bluuebunny/crossref_metadata_2025 huggingface dataset:
Copper sulfide films deposited by cylindrical magnetron reactive sputtering
Authors: Jonath Arthur D. , Anderson William W. , Thornton John A. , Cornog David G.
Published: July 2002

Copper sulfide coatings 150 nm thick were deposited by reactive sputtering using a copper cylindrical magnetron sputtering source in an Ar–H2S atmosphere at constant discharge current and varies H2S injection rates. Borosilicate plate-substrates were maintained at temperatures of 130° and 35°C, which are above and below transition temperatures for the CuxS phases of interest. Above a critical injection rate resistivity data indicate two types of materials: a high-resistivity type (∠100 Ω cm) often exhibiting Cu-rich nodules, and a low-resistivity type (∠0.01 Ω cm). The types are generally associated with the high and low substrate temperatures respectively. Hall mobilities were in the 1–6 cm2/V s range for both materials. Optical absorption, resistivity-versus-temperature, and x-ray diffraction measurements indicate that the high resistivity material consists largely of near-stoichiometric chalcocite and that the low resistivity material is a mixture of chalcocite and djurleite.
Reactive sputtering of carbon and carbide targets in nitrogen
Authors: Cuomo J. J. , Leary P. A. , Yu D. , Reuter W. , Frisch M.
Published: July 2002

Paracyanogenlike films – (CN)n– are prepared by reactive rf sputtering of carbon in nitrogen. The material is deposited on quartz, silicon, metals, sapphire, and mica from 20° to 450°C. Above 450°C, there is no film accumulation on the substrates. The sputtering process yields a deposition rate greater than ten times the best known commercial method for paracyanogen film preparation. Also described are the results of sputtering carbide targets i.e. HfC, TiC, SiC, in the presence of nitrogen. Due to the stability of the C≡N bond, for example, stoichiometric Si3N4 films unexpectedly were deposited from a SiC target sputtered in N2. Similar results are described for HfC and TiC targets.
Relation of Si–H vibrational frequencies to surface bonding geometry
Authors: Lucovsky G.
Published: July 2002

The vibrational frequencies of Si–H groups, SiH, SiH2, and SiH3, in substituted silane molecules, and hydrogenated amorphous solids, display shifts in frequency that can be correlated with the relative electronegativities of the silicon nearest neighbors, i.e, the substituting atoms or groups in the molecules, and the hydrogen second neighbors in the amorphous networks. In this paper, the empirical relations are extended to include a description of Si–H vibrations on semiconductor surfaces.
Optical alignment system for submicron x-ray lithography
Authors: Fay B. , Trotel J. , Frichet A.
Published: July 2002

The alignment system described in this paper is applicable to all proximity mode replication systems. The inherent high accuracy of the method makes it particularly attractive for submicron lithography applications requiring positioning accuracy of better than 0.1 μm. The basic alignment mark on the mask is a one dimensional Fresnel zone whose primary focal length is equal to the proximity gap spacing. Helium–Neon laser illumination is used. Elimination of unwanted diffraction orders is achieved by incorporating a transverse grating structure on the alignment mark on the wafer. The alignment signal sensitivity to gap variation is such that it allows very precise setting of the gap spacing in an unambiguous fashion. Three pairs of such alignment marks are necessary to provide x–y–ϑ registration as well as gap spacing and parallelism settings. A key feature of the alignment system is the time varying incidence angle of the laser beam upon each Fresnel zone mark, which results in a small amplitude scanning of the wafer surface and allows continuous registration throughout the entire exposure duration. A description of the alignment system designed for a submicron x-ray lithography system is given, together with some preliminary results.
Aluminum nitride films by rf reactive ion-plating
Authors: Murayama Yoichi , Kashiwagi Kunihiro , Kikuchi Masasi
Published: July 2002

Aluminum nitride films were synthesized successfully on silicon (111) and spinel (111) single crystal surfaces by rf reactive ion-plating. Aluminum was evaporated from an evaporator in the rf discharge phase of either nitrogen gas or ammonia gas at a pressure of 10−4 Torr (∠10−2 Pa). Film structures were evaluated using reflection high energy electron diffraction (RHEED) and scanning electron microscopy (SEM). The aluminum nitride films synthesized on the spinel (111) surfaces at the substrate temperature of 1000 °C, in the rf discharge phase of both nitrogen gas and ammonia gas, were found to be of single crystal form, having parallel orientation to the substrate surfaces. Aluminum nitride single crystals forming hexagonal pyramids were observed to grow in the perpendicular direction to the substrate surfaces during the study. The growth rate of aluminum nitride film obtained in the ammonia gas discharge, which was about 500 Å min−1, was about two times as fast as that obtained in the nitrogen gas discharge.
An atom probe study of the anomalous field evaporation of alloys containing silicon
Authors: Miller M. K. , Smith G. D. W.
Published: July 2002

