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Plasma Science, 1997. IEEE Conference Record - Abstracts., 1997 IEEE International Conference on

Date 19-22 May 1997

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  • IEEE Conference Record - Abstracts. 1997 IEEE International Conference on Plasma Science

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  • Helicon waves in theory and experiment

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    Summary form only given, as follows. The use of helicon waves to produce high density plasmas for semiconductor chip fabrication tools is by now well known in that industry. Basic research on helicon discharges in the last ten years has greatly improved our understanding of how these plasma sources work. At high magnetic fields, the wave fields have been carefully measured and found to agree well with the classical theory of helicon waves. The theory has been extended to low magnetic fields by including the coupling to cyclotron waves. Experiments in this range have also been done. The transition to zero magnetic field turns out to be nontrivial and rather interesting; this is a region in which many industrial plasma sources operate. As a result of efforts by several groups, numerical computations that include the effects of damping, plasma inhomogeneity and antenna coupling can now be made on a simple computer. Unfortunately, the very nonuniform magnetic fields in production tools still require extensive modeling. We are now in a position to answer several intriguing questions that have puzzled experimentalists for many years: 1) What is the rf absorption mechanism that makes helicon discharges so efficient? 2) Why is the m=-1 azimuthal mode so much harder to excite than the m=+1 mode? 3) What causes the discontinuous jumps in density as the magnetic field or rf power is increased? 4) What fields are generated under and near the antenna? Experimental and theoretical data that bear on these questions will be shown. View full abstract»

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  • Velocity-shear origin of broadband electrostatic noise

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    Summary form only given, as flows. Multiple, independent eigenmodes of an inhomogeneity-driven instability are observed simultaneously with large and comparable amplitude. This is in sharp contrast to the usual case in plasmas in which one eigenmode dominates or, for conditions far above the excitation threshold, a collection of harmonics appears. The significance is that the spectral features are not separated by the ion gyrofrequency /spl omega//sub ci/, or any other normal-mode frequency of the plasma. This has implications regarding the spectral width of the fluctuations, which, in some cases, can exceed 50% of center frequency. Furthermore, the spectral features are Doppler downshifted, in some cases to frequencies associated with ion-acoustic modes. For example, /spl omega///spl omega//sub ci/=0.25 are readily observed (recall that T/sub i//T/sub e/ is of order unity). These facts are particularly unexpected because the plasma conditions correspond to large excitation thresholds for current-driven electrostatic ion-cyclotron (CDEIC) and ion-acoustic (IA) waves. The results have direct relevance to recent SCIFER and AMICIST rocket experiments in the Earth's cleft ion fountain where electrostatic waves (/spl omega/ View full abstract»

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  • Experimental study of polarization of lines, emitted by the plasma of Z-pinch devices

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    Summary form only given. Polarization of X-ray lines is a well known fact in solar plasma. An experimental study of polarization of X-ray line emission from laboratory plasmas (plasma focus device, vacuum spark device) are given in this paper. The Investigation of spectra of He-like Ar in the range of 3.5-5 A, emitted from the plasma of Mather type focus device and spectra of He-like Fe in the range of 1.7-2 A from vacuum spark device were carried out by two focusing spectrographs with quartz crystals (2d=8.5 A; 2d=6, 67 A). The dispersion planes of devices were oriented perpendicular one with respect to another. The main feature of the spectra obtained is the difference between the relative intensities of resonance and intercombination lines, registered in the same experiment with different spectrographs. View full abstract»

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  • Gyrobroadening of fast ion energy spectrum in magnetized plasma

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    Summary form only given, as follows. A gyrobroadening process causing the perpendicular energy of fast ions to be broadened by cyclotron instabilities due to the weak relativistic mass variation of the fast ions in magnetized plasma is reported. At low cyclotron harmonics, a two-gyro-stream instability can be excited with the involvement of thermal ions if the condition l/sub f//spl omega//sub cf/ View full abstract»

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  • Influence of density gradient on absorption of upper hybrid pump energy in turbulent plasma

