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

Issue 2 • Date Mar 2000

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Displaying Results 1 - 25 of 101
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Bipolaron formation in para-sexiphenyl thin films upon Cs doping

    Page(s): 295 - 298
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    The semiconducting electroluminescent oligomer para-sexiphenyl (6P) is a promising candidate for application as the active layer in organic light emitting devices. The interaction of Cs atoms evaporated (in a step-wise manner) in ultrahigh-vacuum on thin 6P films has been studied with synchrotron ultraviolet photoelectron spectroscopy. No formation of metallic Cs or of new chemical compounds has been evidenced, but it appears that a doping of the oligomer occurs for the whole range of Cs concentrations we studied. Our data show a progressive growth of new density of states in the (former empty) band gap. Upon progressively increased doping, the material work function decreases, its Fermi-energy remains well below the newly occupied electronic states measured at 5.8 and 3.6 eV (energies relative to the vacuum level). These observations are interpreted as bipolaron formation in the charged 6P material. © 2000 American Vacuum Society. View full abstract»

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  • Appearance potential mass spectrometry: Discrimination of dissociative ionization products

    Page(s): 299 - 305
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    Appearance potential mass spectrometry (APMS) has recently gained importance for detection and quantitative measurements of reactive radical species in plasmas using line-of-sight sampling of radicals. In this work, we have investigated the assumption that the extraction efficiency of ions produced by direct ionization of radicals, and ions produced by dissociative ionization of the parent molecule used as the reference signal, are equal in the ionizer of the mass spectrometer. We find that the dissociative ionization products are extracted with much lower efficiency (2–50 times smaller for the cases studied) than the direct ionization products. This is expected due to the excess kinetic energy of the dissociatively ionized products as a result of the Franck–Condon effect. Use of this procedure will thus lead to an overestimation of the radical number density by a factor of 2–50, depending on the nature of the parent and the daughter ion. We recommend an alternate procedure for APMS that utilizes an inert gas direct ionization signal as a reference for calibration of the radical signal to calculate the radical number density. The biggest uncertainty in the radical number density estimation with the recommended procedure is expected to be the uncertainty in the published cross sections. © 2000 American Vacuum Society. View full abstract»

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  • Electronic core levels of HgPX3 chalcogenophosphates

    Page(s): 306 - 311
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    X-ray photoelectron spectroscopy and x-ray excited Auger electron spectroscopy have been used to investigate the electronic core levels of mercury chalcogenophosphate HgPS3 and HgPSe3 single crystals. On the basis of the measured chemical shifts relative to the elements information on the bonding state of the compositional atoms has been deduced. Single peak structures have been observed for the analyzed Hg, P, S, and Se core levels. As happens in CdPS3 and ZnPS3 the Hg 5d levels are discrete and well localized. This analogy confirms the validity of the transition-metal weakly interacting model already used satisfactorily for interpreting the optical properties of these chalcogenophosphates. © 2000 American Vacuum Society. View full abstract»

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  • Secondary ion emission from molecular overlayers: Thiols on gold

    Page(s): 312 - 319
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    The secondary ion emission behavior of 10 different thiols (8 alkanethiols, with n=4–18 C atoms, TSA, and MCP) was investigated. In particular, we determined the generated negative secondary ion species Xi-, their yields Y, the corresponding damage cross section σ(Xi-), and the activation energy for desorption ED(Xi-) (from the temperature behavior) of these secondary ions. The results supply important information on the analytical capabilities of secondary ion mass spectrometry (e.g., sensitivity and ultimate lateral resolution), as well as on the capabilities and limits of ion beam induced modification of these molecular overlayers. By comparing spectra and yields for different thiols bonded in the same way to the same substrate, these results give some additional insight into the ion formation process. A comparison of the activation energy for desorption ED(Xi-) with the corresponding damage cross section σ(Xi-) supplies insight into the energy distribution within the impact cascade. © 2000 American Vacuum Society. View full abstract»

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  • Structural analysis of Si(111)-7×7 domain boundaries with takayanaki cores

