were shown to agree well with those obtained by superposing those described by exponential functions, which can be utilized for prediction.

Effect of sputtering-cleaning on adhesion of the metallic films to polymer substrates

Abstract The effect of sputtering-cleaning on adhesion and chemical bonding at the metal/polymer interface was studied. Titanium (Ti) films were deposited on polymer substrates, polyethylene and polytetrafluoroethylene (PTFE) after sputtering-cleaning treatment. The sputteringcleaning treatment consisted of argon ion irradiation at 0.3 keV. Adhesion was measured by a pull test, and the chemical bonding at the interface was investigated by X-ray photoelectron spectroscopy. Adhesion of both polymer substrates was improved by sputtering-cleaning. In the case of PE, the ratio of C-Ti bonding at the interface increased after sputtering-cleaning and resulted in adhesion improvement. C-Ti and F-Ti bonding appeared at the interface between the Ti film and the PTFE substrate, but improvement in adhesion of Ti/PTFE was attributed to the change of the interfacial morphology on the basis of the scanning electron spectroscopy observation and adhesion of Au to PTFE.

Local structure and mean-square relative displacement in SiO2 and GeO2 polymorphs

Extended X-ray absorption fine structure (EXAFS) spectra near the Si and Ge K-edge for SiO_2 and GeO_2 polymorphs were measured in transmission mode with synchrotron radiation at the Photon Factory, Tsukuba. The local structures and mean-square relative displacements were determined in \alpha-tridymite, \alpha-quartz and stishovite. In stishovite, Si is octahedrally coordinated and the four coplanar Si—O bonds [1.755 (8) A] are shorter than the other two axial bonds [1.813 (15) A]. The high-temperature phase tridymite [1.597 (3) A] has a smaller local bond distance than \alpha-quartz [1.618 (5) A]. The temperature variation of the local structural parameters for quartz-type GeO_2 (q-GeO_2) and rutile-type GeO_2 (r-GeO_2) have been determined in the temperature range 7–1000 K. The harmonic effective interatomic potential V(u)=\alpha{u}^2/2 was evaluated from the contribution to the thermal vibration, where u is the deviation of the bond distance from the location of the potential minimum. The potential coefficient \alpha for the Ge—O bond of the tetrahedron in q-GeO_2 is 24.6 eV A−2. The potential coefficients \alpha for the four coplanar Ge—O bonds and the two axial bonds of the octahedron in r-GeO_2 are 12.9 and 14.9 eV A−2, respectively. The potential coefficient \alpha for the second-nearest Ge—Ge distance in q-GeO_2 is 9.57 eV A−2. The potential coefficients \alpha for the second- and third-nearest Ge—Ge distances in r-GeO_2 are 11.6 and 7.18 eV A−2, respectively. The effective interatomic potential is largely influenced by the local structure, particularly by the coordination numbers. The phonon dispersion relations for q-GeO_2 and r-GeO_2 were estimated along [100] by calculating the dynamical matrix using the potential coefficients \alpha for the Ge—O and Ge—Ge motions. The quartz-type structure has a more complex structure with a wide gap between 103 and 141 meV and a highest energy of 149 meV, whereas the rutile-type structure has a continuous distribution and a highest energy of 126 meV.

Evidence of Ga2Se3-Related Compounds on Se-Stabilized GaAs Surfaces

A Se-stabilized GaAs(001) surface is examined by extended X-ray absorption fine structure (EXAFS) analysis. The Se K-edge EXAFS shows components due not only to the first but also the second nearest neighbors, indicating that the Se atoms are incorporated into ordered atomic arrangements. Comparing the interatomic distances to those measured for Ga2Se3 and GaSe, it is concluded that the nature of the surface compound on the Se-stabilized GaAs surface is close to that of Ga2Se3.