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    Summary form only given, as follows. In the present report on the basis of kinetic fluctuation theory we study the absorption of an upper hybrid wave in magnetized inhomogeneous plasma with density gradient. We have calculated the effective collision frequency V/sub eff/ in the turbulent state of such a plasma when the amplitude of pump wave E/sub 0/ exceeds the parametric instability threshold E/sub th/. As it turns out V/sub eff//spl Gt/V/sub ei/ where V/sub ei/ is the electron-ion collision frequency. We have thus deduced the efficiency for the absorption of upper hybrid wave energy in a plasma, as the absorbed power is proportional to V/sub eff/ E/sub 0//sup 2/. Our results can thus be of interest for upper hybrid heating of plasmas. View full abstract»

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  • Cross correlation of the low-frequency electromagnetic excitations and anomalous diffusion in a plasma

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    Summary form only given, as follows. It is known that the magnetic perturbations in a plasma result in enhanced transport. A more interesting and complicated situation arises when the potential and magnetic fluctuations are correlated, requires further analytical investigation. Such a correlation may be induced by an external current and electric field or neutral beam injection etc. The general renormalized statistical approach with cross-field correlations applied to the study of long-wave (wave lengths greater than the ion Larmor radius) low-frequency (frequencies not exceeding the ion Larmor frequency) electro-magnetic plasma fluctuations, yields cross correlations that produce a negative correction to the renormalized damping coefficient of the electro-static perturbations and therefore, attenuate the diffusion. View full abstract»

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  • Boundary conditions for use in plasma simulations

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    Summary form only given, as follows. Boundary conditions are presented for use in magnetohydrodynamic, particle-in-cell, and multi-fluid computer programs. The boundary conditions consist of velocity moments for three plasma species near a plasma-facing surface. The three plasma species are plasma ions, plasma electrons and surface emitted electrons. The boundary conditions are developed using a fully kinetic theoretical description of the plasma sheath which takes into account space-charge saturated electron emission from a plasma-facing surface. It is necessary to take into account space-charge saturated electron emission from the plasma-facing surface because of a recent finding which indicates that most of the commonly-used plasma-facing surface materials can reach secondary electron emission coefficients large enough for the emission to be space-charge limited. The boundary conditions are in terms of sheath and presheath potential drops and simple expressions (which are fits to numerical results) are provided for these potential drops. View full abstract»

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  • Self-sustained oscillations in spatially confirmed beam-plasma systems

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    Summary form only given. This paper is dedicated to stable oscillations that, in our opinion, result from finite dimensions of the beam-plasma system. Both longitudinal restriction and finite radius of the beam create disrupted feedback and supply initial beam bunching. The task has been solved for a self-consistent approach. Neither the travelling nor standing wave is postulated. Non-linear integro-differential equations have been formulated for beam bunching. The equations implicitly include the necessary amplitude and phase relations. The condition of solvability of the equations determines the spectrum of frequencies for possible self-excited oscillations and the solutions give the amplitude of beam bunching wave and its spatial dependence. Also the case of oppositely directed beams in a plasma has been analyzed. View full abstract»

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  • Simulation tools for the design and analysis of plasma processing equipment

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    Summary form only given. Plasma processing equipment has become one of the most important tools used for microelectronics fabrication. The increasing complexity of microelectronics devices is making it imperative to develop a thorough understanding of this equipment. In order to accomplish this goal, a hierarchy of simulation tools have been developed at the University of Illinois in the recent years. These tool are centered around the Hybrid Plasma Equipment Model (HPEM), detailed plasma model. This paper gives an overview of the HPEM, its extensions and the variety of problems these tools can address. View full abstract»

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  • Real time characterization of plasma etch selectivity

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    Summary form only given. In-situ real-time measurement of thin film etching and deposition is necessary for semiconductor process development as well as monitoring and control. The relatively high process rates in high density plasma tools and the shrinking thickness of the films, call for a fast estimate of the process rates. Two-color laser interferometry operated at two locations is used to determine in real-time, within a second, the etch rate and thickness of two thin transparent films. The advantages of two-color laser interferometry will be described. The selectivity of the process is calculated from the ratio of the instantaneous process rates of the films as a function of the tool state. The experiment is carried out in a magnetically confined ICP tool. The tool state, gas flow, pressure, and RF power to the antenna and the electrostatic chuck, used to bias and cool the wafer, are computer controlled and monitored. The etch selectivity of polysilicon and SiO/sub 2/ films using Cl/sub 2/, CF/sub 4/ and CHF/sub 3/ gases over a large parameter space of tool states will be described. The experimental setup is configured to utilize both single and double laser points. Both schemes are used to determine the etch rate of the two films. View full abstract»