In some atom probe microanalytical investigations of homogeneous alloys, the apparent concentrations of certain elements have been found to differ from the expected values. Both the time of flight atom probe and the imaging atom probe have been used to study this phenomenon in detail, in the case of an iron 3 wt.% silicon transformer steel. The apparent concentration of silicon is found to depend on pulse fraction, time between pulses, specimen temperature, and crystallographic area. Low pulse fractions and long periods between pulses both give apparent increases in the silicon level. When the probe aperture is positioned inside the central ring of a (110) pole, the silicon atoms are found to be retained until the end of the evaporation of that layer, and the overall apparent level of silicon is approximately three times higher than expected. These results suggest that certain elements may be preferentially removed from an alloy by dc field evaporation during the interval between the H. T. pulses if incorrect experimental conditions are used. For quantitative atom probe analysis of silicon-containing alloys, it appears that a pulse fraction of at least 15% is required and that analysis inside the central ring of low index poles should be avoided.
Stoichiometry and thickness of the initial oxide formed on clean titanium surfaces determined by quantitative Auger electron spectroscopy, electron energy loss spectroscopy, and microgravimetry
Authors: Burrell M. C. , Armstrong N. R.
Published: July 2002

The initial oxidation of a clean polycrystalline titanium film was studied by Auger electron spectroscopy (AES) and electron energy loss spectroscopy (ELS), while simultaneously monitoring the total oxygen uptake using the quartz crystal microbalance (QCM). Quantitation of the O KLL and Ti LMM AES intensities reveals that the surface stoichiometry at the initial stages of oxidation (<100 L O2 at 1×10−5 Torr) corresponds to that expected for Ti2O3, and the ELS results also suggest the presence of the lower oxidation states of titanium (+2,+3) on the surface. The microgravimetric results indicate that the oxidation is not confined to the region sampled by the electron spectroscopic methods, and a surface layer of Ti2O3 whose thickness is ∼40 Å is consistent with the observed combination of results.
Catalyzed reactions at illuminated semiconductor interfaces
Authors: Wrighton Mark S.
Published: July 2002

Many desirable minority carrier chemical redox processes are too slow to compete with e−−h+ recombination at illuminated semiconductor/liquid electrolyte junction interfaces. Reductions of H2O to H2 or CO2 to compounds having C–H bonds are too slow to compete with e−−h+ recombination at illuminated p-type semiconductors, for example. Approaches to improve the rate of the desired processes involving surface modification techniques are described. Photoanodes are plagued by the additional problem of oxidative decomposition under illumination with ≥Eg illumination. The photo-oxidation of Cl−, Br−, and H2O is considered to illustrate the concepts involved. Proof of concept experiments establish that catalysis can be effective in dramatically improving direct solar fuel production; efficiencies of >10% have been demonstrated.
Diffusion chromium coating of iron magnetic circuit parts for relays
Authors: Jenko M. , Kveder A. , Tavzes R. , Kansky E.
Published: July 2002

With diffusion chromizing the iron magnetic circuit parts in relays, the following improvements were accomplished: surface hardening, corrosion protection, and better magnetic properties. From various procedures under consideration the chromium diffused coating in vacuum was selected. The specimens of pure iron 99.95% of Fe, were buried in a granular chromium (150 μm) and heated at the temperature from 950–1150 °C in vacuum (10−2–10−3 mbar) for durations from 3 to 12 h. The chromized layer thickness, the chromium concentration profiles, the microhardness, the coercive force, and corrosion resistance were measured.
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o passivation of ZrAl alloy bulk getters
Authors: Cecchi J. L. , LaMarche P. H. , Dylla H. F. , Knize R. J.
Published: July 2002

We have developed a method for passivating previously activated ZrAl alloy bulk getters. Such passivation is essential for avoiding embrittlement of the getters during discharge cleaning operations in tokamak fusion devices. The method consists of exposing the getters (at room temperature) to a controlled amount of oxygen, followed by pulse discharge cleaning to restore the vacuum vessel walls to clean conditions. We have tested this method on the Tokamak Fusion Test Reactor (TFTR) and present measurements of the decrease in the hydrogen and oxygen pumping speeds as functions of the quantity of oxygen adsorbed. These measurements are in good agreement with previous laboratory results. Using this method followed by 20 h of pulse discharge cleaning, we have reduced the getter pumping speed by more than a factor of 2×103 and have recovered the same clean vacuum conditions as existed prior to the oxygen exposure.
Alloying effect on a property of hydrogen gettering materials: An empirical formula to estimate heat of hydride formation for metals and alloys
Authors: Watanabe Kuniaki , Matsuyama Masao , Ashida Kan , Miyake Hitoshi
Published: July 2002

Getter materials are promising for the research and development of thermonuclear fusion reactors from a viewpoint of tritium handling as well as fuel and impurity control in tokamaks. Some guiding rules are indispensable in developing a getter material having suitable properties for a given process in tritium handling. In analogy to the relation between the heat of oxide formation and electronegativities of elements, we studied the change in the heat of hydride formation with metals and alloys from this viewpoint: the electronegativities of getter materials and hydrogen. We found a simple relation between them in a form of (−ΔHabs)=23s(χM−2.20)2 +3.72s−3.72, where χM and 2.20 are the electronegativities of getter material and hydrogen, and s is the stoichiometric number of hydrogen in hydride. The standard deviation from the observed values was ∼5 kcal/mol(hydride) and/or 35%. This equation was found to be valid for 70 systems which appear to form metallic hydride. An advantage of this equation can be seen in the fact that it consists of only the electronegativities of getter materials and hydrogen, and the stoichiometric number of hydrogen, both of which can be found in literature or estimated with simple assumptions. Consequently, it will be quite useful as a guiding rule to design a getter material with a given heat of hydride(tritide) formation for metals/alloys and/or heat of hydrogen(tritium) absorption.
Auger parameter measurements of phosphorus compounds for characterization of phosphazenes
Authors: Dake L. S. , Baer D. R. , Friedrich D. M.
Published: July 2002

