Mizuho Morita

Growth of native oxide on a silicon surface

The control factors controlling the growth of native silicon oxide on silicon (Si) surfaces have been identified. The coexistence of oxygen and water or moisture is required for growth of native oxide both in air and in ultrapure water at room temperature. Layer‐by‐layer growth of native oxide films occurs on Si surfaces exposed to air. Growth of native oxides on n‐Si in ultrapure water is described by a parabolic law, while the native oxide film thickness on n+‐Si in ultrapure water saturates at 10 A. The native oxide growth on n‐Si in ultrapure water is continuously accompanied by a dissolution of Si into the water and degrades the atomic flatness at the oxide‐Si interface, producing a rough oxide surface. A dissolution of Si into the water has not been observed for the Si wafer having surface covered by the native oxide grown in air. Native oxides grown in air and in ultrapure de‐ionized water have been demonstrated experimentally to exhibit remarkable differences such as contact angles of ultrapure wa...

Control factor of native oxide growth on silicon in air or in ultrapure water

Native silicon (Si) oxide growth on Siu2009(100) wafers in air and in ultrapure water at room temperature requires coexistence of water and oxygen in the air and ultrapure water ambients. The growth rate data on n‐, n+‐, and p+‐Siu2009(100) in air indicate layer‐by‐layer growth of an oxide. The growth rate on n‐Siu2009(100) in ultrapure water may be governed by a parabolic law. For native oxide growth in ultrapure water, the number of Si atoms dissolved in ultrapure water is over one order of magnitude larger than the number of Si atoms contained in the grown native oxide film. The structural difference between the native oxide film in air and in ultrapure water is also discussed.

Very thin oxide film on a silicon surface by ultraclean oxidation

Very thin oxide films with a high electrical insulating performance have been grown by controlling preoxide growth using the ultraclean oxidation method. The current level through the ultraclean oxide is lower than that through the conventional dry oxide including thicker preoxide. The barrier height at the silicon‐oxide interface for electrons emission from silicon to oxide for the ultraclean oxide is little decreased as the thickness is thinner, while the barrier height for conventional dry oxide is drastically decreased. The growth rate of ultraclean oxide at 900u2009°C is governed by a simple parabolic law even in the range of 5–20 nm.

Characteristics of the metal insulator semiconductor structure:AlN/Si

Single‐crystal AlN layers have been grown on Si substrates at ∼1200 °C using metalorganic chemical vapor deposition. The metal/AlN/Si MIS structures have been investigated by the MIS conductance method. It was found that the interface‐state density Nss and electron capture cross section σn in the depletion region are of the order of 1011 eV−1 cm−2 and 10−17 cm, respectively.

Oxidation process of hydrogen terminated silicon surface studied by thermal desorption spectroscopy

The oxidation process of hydrogen terminated silicon surface is investigated by thermal desorption spectroscopy (TDS). Oxidation proceeds by two steps, at about 500°C and 800°C, by the desorption of hydrogen and the consumption of oxygen and water. Oxygen and water are consumed simultaneously, but water consumption does not change with oxygen supply. The oxidation process changes by the presence of the native oxide.

Neutralization of wafer charging in nitrogen gas

In an attempt to prevent wafers from getting charged in the N/sub 2/ gas sealed semiconductor manufacturing process, the authors have developed a neutralization method employing ultraviolet (UV) irradiation. This method depends on the fact that the N/sub 2/ molecule is ionized when it absorbs ultraviolet light. This method is superior to the neutralization method employing corona discharge in terms of neutralization capability in the inert gas ambient. The neutralization rate is very high; the residual potential caused by the unbalanced ion distribution is always 0 V after the neutralization. Neutralization is rapid. The neutralization capability is enhanced by decreasing the ambient pressure. The neutralization capability is further enhanced by replacing the N/sub 2/ gas ambient with the Ar gas ambient. >

Preoxide-Controlled Oxidation for Very Thin Oxide Films

Very thin oxide films with high insulating performance and high reliability are formed by controlling preoxide growth with an ultraclean oxidation method during heating of the wafer to thermal oxidation temperature. The current level through the preoxide-controlled ultraclean oxide is lower than that through the oxide incorporating a thicker preoxide, and the preoxide-controlled ultraclean oxide has high reliability with respect to hot electron injection.

High‐rate growth at low temperatures by free‐jet molecular flow: Surface‐reaction film‐formation technology

Surface‐reaction film‐formation technology of epitaxial Si and polcrystalline silicon using free‐jet molecular flow is proposed. High‐rate (∼0.5 μm/min or higher) growth of homoepitaxial Si films with high crystallographic perfection has been achieved at temperatures as low as 600u2009°C without the chemical by‐product deposition on the inner surface of the reaction chamber. This result also implies that this system has the cleaning‐free function. The film‐formation mechanism appears to be dominated by the chemical reaction on the substrate surface without the vapor phase reaction.

Measurement of interface-state parameters near the band edge at the Si/SiO2 interface by the conductance method

The interface‐state parameters near the band edge at the Si/SiO2 interface were measured using the MOS conductance method with the reflection technique, extending the frequency up to 100 MHz. The double peaks were observed in the conductance‐vs‐frequency curves. The decrease of the capture cross section toward the band edge was found due to the overlap of the double peaks. The new peak at higher frequencies suggests the existence of new interface states, which has been overlooked so far.

Gate oxide reliability concerns in gate-metal sputtering deposition process: an effect of low-energy large-mass ion bombardment

Abstract The effects of ion species/ion bombardment energy in sputtering deposition process on gate oxide reliability have been experimentally investigated. The use of xenon (Xe) plasma instead of argon (Ar) plasma in tantalum (Ta) film sputtering deposition for gate electrode formation makes it possible to minimize the plasma-induced gate oxide damage. The Xe plasma process exhibits 1.5 times higher breakdown field and five times higher 50%-charge-to-breakdown ( Q BD ). In the gate-metal sputtering deposition process, the physical bombardment of energetic ion causes to generate hole traps in gate oxide, resulting in the lower gate oxide reliability. The simplified model providing a better understanding of the empirical relation between the gate oxide damage and the ion-bombardment energy to gate oxide in gate-metal sputtering deposition process is also presented.