Yuichi Setsuhara

Development of internal-antenna-driven large-area RF plasma sources using multiple low-inductance antenna units

Abstract Large-area and high-density radio frequency (RF) plasmas at 13.56 MHz have been produced by inductive coupling of internal-type low-inductance antenna units. The present study has been carried out to develop the basic discharge techniques which can be applied to production of meter-scale large-area and/or large-volume plasma sources with high density for a variety of plasma processes. The plasma source could be operated stably to attain plasma density as high as 1×1012 cm−3 at argon pressures of approximately 1 Pa. It has been demonstrated that high plasma density can be obtained efficiently using the low-inductance internal antenna configuration with effectively suppressed electrostatic coupling. Discharge experiments in a meter-scale chamber demonstrated uniform plasma production with densities as high as 6×1011 cm−3 at an argon pressure of 1.3 Pa and a RF power of 4 kW.

Structure refinement and hardness enhancement of titanium nitride films by addition of copper

Abstract Titanium nitride films with a low added copper content were synthesized by ion beam-assisted sputtering deposition. The role of copper was examined with regard to the structure, hardness and elastic/plastic deformation capacity of the composite films produced. It was found that copper had significant modifying effects on the structure and property of titanium nitride films. When a very low content of Cu ( 2 at.% copper were comparatively soft, up to 53% of the deformation under indentation could be plastic in this case. In addition, copper additions could also be used to tune the grain size of TiN in the range of 25–5 nm, at the same time causing a transition from a strong (111) preferred orientation to random polycrystalline morphology.

Reactive magnetron sputtering of hard Si-B-C-N films with a high-temperature oxidation resistance

Based on the results obtained for C–N and Si–C–N films, a systematic investigation of reactive magnetron sputtering of hard quaternary Si–B–C–N materials has been carried out. The Si–B–C–N films were deposited on p-type Si(100) substrates by dc magnetron co-sputtering using a single C–Si–B target (at a fixed 20% boron fraction in the target erosion area) in nitrogen-argon gas mixtures. Elemental compositions of the films, their surface bonding structure and mechanical properties, together with their oxidation resistance in air, were controlled by the Si fraction (5–75%) in the magnetron target erosion area, the Ar fraction (0–75%) in the gas mixture, the rf induced negative substrate bias voltage (from a floating potential to −500V) and the substrate temperature (180–350°C). The total pressure and the discharge current on the magnetron target were held constant at 0.5Pa and 1A, respectively. The energy and flux of ions bombarding the growing films were determined on the basis of the discharge characterist...

Production of Inductively-Coupled Large-Diameter Plasmas with Internal Antenna

Large-diameter RF plasmas at 13.56 MHz have been produced by inductive coupling of an internal-type antenna in a discharge chamber of 400 mm diameter and 200 mm height. For minimization of the electrostatic coupling, (i) a double half-loop antenna of 360 mm diameter was employed for the reduction of antenna inductance and (ii) the antenna conductor was terminated by the insertion of a blocking capacitor to satisfy the impedance balance condition where the RF-voltage amplitude could be minimized to 1/2 the terminal voltage. The plasma source could be operated stably at RF input powers of up to 3 kW to attain plasma densities as high as 1012 cm-3 at Ar pressures around 1 Pa. Furthermore, (iii) full covering of the antenna conductor with an insulator tubing exhibited a significant effect on the suppression of the electrostatic coupling with simultaneous achievement of plasma densities as high as 5×1011 cm-3.

Improved anti-wear performance of nanostructured titanium boron nitride coatings

Abstract Titanium boron nitride coatings were synthesized by ion beam assisted sputter deposition. Structural analysis showed that the coatings had a composite structure comprising nanosized TiB 2 /TiN crystallites and a thin layer matrix of hexagonal BN. Although, the hardness of these Ti–B–N coatings was generally lower than that of pure TiB 2 , improved anti-wear performance was observed. This improvement is explained by the beneficial configuration of hard nanoparticles embedded in a soft lubricating matrix, which increases the coating’s capability to dissipate stress without brittle fracture. Effects of process parameters, such as bombarding energy and nitrogen flow rate were also thoroughly studied.

Studies on Magnetron Sputtering Assisted by Inductively Coupled RF Plasma for Enhanced Metal Ionization

Planar magnetron discharge is assisted by inductively coupled plasmas, which are sustained by a helical RF antenna immersed in the plasma. Use of the technique significantly enhances the plasma density. The effects of antenna termination when grounded or floating have been investigated by a simple circuit analysis. The floating antenna configuration effectively suppresses the anomalous rise of the plasma potential and thus the plasma source can be stably operated at a higher input of RF power to generate plasmas with densities as high as >1012 cm-3.