X-ray generated photoelectron and Auger transition data for several phosphorus reference compounds, including PCl3, P3 N5, P2 O5, (C6 H5 )3 P(C5 H4 ), (C6 H5 )4 PBr, KH2 PO4 , NH4H2PO4, and NH4 PF6 are presented. These data have been used to determine the relative ionicity and polarizability of phosphorus in the chlorophosphazene trimer ([NPCl2 ]3 ) and polymer ([NPCl2 ]n ). The results support recent molecular-orbital calculations that predict a highly polarized backbone bond in the phosphazenes. Furthermore, the chlorophosphazene polymer was observed to have a greater value for the Auger parameter than the chlorotrimer, indicating that the bonding environment surrounding the polymer is more polarizable than that surrounding the trimer.
A scanning tunneling microscopy study of the surface microstructure of alpha- and beta-lead dioxide
Authors: Sexton Brett A. , Cotterill Guy F. , Fletcher Stephen , Horne Michael D.
Published: July 2002

The surface microstructures of specimens of pure alpha- and beta-lead dioxide (PbO2 ) have been resolved with scanning tunnel microscopy (STM). Observed crystallite sizes are compared with values deduced from x-ray diffraction (XRD), and the same data are compared with results from other characterization methods including scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area measurements, mercury porosimetry and electrochemical reduction. The large difference in surface area between alpha- and beta-PbO2 is explained by microcracks permeating the beta structure. The STM images show these microcracks clearly.
Chemical vapor deposition of SiC layers from a gas mixture of CH3SiCl3+H2(+Ar), and effects of the linear velocity and Ar addition
Authors: Motojima Seiji , Hasegawa Mitsutaka
Published: July 2002

SiC polycrystalline layers were deposited on a graphite substrate from a gas mixture of CH3SiCl3+H2(+Ar) at temperatures in the range of 800–1200 °C. The effects of the source gas flow rate (CH3SiCl3+H2), total pressure, linear velocity and Ar flux addition on the phase of the deposits were examined in some detail. The deposition of a single-phase of SiC was accelerated at a higher linear velocity by reducing the total pressure and by addition of Ar flux at atmospheric pressure. The effect of Ar addition on acceleration of the SiC deposition may be caused by an increasing linear velocity and ‘‘dilution effect’’ of reactant gases.
Scanning Auger electron spectroscopy of the fiber/matrix interface of SiC fiber/silicate glass matrix composites
Authors: Laube Bruce L. , Brennan John J.
Published: July 2002

SiC fiber/silicate glass matrix composites have been investigated as a replacement material for jet engine components for several years. Scanning Auger electron spectroscopy (AES) has revealed a correlation between the physical properties (strength and toughness) of these composites and the chemistry of the fiber/matrix interface. Analyses of individual fiber surfaces and matrix troughs (areas of matrix exhibiting fiber pull-out) of fractured composites have indicated that fracture toughness is imparted by a 200+ Å layer of carbon formed at the interface during fabrication. Similarly, strong bonding between matrix and fiber is associated with weak and brittle composites. The specific requirements for AES of these composites is presented.
Comparison of the attenuation lengths and the inelastic mean-free path for photoelectrons in silver
Authors: Jablonski A. , Tougaard S.
Published: July 2002

The overlayer method for determining the attenuation length was simulated by the Monte Carlo method. The theoretical model was based on the elastic scattering cross sections resulting from the partial wave expansion method. Multiple elastic electron collisions in the solid were considered. Calculations were made for MgKα excited silver 3d photoelectrons ejected in the silver overlayer. The overlayer was ‘‘deposited’’ on a number of substrates having a wide range of atomic numbers. It was found that the values of attenuation length cover a wide interval (9.14–13.44 Å). The inelastic mean free path for Ag 3d photoelectrons assumed in calculations was equal to 13 Å. This effect is due to elastic photoelectron collisions. It turned out that the attenuation length depends on the substrate material, the range of the considered overlayer thickness, and the geometry of measurements. Thus, the overlayer experiment can provide any value of the attenuation length for considered photoelectrons from the above interval by suitable selection of the experimental conditions. The results obtained here, together with experimental problems in producing well characterized thin films, explain the scatter in the published experimental values of the attenuation length. The reliability of the theoretical model is extensively discussed.
e
−-beam deposition of In2O3 stabilized ZrO2 films
Authors: Qadri S. B. , Skelton E. F. , Harford M. Z. , Jones R. , Lubitz P.
Published: July 2002

Films of ZrO2–In2O3 were deposited by coevaporating ZrO2 and In2O3 using electron beam deposition techniques. During the deposition, the substrate was heated to 300 °C. Postdeposition x-ray diffraction analyses showed that as-deposited films containing an In2O3 mole fraction ranging between 3.5 and 11.0 were crystalline with the zirconia in the cubic phase.
Gettering of hydrogen and oxygen by alkali-metal graphite intercalation compounds
Authors: Ichimura Kenji , Sano Mizuka
Published: July 2002

