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Jul 2008

Volume 26, Issue 4, pp. 561-1097

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W chemical-vapor deposition using (i-C3H7C5H4)2WH2

Atsushi Ogura, Satoshi Imai, Taihei Kagawa, Hirotaka Kurozaki, Masato Ishikawa, Ikuyo Muramoto, Hideaki Machida, and Yoshio Ohshita

J. Vac. Sci. Technol. A 26, 561 (2008); http://dx.doi.org/10.1116/1.2913581 (4 pages)

Online Publication Date: 9 June 2008

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One of the most popular refractory metals is tungsten or W. Therefore, W chemical-vapor deposition (CVD) is expected to be useful for nanotechnology applications. In some cases, the residual atoms, such as halogen and oxygen, in films may degrade their quality. The authors therefore propose (i-C3H7C5H4)2WH2, i.e., (i-PrCp)2WH2, as a new W precursor because the authors expect some advantages from the absence in this molecule of the F and O that exist in the popular W precursors, WF6 and W(CO2)6. The melting point of (i-PrCp)2WH2 is 30 °C and the precursor has a high vapor pressure of 0.1 torr at 110 °C. The authors conducted W CVD with the (i-PrCp)2WH2 as a precursor and obtained conformal W thin film. The deposition rate was 69 nm/min at 750 °C, and the deposited film had resistivity of 2.3×10−4 Ω cm. However, the deposited film included a tremendous amount of C. Therefore, investigating the possibility of reducing the C contamination is necessary.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
64.70.dj Melting of specific substances
73.61.At Metal and metallic alloys
68.55.-a Thin film structure and morphology

Experiments and modeling of dual reactive magnetron sputtering using two reactive gases

T. Kubart, D. H. Trinh, L. Liljeholm, L. Hultman, H. Högberg, T. Nyberg, and S. Berg

J. Vac. Sci. Technol. A 26, 565 (2008); http://dx.doi.org/10.1116/1.2913582 (6 pages) | Cited 3 times

Online Publication Date: 9 June 2008

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Reactive sputtering from two elemental targets, aluminum and zirconium, with the addition of two reactive gases, oxygen and nitrogen, is studied experimentally as well as theoretically. The complex behavior of this process is observed and explained. It is shown that the addition of oxygen to a constant supply of nitrogen significantly changes the relative content of aluminum with respect to zirconium in the film. Moreover, it is concluded that there is substantially more oxygen than nitrogen in the films even when the oxygen supply is significantly lower than the nitrogen supply. It is further shown that the addition of a certain minimum constant flow of nitrogen reduces, and eventually eliminates, the hysteresis with respect to the oxygen supply. It is concluded that the presented theoretical model for the involved reactions and mass balance during reactive sputtering of two targets in two reactive gases is in qualitative agreement with the experimental results and can be used to find optimum processing conditions for deposition of films of a desired composition.
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81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth

Study of electron beam evaporated compositionally modulated Fe/Al multilayers

R. Brajpuriya, S. Tripathi, A. Sharma, S. M. Chaudhari, T. Shripathi, and N. Lakshmi

J. Vac. Sci. Technol. A 26, 571 (2008); http://dx.doi.org/10.1116/1.2924414 (10 pages) | Cited 1 time

Online Publication Date: 9 June 2008

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This article presents temperature dependent magnetic and electronic properties of compositionally modulated electron beam evaporated Fe/Al multilayer samples (MLSs) with an average composition of Fe0.70A10.30 (MLS-A) and Fe0.50Al0.50 (MLS-B). Structural studies show a large amount of intermixing, leading to alloying at the interfaces as a result of annealing. Both multilayer samples show soft ferromagnetic behavior at room temperature with an in-plane easy axis of magnetization. In both cases, coercivity as well as saturation field continuously increase and magnetization decreases with an increase in temperature. The Curie temperature (TC) is found to decrease from ∼ 561 °C for MLS-A to ∼ 288 °C for MLS-B. These modifications can be attributed to the continuous change in electronic structure brought about by the strong hybridization of Fe 3d and Al 3sp states near Fermi level leading to the formation of different Fe–Al phases (Fe3Al in MLS-A) and (FeAl in MLS-B), as seen from valence band photoemission measurements. The formation of these phases is also supported by resistivity measurement.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.21.Ac Multilayers
81.40.Gh Other heat and thermomechanical treatments

Development of a cosputter-evaporation chamber for Fe–Ga films

N. A. Morley, S.-L. Yeh, S. Rigby, A. Javed, and M. R. J. Gibbs

J. Vac. Sci. Technol. A 26, 581 (2008); http://dx.doi.org/10.1116/1.2924416 (6 pages) | Cited 3 times

Online Publication Date: 9 June 2008

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A new deposition technique involving the dc magnetron sputtering of Fe simultaneously with Ga evaporation has been developed to fabricate thin Fe(1−x)Gax (0<x<0.4) films. Simultaneous sputtering and evaporation has been developed as an alternative to the sputtering of alloy targets, where the need for compositional variation can be hard to address. The new technique allows the freedom of composition that cosputtering would offer, but mitigates the issue of being unable to sputter Ga. The need for the preparation of alloy targets is also avoided. To control the concentration of the Ga in the films, the evaporation rate, the dc magnetron power, and the chamber pressure were varied. The films fabricated were studied to determine their magnetic and microstructural properties. The Fe–Ga films fabricated had magnetostriction constants which had increased by a factor of 5 compared to the same thickness of Fe film.
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81.15.Cd Deposition by sputtering
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.at Other materials
75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
68.55.Nq Composition and phase identification

Growth of InN on Si (111) by atmospheric-pressure metal-organic chemical vapor deposition using InN/AlN double-buffer layers

Zhen-Yu Li, Shan-Ming Lan, Wu-Yih Uen, Ying-Ru Chen, Meng-Chu Chen, Yu-Hsiang Huang, Chien-Te Ku, Sen-Mao Liao, Tsun-Neng Yang, Shing-Chung Wang, and Gou-Chung Chi

J. Vac. Sci. Technol. A 26, 587 (2008); http://dx.doi.org/10.1116/1.2929849 (5 pages) | Cited 4 times

Online Publication Date: 9 June 2008

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Indium nitride (InN) epilayers have been successfully grown on Si (111) substrates with low-temperature (450 °C) grown InN and high-temperature (1050 °C) grown AlN (InN/AlN) double-buffer layers by atmospheric-pressure metal-organic chemical vapor deposition (AP-MOCVD). X-ray diffraction characterizations indicated that highly (0001)-oriented hexagonal InN was grown on Si (111) substrate. Photoluminescence (PL) analyses performed at room temperature showed a strong emission at 0.72 eV with a full width at half maximum of 121 meV. Excitation intensity dependent measurements demonstrated the PL mechanism to be the band-to-band transition. Time-resolved PL could be fitted by a single exponential exhibiting an ordered film and a recombination lifetime of around 0.85 ns. In particular, transmission electron microscopy characterizations indicated that the use of AlN first buffer is very important to achieve a structurally uniform (0001)-oriented InN epilayer on Si (111) by AP-MOCVD.
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68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Hx Other solid inorganic materials

Characterization of molecular nitrogen in III-V compound semiconductors by near-edge x-ray absorption fine structure and photoemission spectroscopies

A. Bozanic, Z. Majlinger, M. Petravic, Q. Gao, D. Llewellyn, C. Crotti, and Y.-W. Yang

J. Vac. Sci. Technol. A 26, 592 (2008); http://dx.doi.org/10.1116/1.2929851 (5 pages) | Cited 3 times

Online Publication Date: 9 June 2008

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Formation of molecular nitrogen under low-energy nitrogen bombardment of III-V compound semiconductor surfaces has been studied by photoemission spectroscopy around N 1s core-level and near-edge x-ray absorption fine structure (NEXAFS) around N K edge. Interstitial molecular nitrogen N2 has been formed in all of the samples under consideration. The presence of N2 produces a sharp resonance in low-resolution NEXAFS spectra, showing the characteristic vibrational fine structure in high-resolution measurements, and at the same time, a new peak, shifted toward higher binding energies for several eV, in all N 1s photoemission spectra.
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68.47.Fg Semiconductor surfaces
71.55.Eq III-V semiconductors
78.70.Dm X-ray absorption spectra
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.Hb Impurity and defect levels; energy states of adsorbed species
61.80.Jh Ion radiation effects

Mechanisms and selectivity for etching of HfO2 and Si in BCl3 plasmas

Chunyu Wang and Vincent M. Donnelly

J. Vac. Sci. Technol. A 26, 597 (2008); http://dx.doi.org/10.1116/1.2938396 (8 pages) | Cited 7 times

Online Publication Date: 9 June 2008

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The authors have investigated plasma etching of HfO2, a high dielectric constant material, and poly-Si in BCl3 plasmas. Etching rates were measured as a function of substrate temperature (Ts) at several source powers. Activation energies range from 0.2 to 1.0 kcal/mol for HfO2 and from 0.8 to 1.8 kcal/mol for Si, with little or no dependence on source power (20–200 W). These low activation energies suggest that product removal is limited by chemical sputtering of the chemisorbed Hf or Si-containing layer, with a higher Ts only modestly increasing the chemical sputtering rate. The slightly lower activation energy for HfO2 results in a small improvement in selectivity over Si at low temperature. The surface layers formed on HfO2 and Si after etching in BCl3 plasmas were also investigated by vacuum-transfer x-ray photoelectron spectroscopy. A thin boron-containing layer was observed on partially etched HfO2 and on poly-Si after etching through HfO2 films. For HfO2, a single B(1s) feature at 194 eV was ascribed to a heavily oxidized species with bonding similar to B2O3. B(1s) features were observed for poly-Si surfaces at 187.6 eV (B bound to Si), 189.8 eV, and 193 eV (both ascribed to BOxCly). In the presence of a deliberately added 0.5% air, the B-containing layer on HfO2 is largely unaffected, while that on Si converts to a thick layer with a single B(1s) peak at 194 eV and an approximate stoichiometry of B3O4Cl.
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81.65.Cf Surface cleaning, etching, patterning
81.15.Cd Deposition by sputtering
79.60.Dp Adsorbed layers and thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Classical size effect in oxide-encapsulated Cu thin films: Impact of grain boundaries versus surfaces on resistivity

Tik Sun, Bo Yao, Andrew P. Warren, Vineet Kumar, Scott Roberts, Katayun Barmak, and Kevin R. Coffey

J. Vac. Sci. Technol. A 26, 605 (2008); http://dx.doi.org/10.1116/1.2938395 (5 pages) | Cited 7 times

Online Publication Date: 17 June 2008

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A methodology is developed to independently evaluate surface and grain boundary scattering in silicon dioxide-encapsulated, polycrystalline Cu thin films. The room-temperature film resistivity for samples with film thicknesses in the range of 27 to 1 65 nm and different grain sizes (determined from approximately 400 to 1500 grains per sample) is compared to existing and empirical models of surface and grain boundary scattering. For the combined effects of surface and grain boundary scattering, the surface specularity parameter p is 0.6±0.2 and the grain boundary reflectivity coefficient R is 0.45±0.03. It is thereby shown that the resistivity contribution from grain boundary scattering is significantly greater than that of surface scattering for Cu thin films having Cu/SiO2 surfaces and grain sizes similar to film thickness.
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73.50.Mx High-frequency effects; plasma effects
72.30.+q High-frequency effects; plasma effects
73.61.-r Electrical properties of specific thin films
73.25.+i Surface conductivity and carrier phenomena
61.72.Mm Grain and twin boundaries

Morphological analysis of TiB2 thin film prepared by rf magnetron sputtering

Wei Dai, Tongjun Zhang, Junyou Yang, Rongxing Sun, and Juliang Xu

J. Vac. Sci. Technol. A 26, 610 (2008); http://dx.doi.org/10.1116/1.2943642 (6 pages) | Cited 1 time

Online Publication Date: 17 June 2008

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Superhard TiB2 thin films were deposited on steel substrates using the radio-frequency magnetron-sputtering technique with a low normalized substrate temperature (0.1<Ts/Tm<0.2). The microstructure of these films was observed by a field-emission scanning-electron microscope (FESEM) and grazing-incidence x-ray diffraction (GIXRD), while the composition of films was obtained using Auger electron spectroscopy (AES). It was found that the TiB2 thin films were overstoichiometric and that the diffusion of Ti and B atoms on the substrate surface was greatly improved at a temperature of 350 °C. Moreover, a new dense structure, named the “equiaxed” grain structure, was observed by FESEM at this substrate temperature. GIXRD was carried out at different directions with same the grazing-incidence method and the variation of diffraction intensity of the nonrandom textured grains was confirmed. Combined with FESEM and AES analysis, it is suggested that the equiaxed grain structure was located in zone 2 at the normalized substrate temperature as low as 0.18.
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68.55.J- Morphology of films
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.72.-y Defects and impurities in crystals; microstructure
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.66.Bi Elemental solids
61.66.Dk Alloys
66.30.H- Self-diffusion and ionic conduction in nonmetals

