Books

This book is a result of the IV International Workshop on "Microwave Discharges: Fundamentals and Application" which was held in September 18-22, 2000 in Zvenigorod, Russia. The main purposes where to discuss recent achievements in the study of microwave plasma, identify directions for future researches, and promote close relationship between scientists from different countries.

Topics in this book cover all problems of theoru, experiments and applications of microwave discharges and yield the state-of-the-art and trends in:

  • discharge theory, modelling and diagnostics,
  • methods of microwave plasma generation,
  • high and low pressure microwave discharges,
  • continious wave and pulsed microwave discharges,
  • interaction of microwave with a plasma,
  • applications of microwave plasma (surface treatment, etching, film deposition, growth of structures, light sources, analytical chemistry, etc.)
We hope, this book will be useful for all specialists who work in low temperature plasma physics and processing.

Contents

Theory and modelling
Diagnostics
Microwave Plasma Sources
Microwave Plasma Applications



Theory and modelling



INFLUENCE OF THE WAVE FREQUENCY ON THE HEAVY PARTICLES AXIAL BEHAVIOR IN ARGON SURFACE-WAVE SUSTAINED PLASMA

E. Benova and Ts. Petrova*

Chair of Physics, Department for Language Learning, Sofia University, Sofia, Bulgaria

*Faculty of Physics, Sofia University, Sofia, Bulgaria

The axial behavior of the excited atoms, atomic and molecular ions in argon surface-wave sustained plasma columns is investigated theoretically at various wave frequencies and plasma radii in the pressure range 0.1-10 Torr.

The numerical model is based on self-consistent solving of a full set of electrodynamic and kinetic equations: the local dispersion equation, wave energy balance equation, electron Boltzmann equation, electron energy balance equation, neutral gas thermal equation and the balance equations for the electrons, excited atoms, atomic and molecular ions [1]. We consider an argon level configuration in which the Ar(3p54s) four levels (two metastable and two resonant) are treated separately and the Ar(3p54p) as one lumped block of levels. The processes for electron creation involved in the model are the direct ionization, stepwize ionization, Penning and associative ionization. The loss of electrons is due to diffusion and dissociative recombination. The following processes are taken into account in the heavy particles balances: excitation from the ground state, electron impact excitation and deexcitation between excited states, radiative transitions with accounting for the trapping of radiation, molecular ion formation and diffusion to the wall.

It is found out that, depending on the conditions, the populations of 3p54s levels decrease or increase along the column, while the populations of 3p54p-block of levels and the densities of the charged particles always decrease from the wave launcher to the column end. The dynamics of the excited states populations and partial contributions of different elementary processes in the particle balances is studied. The results are compared with available experimental data [2,3].

References

1. Petrova Ts., Benova E., Petrov G., and Zhelyazkov I. Phys. Rev., 1999, E 60, 875.

2. Böhle A. and Kortshagen U. Plasma Sources Sci. Technol., 1994, 3, 80.

3. Lao C. PhD thesis, Universidad de Sevilla, 1999.

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MOLECULAR DISCHARGES SUSTAINED

BY A TRAVELLING WAVE

C.M.Ferreira, F.M. Dias, V.Guerra and E.Tatarova

Centro de Fisica dos Plasmas, Instituto Superior Tecnico,

1049-001 Lisboa, Portugal

Technological applications involving molecular plasmas usually call for a complex investigation of the transport and reactions of numerous neutral and charged species and of the energy exchange channels within the discharge, in order to predict correctly the discharge behaviour. In particular, concerning microwave discharges in molecular gases, the investigation of discharges sustained by travelling surface waves continues to provide major breakthroughs, due to their flexible operation and easy access to a variety of diagnostics. However, the modelling of travelling wave sustained discharges in molecular gases is a very complex task since it must be based on a self-consistent description of the electron and heavy particle kinetics, wave electrodynamics, gas thermal balance, and plasma-wall interactions. This work presents the state-of-the-art and discusses current issues in the modelling of surface wave sustained discharges in H2 and N2 using a self-consistent approach of this kind. Important problems addressed here are, for example, molecular dissociation of H2, atomic recombination at the wall, and the different H- creation and loss channels. In particular, the correlation between the degree of hydrogen dissociation and the wall temperature in H2 and H2- N2 discharges is discussed. The occurrence of strong, inhomogeneous gas heating in N2 discharges raises the problem of the effects of gas temperature Tg on discharge operation, since changes in Tg induce changes in the neutral density and in numerous reaction rate coefficients. In addition to the gas heating mechanisms usually considered, due to energy exchange processes between vibrationally excited N2 molecules and atoms, gas heating mechanisms involving metastable particles can also contribute significantly at high degrees of ionisation. The creation and loss of nitrogen atoms is also analysed as a function of the discharge operation conditions. The results demonstrate significant influence of metastable atoms and surface kinetics on the number density of ground state nitrogen atoms. All these problems are discussed on the basis of both theoretical and experimental investigations.

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MODELING AND CONTROL OF ECR AND UNMAGNETIZED MICROWAVE PLASMAS USED FOR MATERIALS PROCESSING

T. A. Grotjohn

Michigan State University, East Lansing, Michigan USA

Low pressure microwave plasma sources used for materials processing generally operate as overdense plasmas with the plasma density greater than the critical density. These sources can be operated with a static magnetic field that provides for ECR heating or without a static magnetic field via ohmic, resonance and other non-ohmic and stochastic heating mechanisms. Even when ECR strength magnetic fields are present these other heating mechanism that occur in unmagnetized plasmas can be important and may even dominate. This paper examines via a two-dimensional, self-consistent microwave field and plasma model the heating of low pressure, overdense, magnetized and unmagnetized plasma discharges. Further the models are constructed to closely match an experimental system that has been extensively characterized. This experimental system is a 2.45 GHz resonant cavity plasma source that has been studied while running argon discharges at pressures of 4-60 mTorr using Langmuir probes to determine the plasma density and electron temperature and using microwave field probes to measure the microwave field strength[1].

