Session MPD - Discharge Experiments Poster Session.
POSTER session, Monday afternoon, October 21
Alcove B,

The efficiency and effectiveness of RF plasmas used for materials processing will benefit from a greater degree of control over the physical and chemical interactions in the plasma and these can in principle be manipulated through the electron energy distribution. This work investigates the electrical means of tailoring plasma properties so that more effective use can be made of particular plasma sources. This is achieved by controlled injection of electrons into the plasma. A robust, electron gun has been developed for use with a capacitively driven radio frequency (13.56MHz) discharge. Experiments and particle simulations are in progress. Early results show considerable scope for controlling plasma density, potential structure and electron energy. The location of the gun within the plasma system is found to be critical and the use of two guns at different locations to be advantageous.

[MPD.02] Plasma Generation in High-Current Ion Sources

We are using kA/cm^2 ion sources to generate intense pulsed ion beams for driving Inertial Confinement Fusion targets. These sources are the anode of an ion diode that uses several-Tesla magnetic fields to restrict electron flow across the diode while permitting ion acceleration. Our 2 cm diode anode-cathode gaps have 10 MV applied in order to accelerate Li ions from 100-1000 cm^2 anode areas. During the 50 ns beam pulse, we observe a transition in beam content from Li ions to H,C,O impurity ions. As well, a significant fraction of the total diode current is in electrons leaking across the magnetic insulation to the anode. The several-GW/cm^2 leakage flux of MeV electrons deposits large amounts of energy into the anode surface, releasing physi- and chemi-sorbed impurities in the modest 10^-5-10^-6 Torr diode vacuum. These desorbed impurity neutrals can expand and rapidly ionize within about 200 \mum of the anode during the beam pulse. We are modeling this process in a multi-dimensional hybrid fluid/PIC code and making spectroscopic measurements to quantify these mechanisms.

[MPD.03] Investigations of the 147 nm radiative efficiency of Xe Surface Wave Discharges

The radiative efficiency of the 147 nm resonance radiation of Xe excited in a low-pressure, high-frequency surface wave sustained plasma has been investigated. The radiative UV power has been obtained from optical absorption spectroscopic measurements of the Xe resonance level population and from Monte Carlo calculations of the effective decay rate of this level. Precise measurements of the RF power absorbed by the plasma enable the determination of the absolute UV discharge efficiency for the Xe surface wave discharge. Results show efficiencies as high as 0.80 (10).\footnote Work supported by General Electric and the NIST under the ATP (# 70NANB3H1372).\par \parindent0pt *Dept. of Physics and Astronomy, Denison Univ., Granville, OH 43023\par \parindent0pt **Dept. of Mech. Eng., Univ. of Minnesota, Twin Cities, MN 55455

[MPD.04] Excimer Emission using 20keV Electron Beam Excitation

A small, continuously emitting rare gas excimer light source has been developed. The gas is excited by a 20keV dc-electron beam. A 300nm thick, 1\times1mm^2 SiN_x foil sustaining a pressure difference up to 2bar, separates the target volume from the high vacuum part of the electron gun. Spectra of the rare gases Ar, Kr, and Xe have been studied. The monochromator detector system was intensity calibrated in the wavelength range from 115nm to 320nm. Electron beam currents of typically 1\muA were used for excitation. When used as a VUV lamp on the second excimer continua, energy conversion efficiencies of 30% were obtained. Emissions originating from the so called left turning points have been clearly observed at 155, 173, and 222nm in Ar_2^*, Kr_2^*, and Xe_2^*, respectively. The so called third continua between 185nm and 240nm (Ar), 220nm and 250nm (Kr), and at 270nm (Xe) have been studied. A new continuum in Xe at 280nm was found.

(Funded by the A.v.Humboldt Foundation and NSF (CTS 94-19440). The authors acknowledge support by H. Huggins, A. Liddle and W.L. Brown (Bell Laboratories, Lucent Technologies))

[MPD.05] Experimental and Theoretical Studies in the Pulsed Xenon Medium Pressure Discharge