Gettering of hydrogen and oxygen by alkali-metal graphite intercalation compounds, MC8 (M=K, Rb, and Cs), was investigated by the constant-volume closed method. The rate constants for hydrogen gettering kH are found to be in the order of RbC8 (∼10−3 s−1)≳KC8 (∼10−4 s−1)≫CsC8 (<10−6 s−1), while the rate constants for oxygen gettering kO are all within the range 0.2×10−1–1×10−1 s−1 for MC8 studied. The ratio kO/kH is found to be 34, 69, and more than 5.2×104 for KC8, RbC8, and CsC8, respectively, which indicates that CsC8 has a large pumping selectivity for oxygen in a hydrogen-rich atmosphere.
Sustained self-sputtering using a direct current magnetron source
Authors: Posadowski Witold M. , Radzimski Zbigniew J.
Published: July 2002

Sustained self-sputtering of copper and silver targets has been achieved using a direct current magnetron source. The sputtering was carried out successfully without an inert gas at 8×10−6 Torr. A very high deposition rate was obtained in this mode of operation. The possible mechanism and requirements for sustained self-sputtering are discussed and other potential material candidates are suggested.
Evaluation of molecular arrangement in fatty acid monolayers with transmission electron and atomic force microscopes
Authors: Oishi Y. , Hirose F. , Kuri T. , Kajiyama T.
Published: July 2002

Molecular arrangements and structural defects in lignoceric and stearic acid monolayers were investigated with transmission electron and atomic force microscopes. Lignoceric acid molecules in the monolayer, prepared by a continuous compression method, were regularly arranged in a hexagonal array with the (10) spacing of 0.43 nm. The hexagonal array with crystallographical distortion of 4.0% was extended over 10 nm (crystallographical continuity), and the locally disordered molecular arrangements in the monolayer were also observed. On the other hand, stearic acid molecules in the monolayer, prepared by a multistep creep method, were regularly arranged in a hexagonal array with the (10) spacing of 0.42 nm. The hexagonal array with the crystallograhical distortion of 2.0% was extended over 20 nm. Distinctly disordered molecular arrangement was not observed in the case of the stearic acid monolayer. The higher crystallographical regularity of the stearic acid monolayer might be attributed to effective sintering at interfaces among crystalline domains during the multistep creep procedure.
Imaging extrinsic defects at the NiSi2/Si(111) metal–semiconductor interface
Authors: Kubby J. A. , Greene W. J.
Published: July 2002

The scanning tunneling microscope is used to image properties of the buried NiSi2/Si(111) metal–semiconductor interface using electron interferometry. This technique reveals the presence of multiple domains in conductance images that are not visible in topographic images. The multiple domains are explained in terms of silicide regions of different thicknesses that are separated by step domain boundaries at the buried interface. The possible influence of these extrinsic defects on the formation of the Schottky barrier and on local real space characterization techniques used to measure Schottky barrier heights are discussed.
Effect of annealing on the stoichiometry of SrTiO3(001)*
Authors: Liang Yong , Rothman J. Bruce , Bonnell Dawn A.
Published: July 2002

A quantitative study of the variation of stoichiometry with temperature near the surface of SrTiO3 is conducted. Surface concentrations and the strontium depth profiles are obtained using Rutherford backscattering spectrometry and Auger electron spectroscopy. While the Auger electron spectroscopy demonstrates that the surface is strontium rich after annealing at temperatures ranging from 800 to 1300 °C, Rutherford backscattering measurements show no evidence of strontium enrichment beneath the surface unless the crystal is annealed at 1300 °C or higher. The observations indicate that changes in surface chemistry involve two processes: sublimation and segregation; which play different roles at different temperature ranges.
Plasma diagnostics of a direct-current arcjet diamond reactor. II. Optical emission spectroscopy
Authors: Reeve S. W. , Weimer W. A.
Published: July 2002

Diagnostic analyses were performed on a dc arcjet diamond reactor using optical emission spectroscopy. Rotational and vibrational excitation temperatures were determined from C2 and CH emission spectra and observed to differ widely at all locations in the plasma except near the substrate. Temperatures were observed to converge at the substrate, indicating thermal equilibration of the plasma. Rotational excitation temperatures for C2 and vibrational excitation temperatures for CH appear to closely track the plasma gas temperature, while vibrational excitation temperatures for C2 and rotational excitation temperatures for CH are anomalously high. A detailed analysis was conducted to identify the dominant excitation processes responsible for producing emission. Results show that (1) excitation to the excited state for both C2 and CH is most likely due to thermal excitation near the substrate, (2) in the plasma bulk, emission by CH is produced primarily by chemiluminescent reactions while emission by C2 is produced by electron impact excitation, and (3) optical emission spectroscopy may be used as a nonintrusive probe of the plasma gas temperature.
Remote plasma and ultraviolet–ozone modification of polystyrene
Authors: Callen B. W. , Ridge M. L. , Lahooti S. , Neumann A. W. , Sodhi R. N. S.
Published: July 2002

Remote argon plasma (RP) and ozone in the presence of ultraviolet light (UV–O3) were used to render polystyrene (PS) surfaces hydrophilic in a controlled manner for eventual application in cell-surface interaction studies. X-ray photoelectron spectroscopy (XPS) was used to characterize both methods of modification. The degree of modification on PS was measured by an increase in surface oxygen and concomitant change in C 1s binding energies as a function of time. Both remote plasma and UV–O3 are shown to be partially surface destructive, producing polymer fragments which are easily washed away to leave stable modified surfaces of oxidized polymer comprising of distributions of C–O, C=O and O—C=O type groups. Of the two methods, UV–O3 is shown to be more versatile and conducive to preparing PS surfaces with controllably varying degrees of modification. UV–O3 modified polystyrene is shown to be stable in air for at least eight months. Contact angle methods were used in correlation with XPS in characterizing UV–O3 modified surfaces. It is shown that changes in surface tension and total surface oxygen content were related, however, not directly connected.
The nature of hydrogen in x-ray photoelectron spectroscopy: General patterns from hydroxides to hydrogen bonding
Authors: Kerber S. J. , Bruckner J. J. , Wozniak K. , Seal S. , Hardcastle S. , Barr T. L.
Published: July 2002