X-ray photoelectron spectroscopy studies of water-induced surface reorganization of amphiphilic poly(2-hydroxyethyl methacrylate-g-dimethylsiloxane) copolymers using cryogenic sample handling techniques

Lu Chen, Daniel J. Hook, Paul L. Valint, and Joseph A. Gardella

J. Vac. Sci. Technol. A 26, 616 (2008); http://dx.doi.org/10.1116/1.2943643 (8 pages) | Cited 3 times

Online Publication Date: 17 June 2008

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A series of amphiphilic graft copolymers having a hydrophilic poly(2-hydroxyethyl methacrylate) (HEMA) backbone and hydrophobic polydimethylsiloxane (PDMS) side chains were studied by x-ray photoelectron spectroscopy (XPS) in both dry and hydrated states using cryogenic sample handling techniques. The polymers were synthesized using anionic methods for the PDMS side chains, yielding a tightly controlled PDMS graft chain length in a polymer brush surface configuration. The effects of hydration time and polymer bulk structure (e.g., PDMS graft length) and composition on surface reorganization were examined. XPS studies provided direct quantitative data on the extent of polymer surface reorganization between dry and hydrated states. The dry surface was enriched with PDMS while the hydrated surface was enriched with HEMA. The surface reorganization reaches equilibrium when copolymers were hydrated for 24 h. In the dry state, PDMS graft length and bulk composition have a strong effect on surface composition; while in the hydrated state, the polymer surface composition was nearly independent of bulk structure or composition.
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79.60.Fr Polymers; organic compounds
61.41.+e Polymers, elastomers, and plastics

Can the throttling of a perfect gas through a free molecular orifice produce a cooling effect?

Robert M. Young, Timothy T. Braggins, Christopher F. Kirby, J. Douglas Adam, Michael B. Petach, and Emanuel Tward

J. Vac. Sci. Technol. A 26, 624 (2008); http://dx.doi.org/10.1116/1.2929843 (10 pages)

Online Publication Date: 26 June 2008

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A novel refrigeration cycle using throttling through free molecular orifice(s) was explored experimentally and theoretically, attempting to exploit the heat transfer that occurs by the entropy shift across a discontinuous system formed by a wall containing tens of thousands of micron or submicron free molecular throttling (FMT) orifices. Single stage free molecular throttle cooling is compared in terms of figure of merit and coefficient of performance (COP) against the analogous isothermal entropy shift cooling effect in thermoelectric junctions. Unlike thermoelectric materials, free molecular throttling is predicted to perform increasingly better as the temperature drops below 200 K. Experimentally, the authors have shown in three rounds of progressively smaller dimensions and hence larger heat flux vector magnitude that the simple, isothermal movement of heat, taken in analogy with thermoelectric (Peltier junction) refrigerators, is not valid. By using this information, the authors then show that solid state heat conduction across the orifice wall controls the degree of temperature reduction. This was described in a new dimensionless number which gives the relative importance of the backward thermal leakage due to solid state conduction through the wall thickness, against that of the FMT heat flow, and is thus the means by which a designer would direct the design space toward a functional and practical wall. The largest theoretical temperature drop per stage was found to be ΔT = T0/6, and thus staging would be required to reach cryogenic temperatures from ambient. Single stage FMT refrigeration was derived theoretically to have a peak second law efficiency of 5%–10% of the Carnot COP. The low pressures involved and lack of the regenerative heat exchanger in this new cycle means that it is scalable to very small dimensions, and indeed, since it operates in a regime where the characteristic size of the orifices must be smaller than the mean free path length of the gas molecules, it is already scaled to microscopic dimensions. FMT cooling would appear to have future applications in subwatt heat lift systems with the ultimate lowest temperature of ∼ 10 K being only dictated by the perfect gas limit of He.
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07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
44.10.+i Heat conduction

Survey on measurement of tangential momentum accommodation coefficient

Amit Agrawal and S. V. Prabhu

J. Vac. Sci. Technol. A 26, 634 (2008); http://dx.doi.org/10.1116/1.2943641 (12 pages) | Cited 13 times

Online Publication Date: 26 June 2008

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The value of tangential momentum accommodation coefficient (TMAC) is required while prescribing the boundary condition for flow of gases in the slip and transition flow regimes. The precise determination of its value is important for several other applications as well. This article reviews the experimental techniques employed by researchers over the decades to measure this coefficient and the values reported in the literature, with relevance to calculation of the slip velocity. The review shows that the value of TMAC is dependent on a number of parameters including nature of the gas, pressure of the gas, material of the surface, surface cleanliness and roughness, and surface temperature. For monatomic gases, the TMAC at about 0.93 is almost constant with respect to the Knudsen number, and this value can be employed for most commonly available surface materials. However, for nonmonatomic gases, TMAC decreases with an increase in Knudsen number; a correlation of TMAC with Knudsen number for this class of gases, is proposed based on the available data. It is also revealed that TMAC depends strongly on the surface cleanliness and roughness, while temperature has an influence although it may not be very important for values greater than the room temperature.
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47.45.Gx Slip flows and accommodation
47.45.-n Rarefied gas dynamics
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.-b Solid-gas/vacuum interfaces: types of surfaces
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back to top Applied Surface Science

Bulk ratio method for determining surface enhancement using Auger analysis

J. D. Geller

J. Vac. Sci. Technol. A 26, 650 (2008); http://dx.doi.org/10.1116/1.2908433 (4 pages)

Online Publication Date: 27 June 2008

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The surface analysis techniques of Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) are often used to characterize the near surface composition of stainless steel. AES is most often used to determine the oxide thickness and the maximum chromium to iron ratio as this information is used to determine if the material is properly electropolished. XPS is primarily used to determine the near surface chemistry as well as the chromium to iron ratio. Instrument calibration is critical to reliable composition determination. For AES, the use of elemental sensitivity factors is found to be a significant source of error. Proposed is a new method for the determination of Cr/Fe ratios using AES. The resulting depth profiles show the proper stainless steel composition under the surface enhanced layer.
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82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.20.Fv Electron impact: Auger emission
68.35.Dv Composition, segregation; defects and impurities
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Investigation of thin-oxide-free protective coatings on chromium and 316 L stainless steel formed by treatment with etidronic acid

S. L. Johnson and P. M. A. Sherwood

J. Vac. Sci. Technol. A 26, 654 (2008); http://dx.doi.org/10.1116/1.2902963 (6 pages)

Online Publication Date: 27 June 2008

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In this article, the authors report how thin (10 nm or less) oxide-free phosphorus containing films can be formed on chromium and stainless steel on treatment with an organophosphorus acid (etidronic acid) using an anaerobic cell and a “bench” treatment. Core level and valence band x-ray photoelectron spectroscopy were used to study the films formed. Compositional variations were interpreted through the use of band structure and X-alpha calculations. The chromium study indicates that the etidronate at least partially decomposed to form phosphate. Some phosphide was observed for the bench treatment. Polished 316 L chromium containing stainless steel treated in 3M etidronic acid formed a thin phosphate containing film when using the bench treatment, but a film characteristic of etidronate when the anaerobic cell was used. Film changes during air exposure and exposure to 1M sodium chloride solution showed decomposition, the most resistant film being that of the etidronate on stainless steel. This thin etidronate film result shows that oxide-free etidronate films can be formed on stainless steel and these films have corrosion inhibition properties, which may find application in implant fabrication.
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81.65.Kn Corrosion protection
73.20.At Surface states, band structure, electron density of states
79.60.-i Photoemission and photoelectron spectra
68.55.-a Thin film structure and morphology
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Three dimensional image construction and spectrum extraction from two dimensional elemental mapping in Auger electron spectroscopy

N. Urushihara, S. Iida, N. Sanada, M. Suzuki, D. F. Paul, S. Bryan, Y. Nakajima, T. Hanajiri, K. Kakushima, P. Ahmet, K. Tsutsui, and H. Iwai

J. Vac. Sci. Technol. A 26, 668 (2008); http://dx.doi.org/10.1116/1.2870232 (5 pages) | Cited 2 times

Online Publication Date: 27 June 2008

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Three dimensional Auger elemental distributions have been constructed from the combination of high spatial resolution, two dimensional Auger maps obtained at multiple sputter depths. These three dimensional elemental distributions have been used to compare the interfacial regions for two kinds of silicon on insulator wafers. It is clearly seen that silicon oxide is formed as an island structure for the SIMOX specimen, whereas the UNIBOND specimen has a featureless structure at the Si/SiO2 interface. Linear least squares fitting from several two dimensional maps obtained at different energies have been used to produce energy dispersive spectra from specific regions of high spatial resolution Auger maps. This technique was used to examine the interface region exposed from sputter craters through a silicon dioxide layer on a silicon substrate and through a Ni silicide film on a silicon substrate. The Si LVV spectra for the elemental silicon, oxide, and silicide components extracted from the multiple energy two dimensional maps can be used to map the chemical components in the interfacial regions.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Ct Interface structure and roughness
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
79.20.Fv Electron impact: Auger emission

Electronic states of Fe nanostructures on Pt(997) surface

Ruihua Cheng, E. Ayieta, and Ya. B. Losovyj

J. Vac. Sci. Technol. A 26, 673 (2008); http://dx.doi.org/10.1116/1.2830632 (5 pages) | Cited 1 time

Online Publication Date: 27 June 2008

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A variety of one dimensional atomic chains can be synthesized on stepped surfaces, which provide opportunities for systematically tailoring the surface properties. The electronic structure of the high vicinal surface plays an essential role in determining the physical properties of the atomic chains. The authors have used surface analysis techniques to study the surface of Pt(997) single crystal. Angle resolved ultraviolet photoemission spectroscopy was performed to characterize the electronic states of Pt(997) surface by using a synchrotron radiation light source. Different from the expected free electron model on the flat Pt(111) surface, electron confinement is observed with a wave vector perpendicular to the step direction. Fe was carefully deposited onto Pt(997) substrate at room temperature. The STM data show that Fe atomic chains were formed along the step edges due to the step decoration growth. The exchange splitting of Fe 3d bands is estimated according to the photoemission spectroscopy data of Fe/Pt.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.22.-f Electronic structure of nanoscale materials and related systems
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.70.Gm Exchange interactions

Effect of annealing temperature on the photocatalytic activity of sol-gel derived TiO2 thin films

S. Biswas, Arpi Majumder, M. F. Hossain, T. Takahashi, Y. Kubota, and A. Fujishima

J. Vac. Sci. Technol. A 26, 678 (2008); http://dx.doi.org/10.1116/1.2889416 (5 pages) | Cited 1 time

Online Publication Date: 27 June 2008

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Transparent TiO2 thin films were deposited on glass substrates by a sol-gel dip coating technique, where crystallinity can be achieved at a relatively low annealing temperature. In this sol-gel preparation technique, acetic acid was used as a catalyst. Repetitive dip coating and drying, with a single annealing has made this technique easier to prepare TiO2 thin film with desired thickness within a short period of time. The crystallographic and optical properties of TiO2 films were investigated in detail. The photocatalytic activity was evaluated by the measurement of decomposition of methanol under UV-visible irradiation. The rate of decomposition of gaseous methyl alcohol depends on the structures and surface properties of the TiO2 films. The structure of the TiO2 films, prepared at various annealing temperatures, shows different crystallinities. Although crystallinity has been observed for 300 °C annealing temperature, it improved with increasing annealing temperature. The average transmittances of the TiO2 films slightly decrease with the increase of the annealing temperature in the range of 900–380 nm. The optical transmission edge of the TiO2 films, annealed at different annealing temperatures shifts toward higher wavelength with higher annealing temperature. All the as-deposited TiO2 films successfully photocatalyzed methanol to CO2 and H2O, measured by Fourier transform infrared spectrometer. The decomposition efficiency of TiO2 films increased with decrease of annealing temperature. The surface morphology of all the samples was investigated by field emission scanning electron microscopy and atomic force microscopy measurements. The higher photocatalytic activity of the sample prepared at lower annealing temperature was explained by the effect of more porous structure with smaller grains and open surface morphology of the sample.
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61.72.Cc Kinetics of defect formation and annealing
68.55.ag Semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
82.50.-m Photochemistry
78.66.Li Other semiconductors
back to top Electronic Materials and Processing