In the positive column of a pulsed xenon glow discharge time-resolved measurements of the axial electric field strength, the absolute densities of the 1s_5 (metastable) and the 1s_4 (resonance) state, and the VUV radiation in the range of 140-180 nm have been performed. For gas pressures between 1 and 40 Torr, currents between 100 and 300 mA, and repetition frequencies of some kHz the densities of the excited states, measured by hook method, varied from 1 \times 10^11 to 5 \times 10^12 cm^-3. The experimental results are compared with results obtained by model calculations. In the frame of the model for the pulsed, constricted discharge plasma the time-dependent electron Boltzmann equation for the determination of the electron kinetics, the rate equation system for the relevant heavy particles occurring in the plasma, and an appropriate equation for the axial electric field are self-consistently solved. The time-dependent treatment of the electron kinetic equation (including electron-electron interaction) is based on the conventional two-term approximation and the quasi-steady-state description of the anisotropic part of the velocity distribution. The rate equation system describes the temporal evolution of three excited atomic states, two molecular levels, the atomic and the molecular ion. Based on the theoretical results the time-dependent behaviour of the electron and the heavy particle kinetics is analysed.

[MPD.06] Quantitative Analysis of a Stabilized Discharge-Pumped XeCl Laser

Recently a new method for providing stable, homogeneous electrical discharges for pumping wide-aperture excimer lasers has been proposed (Yu. Bychkov, I. Kostyrya, M. Makarov, A. Suslov, A. Yastremsky, Rev. Sci. Instrum. 65), 793 (1994).. The development of a homogeneous discharge plasma has been achieved by applying a special pumping technique using an additional stabilizing low-current preliminary discharge with a typical duration of 0.5 to 1 \mus. For this excimer laser discharge a theoretical analysis of the kinetics of electrons, heavy particles, and laser photons is given and the impact of various parameters characterizing the discharge on the temporal behaviour of the discharge characteristics is discussed. To model the discharge plasma the equation system for the electrical circuit, the rate equation system for various heavy particles occurring in the plasma and for the laser photons in the optical cavity, and the time-dependent electron Boltzmann equation including the electron-electron interaction has self-consistently been solved. The contribution reports on a XeCl laser with a calculated output energy of about 1.4 J with an efficiency of about 1% and a laser pulse duration of about 400 ns.

[MPD.07] Abnormal beharviors of O_2^- mobility in O_2/O_3 mixtures.

Negative ion mobilities in O_2 have been investigated at atmospheric pressure \footnote H. Itoh, K. Norimoto and T. Hayashi, Proc. Korea-Japan Symp. on Electrical Discharge and High Voltage Engineering, 179 (1996). The measured range of E/p_0 for our experiment is the lowest among in the reported ones. The zero field mobility of O_2^- is determined to 2.07 \pm 0.02 cm^2/V\cdots in 99.9995% O_2. This value agrees well with the value mesured by Sunggs et al \footnote R.M. Sunggs et al, Phys. Rev. A, 3, 477 (1971). These experiment is expanded in O_2/O_3 mixtures. Ozone is produced by a silent discharge tube connected at the upstream side of gas inlet of the main chamber. The concentrations of ozone are maintained at 270 and 500 ppm during the experiment. Our value of mobility of O_2^- in O_2/O_3 mixtures becomes smaller than that in O_2. The dependence of E/p_0 of the mobility do not appeares. We assume the accumulative effect of any neutrals generated by silent discharge.

[MPD.08] New Laser Induced Fluorescence Studies of Low Temperature Noble Gas Discharges

Low temperature noble gas discharges have been investigated both experimentally and theoretically using laser induced fluorescence (LIF) in the pressure and current regimes of 1 - 10 torr and 1 - 10mA, respectively. Here we employ slowly chopped ( 90 Hz) CW laser radiation to perturb the excited-state populations of the noble gases and record the fluorescence as the system relaxes. We have developed a successful rate equation model for the LIF spectrum observed from the positive column of the neon normal glow discharge. We have also carried out experiments with helium and argon and are at present using our model to describe these observations. The model successfully describes the observed primary and secondary (i.e. collisionally coupled) LIF signals in neon and we are confident this will be the case for argon and helium. The theory used to describe the observed LIF complements our work on laser optogalvanic spectroscopy (LOGS),emission and absorption spectroscopy of these discharges. These diagnostics will be discussed along with our experimental and theoretical LIF results.