Low-pressure (collision frequency << excitation frequency) microwave plasma simulations that model the spatial variation of the microwave heating fields and plasma discharge are difficult to use in the local regions where the plasma frequency is near the excitation frequency. In these regions resonance effects occur and the microwave electric field can become large. Because of the localized nature of the resonance (high microwave field strength) region, stochastic heating can occur as the electrons are accelerated/heated in this region and/or transverse through this resonance region via their initial momentum. Simple electron gas descriptions based on a single valued conductivity/dielectric expression or a cold plasma momentum transport equation may not reasonably predict the plasma heating phenomenon/rate and local microwave field strength. Rather an electron gas model that considers the random motion of the electrons via a warm plasma or electron energy distribution function description is needed. To accurately model this localized resonance region heating, this study implemented both warm plasma and electron energy distribution function descriptions for the electron gas, at least in local resonance regions, in a two-dimensional self-consistent electromagnetic field/plasma discharge simulation model. Various implementations of the electron gas energy distribution function calculation in the resonance regions will be discussed and compared.

[1] J. Asmussen, T. A. Grotjohn, and M. Perrin, this workshop.

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THEORY OF THE MICROWAVE HIGH-PRESSURE DISCHARGE

K.Khodataev

Moscow Radiotechnical Institute RAS, Moscow, Russia

The microwave discharge in the focus of electromagnetic radiation with comparatively long pulse duration represents the complicated net of thin bright filaments [1]. The time-resolved photo-registration shows that only several filaments simultaneously exist and they are located inside some layer. At the next time the bright filaments arise inside the other layer which is displaced nearer to source of radiation. Each bright filament has life-time less than 1 mcs and its length achieves a half-wavelength of the radiation. In difference from the discharge in the radiation beam the discharge in the open resonator represents the single bright filament [2]. When the resonant length is achieved the all energy, which stored by the resonator, is absorbed by the streamer with very high efficiency (and partially refracted). The shock wave that is generated by the heated streamer confirms the absorption of the main part of energy stored by the resonator.

The work is devoted to theoretic study of a streamer discharge in the focus of microwave radiation in the open resonator. (The single filament is much simpler for study both experimentally and theoretically that the net of one.) The designed theoretic model takes in to account that the streamer develops in the microwave field of the resonator with finite store of energy, that the streamer length is comparable to wave length [3], that the plasma-gas dynamic and plasma-chemical processes arise [4]. The computations confirm, in general, ideas that were developed earlier [5]. The microwave high-pressure discharges are opening the wide field of applications in aeronautic technology [6]. Some of the applications are being discussed.

References

  1. L.P.Grachev, I.I.Esakov, G.I.Mishin, K.V.Khodataev, V.V.Tsyplenkov. Tech. Phys. 39(1), January 1994, pp. 40-48
  2. L.P.Grachev, I.I.Esakov, G.I.Mishin, K.V.Khodataev. Tech. Phys. 39(2), February 1994, pp.130-136.
  3. K.V.Khodataev. Proc. XXIII ICPIG, 17-22 July 1997, Toulouse-France, Contributed papers, IV-24.
  4. K.V.Khodataev. Chemical Physics, 1993, t.12, v.3, c. 303-315.
  5. K.V.Khodataev. Proc. supplement of 2-nd Weakly Ionized Gases Workshop. Norfolk, VA, USA, 24-25 April, 1998, pp. 309-338.
  6. I.I.Esakov, L.P.Grachev, K.V.Khodataev. Proc. supplement of 3-rd Weakly Ionized Gases Workshop. Waterside Marriott Hotel, Norfolk, VA, USA, 1-5 November, 1999, 99-4821

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MICROWAVE AND OPTICAL DISCHARGES IN THE HIGH POWER WAVE FIELDS AND APPLICATIONS

Rukhadze A.A.

General Physics Institute, Vavilova str. 38, Moscow, Russia

Review of theoretical and experimental investigations of microwave and optical gas discharges in the high power wave fields is presented. In the such fields the oscillation energy of on electron is much higher then the ionization energy of atoms and moreover it may be relativistic. The distribution function of electrons and time dependence of plasma density are determined. It is showed that only plasma density depends on the concrete mechanism of gas ionization and charged particles losses. The distribution function occurs to be the random phase distribution and don't depend on the concrete ionization-recombination mechanisms. The comparison of theoretical and experimental results is done and important complications of such type discharges in the plasma chemistry and thermonuclear fusion physics are discussed.

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Diagnostics



SPECTROSCOPIC STUDY OF A SURFACE-WAVE ARGON DISCHARGE AT ATMOSPHERIC PRESSURE

M.C. Garcia, A. Rodero, A. Gamero, A. Sola, M.C. Quintero

and C. Lao

Departamento de Fisica. Universidad de Cordoba. E-14071 Cordoba. Spain.

The behavior of an argon surface-wave plasma column at atmospheric pressure has been studied by using spectroscopic diagnosis. The surface-wave plasma columns have been produced in a quartz capillary tube (inner radium 1 mm) with an open end, by coupling the 2.45 GHz electromagnetic energy via a Waveguide-Surfatron launcher to produced the azimuthal mode (m=0). The columns were obtained at 60 and 110 W of microwave power and using an argon flow rate of 0.5 and 1.0 slpm.

From the atomic state distribution function (ASDF), the electron density and gas temperature spectroscopically determined, the stage of departure from equilibrium and the electron temperature are deduced. The atomic state distribution function have been obtained from the line intensities emitted by the plasma in the 394.9 to 912.2 nm range, which correspond to transitions coming from 4p up to 7d excited levels.

The difference between the electron temperature and the gas temperature for the different axial positions of the column shows that the discharge is a two-temperature plasma. A careful analysis of the Boltzmann plots reveals that the populations of the top levels in the atomic scheme studied are controlled by Saha balance. So, a partial local thermodynamic equilibrium (pLTE) in the excitation space is reached for 5p and higher levels. The 4p levels do not conform to such an equilibrium state, as confirmed by both the np-ne plots and the axial behavior of the density of these excited species. Moreover, a predominantly ionizing character of the discharge is observed, mainly at positions near the coupling device, which gradually gained recombining behavior as the distance from the launcher grew.

This spectroscopic study has also included power-interruption technique. The instantaneous response of the intensity of some atomic lines to the sudden interruption of the microwave power maintaining the discharge have been observed. These instantaneous responses, in form of abrupt jumps, suggest that the studied levels are controlled at least partially by Saha balances, and that only the levels 5p and higher conform the Saha equilibrium. These results are in agreement with those obtained by using steady-state spectroscopic techniques.

(Thanks to the project no. PB96-0508, DGES of Spanish Ministry of E. & C).