Role of hydrogen bonding environment in a-Si:H films for c-Si surface passivation

M. Z. Burrows, U. K. Das, R. L. Opila, S. De Wolf, and R. W. Birkmire

J. Vac. Sci. Technol. A 26, 683 (2008); http://dx.doi.org/10.1116/1.2897929 (5 pages) | Cited 12 times

Online Publication Date: 30 June 2008

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The search for an ideal surface passivation layer of crystalline silicon (c-Si) to be employed in a silicon heterojunction photovoltaic device has garnered much attention. The leading candidate is a few nanometers of intrinsic amorphous silicon ((i)a-Si:H) film. Reported dependencies of film surface passivation quality on substrate preparation, orientation, and deposition temperature have been extended in this work to include H2 to SiH4 dilution ratio and postdeposition annealing. Simple avoidance of the deposition regimes that lead to epitaxial growth of Si on the c-Si substrate produces decent lifetimes on the order of 500 μs. Subsequent low temperature annealings cause an important restructuring of Si–H bonding at the a-Si:H/c-Si interface increasing the amount of monohydride at the c-Si surface. This restructuring would reduce the c-Si surface defect density and cause an improvement of surface passivation as confirmed by effective lifetime measurements. Final effective carrier lifetimes up to 2550 μs are achieved postannealing. Initial results indicate the improvement depends on surplus SiH2 from the interface region.
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81.65.Rv Passivation
81.40.Gh Other heat and thermomechanical treatments
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Microstructural evolution of nickel-germanide in the Ni1−xTax/Ge systems during in situ annealing

Jae-Wook Lee, Jee-Hwan Bae, Min-Ho Park, Han-Byul Kang, Hyoungsub Kim, and Cheol-Woong Yang

J. Vac. Sci. Technol. A 26, 688 (2008); http://dx.doi.org/10.1116/1.2839763 (4 pages)

Online Publication Date: 30 June 2008

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The formation and morphological evolution of the germanides formed in the Ni1−xTax/Ge (x = 0 and 0.1) systems were examined using ex situ and in situ annealing experiments. It was observed that the Ni-germanide in the Ni0.9Ta0.1/Ge system remained stable at temperatures up to 550 °C whereas the Ni-germanide in the Ni/Ge system agglomerated and was unstable. Microstructural and chemical analyses of the Ni0.9Ta0.1/Ge system during and after in situ annealing in a transmission electron microscope confirmed that the Ta-rich layer was formed by the accumulation of Ta atoms on the interface between the Ni0.9Ta0.1 alloy film and the Ge substrate during the diffusion reaction, and a small amount of residual Ta was found in the Ni-germanide grains. Ultimately, the Ta-rich layer helps reduce the level of agglomeration in the Ni-germanide film and improves the thermal stability of Ni-germanide.
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61.72.Cc Kinetics of defect formation and annealing
68.37.Lp Transmission electron microscopy (TEM)

Effects of hydrogen ambient and film thickness on ZnO:Al properties

Joel N. Duenow, Timothy A. Gessert, David M. Wood, Anne C. Dillon, and Timothy J. Coutts

J. Vac. Sci. Technol. A 26, 692 (2008); http://dx.doi.org/10.1116/1.2891261 (5 pages) | Cited 4 times

Online Publication Date: 30 June 2008

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Undoped ZnO and ZnO:Al (0.1, 0.2, 0.5, 1.0, and 2.0 wt. % Al2O3) films were deposited by rf magnetron sputtering. Controlled incorporation of H2 in the Ar sputtering ambient for films grown at substrate temperatures up to 200 °C results in mobilities exceeding 50 cm2 V−1 s−1 when using targets containing 0.1 and 0.2 wt. % Al2O3. Temperature-dependent Hall measurements show evidence of phonon scattering as the dominant scattering mechanism in these lightly Al-doped films, while ionized impurity scattering appears increasingly dominant at higher doping levels. A combination of compositional and structural analysis shows that hydrogen expands the ZnO lattice normal to the plane of the substrate and desorbs from ZnO at ∼ 250 °C according to temperature-programmed desorption and annealing experiments.
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68.55.ag Semiconductors
68.55.jd Thickness
81.15.Cd Deposition by sputtering
73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.sd Impurity concentration

Main determinants for III–V metal-oxide-semiconductor field-effect transistors (invited)

Peide D. Ye

J. Vac. Sci. Technol. A 26, 697 (2008); http://dx.doi.org/10.1116/1.2905246 (8 pages) | Cited 31 times

Online Publication Date: 30 June 2008

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Lacking a suitable gate insulator, practical GaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) have remained all but a dream for more than four decades. The physics and chemistry of III–V compound semiconductor surfaces or interfaces are problems so complex that our understanding is still limited even after enormous research efforts. Most research is focused on surface pretreatments, oxide formation, and dielectric materials; less attention is paid to the III–V substrate itself. The purpose of this article is to show that device physics more related to III–V substrates is as important as surface chemistry for realizing high-performance III–V MOSFETs. The history and present status of III–V MOSFET research are briefly reviewed. A model based on the charge neutrality level is proposed to explain all experimental work he performed on III–V MOSFETs using ex situ atomic-layer-deposited high-k dielectrics. This model can also explain all reported experimental observations on III–V MOSFETs using in situ molecular-beam-expitaxy-grown Ga2O3(Gd2O3) as a gate dielectric. Related perspectives are also discussed to understand III–V MOS capacitance-voltage measurements.
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85.30.Tv Field effect devices
68.47.Fg Semiconductor surfaces

Characterization of plasma etching induced interface states at Ti/p-SiGe Schottky contacts

M. Mamor and A. Sellai

J. Vac. Sci. Technol. A 26, 705 (2008); http://dx.doi.org/10.1116/1.2913576 (5 pages) | Cited 3 times

Online Publication Date: 30 June 2008

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The authors have used current-voltage (I-V) data measured over a wide temperature range (100–300 K) complemented by deep level transient spectroscopy (DLTS) for the assessment of the defects introduced in Si0.95Ge0.05 by argon plasma sputter etching. From DLTS, defect concentration depth profiling was extracted and revealed that the main defect introduced during argon plasma sputtering is located very close to the surface. I-V-T analysis shows that the electrical characteristics deviated from the ideal case and indicate the presence of interface states, resulting from the plasma etching induced surface states at Ti/Si0.95Ge0.05 interface. The interface state density as well as its temperature dependence were obtained from forward bias I-V-T measurements by considering the bias dependence of effective barrier height Φe. It is found that interface states density is temperature dependent although weakly.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
71.55.Ht Other nonmetals
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning

Fabrication and characterization of a pentacene thin film transistor with a polymer insulator as a gate dielectric

Chulwoo Lee, Jungmin Ko, Junyoung Lee, and Ilsub Chung

J. Vac. Sci. Technol. A 26, 710 (2008); http://dx.doi.org/10.1116/1.2889434 (6 pages)

Online Publication Date: 30 June 2008

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An organic thin film transistor (OTFT) with a back gate structure on a patterned pentacene active region was fabricated. The variations of electrical properties as a function of polyvinylcinnamate (PVCN) concentration used as a gate dielectric were evaluated. In addition, the morphology of the pentacene thin film was characterized by scanning probe microscope by simultaneously obtaining the topology and current image. Within the pentacene thin film, the current was observed to flow through grain rather than through the grain boundaries. Within marginal variations, an OTFT fabricated using 8% PVCN revealed the best electrical properties in terms of mobility, threshold voltage (VT), subthreshold swing, and on/off ratio.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Photoluminescence characterization of polythiophene films doped with highly functional molecules

H. Kato, S. Takemura, H. Kobe, Y. Mori, A. Yamada, Y. Matsuoka, Y. Watanabe, K. Shimada, T. Hiramatsu, N. Nanba, and K. Matsui

J. Vac. Sci. Technol. A 26, 716 (2008); http://dx.doi.org/10.1116/1.2891259 (4 pages) | Cited 1 time

Online Publication Date: 30 June 2008

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Conducting polymer polythiophene (PT) films incorporated with copper phthalocyanine (CuPc) or fullerene C60 or both molecules together were synthesized and characterized by photoluminescence measurements. The hybrid materials were also modified by electrochemically applying positive or negative voltage or by adding the donor molecule tetrathiafulvalene (TTF) or acceptor molecule tetracyanoquinodimethane (TCNQ) into the hybrid films and were investigated by photoluminescence measurements in order to obtain fundamental photoluminescence properties of the hybrid materials. The molecule was injected by electrochemical and diffusion methods. A photoluminescence emission peak was observed at 594 nm in the case of a PT sample doped with CuPc by the diffusion method. Adding C60 molecules to the CuPc diffused PT sample by the diffusion method made the emission peak shift to the higher wavelength at 730 nm, suggesting the molecular interaction between the polymer chain and C60 in the photoluminescence emission process because double emission peaks were observed at 590 and 735 nm in the case of single doping of C60. Electrochemically applying voltages to the films or adding donor molecule TTF and acceptor molecule TCNQ to the polymer hybrid films caused the photoluminescence peak shifts, loss, and enhancement. The present study showed the possibility of control of photoluminescence wavelength of the hybrid films.
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78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
66.30.-h Diffusion in solids

Influence of a post–chemical mechanical polishing cleaning process on the ferroelectric properties of a Pb(Zr,Ti)O3 thin film capacitor fabricated by the damascene process

Nam-Hoon Kim, Young-Kil Jun, Pil-Ju Ko, and Woo-Sun Lee

J. Vac. Sci. Technol. A 26, 720 (2008); http://dx.doi.org/10.1116/1.2900712 (4 pages)

Online Publication Date: 30 June 2008

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The author first applied a chemical mechanical polishing (CMP) process to fabricate a ferroelectric Pb(Zr,Ti)O3 (PZT) capacitor instead of using a plasma etching process for the vertical profile without plasma damage in their previous study. The post-CMP cleaning process was very important in this CMP process. In this study, they investigated the effects of the post-CMP cleaning process on the ferroelectric properties of a PZT thin film capacitor. They proposed an optimized post-CMP cleaning process that uses a SC-1 chemical, diluted HF treatment, and an ultrasonic cleaning process. The slurry residues on the surface of the PZT thin films were removed. The polarization-voltage (P-V) characteristics showed the typical hysteresis loop of PZT thin films after a post-CMP cleaning process with the optimized conditions, while the ferroelectric characteristics could not be observed in the specimen without the post-CMP cleaning process. The remanent polarization (Pr) and coercive voltage (Vc) of the PZT thin films after the post-CMP process with the optimized condition were 17.092 μC/cm2 and 3.252 V, respectively.
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84.32.Tt Capacitors
81.65.Ps Polishing, grinding, surface finishing
81.65.Cf Surface cleaning, etching, patterning

Silicate formation and thermal stability of ternary rare earth oxides as high-k dielectrics

S. Van Elshocht, C. Adelmann, T. Conard, A. Delabie, A. Franquet, L. Nyns, O. Richard, P. Lehnen, J. Swerts, and S. De Gendt

J. Vac. Sci. Technol. A 26, 724 (2008); http://dx.doi.org/10.1116/1.2891257 (7 pages) | Cited 16 times

Online Publication Date: 30 June 2008

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Hf-based dielectrics are currently being introduced into complementary metal oxide semiconductor transistors as replacement for SiON to limit gate leakage current densities. Alternative materials such as rare earth based dielectrics are of interest to obtain proper threshold voltages as well as to engineer a material with a high thermal stability. The authors have studied rare earth based dielectrics such as Dy2O3, DyHfOx, DyScOx, La2O3, HfLaOx, and LaAlOx by means of ellipsometry, time of flight secondary ion mass spectroscopy x-ray diffraction, and x-ray photoelectron spectroscopy. The authors show that ellipsometry is an easy and powerful tool to study silicate formation. For ternary rare earth oxides, this behavior is heavily dependent on the composition of the deposited layer and demonstrates a nonlinear dependence. The system evolves to a stable composition that is controlled by the thermal budget and the rare earth content of the layer. It is shown that silicate formation can lead to a severe overestimation of the thermal stability of ternary rare earth oxides.
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77.55.-g Dielectric thin films
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.60.Dv Thermal stability; thermal effects
82.80.Rt Time of flight mass spectrometry
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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High magnetization FeCo/Pd multilayers

