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

Issue 4 • Date Jul 1988

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Displaying Results 1 - 25 of 126
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Semiconductor/polyimide interface formation: An x‐ray photoelectron spectroscopy study of germanium chemical bonding

    Page(s): 2175 - 2181
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    We have used high‐resolution angle‐dependent x‐ray photoemission to study the evolving interface formed by vapor depositing Ge (0–80 Å) onto cured polyimide (PI). The core level line‐shape changes of PI and Ge demonstrate that Ge reacts chemically with PI for coverages below ∼10 Å. The rapid attenuation of the carbonyl C 1s photoemission intensity shows that Ge reaction preferentially occurs with carbonyl groups for Ge deposition below ∼0.5 Å and charge withdrawal from the imide–benzene ring is reduced. With increasing Ge deposition (between 0.5 and 5 Å), more carbonyl groups are involved in reaction with Ge and the excess of charge carried by carbonyl carbon atoms induces a hyperconjugation form of the imide–benzene ring. These rings are more vulnerable to Ge chemical attack and the formation of Ge–C bonds. Our results indicate multiple Ge–O–C and Ge–C bonding configurations. Once the initial reaction is complete, the growth mode of Ge on PI appears to be layer‐by‐layer‐like. Time‐ and temperature‐dependent x‐ray photoelectron spectroscopy studies of the 40‐Å Ge/PI interface showed no changes below 400 °C. At 400 °C, changes in core level emission intensities indicate clustering and slight intermixing at the interface. View full abstract»

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  • Reflection extended x‐ray absorption fine‐structure measurements on Ni/C and NixSiy/C multilayered reflection coatings

    Page(s): 2182 - 2187
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    A new method is described to measure bond lengths in the interface between thin layers, by using multilayered reflection coatings both as a dispersive element in an x‐ray beam, and as an object of measurement. Extended x‐ray absorption fine‐structure (EXAFS) oscillations can be observed in the reflected spectrum. From multilayered Ni/C and NixSiy/C reflection coatings mounted in a double‐crystal monochromator we determined, from these oscillations above the Ni LII,III edge, bond lengths equal to 1.8, 2.1, and 2.3 Å, which can be assigned to Ni–C, Ni–Si, and Ni–Ni, respectively. NixSiy/C coatings deposited in a 10-6 Torr H2 atmosphere show better resolution than those without. The difference is ascribed to H2 preventing the formation of silicides and the diffusion of the Ni into the carbon; this results in more amorphous layers. A new and simple method is described for obtaining, in the EXAFS analysis, a high‐resolution radial distribution function (RDF) from a small k‐vector space chi function. This method is applied to a chi function with one and a half oscillations, yielding a zero dc‐component RDF. View full abstract»

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  • Complex formation and growth at the Cr– and Cu–polyimide interface

    Page(s): 2188 - 2199
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    In this paper we describe a detailed experimental and theoretical investigation of the initial stages of formation of the metal/polyimide interface. Core and valence level spectroscopies combined with ab initio quantum‐chemical calculations have permitted a unique interpretation of the interface growth in terms of charge transfer complex formation between the deposited metal atom and the underlying polymer. The detailed evidence as well as implications concerning metal layer adhesion will be discussed. View full abstract»

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  • The microstructure of metal–polyimide interfaces

    Page(s): 2200 - 2204
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    We used cross‐sectional transmission electron microscopy techniques to investigate the microstructure of metal/polyimide interfaces. By comparing our results with previously obtained spectroscopy data, we show that the microstructure of these interfaces is strongly related to the tendency of the metal to chemically react with the polyimide at the interface. Cu and Ni do not react with the polyimide and are seen to diffuse inside of the films and form metallic precipitates in the films. Cr reacts with the polyimide at the interface and is thus bounded at the surface, forming a continuous layer on top of the polyimide. Computer simulations are presented that explain the experiment in terms of the different metal–metal and metal–polymer interactions. View full abstract»

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  • Temperature‐dependent x‐ray photoemission studies of metastable Co/polyimide interface formation

