Kiichiro Uchino

MEASUREMENTS OF ELECTRON TEMPERATURE, ELECTRON DENSITY, AND NEUTRAL DENSITY IN A RADIO-FREQUENCY INDUCTIVELY COUPLED PLASMA

Electron temperature, electron density, and neutral atom density were measured in a radio‐frequency (rf) inductively coupled plasma using Thomson and Rayleigh scattering of laser radiation. Measurements were made in an argon discharge for pressures from 1 to 20 mTorr and input rf powers from 100 to 500 W. Spatial distribution profiles were measured for discharges with different aspect ratios. Electron temperature was found to depend on pressure but only weakly on power. Electron density depended strongly on both pressure and power. The neutral density was found to be significantly depleted in the plasma center and this depletion was attributed to heating of the neutrals by charged particle collisions. These results were compared to a simple model of inductively coupled plasmas.

Diagnostics of low-density glow discharge plasmas using Thomson scattering

In recent years, the method of incoherent Thomson scattering has been applied to make measurements of electron properties of glow discharges used for industrial applications. These plasmas have electron density of the order of and electron temperature of a few eV. This paper reviews the recent progress in this research area. Details of the experimental systems are given and examples of measurements made in several different types of glow discharges are presented. A method in which Thomson scattering is combined with Rayleigh scattering to provide direct measurements of the neutral density is also described and an example of measurements is given. The electron velocity and energy distribution functions are also an important property of these plasmas, and the extent to which Thomson scattering can measure the distribution function is discussed. Future trends for Thomson scattering in glow discharges are also discussed.

Direct measurement of electron density and temperature distributions in a micro-discharge plasma for a plasma display panel

Spatial distributions of electron density (ne) and electron temperature (Te) of a micro-discharge plasma for an alternating current plasma display panel cell were directly measured using the laser Thomson scattering method. The use of a triple-grating spectrometer was very successful in suppressing the strong stray laser light and allowed us to perform measurements at 0.1 mm above the surface of the electrode substrate. Values of ne and Te were (0.2–3)×1019 m−3 and (1.6–3.4) eV, respectively, depending on the time from the beginning of the pulsed discharge and the observation position. The structure of the micro-discharge is discussed in terms of the obtained distributions of ne and Te.

Thomson scattering measurements of electron temperature and density in an electron cyclotron resonance plasma

Electron temperature Te and density ne in the source region of an electron cyclotron resonance discharge have been measured by incoherent Thomson scattering of the beam from a 0.5 J yttrium aluminum garnet laser. This is the first experiment in which this technique, routinely used on fusion plasmas, has been applied to a processing plasma. Measurements were made in an argon discharge at pressures from 0.3 to 2 mTorr and microwave powers from 250 to 1000 W. Velocity distributions were measured both parallel and perpendicular to the magnetic field and a slight anisotropy of electron temperature was observed for low‐pressure discharges. Temperatures in the range of 1–5 eV and densities in the range of 2–10×1017 m−3 were measured. Te and ne were found to strongly depend on pressure but only weakly on the input power and discharge magnetic field. No deviations from a Maxwellian velocity distribution were observed.

Two-dimensional structure of PDP micro-discharge plasmas obtained using laser Thomson scattering

Laser Thomson scattering (LTS) has been applied for measurements of the electron density and electron temperature in micro-discharge plasmas for plasma-display panel research. A brief description of the method for overcoming the sparsity of scattered photons by the data accumulation technique is presented. Then, the technique of applying LTS to micro-discharge plasmas is described where the use of a specially designed triple-grating spectrometer has turned out to be essential. Improvements in the experimental setup to allow, for the first time, to collect laser LTS spectra at heights as close as to 60 /spl mu/m from the electrode surface are discussed. Spatial distributions of the electron density and electron temperature in the vertical direction above the electrode surface are presented. Finally, an extension of the measurements into two-dimensions, namely along the electrode surface and at different heights above the electrodes enabling to cover the discharge front to be made, are presented and compared with the results of optical emission measurements.