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HOT-ELECTRONS AND EEDF ANISOTROPY IN LARGE-AREA SURFACE WAVE DISCHARGES

J. Kudela, T. Terebessy * and M. Kando *

Satellite Venture Business Laboratory,

Shizuoka University, Hamamatsu, Japan

*Graduate School of Electronic Science and Technology,

Shizuoka University, Hamamatsu, Japan

In recent years, increasing attention has been paid to so-called large-area surface wave plasma sources. These sources work without the use of static magnetic fields and produce plasmas of high densities over large areas, which makes them attractive for industrial applications. Of a particular interest is the discharge maintenance at low gas pressures, where the electron-neutral collision frequency is lower than the applied field frequency. According to the theoretical work by Aliev et al. [1], under these conditions, local plasma resonances and related electric field enhancement near the plasma-dielectric boundary may play a significant role in discharge heating. The resonantly-enhanced field undergoes a Cherenkov particle-wave interaction with the electrons passing through it. The phenomenon results in the generation of hot-electron tail in the EEDF, which sustains the discharge.

In low-pressure argon discharges sustained in a 2.45 GHz microwave plasma source [2], we have experimentally observed flux of hot electrons directed away from the waveguiding plasma-dielectric interface [3]. We believe that the flux originates from the resonantly-enhanced electric field region localized near the dielectric and provides evidence for the theoretically predicted phenomenon. The existence of such hot-electron flux may be an important factor in processing plasmas affecting the heating and stability of discharges. We will present more details on the observed phenomenon focusing on the anisotropy in EEDF and spatial distribution of plasma parameter profiles.

References

  1. Aliev Yu.M., Bychenkov V.Yu., Maximov A.V. and Schlüter H.: Plasma Sources Sci. Technol., 1992, 1, 126.
  2. Odrobina I., Kudela J. and Kando M.: Plasma Sources Sci. Technol., 1998, 7, 238.
  3. Kudela J., Terebessy T. and Kando M.: Appl. Phys. Lett., 2000, 76, 1249.

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ADDITIONAL MICROWAVE DIAGNOSTICS OF

AFTERGLOW WITH ESR SPECTROMETER

V. Kudrle, A. Tálský, J. Janča

Department of Physical Electronics, Masaryk University,

Kotlářská 2, CZ-61137 Brno, Czech Republic

If a small amount of impurity (O2, H2, Ar, Ne, …) is added to a nitrogen gas flowing through a discharge, one observes increased concentration of atomic nitrogen in the discharge afterglow. It is generally supposed that surface reactions, influencing recombination rate, play a dominant role in this phenomenon [1,2]. Also the electron concentration in the afterglow depends on the amount and the type of impurity.

Plasma was excited in quartz tube with 13 mm inner diameter by means of 2.45 GHz surfatron cavity. At pressure of 450 Pa the power needed to sustain stable discharge was 100 W. Flowing afterglow was observed in 1m long afterglow tube which passed through the measuring resonator of ESR spectrometer. Ratio nitrogen/admixture was set by means of mass flowcontrollers. The distance between the discharge and measuring resonator being variable, the concentrations of various species might be determined in different afterglow positions.

To detect atomic nitrogen non-intrusively, we employed electron spin resonance spectrometry, which is based on resonant absorption of microwaves by electronic transitions between Zeeman split levels. After the calibration by molecular oxygen [3] this method gives absolute concentration of sought paramagnetic particles. Due to the fact that measuring resonator was working with TE011 mode, we were capable to record also electron cyclotron curve by ESR spectrometer and thus determine the electron concentration ne in exactly the same place as the concentrations of other species were measured.

Our results show that for low amounts of the admixture atomic nitrogen concentration nN rises with admixture content. But from certain threshold (which depends on the type of admixture) nN decreases again. In the case of oxygen admixture we observed electrons in the afterglow and their concentration followed the curve of atomic nitrogen concentration. From the dependence of ne on the afterglow position we deduce that electrons are produced by reactions in the afterglow. Interestingly, isotopic composition of atomic nitrogen (14N/15N) also depends on the amount of impurity.

[1] Gordiets B. et al: J.Phys.D: Appl. Phys. 1996, 29, 1021

[2] Zvoníček V.: Proceedings of ICPIG 1997, vol.4, 160

[3] Westenberg A. A.: Prog. React. Kinet. 1973, 7, 23

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INFRARED ABSORPTION DIAGNOSTICS AND CHEMICAL MODELING OF

MICROWAVE PLASMAS CONTAINING HYDROCARBONS

L. Mechold1, J. Röpcke1, D. Loffhagen1 and P.B. Davies2

1Institut für Niedertemperatur-Plasmaphysik, Greifswald, Germany

2 Department of Chemistry, University of Cambridge, Cambridge, U.K.

Low pressure molecular microwave plasmas have been used extensively for surface treatments. The high chemical activity caused by large concentrations of transient or stable reactive neutral species has led to an increasing number of applications in plasma processing and technology.

This contribution presents comprehensive spectroscopic studies of hydrocarbon-containing plasmas in a planar microwave plasma reactor (f=2.45 GHz) [1] using tunable infrared diode laser absorption spectroscopy. The investigation comprises the methyl radical and the stable molecules CH4, CH3OH, C2H2, C2H4, C2H6, CH2O, HCOOH, CO, CO2 and H2O detected in mixed H2-Ar-O2 plasmas containing admixtures of 0.9 to 7.2% of methane or methanol. The molecular concentrations in the plasma and the degree of dissociation of the added precursor were monitored as the hydrogen to oxygen ratio was varied while maintaining constant discharge pressure and gas flow rate. In addition to the experiments for the relatively high gas flow regime, measurements under static conditions were made.

In order to obtain a deeper understanding of the main kinetic processes in methane-containing microwave plasmas, model calculations have been performed. The model is based on a set of rate equations solved by the programming package KINEL [2]. Starting from different mixture compositions the concentrations of the species under static conditions have been determined by means of a time-dependent relaxation procedure. The comparison between theoretical and experimental results for H2-Ar-CH4 and O2-Ar-CH4 plasmas shows satisfactory agreement. The central role of the methyl radical as deduced from measurements was verified by model calculations. Ethane is mainly produced by the recombination of methyl and balanced by reactions of C2H5. The behaviour of acethylene is mainly influenced by electron collisions of C2H4 and reactions of C2H3 and C2H. When oxygen is present formaldehyde is formed first and eventually CO. The final product of oxidation is CO2. Further details of the complex reaction scheme for methane-containing plasmas will be discussed.