M. J. Walock, H. Ambaye, M. Chshiev, F. R. Klose, W. H. Butler, and G. J. Mankey

J. Vac. Sci. Technol. A 26, 731 (2008); http://dx.doi.org/10.1116/1.2830631 (4 pages)

Online Publication Date: 30 June 2008

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We have fabricated multilayer samples with varying superlattice periodicity and interlayer thicknesses to determine the nature of the enhanced moment in this intriguing thin film system. Magnetic characterization experiments show an enhanced magnetic moment in the multilayers as compared to a single layer film containing the same amount of FeCo. However, since the magnetization is defined as the magnetic moment divided by the sample volume, the sample exhibits an overall reduction in the magnetization when the volume of the Pd layers is also taken into account. Our experimental findings are also supported by theoretical calculations which identify the origin of the increased magnetic moment in the multilayer system. Polarized neutron reflectivity experiments will be used to determine the lateral distribution of the magnetization in a number of superlattice samples.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Thermal stability of synthetic antiferromagnet and hard magnet coupled spin valves

Zeenath R. Tadisina, Subhadra Gupta, Patrick LeClair, and Tim Mewes

J. Vac. Sci. Technol. A 26, 735 (2008); http://dx.doi.org/10.1116/1.2912070 (4 pages)

Online Publication Date: 30 June 2008

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The magnetic properties of current-in-plane (CIP) giant magnetoresistive (GMR) spin valves employing synthetic antiferromagnet (SAF) pinning have been investigated. The conventional spin valve structure, with a ferromagnetic (FM) layer pinned by an antiferromagnet (AFM) layer, exhibits high electrical resistance, the AFM typically being a high resistivity material. We have investigated pinning with a Co/Ru/Co SAF trilayer only, with no additional AFM pinning. We have also investigated spin valves employing a hard magnet layer in three different configurations as the pinning/pinned layer. Elimination of the AFM-induced parasitic resistance has the potential for yielding a higher GMR ratio in current-perpendicular-to-the-plane (CPP) structures. The full-film properties have been optimized by using vibrating sample magnetometry and CIP magnetotransport measurements. The thermal stability of SAF-pinned spin valves and hard magnet-pinned spin valves has been characterized through magnetotransport measurements of up to 400 K, and found to have measurable MR even at that temperature. A study of the M-H loops for the SAF spin valve showed no change up to 500 K. Therefore, these non-AFM-containing spin valves appear to be usable in CPP devices under practical head operating temperatures, representing a significant advance in reduced stack resistance, increased MR ratio, and reduced coupling between free and pinned layers in a small-dimensional patterned structure.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
75.50.Ee Antiferromagnetics
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Process development and material characterization of polycrystalline Bi2Te3, PbTe, and PbSnSeTe thin films on silicon for millimeter-scale thermoelectric generators

I. Boniche, B. C. Morgan, P. J. Taylor, C. D. Meyer, and D. P. Arnold

J. Vac. Sci. Technol. A 26, 739 (2008); http://dx.doi.org/10.1116/1.2841522 (6 pages) | Cited 6 times

Online Publication Date: 30 June 2008

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In this work, deposition, patterning, and metallization of vapor-deposited polycrystalline thermoelectric (TE) thin films of Bi2Te3, PbTe, and PbSnSeTe on silicon (Si) substrates are investigated. These fundamental microfabrication methods are intended for use in integrating TE films into thermally powered micro-electro-mechanical systems (MEMS)-based power generators. P-type polycrystalline Bi2Te3, PbTe, and PbSnSeTe films were successfully deposited on thermally oxidized (100) Si substrates to thicknesses ranging from 0.4 to 9 μm. Dry etch rates of about 0.6−0.7 μm/min were achieved for Bi2Te3 and PbTe/PbSnSeTe using methane-based gases. Wet etch rates of ∼ 3 μm/min were achieved using various acid wet chemistries. Films were electrically characterized using van der Pauw and transfer length method (TLM) test structures. Postdeposition resistivities were measured as low as 23 mΩ cm for Bi2Te3, 134 mΩ cm for PbTe, and 52 mΩ cm for PbSnSeTe. The Seebeck coefficients were measured at up to 94 μV/K for undoped Bi2Te3, and 160 and 42 μV/K for doped PbTe and PbSnSeTe, respectively. Metal contact resistivities (0.18−42 mΩ cm2) were also extracted for a variety of thin film metals (Pt, Au, Cu, Ni, Cr/Pt/Au, Ti/Pt). Various postdeposition annealing treatments were explored for reducing film resistivity that would enable higher power delivery for TE generator applications. Rapid thermal annealing in nitrogen at 400 °C was shown to reduce the resistivity of PbTe and improve film adhesion to oxidized silicon substrates. Also, after successive heatings in air at 200 °C, the resistivity of the PbTe films remained stable while that of the PbSnSeTe increased up to 10×.
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85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Ns Metal-nonmetal contacts
81.05.Hd Other semiconductors

Fabrication of metal-based high-aspect-ratio microscale structures by compression molding

J. Jiang, Fanghua Mei, and W. J. Meng

J. Vac. Sci. Technol. A 26, 745 (2008); http://dx.doi.org/10.1116/1.2912078 (7 pages) | Cited 3 times

Online Publication Date: 30 June 2008

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Metal-based high-aspect-ratio microscale structures (HARMSs) are basic building blocks for metallic microdevices such as microelectromagnetic relays and microchannel heat exchangers. Metallic microdevices may have advantages over Si-based devices when subjected to high stresses, high temperatures, and other harsh conditions. In this article, the authors summarize our recent results on molding replication of metal-based HARMS. The micromolding response was experimentally measured in Al and Cu, and rationalized with companion high-temperature tensile testing and finite element analysis. Successful replication of Ni-based and NiTi-based HARMS was demonstrated.
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81.70.Bt Mechanical testing, impact tests, static and dynamic loads
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.10.Fq Growth from melts; zone melting and refining

Design and fabrication of a multilayer micro-/nanofluidic device with an electrically driven nanovalve

Hao Li, Leonidas E. Ocola, Orlando Auciello, and Millicent Firestone

J. Vac. Sci. Technol. A 26, 752 (2008); http://dx.doi.org/10.1116/1.2936227 (5 pages)

Online Publication Date: 30 June 2008

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A device containing microfluidic and nanofluidic channels was designed and fabricated to study the performance of an electrically driven nanovalve controlled by induced polarization of a ferroelectric substrate. The microfluidic component was fabricated in polydimethylsiloxane and designed to provide adequate driving pressure and flow rate for fluid flow in the nanofluidic component using only a common syringe pump. The nanofluidic component was fabricated on a glass substrate, coated with a thin film of lead-zirconium-titanate (PZT) substrate, and integrated with nanoelectrodes to induce surface polarization. The experimental concept is to use the polarizable surface of the PZT layers to control the motion of a nanovalve made of charged nanowires or biological molecules. The function of the nanovalve would be demonstrated by observing the fluid mixing behavior variation in the nanofluidic channels before and after the polarization of the PZT substrate. A successful device will prove useful for many applications including laboratory on a chip and release-on-demand drug delivery systems. This device can also be used to study the basic science of fluid flow and heat transfer at the nanoscale with the purpose of improvement in flow and heat transfer efficiency in nanoscale devices.
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47.85.Np Fluidics
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.60.Dx Flows in ducts and channels
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Advances in magnetometry through miniaturization

A. S. Edelstein, J. Burnette, G. A. Fischer, S. F. Cheng, W. F. Egelhoff, P. W. T. Pong, R. D. McMichael, and E. R. Nowak

J. Vac. Sci. Technol. A 26, 757 (2008); http://dx.doi.org/10.1116/1.2841516 (6 pages) | Cited 2 times

Online Publication Date: 30 June 2008

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Recent innovations may lead to magnetic sensors that are smaller, more sensitive, and/or cost less than current magnetometers. Examples of this are the chip scale atomic magnetometer, magnetic tunnel junctions with MgO barriers, and a device for minimizing the effect of 1/f noise, the microelectromechanical system (MEMS) flux concentrator. In the chip scale atomic magnetometer, researchers have been able to fabricate the light source, optics, heater, optical cell, and photodiode detector in a stack that passes through a silicon wafer. Theoretical and subsequent experimental work has led to the observation of magnetoresistance values of 400% at room temperature in magnetic tunnel junctions with MgO barriers. This large magnetoresistance occurs because electrons in the majority band can tunnel more easily through the MgO barrier than electrons in the minority band. The MEMS flux concentrator has the potential to increase the sensitivity of magnetic sensors at low frequencies by more than an order of magnitude. The MEMS flux concentrator does this by shifting the operating frequency to higher frequencies where the 1/f noise is much smaller. The shift occurs because the motion of flux concentrators on MEMS flaps modulates the field at kilohertz frequencies at the position of the sensor. Though miniaturization is generally beneficial, trade-offs are necessary because some properties, such as noise, worsen with decreasing size.
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07.55.Ge Magnetometers for magnetic field measurements
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
72.20.My Galvanomagnetic and other magnetotransport effects
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Fabrication of stationary micro-optical shutter based on semiconductor-to-metallic phase transition of W-doped VO2 active layer driven by an external voltage

M. Soltani, M. Chaker, E. Haddad, R. Kruzelecky, J. Margot, P. Laou, and S. Paradis

J. Vac. Sci. Technol. A 26, 763 (2008); http://dx.doi.org/10.1116/1.2870227 (5 pages) | Cited 4 times

Online Publication Date: 30 June 2008

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The authors have successfully fabricated stationary micro-optical shutter arrays based on the well-known transmitting semiconductor (on) to the reflecting metallic (off) phase transition of thermochromic W-doped VO2 active layers operating at room temperature and driven by an external voltage. This shutter consists of 16 active planar micro-optical slits for which the optical switching (either transmittance or reflectance) can be controlled individually. This allows performing any desirable on-off switching combinations. The current-voltage characteristic of the micro-slit shows that the current jumps when the phase transition occurs. Transmittance switching as high as 25 dB and reflectance switching of about 6 dB were achieved with this device at λ = 1.55 μm. Therefore, this electrically controllable VO2-array can be used as a stationary Hadamard shutter to increase the sensitivity of infrared spectrometers.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Wc Optical coatings

Nanotribological and nanomechanical properties of lubricated PZT thin films for ferroelectric data storage applications

Manuel Palacio and Bharat Bhushan

J. Vac. Sci. Technol. A 26, 768 (2008); http://dx.doi.org/10.1116/1.2870230 (9 pages) | Cited 7 times

Online Publication Date: 30 June 2008

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Lead zirconate titanate (PZT) is a desirable material for nonvolatile data storage due to its ferroelectric properties. Evaluating the nanoscale mechanical and tribological performance of PZT is crucial in understanding the reliability of this material. To this end, the mechanical properties of the PZT film were characterized by nanoindentation. Nanoscratch studies reveal that the PZT film is removed by a combination of plastic deformation and brittle failure. The adhesion, friction, and wear properties of PZT were evaluated before and after application of two lubricants, namely, the perfluoropolyether Z-TETRAOL and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6). Wear at ultralow loads was simulated and the lubricant removal mechanism was investigated for the first time using atomic-force-microscopy-based surface potential and contact resistance techniques. From this study, ionic liquids were found to exhibit comparable nanotribological properties with Z-TETRAOL.
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77.55.-g Dielectric thin films
85.50.Gk Non-volatile ferroelectric memories
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
68.60.Bs Mechanical and acoustical properties
77.80.-e Ferroelectricity and antiferroelectricity

Technique to measure contact angle of micro/nanodroplets using atomic force microscopy

Yong Chae Jung and Bharat Bhushan

J. Vac. Sci. Technol. A 26, 777 (2008); http://dx.doi.org/10.1116/1.2832409 (6 pages) | Cited 2 times

Online Publication Date: 30 June 2008

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Contact angle is the primary parameter that characterizes wetting; however, the measurement techniques have been limited to droplets with a diameter as low as about 50 μm. The authors developed an atomic force microscopy-based technique to measure the contact angle of micro- and nanodroplets deposited using a modified nanoscale dispensing tip. The obtained contact angle results were compared with those of a macrodroplet (2.1 mm diameter). It was found that the contact angle on various surfaces decreases with decreasing the droplet size.
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68.37.Ps Atomic force microscopy (AFM)
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.79.Lh Atomic force microscopes
61.46.-w Structure of nanoscale materials
68.08.Bc Wetting

Platinum-coated probes sliding at up to 100 mm/s against lead zirconate titanate films for atomic force microscopy probe-based ferroelectric recording technology

