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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 76-78 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Etch rates of up to 2200 Å/min have been achieved on hexagonal silicon carbide (SiC) using dilute mixtures of SF6:Ar in a standard 13.56 MHz asymmetric parallel plate discharge. Furthermore, these etch rates have been realized with excellent pattern anisotropy profiles of approximately 1 at pressures in the range of 100–350 mTorr and the SF6 fraction at or below 50%. An understanding of the mechanisms responsible for the high etch rates in this simple, dilute, gas mixture can be achieved by considering the electrical characteristics of the radio frequency plasma. The conditions defining maximum etch rates are associated with peak fluorine ion and/or radical production, and can be defined entirely in terms of the relative current–voltage phase shift leading to optimal plasma impedance conditions and ultimately to maximal power deposition into the plasma. In addition, this study shows that the pervasive practice of utilizing oxygenated gas chemistries for SiC etching is not required, as previously thought, for carbon saturation and removal in order to obtain high etch rates, good surface morphology, and reliable pattern definition on SiC.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1476-1479 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of plasma surface interactions on the radial variation of H atom density has been measured in a low pressure pure H2 rf discharge by two-photon (electric quadrupole and magnetic dipole) allowed laser induced fluorescence using a standard reference cell. Measurements were made in the pressure range from 0.5 to 7 Torr and at a rf power of 35 W into the plasma. The influence of different electrode materials on the H atom density close to the electrode surface and in the discharge volume was measured. The data shows that the radial density distribution, under our discharge conditions, is primarily determined by the plasma-surface interactions and not by the discharge current uniformity (or nonuniformity). We have clearly demonstrated the ability of this measurement technique to monitor in situ, plasma induced surface property changes.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4341-4346 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low Mach number shock waves propagating through a low pressure, nonequilibrium positive column gas discharge have been observed to experience dispersion and velocity changes. It is shown that these effects depend on discharge polarity. Optical and electrical measurements are described which show further polarity-dependent effects in discharge light emission and changes in electrical properties. Using two types of probes, electrical measurements were made of both the global changes in discharge voltage and current and time resolved local electric field changes. The measured behaviors of discharge and shock wave point to very localized triple or quadruple layer electric sheaths connected with the propagating shock wave, which provide local enhanced ionization at the shock front which can sustain the discharge, at least during the short shock propagation time. The postulated density gradient driven large local recirculation current in the potential minimum near this sheath [H. S. Maciel and J. E. Allen, J. Plasma Phys. 42, 321 (1989)] at the shock front will result in large local Joule heating, causing the shock dispersion and shock speed increase, which have been observed in many experiments. Thus, the conclusion is that the effects are due to highly localized gas heating which is facilitated by the response of the positive column plasma to the acoustic shock. © 2000 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1414-1417 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Time-resolved electric field profile measurements were made in a driven 15 kHz parallel plate helium glow discharge using optogalvanic spectroscopy. Electric field values in the sheath region were determined from the energy splitting of the helium Rydberg state Stark manifolds due to the local applied electric field as a function of position and phase. The measured field values in the cathode sheath region range from about 800 to 300 V/cm; the measurement accuracy of electric field values are ±25 V/cm. The line of sight laser probe measurements have a spatial resolution of 200 μm and a temporal accuracy of better than 1% of the driving cycle. The low driving frequency allows for a comparison with the dc discharge approximation. The spatial electric field profile is identical to a dc discharge operating at the same peak current and voltage values and the temporal field profile is symmetric about the current wave form extremum.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 2778-2783 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electric-field profile in the cathode-fall region of a low-pressure helium gas discharge has been measured by high-level Rydberg state Stark spectroscopy using optogalvanic detection. The Stark manifolds of triplet atomic helium Rydberg states with principal quantum numbers n=15 up to 20 have been used to measure the electric-field vector using both Δmj=0 and ||Δmj||=1 laser polarizations. The absolute accuracy of the electric-field measurement was found to be 5% or better. The ||Δmj||=1 polarization Stark spectra exhibit pseudohydrogenic behavior in Stark splitting, as well as in the manifold intensity distribution. The Stark splitting of states corresponding to 1〉4 was almost hydrogenic for all the measured principal quantum-number states and the intensity distribution became approximately hydrogenic for n≥16 at electric fields ≤700 V/cm.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 4856-4860 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Allowed and forbidden transitions of singlet helium from 2s1S to ns1S, np1P, and nd1D states have been measured between n=8 and 31 by optogalvanic spectroscopy in a dc discharge positive column. The addition of neon in the discharge was found to increase the relative intensities of the forbidden transitions. For similar photon flux, the optogalvanic signal reaches a maximum at n=11 and decreases thereafter. Neutral collisional ionization of the excited states from n=13 and above was found to be responsible for the increased ionization efficiency of the high Rydberg states.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 621-627 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spatially resolved electric field, emission intensity, and linewidth profiles have been measured in a dc low current, low pressure obstructed hydrogen discharge with a planar electrode configuration. The polarization-dependent Stark splitting of the Hβ line has been used to measure the electric field. The axial electric field was high over the entire interelectrode space. The radial variations of electric field and emission intensity show that the discharge is almost annular. The Hα spectra indicate that, except in a plasma region at an edge of the anode, heavy-particle excitations exceed electron-impact excitation and that the kinetic energy of much of the excited atomic hydrogen was as high as 450 eV. This dc discharge exhibits current-voltage oscillations which appear to be caused by the periodic collapse of the wall sheath. For these discharge conditions, the Hβ Stark spectrum yields electric field measurements with an accuracy of better than 5%.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 27-33 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron excitation temperatures have been measured in a low-pressure (0.05-Torr Cs, 2-Torr total pressure) argon-cesium discharge that uses a heated cathode (900–1100 K). The excitation temperature determinations are based upon a model that allows calculation of cesium excited state densities for low electron density (〈1011 cm−3). The model assumes that the dominant creation processes for excited states are electron impact excitation from the ground state and radiative cascade from higher levels, while destruction is by spontaneous emission. Maxwellian electron energy distributions were used and the plasmas were considered to be optically thin. The model indicates that cascade contributions to the production of excited states can be as high as 50% for some cesium levels. Predicted emission spectra with cascade contributions to spontaneous emission intensities agree well with measured spectra except for radiation trapped transitions from low nP states to the ground state. Excitation temperatures are determined by fitting measured and calculated spectra.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 571-576 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The high Rydberg spectra of atomic helium np 1P states were measured up to n=46 in the negative glow region of a discharge, with mJ=±1 polarization, by optogalvanic spectroscopy. The net electric field values in the negative glow region, in the transition region between the negative glow and the positive column, and also on the radial axis of the positive column were determined from series-termination measurements. The spatial variations of the ion density in the negative glow region were also obtained from the net-field measurements.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 4772-4776 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two-photon laser induced fluorescence measurement of H atom density in %H2–%N2 gas mixture discharges has shown that the flux of H atom remains nearly constant over a wide range of gas compositions and pressures in three types of discharge devices. This unique feature is attributable to an efficient multiquantum N2 vibrational energy transfer to the dissociation of H2. This result shows that an appropriate choice of molecular gas mixtures can be used to extend the discharge operating conditions and device size scaling without compromising atom flux production. © 1997 American Institute of Physics.
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