1. Ohl, A. in Microwave Discharges, Ed. C.M. Ferreira & M. Moisan, New York, Plenum Press, 1993, 205.

2. Levchenko, A. and Alexeev, G., KINEL Manual, Moscow, 1994.

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Microwave Plasma Sources



MICROWAVE DISCHARGE IN SUPERSONIC AIRFLOW

AND RELATED PHENOMENA

V.Brovkin, A.Klimov, Yu. Kolesnichenko,

D.Khmara, A. Krylov, V. Lashkov,

S. Leonov, I. Mashek, M. Ryvkin

IHT RAS - MRTI, Moscow, - St.-Petersburg State

University - ARSRI Radio Apparatus, St.-Petersburg

The free localized microwave (MW) discharge in a linear and circular polarized beam was generated for the first time in a supersonic flow. The possibility of using MW plasma technology in a plasma-airflow interaction area, in particular, to change an aerodynamic drag of a body was demonstrated [1]. To realize these aims the unique experimental installation was created. It consists of: MW generator of X-band range, with peak power up to 200kW, pulse duration 1.3-2.2m s, repetition frequency before 1.5kHz; gas-dynamic stand, which provides a fairly uniform working flow of 20 mm diameter with Mach number M = 1.45, static pressure 60Torr and static temperature 200 K. The block of diagnostics involves Schlieren-system with time gating; spectral system; pressure sensors with the possibility to select a necessary phase of process. All this allows to research in detail the processes of interaction of MW plasmas with AD bodies in supersonic flows.

In recent investigations we focused our attention on investigation of MW plasma characteristics and eliminating the detailed structure of the interaction processes. The existence of phase of bow shock wave instability under its interaction with MW plasma in the supersonic flow of air is confirmed. The following results were obtained for discharge parameters at the end of MW pulse: gas temperature 240± 10K, vibrational temperature 1500± 200K, electron temperature 2.1-2.3 eV, specific energy input in the discharge 0.4 J/(cm3× atm), average concentration of electrons in the discharge 3× 1012cm-3. Experiments were also made with using circular polarized radiation. Numeric modeling of the kinetic processes during MW discharge and in afterglow has been done.

References

1. Proc. 2nd Workshop on Weakly Ionized Gases, AIAA, Norfolk, 24-25 April 1998, 193.

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ELECTRICAL AND SPECTROSCOPIC CHARACTERIZATIONS OF A HELICOIDAL RESONATOR FOR PLASMA GENERATION : DEVELOPPEMENT OF A NEW PLASMA SOURCE TYPE

C. Dupret, C. Foissac, P. Supiot,

O. Dessaux and P. Goudmand

Laboratoire de Génie des Procédés d’Interaction Fluides Réactifs Matériaux, Villeneuve d’Ascq , France

The present work deals with diagnostics implemented to characterize a helicoidal resonator (13.6 MHz) used as plasma source and to define the basic parameters controlling its features.

A first diagnostic have been achieved on the unloaded (in absence of plasma) coupling device by intracavity measurements (but outside of the discharge tube). By an electrical probe and a magnetic loop, we have determined the field lines spatial configuration. A measured p/2 phase-shift between electric and magnetic fields confirms theoretical description of this resonator]. The overall impedance of the plasma-coupling device system has been determined thanks to an impedance probe inserted in the energy coupling network. The known complex impedance allows one to make an energy balance on the unloaded but also on the loaded coupling device. Measurements are made on the cavity filled with a N2 plasma generated at low pressures (100 and 330 Pa) with powers equal to 50-100W. The impedance measurements allows one to determine the plasma parameters (average electron density and e-neutral collision frequency).

To complete this energetic analysis, the dominant plasma emissions and the different basic quantities (rotational and vibrational temperatures of some molecular species (N2(C), N2(B)), discharge’s length) are determined by optical emission spectroscopy. This spectroscopic diagnostic has been achieved along the discharge tube axis and the results are in good agreement with those of the electrical measurements.

This study accomplished on a high frequency plasma device is used to determine the basic behavior of the helical resonator as a plasma source. As an extension, another slow-wave cavity has been designed and tested for microwave plasma generation.

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SLOT-ANTENNA SURFACE WAVE EXCITATION IN INHOMOGENEOUS PLANAR PLASMAS WITH A LOCAL

PLASMA RESONANCE

I. Ghanashev, K. Mizuno, E. Abdel-Fattah and H. Sugai

Department of Electrical Engineering, Nagoya University, Nagoya, Japan

Planar surface-wave plasma sources, as reviewed in [1], have been found to have very good performance for dry processing in the semiconductor industry. Much effort is being made to improve the microwave power coupling to the plasma. This is of crucial importance for the operation of the planar SW plasma sources, because of the jumps of the electron density n and the related hysteresis phenomena [2]. The latter were shown [2] to be caused by the resonance minima in the n dependence of the microwave power reflection coefficient R. The widely used free-oscillation analysis from the closed-cavity model [3] can predict successfully the resonance densities at which the resonance minima will occur. However, since the coupling geometry is not included in the aforementioned model, it cannot estimate the width or depth of those minima. Therefore, the coupling optimisation is still performed experimentally on a cut-and-try basis. Recently [4] we proposed a multi-mode excitation model for slot-antenna excited planar SW plasmas of uniform density, which takes into account the actual coupling geometry. It reproduces correctly the experimentally observed phenomena and gives a theoretical bases for computer-aided optimisation. In the present contribution we consider inhomogeneous plasma with underdense and overdense regions separated by a local electron plasma oscillation resonance surface. The latter leads to broadening and overlapping of the individual eigenmode resonance curves, smoother R vs. n dependence and fewer density jumps. We present experimental results confirming the occurrence of a local electron plasma oscillation resonance, as already observed earlier in test-wave experiments [5]. Plasma parameter measurements at the resonance position confirm that the local electron density is equal to the cut-off plasma density and reveal a local peak of the electron temperature.

References:

1. Sugai et al., Plasma Sources Sci. Technol. 7 (1998) 192.

2. Ghanashev et al., Jpn. J. Appl. Phys. 36 (1997) 4704.

3. Ghanashev et al., Jpn. J. Appl. Phys. 36 (1997) 337.

4. Ghanashev et al., Proc. 17th Symp. Plasma Processing, Nagasaki, 2000 (JSAP, Tokyo, 2000, JSAP Publ. No. AP002206), p. 291.