Important progressive alterations in chemical bonding are often realized through correlations with shifts in the x-ray photoelectron spectroscopy (XPS) binding energies of key elements. For example, there are useful general XPS shifting schemes for such systems as oxides, nitrides, halides, and even various functional groups in organics. Very general patterns, based upon location in the periodic table, exist for many of these materials even when the structure is not strongly considered. Unfortunately, apparently because of the lack of direct XPS detection of hydrogen, there seems to be no general statements in the literature for describing hydrogen-containing compounds, despite the fact that synergistic shifts obviously exist in the XPS spectra of elements attached to hydrogen (e.g., for M–O–H vs M–O–M units, where M is a typical metal). While not attempting a complete review paper, in the present work we use XPS shifting patterns to evolve a series of interrelated covalency/ionicity arguments to help explain the progressive, periodic changes in XPS peak locations for such common cases as M–O–H- and M–N–H-containing systems. These arguments are followed by consideration of the less dramatic XPS shifting patterns exhibited by metal and metalloid hydrides, including organic bonding. The formalism concludes with a discussion of hydrogen bonding detected by XPS. After a select review of the infrequent use made by others to attribute XPS peak shifts to hydrogen bonding, we consider in some detail two cases recently published by members of our group. One case involves the formation of –N–H–N– bonds in proton sponge organic systems, while the other uses XPS to examine the formation of surface oriented –O–H–––O– bonds in the adsorption of peptides on oxidized metals. In the present article, the XPS patterns for these two seemingly divergent cases are explained by closely related arguments that may have far reaching generalities.
Surface structure and composition of NiAl(100) by low-energy ion scattering
Authors: Roos W. D. , du Plessis J. , van Wyk G. N. , Taglauer E. , Wolf S.
Published: July 2002

The atomic structure of the (100) surface of NiAl was investigated by low-energy ion scattering spectrometry (LEISS) using 1000 eV He+ ions as well as alkali ion impact collision ion scattering spectrometry (ALICISS), using 1450 eV Na+ ions. The ALICISS results were analyzed with a computer program based on a model using hitting probability concepts. The LEISS results showed that the top layer consisted mainly of Al with an Al/Ni ratio of 76/24 and the second layer entirely Ni. The ALICISS results could be best explained by a vertical relaxation of 25% (Δd12=−0.36 Å) between the first and second layers and a relaxation of 15% (Δd24=−0.43 Å) between the second and fourth layers. These results are discussed in terms of published data from the literature.
Effect of the Cr-rich oxide surface on fast pumpdown to ultrahigh vacuum
Authors: Chun I. , Cho B. , Chung S.
Published: July 2002

The outgassing characteristic of an ordinary stainless-steel ultrahigh vacuum (UHV) chamber was determined using an extremely dry nitrogen venting system, and compared with that of an extreme high vacuum (XHV) chamber. A marked sorption resistance effect of the vacuum surface of the XHV chamber was found. The outgassing rate of the XHV chamber was about 100 times lower than that of the ordinary UHV chamber in the unbaked case. It is believed that the recent achievement of fast pumpdown to UHV is the result of not only the reduction of the water content of the venting gas, but also the low gas-sorbability of the vacuum surface.
Constant power operation of incandescent micromachined polysilicon microresistors for use as vacuum pressure sensors
Authors: Kleckner T. C. , Lawson R. P. W. , Robinson A. M.
Published: July 2002

As a proof of concept study, a micromachined polysilicon resistor was used as a vacuum pressure sensor. The resistor was heated to incandescence and operated with a constant electrical power input. A photodiode monitored light intensity changes as the pressure of the surrounding nitrogen gas was varied over the pressure range of 10−2–104 Pa. This optical method to measure pressure was nine times more sensitive than one based on electrical resistance variations. This measurement method is thus both more sensitive and it operates over a large pressure range than conventional thermal conductivity sensors.
Tribological properties of diamond-like carbon films deposited by negative carbon ion beam
Authors: Sohn M. H. , Ahn Y. O. , Ko Y. W. , Hah S. R. , Fischer T. E. , Kim S. I.
Published: July 2002

Excellent antiwear diamond-like carbon (DLC) films were prepared on silicon wafers by a novel negative carbon ion beam deposition system. This system does not need any gas in the chamber; deposition occurs under high vacuum. The ion source has good control of the C− beam energy (from 50 to 150 eV) and produces a 0.5-in.-diam ion beam for DLC coating. All coatings showed ultrasmooth surfaces (Ra∼1 nm) and good adhesion. The results of infrared and Raman spectroscopy show that the degree of diamond-like character in the films, the sp3 fraction, increases as a function of deposition energy in this particular energy range. The nanoindentation hardness of the films also increases from 15 to 50 GPa as deposition energy increases. The wear rates and friction coefficients against a M-50 steel bearing ball were measured in a pin-on-disk tribometer with a normal load of 9.8 N, calculated nominal Hertzian stress of 0.8–1.8 GPa. The measured wear rates of the DLC films were of the order of 10−7 and 10−8 mm3/N m depending on the deposition energy of the carbon beam. The friction coefficients in the steady state were found to be around 0.1. These results indicate excellent applications for abrasion resistant DLC coatings. We are developing a rectilinear negative carbon ion beam deposition system (up to 8 in.) for large area application, and many of the process scale-up issues have been solved.
Use of reactive ion sputtering to produce clean germanium surfaces in a carbon rich environment—an ion scattering study
Authors: Smentkowski V. S. , Holecek J. C. , Schultz J. A. , Krauss A. R. , Gruen D. M.
Published: July 2002

