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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

Issue 2 • Date Mar 1996

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Displaying Results 1 - 25 of 72
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Dynamic rate and thickness metrology during poly‐Si rapid thermal chemical vapor deposition from SiH4 using real time in situ mass spectrometry

    Page(s): 267 - 270
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    Real‐time in situ mass spectrometry has been applied to poly‐Si rapid thermal chemical vapor deposition (RTCVD) (from SiH4) on thermally grown SiO2 as a way to determine film thickness at the end of the process and to infer dynamic deposition rate during the process for run‐to‐run and real‐time control applications. Monitoring process ambient at 5 Torr is achieved using two‐stage differential pumping of a sampling aperture in the exhaust stream, and a rapid response time (∼1 s for a ∼30 s process cycle) allows for real time sensing of reactant input, product generation, and reactant depletion. Active mass spectrometric sampling of the reaction by‐product (H2 generated by SiH4 decomposition) provides a monitor of the total reaction/deposition rate during poly‐Si RTCVD in the range 550–850°C. Product generation as a function of temperature is readily distinguished from reactant cracking fragments by spectral analysis. A well‐defined monotonic correlation between the time‐integrated H+2 product signal and the poly‐Si film thickness, determined ex situ by single‐point interferometry (Nanometrics), demonstrates that the integrated mass spectrometric signal can provide real‐time thickness metrology. In addition, the time‐dependence of product and reactant signals provides a real‐time indication of detailed equipment behavior during the process. © 1996 American Vacuum Society View full abstract»

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  • Optical temperature measurement by grating expansion for rotating semiconductor wafers

    Page(s): 271 - 277
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    A noncontact temperature measurement technique, diffraction‐order analysis, based on monitoring the change in diffraction angle from a grating as a result of thermal expansion, is described and results for both Si and GaAs are presented. Two incident beams are used to provide a differential measurement, independent of wafer tilt. Image processing techniques are used to calculate the relative temperature in near real time from the optical signals. Good agreement between optical and the thermocouple temperature measurements is obtained, with an accuracy and precision of ±0.3 °C demonstrated over a 20–600 °C temperature range for a GaAs sample. Analysis of the effects of all six rigid‐body motions of the wafer on the measurement is presented. The measurement is independent of all translational motions; rotational motions (pitch, roll, and yaw) can all be monitored with the same measurement scheme and the temperature measurement corrected for their effects. In many applications in semiconductor manufacturing, wafers are rotated to ensure uniformity. The diffraction‐order analysis technique is demonstrated for a rotating wafer with a 3σ precision of 1.95 °C. © 1996 American Vacuum Society View full abstract»

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  • Adsorption induced gas transport phenomena in narrow air channels recorded with work function detectors

    Page(s): 278 - 285
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    Gas transport in narrow air channels (length‐to‐height ratio 1 mm/1 μm) is characterized by work function detectors like hybrid suspended gate field effect transistors (HSGFETs) with sensitive areas located in the middle of the channel. A thin platinum layer covered one side of the channel. In order to separate the influence of the size of the channel structure on the gas exchange Kelvin probe measurements with platinum coated reference electrodes were carried out simultaneously. For the HSGFET we have observed time lags and suppressions of reactions, which indicate a strong adsorption dependence of gas exchange for the investigated testing gas mixture of hydrogen in nitrogen or synthetic air, respectively. The results are discussed in relation to common models for the flow in thin capillaries. We also point out the special features of narrow air channels for investigating adsorption related phenomena and for improving chemical sensor characteristics by incorporating them into small air gaps. © 1996 American Vacuum Society View full abstract»

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  • Irradiation‐induced decomposition of Al2O3 during Auger electron spectroscopy analysis

