Yuzuru Ogura

Multilayer coating for carbon-carbon composites

Abstract Because of the excellent mechanical properties at elevated temperature, carbon-fiber reinforced carbon (carbon-carbon) composites have received much attention for high-temperature structural applications. One serious drawback against actual use of carbon-carbon composites is their poor oxidation resistance in high-temperature oxidizing atmospheres. In many attempts to develop an effective oxidation-protection coating, silicon carbide coating has shown the best performance for short periods of up to 1900 K. For longer periods and higher temperature applications, a challenging coating system should be developed. There exist certain difficulties in establishing a new coating system, such as coefficients of thermal expansion (CTE) mismatch between coating layer and carbon-carbon composites, and chemical stability of the interface. This paper describes a basic idea for a new multilayer coating system, the candidate materials for each coating layer, and the characteristics of the new coating system.

Mass Spectrometric Study of Oxidation of SiC in Low-Pressure Oxygen

Passive-to-active oxidation transitions in chemical vapor deposited (CVD) SiC under low total pressures (0.8-440 Pa) in the temperature range 1250-1700°C have been investigated. A mass spectrometer sampling system equipped with a xenon image furnace was used to detect the transition points. As the temperature increased under fixed oxygen pressure, the ion current at m/e 28, which corresponds to the partial pressure of CO(g) on the surface of CVD-SiC samples, indicated two distinct changes in the measured partial pressure of CO(g). One can be assigned to a transition from the passive oxidation to bubble formation and the other can be assigned to a transition from bubble formation to active oxidation. An explanation is proposed based on available kinetic and thermodynamic data for these.

A Method for Copper Film Deposition with Cl2 Plasma

This study introduces a method for copper film growth with Cl 2 plasma. The method consists of two stages: generation of the precursor, CuCl, by etching a bulk copper target, and reduction of CuCl adsorbed on a substrate surface. In both reactions, atomic chlorine (Cl*) generated from the same Cl 2 plasma played the leading role. Copper films were grown on a TaN film (50 nm) adhesively at a growth rate of 118 nm/min. The obtained copper films had a resistivity of 2.0 μΩ cm and a Cl content of less than 15 ppm. This method also makes it possible to fill the 0.1 μm gap with an aspect ratio of 10.

Metal Chloride Reduction Chemical Vapor Deposition for Ta, Mo and Ir Films

Tantalum, molybdenum and iridium thin films are deposited by metal chloride reduction chemical vapor deposition (MCR-CVD) process using Cl2 plasma. In the process, Cl2 plasma, which is generated between a substrate and a metal plate, produces volatile chlorides by chlorination of the metal plate and also acts as a reducing agent. A conformal coverage of the tantalum film on a patterned surface is observed. MCR-CVD using Cl2 plasma is expected to be applied to the deposition of extensive metals, whose chlorides exhibit reasonably high vapor pressures at low temperatures.

Structural Evaluation of Cu Films Grown by Cl2 Plasma

We evaluated the morphology and crystallinity of copper films which were grown by the new chemical vapor deposition (CVD) method with Cl2 plasma using field emission scanning electron microscopy (FESEM) and electron back scattering pattern (EBSP). The obtained films consisted of large grains of 0.5–1 µm size, and filling with high crystallinity was indicated. Moreover, we observed the time evolution of the morphology of the films by FESEM. On the basis of the results, the mechanism of the copper film growth and the bottom-up filling by the new CVD method was discussed.

Low-temperature fabrication of nickel silicide metal oxide semiconductor capacitors at 280 °C by metal chloride reduction chemical vapor deposition

We have successfully fabricated nickel silicide metal–oxide–semiconductor (MOS) capacitors at 280 °C by metal chloride reduction chemical vapor deposition (MCR-CVD). In this process, we first prepared polycrystalline silicon (poly-Si)/SiO2-overcoated Si wafers and exposed the wafers to Cl plasma containing NiCl for 40 min with a substrate temperature of 280 °C. During this process, the top layer of poly-Si is changed to a nickel silicide film with the Ni concentration at approximately 50%. Depth-resolved X-ray photoelectron spectroscopy (XPS) showed a uniform profile of the top film and a sharp interface on the SiO2 surface at such Ni concentration. We have also obtained capacitance–voltage (C–V) characteristics using a MOS capacitor from the processed wafer. We demonstrate the possibility and applicability of MCR-CVD in the near room temperature (RT) fabrication of metal gate MOS capacitors.