Kwang Joo Kwak and Bharat Bhushan

J. Vac. Sci. Technol. A 26, 783 (2008); http://dx.doi.org/10.1116/1.2832362 (11 pages) | Cited 4 times

Online Publication Date: 30 June 2008

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With the advent of scanning probe microscopes, probe-based data recording technologies are being developed for ultrahigh areal density. In alternative ferroelectric data storage, a conductive atomic force microscope (AFM) tip is placed in contact on a lead zirconate titanate (PZT) layer as the ferroelectric film. Ferroelectric domains can be polarized by applying short voltage pulses between the AFM tip and the bottom electrode that exceed the coercive field of the PZT layer, resulting in local, nonvolatile changes in the electronic properties of the underlying film. By monitoring the piezoelectric vibration of the ferroelectric film caused by an external ac voltage, the domain structure can be visualized. A degradation due to a voltage pulse to the PZT film occurs and is one reliability concern, called ferroelectric fatigue. Another important reliability concern is tip wear during tip-sample contact. The understanding and the improvement of tip wear, particularly at high velocities needed for high data rate recording, is critical to the commercialization of ferroelectric memories. In this study, wear experiments are performed using a Pt-coated tip sliding against a PZT layer at sliding velocities ranging from 0.1 to 100 mm/s. A silicon grating sample and software to deconvolute tip shape are used to characterize the change in the tip shape and evaluate the tip radius and its wear volume. The tip wear mechanism is dependent on the operating conditions. At velocities up to 1 mm/s, it is adhesive wear assisted with thermally activated stick slip and, at higher velocities, it is adhesive and impact wear. In wear life threshold experiments, the threshold reaches a smaller sliding distance at higher loads. In high-temperature experiments at 80 °C, the wear rate is high compared to that at 20 °C.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects
77.55.-g Dielectric thin films
68.37.Ps Atomic force microscopy (AFM)
07.79.Lh Atomic force microscopes

Improvement of the surface roughness and sensing properties of cerium dioxide thin film by chemical mechanical polishing

Nam-Hoon Kim, Pil-Ju Ko, and Woo-Sun Lee

J. Vac. Sci. Technol. A 26, 794 (2008); http://dx.doi.org/10.1116/1.2885208 (4 pages)

Online Publication Date: 30 June 2008

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Cerium dioxide (CeO2) is one of the most widely used materials for oxygen gas sensors. The surface roughness of CeO2 thin films must be improved because the electrical and sensing properties of CeO2 thin films are determined by these characteristics. The authors selected chemical mechanical polishing (CMP) processing for improving the surface roughness of CeO2 thin films. The authors examined the removal rate and surface roughness of spin coated CeO2 thin films with a change of CMP process parameters such as pressure (down force) and velocity (table speed). An optimized process condition, reflected by not only the surface roughness with a hillock-free surface but also an excellent removal rate with good uniformity, was obtained. The effects of the improved surface roughness on the sensing property of CeO2 thin films were also confirmed. The authors obtained improved sensitivity of CeO2 thin films for oxygen sensors after the CMP process by the improved surface morphology. Therefore, the authors concluded that the sensing property of CeO2 thin film was strongly dependent on the surface roughness of CeO2 thin films by using a CMP process.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
81.65.Ps Polishing, grinding, surface finishing

Evaluation of bond quality and heat transfer of Cu-based microchannel heat exchange devices

Fanghua Mei, J. Jiang, and W. J. Meng

J. Vac. Sci. Technol. A 26, 798 (2008); http://dx.doi.org/10.1116/1.2913580 (7 pages) | Cited 4 times

Online Publication Date: 30 June 2008

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Metal-based microchannel heat exchangers (MHEs) promise high heat transfer coefficients together with mechanical robustness, and are of interest for a wide range of applications. Fabrication technologies capable of creating high-aspect-ratio microscale structures in metals such as Cu at low cost and high throughput are of particular interest. Likewise, simple and reliable bonding and assembly techniques are critical for building functional metal-based microfluidic devices. In this article, the authors report successful fabrication, bonding, and assembly of Cu-based MHE prototypes. Bonding of Cu specimens was achieved through Al thin foil intermediate layers. Quantitative evaluation of bond strengths was carried out as a function of various bonding parameters. Results of preliminary heat transfer testing carried out on assembled Cu-based MHE prototypes are reported.
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44.15.+a Channel and internal heat flow
47.15.Rq Laminar flows in cavities, channels, ducts, and conduits
back to top Manufacturing Science and Technology

Gate oxide process control optimization by x-ray photoelectron spectroscopy in a semiconductor fabrication line

A. Le Gouil, N. Cabuil, P. Dupeyrat, B. Dickson, M. Kwan, D. Barge, E. Gurer, O. Doclot, and J.-C. Royer

J. Vac. Sci. Technol. A 26, 805 (2008); http://dx.doi.org/10.1116/1.2902966 (7 pages)

Online Publication Date: 1 July 2008

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X-ray photoelectron spectroscopy is a metrology technique that is used for in-line control of decoupled plasma nitridation processes in the fabrication of logic devices. This article shows XPS results of thickness and composition obtained on two types of gate oxide nitrided by a decoupled plasma nitridation process. Measurements are performed in specific test structures with an x-ray spot which can be focused down to 35 μm, enabling process control directly on products. First, XPS is used to characterize and quantify the chemical composition of a SiON layer. The Results show that the nitrogen composition in a SiON layer decreases at a fast rate during the initial days after nitridation processing and stabilizes with time. Second, measurements are performed on products with the objective of transferring process control from monitor to product wafers. In this regard, comparison of nitrogen dose and thickness uniformity on monitor and pattern wafers show similar trends, indicating that measurements of nitrogen dose and thickness on monitor and product wafers give the same information. Third, different mapping protocols are studied on products to identify the best compromise between throughput and an optimized mapping representative of the process distribution. An optimized process control strategy of gate oxides with results is discussed in this article.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Photoconductive analysis of ion implantation damage and annealing in silicon wafers

R. K. Ahrenkiel

J. Vac. Sci. Technol. A 26, 812 (2008); http://dx.doi.org/10.1116/1.2919144 (7 pages)

Online Publication Date: 1 July 2008

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This work describes the use of a new method of detecting residual damage centers, which are produced in ion-implanted silicon. Contactless resonant-coupled photoconductive decay (RCPCD) measures the minority-carrier lifetime in the unimplanted region of the wafer. The analysis and data show that the lifetime is dominated by recombination in the implanted volume. By varying the wavelength of the RCPCD excitation, one can determine that the dominant recombination occurs in the implanted region. The data show that the carrier lifetime increases by orders of magnitude as the recombination mechanism changes from defect to Auger recombination. The latter arises from high-density, electrically activated acceptors in p-type silicon after thermal annealing.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors
61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
back to top Nanometer-Scale Science and Technology

Nanometer-scaled triangular platinum islands fabricated using the bridge phenomenon of polystyrene beads

Byoung-Kyu Lee, Kyoung Seob Kim, Ji-Hye Lee, Nam-Hoon Kim, and Yonghan Roh

J. Vac. Sci. Technol. A 26, 819 (2008); http://dx.doi.org/10.1116/1.2936230 (5 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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The authors optimized the fabrication of nanometer-scaled triangular platinum islands using the bridge phenomenon of polystyrene beads. Both the mixture ratio of polystyrene beads and the spin coating process were optimized to array a uniform monolayer of polystyrene beads at a high density over a large area. The length of the bridge between the adjacent polystyrene beads as well as the size of polystyrene beads could be controlled using the oxygen plasma ashing process with an adjustment in the ashing time. Platinum was deposited on the ashed polystyrene beads with the bridges as a mask, and the hexagonally arrayed triangular platinum islands were obtained through the dense and uniform triangular structures surrounded by the polystyrene bead bridges with dimensions of less than 45 nm2 on the silicon substrate.
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81.07.Bc Nanocrystalline materials
81.65.Cf Surface cleaning, etching, patterning

Conducting polymer nanofilm growth on a nanoscale linked-crater pattern fabricated on an Al surface

H. Kato, S. Takemura, A. Ishii, Y. Takarai, Y. Watanabe, T. Sugiyama, T. Hiramatsu, N. Nanba, O. Nishikawa, and M. Taniguchi

J. Vac. Sci. Technol. A 26, 824 (2008); http://dx.doi.org/10.1116/1.2889420 (8 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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A linked-crater structure was fabricated on an Al surface by chemical and electrochemical combination processes. The surface of an Al plate was treated with semiClean and was successively processed in anodization in H2SO4. Dynamic force microscopy image showed that a linked-crater structure was formed on the Al surface. The crater size ranged from 80 to 200 nm. It turned out that a lot of pores with 9 nm in diameter were created inside each crater. The depth of each crater was approximately 7–17 nm. At the next stage, the thin film growth of polythiophene on the linked-crater structured Al surface was conducted by an electrochemical synthetic method. The electrochemical polymerization on the Al surface was performed in acetonitrile containing thiophene monomer and (Et)4NBF4 as a supporting electrolyte. After being electrochemically processed, the contour image of each crater was still recognized implying that the polymer nanofilm was grown on the nanoscale structured Al surface. The cross section analysis demonstrated that the nanofilm was grown along the linked-crater structure because the contour of each crater became thick. The average thickness of the polymer film was estimated as 10–20 nm. Furthermore, copper phthalocyanine molecules were successfully injected into the polymer nanofilm on the Al surface in order to functionalize the nanoscale material.
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61.41.+e Polymers, elastomers, and plastics
68.55.am Polymers and organics
81.16.Rf Micro- and nanoscale pattern formation
82.35.-x Polymers: properties; reactions; polymerization

Growth and characterization of carbon nanotubes on constantan (Cu–Ni–Mn alloy) metallic substrates without adding additional catalysts

C. V. Varanasi, J. Bulmer, L. Brunke, J. Burke, J. Baca, K. Yost, and P. Barnes

J. Vac. Sci. Technol. A 26, 832 (2008); http://dx.doi.org/10.1116/1.2841520 (4 pages)

Online Publication Date: 1 July 2008

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In this study, metallic constantan (Cu55–Ni44–Mn1 wt %) alloy substrates were investigated as an alternate choice of substrates to grow carbon nanotubes (CNTs). No additional catalysts were used other than the as-rolled and annealed substrates to process CNTs on them. High density CNT growth was observed to take place on these substrates when suitable conditions were used in a thermal chemical vapor deposition (CVD) furnace with C2H2 as the carbon precursor. Scanning electron microscopy and transmission electron microscopy on these samples indicated the presence of several micron long CNTs ranging in 20–100 nm in diameter. Raman spectra taken from the samples confirmed the presence of G band peaks (peak at ∼ 1580 cm−1) and D band peaks (peak at ∼ 1320 cm−1) commonly observed in CVD grown multiwall CNT samples with varying intensity ratios depending on the processing conditions.
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81.07.De Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.46.Fg Nanotubes
78.30.Na Fullerenes and related materials
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
back to top Plasmonics Topical Conference

Thermoplasmonic shift and dispersion in thin metal films

A. L. Lereu, A. Passian, R. H. Farahi, N. F. van Hulst, T. L. Ferrell, and T. Thundat

J. Vac. Sci. Technol. A 26, 836 (2008); http://dx.doi.org/10.1116/1.2900713 (6 pages)

Online Publication Date: 1 July 2008

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In 2004, the authors reported two coupling schemes based on the thermo-optic properties of thin metallic films and their associated sub- and superstrates, by utilizing surface plasmons. These studies showed a potential for all-optical modulation at low rates that may be used for sensing purposes. In this article, they continue by investigating thermal processes involved in thin metallic films with different approaches. They first experimentally imaged the shift of the surface plasmon dispersion relation in the visible spectrum, as the thin film temperature is externally varied. They then reinforce the previous observations by collecting the absorption curves at selected visible photon energies of excitation, as the film temperature in the excitation region increases. Utilizing the absorption measurements, they briefly address how one may obtain the real and imaginary parts of the index of refraction of the thin film as a function of temperature for each involved wavelength. Finally, they investigate the local physical state of the film by optically profiling the surface plasmon excitation region.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.66.Bz Metals and metallic alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
back to top Plasma Science and Technology

Effect of capacitive to inductive coupling transition in multiple linear U-type antenna on silicon thin film deposition from pure SiH4 discharges