    Page(s): 2205 - 2212
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    High‐resolution x‐ray photoelectron spectroscopy has been used to study the reactive Co/polyimide interface for temperatures 20≤T≤400 °C. Coverage‐dependent studies indicate vigorous but selective reaction for coverages below ∼5 Å, followed by the evolution of a Co overlayer containing polymer fragments in solution. Stepwise heating of PI with a 40‐Å Co overlayer enhanced reaction but also showed degradation of the reaction products. Annealing at 400 °C resulted in Co clustering on the surface and a decomposed Co/PI composite. View full abstract»

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  • Argon and oxygen sputter etching of polystyrene, polypropylene, and poly(ethylene terephthalate) thin films

    Page(s): 2213 - 2220
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    Surface chemical modification of polymer thin films induced by sputter etching was studied by x‐ray photoelectron spectroscopy (XPS) and infrared reflection–absorption spectroscopy (IRRAS). The polymers studied were polystyrene, polypropylene, and poly(ethylene terephthalate) (PET). Oxygen and argon sputter etching of these polymers causes surface oxidation and possibly crosslinking; trends in polymer oxidation can be correlated with the etchant gas, etch power, and initial material properties. For polystyrene and polypropylene, the predominant new functionalities formed are C=O and C–O groups; the breadth of the infrared absorption bands suggests that many different types of these groups exist. For PET, the predominant damage mechanism is crosslinking, with only a slight degree of oxidation resulting from oxygen sputter etching. This work suggests that the information provided by XPS and IRRAS is highly complimentary and will be useful in future studies of polymer functionalization and derivatization. View full abstract»

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  • The radiation chemistry of poly(methyl methacrylate) polymer resists

    Page(s): 2221 - 2225
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    Poly(methyl methacrylate) (PMMA) films of approximately 2.5 μm have been irradiated to various doses using Al x rays. The effect of this irradiation is shown by monitoring the variation in intensity of the Raman vibrational bands of the major constituent species of PMMA, as a function of dose. It is shown that at low doses the molecular weight is reduced as a consequence of main chain scission arising from abstraction of the ester group. This substantiates the previously reported increase in dissolution rate in this dose regime. However, at larger doses it is shown that a cross‐linking reaction generated primary C=C bonds between chain molecules at end‐group sites previously activated by the scission process. This is believed to increase the molecular weight of the polymer resist at larger doses and explains the previously reported drop in the resist dissolution rate at large x‐ray doses. The Raman data suggest that scission and cross‐linking proceed concurrently in response to incident radiation. A model to predict the dissolution rate of the resist as a function of dose based on this dependence of cross‐linking on scission is presented. The results generated from this model are compared to our previously reported experimental resist dissolution data to substantiate conclusions drawn from the Raman results. View full abstract»

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  • X‐ray photoelectron and Auger electron spectroscopy studies of photochemical vapor deposition silicon nitrides

    Page(s): 2226 - 2231
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    Silicon nitride films, deposited by a low‐temperature photochemical vapor deposition method, were characterized by optical, physical, and chemical methods. The film reflectivity was a function of the wavelength of the incident beam and varied from 0.45 to 0.02 in the 4000–7000 Å region. These values changed upon annealing at high temperatures. Film uniformity, in terms of thickness and refractive index, was good over the substrate (±5% and ±0.5%, respectively). The refractive index was 1.95 in the as‐deposited condition and upon annealing exhibited a significant increase due to densification and a decrease in the nonstoichiometric nitride component along with a concurrent increase in the Si3N4 and excess Si amounts. The dramatic decrease in etch rate in buffered HF, from ∼1200 Å/min in the as‐deposited condition to ≪80 Å/min after annealing at 800 °C, was also consistent with the above observations. The pinhole density in these films also decreased considerably after annealing (from ∼100/cm2 to ≪15/cm2). X‐ray photoelectron and Auger electron spectroscopy were used to characterize the composition of these films. The composition profiles exhibited good uniformity through the films, with oxygen and carbon contamination limited to within 100 Å from the surface. The Si 2p photoelectron and the Si KLL Auger electron spectra were broad and upon deconvolution indicated the presence of four different silicon containing species. These were identified as SiO2, stoichiometric nitride (Si3N4), nonstoichiometric nitride (SiNx, 0≪x≤1), and excess silicon bonded with hydrogen (SiHy, 0≪y≪2). SiO2 was detected only on the surface, due to exposure to atmosphere. After high‐temperature annealing, the i- - ntensities of the nonstoichiometric nitride component in both the Si 2p and the Si KLL spectra decreased and the intensities of the Si3N4 and excess Si peaks increased suggesting partial decomposition of SiNx to Si3N4 and excess Si. View full abstract»