    Page(s): 320 - 324
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    Regular domain boundaries (RDBs) on a Si(111)-7×7 surface are investigated both theoretically and experimentally. Based on the assumption that the RDBs form from a relative shift between two adjacent parts of the perfectly reconstructed lattice, a set of indexes is proposed to classify the RDBs. The irreducible indexes are obtained according to the constraints derived from the lattice-matching condition and the symmetry of the Si(111)-7×7 structure. Along the RDBs, dimer rows should be constructed serving as backbones, and the defects in the RDB should be accompanied by a dimer-adatom stacking fault subunit or unit spanning the RDB as a matching bridge. Most of the RDBs we obtained by direct annealing of the Si(111) surface and through solid phase growth have such features. The atomic structural models compared to the STM images of several examples are presented. © 2000 American Vacuum Society. View full abstract»

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  • Photoemission studies of K-promoted oxidation of the GaAs(110) surface

    Page(s): 325 - 328
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    Core-level and valence-band photoemission have been used to investigate oxidation at the K/GaAs(100) interface. The results show that potassium deposited on the top of a substrate forms a polarized layer. The K-promoted oxidation mainly involves As. The initial bonds between an alkali metal and a semiconductor have less of a relation with the amount of adsorbed oxygen, but the disruption of K–As bonds restores a large density of As dangling bonds, and the adsorbed oxygen coupling of these dangling bonds leads to the out-of-proportional function of the As oxide. © 2000 American Vacuum Society. View full abstract»

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  • Effect of CaO addition on properties of ion-induced secondary electron emission of MgO films

    Page(s): 329 - 333
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    An excellent correlation exists between the firing voltage and the secondary electron emission coefficient (γ) in MgO films used as protective layers in ac plasma display panels. In order to make a new protective layer with a high secondary electron emission coefficient and with a reduction in the demanding voltage required for discharge, we have studied the effect of CaO addition on the secondary electron emission characteristics of MgO film. Mg1-xCaxO films were prepared by the e-beam evaporation method. As a large number of Ca atoms were substituted for Mg atoms, lattice distortion occurred in MgO films (NaCl crystal structure) in accordance with the increase in the lattice parameter. When the cation ratio in films was 0.088, relaxation of compressive stress seems to be caused by crack formation in the film. The density of pure as grown MgO was 3.214 g/cm3, which was 88% of the bulk MgO’s density. The density of the Mg1-xCaxO films gradually increased by about 14% with CaO addition to MgO. Secondary electron emission yield of pure MgO film was 0.33. Addition of a controlled amount of CaO to MgO resulted in a rapid increase in the secondary electron emission yield. The film with a [Ca/(Mg+Ca)] ratio of 0.134 yielded a secondary electron emission coefficient as high as 0.58. © 2000 American Vacuum Society. View full abstract»

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  • Desorption of fragment ions from condensed Si(OCH3)4 by localized inner-shell electron excitation at the silicon, oxygen, and carbon K edges

    Page(s): 334 - 337
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    Desorption of fragment ions from condensed Si(OCH3)4 (tetramethoxysilane) following localized inner-shell electron excitation at the silicon, oxygen, and carbon K edges has been investigated using monochromatized synchrotron radiation in the soft x-ray region. For Si K-edge excitation, the predominant species of the desorbed ions were Si(OCH3)n+ where n=2, 3, 4, which resembles the cracking pattern of gas-phase molecules excited by 70 eV electrons. In contrast, the CH3+ ions were the main species of the desorbed ions for the C and O K-edge excitations. The photon-energy dependencies of the CH3+ yield at the C K edge revealed that the CH3+ desorption happens only at the resonant excitation from C 1s to the σ* orbit localized at the C–O bond, which suggests that the core-to-valence resonant excitations are localized around the C–O bond until the C–O bond breaks. These results shed light on the possibility of low-temperature SiO2 deposition on a silicon surface by an x-ray-induced photochemical reaction through selective C–O bond scission using monochromatized synchrotron radiation. © 2000 American Vacuum Society. View full abstract»

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  • Determination of atomic oxygen density with a nickel catalytic probe