Fundamental study of ion-irradiation effects on the columnar growth of chromium films prepared by ion-beam and vapor deposition

The effects of ion irradiation during deposition on columnar growth of Cr thin films prepared by ion-beam-assisted deposition were studied. Cr films were prepared by evaporation of Cr metal and simultaneous irradiation of Ar ions onto Si 〈100〉 wafers. The energies of Ar ions were varied over the range of 0.5–20.0 keV, and the transport ratios of irradiating Ar ions to depositing Cr atoms, TR(Ar/Cr), to the substrates were also varied between 0.01 and 0.20. Vaporized Cr atoms were deposited onto substrates at an angle of 45° from the substrate normal and Ar ions were irradiated perpendicular to the substrate surface. Si substrates were not rotated and were kept at low temperature during deposition by a water-cooling system. The experimental results showed that every Cr film had a columnar structure regardless of ion-irradiation conditions. The column size became larger with increasing ion energy and TR(Ar/Cr). The growth direction of the column tilted considerably with increasing ion energy and TR(Ar/Cr) i...

Effects of arrival rate and gas pressure on the chemical bonding and composition in titanium nitride films prepared on Si(100) substrates by ion beam and vapor deposition

Thin titanium nitride films were prepared at room temperature by titanium metal vapor deposition on silicon substrates with simultaneous irradiation by a 2 keV nitrogen ion beam. Arrival rate ratios, ARR(N/Ti), defined as the ratio of the flux of incident atomic nitrogen particles in the ion beam relative to the flux of titanium atoms transported to the substrate, ranged from 0.17 to 2.5. The gas pressure in the vacuum chamber was maintained at 1.3×10−3 or 6.7×10−3Pa during the deposition and irradiation process. Analyses of Ti 2p x-ray photoelectron spectroscopy spectra indicated the presence of metal Ti0, nitride TiN, oxide TiO2, oxynitride TiNxOy, and carbide TiC phases. The Ti0 phase was observed exclusively and predominantly in the films prepared at 1.3×10−3Pa and ARR(N∕Ti)=0.17, 0.21, and 0.28, and the TiN phase is major in the others, as confirmed by the x-ray diffractometry analyses. The chemical composition ratio N/Ti in the films prepared at 1.3×10−3Pa increased linearly with increasing ARR(N/Ti...

Low-Temperature Microcrystalline Silicon Film Deposited by High-Density and Low-Potential Plasma Technique Using Hydrogen Radicals

As a novel direct deposition method of microcrystalline silicon, we have developed the high-density and low-potential plasma-enhanced silane generating chemical vapor deposition (CVD) system. We have studied a two-step deposition process which consists of the silicon nucleation step using atomic hydrogen (radicals) and the microcrystalline growth step using silane plasmas at low temperature. Transmission electron microscopy (TEM) and micro-ultraviolet Raman spectrometry (UV-Raman) analyses reveal that silicon films crystallize with a low defect density starting from the interface between the SiO2 substrate and the film. Furthermore, the electron mobility determined on the basis of the TFT characteristics indicates that this method is highly effective for the direct deposition of microcrystalline silicon.

Effect of grain size on degradation of Pt/PLZT/Pt capacitor

Abstract The effect of grain size on electric properties has been investigated. Various (111) oriented PLZT films were prepared using the RF magnetron sputtering method on Pt/Ti/SiO2/Si substrates. Grain size and surface roughness were observed by AFM. The results showed that; 1) surface roughness depends on average grain size and 2) decreasing grain size decreases process degradation and fatigue. The grain boundary was thought to be responsible for process damage, such as reduction by hydrogen, at electrode interface tops. Electric field strength at grain boundaries also increased with increases in surface roughness.

Influences of intermediate Si-Ni thin film conditions on adhesion of Ni-TiN gradient thick films

The influences of the intermediate thin film properties, that is internal stress and preferred orientation, on the adhesion of thick film were studied. The intermediate layers were designed Si and Ni multilayer structures, which were formed by the ion beam and vapor deposition method. Si films were prepared by evaporation of Si and simultaneous irradiation with Ar ions on to WC-Co substrates after surface cleaning by Ar ion beam irradiation. After the preparation of Si films, Ni films were also prepared by evaporation of Ni and Ar ion irradiation simultaneously. The internal stresses and preferred orientations of both films were controlled by changing the ion beam energy. Ni-TiN gradient thick films were formed on to these Si-Ni multilayer films by the cathodic arc ion plating method. It was found that the improvements of the internal stress and the preferred orientation conformities at the interface between the intermediate films and the thick films were important factors for high adhesion of thick film. The Ni-TiN gradient thick film reached a thickness of 600 μm with an adhesion high enough for practical use.