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  • 1
    Electronic Resource
    Electronic Resource
    The role of negative ions in the formation of particles in low-pressure plasmas (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 853-861 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Large particles (tens of nm to tens of μm in diameter) are problematic in low-pressure (〈1 Torr) plasma processing (etching, deposition) discharges because they can contaminate the product and can perturb electron transport. Although the source of these particles has been studied by a number of groups, a definitive explanation is still lacking. In this paper, we theoretically investigate the role of negative ions in the formation of large clusters, the precursors to particles, in low-pressure plasmas. We find that the formation of particles requires a critically large cluster. Forming the critically large cluster requires longer residence times in the plasma than is usually possible if clustering involves only neutral particles. We propose that negatively charged intermediates, which are trapped in electropositive plasmas, increase the average residence time of clusters to allow the growth of critically large clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354877
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  • 2
    Electronic Resource
    Electronic Resource
    Plasma chemistry of He/O2/SiH4 and He/N2O/SiH4 mixtures for remote plasma-activated chemical-vapor deposition of silicon dioxide (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6538-6553 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Remote plasma-activated chemical-vapor deposition (RPACVD) provides a means to deposit thin dielectric films with low ion bombardment and while having high selectivity in generating precursors. In RPACVD of SiO2, gas mixtures of He/O2 or He/N2O are passed through a plasma, producing radicals and excited states that are mixed with silane downstream. Excited states produced in the plasma and precursor species produced by these reactions then flow to the substrate. Although high-quality SiO2 films can be produced by RPACVD, the gas-phase deposition precursors have not been identified. A two-dimensional plasma chemistry model is described, and results from that model are used in a discussion of possible gas-phase precursors for SiO2 deposition. In particular, the formation and transport of silanols (SiH2O and SiH3O) are examined as a function of gas mixture, power deposition, and geometry. It is found that the fluxes of SiH2O, SiH3O, and SiH3 are sufficient to account for the observed deposition rates; while systematic dependencies of the fluxes of HSiO and SiO discount them as being deposition precursors. He/N2O/SiH4 mixtures differ from He/O2/SiH4 mixtures by providing larger fluxes of SiH3 to the substrate, while the fluxes of SiH2O, SiH3O, and O2(1Δ) are significantly less.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355115
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  • 3
    Electronic Resource
    Electronic Resource
    Pulsed plasma-pulsed injection sources for remote plasma activated chemical vapor deposition (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4098-4100 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Remote plasma activated chemical vapor deposition (RPACVD) is an attractive fabrication technique owing to the increased selectivity of radical generation which can be obtained compared to deposition techniques in which the substrate is immersed in the plasma. This selectivity can be compromised if the deposition gases, which are typically injected downstream of the plasma zone, back-diffuse into the plasma where indiscriminate electron impact dissociation occurs. In this communication, a new RPACVD technique is described in which the plasma and injected gases are sequentially pulsed to temporally isolate the injected gases from the plasma. This method reduces, or eliminates, indiscriminate dissociation of the injected gases and improves the selectivity of radical fluxes to the substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352840
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  • 4
    Electronic Resource
    Electronic Resource
    Predictions for gain in the fission-fragment-excited atomic xenon laser (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 2686-2694 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The infrared atomic xenon laser (5d→6p) is an attractive candidate for fission fragment excitation, which provides low-power deposition (1–100 W cm−3), long pulse lengths (1–10 ms), and high-energy deposition (100s J l −1). Optical gain at 1.73 and 2.03 μm has recently been measured in a reactor-excited xenon laser yielding values exceeding 0.03–0.05 cm−1 at power depositions of less than 10s W cm−3. Gain was also found to rapidly terminate before the peak of the pump pulse for some experimental conditions. A computer model has been developed to predict gain in fission-fragment-excited xenon lasers and these experiments have been analyzed. It is found that the termination of gain is most likely attributable to gas heating which increases the electron density, leading to electron collision quenching. The specific dependence of gain on pump rate suggests that a reduced rate of recombination of molecular ions with increasing gas temperature is partly responsible for this behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353039
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  • 5
    Electronic Resource
    Electronic Resource
    Short pulse electron beam excitation of the high-pressure atomic Ne laser (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 8059-8065 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The high-pressure atomic Ne laser operates on four visible transitions between the 3p and 3s manifolds. Oscillation at 585 nm (3p'[1/2]0→3s'[1/2]10) at efficiencies of (approximately-greater-than)1% have been demonstrated by others. The upper laser level is believed to be populated by dissociative recombination of Ne2+, while state-selective Penning reactions relax the lower laser levels. To investigate these pumping mechanisms, experimental and modeling studies have been performed on a short pulse e-beam excited Ne laser using He/Ne/Ar mixtures. We found that the electron temperature in the afterglow following the e-beam pulse largely determines the time at which oscillation starts. The electron temperature during the afterglow is partly controlled by a slow relaxation of excited states in Ar. Laser oscillation does not occur until these manifolds are depleted and the electron temperature decreases, thereby increasing the rate of dissociative recombination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353921
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  • 6
    Electronic Resource
    Electronic Resource