    Page(s): 286 - 292
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    The effect of electron fluence on the decomposition of sapphire (Al2O3) was studied in situ by Auger electron spectroscopy (AES). The decomposition was primarily detected by monitoring the evolution of the low kinetic energy Auger transitions of aluminum in Al2O3 (54 eV) and in metallic aluminum (68 eV). The decomposition of sputter‐cleaned sapphire started at a fluence of ∼4.9×1019 electrons/cm2 (7.8 C/cm2). This fluence was independent of the electron fluxes used in this work, except the lowest, which indicates that heating due to electron bombardment does not significantly affect the decomposition behavior. Electron‐induced decomposition takes place in a minimum of the first five atomic layers of the substrate, as revealed by the evolution during irradiation of the high energy Al peaks associated with Al2O3 (1388 eV) and metallic aluminum (1396 eV). Comparison of the evolution of low and high kinetic energy Auger transitions demonstrates that the decomposition kinetics are much faster for the first monolayer than for the subjacent atomic layers. The surface condition strongly influences the decomposition kinetics. Thus, a carbon layer adsorbed at the alumina surface significantly increases the threshold dose for decomposition. The carbon layer most probably acts as a diffusion barrier for the oxygen produced during decomposition. An equation for the decomposition rate of the first monolayer of alumina is established. The integral of this equation gives a good fitting to the experimental data. It is found that the Auger signal of aluminum from sapphire does not disappear even if the entire region has been decomposed. This effect is due to backscattered electrons that promote Auger electron excitations outside the irradiated region. © 1996 American Vacuum Society View full abstract»

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  • Characterization of low‐resistivity indium oxide films by Auger electron spectroscopy, x‐ray photoelectron spectroscopy, and x‐ray diffraction and correlation between their properties, composition, and texture

    Page(s): 293 - 298
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    Auger electron spectroscopy, x‐ray photoelectron spectroscopy, and x‐ray diffraction (XRD) were employed to investigate the stoichiometry and texture of the indium‐oxide films. The films were prepared by the reactive evaporation and reactive ion plating of pure indium in an oxygen atmosphere of ∼10-4 Torr. Standard In and In2O3 grains were used to estimate the atomic concentration of the indium‐oxide films and to identify the film orientation. We correlated the electrical and optical properties of the films with their atomic concentration and texture. It was found that the films exhibiting low resistivity have atomic ratios of O to In of 1.29–1.31 and full widths at half‐maximum for (222) XRD peaks of 0.32°–0.34°. © 1996 American Vacuum Society View full abstract»

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  • X‐ray photoelectron spectroscopy studies of alkoxide‐derived lithium niobate

    Page(s): 299 - 305
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    X‐ray photoelectron spectroscopy was used to study the thermal conversion of Li, Nb alkoxide derived thin layers on Si(100). Changes in the surface composition with temperature indicated a decomposition process involving lithium transport to the surface, lithium carbonate or oxycarbonate formation, and subsequent reaction to form lithium niobate. For comparison purposes, spectra were also obtained for a single crystal of lithium niobate and layers prepared from sol‐gel derived lithium ethoxide and niobium ethoxide. Heat treatment of the individual precursors gave lithium carbonate (or oxycarbonate) and niobium oxide, respectively. © 1996 American Vacuum Society View full abstract»

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  • Chemical vapor deposition of aluminum and gallium nitride thin films from metalorganic precursors

    Page(s): 306 - 311
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    Nearly stoichiometric aluminum and gallium nitride thin films were prepared from hexakis(dimethylamido)dimetal complexes, M2[N(CH3)2]6 (M=Al,Ga), and ammonia at substrate temperatures as low as 200 °C by using low pressure thermal and plasma enhanced chemical vapor deposition (CVD). Both processes gave films that showed little or no carbon (≪5 at. %) and no oxygen (≪few at. %) contamination, but in all cases there was hydrogen incorporation. The films were highly transparent in the ultraviolet and visible regions. The barrier properties of the aluminum nitride films in a Si/AlN/Au metallization scheme were examined by using backscattering spectrometry. The growth rate of the aluminum nitride films was as high as 1300 Å /min. Overall, the results suggest that M2[N(CH3)2]6 (M=Al,Ga) are promising precursors for low‐temperature/low‐pressure thermal and plasma‐enhanced CVD of group III nitride thin films. © 1996 American Vacuum Society View full abstract»