5. Ghanashev et al., Plasma Sources Sci. Technol., 8 (1999) 363.

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INFLUENCE OF THE PLASMA INHOMOGENEITY

ON THE RF POWER DEPOSITION IN HELICON DISCHARGES

M. Krämer and B. Lorenz

Experimentalphysik II, Ruhr-Universität Bochum, D-44780 Bochum, Germany

Because of their high electron densities, helicon discharges are attractive sources for plasma applications. If the rf power is launched to the plasma by helical antennas, helicon discharges reveal a pronounced axial asymmetry (see, e.g., [1]). This finding which is the main issue of the present work can be attributed to the fact that the rf power is predominantly deposited in the plasma through helicon modes with azimuthal mode numbers m > 0 travelling in positive magnetic field direction [2].

The investigations have been carried out on a pulsed large-volume helicon discharge with m = 1 and m = 2 helical antenna coupling (tpulse = 2 – 3 ms , fpulse = 25 Hz, PRF < 3 kW, fRF = 13.56 MHz, ne < 2x1019 m-3 , Te = 3 eV, B0 < 0.1 T, p = 0.1 - 5 Pa argon gas, rp = 7.4 cm, Lp = 200 cm) [3]. Electric probe diagnostics as well as 1 mm and 8 mm interferometry was applied to determine the spatial distribution of the plasma parameters. The 3D helicon wave field pattern was obtained from an array of movable magnetic (B-dot) probes. An rf electric double probe was employed to sense the small-scale Trivelpiece-Gould waves which are excited in the outer plasma zone.

We focussed on the temporal development of the helicon discharge, i.e., the transition from an inductively coupled plasma (ICP) concentrated on the region under the antenna to the helicon discharge sustained by m = +1 or m = +2 helicon modes. In particular, we are interested in the competition between the helicon modes and the Trivelpiece-Gould waves during the formation of the helicon discharge as well as the close relation between the rf field distribution and the density profile.

The degree of axial asymmetry of the discharge is closely connected with the helicon mode propagation in non-uniform plasmas. To separate the plasma production from the wave propagation, we carried out additional wave studies in the afterglow of the discharge with strongly reduced wave field amplitudes. Our results are compared with computations from a model for the helicon mode propagation in a non-uniform plasma column as well as a fully electromagnetic antenna-plasma model [2,4].

  1. F. F. Chen, I. D. Sudit, M. Light, Plasma Sources Sci.Techn.. 5 (1996) 173.
  2. M. Krämer, Phys. Plasmas 36 (1999) 1052.
  3. M. Krämer, Th. Enk and B. Lorenz, Physica Scripta T84 (2000) 132.
  4. B. Fischer, M. Krämer and Th. Enk, Plasma Phys. Control. Fusion 36 (1994) 2003.

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ELECTRODE MICROWAVE DISCHARGES

IN MOLECULAR GASES

Yu.A. Lebedev, M.V. Mokeev, A.V. Tatarinov

A.V. Topchiev Institute of Petrochemical Synthesis RAS, Moscow, Russia

Nonequilibrium microwave discharges (2.4 GHz, absorbed power < 50 W) are described which are generated at the antenna introduced into a metal chamber (diameters were 8 and 14 cm) at pressures 0.5-15 Torr in H2, N2, air, and mixtures with CH4, [1-4]. Discharge dimensions are less than that of the chamber. Rods and tubes of different diameters, spiral and bent wire were tested as the antenna. The role of antennas is to create the nonuniforn electromagnetic field. Discharges were studied by emission spectroscopy with spatial resolution and double probe method. The discharge was successfully used in plasma chemistry for diamond growth and CNx films deposition [5,6].

Discharge can exist at absorbed power less than 1 W. Discharge has a nonuniform structure with sharp ball-shape periphery (diameter 1.5-3 cm) and bright thin region (thickness of 1 mm) surrounding the exciting electrode-antenna. Slight increase in the boundary layer intensity was observed in H2 discharge.

Estimations showed that thin bright layer is the region of main power absorption. Probe measurements indicated the existence of direct field potential differences between the probes inside the plasma ball which sharply decreases to the zero outside the plasma ball. This field can be resulted from differences in microwave field in the probes positions or from nonlinear interaction of electromagnetic field with the plasma. Observed increase in the plasma emission near the discharge boundary can be explained, as follows from probe measurements, by the surface wave existing in this discharge region.

This study was partly supported by NWO grant 047.011.000.01.

References

  1. Bardos L., Lebedev Yu.A. Plasma Phys. Reports, 1998, 24, 956.
  2. Bardos L., Lebedev Yu.A. Technical Physics, 1998, 43 , 1428.
  3. Lebedev Yu. A., Mokeev M.V., Tatarinov A.V. Plasma Phys. Reports, 2000, 26, 272.
  4. Lebedev Yu. A., Mokeev M.V. High Temp.,v. 38, 2000.
  5. Bardos L, Barankova H, Lebedev Yu.A., Nyberg T., Berg S. Diamond and related materials, 1997, 6, 224.
  6. Bardos L, Barankova H, Lebedev Yu.A. Proc. 42-nd Ann. Conf. of Soc. of Vac. Coaters, Chicago, 1999, paper E-7.

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MODE STRUCTURES OF SURFACE WAVE PLASMA

EXCITED AT 915 MHz

M. Nagatsu, A. Ito, N. Toyoda*, H. Sugai

Graduate School of Engineering, Nagoya University, Nagoya, Japan

*Nissin Inc., Takarazuka, Japan

Surface-wave plasmas (SWPs) have been noticed as a promising plasma source for large-area etching, ashing and CVD processes, since the largeñarea, high density (>1011 cmñ3) plasma can be efficiently produced even at low pressures, typically 10 mTorr. Up to now, we have studied the largeñarea SWP excited by a 2.45 GHz microwave using a slot antenna excitation, especially aiming at figuring out what antenna structure is optimum for achieving the efficient plasma production and the plasma homogeneity[1]. Further, characteristics of the surface wave mode structures have been also experimentally and theoretically studied to understand the dispersion relations of the SWs under the boundary condition of cylindrical configuration[2]. Recently, we have also tried to investigate the SWPs produced by a lower frequency electromagnetic wave, say 915 MHz UHF waves, which was motivated from an idea that the plasma enlargement will be more easily achieved and the SWP can be produced at and controlled from the lower electron densities than a 2.45 GHz MW plasma[3]. In this study, the characteristics of surface wave modes in a 40 cmñsized planar SWP excited by 915 MHz waves using various types of slot antennas have been investigated in detail. The transverse magnetic(TM) mode having mode numbers of m=3 and n=2, i.e., TM32 mode, was observed just below the square quartz window in both the cases of two-longitudinal slots and crossed slot antennas. In case of the crossed slot antenna, we also observed that the optical emission pattern clearly changed from TM32 to TM14 when decreasing the incident power and pressure. Theoretical analysis of TM modes in the present geometry agrees with experimental results of spatial distributions of electric field components. The present results indicate that TM modes can be sustained even when the quartz plate was occupied not fully, but partly in the interface between the top lid and plasma, as in the present case. As for the antenna-plasma coupling, however, the antenna structures having two transverse slots, where multi-modeñlikeñemission patterns were observed, are more efficient among the various slot antennas tested here.