    Destruction mechanisms for formaldehyde in atmospheric pressure low temperature plasmas (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 51-55 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Formaldehyde (CH2O) is a common pollutant of indoor air in residences and commercial buildings. The removal of CH2O from atmospheric pressure gas streams (N2/O2/H2O/CH2O) using plasmas generated by a dielectric barrier discharge has been theoretically investigated with the goal of cleansing indoor air. The model consists of a full accounting of the electron, ion, and neutral chemical kinetics in contaminated humid air. We find that the destruction of CH2O results dominantly from chemical attack by OH and O radicals, with the primary end products being CO and H2O. The predicted destruction rates for CH2O are typically 2–8 ppm/(mJ cm−3) (parts per million of CH2O in air/energy deposition). The elimination of the unwanted byproducts, CO and NO, using a platinum catalyst is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353828
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  • 7
    Electronic Resource
    Electronic Resource
    Cathode heating mechanisms in pseudospark plasma switches (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 3374-3383 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pseudosparks, and the back-lighted thyratron (BLT) in particular, are finding increasing application as pulse power switches. An attractive feature of BLTs is that high current densities (≥ tens of kA cm−2) can be sustained from metal cathodes without auxiliary heating. The source of this current is believed to be electric-field-enhanced thermionic emission resulting from heating of the cathode by ion bombardment during commutation which ultimately melts the surface of the cathode. It is proposed that a photon-driven ionization mechanism in the interelectrode gap of the BLT is responsible for initiating the observed patterns of cathode surface melting and electron emission. A 21/2-dimensional computer model is presented that incorporates a photo-induced ionization mechanism to spread the plasma into the interelectrode gap. It predicts a melting of the cathode in a pattern similar to that which is experimentally observed, and predicts a rate of field-enhanced thermionic electron emission that is sufficient to explain the high BLT conduction current density. In the absence of these mechanisms, the model does not predict the observed large-area melting of the face of the cathode. The cathode heating rate during the BLT switching phase is maximum for operating parameters that are very close to the limit for which the switch will close (that is, the smallest possible pressure-electrode spacing product and smallest possible electrode holes).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351459
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  • 8
    Electronic Resource
    Electronic Resource
    Electron energy distributions in electron cyclotron resonance discharges for materials processing (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 33-42 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron cyclotron resonance (ECR) reactors are now being investigated for use in the plasma processing of semiconductors. The attractive feature of ECR excitation is that high plasma densities (1010–1012 cm−3) can be obtained at low pressures (0.1–a few mTorr). In this paper, we present results from a computer simulation of the electron kinetics in ECR reactors. The model is a multidimensional Monte Carlo simulation coupled with a fluid simulation with which the electron energy distribution (EED) may be calculated. We find that the electron temperature (Te =2/3〈ε〉) in Ar plasmas (0.1–10 mTorr, 100s W) is 10–20 eV in the ECR zone, falling to a few to 5 eV downstream of the ECR zone, in general agreement with experiments. The EED can be described as being multitemperature with a low energy component (5–10 eV) and a high energy tail extending to many 10s to 100s eV. Predicted ambipolar potentials are 10–30 V, increasing with decreasing pressure and increasing power deposition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352144
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  • 9
    Electronic Resource
    Electronic Resource
    Numerical investigation of the kinetics and chemistry of rf glow discharge plasmas sustained in He, N2, O2, He/N2/O2, He/CF4/O2, and SiH4/NH3 using a Monte Carlo-fluid hybrid model (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1654-1673 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Capacitively coupled radio-frequency (rf) glow discharges are standard sources in plasma assisted materials processing. Theoretical analyses of rf discharges have been hampered by the computational difficulty of simultaneously resolving nonequilibrium electron transport and plasma chemistry. We have developed a hybrid Monte Carlo-fluid simulation that can simulate nonequilibrium electron transport while executing with the speed of a fluid simulation. An electron Monte Carlo simulation (EMCS) is used to calculate the electron energy distribution (EED) as a function of position and phase in the rf cycle. Collision rates and transport coefficients are calculated from the EED and used in a self-consistent fluid model (SCFM) of charged particle behavior and a neutral chemistry/transport model. Electric fields from the SCFM are cycled back to the EMCS, and the process is iterated until convergence. All pertinent heavy particle (charged and neutral) reactions can be included as well as collisions of electrons with ions, excited states, and reaction products. The hybrid model is applied to a variety of gas mixtures of interest to materials processing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351196
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  • 10
    Electronic Resource
    Electronic Resource
    The effects of He addition on the performance of the fission-fragment excited Ar/Xe atomic xenon laser (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 1843-1848 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The intrinsic power efficiency of the atomic xenon laser depends upon the electron density because of the mixing of the laser levels by electron collisions while the electron density in high-pressure particle-beam excited plasmas increases with increasing gas temperature. Therefore, in order to reduce the amount of electron collisional mixing when operating at high-energy loadings ((approximately-greater-than)100's J/1-atm) mixtures having a high-heat capacity are required. In particle-beam excited Ar/Xe mixtures, which typically yield the highest intrinsic laser efficiencies, increasing the gas pressure to increase the heat capacity is not always practical due to the high-stopping power of the gas mixture. For this reason we have experimentally and theoretically investigated adding He to Ar/Xe mixtures in studies of a fission-fragment excited atomic xenon laser. Adding He increases the heat capacity without appreciably perturbing the favorable kinetics resulting in efficient operation of the laser in Ar/Xe mixtures. We find that when adding He to Ar/Xe mixtures the dominant laser transition switches from 1.73 to 2.03 μm without significantly decreasing the efficiency. The laser pulse length also increases, an effect attributed to a lowering of both the electron temperature and gas temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348752
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