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  • Nucleation behavior in molecular beam and chemical vapor deposition of silicon on Si(111)‐(7×7)

    Page(s): 312 - 318
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    The nucleation behavior during chemical vapor deposition (CVD) of silicon on Si(111)‐(7×7) using disilane (Si2H6) is investigated with a scanning tunneling microscope. In the temperature range from 450 to 540 °C it is compared to molecular beam epitaxy (MBE). Whereas the latter is very well described within the framework of classical rate equation based nucleation theories in the complete condensation regime, the same approach fails for CVD growth. For MBE a critical nucleus i*=5–7 is found. Although the relationship between island density and growth rate in CVD also follows a power law as does MBE, the exponent is significantly higher than the theoretically expected value. The influence of hydrogen present on the surface during CVD growth is also discussed. © 1996 American Vacuum Society View full abstract»

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  • Enhanced adherence of area‐selective electroless metal plating on insulators

    Page(s): 319 - 326
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    We describe a simple way of producing adherent metal films (Cu or Ni) on insulator surfaces [SiO2, glass, or polyphenylquinoxaline (PPQ), an insulating polymer] by electroless growth on a thermally activated palladium acetylacetonate [Pd(acac)2] seeding layer. Using this process, we produced tiny metal patterns on insulators by localized laser pyrolysis (using either a pulsed Cu vapor or a cw Ar+ laser) of the spun‐on seeding layer. A tensile stress test applied to a Ni deposit on SiO2 reveals bonding strengths as high as 2 N/mm2. The mechanisms of such an increased adherence have been studied using x‐ray photoemission spectroscopy (XPS). The critical role of the chemical environment of the Pd clusters obtained by pyrolytic decomposition of the Pd(acac)2 seeding layer is shown. In particular, XPS reveals that most of the Pd atoms left at the surface after thermal decomposition still remain bonded to an organic aromatic species identified as one of the two acetylacetonate ‘‘wings’’ of the parent molecule. A wear‐resistant metal deposit on insulators can only be formed when these remaining ligands are removed by an additional acetic acid treatment. © 1996 American Vacuum Society View full abstract»

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  • Role of chemical bonding in the epitaxial growth of noble metals on ionic crystal substrates

    Page(s): 327 - 331
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    Thin films of Au were deposited onto MgO substrates cleaved in ultrahigh vacuum. The films, which were examined by transmission electron microscopy and electron diffraction, did not grow with a (111) orientation observed in a Au/NaCl system but with a (100) orientation which had been observed in a Pd/MgO system. In order to obtain some insight into the differences in the epitaxial orientations, we studied interfacial chemical bonding states in Au/MgO(100), Pd/MgO(100), and Au/NaCl(100) systems using total pair‐potential calculations and discrete variational Xα calculations. The results show that interfacial interaction in both the Au/MgO and the Pd/MgO system is stronger than that in the Au/NaCl system. The relation between the strength of the interfacial chemical bond and the epitaxial orientation in the above systems is discussed. © 1996 American Vacuum Society View full abstract»

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  • Fabrication and characterization of extremely smooth large area gold surfaces

    Page(s): 332 - 335
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    We describe our work on gold surfaces that are made by peeling gold films off various smooth glass substrates. We find that we are able to routinely and reliably produce extremely smooth, large area gold surfaces: typically, for areas ≤40 μm square we find the residual roughness of our samples is an order of magnitude less than that of surfaces produced using conventional techniques. While we intend to use these to measure the van der Waals force between alkali atoms and gold surfaces, other potential uses include samples for fundamental surface physics investigations, scanning tunneling microscopy substrates, and reflective optics. We provide details as to how we make these extremely smooth samples and discuss our activities to characterize them. © 1996 American Vacuum Society View full abstract»