    Page(s): 338 - 342
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    A nickel catalytic probe was used to determine the density of neutral oxygen atoms in a glass tube. The O source was a low pressure weakly ionized inductively coupled rf oxygen plasma. The recombination coefficient for polycrystalline nickel (purity 99.8 at. %) was determined experimentally by use of a nickel tube with a well activated surface, recombining almost all the atoms entering the experimental chamber. The recombination coefficient was found to be constant over the temperature range of 500–1100 K with a value of 0.27±0.04. The catalytic probe was a disk with a diameter of 2 mm and thickness of 0.2 mm made of the same material. The O density was measured along a glass tube (Schott 8250) with an inner diameter of 3.6 cm and length of 40 cm. The density depended on the pressure in the experimental chamber and was found to decrease exponentially along the glass tube. The characteristic penetration depth depended slightly on pressure and was 60±16 cm. Comparison of the experimental data with theoretical predictions allowed estimation of the recombination coefficient for O atoms on a Schott 8250 glass surface: γ=(1.9±0.5)10-4. © 2000 American Vacuum Society. View full abstract»

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  • Apparatus for quantitative analysis of residual gases in flat panel vacuum packages

    Page(s): 343 - 348
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    We describe an apparatus for quantitative determination of residual gases in flat panel display vacuum tubes like field emission displays, vacuum fluorescent displays, and plasma displays. This system is based on the principle of expansion of gases from the test device into a reference volume, where the gases are analyzed using a quadrupole mass spectrometer. The system was calibrated using gas expansion from reference gas cells and vacuum envelopes with known pressures. The effectiveness of the system was demonstrated by measuring the residual gases inside flat vacuum tubes, commercial vacuum fluorescent displays modulus, and field emission displays. © 2000 American Vacuum Society. View full abstract»

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  • New combination of a three-component gas, Ne–Xe–Ar, for a high efficiency plasma display panel

    Page(s): 349 - 355
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    The luminous efficiency improvement is a key issue for making a plasma display into a large flat panel device. We suggest a new combination of a three-component gas, Ne–Xe–Ar, to achieve a high luminous efficiency of a color plasma display panel. The densities of 26 species and the electron temperature were calculated by zero-dimensional simulation, and we compared the results of zero-dimensional simulation with a measurement of vacuum ultraviolet (VUV) intensity covering a 140–180 nm wavelength range, in order to find the optimum mixing condition of Ne–Xe–Ar gas in a color plasma display panel. Reaction mechanism was analyzed by a computational work to comprehend the mechanism of discharge in Ne–Xe–Ar as well as Ne–Xe. The maximum peak point of the Xe*(1S4) state was obtained in 0.5% of Ar mixing ratio by simulation and the maximum luminous efficiency was measured at the same point of 0.5% Ar mixing ratio in VUV measurement. The luminous efficiency has been improved considerably (about 30%) with a 0.5% Ar addition, compared with the Ne–4% Xe mixing gas. © 2000 American Vacuum Society. View full abstract»

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  • Wide band gap amorphous hydrogenated carbon films grown by plasma enhanced chemical vapor deposition

    Page(s): 356 - 360
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    We have fabricated amorphous hydrogenated carbon films by rf plasma enhanced chemical vapor deposition with very low ion bombardment energy. We demonstrate that the optical gap of the films can be tuned in a wide range, from 3.46 up to 4.95 eV, i.e., close to the diamond gap (5.5 eV), by proper control of the negative dc self-bias voltage. This behavior suggests that a dramatic reduction in the content and clustering of the sp2 sites occurs by lowering the ion bombardment energy. © 2000 American Vacuum Society. View full abstract»

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  • Growth characteristics and deposition mechanism of SrTiO3 thin films by plasma enhanced metalorganic chemical vapor deposition

    Page(s): 361 - 366
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    Dielectric SrTiO3 thin films were deposited on Pt/Si and Ir/Si substrates by plasma enhanced metalorganic chemical vapor deposition using high purity Ti(O-i-C3H7)4, Sr(tmhd)2, and oxygen. The deposition rates were quite dependent on bubbler temperature, substrate temperature, and rf source power. The dissociation of Ti(O-i-C3H7)4 was substantially enhanced by increasing the rf source power, while that of Sr(tmhd)2 increased with the substrate temperature. Surface morphology showed a smooth surface and good adhesion at the interface. Based on the growth characteristics of films, it was found that the deposition of SrTiO3 films was controlled by the decomposition rate of Sr(tmhd)2 on the substrate surface. © 2000 American Vacuum Society. View full abstract»

