Yoshitaka Iwasaki

Low-Temperature and Low-Activation-Energy Process for the Gate Oxidation of Si Substrates.

A low-temperature and low-activation-energy process for the gate oxidation of Si substrates has been proposed. Using the energy-controlled excited oxygen generated in rare-gas and O2 molecule mixture plasma, the enhancement of the oxidation rates was achieved. In addition, the oxidation rates and kinetics drastically change with the type of mixed rare gas in the plasma. Using Kr as the mixed rare gas, the interface trap density near the mid gap [Dit(mid)] of the SiO2/Si interface grown at 500°C was 2.6×1011/cm2/eV, which was comparable to that of the as-grown one using conventional thermal oxidation at a higher temperature. For this process, the oxidation rates were shown to be hardly dependent on the substrate temperature, and the activation energy of B, which is the parabolic rate constant, was found to be low, 0.14 eV.

Characterization of Pb(Zr, Ti)O3 Thin Films on Si Substrates Using MgO Intermediate Layer for Metal/Ferroelectric/Insulator/Semiconductor Field Effect Transistor Devices

Pb(Zr, Ti)O3(PZT)/MgO/Si(001) stacked structures, one of the potential components of ferroelectric-gate field effect trnsistors, have been fabricated and characterized. According to the electrical characterization of MgO/Si structures, MgO thin films prepared on Si substrates at a low growth rate showed a small leakage current of ~10-8 A/cm2 order in an electric field of 1 MV/cm. In C-V measurements of as-grown MgO/Si interfaces, injection-type hysteresis was observed because of crystal defects in the MgO film adjacent to the interface. After oxygen annealing at 400°C, however, it showed no hysteresis and a low interface trap density of the order of 1011 cm-2eV-1 was achieved with no formation of a low-dielectric layer at the MgO/Si interface. These results indicate that MgO thin films are applicable as gate insulators of FETs. After a PZT film was deposited on the MgO/Si structure, the C-V characteristic of the stacked structure showed a ferroelectric hysteresis curve and a low interface trap density of 5×1011 cm-2eV-1. A maximum memory window width of 1.2 V was obtained for the PZT thin film on Si substrate with a MgO intermediate layer.

Complex Nature of Acceptor Levels in Aluminum Gallium Nitrides Doped with Magnesium

Frequency (ω) dependent conductance (G) has been measured of the reverse-biased blue and green light-emitting diodes consisting of nitride semiconductors, in order to study the electronic behavior of the Mg acceptor in metalorganic chemical vapor deposition grown p-Al0.2Ga0.8N. Four peaks with activation energies of 14, 63, 115, and 166 meV were found in the G/ω vs ω characteristics of the diodes. Although these activation energies do not correspond directly to the energy depths above the valence band edge, it is likely that they reflect the complex electronic structure of the Mg acceptor levels.

Application of high-intensity vacuum ultraviolet light for amorphous silicon film fabrication using a windowless photochemical vapor deposition system☆

Abstract Windowless photochemical vapor deposition (photo-CVD) system for hydrogenated amorphous silicon (a-Si:H) film fabrication has been established. Vacuum ultraviolet (VUV) light with a wavelength of 121.6 nm (a Rydberg transition of the hydrogen atom) was obtained using microwave discharge in active medium, i.e., a mixture of helium and hydrogen. The maximum intensity of 121.6 nm VUV light was achieved at a mixing ratio of helium to hydrogen of 25:1. A large amount of helium would consume wide distributed energy in the microwave discharge, and energy transfer would occur from the metastable helium to hydrogen molecules. Backward flowing of the source gas into the microwave discharge region was prevented with a large flow rate of the active medium, such as 100 sccm. Using the 121.6 nm VUV light for the direct dissociation of monosilane molecule, a-Si:H film with less silicon-dihydride bondings was deposited.