Hidehiko Nonaka

High-quality SiO2 film formation by highly concentrated ozone gas at below 600°C

Highly concentrated (>93 vol %) ozone (O3) gas was used to oxidize silicon for obtaining high-quality SiO2 film at low temperature. Compared to O2 oxidation, more than 500 °C lower temperature oxidation (i.e., from 830 to 330 °C) has been enabled for achieving the same SiO2 growth rate. A 6 nm SiO2 film, for example, could be grown at 600 °C within 3 min at 900 Pa O3 atmosphere. The temperature dependence of the oxidation rate is relatively low, giving an activation energy for the parabolic rate constant of 0.32 eV. Furthermore, a 400 °C grown SiO2 film was found to have satisfactory electrical properties with a small interface trap density (5×1010 cm−2/eV) and large breakdown field (14 MV/cm).

Preparation of NdBa2Cu3O7−δ films in ultrahigh vacuum with a NO2 supersonic molecular beam

Superconducting NdBa2Cu3O7−δ thin films have been prepared in ultrahigh vacuum by the molecular beam epitaxy (MBE) method using a supersonic molecular beam of nitrogen dioxide as an oxidizing agent. A new type of supersonic molecular beam source has been developed, which has a liquid nitrogen trap for cryogenic pumping and is small enough in size to be installed in a conventional MBE system. Films with a transition temperature of about 30 K have been obtained in situ without post‐deposition annealing. Throughout deposition epitaxial growth of the films was observed in situ by reflection high‐energy electron diffraction.

Depth resolution improvement in secondary ion mass spectrometry analysis using metal cluster complex ion bombardment

Secondary ion mass spectrometry analyses were carried out using a metal cluster complex ion of Ir4(CO)7+ as a primary ion beam. Depth resolution was evaluated as a function of primary ion species, energy, and incident angle. The depth resolution obtained using cluster ion bombardment was considerably better than that obtained by oxygen ion bombardment under the same experimental condition due to reduction of atomic mixing in the depth. The authors obtained a depth resolution of ∼1nm under 5keV, 45° condition. Depth resolution was degraded by ion-bombardment-induced surface roughness at 5keV with higher incident angles.

Ion-beam characteristics of the metal cluster complex of Ir4(CO)12

Tetrairidium dodecacarbonyl, Ir4(CO)12, is a metal cluster complex which has a molecular weight of 1104.9. Using a metal-cluster-complex ion source, it has been demonstrated that stable ion beams of Ir4(CO)7+ were produced. Energy dependence of sputtering yield of silicon bombarded with Ir4(CO)7+ ions was investigated at a beam energy from 2to10keV at normal incidence. Experimental results showed that the sputtering yield varied substantially with beam energy. The sputtering yield at 10keV was higher than that with SF5+ or Ar+ ions by a factor of 3–24, whereas the sputtering yield at 3keV was lower than that with Ar+ ions. In the case of 2keV, deposition was found to occur. The substantial variation in the sputtering yields was examined using empirical equations for calculating sputtering yields. It was shown that the high sputtering yield at 10keV would be due to what is called “nonlinear effect” unique to complex-projectile bombardment. It was also indicated that the substantial variation in the sputter...

Photochemical vapor deposition of amorphous silica films using disilane and perfluorosilanes: Defect structures and deposition mechanism

Amorphous silicon dioxide films were deposited from oxygen, disilane (Si2H6), and perfluorosilanes (Si2F6 or SiF4) by photochemical vapor deposition using a deuterium lamp at a substrate temperature of as low as 200 °C. It was found that by mixing Si2F6, defects such as H and OH in the films were effectively removed with an enhancement in the growth rate and a slight doping of fluorine into the films, while SiF4 had no effect except a little doping of fluorine. The generation and extinction of defects including H, OH, and SiSi were investigated quantitatively by measuring infrared spectra and vacuum ultraviolet absorptions at the optical band edge. The model on the deposition process was proposed that photodissociated F‐containing radicals eliminate H and activate the growing surface, resulting in enhancing the deposition rate.