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  • Real-time control and modelling of plasma etching

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    Summary form only given. To meet the challenge of real-time advanced process control, the instantaneous process state needs to be determined. The relatively high process rates in high density plasma tools as well as the shrinking thickness of the films, require a fast estimate of the process state in order to implement process control. The research objective is to determine within a second the process rates and to implement real-time control of the films etch rate. Several in-situ, non-invasive and non-destructive sensors such as a laser interferometer and a full wafer interferometer are used to monitor the process state in a magnetically confined ICP tool. The advantages of two-color laser interferometry for real-time process monitoring and control is described. Langmuir kinetics modeling of the measured etch rates of polysilicon and SiO/sub 2/ films using Cl/sub 2/, CF/sub 4/ and CHF/sub 3/ gases over a large parameter space of antenna and wafer-stage RF power, gas flow, pressure and gas additives is described. Etch modeling enabled us to develop a real-time control algorithm. The results of real-time etch rate control of unpatterned SiO/sub 2/ and polysilicon films is described. View full abstract»

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  • Model etch profiles for argon and chlorine ion energy distribution functions in inductively coupled discharge plasmas

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    Summary form only given. Measured argon and chlorine ion energy and angular distribution functions are fitted to drifted Maxwellian distribution functions by a simulated annealing procedure. The ion energy and angular distribution functions have been measured in inductively coupled radio frequency discharges in argon and chlorine plasmas in a modified GBE reference cell. The ion energy distribution function data for several gas pressures and RF powers are a good fit to one drifted Maxwellian and an excellent fit to two drifted Maxwellians in most cases. Etch rates for trenches are calculated for the fitted ion energy distribution functions from approximate analytical expressions found previously for drifted Maxwellians. The etch rate expressions are valid in the ion flux-limited regime where the etch rate is proportional to the ion energy flux for long rectangular trenches. Trench etch profiles on semiconductor wafers are calculated numerically from the trajectory equations of the etch profile equation with the computer program MatLab. View full abstract»

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  • Characterization of stationary and rotating magnetic fields in an MERIE

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    Summary form only given. Magnetically enhanced reactive ion etchers (MERIE) have been shown to be useful for etching half micron features and below. The benefits of adding a magnetic field are two fold: a higher plasma density and low ion energies. Rotation of the magnetic field results in excellent etch uniformities. The etch rate uniformity across the blanket and thermal oxide wafers was studied for stationary and rotating magnetic fields under a variety of typical contact etch processing conditions. The plasma uniformity has been mapped through measurement of the wafer etch pattern under conditions of a stationary B field. Of particular interest is the correlation between the instantaneous plasma uniformity and the resulting (time averaged) uniformity seen by the wafer as the B field is rotated. Process conditions that gave not only the best etch uniformity but also exhibit the best instantaneous plasma uniformity were the goal of the study. View full abstract»

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  • Plasma-ion beam treatment of Al for enhanced corrosion

    Page(s): 119 - 120
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    Summary form only given. The micro-second Plasma Opening Switch (MPOS) provides an innovative approach for efficient generation (up to 50% and higher) of large area (10/sup 2/-10/sup 3/ cm/sup 2/) intense ion beams with variable and controlled density in the range of 10-10/sup 2/ A/cm/sup 2/, and energy of 10/sup 5-6/ eV. The paper describes the experimental device and results on the application of low voltage ion beams generated in MPOS for various metals surface modification with focus on Al alloys (Al 2014-24, Al 7075, Al-6061). At a charging voltage of 40 kV, the induced voltage, total MPOS stored current, and ion current amplitudes are 150-200 kV, 100-130 kA and 25 kA, respectively, with the ion current density varying in the range of 10-120 A/cm/sup 2/ along the inner cathode surface. Analysis of structural and electro-chemical properties of the MPOS treated Al samples are given, supported by computer simulation results on the solid/melted/gas phases transition dynamics in the upper layer. View full abstract»