References

[1] Nagatsu M, Morita S, Ghanashev I, et al. submitted to J. of Phys. D (1999).

[2] Sugai H, Ghanashev I, Nagatsu M Plasma Sources Sci. Technol. 7 (1998) 192.

[3] Nagatsu M, Ito A, Toyoda N, Sugai H Jpn. J. Appl. Phys. 38 (1999) L679.

SURFACE MICROWAVE DISCHARGE ON DIELECTRIC BODY

IN A SUPERSONIC FLOW OF AIR

V.M.Shibkov, V.A.Chernikov, A.P.Ershov, L.V.Shibkova, I.B.Timofeev, D.A.Vinogradov, A.V.Voskanyan

Department of Physics, Moscow State University, 119899, Moscow, Russia

Recently the interest to use for various applied tasks of a low-temperature plasma has revived again. So, for example, a new direction of aerodynamics - so-called plasma supersonic aerodynamics was arisen. In this case the various type of the gas discharges are applied with the purpose of influence on the characteristics of a gas flow near a surface of the flying bodies. However a physics of the gas discharge in a supersonic flow until the present time is in a phase of development. There are many unsolved questions, so as a problem of a gas breakdown in a flow, a creation and maintenance of the stable discharge in a supersonic flow of air, an influence of a flow on the parameters of the gas discharge plasma and an influence of the discharge on the characteristics of a supersonic flow. The first laboratory experiments have shown an opportunity of a drag reduction at creation of the discharges of direct and alternative currents before a body, streamlined a supersonic airflow. However the electrode discharges in a flow are unstable and spatially non-uniform. Such discharges result in strong erosion of the electrodes and model surface and reliably are not reproduced in a various realizations. There was a task of search of optimum ways of creation of nonequilibrium plasma in a supersonic flow. One of such ways offered in our laboratory, is the new version of a surface microwave discharge, namely, the microwave discharge on an external surface of a dielectric body, streamlined a supersonic flow of air.

In the report the following problems are considered:

  • Development of the new way of creation of a surface microwave discharge.
  • Experimental approbation of the new way of creation of a surface microwave discharge in a boundary layer near a body, streamlined a supersonic flow of air.
  • Study of the power characteristics determining a threshold of an appearance of a surface microwave discharge
  • Research of dynamics of a surface microwave discharge in air.
  • Measurement spatial-temporary evolution of gas and vibrational temperatures in plasma of a surface microwave discharge in air.
  • Definition of a degree of influence of a supersonic air flow on a general view of a surface microwave discharge and its parameters.

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CW LARGE VOLUME MICROWAVE DISCHARGE AT LOW PRESSURE

A.A.Skovoroda, V.A.Zhil’tsov

NFI, RRC Kurchatov Institute, Moscow, Russia

The experiment on installation PNX-U is described. PNX-U is the prototype of plasma neutralizer of 1MeV negative H ions in injector developed for ITER. The plasma neutralizer on a basis of ECR microwave discharge of low pressure in multipole magnetic trap (three-dimensional magnetic wall) is used [1-2]. The basic purpose of the present experiment consists in check of the basic principles: CW and high power efficiency of plasma production.

The experiments was curried out at gas (H2, Ar) pressure < 10-4 torr at stationary magnetic field in slits 0.35T at quasi CW (0.3s) input of 40êW microwave power on frequency 7GHz. The linear density nl = 2 1014 cm-2 at plasma length l = 2.1m (volume of plasma ~ 0.7m3) is obtained. The electron temperature 20-30eV is maximal on periphery of installation (on distance ~ 10ñm from a wall) in ECR area and falls up to 5-10eV at the center (radius of plasma 0.3m), where practically there is no magnetic field.

The total energy confinement time is 1ìs. The time is determined not only by magnetic confinement of the charged particles, but also by radiation losses. The confinement of particles is essential different for peripheral and central areas. At microwave power switch off fast decay of the peripheral hot electrons (in time ~ 0.03ìs) and slow decay of the central cold plasma (in time ~ 3ìs = classical cusp life time) were observed. At microwave power switch on the potential barrier (~ 50V) was formed because of peripheral ECR heating. Potential confinement increases confinement time of peripheral plasma up to ~ 0.4 ìs and central plasma up to 0.4s.

References

  1. Kulygin V. M., Skovoroda A. A., Zhil’tsov V. A. Plasma Devices and Operations, 1998, 6, 135
  2. Zhil'tsov V.A.,Klimenko E.Yu.,Kosarev P.M. et al.,1998,IAEA–FI–CN–69/ITERP2/04

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SURFACE WAVE PLASMA EXCITATION AT INNER TUBE

OF A COAXIAL QUARTZ GLASS TUBE

T.Yamamoto and M.Kando

Graduate School of Science and Engineering,

Shizuoka University

Johoku 3-5-1,Hamamatsu 432-8561, Japan

As it is well known, surface-wave plasmas have excellent properties such as wide gas pressure and frequency range, and flexible structure and size of discharge chamber. Therefore, they are quite attractive for industrial use. A promising field seems to be electrodeless and mercury-free light sources. Normally, surface waves are excited at outer surface of a cylindrical glass tube and propagate along the tube axis. In this configuration, the electromagnetic wave radiated from the plasma can disturb electronic instruments or can be a matter of concern for human body.