Hong Bum Kim, Hyoung Cheol Lee, Kyong Nam Kim, and Geun Young Yeom

J. Vac. Sci. Technol. A 26, 842 (2008); http://dx.doi.org/10.1116/1.2924340 (5 pages) | Cited 1 time

Online Publication Date: 1 July 2008

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Using a large area internal-type inductively coupled plasma (ICP) source called “multiple U-type ICP source” having the size of 1020×830 mm2, the electrical properties of the antennas and the dissociation characteristics were investigated as a function of rf power using pure SiH4 and their influence on the deposited silicon films was studied. With increasing rf power, the plasma mode has changed from capacitively coupled plasma (E mode) to inductively coupled plasma (H mode), and the change of plasma mode increased the ratios of HFulcher*/SiH* and Si*/SiH* by changing the electron energy distribution function. In addition, the increase in HFulcher*/SiH* changed the microstructure of a silicon thin film deposited on glass substrates from amorphous to microcrystalline. At the high rf power regime of 4000 W, a silicon films having the crystalline volume fraction of 53% with optical band gap (Tauc’) of about 2.1 eV and dark conductivity of 2.4×10−5 Ω−1 cm−1 could be obtained at 20 mTorr of SiH4 [70 SCCM (SCCM denotes cubic centimeter per minute at STP)].
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81.05.Cy Elemental semiconductors
68.55.ag Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
84.40.Ba Antennas: theory, components and accessories

Study on plasma assisted metal-organic chemical vapor deposition of Zr(C,N) and Ti(C,N) thin films and in situ plasma diagnostics with optical emission spectroscopy

S. J. Cho, S.-H. Nam, C.-K. Jung, H.-G. Jee, J.-H. Boo, S. Kim, and J. G. Han

J. Vac. Sci. Technol. A 26, 847 (2008); http://dx.doi.org/10.1116/1.2944262 (7 pages)

Online Publication Date: 1 July 2008

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Zr(C,N) and Ti(C,N) films were synthesized by pulsed dc plasma assisted metal-organic chemical vapor deposition method using metal-organic compounds of tetrakis diethylamido titanium and tetrakis diethylamido zirconium at 200–300 °C. To change the plasma characteristics, different carrier gases such as H2 and He/H2 were used and, as the reactive gas, N2 and NH3 were added to the gas mixture. The effect of N2 and NH3 gases was also evaluated in the reduction of C content of the films. Radical formation and ionization behaviors in plasma were analyzed by optical emission spectroscopy and mass spectrometry at various pulsed biases and gas conditions. The gas mixture of He and H2 as the carrier gas was very effective in enhancing the dissociation of molecular gases. In the case of N2 addition, N2 as reactive gas resulted in higher hardness. However, NH3 as reactive gas highly reduced the formation of CN radical, thereby greatly decreasing the C content of Zr(C,N) and Ti(C,N) films. The hardness of the film is 1400–1700 HK depending on gas species and bias voltage. Higher hardness can be obtained for a H2 and N2 gas atmosphere and bias voltage of −600 V. Plasma surface cleaning using N2 gas prior to deposition appeared to increase the adhesion of films on steel. The changes of plasmas including radicals and film properties are illustrated in terms of carrier and reactive gases, as well as pulsed power variation.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
52.77.Dq Plasma-based ion implantation and deposition
68.55.A- Nucleation and growth
68.60.-p Physical properties of thin films, nonelectronic
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Exotic shapes of gold nanoparticles synthesized using plasma in aqueous solution

Junko Hieda, Nagahiro Saito, and Osamu Takai

J. Vac. Sci. Technol. A 26, 854 (2008); http://dx.doi.org/10.1116/1.2919139 (3 pages) | Cited 3 times

Online Publication Date: 1 July 2008

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Gold nanoparticles with exotic shapes, such as triangle, pentagon, and hexagon, have been synthesized by glow discharge in aqueous solutions. A pulsed power supply was used to generate discharges in the aqueous solutions. Pulse width and frequency were 2 μs and 15 kHz, respectively. Discharges were generated at applied voltages of 1600 and 3200 V. The shapes of the gold nanoparticles and electron diffraction patterns were observed by transmission electron microscopy. The nanoparticles obtained were about 20 nm in diameter. In particular, at the higher voltage of 3200 V, nanoparticles with anisotropic shapes were synthesized. In the initial stages of synthesis, diameter decreased with discharge time as the nanoparticles redissolved in the solution. After discharge for 25 min, nanoparticles with anisotropic shapes appeared. This discharge led to the generation of H2O2 and a decrease in pH as a result of the consumption of OH radicals during the generation of H2O2 and electron donation of H radicals to the solution. After the pH stopped decreasing, H radicals mainly reacted as a reducing agent. The decrease in pH allowed redissolution of the gold nanoparticles. The gold dust particles that were not completely dissolved acted as new seeds for nucleation. Thus, the two reaction steps, nucleation and nuclear growth, occur during the formation of gold nanoparticles with exotic shapes.
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81.07.Bc Nanocrystalline materials
52.77.-j Plasma applications
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Dry etching of extreme ultraviolet lithography mask structures in inductively coupled plasmas

D. Y. Kim, H. J. Lee, H. Y. Jung, N.-E. Lee, T. G. Kim, B. H. Kim, Jinho Ahn, and C. Y. Kim

J. Vac. Sci. Technol. A 26, 857 (2008); http://dx.doi.org/10.1116/1.2902964 (4 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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Extreme ultraviolet lithography (EUVL) is currently being examined for its potential use in the next generation of lithography techniques. Among the core EUVL technologies, mask fabrication is of considerable importance due to the use of new reflective optics. This study investigated the etching properties of EUVL mask materials, such as Al2O3 antireflection coating (ARC), TaN (absorber layer) and Ru (buffer/capping layer), by varying the Cl2/Ar gas flow ratio, dc self-bias voltage (Vdc) and top electrode power in inductively coupled plasma. The Al2O3 (ARC) layer could be etched with an etch selectivity approaching 0.5 over the TaN absorber layer. The ARC/TaN stack could be etched with an infinitely high etch selectivity over the Ru layer. Etching of the stacked mask structures with a 200 nm line/space hydrogen silsesquioxane e-beam resist pattern showed a profile angle of 85° and an etch stop on the Ru buffer/capping layer.
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85.40.Hp Lithography, masks and pattern transfer

Etching characteristics and application of physical-vapor-deposited amorphous carbon for multilevel resist

H. T. Kim, B. S. Kwon, N.-E. Lee, Y. S. Park, H. J. Cho, and B. Hong

J. Vac. Sci. Technol. A 26, 861 (2008); http://dx.doi.org/10.1116/1.2936231 (4 pages) | Cited 5 times

Online Publication Date: 1 July 2008

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For the fabrication of a multilevel resist (MLR) based on a very thin, physical-vapor-deposited (PVD) amorphous carbon (a-C) layer, the etching characteristics of the PVD a-C layer with a SiOx hard mask were investigated in a dual-frequency superimposed capacitively coupled plasma etcher by varying the following process parameters in O2/N2/Ar plasmas: high-frequency/low-frequency combination (fHF/fLF), HF/LF power ratio (PHF/PLF), and O2 and N2 flow rates. The very thin nature of the a-C layer helps to keep the aspect ratio of the etched features low. The etch rate of the PVD a-C layer increased with decreasing fHF/fLF combination and increasing PLF and was initially increased but then decreased with increasing N2 flow rate in O2/N2/Ar plasmas. The application of a 30 nm PVD a-C layer in the MLR structure of ArF PR/BARC/SiOx/PVD a-C/TEOS oxide supported the possibility of using a very thin PVD a-C layer as an etch-mask layer for the TEOS-oxide layer.
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81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer
52.77.Dq Plasma-based ion implantation and deposition
68.55.A- Nucleation and growth
81.10.Bk Growth from vapor
back to top Plasma Science and Technology I

Global plasma simulations using dynamically generated chemical models

James J. Munro and Jonathan Tennyson

J. Vac. Sci. Technol. A 26, 865 (2008); http://dx.doi.org/10.1116/1.2889433 (5 pages)

Online Publication Date: 1 July 2008

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Extensive molecular data are a key requirement in understanding modern technical plasmas. A method for coupling molecular data with chemical models in a global plasma simulation to enable rapid testing and evaluation of new plasmas is presented. A global plasma model (GLOBALKIN) is extended using an expert system (Quantemol-P) to enable ad hoc simulations using new plasma recipes. A set of atomic and molecular species to be considered in the plasma simulation is specified by the user. The expert system generates a complete set of reaction pathways for both the gas and surface reactions in a plasma. This set is pruned by discarding unphysical reactions and reaction data not appropriate to technical plasmas (such as autodetachment). The species, gas phase reactions, surface reactions, and plasma properties can be adjusted to control the simulation. The reaction list is populated through a database of molecular parameters and cross sections; missing data can be calculated through molecular cross sections using a further expert system (Quantemol-N) which applies the R-matrix method to electron-molecule collisions. For cases where the R-matrix method is not appropriate, other methods are used to maximize the range of cross-section data available. The Quantemol-P expert system allows rapid creation of new plasma recipes and investigation of their effects allowing a greater level of flexibility than previously achievable.
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52.80.-s Electric discharges
52.65.-y Plasma simulation
52.70.Ds Electric and magnetic measurements
52.80.Wq Discharge in liquids and solids

Surface reactions during low-k etching using H2/N2 plasma

Masanaga Fukasawa, Tetsuya Tatsumi, Keiji Oshima, Kazunori Nagahata, Saburo Uchida, Seigo Takashima, Masaru Hori, and Yukihiro Kamide

J. Vac. Sci. Technol. A 26, 870 (2008); http://dx.doi.org/10.1116/1.2839764 (5 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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We investigated the relationship between the hard mask faceting that occurs during organic low-k etching and the ion energy distribution function of a capacitively coupled plasma reactor. We minimized the hard mask faceting by precisely controlling the ion energy. This precise control was obtained by selecting the optimum bottom frequency and bias power. We measured the amount of damage done to a SiOCH film exposed to H2/N2 plasma in order to find the H2/N2 ratio at which the plasma caused the least damage. The amount of moisture uptake by the damaged SiOCH film is the dominant factor controlling the dielectric constant increase (Δk). To suppress Δk, the incident ion species and ion energies have to be precisely controlled. This reduces the number of adsorption sites in the bulk SiOCH and maintains the hydrophobic surface that suppresses water permeation during air exposure.
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81.65.Cf Surface cleaning, etching, patterning
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.43.Mn Adsorption kinetics
52.77.Bn Etching and cleaning

Low-damage low-k etching with an environmentally friendly CF3I plasma

Eiichi Soda, Seiichi Kondo, Shuichi Saito, Yoshinari Ichihashi, Aiko Sato, Hiroto Ohtake, and Seiji Samukawa

J. Vac. Sci. Technol. A 26, 875 (2008); http://dx.doi.org/10.1116/1.2919137 (6 pages) | Cited 5 times

Online Publication Date: 1 July 2008

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The feasibility of etching Cu/low-k interconnects by using a low global warming potential CF3I plasma was studied. Low-damage etching was done and porous SiOC (p-SiOC, k<2.6) film with low roughness was produced. Exposing p-SiOC film to CF3I plasma was found to suppress the decrease in the CH3 group and the increase in the k value compared to those of conventional CF4 and C4F6 plasmas. These effects are due to the low UV intensity and small amount of F radicals of CF3I plasma. The authors also found that the etching profile of CF3I plasma was comparable with that of CF4 plasma. Since the etching selectivity (p-SiOC/ArF photoresist) of CF3I plasma is higher than that of CF4 plasma, the remaining photoresist thickness increases after etching, thus suppressing line edge roughness (LER). The decreased LER mitigated degradation of IV and time dependent dielectric breakdown characteristics in Cu interconnects. They also found that the roughness on the bottom surface of the p-SiOC trench was reduced. These benefits are due to CF3I plasma’s low reactivity with the carbon in photoresists and p-SiOC films. Based on these findings, they believe that the environmentally friendly CF3I gas has great promise as a p-SiOC etching material.
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81.65.Cf Surface cleaning, etching, patterning
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
77.22.Jp Dielectric breakdown and space-charge effects
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
52.77.Bn Etching and cleaning
back to top Advanced Surface Engineering

