ZIB

1

Digitale Medien

Morphology and microstructure of epitaxial Cu(001) films grown by primary ion deposition on Si and Ge substrates (1996)

Karr, Brian W. ; Kim, Y. W. ; Petrov, I. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 80 (1996), S. 6699-6705

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A low-energy, high-brightness, broad beam Cu ion source is used to study the effects of self-ion energy Ei on the deposition of epitaxial Cu films in ultrahigh vacuum. Atomically flat Ge(001) and Si(001) substrates are verified by in situ scanning tunneling microscopy (STM) prior to deposition of 300 nm Cu films with Ei ranging from 20 to 100 eV. Film microstructure, texture, and morphology are characterized using x-ray diffraction ω-rocking curves, pole figure analyses, and STM. Primary ion deposition produces significant improvements in both the surface morphology and mosaic spread of the films: At Ei〉37 eV the surface roughness decreases by nearly a factor of 2 relative to evaporated Cu films, and at Ei(approximately-equal-to)35 eV the mosaic spread of Cu films grown on Si substrates is only (approximately-equal-to)2°, nearly a factor of 2 smaller than that of evaporated Cu. During deposition with Ei(approximately-equal-to)25 eV on Ge substrates, the film coherently relaxes the 10% misfit strain by formation of a tilt boundary which is fourfold symmetric toward 〈111〉. The films have essentially bulk resistivity with ρ=1.9±0.1 μΩ cm at room temperature but the residual resistance at 10 K, ρ0, shows a broad maximum as a function of Ei, e.g., at Ei(approximately-equal-to)30 eV, ρ0=0.5 μΩ cm. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.363795

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2

Digitale Medien

Reaction paths and kinetics of aluminide formation in Al/epitaxial-W(001) model diffusion barrier systems (1995)

Bergstrom, D. B. ; Petrov, I. ; Allen, L. H. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 78 (1995), S. 194-203

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Single-crystal bcc W(001) layers, 140 nm thick, were grown on MgO(001) substrates by ultrahigh-vacuum (UHV) magnetron sputter deposition at Ts=600 °C. Al overlayers, 190 nm thick with strong (001) and (011) preferred orientation and an average grain size of 200 nm, were then deposited at Ts=100 °C without breaking vacuum. Changes in bilayer sheet resistance Rs were monitored continuously as a function of time ta and temperature Ta during UHV annealing. In addition, Rutherford backscattering spectroscopy, x-ray diffraction, transmission electron microscopy (TEM), and scanning TEM, in which cross-sectional specimens were analyzed by energy-dispersive x-ray analysis with a 1 nm resolution, were used to follow area-averaged and local interfacial reaction paths as well as microstructural changes as a function of annealing conditions. The initial reaction products were discontinuous regions of monoclinic-structure WAl4 which exhibit a crystallographic relationship with the underlying W layer. bcc WAl12 forms at a later stage and grows conformally to cover both W and WAl4. WAl4 and WAl12 continue to grow, with W being the primary mobile species, until the Al layer is completely consumed. Information from the microchemical and microstructural analyses was used to model the Rs(Ta,ta) results based upon a multielement equivalent circuit approach which accounts for the observed nonplanar nature of the reaction front. Reaction kinetics and activation energies were determined. The results show that the growth of WAl4 is diffusion limited with an activation energy Ea of 3.1 eV while the formation of WAl12 is reaction limited with Ea=3.3 eV. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.360651

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3

Digitale Medien

High-flux low-energy ((approximately-equal-to)20 eV) N+2 ion irradiation during TiN deposition by reactive magnetron sputtering: Effects on microstructure and preferred orientation (1995)

Hultman, L. ; Sundgren, J.-E. ; Greene, J. E. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 78 (1995), S. 5395-5403