Production of Stable Ion Beam of Os3(CO)12 with Compact Metal-Cluster-Complex Ion Source

Metal-cluster-complex ion beams were produced stably using a cluster ion source, which is compact enough to be installed in commonly used secondary ion mass spectrometry (SIMS) systems. As a metal cluster complex, triosmium dodecacarbonyl, Os3(CO)12, was utilized, which has a molecular weight of 906.7. Since precise temperature control is necessary to sublimate the metal cluster complex stably without thermal decomposition, the ion source was equipped with compact heat-removal devices in addition to an external heater. Experimental results showed that the crucible temperature of the metal cluster complex can be maintained at about 130 °C in continuous operation, which is an appropriate temperature for sublimation without the problem of decomposition. The ion source produced steady-state beams of Os3(CO)n+ (n=7 or 8) ions with a beam current exceeding 10 nA at 10 keV. Beam current increased with gas pressure, depending on the temperature of the crucible holding the metal cluster complex. The rate of the change in beam current was within a few percent per hour; hence, in view of stability, the ion source was confirmed as usable in SIMS. Furthermore, beam profile was investigated using a Faraday cup with a knife-edge as well as a GaAs/AlAs multilayer substrate as a beam target.

Growth behavior of YBa2Cu3O7−δ and NdBa2Cu3O7−δ thin films observed by electron diffraction

Growth behavior of thin films of YBa2Cu3O7−δ and NdBa2Cu3O7−δ has been observed in reflection high‐energy electron diffraction (RHEED) during coevaporation of constituent metal atoms with a NO2 supersonic molecular beam. The intensity oscillations of RHEED specular beam have been observed during deposition. The nucleation behavior of NdBa2Cu3O7−δ is found to be different from that of YBa2Cu3O7−δ in RHEED observation.

Secondary Ion Mass Spectrometry of Organic Thin Films Using Metal-Cluster-Complex Ion Source

Tetrairidium dodecacarbonyl, Ir4(CO)12, is a metal cluster complex that has a molecular weight of 1104.9. Using a metal-cluster-complex ion source, secondary ion mass spectrometry (SIMS) of poly(methyl methacrylate) (PMMA) thin films on silicon substrates was performed with a quadrupole mass spectrometer. The secondary ion intensity of PMMA bombarded with Ir4(CO)7+ ions was investigated in the beam energy ranging from 3 to 10 keV at an incident angle of 45°. For comparison, bombardment with oxygen ions, O2+, was also tested. It was confirmed that the use of Ir4(CO)7+ ions enhanced secondary ion intensity by at least one order of magnitude compared with that of O2+ ions. Experimental results also showed that secondary ion intensity increased with beam energy; particularly, high-mass secondary ion intensity markedly increased.

Development of a continuous generation/supply system of highly concentrated ozone gas for low-temperature oxidation process

A system is described which can continuously generate/supply highly concentrated (HC) ozone gas to satisfy the future need for practical low-temperature oxidation. This system comprises four ozone vessels, each with independent temperature control. The system can supply a constant flow of HC ozone gas by allocating one of four modes of operation, i.e., accumulation/storage, vaporization (supply), evacuation, and cooling, to each of the ozone vessels so that all the modes can be simultaneously addressed. The maximum flow rate is 60 sccm with a flux stability of ±1.1%, and an ozone concentration of over 99.5 vol % can be achieved at the system outlet. The system was applied to the formation of an ultrathin SiO2 film on a 4 in. diameter silicon wafer substrate.

Reactive oxygen beam generation system using pulsed laser evaporation of highly concentrated solid ozone

A reactive oxygen beam generation system is described for the formation of high-quality and high-precision films. This system utilizes pulsed laser evaporation of highly concentrated solidified ozone (O3). The equipment for safely generating and handling a large amount of high-purity liquid and solid O3 was also developed for this purpose. The beam is characterized by its high concentration of oxygen atoms in an excited state [O(1D)], constant flux per laser shot (4×1017 molecules cm−2 shot−1), appropriate level of kinetic energy (KE) for enhancing the surface reaction (mean KE of 0.4 eV, maximum KE of 2 eV) and small angular spread (6°). These characteristics enabled us to precisely control the SiO2 film thickness by the number of laser shots, and achieve an enhanced Si oxidation rate and new local oxidation process.