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  • Surface characterization of various graphites by x‐ray photoelectron, secondary ion mass, and Raman spectroscopies

    Page(s): 2232 - 2237
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    Graphite is the primary candidate for the first wall of magnetically confined fusion devices. For this purpose, it is important to know the surface properties of graphite to understand the plasma–surface interactions as well as vacuum properties of graphite. From this viewpoint, we examined the binding states of carbon atoms, inherent hydrogen content, and crystallinity of the surfaces of isotropic graphites prepared by several Japanese companies as well as anisotropic ones with x‐ray photoelectron (XPS), secondary ion mass (SIMS), and Raman (RS) spectroscopies. Although no measurable difference in the binding state of carbon atoms was detected among the isotropic and anisotropic graphites with XPS, RS revealed that their crystallite sizes differed from each other. Namely, the crystallite sizes of the isotropic graphites were in the range from 100 to 300 Å, whereas those of the anisotropic graphites were more than ∼1000 Å. In addition, nongraphitized carbon which was not observed for the anisotropic graphites was present in the surface layers of the isotropic ones. SIMS revealed that the inherent hydrogen contents in the isotropic graphites were larger than those in the anisotropic ones. The results indicate that the larger hydrogen contents in the isotropic graphites are due to the presence of nongraphitized carbon which acts as the trapping site of hydrogen atoms. View full abstract»

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  • State identification of GaAs(1¯1¯1¯) oxidized surfaces by an x‐ray photoemission decomposition method

    Page(s): 2238 - 2242
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    An x‐ray photoemission (XPS) decomposition method has been applied to the oxidation of GaAs(1¯1¯1¯) surfaces, in order to identify the oxidation states. The method, which is based on Fourier transform theory, provides separation of overlap composite spectra into its individual components. The incorporation of truncation techniques, which reduces the spurious structure, allows its application to real unresolved As, Ga, and oxygen core level XPS spectra of oxidized GaAs surfaces. The calculated number and chemical shifts of the Ga and As oxide compounds are in very good agreement with the results obtained by the synthesis method. At least three different forms of bound oxygen, β2, β1, and O=, with chemical shifts of -0.7 eV for the β2 and 0.9 eV for the O= referred to the β1 state, are resolved in the oxygen (1s) XPS spectra. View full abstract»

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  • Secondary ion mass spectrometry quantification of Be in AlxGa1-xAs/GaAs multilayer structures

    Page(s): 2243 - 2247
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    The 84AsBe- molecular ions under Cs+ bombardment were used to detect Be atoms in AlGaAs/GaAs heterostructures. They showed a negligible matrix dependence, compared to that of the 9Be+ ions under O+2 bombardment. The suppressed matrix effect in the former case provided a more straightforward and accurate way for secondary ion mass spectrometry quantification. View full abstract»

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  • Positron annihilation spectroscopy of AlGaAs/GaAs interfaces in metalorganic chemical vapor deposition grown GaAs heterojunction solar cells

    Page(s): 2248 - 2252
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    The defect density profile of high‐efficiency epitaxial metalorganic chemical vapor deposition (MOCVD) grown GaAs heterojunction solar cell structures has been characterized using a variable‐energy positron beam. Spatial defect changes, film thickness variations, and possibly interfacial space charge and disorder may be resolved from annihilation characteristics by control of the implantation depth of positrons. Correlations were made relating positron annihilation spectroscopy (PAS) measurements to surface photovoltage data, band bending, and known MOCVD growth parameter variations. Based upon these correlations, it is expected that PAS may provide a valuable means for probing defect profiles that may affect the electrical and optical response of MOCVD‐grown semiconductor materials. View full abstract»

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  • Calibration of Auger spectra and equilibrium surface composition in a dilute copper–gold alloy

