Yukio Okamoto

High-Power Microwave-Induced Plasma Source for Trace Element Analysis

A high-power microwave-induced plasma source (2.45 GHz, 1.2 kW) for trace element analysis is presented. The plasma is generated by a circularly polarized wave induced by a helical coil with a mode transformer. The sample introduction system consists of a pneumatic nebulizer with no dehydration system, i.e., utilizing direct introduction of aqueous solutions. An annular-shaped argon plasma was generated at atmospheric pressure in a 2.3–4.2-mm i.d. quartz discharge tube with a low gas flow rate (2 l/min). Preliminary analytical results were otained using an aqueous Ca(10 ppm)+Zr(200 ppm) solution sample and compared to those obtained with the argon inductively coupled plasma.

High-Power Microwave-Induced Helium Plasma at Atmospheric Pressure for Determination of Halogens in Aqueous Solution

A high-power (~1000 W CW, 2.45 GHz) annular-shaped microwave-induced helium plasma was developed for determination of halogens in the aqueous solutions, and the preliminary characteristics are presented. The plasma was generated at atmospheric pressure by an Okamoto cavity which was modified to focus the energy. No external cooling was used to stabilize the plasma. An aqueous solution was injected into the plasma by an ultrasonic system with desolvation and condensation. The electron density and iron-excitation temperature were on the order of 1014/cm3 and 5000 K, respectively. Introduction of aqueous chloride in the form of NaCl and bromide in the form of KBr produced intense ion emission and detection limits of 0.1 ppm (µg/ml) for Cl II (479.5 nm) and 0.2 ppm (µg/ml) for Br II (470.5 nm) were obtained.

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.

Characteristics of a Large-Diameter Surface-Wave Mode Microwave-Induced Plasma

A large-diameter unmagnetized argon plasma is generated by an Okamoto cavity operated in a surface-wave mode. A quartz discharge tube (16 cm inner diameter, 12 cm long) is placed inside the cavity. An argon plasma is produced in the discharge tube and effuses in a process chamber. The electron density, electron temperature, ion current density and floating potential in the chamber are measured as a function of spatial position using a Langmuir probe. An electron density over 1011 cm-3, with an electron temperature in the range of 2–3 eV and a floating potential with respect to the chamber wall of less than 5 V is obtained at pressure in the mTorr range with 2.45 GHz, 700 W input microwave power. A high ion current density (over 10 mA/cm2) of uniformity (standard deviation/average) within 4.4% over 16 cm is achieved.

DC Gas-Discharge Display Panel with LaB6 Thin-Film Cathode

A dc gas-discharge display panel with LaB6 thin-film cathodes is proposed for data information systems. A thin-film, having a crystallographic orientation of [100], was formed on a Ni thick-film using the electron-beam evaporation technique. The low work function of the crystallographic orientation provided a low operating voltage. The normal cathode fall potential for the thin-film cathode in a Ne+Ar (0.4%) gas discharge was approximately 80 V, about 1/2 that of the commonly used Ni thick-film cathode. The display panel consisted of two glass plates: cathodes were formed on one plate (substrate) and anodes on the other. The cathodes and anodes were perpendicular to each other, and were separated by barriers formed in parallel between the anodes. Low voltage, high luminance, high luminous efficiency and stable operation were attained without the use of Hg.

Efficiency Enhancement in DC Pulsed Gas Discharge Memory Panel

Much improvement in the luminous efficiency of a dc pulsed gas discharge memory panel for color TV display was achieved by shortening the sustaining pulse duration. High energy electrons can thus be produced in the pulsed discharge with fast rise times. Calculated optimum value of E/P in a Xe gas discharge is 7–8 V/cmTorr.

A microwave-induced unmagnetized plasma source for plasma processing

A simple microwave-induced large-diameter unmagnetized plasma at low pressure with an Okamoto cavity for plasma processing is presented. A quartz discharge tube (6.4 cm in diameter and 10 cm long) is placed inside the cavity. An argon plasma is produced in the discharge tube and effuses into a process chamber (stainless steel, 14 cm in diameter and 24 cm long). The electron density, electron temperature, ion current density and floating potential in the chamber were measured as a function of spatial position using a Langmuir probe. An electron density over , with an electron temperature in the 3 eV range, was obtained at pressures in the mTorr range with 2.45 GHz 500 W input microwave power.

SOME FEATURES OF AN ELECTRON CYCLOTRON RESONANCE PLASMA PRODUCED BY MEANS OF A LISITANO COIL.

Characteristics of an ECR plasma produced by means of an L-coil are studied in changing the location of exact ECR condition on the coil. It can be seen that the energy distribution function for ions changes from double-humped to Maxwellian, and the quiescent plasma is obtained. Ion compositions of the plasma are measured as a function of electron temperature, and the chemical reactions in the plasma are discussed.

Time-Resolved Electron Energy Distribution Function in Pulsed Surface Wave Plasma Generated by Ring-Slot Antenna

Time-resolved probe measurements of the electron energy distribution function (EEDF) in a substrate (wafer) holder were performed in a pulse-modulated argon plasma of high density (>1011/cm3), low electron temperature (<2 eV) and excellent uniformity (±3% over 24 cm diameter). The plasma was produced by a time-modulated surface wave power with a ring-slot antenna. Microwave power (2.45 GHz, 1 kW max.) was modulated with a square wave pulse of 100 µs duration and 20–90% duty ratio. The temporal evolution of the EEDF was divided into two zones, namely, the zone where the microwave power is turned on (active plasma region: on-time) and that where the power is turned off (afterglow plasma region: off-time). In the first zone, the EEDF shows a fast evolution in which the number of high-energy electrons (high-energy tail of EEDF) increases with time. The second zone is characterized by a significant decrease in the number of high-energy electrons and an increasing EEDF that shifts to low energy values. These characteristics were compared with those of the continuously driven (CW) plasma.

Production of a large-area argon microwave plasma by a ring slot antenna

Abstract A large-area, uniform, low-temperature and high-density microwave argon plasma is produced using a simple flat ring slot antenna without a magnetic field. The plasma production is based on the absorption of the energy of microwave propagating in the dielectric plate (quartz glass) along the plasma surface. The power is coupled to the dielectric plate by azimuthal symmetrical mode. An electron density of >1011/cm3 with an electron temperature