Temperature effect on the glancing angle deposition of Si sculptured thin films

Christian Patzig and Bernd Rauschenbach

J. Vac. Sci. Technol. A 26, 881 (2008); http://dx.doi.org/10.1116/1.2834684 (6 pages) | Cited 3 times

Online Publication Date: 1 July 2008

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Si sculptured thin films consisting of spiral-, screw-, and columnlike-shaped nanostructures were grown by ion beam-induced glancing angle deposition of Si on rotating bare Si[001] substrates at different substrate rotational speeds and substrate temperatures ranging from room temperature to (360±10)°C. For rotational speeds leading to the growth of nanoscrews at room temperature, morphology changes are observed with increasing temperature, such as an increase of the critical height at which single spiral fibers start merging to screws, thus giving the possibility to grow separated nanospirals with diameters of about 30 nm over a large thickness range. A decrease of the overall film thickness, indicating a change in the film density, is also observed with increasing the substrate temperature. For deposition conditions leading to the growth of vertical columns at room temperature, the substrate temperature influences the total number of columns, the column diameter, and the total structure height. The temperature-related changes in structure morphology show that surface diffusion effects play an important role in the morphological evolution of sculptured thin films consisting of helicoidal and columnlike structures during their growth by glancing angle deposition.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.ag Semiconductors
81.05.Cy Elemental semiconductors

Effect of swift heavy ion irradiation on the hardness of chromium nanorods

Rupali Nagar, B. R. Mehta, J. P. Singh, D. Jain, V. Ganesan, S. V. Kesapragada, and D. Gall

J. Vac. Sci. Technol. A 26, 887 (2008); http://dx.doi.org/10.1116/1.2834683 (6 pages) | Cited 4 times

Online Publication Date: 1 July 2008

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The present study reports the use of swift heavy ion irradiation as a means to tailor the hardness of chromium nanorod coatings. Arrays of slanted and straight Cr nanorods, 1–2 μm long and 300–500 nm in diameter, were grown by dc magnetron sputter glancing angle deposition on Si(100) substrates patterned with 500 nm diameter polystyrene spheres. The samples were irradiated with 100 MeV Ag+8 ions at three different fluence values of 1013, 5×1013, and 1014 ions/cm2, while maintaining the samples at 80 K temperature. The as-deposited samples exhibit a fibrous structure that smoothens after irradiation. Nanoindentation tests performed on these samples reveal that the hardness of the nanorods increases with fluence. For slanted nanorods, the samples irradiated at maximum fluence show an almost 300% increase in hardness as compared to their pristine counterparts. The corresponding increase in the case of straight nanorods was observed to be 77%. This fluence-dependent hardness in Cr nanorods is explained in terms of an ion-irradiation induced defect formation and a decrease in the grain size, as confirmed by glancing angle x-ray diffraction.
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81.07.Bc Nanocrystalline materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
61.82.Bg Metals and alloys
61.80.Jh Ion radiation effects
81.15.Cd Deposition by sputtering

High rate deposition of photocatalytic TiO2 films with high activity by hollow cathode gas-flow sputtering method

Yoshiyuki Kubo, Yoshinori Iwabuchi, Masato Yoshikawa, Yasushi Sato, and Yuzo Shigesato

J. Vac. Sci. Technol. A 26, 893 (2008); http://dx.doi.org/10.1116/1.2836425 (5 pages)

Online Publication Date: 1 July 2008

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Photocatalytic TiO2 films were deposited by a hollow cathode gas-flow sputtering method using two Ti metal targets mounted parallel to each other. The Ar and O2 flow rates were 3000 and 0–50 SCCM (SCCM denotes cubic centimeter per minute at STP), respectively, and total gas pressure during the deposition was maintained at 45 Pa. The highest deposition rate for the photocatalytic TiO2 films was 162 nm/min at 30 SCCM of O2 flow. The as-deposited films and postannealed films, annealed in air at 300 °C for 1 h, were used to carry out photocatalytic decomposition of acetaldehyde (CH3CHO). In particular, the postannealed films showed extremely high photocatalytic activity compared to the photocatalytic activity of films deposited by conventional reactive sputtering.
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81.15.Cd Deposition by sputtering
82.50.Hp Processes caused by visible and UV light
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.55.at Other materials
81.40.Gh Other heat and thermomechanical treatments

Preparation of TiO2 thin films by laser ablation for photocatalytic applications

S. J. Wang, W.-T. Chang, J.-Y. Ciou, M.-K. Wei, and M. S. Wong

J. Vac. Sci. Technol. A 26, 898 (2008); http://dx.doi.org/10.1116/1.2870228 (5 pages)

Online Publication Date: 1 July 2008

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Thin titanium dioxide (TiO2) films were deposited by pulsed KrF excimer laser ablation deposition system using a titanium oxide target. The effects of substrate temperature and oxygen partial pressure on the phase formations of various microstructures were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), Raman scattering spectroscopy, and UV-Vis spectrophotometer. The film structures range from amorphous to mixed phase of anatase and rutile to pure anatase. Increasing the substrate temperature improves the quality of anatase phase of crystalline TiO2 films. The oxygen pressure in the range between 15 and 60 mTorr shows a single anatase phase in TiO2 films while the rutile and anatase mixed phases were observed elsewhere. The band gap of TiO2 films varied from 2.72 to 3.27 eV with increasing oxygen partial pressure while the film structures changed from rutile phase to anatase phase. The surface area of TiO2 films increased as oxygen partial pressure in film deposition. The photocatalytic performance evaluated by degradation of methylene blue in UV light was distinguishable in the TiO2 films with high anatase phase and surface area.
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68.55.ag Semiconductors
81.15.Fg Pulsed laser ablation deposition
78.30.Am Elemental semiconductors and insulators
71.20.-b Electron density of states and band structure of crystalline solids
78.40.Fy Semiconductors

High rate deposition of photocatalytic TiO2 films by dc magnetron sputtering using a TiO2−x target

Yasushi Sato, Akira Uebayashi, Norihiro Ito, Toshihisa Kamiyama, and Yuzo Shigesato

J. Vac. Sci. Technol. A 26, 903 (2008); http://dx.doi.org/10.1116/1.2870226 (5 pages) | Cited 1 time

Online Publication Date: 1 July 2008

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Photocatalytic TiO2 films were deposited on glass substrates by dc magnetron sputtering using a slightly reduced TiO2−x target (2−x = 1.986; conductivity, 3.7 S cm−1; density, 4.21 g/cm3). The variation in the deposition rate as a function of the O2 flow ratio did not show a hysteresis curve at the “transition region” as seen in the case of a Ti metal target. The deposition rate using the TiO2−x target in 100% Ar gas was approximately seven times higher than that using the Ti metal target in an “oxide mode.” The films postannealed in air at temperatures ≥ 200 °C showed excellent photodecomposition characteristics of acetaldehyde (CH3CHO) as well as photoinduced hydrophilicity.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.50.-m Photochemistry
81.15.Cd Deposition by sputtering
81.40.Gh Other heat and thermomechanical treatments
68.55.-a Thin film structure and morphology
back to top Surface Science

Plasma modification of CoPt3 nanoparticle arrays: A route to catalytic coatings of surfaces

Bernhard Gehl, Jan Ingo Flege, Vesna Aleksandrovic, Thomas Schmidt, Andreas Kornowski, Sigrid Bernstorff, Jens Falta, Horst Weller, and Marcus Bäumer

J. Vac. Sci. Technol. A 26, 908 (2008); http://dx.doi.org/10.1116/1.2936222 (5 pages)

Online Publication Date: 1 July 2008

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Two-dimensional layers of bimetallic cobalt-platinum nanoparticles were prepared from colloidal suspension to serve as model systems for catalytic surface coatings with well-defined chemistry and geometry. After deposition, the particle surfaces were exposed to mild rf plasmas in order to remove the passivating shell of organic ligands that covered their surfaces after preparation. X-ray photoelectron spectroscopy subsequently carried out without exposing the samples to air revealed that all carbon species can be quantitatively removed due to the treatment and that selective oxidation/reduction of the particles is possible. Grazing-incidence small-angle x-ray scattering was used to study plasma-induced changes in the particle ordering with high precision. The measurements prove that even for closely packed layers with lateral distances of less than 2 nm, changes in the mean diameters of the particles can be kept in the order of just 1%–2%.
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81.65.Rv Passivation
81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.70.Ck X-ray scattering
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
back to top Surface Science I

Preparation of nickel nanoparticles and their catalytic activity in the cracking of methane

Juan Carlos De Jesús, Ismael González, Miguel García, and Caribay Urbina

J. Vac. Sci. Technol. A 26, 913 (2008); http://dx.doi.org/10.1116/1.2885212 (6 pages)

Online Publication Date: 1 July 2008

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Metallic nickel nanoparticles are excellent catalysts for the cracking of methane into carbon nanotubes and hydrogen. Decomposition of tetrahydrate nickel acetate proceeds readily in inert or hydrocarbon streams to produce metallic nickel agglomerates (average size of 10–80 nm) at around 350 °C. In the present study, this parent salt is thermally treated in methane streams in situ in a thermogravimetric analyzer (TGA), and weight changes corresponding to the carbon buildup in the metallic nickel particles are analyzed to provide some insight into the nickel-catalyzed cracking process. C to Ni atomic ratios (C/Ni) estimated directly from TGA data provided a systematic approach to study the catalytic activity of the nickel nanoparticles. Methane cracking starts at temperatures as low as 400 °C and continues efficiently until approximately 600 °C. Between 600 and 660 °C, methane decomposition momentarily breaks off, while presumably the catalytic system undergoes a self-reorganization. Cracking resumes at 660 °C and continues slowly up to 950 °C. The amount of carbon deposited in the 600–660 °C interval shows a linear dependence with methane concentrations, with C/Ni ratios ranging from 6 to 31. Transmission-electron microscopy images of the different C/Ni residues collected at 660 °C show, that during cracking, narrower carbon nanotubes are produced at elevated methane concentrations, suggesting dispersion of nickel nanoparticles.
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81.16.Hc Catalytic methods
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
64.75.Jk Phase separation and segregation in nanoscale systems
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mt Cracks

Surface science investigations of photoprocesses in model interstellar ices

J. D. Thrower, M. P. Collings, M. R. S. McCoustra, D. J. Burke, W. A. Brown, A. Dawes, P. D. Holtom, P. Kendall, N. J. Mason, F. Jamme, H. J. Fraser, I. P. Clark, and A. W. Parker

J. Vac. Sci. Technol. A 26, 919 (2008); http://dx.doi.org/10.1116/1.2834687 (6 pages) | Cited 4 times

Online Publication Date: 1 July 2008

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The kinetic energy of benzene and water molecules photodesorbed from astrophysically relevant ices on a sapphire substrate under irradiation by a UV laser tuned to the S1←S0 π→π* transition of benzene has been measured using time-of-flight mass spectrometry. Three distinct photodesorption mechanisms have been identified—a direct adsorbate-mediated desorption of benzene, an indirect adsorbate-mediated desorption of water, and a substrate-mediated desorption of both benzene and water. The translational temperature of each desorbing population was well in excess of the ambient temperature of the ice matrix.
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79.20.La Photon- and electron-stimulated desorption
68.43.Nr Desorption kinetics
82.80.Rt Time of flight mass spectrometry
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
82.50.Hp Processes caused by visible and UV light
95.30.Ft Molecular and chemical processes and interactions
back to top Surface Science II

Photo-induced surface functionalization of carbon surfaces: The role of photoelectron ejection

Paula E. Colavita, Bin Sun, Kiu-Yuen Tse, and Robert J. Hamers

J. Vac. Sci. Technol. A 26, 925 (2008); http://dx.doi.org/10.1116/1.2908435 (7 pages)

Online Publication Date: 1 July 2008

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Carbon-based materials are attractive for a wide range of applications, from biomaterials to fuel cells; however, their effective use often requires controlling the surface chemistry to incorporate recognition moieties or reactive centers. The high stability of carbon also makes it a challenging material to functionalize; recently, the use of ultraviolet light (254 nm) to initiate functionalization of carbon surfaces has emerged as a way to obtain carbon/organic interfaces with tailored properties. The authors have investigated the mechanism of covalent grafting of amorphous carbon surfaces with functional organic molecules using the photochemical reaction of terminal alkenes. Measurements comparing the reactivity of different n-alkenes bearing different terminal groups at the terminus opposite the olefin showed pronounced differences in reactivity. They characterized the rate and final coverage of the resulting organic layers using x-ray photoelectron spectroscopy and infrared reflection-absorption spectroscopy. Ultraviolet photoelectron spectroscopy and photocurrent measurements suggested that the reaction involves photoelectron emission from the carbon surface into the liquid phase. Density functional calculations show a strong correlation between the electron affinity of the alkenes and the observed reactivity. The specific terminal group opposite to the olefin was found to play an important role in the stabilization of excess negative charges on the molecule, thus explaining the strong dependence of reactivity on the particular terminal group. These findings suggest that the reaction involves injection of photoelectrons into the alkene acceptor levels, leading to the formation of radical anions in the liquid phase. Finally, the authors demonstrate that the grafting of marginally reactive alkenes can be enhanced by seeding the surface with a small amount of good electron accepting groups. These results provide fundamental new insights into the role of electronic excitations in controlling rates and mechanisms of olefin reactions at surfaces. While demonstrated here for amorphous carbon, these results may also be significant for the UV initiated grafting of olefins on other semiconductors.
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82.50.Hp Processes caused by visible and UV light
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.40.Pg Disordered solids
79.60.Ht Disordered structures
back to top Thin Films