We have used the ion spectroscopic techniques of direct recoil spectroscopy and mass spectroscopy of recoiled ions to demonstrate that low energy reactive ion sputtering of Ge is capable of removing surface impurities such as carbon. The experiments were performed in a vacuum chamber maintained at 3.5×10−7 Torr. At these pressures, physical sputtering using noble gas is not effective for cleaning Ge surfaces as carbon redeposits onto the surface. In this article, we demonstrate that reactive sputtering of Ge using 4.0 keV nitrogen at a Ge surface temperature of ∼740 K and above removes surface carbon and deposits nitrogen on the Ge surface. Heating the nitrogen exposed Ge surface to above ∼880 K results in the desorption of nitrogen and generates an atomically clean Ge surface, under poor vacuum conditions.
Reaction of 1,2-ethanedithiol on clean, sulfur-modified, and carbon-modified Mo (110) surfaces
Authors: Roe Charles L. , Schulz Kirk H.
Published: July 2002

The reactivity of 1,2-ethanedithiol on the clean Mo (110) and p(4×4)-C/Mo (110) surfaces has been investigated as a function of sulfur coverage using temperature programmed desorption (TPD), Auger electron spectroscopy, and low energy electron diffraction. TPD experiments performed on both surfaces produced similar reaction products, although changes were observed in selectivity. On the clean Mo (110) surface, the major products observed during TPD experiments were acetylene, ethylene, vinyl thiol, and ethanethiol. However, the reaction of ethanedithiol on the p(4×4)-C/Mo (110) surface produced acetylene, ethylene, and ethanedithiol. Product molecules are thought to arise from two distinct types of surface intermediates: (1) a monodentate thiolate species bound to the surface through only one of the ethanedithiol sulfur atoms, and (2) a bidentate organosulfur metallocycle bound to the surface through both of the ethanedithiol sulfur atoms. We propose that vinyl thiol and ethanethiol are produced via C–S bond scission and subsequent hydride elimination of the monodentate thiolate intermediate, and that the bidentate surface metallocycles undergo C–S bond scission to yield acetylene and ethylene. On the carbon-modified surface, complete desulfurization of ethanedithiol occurs upon decomposition, yielding only hydrocarbon products. With increasing sulfur coverage, a decrease in reactivity and a shift in desorption features to lower temperatures is observed for ethanedithiol on the clean and carbon-modified surfaces.
X-ray photoelectron spectroscopy characterization of the oxidation of electroplated and sputter deposited copper surfaces
Authors: Apen Elizabeth , Rogers B. R. , Sellers James A.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) was used to study the surface oxidation of sputtered and electroplated copper films following exposure to ambient air and chemical processing reagents used during the fabrication of interconnect structures. Exposure of both sputtered and electroplated copper films to ambient air and deionized (DI) water resulted in the formation of thin copper oxide layers. For ambient exposed copper films, the topmost layer contains Cu2+ oxide species, and the next Cu+ oxides. For DI water exposure, only Cu+ oxide species were observed. Oxidation was more rapid for the electroplated compared to the sputtered copper films as measured by copper oxide to copper metal concentration ratios calculated from XPS curve fitting results and photon-induced Auger peak height measurements. For the electroplated copper films, oxygen uptake was slower as a result of exposure to ambient compared to DI water treatments. Electroplated copper films exposed to common wet chemical etchants also show indications of oxidation of the copper surface region with evidence of mechanical instability between the formed oxide and underlying copper film, resulting in adhesion loss. A method for the removal of the oxide layer has also been investigated to improve adhesion to overlying passivation films.
Improvement of turbomolecular pumps for ultraclean, low-pressure, and high-gas-flow processing
Authors: Ino Kazuhide , Sekine Katsuyuki , Shibata Tadashi , Ohmi Tadahiro , Maejima Yasushi
Published: July 2002

Turbomolecular pumps (TMP) have been widely used in low-pressure processing, because TMP can pump a large flow of gas as well as can exhaust the system to a suitable base pressure. A TMP, however, has the problem that its pumping speed is severely degraded at inlet pressures higher than ∼10 mTorr, where most of the low-pressure processing of semiconductor manufacturing is performed. In this study, it is confirmed that the occurrence of such a degradation in TMP performance is primarily determined by the inlet pressure of TMP and not by the outlet pressure. As the inlet pressure is increased to ∼10 mTorr, the gas flow in the front blades as well as the rear blades of the TMP goes into the transition flow, and TMP pumping speed consequently begins to decrease. Once the degradation occurs, however, the pumping speed is strongly dependent upon the pumping speed of the backing pumps, namely the foreline pressure. In order to improve the TMP performance under high gas flow, a characteristic dimension in the pump, particularly at the entrance, such as the distance between each blade vane and the distance between the rotor blade and the stator blade, was shortened to increase Knudsen’s number. This enables us to maintain the molecular flow region at higher pressures and to improve the TMP performance under high gas flow. The newly developed TMP can endure a gas flow as great as ∼1500 sccm with maintaining the acceptable pumping speed. We have also experimentally measured the impurity level in the chamber due to back-diffusion through TMP, as well as the impurity compression ratio under high gas flow. It is demonstrated that the impurity level in the chamber can be made several orders of magnitude lower than that for the best performance of TMP under ultrahigh vacuum operation when adequate gas flow is fed into the chamber.
Plasma diagnostics in a triode ion plating system*
Authors: Wouters Stan , Kadlec Stanislav , Quaeyhaegens Carl , Stals Lambert M.
Published: July 2002