    Page(s): 2253 - 2259
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    The enthalpy and entropy of segregation for gold to the surface of a Cu–6.6% Au alloy are reported together with the calibration procedure used to obtain surface compositions in the presence of overlapping Auger electron peaks. Additionally, a chemical shift in the Au 69‐eV Auger transition for Cu–Au alloys is demonstrated via comparison of Auger spectra from homogeneous Cu–Au alloys with those from a composite Cu/Au sample. Finally, the experimental enthalpy of segregation, -7.53 kJ/mol, is compared with that of a statistical thermodynamic model and other theoretical values from the literature. View full abstract»

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  • X‐ray photoelectron spectroscopy, scanning Auger microprobe, and scanning electron microscopy study of the Ti–6Al–4V surface irradiated with a pulsed Nd:YAG laser in air

    Page(s): 2260 - 2264
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    Ti–6Al–4V alloy surfaces were examined with x‐ray photoelectron spectroscopy (XPS), scanning Auger microprobe (SAM), and scanning electron microscopy before and after irradiation with a pulsed Nd:YAG laser (1.06 μm) operating at power levels between 0.25 and 9.0 W. At low power, where little melting occurs, much of the surface C contamination was removed. Also, thinning of the TiO2 overlayer occurred as evidenced using XPS by the intensity increase of the metallic Ti peak compared to that of the oxide. Small amounts of TiC and TiN are also formed during irradiation. SAM images indicate a large loss of C and O and a decrease in the TiO2 with residual amounts of N and C present. Plots of normalized total XPS area versus watts for the C(1s), O(1s), Ti(2p), Al(2p), and N(1s) lines reveal that all of these elements reach a steady‐state concentration at high power levels. Carbon decreases to 20% of the original amount found on the untreated surface. Nitrogen shows the largest percentage change reaching nearly three times greater than the untreated surface at low power levels. View full abstract»

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  • Relative elemental sensitivity factors in secondary neutral mass spectrometry

    Page(s): 2265 - 2270
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    Using the first commercially available electron gas secondary neutral mass spectrometer (SNMS) the relative sensitivity factors D0Fe/D0X were determined for 29 elements from a variety of standards of known composition. The results show an average standard deviation which increases with decreasing energy of the bombarding Ar+ ions from 30% at 2 keV to 53% at 250 eV. Detailed analysis revealed that a standard deviation of 2% is due to the day‐to‐day reproducibility of the experimental system conditions, e.g., plasma and ion optics parameters. The remaining variations observed between different samples are attributed at least partly to matrix‐dependent angular distributions of the sputtered neutral particles. Particularly the observed difference between angular distributions of alloy constituents, being most pronounced if elements of very low mass like Be, B, C, N, and O, are present in the sample, leads to a characteristic dependence of the relative sensitivity factors for these elements on the bombarding energy. It is concluded that the most reliable quantification is obtained with SNMS data taken at bombarding energies E0≳1 keV. With few exceptions, the average D0Fe/D0X values measured for E0=2 keV are found to agree reasonably well with theoretical predictions. View full abstract»

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  • Quantitative depth profile and bulk analysis with high dynamic range by electron gas sputtered neutral mass spectrometry

    Page(s): 2271 - 2279
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    The need for quantification in thin‐film and surface analysis has increased the interest in sputtered neutral mass spectrometry (SNMS) since this method is less affected by matrix effects than secondary ion mass spectrometry (SIMS) and in addition does not suffer from preferential sputtering like Auger electron spectroscopy and x‐ray photoelectron spectroscopy depth profiles, as it measures sputtered fluxes instead of surface concentrations. Among the different postionization techniques, electron gas SNMS [H. Oechsner and W. Gerhard, Z. Phys. B 221, 41 (1975)] using a hot and high‐density rf‐coupled plasma, is the one most established. Its field of applications has until recently been limited by two artifacts: mass resolved residual gas line interferences in SNMS spectra and structureless background induced by photons and electrons of the plasma. Both problems are overcome by a new ion optical arrangement which combines a three‐electrode retarding field configuration, adjusted to the maximum of plasma potential, with a simulated spherical deflection capacitor in front of a quadrupole mass filter. Theory, design, and analytical performance of this combined SNMS and SIMS spectrometer will be discussed and results of depth profiling of semiconductor layer structures and bulk trace analysis will be given. For these applications quantification is discussed in terms of plasma control (electron temperature and density) and particle emission process (energy and angular distribution, molecular emission, secondary ion yield) parameters. View full abstract»