A study of electron energy distributions in an inductively coupled plasma by laser Thomson scattering

The electron energy distribution function (eedf) in an inductively coupled plasma was studied using the method of laser Thomson scattering. eedfs were measured for various plasma conditions, at different gas pressures, and at different input rf powers. In high electron density plasmas, the eedf was observed to be Maxwellian, while in low electron density plasmas, a non-Maxwellian eedf was observed. The transition between Maxwellian and non-Maxwellian eedfs was attributed to the thermalization of the electron population in higher density plasmas. In order to completely characterize the eedf, spatial and temporal dependencies were measured and measurements were also made in the afterglow period of a pulsed discharge. Discussions are made of the electron behavior and the shape of the eedf.

OBSERVATION OF SI CLUSTER FORMATION IN SIO2 FILMS THROUGH ANNEALING PROCESS USING X-RAY PHOTOELECTRON SPECTROSCOPY AND INFRARED TECHNIQUES

SiO2 films having high breakdown characteristics were deposited by a sputtering-type electron cyclotron resonance microwave plasma at room temperature. As-deposited films were annealed in an Ar ambient at temperatures ranging from 450 to 1000 °C. Transmitted infrared (IR) absorption and x-ray photoelectron spectroscopy (XPS) were used to characterize the as-deposited and annealed films. XPS measurements indicated that the as-deposited films had an approximately stoichiometric composition containing a few intermediate SiOx(x≠2) species and Ar atoms around some dangling-bond defects. The dependence of XPS spectra on annealing temperature showed that steep diffusion of the Ar atoms occurs at annealing temperatures of 450–550 °C and the SiOx species separate into SiO2 phase and Si clusters by an annealing process of 750–950 °C. Based on the full width at half-maximum variations of Si 2p XPS spectra and Si–O stretching mode of IR spectra for the annealed films, we discuss the Si cluster formation in SiO2 films...

Energy Dependence of Angular Distributions of Sputtered Particles by Ion-Beam Bombardment at Normal Incidence

The angular distributions of sputtered Fe-atoms were measured using the laser fluorescence technique during Ar-ion bombardment for energies of 0.6, 1, 2 and 3 keV at normal incidence. The measured cosine distribution at 0.6 keV progressively deviated to an over-cosine distribution at higher energies, and at 3 keV the angular distribution was an over-cosine distribution of about 20%. The experimental results agree qualitatively with calculations by a recent computer simulation code, ACAT. The results are explained by the competition between surface scattering and the effects of primary knock-on atoms, which tend to make the angular distributions over-cosine and under-cosine, respectively.

Measurements of electron temperature and density of a micro-discharge plasma using laser Thomson scattering

Laser Thomson scattering was successfully applied to measure electron temperature (Te) and electron density (ne) in a micro-discharge plasma. This is the first time that this method has been used to obtain otherwise inaccessible plasma information from the near vicinity (0.3 mm) of a material surface. The key of the success was the suppression of strong stray laser light by using a triple-grating spectrometer. Values of electron temperature and density were Te=(0.4–1.6) eV and ne=(6–10)×1018 m-3, depending on the time from the beginning of the pulsed discharge. The technique developed here is readily applicable to plasma display panel (PDP) discharges.

Studies on the optimum condition for the formation of a neutral loop discharge plasma

In order to obtain guidelines for the design and operation of a new plasma source by a magnetic neutral loop discharge, electron behavior was studied experimentally and numerically. Experimentally, the magnetic field gradient was changed over a wide range, and it was found that there existed an optimum value for efficient plasma production. Analyses of the electron behavior were performed using a model that included effects of a three-dimensional electromagnetic field with spatial decay of the rf electric field, and the limitation of the spatial extent of the electron motion (the existence of walls and the electron loss at wall surfaces). These factors were found to explain the existence of the optimum magnetic field gradient.