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  • Pure and fluorine‐doped silica films deposited in a hollow cathode reactor for integrated optic applications

    Page(s): 336 - 345
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    Silica films have been deposited in a high density hollow cathode plasma deposition system from silane and oxygen gas mixtures. Additions of carbon tetrafluoride (CF4) were used to fluorine dope the silica. The deposited films were characterized by means of Fourier transform infrared (FTIR) spectroscopy, wavelength dispersive x‐ray spectroscopy, chemical etch rate (P etch), stress and refractive index measurements. The pure silica films, though deposited at a high rate (over 1500 Å/min), exhibit a P‐etch rate only 1.3 times that of thermal oxide. The refractive index of the as‐deposited silica is higher than that of thermal oxide, but reduces to the thermal oxide value after high‐temperature (1000 °C) annealing. Based on the thickness change measurements, the higher refractive index was attributed to a higher density of the deposited silica due to a smaller Si–O–Si bond angle, as supported by FTIR data. Fluorine doping results in a reduction in film stress by a factor of 4 over pure silica, as well as a reduction in OH content from about 1 at. % in pure silica to below the FTIR detection limit (0.1 at. %). The refractive index initially decreases with CF4 flow rate, concomitant with an increase in fluorine content, but then rises above the refractive index of pure silica. This increase has been found to be due to the deposition of silicon‐rich oxide at the higher CF4 flow rates, which is attributed to an increasingly oxygen deficient discharge resulting from oxygen consumption by the dissociation products of CF4. © 1996 American Vacuum Society View full abstract»

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  • Development of 111 texture in Al films grown on SiO2/Si(001) by ultrahigh‐vacuum primary‐ion deposition

    Page(s): 346 - 351
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    A high degree of 111 preferred orientation with minimal mosaic spread has been shown by many researchers to be essential for electromigration resistance in Al‐based interconnects. We have found that 111 texture can be greatly enhanced through the use of low‐energy self‐ion irradiation during deposition. In these experiments, 300‐nm‐thick Al layers were grown on SiO2 at 65 °C from highly ionized beams provided by an ultrahigh‐vacuum primary‐ion deposition (PID) source. Al+ ion energies EAl+ and ion/neutral ratios JAl+/JAl were independently varied from 10 to 120 eV and from 0% to 68%, respectively. All PID Al films exhibited very strong 111 preferred orientations, which increased with increasing EAl+ and/or JAl+/JAl, and azimuthally symmetric x‐ray diffraction pole figures with no measurable tilt. The full width at half‐maximum intensity Δω of 111 ω‐rocking curves decreased continuously from 9.6° with EAl+=10 eV and JAl+/JAl=68% to 2.2° with JAl+/JAl=120 eV compared to 10.6° for films deposited by thermal evaporation. This was accompanied by a continuous decrease in the average grain size from 370 nm for thermal deposition to 90 nm with EAl+=120 eV. The PID Al films exhibited a columnar microstructure with weak competitive column growth. Changing the beam energy after the formation of a continuous layer had only a minor effect on film texture, indicating that the degree of ion‐irradiation‐induced preferred orientation is controlled during nucleation and/or coalescence while local pseudomorphic forces dominate thereafter. ω‐rocking curves from a bilayer film consisting - - of a 20‐nm‐thick Al buffer layer grown by PID followed by a 280‐nm‐thick thermally evaporated Al overlayer were essentially identical to those obtained from 300‐nm‐thick single‐layer PID Al films. © 1996 American Vacuum Society View full abstract»

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  • Effects of oblique energetic bombardment on the morphology and microstructure of triode ion plated titanium films