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  • Thickness distribution of large-area diamondlike carbon films formed by CH4/H2 supermagnetron plasma chemical vapor deposition with application of a stationary magnetic field

    Page(s): 367 - 371
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    Thickness uniformity of diamond-like carbon (DLC) films formed on 5 in. Si wafers by a supermagnetron plasma chemical vapor deposition with applying a static magnetic field was evaluated as a function of radio-frequency (rf) phase difference (RFPD) between two synchronized rf powers (13.56 MHz) supplied to parallel electrodes. When RFPD was 0°, the uniformity of DLC film formed on a lower electrode became poor (about ±9%), and at RFPD of about 180°, it became excellent (about ±3%). Thickness distributions were measured as a function of upper-electrode rf power (UPRF) at lower-electrode rf power (LORF) of 400 W. When UPRF was 0 W (conventional magnetron plasma mode), linearly graded thickness distribution was observed along perpendicular direction to magnetic field lines. At UPRF of 100 W, almost uniform distribution of ±2.9% was obtained, and an inverse thickness distribution to the distribution at UPRF of 0 W was observed at UPRF of 200 W, i.e., inverse magnetron plasma mode. Thickness uniformity also depended on electrode spacing, and good uniformity of ±3% was obtained at a separation of 40–45 mm. By applying a rotating magnetic field, extremely good uniformity of ±1.3% could be obtained. © 2000 American Vacuum Society. View full abstract»

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  • A comparative study on inductively-coupled plasma high-density plasma, plasma-enhanced, and low pressure chemical vapor deposition silicon nitride films

    Page(s): 372 - 376
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    Silicon nitride films have been deposited using inductively-coupled plasma high-density plasma chemical vapor deposition (HDP CVD), plasma-enhanced chemical vapor deposition (PECVD), and low pressure chemical vapor deposition (LPCVD) methods. Characterization and comparison of the three films were performed using Fourier-transform infrared spectroscopy, secondary-ion mass spectroscopy, Rutherford backscattering spectrometry, and hydrogen forward-scattering spectrometry, in addition to wet-etch rate and stress measurement studies. It was found that silicon nitride films deposited using HDP CVD method have several advantages over the silicon nitride films that were deposited using the LPCVD and PECVD methods. The HDP CVD silicon nitride film can be deposited at much lower temperatures (⩽400 °C) than LPCVD silicon nitride, and has substantially less hydrogen (5.5 at. %) than the PECVD film. In addition, the PECVD film contains some oxygen in the film. The wet-etch rate of HDP CVD silicon nitride film is comparable to that of LPCVD film and is significantly less than that of PECVD film in both hot phosphoric acid and buffered HF solutions. The stress of the HDP CVD film is similarly compressive to the PECVD silicon nitride, and not as highly tensile as that of LPCVD silicon nitride. © 2000 American Vacuum Society. View full abstract»

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  • Plasma enhanced chemical vapor deposition of fluorocarbon thin films via CF3H/H2 chemistries: Power, pressure, and feed stock composition studies

    Page(s): 377 - 384
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    Since fluorocarbon thin films exhibit unique properties such as a low coefficient of friction, a low index of refraction, chemical inertness, and hydrophobicity they continue to have industrial interest. The ease by which plasma enhanced chemical vapor deposition fluorocarbon thin films properties can be varied is of interest to the present study. Further, it has been found that these properties, such as index of refraction, hydrophobicity, stress and film hardness can be varied much more easily and substantially with the addition of hydrogen to a CxFy feed stock. The present study is continued work which has investigated the chemical structure and properties of fluorocarbon films as a function or pressure, radio frequency (rf) power density and H2/CF3H feed stock. As a function of rf power density, the index of refraction exhibited a large dependence for the thin films deposited from CF3H with 10 sccm H2. Namely, at 0.0877 W/cm2 the film had an index of 1.420 which dropped to 1.388 at 0.219 W/cm2. The addition of H2 to the CF3H feed stock decreased the intrinsic stress from 430 MPa tensile with no H2 added to 70 MPa tensile with a H2/CF3H ratio of 0.75 (30 sccm H2). Further, the addition of hydrogen qualitatively increased the hardness of the films due to a higher crosslinking density and increased the film thickness uniformity due to the high molecular diffusivity of hydrogen. © 2000 American Vacuum Society. View full abstract»

