Shoji Den

Initial growth process of carbon nanowalls synthesized by radical injection plasma-enhanced chemical vapor deposition

We synthesized carbon nanowalls (CNWs) using radical injection plasma-enhanced chemical vapor deposition. The initial growth process of CNWs was investigated with and without O2 gas addition to a C2F6 capacitively coupled plasma with H radical injection. In the case of the CNW synthesis without the addition of O2 gas, scanning electron microscopy (SEM), transmission electron microscopy, x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy revealed that a 10-nm-thick interface layer composed of nanoislands was formed on a Si substrate approximately 1 min prior to CNW formation. In contrast, with O2 gas addition, SEM and XPS revealed that an interface layer was not formed and that CNWs were grown directly from nanoislands. Moreover, Raman spectroscopy suggested that the interface layer was composed of amorphous carbon and that O2 gas addition during CNW growth is effective for achieving a high graphitization of CNWs. Therefore, O2 gas addition has the effect of reducing the amorphicity and disorde...

Highly reliable growth process of carbon nanowalls using radical injection plasma-enhanced chemical vapor deposition

Two-dimensional carbon nanostructures, carbon nanowalls (CNWs), were fabricated on a Si substrate using radical injection plasma-enhanced chemical vapor deposition, employing fluorocarbon (C2F6) and hydrogen (H2) mixtures. The influence of the surface conditions of the chamber wall on CNW growth was investigated in order to determine the optimum conditions for CNW growth with high stability and reproducibility. In order to monitor the surface conditions of the chamber wall, optical emission spectroscopy in the plasma was measured, and the correlation between CNW growth and the surface conditions in the chamber wall was investigated. The growth rate and morphology of grown CNWs were determined to be influenced by the surface conditions of the chamber wall. Furthermore, O2 plasma chamber cleaning followed by predeposition for passivation was found to be effective for maintaining steady conditions to attain CNWs with high reproducibility.

Development of atomic radical monitoring probe and its application to spatial distribution measurements of H and O atomic radical densities in radical-based plasma processing

Atomic radicals such as hydrogen (H) and oxygen (O) play important roles in process plasmas. In a previous study, we developed a system for measuring the absolute density of H, O, nitrogen, and carbon atoms in plasmas using vacuum ultraviolet absorption spectroscopy (VUVAS) with a compact light source using an atmospheric pressure microplasma [microdischarge hollow cathode lamp (MHCL)]. In this study, we developed a monitoring probe for atomic radicals employing the VUVAS with the MHCL. The probe size was 2.7 mm in diameter. Using this probe, only a single port needs to be accessed for radical density measurements. We successfully measured the spatial distribution of the absolute densities of H and O atomic radicals in a radical-based plasma processing system by moving the probe along the radial direction of the chamber. This probe allows convenient analysis of atomic radical densities to be carried out for any type of process plasma at any time. We refer to this probe as a ubiquitous monitoring probe for atomic radicals.

Ultrahigh-speed etching of SiO2 with ultrahigh selectivity over Si in microwave-excited non equilibrium atmospheric pressure plasma

Etching of a SiO2 film [Boro-phospho silicate glass (BPSG)] has been performed in a continuous-wave microwave-excited nonequilibrium atmospheric pressure plasma using a microgap discharge. A NF3∕He gas mixture with added H2O was employed as the feed gas. An ultrahigh etch rate for SiO2 (BPSG) of 14μm∕min and an ultrahigh selectivity over Si(SiO2∕Si) of 200 was obtained. A mechanism for the selective etching is proposed based on results obtained using Fourier transform infrared spectroscopy and spatially imaged optical emission spectroscopy with an intensified charge-coupled device camera. This process could offer a breakthrough for ultrahigh-speed, damage-free micromachining of SiO2 in microelectromechanical system devices.

Development and Applications of a Compact Electron Cyclotron Resonance Source

A new compact ECR plasma source has been developed. The characteristics of this source and its applications are discussed. Irradiation by oxygen radicals O* for the oxidation during deposition process was found to produce high quality superconducting thin films with increased characteristic temperatures. Hydrogen radical H* beam cleaning of GaAs substrate surfaces was achieved at temperatures as low as 100°C.