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The effects of the incident ion/metal flux ratio (1≤Ji /JTi≤15), with the N+2 ion energy Ei constant at (approximately-equal-to)20 eV ((approximately-equal-to)10 eV per incident accelerated N), on the microstructure, texture, and stoichiometry of polycrystalline TiN films grown by ultrahigh-vacuum reactive-magnetron sputtering have been investigated. The layers were deposited in pure N2 discharges on thermally oxidized Si(001) substrates at 350 °C. All films were slightly overstoichiometric with a N/Ti ratio of 1.02±0.03 and a lattice constant of 0.4240±0.0005 nm, equal to that of unstrained bulk TiN. Films deposited with Ji/JTi=1 initially exhibit a mixed texture—predominately (111), (002), and (022)—with competitive columnar growth which slowly evolves into a pure (111) texture containing a network of both inter- and intracolumn porosity with an average column size of (approximately-equal-to)50 nm at t=1.6 μm. In contrast, films grown with Ji/JTi≥5 do not exhibit competitive growth. While still columnar, the layers are dense with an essentially complete (002) preferred orientation and an average column size of (approximately-equal-to)55 nm from the earliest observable stages. The normalized x-ray diffraction (002) intensity ratio in thick layers increased from (approximately-equal-to)0 to 1 as Ji/JTi was varied from 1 to ≥5. Both 111 and 001 interplanar spacings remained constant as a function of film thickness for all Ji/JTi. Thus, contrary to previous models, strain is not the dominant factor in controlling the development of preferred orientation in these films. Moreover, once film texture is fully evolved—whether it be (002) or (111)—during deposition, changing Ji/JTi has little effect as preferred orientation becomes controlled by pseudomorphic forces. Film porosity, however, can be abruptly and reversibly switched by increasing or decreasing Ji/JTi. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.359720

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4

Digitale Medien

Al/TixW1−x metal/diffusion-barrier bilayers: Interfacial reaction pathways and kinetics during annealing (1997)

Bergstrom, D. B. ; Petrov, I. ; Greene, J. E.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 82 (1997), S. 2312-2322

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Polycrystalline bcc TixW1−x layers with mixed 011 and 002 texture were grown on oxidized Si(001) substrates at 600 °C by ultrahigh-vacuum (UHV) magnetron sputter deposition from W and Ti0.33W0.67 targets using both pure Ar and Xe discharges. Ti concentrations in the 100-nm-thick layers were 0, 6, and 33 at. % depending on target composition and sputtering gas. Al overlayers, 190 nm, thick with strong 111 preferred orientation, were then deposited in Ar at 100 °C with and without breaking vacuum. Changes in bilayer sheet resistance Rs were monitored as a function of time ta and temperature Ta during subsequent UHV annealing. Thermal ramping of Al/W and Al/Ti0.06W0.94 bilayers at 3 °C min−1 resulted in large (〉fourfold) increases in Rs at Ta(similar, equals)550 °C, whereas Rs in the Al/Ti0.33W0.67 bilayers did not exhibit a similar increase until (similar, equals)610 °C. Area-averaged and local interfacial reactions and microstructural changes were also followed as a function of annealing conditions. The combined results indicate that Al/W and Al/Ti0.06W0.94 bilayer reactions proceed along a very similar pathway in which monoclinic WAl4 forms first as a discontinuous interfacial phase followed by the nucleation of bcc WAl12 whose growth is limited by the rate of W diffusion, with an activation energy of 2.7 eV, into Al. In contrast, the W diffusion rate during the early stages of Al/Ti0.33W0.67 annealing is significantly higher allowing the formation of a continuous WAl4 interfacial blocking layer which increases the overall activation energy Ea, still limited by W diffusion, to 3.4 eV and strongly inhibits further reaction. We attribute observed increases in WAl4 nucleation and growth rates in interfacial Al/Ti0.33W0.67 to a "vacancy wind" effect associated with the very rapid (Ea=1.7 eV) diffusion of Ti into Al. © 1997 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.366039

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5

Digitale Medien

Origin of compositional variations in sputter-deposited TixW1−x diffusion barrier layers (1995)

Bergstrom, D. B. ; Tian, F. ; Petrov, I. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 67 (1995), S. 3102-3104

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Sputter-deposited Ti1−xWx diffusion barriers in microelectronic devices have been reported by many groups to be Ti deficient with respect to the target composition. In the present experiments, polycrystalline TixW1−x alloys were grown on oxidized Si(001) substrates at temperatures Ts between 100 and 600 °C by ultrahigh-vacuum magnetron cosputter deposition from pure W and Ti targets in 5 mTorr (0.65 Pa) Ar and Xe discharges. Films deposited in Ar were found by Rutherford backscattering and Auger electron spectroscopies to be increasingly Ti deficient with increases in the Ti sputtering rate and/or Ts at a constant W sputtering rate. TRIM calculations and Monte Carlo gas-transport simulations were used, in combination with the experimental results, to show that the Ti loss was due primarily to differential resputtering of the growing film by energetic Ar particles backscattered from the heavier W target. This effect is exacerbated at elevated film growth temperatures by Ti surface segregation in the alloy. The use of Xe, rather than Ar, as the sputtering gas greatly reduces both the flux and the average energy of backscattered particles incident at the substrate such that measurable Ti loss is no longer observed. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.114878

