Shinichi Urabe

Tunneling Current through Ultrathin Silicon Dioxide Films under Light Exposure

Tunneling current through ultrathin silicon dioxide films with a thickness of approximately 3.1 nm, formed on n-Si (100) by controlling preoxide growth during heating, is examined using Al/oxide/n-Si structures. Electron tunneling current through the oxide from n-Si to Al is decreased and the dielectric breakdown voltage is increased by the preoxide growth control. Electron tunneling current from Al to n-Si is increased by light exposure. The increase in electron tunneling current can be explained by the increase in oxide voltage with an inversion layer formed by photoexcitation.

Metal-Insulator-Gap-Insulator-Semiconductor structure for Biological Sensors

A metal-insulator-gap-insulator-semiconductor sensing device has been characterized in different pH solutions and with different single strand DNA solutions by capacitance-voltage measurements. The capacitance-voltage curves show the difference from pH and the difference from DNA base by hysteresis and flat band voltage shift due to mobile ionic charge in the solution. As the pH decreases, the flat band voltage shift increases in the pH range of 2.7 to 7.0. The hysteresis in the capacitance-voltage curves shows the influence of ionic charge in the solutions and the change of the sensing surface condition. The difference of the flat band voltage shift in the capacitance-voltage curves is related to the mobile ionic charge in the solutions due to pH or DNA molecules.

Reaction of Hydrogen-Desorbed Si(100) Surfaces with Water during Heating and Cooling

The reaction of hydrogen-terminated Si(100) surfaces with water during heating is analyzed using a combination of heating and cooling in thermal desorption spectroscopy. The reaction of the Si surface with water after hydrogen desorption is observed even at about 400°C at a low concentration of water molecules. An estimation method of surface hydrogen coverage by the combined measurement is proposed and the surface coverage as a function of temperature is estimated for quantitative understanding of hydrogen desorption and the subsequent reaction during heating. The combined measurement in thermal desorption spectroscopy is useful for revealing the reaction after hydrogen desorption during heating and for estimating the surface coverage.

Characterization of Tunneling Current through Ultrathin Silicon Dioxide Films by Different-Metal Gates Method

The tunneling currents through ultrathin silicon dioxide films from metal to silicon in the oxide thickness regime between 1.4 and 3.5 nm are characterized using different-metal gates. The energy barrier heights and the effective mass of the silicon dioxide films are determined by the curve fitting of the data calculated by the transfer matrix method with current density–oxide voltage characteristics of metal–oxide–semiconductor (MOS) diodes with aluminum or gold gates. As the oxide thickness decreases, the energy barrier height decreases and the effective mass of the silicon dioxide film increases. The difference in the energy barrier heights between aluminum–oxide and gold–oxide interfaces nearly corresponds to the flatband voltage difference multiplied by the electron charge in the capacitance–voltage curves between MOS diodes with aluminum and gold gates. This makes it possible to precisely characterize tunneling currents by a new different-metal gates method for individually determining the energy barrier heights and the effective mass using the height difference obtained from the flatband voltage difference.

Reaction of Hydrogen-Terminated Si(100) Surfaces with Oxygen at Very Low Pressures during Heating

Reactions of hydrogen-terminated Si(100) surfaces with oxygen at very low pressures during heating are characterized by a method that combines heating and cooling in thermal desorption spectroscopy. Surface hydrogen coverage as a function of temperature is estimated from the hydrogen desorption spectrum obtained by the combination measurement. The surface coverage under the condition with or without introducing oxygen gas indicates that the hydrogen of silicon monohydride begins to desorb after almost half the hydrogen of silicon dihydride desorbs. The hydrogen desorption behavior under the introduction of oxygen gas suggests that bonding between Si and hydrogen atoms for silicon monohydride at the Si(100) surface is stabilized by adsorption of oxygen atoms on surface Si back bond sites during heating.

Tunneling current through ultra-thin silicon dioxide films formed by controlling preoxide in heating-up

With the down-scaling of metal-oxide-semiconductor field effect transistors (MOSFETs), the gate oxide thickness becomes extremely thin. Ultrathin silicon dioxide films with high electric insulating performance and high reliability are demanded in order to realize ultra-small MOSFETs for large scale integration (LSI) chips. The influence of a preoxide grown during silicon wafer heating up to thermal oxidation temperature on the dielectric performance cannot be neglected as the gate oxide becomes thin. Thick preoxides in ultrathin gate oxide films can induce degradation of the electric insulating performance. In this study, we have investigated the influence of the preoxide on the dielectric characteristics and have examined the characteristics of silicon dioxide films with thicknesses of 1-3 nm.