Ultrahigh-speed etching of organic films using microwave-excited nonequilibrium atmospheric-pressure plasma

An ultrahigh etch rate (24μm∕min at 155°C and 0.3mm∕min at 325°C) of an organic film was successfully achieved using a microwave-excited nonequilibrium atmospheric-pressure plasma source employing He and O2 gases. This has the potential to be applied to various kinds of fabrication of structures for microelectromechanical systems and bionanotechnology. A stable glow discharge was realized between the narrow gap (200μm) electrodes covered with a dielectric film in atmospheric pressure. The etching characteristics were investigated by changing the O2 flow rate and the distance of the substrate from the electrode. In order to clarify the ultrahigh etching mechanism, in situ diagnostic methods, including two-dimensional imaging of optical emissions in the plasma with an intensified charge-coupled device camera, electron-density evaluation using the Stark-broadened profile of the hydrogen Balmer beta line in optical emission spectroscopy, and two dimensional spatial distribution of ozone density measured with ...

A large-area ECR processing plasma

This paper describes an improved large-diameter electron cyclotron resonance (ECR) source which employs a strip-bar antenna. By launching a 2.45 GHz microwave near the magnetic field of permanent magnets of alternative polarity set along closed loops, an ECR plasma is produced. The source diameter is 30 cm. The characteristics of an oxygen plasma produced with this modified source are an electron density of , electron temperature of 3 eV and space potential with respect to the chamber wall of less than 20 V. A high plasma density of uniformity within % over 30 cm is achieved.

Etching process of silicon dioxide with nonequilibrium atmospheric pressure plasma

An ultrahigh etch rate (14μm∕min) of SiO2 and a high selectivity of SiO2∕Si over 200 were achieved using a microwave-excited nonequilibrium atmospheric pressure plasma source employing He, NF3, and H2O gases, which have been developed for application to microelectromechanical systems and other bionanotechnology fields. In order to clarify the etching mechanism, two diagnostic methods have been performed: (1) imaging of plasma emission with an intensified charge-coupled device camera, and (2) absorption measurements using Fourier transform infrared spectroscopy. The etching characteristics are discussed in relation to the spatial distributions of the species involved. The etch rate depended considerably on the distance between the plasma and the substrate. Some radicals generated from the feed gases reached the substrate directly, while other radicals recombined into different species, which reached the substrate. An abundance of HF molecules were produced through a reaction between radicals generated by t...

The Irradiation Effects of an Oxygen Radical Beam on the Preparation of Superconducting Thin Films

Irradiation using oxygen radicals O* and ions O2+ from an active ECR oxygen plasma source has been applied to the preparation of Y-Ba-Cu-O superconducting films. Irradiation by oxygen radicals O* was found to drastically improve the films characteristics over those prepared in the presence of oxygen ions O2+. This effect is considered to be as a result of enhanced and damage-less surface interactions due to oxygen radicals.

Influence on Selective SiO2/Si Etching of Carbon-Atoms Produced by CH4 Addition to a C4F8 Permanent-Magnet Electron-Cyclotron-Resonance Etching Plasma

Changes in the densities of fluorocarbon radicals and fluorine atoms in a size-scalable large-area compact permanent magnet electron cyclotron resonance etching plasma source employing C4F8 gas with CH4 addition have been investigated. Measurements using infrared laser absorption spectroscopy and actinometric optical emission spectroscopy show that, for a pure C4F8 plasma, the dominant species is CF2 radicals with a density of the order of 1013 cm−3, followed by fluorine atoms, CF3 and CF2 radicals which have a density an order of magnitude lower at 1012 cm−3. The densities of the different fluorocarbon radical species were found to display different dependencies on increasing CH4 gas addition. Hollow cathode absorption spectroscopy was used to estimate the carbon atom density for the first time, to the best of our knowledge, in an etching plasma. The carbon atom density in the plasma increases linearly with CH4 gas addition between 20 and 80%. Analysis of actual SiO2/Si etching revealed that the etch sel...