Akira Wada

Analysis of decomposition process of BrCN with microwave discharge flow of Ar

CN(Xu20092Σ+) radicals were produced from the dissociative excitation reaction of BrCN with the microwave discharge flow of Ar. This plasma reaction was studied by the combined analysis of the laser-induced fluorescence (LIF) and electrostatic-probe measurements. The Ar pressure, PAr, was in the range 0.2–0.5u2009Torr. The absolute densities of CN(Xu20092Σ+) radicals, nCN(X), and that of the metastable state of Ar atoms, nM, were determined by observing the CN(Au20092Πi–Xu20092Σ+) and Ar(3P1–3P2) transitions, respectively. The temperature, Te, and the density, ne, of free electrons were determined from the electrostatic-probe measurement. When a trace amount of H2O vapour was introduced into the reaction system, nCN(X), nM, Te and ne were varied. By comparing the decrements of nCN(X), nM and ne upon the addition of H2O vapour into the reaction system, the production process of CN(Xu20092Σ+) was found, predominantly, to be the energy transfer from the metastable state of Ar atoms.

High-quality germanium dioxide thin films with low interface state density using a direct neutral beam oxidation process

High-quality germanium dioxide (GeO2) as a gate oxide is in high demand for use in future high mobility Ge-channel field-effect transistors. GeO2 thin films were directly formed by using a damage-free and low-temperature process of neutral beam oxidation (NBO) after treatment with hydrogen (H) radicals. GeO2 thin films (equivalent oxide thickness (EOT)u2009=u20091.7u2009nm) with a high-quality interface and an extremely low interface state density (<1u2009×u20091011u2009cm−2u2009eV−1) could be formed even at low temperature (300u2009°C) by combining the H radical treatment, which resulted in the removal of native oxides, with the NBO process we developed.

High-Performance Three-Terminal Fin Field-Effect Transistors Fabricated by a Combination of Damage-Free Neutral-Beam Etching and Neutral-Beam Oxidation

Three-terminal fin field-effect transistors (3T-FinFETs) were fabricated by neutral-beam oxidation (NBO) to form gate silicon dioxide (SiO2). The 3T-FinFET fabricated by NBO showed higher device performance – namely, a higher subthreshold slope and a higher effective mobility – than that fabricated by conventional thermal oxidation. It is considered that those improved subthreshold slope and mobility are due to the fact that the three-dimensional structure of a SiO2 film fabricated by NBO has a lower interfacial state density and a lower roughness than a similar structure fabricated by the conventional thermal oxidation of a SiO2 film. The reasons for the lower interfacial state density and lower roughness are the low temperature and lattice plane independence of NBO in comparison with conventional thermal oxidation processes.

Structural Changes in Diamond-Like Carbon Films Fabricated by Ga Focused-Ion-Beam-Assisted Deposition Caused by Annealing

The desorption processes of H and Ga from diamond-like carbon (DLC) film synthesized by focused-ion-beam chemical vapor deposition (FIB-CVD) were investigated by elementary analysis and local structure analysis after heat treatment under various conditions. The elementary composition of FIB-CVD DLC film was determined using a combination of Rutherford backscattering spectra and elastic recoil detection analysis spectra. Local structure analysis was performed by the measurement of near-edge X-ray absorption fine structure using synchrotron radiation. Desorption of H from FIB-CVD DLC film by heat treatment was found to comprise two types of process. One is the local graphitization along paths, where residual Ga atoms move by annealing. In this process, Ga acts as a catalyst for the graphitization of DLC. The other process is derived from the graphitization of the whole DLC film by heat, regardless of Ga. In this process, the sp2 content increases considerably.

Comprehensive Classification of Near-Edge X-ray Absorption Fine Structure Spectra of Si-Containing Diamond-Like Carbon Thin Films

Structural analysis by the measurement of carbon K-edge near-edge X-ray absorption fine structure (NEXAFS) using synchrotron radiation was performed on 23 types of silicon-containing diamond-like carbon (Si-DLC) film fabricated by various synthesis methods. In addition, elementary composition in the Si-DLC films was determined by the combination of Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA) using an electrostatic accelerator. In the C K-edge NEXAFS spectra of Si-DLC films, the σ* band shrunk and shifted to the lower-energy side, and the π* peak broadened with increasing silicon content in the Si-DLC film. The observed NEXAFS spectra of Si-DLC films were classified into four types.