In the present work, reduction of the electromagnetic radiation from the discharge chamber is examined by changing the tube structure and the means of surface wave excitation. We use a coaxial quartz glass tube configuration. The outer diameter of the outer tube and the inner diameter of the inner tube are 45 mm and 13 mm, respectively, with length 300 mm. A coaxial waveguide with 1-mm-slot antenna inside the inner quartz tube is used as a surface-wave exciter. The plasma uniform in the axial direction can be produced throughout the chamber filled with Argon at gas pressures from 20 to 50 mTorr by applying 2.45 GHz microwaves of about 300 W. The reflected microwave is less than 10 % and the microwave radiation from the discharge tube is as low as 1/3 compared with that from normal surface wave plasma. The plasma is investigated by Langmuir probe and microwave field measurements by interferometric method. The electric field antenna with a cylindrical probe tip was inserted inside the inner tube and moved axially along the tube. The detected surface-wave wavelength is around 50 mm. The plasma density in the order of 1011 cm-3 estimated by theoretical dispersion relation agreed with that measured by double probe.

In summary, it is possible to reduce substantially the leakage of microwaves from the discharge tube when the surface wave is surrounded by overdense plasma.

 

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Microwave Plasma Applications



DEVELOPMENT OF MICROWAVE POWERED ELECTRODELESS LIGHT SOURCE IN MEPhI

A.Didenko, B.Zverev, A.Koljaskin, A.Ponomarenko, A.Prokopenko

Moscow state engineering physics institute, Moscow, Russia

At the end of the 20th century microwave power engineering was enriched by a new direction, which was connected with development of high-efficient microwave powered light source. The phenomena for conversion of MW energy to broad spectrum visible light by molecular irradiation from sulfur were developed in MEPhI. Analysis processes in plasma submersed MW fields testifies to high power efficiency of such lamps, and the tests confirm these conclusions. The bulb filled with Ar at pressure 150 Pa and sulfur dust is placed in a MW field. The microwave discharge occurs in argon, and electrons, torn off from its atom, excite sulfur. The sulfur begins to sublimate from Ts=444,6 oC and its molecules transfer into an atomic state at temperature 1200 oÑ, however such temperature is not reached in the bulb.

The molecular spectrum of sulfur having 6 modifications consists of set of close lines and is rather similar to the solar spectrum and spectral characteristics of eye. Microwave discharge with sulfur vapour admixture allows to receive not only highly effective light source (~ 20%), but also light source with a high light coefficient (70-85 %). Calculations show that to start discharge in Ar at frequency 2450 MHz is necessary to have electric field strength of the order 1 kV/cm, while for excitation of sulfur is sufficient 150 V/cm. Such field strengths are easily achieved in microwave cavities at feeding power in hundreds watts.

When practically realising the idea of new light some problems arise: a) to provide reasonable thermal regime of non-destructive for quartz envelope with Ar-S filling; b) to extract light energy from building bag of installation at microwave radiation ecological safety; c) to provide operational stability of a feeding magnetron on a resonator loading with a variable input impedance. All these problems are successfully solved for a microwave sulfur electrodeless source of visible light designed in MEPhI. To solve the first problem are proposed working cavities with an axial-symmetric electromagnetic fields. The thermal mode of a quartz bulb is essentially facilitated, then it being coaxial with the resonator and the electric field is tangential to its surfaces. Practically complete yield of a light is gained through cat-of for microwave-field holes in resonators. Frequency control system of a feeding magnetron by means of resonator loading provides the required stability of a microwave cavity.

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DEPOSITION OF CARBON MATERIALS

IN THE ECR APPARATUS

O.Matsumoto, K. Itoh, Y. Takhashi

Aoyama Gakuin University, Tokyo, Japan

We have studied the deposition of carbonaceous thin films from the pure methane plasma prepared using the ECR plasma apparatus at pressure of 4×10-2 Pa. In this case, transparent and semiconducting polymer-like carbonaceous thin films were deposited on the –45 V negatively self-biased fused silica substrate placed on the wall of the fused silica discharge tube inserted into the ECR apparatus. The deposit consisted with three dimensional cross-linked polymer including graphite [1]. The effects of the bias voltage, the pressure, and the addition of hydrogen on the deposition of the unique carbonaceous film in the ECR plasma were investigated.

In the effect of the bias voltage, the transparent and semiconducting carbonaceous film was deposited on the substrate negatively biased at the voltage of around –50 V. By the application of higher negative bias voltage, graphite-like carbon was deposited. When the bias voltage was not applied on the substrate, polyethylene-like polymer film was deposited. The acceleration of species formed in the plasma would contribute to the deposition of carbonaceous films. With increasing pressure, the deposit changed from the transparent and semiconducting film at the pressure of around 4×10-2 Pa to polyethylene-like film at the pressure of around 1 Pa. With increasing pressure, the plasma potential and floating potential decreased. As a result, the self-bias voltage was decreased with increasing pressure. When methane was diluted with hydrogen to 1:1 mixture, the deposit changed from the transparent and semiconducting film to polyethylene-like film. Moreover, diamond was deposited in the methane (10%)-hydrogen plasma prepared at the pressure of 1 Pa, whether the plasma prepared at the pressure of 1 Pa is the ECR plasma or not.

The several carbon materials were deposited from the methane including plasmas prepared in the ECR apparatus. The deposits considerably depend on the plasma conditions.

Reference

  1. T. Fujita , O. Matsumoto, J. Electrochem. Soc., 1989, 136, 2624.

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MICROWAVE PLASMA ASSISTED CHEMICAL MICROPATTERNING OF POLYMERIC BIOMATERIALS

A. Meyer-Plath, D. Keller, K. Schröder, G. Babucke, A. Ohl*

Institut für Niedertemperatur-Plasmaphysik D-17489 Greifswald, Germany

For several reasons microwave afterglow plasmas are advantageous for chemical surface modification, i.e. for the generation and alteration of functional groups. While maintaining sufficient reactivity concerning the desired modification the number of undesired reactive species in the gas phase can be expected to be quite low and thermal loads of substrates can be controlled effectively. This is of special interest e.g. for polymer surface modification.

Here we discuss the use of MW plasmas for plasma induced chemical micro-patterning. This technique is based on a sequence of plasma processing steps. In a first step the whole polymer surface is modified by a plasma process to get the desired functionalities. Then, another plasma process, which generates a different surface functionality is applied to regions of the polymer surface that were selected by an adequate micromasking technology. For example, the downstream of a H2/NH3 MW plasma (p = 0.3 - 0.8 mbar, P = 700 W) was used to create surfaces containing up to 4 % nitrogen, compared to the surface carbon content. Special attention was given to high surface densities of NH2-groups reaching up to 50% of the overall introduced nitrogen. In a subsequent step, a downstream Ar/H2 MW plasma (p = 0.3 mbar, P = 70 W) was used to remove these functionalities and create a low energetic surface.