Magnetron sputtered Si–B–C–N films with high oxidation resistance and thermal stability in air at temperatures above 1500 °C

Novel quaternary Si–B–C–N materials are becoming increasingly attractive because of their possible high-temperature and harsh-environment applications. In the present work, amorphous Si–B–C–N films were deposited on Si and SiC substrates by reactive dc magnetron cosputtering using a single C–Si–B or B4C–Si target in nitrogen-argon gas mixtures. A fixed 75% Si fraction in the target erosion areas, a rf induced negative substrate bias voltage of −100u2002V, a substrate temperature of 350u2009°C, and a total pressure of 0.5 Pa were used in the depositions. The corresponding discharge and deposition characteristics (such as the ion-to-film-forming particle flux ratio, ion energy per deposited atom, and deposition rate) are presented to understand complex relationships between process parameters and film characteristics. Films deposited under optimized conditions (B4C–Si target, 50%u2009N2+50%u2009Ar gas mixture), possessing a composition (in at.u2009%) Si32–34B9–10C2–4N49–51 with a low (less than 5u2002at.u2009%) total content of hydrog...

Properties of cubic boron nitride films with buffer layer control for stress relaxation using ion-beam-assisted deposition

Abstract Significant ion irradiation during film growth is required for the formation of cubic boron nitride (cBN) films. Meanwhile, a huge level of intrinsic stress possibly induced by the ion bombardment has been frequently reported to result in cracking and/or lack of adhesion of deposited cBN films. The present work has been performed to investigate the interfacial and/or the buffer layer structures with better matching to the cBN film by relaxation of the film stress using ion-beam-assisted deposition (IBAD). Boron nitride films have been synthesized on Si(100) wafer and tungsten carbide (WC) substrates by depositing boron vapor under simultaneous bombardment with nitrogen ions and nitrogen–argon mixture ions in the energy range of 0.5–10 keV. Cubic BN films with enhanced tribological properties have been explored by inserting a BN layer with various B/N compositions as a controlled buffer at the interface. Significant relaxation of the film stress has been observed for the buffer layer with a boron-rich (B-rich) composition (B/N∼10) with hardness maintained at a relatively high value (∼30 GPa). A structural analysis by Fourier transform infra-red spectroscopy (FTIR) and cross-sectional transmission electron microscopy (TEM) confirms that polycrystalline films with a high cBN fraction were synthesized on the B-rich layer. Formation of the cBN films with a B-rich buffer layer enabled the tribological characterizations to be performed, and the tribological properties have been observed to be significantly enhanced with the insertion of the B-rich buffer and the enhancement of atomic intermixing at the initial stage of cBN layer growth. Using the nanoindentation method, the hardness of the cBN films with a high cubic fraction was found to be as high as the values for the bulk cBN.

Formation of Carbon Nitride Films by Helicon Wave Plasma Enhanced DC Sputtering.

Carbon nitride films have been synthesized on Si(100) substrates by using DC sputtering assisted with a high density m=0 mode helicon wave-excited plasma in Ar and N2 mixture. The composition, structure and bonding state of the films were investigated by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy. From the XPS analysis it was found that the nitrogen to carbon (N/C) ratio in the films could be controlled over a wide range of 0.2–0.9 by changing the target voltage and nitrogen mixing rate via the production of a high density plasma of 1012–1013 cm-3. FT-IR spectroscopy indicated the appearance of an absorption band near 2200 cm-1 corresponding to C≡N covalent bonding. The XPS analysis also suggested the existence of a β-C3N4 phase with sp3 bonding correlated with the variation of the film microhardness.

Characterization of porosity and dielectric constant of fluorocarbon porous films synthesized by using plasma-enhanced chemical vapor deposition and solvent process

Fluorocarbon films obtained in plasma-enhanced chemical vapor deposition with a C4F8 compound were composed of a carbon cross-linked network and unlinked species encapsulated in the network [J. Appl. Phys. 89, 893 (2001)]. The unlinked species were effectively removed from the films. Then, the network probably containing the pore of the species was extracted on wafers when the films were dipped into tetrahydrofran (THF) solvent. The fact implied that fluorocarbon porous films with a low-dielectric constant might be formed by using dry and wet processes. In the present study, x-ray analyses showed that the THF-treated films actually became porous in the dipping process. The dielectric constant of the THF-treated films was consistently low (<1.9) and reduced by 10% from that of as-deposited films. The fluorocarbon network as a porous medium may be applied to interlayer dielectrics for ultralarge-scale integrated circuits.