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  • Ionized physical vapor deposition characterized for ionization fraction and deposition rate

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    Summary form only given. An inductively coupled plasma (ICP) RF antenna is added to a commercial magnetron sputtering machine. The power absorbed by this multi-turn water-cooled coil heats the electrons and raises their density, thereby increasing the ionization cross section for the metal sputtered neutrals. This creates up to 78% ionization of the depositing flux with less than 800 W of RF power at 2.5 kW of magnetron power. By applying a bias to the substrate the majority of the metal can be deposited normally, and at energies controllable by the set bias level. Aluminum and copper targets are used with argon and neon working gases. Operating pressures of 15 to 35 mTorr are investigated. Alternate ionization schemes not requiring an in-situ antenna are also investigated. The applications of this design to higher aspect-ratio trenches and sub-.5 /spl mu/m features is discussed. View full abstract»

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  • Investigation of diagnostic sensors and control models for a compact ion source

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    Summary form only given, as follows. The diagnostic measurement, modeling, and control of a compact ion/radical source operating at 2.45 GHz microwave frequency is investigated for argon and hydrogen discharges. The investigation of the plasma source includes relating the run-time adjustable inputs, plasma source sensor outputs and process control models. The adjustable inputs include input microwave power, chamber pressure, gas flow rate, and resonant cavity tuning. The plasma source sensor outputs include reflected microwave power, electron temperature, ion density, electron/ion energy distribution and plasma potential. In order to determine the neutral and charged species in the hydrogen discharge, actinometry and OES measurements are used. The process model is the relationship between sensor measurements and input settings or the relationship of output parameters to the input and sensor readings. The sensor measurements combined with analytical and numerical models are used to estimate the plasma source output at various positions. View full abstract»

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  • Laser-driven ion sources for high-brightness high-purity ion beams

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    Summary form only given. Surface-plasma ion sources are critical to generating high-brightness, high purity ion beams on applied-B ion diodes. The source plasma must meet requirements for species, thickness, purity, degree of conductivity, formation timescale, and feasibility. Laser ionization schemes have been used on high-power ion diodes with encouraging but inconsistent results in diode impedance and beam purity. We are characterizing two laser-driven Li/sup +/ schemes for 100-200 cm/sup 2/ sources: a single 10 ns Nd:YAG pulse at 0.3-1 J/cm/sup 2/, or the 2-laser LEVIS scheme. Recognizing anode surface contamination as a key issue in 10/sup -5/-10/sup -6/ Torr pulsed power vacuum, we subject well-characterized 0.5 /spl mu/m LiAg films on stainless substrates to extended 150-400/spl deg/C heating and plasma discharge sputter cleaning after pumpdown in a test chamber, prior to pulsing the source lasers. A detailed diagnostic set includes absolutely-calibrated, streaked, CCD-imaged spectrographs for plasma properties, 2-color laser deflection for plasma/neutral expansion, ion time-of-flight spectrograph with ionizer for species content, and a tunable narrow-band dye laser for near-resonant absorption. View full abstract»

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  • A plasma purification method for plasma source ion implantation doping of semiconductors

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    Summary form only given. Using plasma source ion implantation (PSII) to create the shallow source and drain structures required for next generation devices may be a necessity. For example, future devices are predicted to require heavy metal doses be kept less than 3/spl times/10/sup 9/ atoms per square centimeter. Plasma purification is done using ion cyclotron resonance to selectively expel unwanted ions from the plasma where they are neutralized upon collision with the chamber wall and no longer an implantation hazard. With a computer simulation we determine the necessary field strengths and uniformity for plasma purification, cleaning efficiency and frequency/mass resolution of the method. View full abstract»

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  • Evaluation of the resonant mode behaviour of a compact, end feed, microwave plasma source