Langmuir probes combined with an energy resolved mass analyzer make satisfying contributions to the characterization of plasmas. The probes provide spatially resolved information on the well known plasma parameters, while the mass analyzer gives information on the energy distribution functions for ions/neutrals originating from some point in the plasma volume. These diagnostic tools have been used to investigate the glow discharge of the triode ion plating system of Balzers (BAI 640), a physical vapor deposition installation for the production of hard coatings. Two identical, planar Langmuir probes, positioned in the main argon plasma body, and an energy-resolved mass analyzer (Balzers PPM 421), directed to the crucible, were used to investigate the influence of the four most important process parameters, i.e., (1) the low voltage (LV) arc current, (2) the high voltage (HV) electron gun current, (3) the total pressure, and (4) the substrate voltage on the plasma parameters and on the energy spectra of ions and neutrals, during the evaporation of titanium without reactive gases. The substrate bias had no significant influence on the plasma parameters and on the energy spectra, but is very important for the microstructure of the thin film. The HV electron gun, used to melt the titanium, changed the plasma parameters only at high current values, but the energy spectra of the Ti ions changed drastically. The LV arc current and the total pressure are the process parameters that do affect both the probe characteristics and the energy spectra of ions and neutrals.
New-type microwave plasma source excited by azimuthally symmetric surface waves with magnetic multicusp fields
Authors: Tuda Mutumi , Ono Kouichi
Published: July 2002

A new-type microwave plasma source has been developed for materials processing. The plasma reactor employed a launcher of azimuthally symmetric surface waves at a frequency of 2.45 GHz and also magnetic multicusp fields around the reactor chamber walls. This configuration yielded high-density (Ne≳1011 cm−3) plasmas sustained by surface waves even at low gas pressures below 10 mTorr, following easy plasma ignition by electron cyclotron resonance (ECR) discharges. Electrical and optical diagnostics were made to obtain the plasma properties in Ar. It was shown that a transition occurs from ECR exited to surface-wave excited plasmas under conditions where the plasma electron density exceeds a critical value of Ne∼1×1011 cm−3.
Surface modification of α-Al2O3(0001) by N2+ ion irradiation
Authors: Choi Won-Kook , Choi Sung-Chang , Jung Hyung-Jin , Koh Seok-Keun , Byun DongJin , Kum Dong-Wha
Published: July 2002

The surface of sapphire most widely used as a substrate for III-V nitride growth was modified by N2+ ion irradiation with ion-beam energies from 100 to 1000 eV. As the ion-beam energy increased from 100 to 500 eV, the root-mean-square roughness of the surface morphology decreased. However no significant change in surface roughness at energy higher than 500 eV was observed. From the N 1s x-ray photoelectron spectroscopy core-level spectra, no peak related to a nitrogen bond could be found in the samples irradiated with ion energy below 500 eV. An AlON peak began to appear in the samples irradiated with 600–900 eV N2+ ions, and two peaks corresponding to AlON and AlN were distinctively observed in the sample irradiated at 1 keV.
Transmission electron microscopy study of platinum clusters on Al2O3/NiAl(110) under the influence of electron irradiation
Authors: Nepijko S. A. , Klimenkov M. , Kuhlenbeck H. , Freund H.-J.
Published: July 2002

Using transmission electron microscopy we have studied the influence of the electron beam in an electron microscope onto platinum clusters deposited on a thin single crystalline γ-Al2O3 film grown by oxidation of NiAl(110). At electron current densities below j≈1 A/cm2 no influence is observed. Movement and coalescence of clusters occur at electron beam current densities between j=2 and some 10 A/cm2. For current densities around j=50 A/cm2 decoration of steps takes place. Further increase to j=100  A/cm2 and above induces drilling of holes into the substrate by clusters. At such current densities also melting of the clusters may occur. Due to the heat capacity of the system the result does not only depend on the electron current density but also on the irradiation time.
Dislocation network developed in titanium nitride by ion implantation
Authors: Perry Anthony J. , Sharkeev Yuri P. , Geist Daniel E. , Fortuna Sergey V.
Published: July 2002

The present work is concerned with microstructural changes brought about by ion implantation into TiN as-deposited by classical chemical vapor deposition onto cemented carbide substrates. After implantation the ions occupy an implanted zone (IZ) extending to a depth of about 80 nm. The transmission electron microscopy study shows that implantation can lead to the formation of subgrains in the IZ within the original grain structure without changing the grain size. The energy carried by the ions affects the material to far greater depths and a dislocation network is formed below the IZ, termed the implantation affected zone (IAZ). The dislocation density in the IAZ as determined here by x-ray diffraction depends on the total energy carried by the implanted ions. There is a threshold level before a compressive residual stress is developed after which the stress is proportional to the energy, reaching values as high as 3–4 GPa. A mechanism is proposed for the development of the IAZ where an oscillating stress field is developed at the boundary between the IZ and the IAZ and allows the local emission of dislocation fluxes in mezobands into the IAZ.
Vacuum deposited biaxial thin films with all principal axes inclined to the substrate
Authors: Hodgkinson Ian , Wu Qi Hong
Published: July 2002