    Page(s): 352 - 358
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    The effect of angle of incidence of ions, varied between 45° and 90°, generated in a triode ion plating system on the morphology and microstructure of titanium films, has been investigated. It has been found that intensity of reflections, lattice parameters, stress, and grain size are strong functions of the angle of incidence of the ions. The same properties were studied for their variation with bias voltage between 0 and 2 kV at a constant substrate bias current of 10 mA. It was found that the intensity of the (002) reflection increases with an increase in angle of ion incidence up to 60°. The lattice parameter and stress reach a minimum while the grain size goes through a maximum at this value. All the films show a tensile stress independent of deposition parameters. To isolate the effects due to ion bombardment the films have been coated in high vacuum, in a diode mode, and finally the triode configuration. It has been conclusively found that the angle of incidence of ions is very important in controlling properties and growth of the films. © 1996 American Vacuum Society View full abstract»

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  • Chemical shifts and optical properties of tin oxide films grown by a reactive ion assisted deposition

    Page(s): 359 - 366
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    Highly oriented nonstoichiometric tin oxide thin films were grown by a reactive ion assisted deposition onto Si(100) and glass substrates at room temperature as a function of relative ion (O)/atom (Sn metal) arrival ratio, and concurrently the deposited ion energy per atom (eV/atom) were changed from 10 to 100 eV/atom. As‐deposited tin oxide films show preferred orientation along the SnO2〈101〉 axis and the x‐ray diffraction peak intensity appears maximum at an average energy of about 50 eV/atom. From quantitative Auger electron spectroscopy, characteristic transitional Auger peaks of Sn metal MNN transitions were shifted to lower kinetic energies by 4–6±1.0 eV as the Sn4+ component becomes dominant in the deposited tin oxide films and the position of O KL1,2L2,3 transition line was also shifted to lower kinetic energy by 1–2±1.0 eV as the composition of deposited tin oxide films were changed from SnO to SnO2, respectively. On the basis of a tin 3d core level and O 1s spectra analysis by x‐ray photoelectron spectroscopy, the sizable chemical shift of different valencies between stannous tin (Sn2+:SnO) and stannic tin (Sn4+:SnO2) was 1.0±0.02 eV and that of O 1s was 0.87±0.02 eV, and those values show larger shifts than previously reported ones. The refractive index n of as‐deposited tin oxide films was evaluated from an ellipsometer, and spectrophotometric transmittances were measured in the wavelength range of 200–800 nm. In the luminous range, the refractive index varied from n=2.36 to 2.04 as oxygen contents increased. © 1996 American Vacuum Society View full abstract»

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  • New method of tubular material inner surface modification by plasma source ion implantation

    Page(s): 367 - 369
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    Plasma source ion implantation is a non‐line‐of‐sight ion implantation technique for surface modification of materials, but that technique is only suitable for outer surface modification of hollow targets, not for inner surface modification. In this article we present a new method that applies to inner surface implantation. Preliminary experimental results show that this new method increases plasma density and uniformity inside the tubular target with the inner surface, generates a plasma sheath between the inner surface of the target and the plasma to implant the inner surface of the target effectively, and achieves a dose uniformity that is acceptable for industrial applications. © 1996 American Vacuum Society View full abstract»

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  • Ion deposition by inductively coupled plasma mass spectrometry

    Page(s): 370 - 373
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    An atmospheric pressure inductively coupled plasma (ICP) is used with a quadrupole mass spectrometer (MS) for ion deposition. The deposited element is introduced as a nebulized aqueous solution. Modifications to the ICP‐MS device allow generation and deposition of a mass‐resolved beam of 165Ho+ at 5×1012 ions s-1. The ICP is a universal, multielement ion source that can potentially be used for applications such as deposition of mixtures of widely varying stoichiometry or of alternating layers of different elements. © 1996 American Vacuum Society View full abstract»

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  • Pulsed plasma deposition of chromium oxide/chromium‐cermet coatings