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    Summary form only given. Investigations of a small end excited microwave ECR plasma source have uncovered cavity resonances in the operational parameter space that are not fully explained by existing theory. One of the resonances involves the TE/sub 111/ cylindrical cavity mode excitation. However, the other resonance involves TM-like or TEM-like excitation. The plasma source in this investigation consists of: microwave applicator, quartz discharge chamber, and ECR magnet array. The microwave applicator is a cylindrical stainless steel microwave cavity, of 9.8 cm inner diameter. The cavity is internally tuned, by the adjustment of: 1) a sliding short, and 2) an adjustable end feed loop. The cylindrical quartz discharge chamber has an inner diameter of 70 mm and height of 56 mm. An eight pole 45 MGO permanent magnet array is placed around the circumference of the discharge chamber. This ERC source is operable over a range of power from 50 Watts to 300 W and a range of pressures from 0.5 mtorr to 100 mtorr. View full abstract»

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  • Two-dimensional MHD simulation of plasma closure in high current-density diodes

    Page(s): 122 - 123
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    Summary form only given. Operation of charged-particle beam diodes is often limited by closure of the interelectrode gap due to plasmas created at the electrode surfaces. In particular, cold-emission cathodes that depend on the generation of plasmas by external means or by explosion of surface asperities (e.g., whiskers) are immediately subject to the consequences of such plasmas. These consequences include variation of the diode impedance with time during the current pulse, curtailment of the pulsetime, and limitation of the ability to operate the diode repetitively. Plasma closure in diodes has been observed experimentally for many years and found to depend strongly on the cathode material, but relatively weakly on operating current and voltage. The present paper describes the use of the MACH2 code to simulate the dynamics of a plasma layer adjacent to the cathode of a high current-density diode. MACH2 is a 2-1/2 dimensional MHD code that includes resistive diffusion of magnetic flux, thermal transport by conduction and radiation, separate ion, electron and photon temperature, anomalous resistivity models, and access to properties of partially-ionized gases (e.g., SESAME tables). View full abstract»

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  • Preliminary design and experimental evaluation of carbide field emitters in mTorr pressure environments

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    Summary form only given. This report describes an on-going effort to develop field emitter cathodes for mTorr-level discharges. Hafnium carbide and zirconium carbide emitters were used for their hardness, chemical inertness and low work functions. Single HfC emitters were tested in oxygen at mTorr pressures. They showed resistance to damage due to backsputtering even at relatively large extraction voltages. Emitter-gate electrode configurations were then optimized for mTorr pressure environments to prevent catastrophic failure of the arrays from arcing. The results of the design analysis, emission measurements under various gases and pressures, and experimental evaluations of the design are presented in this report. View full abstract»

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  • Beam discharge for new technology

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    Summary form only given. For new technological developments, we propose a high efficiency ionization method-Plasma beam discharge in a magnetic field. This type of discharge makes it possible to obtain a highly ionized plasma in a large volume. A great variety of substances can be used for plasma generation (gases and metal vapors), for instance air, nitrogen, oxygen, hydrogen, methane, carbon dioxide, feron, argon, and etc. View full abstract»

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  • Thermal and mechanical loading of particle and RF transmission windows exposed to atmospheric pressure

    Page(s): 123 - 124
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    Summary form only given. The mechanical design of a transmission window that seals a port between a low-pressure side and an atmospheric-pressure side for the purpose of passing a high-energy particle beam or radio-frequency waves has many forms. Thermal loading due to energy loss from the beam or the waves and mechanical loading due to the pressure differential across the window constrain the window design. Techniques to dissipate heat such as radiation, conduction, natural convection, evaporation, and forced convection are discussed in general. Specific details of forced convective cooling with fluids within the transmission window are also discussed. View full abstract»

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  • Production of X-rays from laser-heated gas targets

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    Summary form only given. Debris-free and efficient multi-kilovolt X-ray sources are needed for materials testing and for use as backlighters in future inertial confinement fusion experiments. Laser-plasma X-ray sources are particularly attractive for these uses since their spectrum can be controlled by proper choice of plasma material and laser intensity, and because many laser-plasma sources can be designed to produce little or no particulate debris. We investigate the use of laser-heated gas to produce multi-KeV X-rays. In one experiment 20 kJ of 0.35 /spl mu/m pulse from the Nova laser heats 1-2 atm. of Xe gas confined in a Be can. View full abstract»

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