Junzo Ishikawa

Transparent carbon film prepared by mass‐separated negative‐carbon‐ion‐beam deposition

A carbon film was deposited by mass‐separated negative‐carbon‐ion‐beam deposition in the energy range of 25–1000 eV. The carbon film deposited by a C− ion beam was optically transparent (the maximum optical gap was 0.96 eV) and served as an electrical insulator (the maximum electrical resistivity was 1.5×108 Ω cm). The film property strongly depended on the ion‐beam energy for deposition and, the film obtained at the deposition energy of 115–215 eV was the most transparent and the best insulator. Its atomic density was also the highest and was almost the same as that of diamond. The carbon film deposited at room temperature was amorphous and showed no IR absorption. On the other hand, the film deposited at a substrate temperature of 800 °C showed graphitelike rings in reflection high‐energy electron‐diffraction patterns and an IR absorption such as graphite. Its electrical resistivity was much lower. The property of the film deposited by a C−2 ion beam was more strongly dependent on the ion‐beam energy th...

Negative-ion implantation technique

Abstract Negative-ion implantation is a promising technique for charging-free implantation for the forthcoming ULSI fabrication, in which the water charging by positive-ion implantation will become a troublesome problem even with an electron shower. The negative-ion implantation technique remarkably ameliorates such a charging problem since the incoming negative charge of implanted negative ions is easily balanced by the outgoing negative charge of a part of secondary electrons. Thus, the surface charging voltage is maintained to within about ± 10 V for isolated conducting materials and insulators, and is free from space and time fluctuations. A high-current negative-ion source and a medium current negative-ion implanter developed for this technique are described with the design concepts. In addition, the fundamental measurements of interactions between the negative-ion beam and the gas/solid are also described.

Axial magnetic field extraction-type microwave ion source with a permanent magnet

We have developed a new type of microwave ion source which has an axial magnetic field generated by a permanent magnet. By the combination of the permanent magnet and ferromagnetic materials, a closed magnetic circuit is formed through an ion extraction electrode. This axial magnetic field is utilized both for the high‐density plasma production by the electron‐ cyclotron resonance process and for the high efficient ion extraction by transporting the generated ions along the magnetic force lines. The continuous ion beams of 2–3 mA are delivered from the extraction aperture (2 mm in diameter) when various gases (Ar, N2, CO2), metal vapors (Cs, Rb), and reactive gas (O2) are used. Extremely low impurities are present in the extracted ion beam. An ion beam with low emittance of 10−8 m rad order and high brightness of 1011 A m−2 rad−2 order is obtained. The size of this ion source is 50 mm in diameter and 65 mm in height. The discharge power of the microwave with the frequency of 2.45 GHz is 7 to 30 W. Thus, a...

Development of an ultrasmall C-band linear accelerator guide for a four-dimensional image-guided radiotherapy system with a gimbaled x-ray head.

We are developing a four-dimensional image-guided radiotherapy system with a gimbaled x-ray head. It is capable of pursuing irradiation and delivering irradiation precisely with the help of an agile moving x-ray head on the gimbals. Requirements for the accelerator guide were established, system design was developed, and detailed design was conducted. An accelerator guide was manufactured and basic beam performance and leakage radiation from the accelerator guide were evaluated at a low pulse repetition rate. The accelerator guide including the electron gun is 38 cm long and weighs about 10 kg. The length of the accelerating structure is 24.4 cm. The accelerating structure is a standing wave type and is composed of the axial-coupled injector section and the side-coupled acceleration cavity section. The injector section is composed of one prebuncher cavity, one buncher cavity, one side-coupled half cavity, and two axial coupling cavities. The acceleration cavity section is composed of eight side-coupled nose reentrant cavities and eight coupling cavities. The electron gun is a diode-type gun with a cerium hexaboride (CeB6) direct heating cathode. The accelerator guide can be operated without any magnetic focusing device. Output beam current was 75 mA with a transmission efficiency of 58%, and the average energy was 5.24 MeV. Beam energy was distributed from 4.95 to 5.6 MeV. The beam profile, measured 88 mm from the beam output hole on the axis of the accelerator guide, was 0.7 mm X 0.9 mm full width at half maximum (FWHM) width. The beam loading line was 5.925 (MeV)-Ib (mA) X 0.00808 (MeV/mA), where Ib is output beam current. The maximum radiation leakage of the accelerator guide at 100 cm from the axis of the accelerator guide was calculated as 0.33 cGy/min at the rated x-ray output of 500 cGy/min from the measured value. This leakage requires no radiation shielding for the accelerator guide itself per IEC 60601-2-1.

