Toshihiko Nishimori

n-type high-conductive epitaxial diamond film prepared by gas source molecular beam epitaxy with methane and tri-n-butylphosphine

An n-type phosphorous (P) doped epitaxial diamond film with high conductivity was grown on a C(001) substrate by gas source molecular beam epitaxy using methane and tri-n-butylphosphine. The electrical conductivity of the diamond film was measured to be 0.33 (Ω cm)−1 at 23 °C with its activation energy to be 0.12 eV. The Hall measurements showed n-type conduction and a carrier concentration of 1.6×1018 cm−3 at 400 °C, which is comparable to the P concentration determined by secondary-ion-mass spectroscopy. These indicate the formation of shallow P donors with high electrical activation efficiency. A p-n junction diode was fabricated by growing a P-doped epitaxial film on a boron-doped C(001) substrate, which showed for the first time a rectification ratio of ∼103 at 10 V.

Photoelectron intensity oscillation during chemical vapor deposition on Si(100) surface with Si2H6

We have found that the photoelectron intensity of the dimer‐dangling‐bond‐derived surface state on Si(100) shows a periodic oscillation during chemical vapor deposition with Si2H6 gas. The substrate temperature and Si2H6‐pressure dependence of the oscillation period was measured. By use of a selective‐growth method using SiO2‐patterned wafers, one oscillation period was clarified to correspond to the Si growth of one atomic layer of the Si(100) plane with a thickness of 1.36 A.

Methane adsorption and hydrogen isothermal desorption kinetics on a C(001)–(1×1) surface

Methane (CH4) adsorption and isothermal hydrogen (H2) desorption kinetics on a C(001)–(1×1) surface have been investigated by observing the surface hydrogen coverage θH which is estimated from the electron‐stimulated desorption yield of H+ ions. The time evolution of θH under CH4 exposure, in pressure and temperature ranges of 1×10−8–5×10−7 Torr and 600–800 °C, reveals that the CH4 adsorption is a first‐order reaction. The isothermal H2 desorption is conducted in a temperature range of 1095–1270 °C. The time evolution of θH shows that the isothermal H2 desorption is also a first‐order reaction. From Arrhenius plots of the reaction coefficients, the activation energies of CH4 adsorption and H2 desorption are evaluated to be 7.3±1.7 and 21±4.9 kcal/mol, respectively. Atomistic kinetics model for CH4 adsorption and H2 desorption are discussed, especially in connection with a recent finding of gas source molecular beam epitaxy of diamond (001) with pure CH4 without any hydrogen or oxygen radicals.

Diamond Epitaxial Growth by Gas-Source Molecular Beam Epitaxy with Pure Methane

Diamond epitaxial films with a thickness of 200-350 A have been successfully grown on C(100) surfaces by gas-source molecular beam epitaxy (GSMBE) with methane without addition of hydrogen or oxygen. The activation energy was measured by a selective growth method using Ta-patterned substrates to be 15 kcal/mol. This value is close to the activation energy of H2 desorption on C(100), suggesting that the diamond epitaxial growth rate by this GSMBE is limited by hydrogen desorption.

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.

Crystallinity evaluation of phosphorus-doped n-type diamond thin film

The crystallinity of a phosphorus-doped n-type diamond thin film as grown on a C(001) substrate by gas source molecular beam epitaxy has been examined by x-ray photoelectron diffraction (XPD) and atomic force microscopy (AFM). AFM showed that the growth mode of the n-type film is not an island-growth type that hinders the application of XPD. C 1s XPD patterns for the n-type film and the substrate showed almost perfect similarity. This proves that, like the substrate, the phosphorus-doped n-type thin film is in a good diamond structure.