We begin by considering the three effective principal refractive indices and the effective axes of a periodic layered medium in which the component layers are tilted- columnar biaxial films formed by vacuum deposition in different planes. A parameter window within which the effective principal refractive indices are well separated and all three effective axes are inclined to the substrate is found for titanium oxide. Next, a set of parameters from the window is transported directly to the regime of bideposition, in which nanometer-scale subdeposits of the components are made serially as starting values for the automated growth of inclined biaxial media. Finally index values and angles are estimated for three samples, using an optimization technique in which experimental and computed angular phase retardance maps are matched.
Selective etching of SiO2 over polycrystalline silicon using CHF3 in an inductively coupled plasma reactor
Authors: Rueger N. R. , Doemling M. F. , Schaepkens M. , Beulens J. J. , Standaert T. E. F. M. , Oehrlein G. S.
Published: July 2002

Selective etching of SiO2 over polycrystalline silicon has been studied using CHF3 in an inductively coupled plasma reactor (ICP). Inductive powers between 200 and 1400 W, as well as pressures of 6, 10, and 20 mTorr were used in this study of the etch rate and selectivity behaviors for silicon dioxide, silicon, and passively deposited fluorocarbon films. Using in situ ellipsometry, the etch rates for all three of these materials were obtained for a self-bias voltage of −85 V, as well as passive deposition rates of fluorocarbon films. X-ray photoelectron spectroscopy has been used to examine the composition of steady-state fluorocarbon films present on the surfaces of polycrystalline silicon, and silicon dioxide during etching at high and low inductive powers. The dependence of the silicon etching behavior is shown to be clearly linked to the fluorocarbon polymerization and etching behavior. Thus, the polymerization and etching behavior of the fluorocarbon is the overwhelming parameter that governs the etch selectivity process within the ICP. Selectivities of oxide to silicon are determined to increase with the inductive power, and are found to be the highest at the intermediate pressure of 10 mTorr. While the stoichiometry of the fluorocarbon films are critical factors in determining the overall etch rate behavior, the fluorocarbon film thickness on the polycrystalline and crystalline silicon is the dominant factor in determining the SiO2 over silicon etch selectivity. The mechanisms involved in attaining high selectivity are dominated by a defluorination of the fluorocarbon steady-state film on polycrystalline silicon, while maintaining a high ion current to the wafer.
Very uniform and high aspect ratio anisotropy SiO2 etching process in magnetic neutral loop discharge plasma
Authors: Chen W. , Morikawa Y. , Itoh M. , Hayashi T. , Sugita K. , Shindo H. , Uchida T.
Published: July 2002

Magnetic neutral loop discharge (NLD) plasma is a new type for dry etching process characterized by effective coupling of the input electric field electron electron motion near the magnetic neutral loop (NL) region. Therefore, dense plasma can be produced and controlled spatially by changing the position of the NL. Uniformity was controlled by changing the radius of NL temporally during the etching using a repetition frequency of 0.1 Hz, so that the deviation of the SiO2 etch rate was within 2% (3σ) on 200-mm-diam wafer. In nanoscale pattern etching processes, we found that CHF2+ ions played an important role in very high aspect ratio profile etching. In CHF2+ ion-rich plasma, ZEP photoresist patterned 20 nm space was successfully etched 800 nm in depth at the pressure of about 0.3 Pa, using CH2F2, C4F8, and O2.
Silicon nitride thin films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition
Authors: Lapeyrade M. , Besland M. P. , Meva’a C. , Sibaï A. , Hollinger G.
Published: July 2002

Using an electron cyclotron resonance plasma compact source, we have studied the deposition of silicon nitride films at low deposition temperature (<300 °C) and low microwave power (<250 W). Nitrogen plasma and pure silane have been used as gas precursors. We report on the effect of the main process parameters on the composition and properties of the films. We show that each experimental parameter has an optimal range of values or a threshold value necessary to obtain films with high dielectric quality. For a deposition temperature of 300 °C, the best films exhibit a resistivity of 1015 Ω cm and a soft breakdown field (at 10−9 A cm−2) of 3 MV cm−1. The physicochemical properties of the films are close to those of stoichiometric silicon nitride: N/Si ratio of 1.33, optical index value of 2 at 3 eV and etch rate of 10 Å/min. Moreover, we observed strong correlations between the physicochemical and the electrical properties of the deposited films, over the entire range of process parameters.
Residual stress in GaN epilayers grown on silicon substrates
Authors: Fu Yankun , Gulino Daniel A. , Higgins Ryan
Published: July 2002

GaN films on AlN buffer layers were grown on (111) silicon substrates in a vertical rotating disk metal–organic chemical-vapor deposition reactor (CVD, Inc.). The dependence of residual stress in GaN films on the V/III molar flow ratio was studied. The crystalline quality of GaN films was analyzed by x-ray diffractometry, and the x-ray lattice parameter method was used to determine the residual stress in the films by measuring the c-axis and a-axis strain separately. The x-ray results show that the residual stress decreases with an increasing V/III molar flow ratio if all other growth parameters are kept constant.