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  • Anisotropic plasma etching of polymers using a cryo-cooled resist mask

    Page(s): 385 - 387
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    An anisotropic etching process of a perfluorocyclobutene polymer that makes use of a spin-coated photoresist mask instead of a commonly used thin metal layer is reported. We demonstrate that such masking can be applied to advantage for anisotropic reactive ion etching of polymers if the wafer is cooled down to T=-50 °C. For the fabrication of integrated optical waveguides, the choice of an appropriate photoresist is very important if the edge roughness needs to be low in order to avoid optical scattering losses. For such applications, the Microresist Technology ma-P 1275 has been found to be very suitable. © 2000 American Vacuum Society. View full abstract»

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  • Improvement in downflow etching rate using Au as a catalyst

    Page(s): 388 - 392
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    We studied the improvement in the polycrystalline silicon (poly-Si) etching rate in the downflow etching process using microwave-excited CF4/O2 plasma by enhancing the dissociation reaction of the etching gas and the etching reaction on the poly-Si film surface through the use of a catalyst. A piece of platinum (Pt), gold (Au) or silver (Ag) was placed in a quartz tube as a potential catalyst for the downflow etching of poly-Si films. The results revealed that the etching rate using Au was up to 3.6 times higher than that without any catalyst. The mechanism for the improvement in the etching rate using a Au catalyst was analyzed by evaluating the plasma and etching species in transportation paths using optical emission spectral analysis and mass spectrometry, and by examining the poly-Si film with thermal desorption spectrometry, scanning electron microscopy and x-ray photoelectron spectroscopy. The Au placed between the plasma and the sample is oxidized by the active gas dissociated from CF4/O2 gas, and Au oxides and their compounds including F and CFx are transported and deposited onto the surface of the poly-Si film. Although, the precise mechanism of these reactions is not clear, it was presumed that the gold oxides and their reaction compounds acted as catalysts in the etching reaction of the poly-Si film and significantly accelerated the etching rate. © 2000 American Vacuum Society. View full abstract»

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  • Inductively coupled, point-of-use plasma abatement of perfluorinated compounds and hydrofluorinated compounds from etch processes utilizing O2 and H2O as additive gases

    Page(s): 393 - 400
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    A current major environmental concern involves the emission of fluorinated compounds (FCs) used in semiconductor manufacturing for dielectric etching and plasma-assisted chamber cleaning processes in dielectric film chemical vapor deposition (CVD) systems. While progress has been made in reducing FC emissions from CVD tools using alternative chemistries and process optimization, the stringent demands of dielectric etch processes have limited emission reduction from this source. A promising strategy for reducing FC emissions from etch processes is point-of-use plasma abatement. In this approach, a high-density plasma is generated by a device installed downstream of the process chamber in the foreline that dissociates the FC effluent species and recombines the resulting fragments with additive gas fragments to create by-products that are either environmentally benign or scrubbable. In this work, the performance of an inductively coupled plasma abatement device is examined for the treatment of exhaust from a commercial, magnetically enhanced reactive ion etcher. Using either O2 or H2O vapor as abatement additives, FC destruction and removal efficiencies (DREs) of greater than 95% were observed for most process conditions tested. Abatement by-product distributions were found to vary significantly with additive gas identity. Oxygen addition abatement by-products consisted primarily of HF, CO2, COF2, and F2, while H2O addition abatement by-products were primarily HF and CO. Abatement input power was found to be the most significant factor affecting DREs, while argon dilution and total gas load showed little impact over the ranges tested. In additio- - n, wafer metrology indicated no negative process impacts due to abatement device operation. Estimation of the Peclet number within the foreline indicates virtually no probability of abatement product backdiffusion at the foreline pressures and flows tested. © 2000 American Vacuum Society. View full abstract»