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  • A method for rapid collection of high‐energy‐resolution Auger electron spectroscopy data: The digital‐derivative‐generation technique

    Page(s): 2280 - 2286
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    A new technique for collecting Auger electron spectroscopy (AES) spectral data, referred to as the digital‐derivative‐generation technique, is presented. The function of the lock‐in amplifier is performed with the computer. Data are collected in the dN/dE mode and then integrated to produce N(E) spectra. The technique offers high speed and high energy resolution making it attractive for obtaining chemical state information from AES. No artifical smoothing of the AES data is required beyond that which is inherent in the integration process. Transients in the system are reduced to submillisecond intervals so that data may be taken intermittently. This feature is useful for performing AES at elevated temperatures or time‐resolved AES. View full abstract»

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  • Calculation of postionization probabilities as a function of plasma parameters in electron gas secondary neutral mass spectrometry

    Page(s): 2287 - 2292
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    Using the semiempirical cross‐section functions for electron impact ionization developed by Lotz, we calculated the ionization rate constants for most elements as a function of the electron temperature in a low‐pressure noble gas plasma typically employed in electron gas secondary neutral mass spectrometry (SNMS). After first‐order corrections accounting for (a) the different mean energies of sputtered neutral particles and (b) signal losses due to heavy particle scattering by discharge gas particles (e.g., Ar), the neutral‐to‐ion conversion factors α0X are calculated for the Leybold INA 3 system for most elements X across the Periodic Table. Assuming uniform (mass independent) transmission in the detection system the ratios α0Fe0X are equivalent with the relative sensitivity factors D0Fe/D0X in SNMS. View full abstract»

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  • Plasma studies on the Leybold–Heraeus INA3 secondary neutral mass spectrometry system

    Page(s): 2293 - 2298
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    Electron gas secondary neutral mass spectrometry (SNMS) has been introduced recently by Leybold–Heraeus (LH) as a commercially available method for quantitative surface and bulk analysis of solids. Being the central part of electron gas SNMS, the employed special low‐pressure rf discharge has to be characterized carefully in terms of electron temperature Te , plasma (or electron) density ne, and plasma potential in order to ensure reproducible sensitivity factors for different elements. In the present study the fundamental dependences of Te and ne on adjustable experimental parameters have been established on the first INA3 combined SNMS–secondary ion mass spectrometer system. The results could be explained semiquantitatively by means of the charge carrier and power balances of the plasma. The INA3 system features two measurable parameters for plasma characterization: the floating potential Up of an insulated Langmuir probe and the current Ip measured on a second negatively biased probe. Unique relations could be determined between Up ,Ip and Te , ne (Te)1/2 , respectively, as predicted by plasma theory. Furthermore, the variation of Te and ne as a function of discharge burning time was measured in order to investigate warm‐up effects which were found to affect the residual gas suppression efficiency of the system. A detailed study of residual gas influence by adsorption and resputtering from the sample surface showed evidence for a significant reduction of the detection sensitivity of reactive elements like C, N, and O, which may occur on samples with high sticking probabilities for residual gas components. View full abstract»

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  • NbN thin films reactively sputtered with a high‐field direct‐current magnetron

    Page(s): 2299 - 2303
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    The chemical (Auger electron spectroscopy) and electrical characterizations of NbN thin films reactively sputtered with a high‐field dc magnetron under varying conditions are described. The films were deposited onto polished silicon and glass substrates which were maintained at close to ambient temperature. A study of the chemical composition, transition temperature, transition width, and sheet resistance ratio was made to determine the optimum conditions for the NbN thin‐film preparation. The transition temperature and sheet resistance ratio increases monotonically as the oxygen content of the films decreases and the NbN thin films approach stoichiometry. For films deposited by sputtering at 490 W with 15% nitrogen, 85% argon at 6.6‐mTorr total pressure, the transition temperature was 14.7 K, the transition width was 0.2 K, the sheet resistance ratio was 0.90, and the composition was nearly stoichiometric with ≪1 at. % oxygen and ≪1 at. % carbon contamination. View full abstract»