    Page(s): 374 - 379
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    A novel radio frequency magnetron sputtering method for the deposition of composite films which consist of chromium oxide and chromium (Cr2O3/Cr‐cermet) is presented. As an extension to conventional reactive sputtering of a Cr target in an argon and oxygen atmosphere the oxygen flow into the process chamber is switched periodically on and off. This leads to an oscillating oxygen partial pressure during the sputtering process and an alternating deposition of metallic chromium and chromium oxide. In situ x‐ray and ultraviolet photoelectron spectroscopy are used to monitor the oxidation state of chromium at the film surface and to study the chemical interactions between adjacent layers. Ex situ x‐ray diffraction analysis reveals the multilayered and nanocrystalline structure of the deposited films. The overall chromium and chromium oxide concentration is estimated from the optical constants n and k determined by reflectance and transmission measurements in the wavelength range between 400 and 2200 nm. © 1996 American Vacuum Society View full abstract»

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  • Measurement of the gas temperature in fluorocarbon radio frequency discharges using infrared absorption spectroscopy

    Page(s): 380 - 383
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    The translational gas temperature was measured in 13.56 MHz radio‐frequency (rf) discharges in CF4 and CHF3. Infrared absorption spectra of CF4 and CF2 were recorded using a tunable diode laser and the gas temperature was deduced from the linewidths of the absorption lines of these molecules. It is shown that linewidth measurements yield a simple and direct method to determine the gas temperature, with an accuracy up to ∼10 K. The results obtained in CF4 and CHF3 plasmas indicate that the translational temperatures of all particles investigated in these plasmas are, at most, 50 K above the room temperature. The temperature increases with increasing gas pressure and rf power, but it is independent of the flow rate. This is attributed to an increased heating rate of the gas. Moreover, it was found that the temperature rise is significantly smaller in CHF3 than in CF4, under the same plasma conditions. This can be attributed to a higher power dissipation by chemical conversion of the parent gas in a CHF3 discharge, as compared with a CF4  plasma. © 1996 American Vacuum Society View full abstract»

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  • Production and destruction of CFx radicals in radio‐frequency fluorocarbon plasmas

    Page(s): 384 - 390
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    Spacially resolved densities of CF, CF2, and CF3  radicals in capacitively coupled 13.56 MHz radio‐frequency (rf) discharges in CF4 and CHF3 were determined by means of infrared absorption spectroscopy employing a tunable diode laser spectrometer. It was established that the stationary CF2 density and density profile in a CF4 plasma depend strongly on the electrode material. This is attributed to different sticking coefficients of CF2 on different surfaces. Furthermore, it was found that the densities of all CFx radicals increase near the electrodes at high gas pressures and rf powers in a CHF3 plasma. This leads to the conclusion that production of CFx radicals takes place in the sheath region close to the electrodes. It is proposed that collisions between ions and source gas molecules are responsible for this production of CFx radicals. In the presence of a destruction process in the plasma glow (e.g., by three‐body recombination with other radicals) and the absence of a fast surface loss process this results in the observed increase of CFx densities near the electrodes. In order to study the radical kinetics time dependent measurements were performed during power modulation of the plasma. It was found that the decay time of the CF2 density in the afterglow of a CF4 plasma is much shorter than the corresponding decay time in a CHF3 discharge. This suggests that the surface loss is relatively less important in the latter case, in agreement with measurements of spatial density distributions. This is explained by the presence of a (CFx)n layer, which is readily deposited on the electrodes in a CHF3 discharge, and by low sticking probabilities of CF and CF2 radicals on such a layer. © 1996 American Vacuum Society View full abstract»

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  • Measurements of pulsed‐power modulated argon plasmas in an inductively coupled plasma source

    Page(s): 391 - 397
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    The behavior of pulsed‐power (square wave) modulated argon plasmas generated by an inductively coupled plasma (ICP) source is experimentally investigated. The apparatus is an ICP source with a flat coil geometry equipped with a cylindrical Langmuir probe on the axis of the cylindrical chamber. The evolution of the plasma density is determined from the wave forms of ion saturation currents. The rise and fall of the density had a time scale of a few tens of microseconds. The time average plasma density is also measured as a function of pulse frequency and duty ratio, holding the average absorbed power constant. When the plasma is modulated, the density is larger than that for a continuous wave excitation of the same average power. Larger densities are obtained for smaller duty ratios. The density increases monotonically as the period is decreased down to 100 μs. This agrees qualitatively with the modeling result, which accounts for the higher density by the difference of time scales for the generation and the loss of charged particles. The results for electron temperature measurements also show good agreement with the model quantitatively during the pulse ‘‘on’’ times. If the period is long enough, it is found that the electron temperature rises abruptly at the initial stage of power application, in agreement with the calculation. © 1996 American Vacuum Society View full abstract»