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  • Effects of chemical etching with sulfuric acid on glass surface

    Page(s): 401 - 404
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    Glass slides were chemically etched with sulfuric acid using five different methods. We investigated the effects of chemical etching condition on such properties as chemical composition, surface roughness, and thermal stability of the glass. Sodium and carbon atoms on the surface of the glass are effectively eliminated by chemical etching with sulfuric acid. The glass slides were boiled for 30 min in 95% sulfuric acid and were depth profiled at room temperature with x-ray photoelectron spectroscopy (XPS), the Na 1s signal was not detected in the resolution limit of XPS. Surface morphology of the glass was very different depending on the concentration of sulfuric acid. The surface of the glass etched with 50% sulfuric acid was rougher than that of glass etched with 95% sulfuric acid. The sodium concentration of the glass boiled for 30 min in 95% sulfuric acid was nearly zero at the glass surface, and the sodium composition changed very little with annealing temperatures up to 350 °C in a vacuum environment. However the sulfur concentration at the glass surface due to the sulfuric acid increased with increasing temperature. © 2000 American Vacuum Society. View full abstract»

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  • Application of direct bias control in high-density inductively coupled plasma etching equipment

    Page(s): 405 - 410
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    The use of a novel method of power delivery control at the wafer chuck in a high-density inductively coupled plasma reactor has been investigated. This method involves using a peak voltage sensor mounted immediately below the chuck in a feedback loop to the rf generator such that the rf peak voltage can be set as a recipe parameter. By controlling the power delivery in this manner, it is demonstrated that the effects of power losses in the rf circuit between the generator and the chuck, especially in the match network, can be compensated for. In addition, the effect of interactions among source power, bias power and other process parameters on sheath voltage can also be eliminated. In this manner a more complete decoupling of plasma density and ion energy can be achieved than more conventional methods of power delivery allow. © 2000 American Vacuum Society. View full abstract»

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  • On the active surface layer in CF3+ etching of Si: Atomistic simulation and a simple mass balance model

    Page(s): 411 - 416
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    Molecular dynamics (MD) simulations of CF3+ ion bombardment of Si predict the formation of a steady-state fluorocarbosilyl mixing layer that actively participates in the etching of the underlying Si. The active nature of this mixing layer has been characterized by computing atomic residence time distributions (RTDs) for adsorbed fluorine and carbon. The average residence time of carbon in the layers is seen to increase dramatically as ion energy increases, while that of fluorine is not sensitive to ion energy. The overall RTDs compare well with those of an ideal stirred tank. A simple “well-mixed” transient mass balance model is presented. The phenomenology of this model is based on interpretations of the MD results. The model correctly predicts the evolution of atomic concentrations in the mixing layer. Both the MD and model results shed new light on how CF3+ ions etch Si. © 2000 American Vacuum Society. View full abstract»

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  • Use of neural networks to model low-temperature tungsten etch characteristics in high density SF6 plasma

    Page(s): 417 - 422
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    A tungsten (W) etch process in a SF6 helicon plasma has been modeled using neural networks. The process was characterized by a 24-1 fractional factorial experimental design. The design factors that were varied include source power, bias power, chuck holder temperature, and SF6 flow rate. The responses modeled include etch rate, selectivity, anisotropy, and nonuniformity. With optical emission spectroscopy, spectra of radical F intensity were collected to investigate the etch mechanisms. High prediction accuracy was achieved in the etch models. The root mean-square prediction errors were 249 Å/min, and 0.41, 0.16 and 0.83 for the etch rate, selectivity, anisotropy, and uniformity models, respectively. While exerting little impact on the selectivity, the temperature greatly affected the etch rate and anisotropy. In particular, the etch nonuniformity was improved at low temperature. Both the selectivity and nonuniformity were predominantly determined by the bias power. The anisotropy was inversely related to the F intensity. Consequently, W etching at temperatures ranging from -50 to -40 °C offers advantages in anisotropy and uniformity, without much sacrifice of the selectivity. © 2000 American Vacuum Society. View full abstract»

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Aims & Scope

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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Meet Our Editors

Editor
G. Lucovsky
North Carolina State University