[MPD.09] Diffusive Cooling of Ions in a Hollow Cathode Discharge

From ndgibson@facstaff.wisc.edu Fri Jun 7 09:48:11 1996 Received: from audumla.students.wisc.edu by aps.org (8.6.12/1.35) id NAA17144; Fri, 7 Jun 1996 13:52:18 GMT Received: from Lawler by audumla.students.wisc.edu; id IAA25920; 8.6.9W/42; Fri, 7 Jun 1996 08:50:47 -0500 Date: Fri, 7 Jun 1996 08:50:47 -0500 Message-Id: <199606071350.IAA25920@audumla.students.wisc.edu> X-Sender: ndgibson@facstaff.wisc.edu Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" To: abs-submit@aps.org From: ndgibson@facstaff.wisc.edu (N. D. Gibson) Subject: GEC96 X-Mailer:

\documentstyle[11pt,apsab] article \nofiles \MeetingID GEC96 \SubmittingMemberSurnameMullman \SubmittingMemberGivenNameKrista \SubmittingMemberEmailmullman@wishep.physics.wisc.edu \SubmittingMemberAffilPhysics Department, University of Wisconsin, Madison, WI

\PresentationType poster \SpecialInstructions \SortCategoryC2 \DPPType \lognumber5023 \received7 Jun 1996 \begindocument \TitleDiffusive Cooling of Ions in a Hollow Cathode Discharge

\AuthorSurnameMullman \AuthorGivenName K. L.

\AuthorSurnameSakai \AuthorGivenNameM. \AuthorSurnameLawler \AuthorGivenNameJ. E. \AuthorAffilPhysics Department, University of Wisconsin, Madison, WI 53706

\begin abstractWe present evidence of diffusive cooling of ions in the negative glow (NG) of a hollow cathode discharge (HCD). For typical radius-gas density products in a HCD, the ambipolar diffusion (ion loss) rate from the NG and the collisional thermalization rate are nearly same. Since collisional thermalization fills out the tail of the Maxwellian distribution, the competition results in a somewhat truncated ion velocity distribution. This effect is observed in our High Sensitivity Absorption experiment on iron ions. The curve-of-growth for the analysis of our absorption data uses a Voigt spectral lineshape. The most satisfactory "effective" ion temperature in the Voigt lineshape is unphysically low (below the water cooled cathode temperature) under low current conditions. Effective ion temperatures are determined by requiring that the curve-of-growth analysis of the absorption data accurately reproduce well known oscillator strength ratios for singly ionized iron. \footnote Supported by the NASA and the NSF.

[MPD.10]

This abstract was not submitted electronically.

[MPD.11] Pulsed Discharge Excited Argon Clusters Formed in a Supersonic Slit Expansion

The argon second continuum excimer emission is observed in a pulsed discharge excited pulsed supersonic jet. The expansion nozzle is a 15 cm long slit with a width which can be varied from 35 \mu m to 250 \mu m. The intensity of the argon excimer emission near 126nm is investigated as a function of the width of the expansion nozzle slit, position within the cathode-anode gap and electrode configuration. The pressure within the nozzle has been measured as 2--4 bar and the excitation consists of a 50 ns negative (or positive) current pulse of about 15kV and 700A. The observation of the emission depends directly on the size and quantity of clusters formed in the expansion.(M.F. Masters et. al. J. Appl. Phys. \bf75) 3777 (1994),(K. Mitsuhashi et al. Opt. Lett. \bf20) 2423 (1995) To determine the dependence of the emission upon clusters and the cluster size distribution, the cluster size distribution is varied by varying the expansion nozzle slit width. The temporal evolution of the second continuum emission and the observed spectra are presented as a function of nozzle slit width. The observed behavior are modeled using a kinetics code.

[MPD.12] Radical Density Measurements in an Oxyacetylene Torch Diamond Growth Flame

The densities of several molecular radicals are measured in an oxyacetylene torch flame during the growth of diamond films. The densities of radicals such as CH, C_2, CN, and OH are determined by high sensitivity absorption spectroscopy. The radical densities are measured as a function of position in the flame for different fuel/oxidant ratios. The growth of diamond is confirmed by scanning electron microscopy and Raman spectroscopy. The measured densities are compared with other theoretical and experimental values.

[MPD.13] Contaminant Ion Effects on PSII Fabricated Diodes

Plasma Source Ion Implantation\footnote J.R. Conrad, J.L. Radke, R.A. Dodd, F.J. Worzala and N.C. Tran, J. Appl. Phys. 62, 4591 (1987). has long been regarded as an alternative to classical ion implantation. An open question concerns the effect of plasma- sputtered contaminant ions on device characteristics. A suite of experiments is currently underway which quantifies the allowable level of contamination in a diode array fabricated on 3 inch N type <100> silicon wafers. The processing of the wafers is standard except for the implantation step which introduces measured quantities of both boron and contaminant ion species. The energies of both ion species is the same to simulate conditions found in the PSII chamber. The first contaminant to be studied is aluminum since it represents the material of choice for constructing PSII chambers. Other contaminants will be investigated as well. Supported by NSF Grant EEC-8721545.