Ion beam assisted deposition of niobium nitride thin films for vacuum microelectronics devices

Abstract We have deposited niobium nitride thin films by ion beam assisted deposition and evaluated their properties from the viewpoint of a cathode material for vacuum microelectronics devices. Substrate temperature and ion–atom arrival rate ratio were selected as deposition parameters. The film properties of nitrogen composition, crystallinity, electric resistivity, work function and sputtering yield against a low-energy argon ion bombardment were investigated. It was found that polycrystalline films could be obtained at the substrate temperature higher than 500°C, and the composition could be controlled by the ion–atom arrival rate ratio. The results also showed that the stoichiometric nitride film exhibited superior properties of a lower work function and a lower partial sputtering yield of niobium. The electron emission test also demonstrated a lower current fluctuation for the stoichiometric films. In summary, ion beam assisted deposition provided a low temperature process which could control the film properties suitable to a cathode material.

Influence of cathode material on emission characteristics of field emitters for microelectronics devices

In order to find out the cathode material suitable to vacuum microelectronics devices, dependence of cathode material of field emitters was investigated with respect to the emission characteristics. Since the field emitters for vacuum microelectronics devices are fabricated by thin film processes, the characteristics of the electron emission from deposited materials should be examined. In the present study, a dozen materials were deposited onto the tungsten needle fabricated by well‐controlled electrochemical etching. Measurement of the emission was performed at the pressure of 10−9 Torr range. The current–voltage characteristics and the stability measurements revealed that the gold emitters indicated excellent properties: stable and high current at low extraction voltage. The effective surface work function and the effective emission area were evaluated from the Fowler–Nordheim theory, assuming that the emission area rapidly decreases with reducing the apex radius. From this analysis, it is clarified tha...

CONTACT ANGLE LOWERING OF POLYSTYRENE SURFACE BY SILVER-NEGATIVE-ION IMPLANTATION FOR IMPROVING BIOCOMPATIBILITY AND INTRODUCED ATOMIC BOND EVALUATION BY XPS

Abstract Negative-ion implantation technique is expected as an effective surface modification method for insulators of polymer, since in negative-ion implantation into insulators the charge-up potential of the surface is in several volts. Polystyrene dishes were implanted with Ag − ions in an ion energy range under 30 keV in order to bring hydrophilic property to their surface for improving surface biocompatibility of cell adhesion property, and contact angles to water were measured. Contact angle was found to be lowered to 73° by the Ag-ion implantation from an original value of 86°, and it decreased with increase in both ion dose and ion energy below 20 keV. Atomic bonds of C–O, CO, and OC–O were introduced by ion implantation, these were increased in number with increase in dose and energy of implantation. These atomic bonds were considered to bring the hydrophilic property to the polystyrene surface. Human umbilical vascular endothelial cell (HUVEC) was cultured on each sample with a 199 medium. The cell growth and attachment were observed only for Ag-implanted surfaces.

Negative‐ion sources for modification of materials (invited)

The properties of negative ions, such as charging–free ion implantation and new materials syntheses by pure kinetic bonding reaction, have been shown to be promising in terms of their interaction with material surfaces. However, high‐current or high‐brightness negative‐ion sources are required for these purposes. Several kinds of sputter‐type negative‐ion sources have been developed for negative‐ion implantation and deposition in order to obtain high‐current heavy negative ions. Recently, a microwave discharge oxygen negative‐ion source for negative‐ion beam deposition and a surface plasma type hydrogen negative‐ion source for projection ion‐beam lithography have been investigated. In this article, these negative‐ion sources for modification of materials are reviewed.

Impregnated‐electrode‐type liquid metal ion source

An impregnated‐electrode‐type liquid metal ion source has been developed in which a sintered porous tungsten tip is used. The flow rate of the liquid metal can be controlled by selecting the diameters of the tungsten powders to be sintered (10 and 100 μm). Since the liquid metal can be stably supplied to the tip head, stable operation in a wide range from low (a few μA) to high ion current (a few hundred μA) is possible for various metals such as gallium and gold. Moreover, it is also a potential ion source with liquid metals such as silver with high vapor pressure at the melting point. A new method of holding and directly heating the main component of the ion source by means of knife‐edged electrodes with a spring is extremely effective for high temperature operation.

Negative ion beam technology for materials science (invited)

Negative‐ion beams can be used in materials science, i.e., ion implantation and ion beam deposition, since various types of high current negative‐ion sources have recently been developed. Two types of these the NIABNIS and rf sputter types, were developed by the present authors. There are major differences between negative‐ and positive‐ion implantations with regard to beam transport (collisional cross sections with residual gas particles) and secondary electron emission factors, but little difference in the projected ranges of implanted ions. By using negative ions in ion beam deposition, the effects of the kinetic energy and number of atoms of an ion may be clarified because negative ions have much less reactivity resulting from their internal potential energy of electron affinity than do positive ions resulting from their ionization potential.