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  • Simulation of microloading in aluminum etching

    Page(s): 398 - 403
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    A simulator for aluminum etching was developed in order to analyze the microloading effect. We have adopted the procedure that the flux rates (gas particles, ions, and sputtered mask fragments) are calculated independently as a function of trench aspect ratio; then the etching rate is calculated with these flux rates at each aspect ratio. The simulator can be operated on a personal computer by this simple procedure and the characteristics of aluminum etching can be obtained quickly. The surface reaction parameters were determined by fitting the calculated result to the basic experimental etching rate data. By using these surface reaction parameters the simulator can predict the characteristics of aluminum etching such as etching rate, selectivity, etc. The difference of the microloading effect between photoresist and oxide mask was also analyzed. It was confirmed by this simulator that the microloading effect was affected by the sputtered photoresist fragments. © 1996 American Vacuum Society View full abstract»

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  • H2O pumping by sputter discharge with a LaB6 cathode

    Page(s): 404 - 407
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    Properties of H2O water vapor pumping by glow discharge sputtering with a LaB6 cold cathode are studied experimentally. For the purpose of developing a new type of sputter ion pump, lanthanum hexaboride (LaB6) is applied as the cathode material on the basis of a preliminary study. The application of LaB6 as the cathode of sputter discharge was proposed at first to obtain a low outgassing wall for a plasma vacuum chamber. The experiments showed that the vacuum chamber with the LaB6 sputter coating reached a lower ultimate pressure than that without the coating. LaB6 coating by glow discharge on a stainless steel wall is effective to reduce the H2O outgassing rate of a vacuum wall as shown by mass spectrometric analysis. The pumping speed of H2O by the coated wall is estimated experimentally. Characterization of the LaB6 coated films is also made by x‐ray photoelectron spectroscopy measurements. © 1996 American Vacuum Society View full abstract»

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  • Extraction of oxygen from CO2 using glow‐discharge and permeation techniques

    Page(s): 408 - 414
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    A promising method to extract oxygen from CO2, which constitutes more than 95% of the Mars atmosphere, is by using glow‐discharge dissociation of CO2 combined with the permeation of the generated oxygen through a Ag membrane. Quadrupole mass spectrometry was utilized to measure the oxygen flux through a 0.35‐mm‐thick, 2.01 cm2 area membrane separating a two‐chamber system. On the upstream side of the membrane, a dc glow discharge was established with 350 V and 5 mA current. It was found that as much as 75% of the CO2 was dissociated to form CO and O (part of which recombined to form O2). The atomic and molecular oxygen generated were adsorbed on the membrane surface, subsequently dissolved into the Ag, and diffused through the membrane thickness to the downstream surface where it desorbed as molecular oxygen. The resulting oxygen flux was studied as a function of upstream CO2 pressure, discharge current, discharge probe to membrane distance, and membrane temperature. It was found that the atomic oxygen generated a much higher concentration gradient across the membrane than did the molecular oxygen which resulted in a correspondingly higher oxygen flux through the membrane. The total oxygen flux through the membrane with a CO2 glow‐discharge pressure of 5 Torr and a membrane temperature of 450 °C was found to be greater than 1014 cm-2 s-1. This method can be used to continuously and efficiently supply oxygen for astronauts in a future manned mission to Mars. © 1996 American Vacuum Society View full abstract»

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The Journal of Vacuum Science and Technology A is devoted to reports of original research, review articles, and Critical Review articles.

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Editor
G. Lucovsky
North Carolina State University