[MPD.14] The Kinetics of processes in decaying plasma of a Jet Diaphragm-Type Discharge

This abstract was not submitted electronically.

[MPD.15] The Effect of Precursor Composition on 2-D CF_2 Concentration in C_xH_yF_z/Ar Plasmas in the GEC rf Reference Cell Measured by Planar Laser-Induced Fluorescence

Although low-pressure radiofrequency (rf) plasmas are extensively used during microelectronics device fabrication, the chemical processes occurring in these plasmas are not well-understood. Because a clear understanding of the chemistry of such plasmas would aid in ensuring reproducibility during plasma processing, both model development and experimental investigations concerning the chemistry of these plasmas are currently underway. Spatially-resolved, two-dimensional species concentrations in the plasmas measured in a standardized reactor add insight into the important chemistry occurring in the plasmas and also provide necessary experimental input and verification of the models. In this work, planar laser-induced fluorescence (PLIF) is used to determine the spatial distribution and relative density of CF_2 in low-pressure C_xH_yF_z/Ar plasmas generated in a 13.56 MHz parallel-plate Gaseous Electronics Conference (GEC) reference cell. By using various C_xH_yF_z precursors including CF_4, CHF_3, CH_2F_2, CHF_3 and C_2F_6, the effects of precursor stoichiometry (C:H:F ratio) and precursor chemical form on the spatial distribution and density of gaseous CF_2 was investigated. These results provide insight into possible chemical mechanisms important in plasma chemistry.

[MPD.16] Time-resolved negative ion flux from a pulsed inductive discharge

Pulsed rf discharges are gaining popularity in research into plasma processing because of the potential benefits of reduced particulate formation, lowered electron temperature, and the possibility of new surface reactions arising from the presence of negative ions at the substrate. The time-evolution of a pulsed inductive discharge is revealed by several diagnostics, including a mass spectrometer, ion energy analyzer, langmuir probe, B-dot probe, and microwave interferometer. We will present measurements of the negative ion flux from plasmas in common electronegative processing gases, including SF6, correlated with density, temperature, potential, and field measurements to present an overall picture of the properties of pulsed inductive discharges.

[MPD.17] Compact slot antenna type plasma source: Improvement of performance by magnet confinement

A new compact 2.45 GHz magnetically enhanced plasma source of slot antenna type is presented. Plasma is generated in a quartz tube with diameter of 40 mm and a length of 500 mm. The microwave power is supplied from an annular cavity through four slot antennae positioned equidistantly around the inner wall of an application space. The application space is closed in axial direction by two permanent magnet holder. The plasma ignition/extinction performance of the source and plasma parameter for different atomic (Ar, He) and molecular (oxygen, nitrogen) gases were studied. Ion concentrations and electron temperatures were measured by use of a double Langmuir probe technique in the pressure range from 0.0008 to 0.5 Pa. Typical ion concentration achieved for 600 W microwave power

is 4 x 10^11 cm^-3 at a pressure of 0.005 Pa for argon and 0.02 Pa for

oxygen. Electrone temperatures in plasma confined between magnet holders are as high as 10 eV. Out of this region values from 1 to 4 eV are measured. The results for three different magnetic confinements: the axial, multi-cusp and the filter one were compared. The higher values of ion concentration are achieved for axial confinement with vector of magnetization azimuthally oriented accordinbgly to the slot antenna position. The ionization ratio of 55% for argon and 12% for oxygen are obtained. Axial

distributions of plasma parameter were used to examine the influence of the application volume length on the plasma parameter distributions.

[MPD.18] Positive voltage-current characteristics caused by electron-impact mixing of excited atomic levels

Electric discharge plasmas generally exhibit a negative V-I (voltage-current) characteristic and hence require a ballast for stable operation on ordinary voltage sources. However, there are instances in the literature of positive V-I characteristics in the positive column itself which cannot be attributed to the usual suspects: electrode phenomena, species segregation, high ionization fraction, and so on. An explanation for positive voltage-current characteristics (PVICs) seen in low-pressure argon-mercury discharges has been constructed using both a comprehensive model(T. J. Sommerer, J. Phys.\ D 29), 769 (1996). and simplified rate equation models, along with various published and unpublished data. The cause of the PVIC is electron-impact ``conversion'' of metastable mercury atoms into resonance-level atoms, a process which interferes with the dominant ionization mechanism over discharge current densities 0.1--10 mA/cm^2.

Part M of program listing