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  • Effect of radio‐frequency‐induced substrate biasing on the microstructure of palladium films

    Page(s): 2304 - 2306
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    Palladium films were deposited by dc planar magnetron sputtering while biasing the film substrate. The pseudodielectric function of the films was measured by spectroscopic ellipsometry in the spectral range 1.5–6.0 eV. The films were best described by the two‐dimensionally isotropic Sen, Scala, and Cohen effective medium theory. With increasing rf‐induced substrate biasing the Pd film microstructure was modified in a manner similar to that obtained by varying the film–substrate temperature alone. View full abstract»

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  • Structure and properties of sputtered carbon overcoats on rigid magnetic media disks

    Page(s): 2307 - 2315
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    Sputtered carbon overcoats on commercial rigid disks with thin‐film magnetic media are studied using transmission electron analysis (microscopy, microdiffraction, and energy‐loss spectroscopy), Raman spectroscopy, Auger spectroscopy, ellipsometry, x‐ray diffraction, and microhardness testing. Data from transmission electron analysis, Raman spectroscopy, and ellipsometry suggest that the carbon overcoats are composed of small graphite crystallites (≤2 nm), randomly oriented, with a small percentage (0%–5%) of fourfold coordinated carbon bonds. Auger spectroscopy and transmission electron energy‐loss spectroscopy indicate the presence of a small amount of oxygen. Auger spectroscopy also shows some surface nitrogen. The optical constants, n=2.1 and k=0.78, exhibit a small wavelength dependence. In addition, the extinction coefficient k shows a dependence upon film thickness. X‐ray diffraction and microhardness testing did not yield any information concerning the carbon overcoats. There was no indication of diamond from any of the techniques which distinguish between diamond and other forms of carbon. Differences in structure and bonding are seen with Raman spectroscopy in samples from different manufacturers and in annealed samples. View full abstract»

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  • Angular distribution of particles sputtered from metals and alloys

    Page(s): 2316 - 2318
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    The angular distributions of atoms sputtered from pure Cu and Be as well as Cu98Be2, Cu71Zn29, Co3Au, and WSi2.3 were investigated for bombardment with Ar+ ions of 250 eV and 2 keV under normal incidence. Between polar emission angles θ=0° and 60°, for the higher bombarding energy all observed angular distributions look very much alike and follow essentially a cos3 θ law. For the low bombarding energy, however, significant differences between the angular distributions of the alloy constituents are found. The effect, which is most pronounced for CuBe, seems to scale with the atomic mass in the way that the lower mass particles are sputtered preferentially along the surface normal. View full abstract»

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  • Physicochemical properties in tungsten films deposited by radio‐frequency magnetron sputtering

    Page(s): 2319 - 2325
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    The microstructure, reflectivity, resistivity, and oxygen contamination of thin tungsten films (≪250 nm) deposited by rf magnetron sputtering on silicon substrates are reported. Three structural stages, depending on the operating conditions, are found to occur during the deposition: (i) In the range of the rf applied power density studied (≪6 W cm-2), an amorphous structure is always observed when the film thickness does not exceed ∼80 nm. The resistivity remains at a fairly high level (≂1.3 μΩ m). (ii) Upon further deposition and if the power density is ≪0.6 W cm-2, the β‐W phase is detected. (iii) A thermally activated transformation of the β‐W phase into pure α–W occurs for a critical temperature ∼150 °C during depositions carried out at higher powers(≥1 W cm-2). The resulting β‐W or α‐W films consist of small grains (5–20 nm) which present a low dislocation density. Resistivity and reflectivity are mainly related to the oxygen content of the films. When the rf deposition power density is low (≤0.6 W cm-2), both high oxygen contamination levels (≫10 at. %), large resistivity (≫1 μΩ m), and low reflectivity (≪48%) are concurrently observed, whatever the thickness. The oxygen contamination is controlled by the deposition rate and by the substrate temperature. Long‐run depositions carried out at high power densities (≫2 W cm-2) exhibit a very low contamination degree (≪1 at. %). The resulting lower limit of the resistivity is 0.25 μΩ m and the upper one for the reflectivity is 54%. 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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Editor
G. Lucovsky
North Carolina State University