The chemical micropattern generated this way are intended for use in biomedical application, i.e. in cell culturing applications. In this case, but also for other applications, the requirements to be met by the functionalized surfaces are high. Therefore, both of the processing steps need extremely well defined plasma conditions. This includes specially designed plasma sources.

We describe the design and characteristic plasma properties of the two different MW plasma sources used for the two processing steps. For the first processing step a new version of MW plasma sources using horn antenna MW field applicators was used. It allows the generation of disk-like active, i.e. power absorbing plasma regions with diameters of about 8” thus enabling the treatment of substrates of the same size. For the purpose of the second processing step a specially prepared downstream MW plasma source was used which consists of a quartz discharge tube inserted into a standard waveguide and fitted to a large diameter substrate treatment chamber.

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MICROWAVE PLASMA JET FOR SENSITIVE SPECTROSCOPY

K.F.Sergeichev, I.A.Sychov, D.V.Vlasov

General Physics Institute of the Russian Academy of Sciences

38 Vavilov St., Moscow, Russia, 117942

It is known that plasmatrons working at high pressures allow to get high temperatures of plasmas much more those which could be achieved by means of chemical ways in result of exothermic reactions. Owing to high plasma temperature and high brightness the plasma jets are wide applied in a spectroscopy last time because the torches increase sensitivity of spectral technique by orders. This circumstance is very important for measuring of chemical element traces in different probes. It is naturally that HF and microwave jet discharges are most pure for the spectroscopy because both doesn’t need electrodes.

In this work the coaxial microwave torch is used for spectrum emulation. Such torches were used in the 60’s both for plasma chemical reactions and for welding small parts of metals under reducing atmosphere [1]. The interest is now revived with respect to melting of refractory metals [2].

Data of both the jet microwave discharge parameters and the spectroscopy technique tests are presented.

 

References:

  1. G. Puschner, Heating with microwaves. Fundamentals, components and circuit technique. 1966.
  2. S.I.Gritsinin, I.A.Kossyi et al., Plasma coaxial discharge as a new type of the microwave surface wave discharge. Preprint GPI, 1999, N 1.

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ACTIVITIES FOR DIAMOND DEPOSITION

USING DIFFERENT PULSED DISCHARGES

A.L. Vikharev

Institute of Applied Physics, RAS, Nizhny Novgorod, Russia

The paper reviews works on deposition of diamond films by using microwave discharges ignited in the pulse-periodic regime. Plasma parameters, kinetic processes, growth rate and quality of the diamond films in microwave reactors operating in the CW and pulse regimes are compared. The results of numerically modeling the reactor based on the cylindrical cavity excited in the CW and pulse regimes at the TM013 mode are compared. Basing on the results of experimental and theoretical studies the possibility to apply pulse-periodic microwave discharges for diamond film deposition is estimated.

 

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RESIST ASHING EMPLOYING MICROWAVE OXYGEN PLASMA

WITH HIGH PERMITTIVITY MATERIAL WINDOW

Kouta KUSABA, Keisuke Shinagawa*, Masakazu FURUKAWA*,

Katsufumi KAWAMURA* and Haruo SHINDO

Department of Applied Physics, Tokai University, Kitakaname 1117,

Hiratsuka 259-1292

*Canon Sales Corporation, Process Equipment Division, Kounan 2-13-29, Minatoku, Tokyo 108-0075

Microwave plasma is one of candidates for large diameter plasma sources of the next generation. One issue in large diameter microwave plasma sources is on dielectric window material for microwave introduction.

In this work, the microwave plasma production in a large diameter was studied employing a high permittivity window material. Especially, the plasma properties in O2 were examined in a viewpoint of the permittivity of the window material. If the microwave power is transferred into plasma in a surface wave mode, the plasma behaves depending on the permittivity of the window material.

The plasma was produced in an aluminum chamber of 240 mm in diameter by introducing 2.45GHz microwave through a dielectric window of disc plate of 240 mm in diameter. Two kinds of dielectric materials, the quartz and alumina, were employed in this experiment and their permittivities were, respectively, 3.86 (14.9 GHz) and 9.7 (10 GHz), where the frequency used for the permittivity measurement was given in the parenthesis. The plasma parameters were measured by Pt plane probe of 1 or 0.5 mm in diameter in O2 plasma. The ashing rate of the photo-resist (PFI-58) was also measured at the substrate temperature of 200.

The results showed that the higher permittivity alumina window yielded two times higher electron density than the other in the regime above the cutoff of the microwave. Since the modes observed by the magnetic probe was consistent with the dispersion, it was concluded that the plasma production is due to the surface wave. The resist ashing experiments, which was performed in 8 inch wafer, showed that the rate was 2 times higher with the alumina than the other and the activation energy of resist ashing reaction was very close to that obtained for a purely chemical reaction. A wafer damage was analyzed by both DLTS and carrier life time measurement, and it was concluded that a choice of the high permittivity window material provided one novel method for a large diameter wafer ashing processes with a high rate and low damage.

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ELECTRODLESS MICROWAVE DISCHARGES AS SOURCES

OF LIGHT AND UV-EMISSION FOR

THE ILLUMINATION AND BIOMEDICAL APPLICATIONS

A.Kozlov1, V.Perevodchikov2, R.Umarhodzaev3, E.Shlifer2

1 – IZMIRAN, 2 – VEI, 3 – NIINPh MSU; all – Moscow.

The report contains some results of the researches and designings of Microwave-light modules for the Illuminating and Irradiating plants, which use the electrodless Microwave discharges in the different gases.

The main problems and their solutions are considered for use in the plants of quasi-Sunlight and UV-irradiation.

The features of designing of Microwave structures, field distributions are required in the interaction space, providing the stability of magnetron generation when it works at the large alternating reflections, and others are estimated.

The phenomenological picture of discharge excitation and stabilization is presented.

The irradiation spectrums are shown.

Some results and features of the creation the bactericidal plant for the complex Microwave, UV- and ozone treatment are presented. The original UV-electrodless lamps, which used the Microwave excitation are applicated in this plant.

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