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6

Digitale Medien

Development of preferred orientation in polycrystalline TiN layers grown by ultrahigh vacuum reactive magnetron sputtering (1995)

Greene, J. E. ; Sundgren, J.-E. ; Hultman, L. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 67 (1995), S. 2928-2930

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The preferred orientation of polycrystalline TiN films grown by ultrahigh-vacuum reactive-magnetron sputter deposition on amorphous SiO2 at 350 °C in pure N2 discharges was controllably varied from (111) to completely (002) by varying the incident ion/metal flux ratio Ji/JTi from 1 to ≥5 with the N+2 ion energy Ei maintained constant at (approximately-equal-to)20 eV ((approximately-equal-to)10 eV per incident accelerated N). All samples were slightly over-stoichiometric with N/Ti=1.02±0.03. Films deposited with Ji/JTi=1 initially exhibit a mixed texture with competitive columnar growth which slowly evolves into a nearly complete (111) texture at film thicknesses greater than 1 μm. However, films grown with Ji/JTi≥5 exhibit an essentially complete (002) preferred orientation from the earliest observable stages. The normalized XRD (002) intensity ratio in thick layers increased from (approximately-equal-to)0 to 1 as Ji/JTi was varied from 1 to ≥5. Both (111) and (001) interplanar spacings remained constant as a function of film thickness yielding a lattice constant of 0.4240±0.0005 nm, equal to that of unstrained bulk TiN. Contrary to previous models, the present results establish that TiN preferred orientation can be controlled without introducing large in-plane compressive stress and/or changes in the strain energy as a function of layer thickness. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.114845

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7

Digitale Medien

Aluminide formation in polycrystalline Al/W metal/barrier thin-film bilayers: Reaction paths and kinetics (1997)

Bergstrom, D. B. ; Petrov, I. ; Allen, L. H. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 82 (1997), S. 201-209

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Polycrystalline bcc W layers, 110 nm thick with 011 preferred orientation and an average grain size of 40 nm, were grown on amorphous-SiO2/Si(001) substrates by ultrahigh vacuum (UHV) magnetron sputter deposition at Ts=600 °C. Al overlayers, 170 nm thick with strong 111 preferred orientation and an average grain size of 120 nm, were then deposited at Ts=100 °C without breaking vacuum. Changes in bilayer sheet resistance Rs were monitored continuously as a function of time ta and temperature Ta during UHV annealing. In addition, area-averaged and local interfacial reaction paths, as well as microstructural changes as a function of annealing conditions, were determined by x-ray diffraction, Rutherford backscattering spectroscopy, transmission electron microscopy (TEM), and scanning TEM in which compositional distributions in cross-sectional specimens were obtained by energy-dispersive x-ray analysis using a 1 nm diam probe beam. The two tungsten aluminides which form, WAl4 and WAl12, are nucleated essentially immediately with no measurable induction time. WAl4 grains, extensively twinned, increase in size during the initial reaction, then stop growing as competitive growth in the diffusion limited regime favors WAl12. Information from microstructural and microchemical analyses was used to model the Rs(Ta,ta) data in order to determine reaction kinetics and activation energies. The results show that WAl12 growth is limited by W diffusion, with an activation energy of 2.7 eV, to the Al/aluminide interface. © 1997 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.365798

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8

Digitale Medien

Modelling mass transfer entrance lengths in turbulent pipe-flow with applications to small cathodes for measuring local mass transfer rates (1996)

Wang, Y. ; Postlethwaite, J. ; Bergstrom, D. J.

Springer

Journal of applied electrochemistry 26 (1996), S. 471-479

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ISSN: 1572-8838

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: Abstract Pipe-wall mass transfer, in the developing concentration boundary layer region, under fully developed hydrodynamic conditions is simulated with a low-Reynolds number,k−ε, eddy viscosity turbulence model. The predictions are in good agreement with the electrochemical measurements of Berger and Hau, in the rangeRe=104 to 105, forSc=2244, and of Son and Hanratty, in the rangeRe=1×104–5×104, forSc=2400, in both the developing boundary layer region and the fully developed region. The application of small cathodes embedded in a larger active cathode to measure local mass transfer rates is also simulated. The size of the electrode and the thickness of the electrical insulation around the small electrode give rise to errors that increase as the insulation thickness increases and the electrode size decreases.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01021969

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