Sticking probability of CN(X2Σ+) radicals onto amorphous carbon nitride films formed from the decomposition of BrCN induced by the microwave discharge flow of Ar

The sticking probability, s, of CN(X(2)Σ(+)) radicals onto amorphous carbon nitride (a-CN(x)) films with high [N]/([N]+[C]) ratios (≤0.5) was evaluated. CN(X(2)Σ(+)) radicals were generated from the decomposition of BrCN with the microwave discharge flow of Ar in the two experimental configurations, I and II, where the distance between the tip of the nozzle introducing BrCN is close (≈10 mm) to and distant (≈0.3 m) from the laser-beam path or the Si substrate, respectively. For each configuration, s was evaluated both under the desiccated and H(2)O-added conditions from the number density of CN(X(2)Σ(+)) evaluated from the intensity of the CN(A(2)Π(i)-X(2)Σ(+)) laser-induced fluorescence spectrum calibrated against Rayleigh scattering intensity of Ar, the flow speed measured by a time-resolved emission, and the film mass. The [N]/([N]+[C]) ratios of films were evaluated as 0.4-0.5 and 0.3 in the configurations I and II, respectively, from the compositional analysis using Rutherford back scattering and elastic recoil detection analysis together with the XPS analysis. The variation of s under various experimental conditions was discussed based on the electron densities in the reaction region and the relative density of the hydrogen-termination structures of the film surface.

Annealing Effect of W Incorporated Diamond-Like Carbon Fabricated by Ga Focused Ion Beam Chemical Vapor Deposition

The effects of thermal annealing of W incorporated diamond-like carbon (W-DLC) films fabricated with focused ion beam chemical vapor deposition (FIB-CVD) were investigated using X-ray absorption fine structure near the carbon K-edge (C-K NEXAFS) and the combination of Rutherford backscattering (RBS) and elastic recoil detection analysis (ERDA). W-DLC films were annealed for 32 h at temperatures, Ta, between 673 and 1073 K. Comparing the Ta dependences of Ga and H contents obtained from RBS-ERDA and the sp2/(sp2 + sp3) ratios from C-K NEXAFS, it was found that even a trace amount of W incorporation into DLC films fabricated by Ga+ FIB-CVD may cause a significant sp3 →sp2 structural change.

Supercontinuum generation using a selectively water-filled photonic crystal fiber for enhancement in the visible spectral region

We generated a supercontinuum from a selectively water-filled photonic crystal fiber (PCF) for enhancement in the visible spectral region using an optical pulse from a Ti:sapphire oscillator at 804 nm. We prepared a 7-cm-long fused silica PCF, where the holes adjacent to the central core were filled with water, using a UV-curable adhesive to close holes selectively before filling holes with water by capillary force. Compared with that of the PCF without water, the group velocity dispersion curve of the selectively water-filled PCF became flatter near 800 nm and the intensity in the visible spectral region of the supercontinuum became higher and more uniform. The spectra simulated using the calculated dispersion properties of the selectively water-filled PCF showed good agreement with the experimental spectra.

Mechanism of Production of CN(X2Σ+) Radicals from the Decomposition Reaction of CH3CN with Microwave Discharge Flow of Ar

AbstractnCN(X2Σ+) radicals were produced from the dissociative excitation reaction of CH3CN with the microwave discharge flow of Ar. The mechanism of the production of these radicals was studied on the basis of a combined analysis of the laser-induced fluorescence (LIF) and electrostatic-probe measurements. The densities of CN(X2Σ+) and the metastable states of Ar, Ar(3P0,2), were determined by observing the LIF spectra of the CN(A2Πi–X2Σ+), Ar(3P1–3P2), and Ar(3P1–3P0) transitions. A chemical–kinetic analysis of the above densities together with the temperature and the density of free electrons was carried out to elucidate that the dominant mechanism of the production of CN(X2Σ+) is the energy transfer from Ar(3P0,2). The rate constant of the production of CN(X2Σ+) is determined to be (4.6xa0±xa00.4)xa0×xa010−17xa0m3xa0molecule−1xa0s−1. Based on the results of the present and our previous studies (Ito et al. in Diam Relat Mater 24:121–125, 2012) , a quantitative description was made on the incorporation of N atoms into hydrogenated amorphous carbon nitride films formed in the present reaction system.

Super-Low-k SiOCH Film with Sufficient Film Modulus and High Thermal Stability Formed by Using Admixture Precursor in Neutral-Beam-Enhanced Chemical Vapor Deposition

To fabricate a low-k-value interconnect film with a sufficient modulus and high thermal stability, we investigated using an admixture precursor (dimethoxytetramethyldisiloxane and methyltrimethoxysilane) in a neutral beam enhanced chemical vapor deposition (NBECVD) process. It was possible to precisely control the film properties because the NBECVD process can precisely control the molecular level structures, such as the composition ratio of linear and network/cage Si–O structures, by changing the precursor mixture ratio. Experimental results showed that the SiOCH low-k film had a super-low k-value of less than 2.1 and a sufficient modulus of more than 6 GPa. A high thermal stability was also achieved by stacking a 20-nm-thick methyltrimethoxysilane (MTMOS) cap layer on the NBECVD super-low-k film.