Atomic-scale investigation of graphene formation on 6H-SiC(0001)

N. P. Guisinger, G. M. Rutter, J. N. Crain, C. Heiliger, P. N. First, and J. A. Stroscio

J. Vac. Sci. Technol. A 26, 932 (2008); http://dx.doi.org/10.1116/1.2900661 (6 pages) | Cited 3 times

Online Publication Date: 1 July 2008

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The growth of graphene on the silicon-terminated face of 6H-SiC(0001) was investigated by scanning tunneling microscopy (STM) measurements. The initial stages of ultrahigh vacuum graphitization resulted in the growth of individual graphene sheets on random SiC terraces. These initial graphene sheets contained few defects, and the regions of clean SiC were free of contamination, exhibiting a 6math×6mathR30° surface reconstruction. However, graphitization to multilayer thickness resulted in multiple defects, as observed with the STM. A high density of defects was observed, which may be attributed to the initial treatment of the SiC wafer. We characterize these defects, showing that they are located predominantly below the first layer of graphene.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.bg Semiconductors
68.65.Ac Multilayers
68.35.Dv Composition, segregation; defects and impurities

Structural and electronic properties of bilayer epitaxial graphene

G. M. Rutter, J. N. Crain, N. P. Guisinger, P. N. First, and J. A. Stroscio

J. Vac. Sci. Technol. A 26, 938 (2008); http://dx.doi.org/10.1116/1.2944257 (6 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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Scanning tunneling microscopy and scanning tunneling spectroscopy (STS) are used to study the structural and electronic properties of bilayer epitaxial graphene on SiC(0001). Topographic images reveal that graphene conforms to the SiC interface morphology and is observed to be continuous across steps separating adjoining terraces. Bilayer epitaxial graphene is shown to be Bernal stacked as is evidenced by bias-dependent topographic imaging. STS maps of the differential conductance show that graphene lattice defects cause scattering of charge carriers near the Fermi level. An analysis of stationary scattering patterns observed in the conductance maps determines the energy-momentum dispersion relation within 100 meV of the Fermi level. In contrast to lattice defects, disorder at the SiC interface and at subsurface steps plays a much lesser role in the scattering of charge carriers.
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68.55.J- Morphology of films
68.47.-b Solid-gas/vacuum interfaces: types of surfaces
71.20.Tx Fullerenes and related materials; intercalation compounds

Photoluminescence and electroluminescence from Eu-activated CaAl2O4-based multicomponent oxide thin-film phosphors

Haruki Fukada, Shun Matsui, Toshihiro Miyata, and Tadatsugu Minami

J. Vac. Sci. Technol. A 26, 944 (2008); http://dx.doi.org/10.1116/1.2913577 (5 pages)

Online Publication Date: 1 July 2008

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Photoluminescence (PL) and electroluminescence (EL) from newly developed Eu-activated CaAl2O4 -based multicomponent oxide phosphor thin films prepared by rf magnetron sputtering are described. Yellowish green and blue emissions in PL were obtained in as-deposited and postannealed ((CaAl2O4)1−x–(BaAl2O4)x):Eu and ((CaAl2O4)1−x–(MgAl2O4)x):Eu thin films, respectively. In addition, blue emission in EL was observed from thin-film electroluminescent (TFEL) devices fabricated by using ((CaAl2O4)1−x–(BaAl2O4)x):Eu thin films postannealed at 1000 °C in an Ar+H2(5%) gas atmosphere. A luminance of 3.2 cd/m2 for blue emission was obtained in a ((CaAl2O4)0.44–(BaAl2O4)0.56):Eu TFEL device driven by a 1 kHz sinusoidal wave ac voltage; the blue EL emission corresponds to the CIE color coordinates of (x = 0.24, y = 0.13).
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices

Single-chamber plasma enhanced chemical vapor deposition of transparent organic/inorganic multilayer barrier coating at low temperature

S. M. Park, D. J. Kim, S. I. Kim, and N.-E. Lee

J. Vac. Sci. Technol. A 26, 949 (2008); http://dx.doi.org/10.1116/1.2940348 (7 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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Deposition of organic/inorganic multilayers is usually carried out by two different process steps by two different deposition methods. A single-chamber process for the deposition of multilayer stacks can make the process and deposition system simpler. In this work, SiOCH and plasma-polymerized methylcyclohexane (pp-MCH) films and their multilayer stacks for application to transparent diffusion barrier coatings were deposited in a single low-temperature plasma enhanced chemical vapor deposition reactor using hexamethyldisilazane/N2O/O2/Ar and methylcyclohexane/Ar mixtures for SiOCH and pp-MCH layers, respectively. The deposition rates of the SiOCH and pp-MCH layers were increased with increasing the N2O:O2 gas flow ratio and rf plasma power, respectively. Oxygen concentration in the SiOCH films was decreased and carbon and hydrogen incorporation was increased when increasing the N2O:O2 gas flow ratio from 0:1 to 3:1. In this work, the water vapor transmission rate of polyester sulfone substrate could be reduced from a level of 50 (bare substrate) to 0.8 g/m2 day after deposition of a pp-MCH/SiOCH/pp-MCH multilayer coating.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.Ac Multilayers
66.30.-h Diffusion in solids
52.77.-j Plasma applications

An electron impact emission spectroscopy flux sensor for monitoring deposition rate at high background gas pressure with improved accuracy

C. Lu, C. D. Blissett, and G. Diehl

J. Vac. Sci. Technol. A 26, 956 (2008); http://dx.doi.org/10.1116/1.2830633 (5 pages)

Online Publication Date: 1 July 2008

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Electron impact emission spectroscopy (EIES) has been proven to be a critical tool for film composition control during codeposition processes for the fabrication of multicomponent thin film materials including the high-efficiency copper-indium-gallium-diselenide photovoltaic cells. This technique is highly specific to atomic species because the emission spectrum of each element is unique, and the typical width of atomic emission lines is very narrow. Noninterfering emission lines can generally be allocated to different atomic species. However, the electron impact emission spectra of many molecular species are often broadband in nature. When the optical emission from an EIES sensor is measured by using a wavelength selection device with a modest resolution, such as an optical filter or monochromator, the emissions from common residual gases may interfere with that from the vapor flux and cause erroneous flux measurement. The interference is most pronounced when measuring low flux density with the presence of gases such as in reactive deposition processes. This problem is solved by using a novel EIES sensor that has two electron impact excitation sources in separate compartments but with one common port for optical output. The vapor flux is allowed to pass through one compartment only. Using a tristate excitation scheme and appropriate signal processing technique, the interfering signals from residual gases can be completely eliminated from the output signal of the EIES monitor for process control. Data obtained from Cu and Ga evaporations with the presence of common residual gases such as CO2 and H2O are shown to demonstrate the improvement in sensor performance. The new EIES sensor is capable of eliminating the effect of interfering residual gases with pressure as high as in the upper 10−5 Torr range.
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78.60.Hk Cathodoluminescence, ionoluminescence
07.81.+a Electron and ion spectrometers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Top-emitting organic light-emitting diodes with Ba/Ag/indium tin oxide cathode and built-in potential analyses in these devices

J. T. Lim, J. H. Lee, G. Y. Yeom, E. H. Lee, and T. W. Kim

J. Vac. Sci. Technol. A 26, 961 (2008); http://dx.doi.org/10.1116/1.2924333 (5 pages)

Online Publication Date: 1 July 2008

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Top-emitting organic light-emitting diodes (TEOLEDs) with a thin semitransparent conducting cathode (STCC) of Ba/Ag/indium tin oxide (ITO) were fabricated and their electric/optical characteristics were investigated. At the wavelength of 520 nm, optical properties of STCC of the Ba(3 nm)/Ag(15 nm)/ITO (100 nm) structure showed the transmittance of 63% and the reflectance of 37%. The light out-coupling properties of the TEOLED, which is composed of glass/Ag(150 nm)/ITO (130 nm)/4,4′,4″-tris[2-naphthylphenyl-1-phenylamino]triphenylamine (2-TNATA, 30 nm)/4,4′-bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (18 nm)/tris(8-quinolinolato)aluminum (III) (62 nm)/Ba (x nm,x = 3,2, and 1 nm)/Ag(15 nm)/ITO (100 nm), was increased as the deposition thickness of Ba is increased. This driving performance of the devices could be interpreted on the base of carrier injection barrier by measuring built-in voltage as well as both the optical properties and electric properties of the cathode. The optical properties (e.g., transmittance and reflectance) and electric properties of all STCCs (Ba/Ag/ITO) used in this study were nearly equal. However, built-in voltage studied using modulated photocurrent technique was increased as the thickness of barium composing of STCC was increased. This rising of a built-in voltage means a lowering of barrier height for electron injection in the devices.
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85.60.Jb Light-emitting devices

Effect of substrate temperatures on amorphous carbon nitride films prepared by reactive sputtering

Masami Aono, Hidenobu Akiyoshi, Shunsuke Kikuchi, Nobuaki Kitazawa, and Yoshihisa Watanabe

J. Vac. Sci. Technol. A 26, 966 (2008); http://dx.doi.org/10.1116/1.2919140 (4 pages)

Online Publication Date: 1 July 2008

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Amorphous carbon nitride, a-CNx, films were deposited by reactive radio frequency magnetron sputtering of a graphite target in nitrogen gas. This kind of films could be used as novel electric and optical devices. The authors investigated effects of the substrate temperature up to 873 K on the films in this study. The films were characterized with x-ray photoelectron spectroscopy (XPS), ellipsometry, atomic force microscopy, and nanoindentation tests. XPS studies show that the decreasing tendency in the composition ratio of carbon to nitrogen in a-CNx films with the substrate temperature is observed; however, the bonding fraction of sp3C–N increases depending on the substrate temperature. The nanoindentation tests reveal that the film hardness increases from 2 to 12 GPa as the substrate temperature increases from room temperature to 823 K. These results suggest that the film hardness is closely related to the bonding states between carbon and nitrogen.
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81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness

Optical radiation selective photodetectors based on III nitrides

R. Pillai, D. Starikov, C. Boney, and A. Bensaoula

J. Vac. Sci. Technol. A 26, 970 (2008); http://dx.doi.org/10.1116/1.2940347 (4 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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Wide direct band gap III nitride materials have opened up many new optoelectronic applications because they allow access to a very wide spectral range, from 200 nm to 1.77 μm, from a single material system. Both light emission sources and photodetectors with advanced properties can be achieved through tailoring layered III nitride structures with various layer orders, chemical compositions, conductivities, and thicknesses. In addition, substrate selection plays an important role in the fabrication of these devices as well as in achieving desired device properties. Along with the efficiency of detection, in most cases it is important to provide selectivity of the optical radiation sensed by the optical device. Such selectivity can be achieved by using spectral properties of optical radiation. In this article the authors present results on the modeling of dual-band photodiode structures based on III nitrides, grown on silicon substrates. UV/IR visible- and solar-blind UV/IR photodetectors have been demonstrated. The peak responsivities of the dual-band photodetectors are 3.8 and 55 mA/W at wavelengths of 349 and 1000 nm, respectively. Results on the modeling of the dual-band photodiodes in order to optimize the IR response and realize the solar-blind capability are presented.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Effects of P on amorphous chemical vapor deposition Ru-P alloy films for Cu interconnect liner applications

Jinhong Shin, Hyun-Woo Kim, Kyriacos Agapiou, Richard A. Jones, Gyeong S. Hwang, and John G. Ekerdt

J. Vac. Sci. Technol. A 26, 974 (2008); http://dx.doi.org/10.1116/1.2832360 (6 pages) | Cited 4 times

Online Publication Date: 1 July 2008

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Amorphous Ru(P) films grown by chemical vapor deposition at 575 K using a single source precursor, cis-RuH2(P(CH3)3)4, or dual sources, Ru3(CO)12 and P(CH3)3 or P(C6H5)3, are studied. The phosphorus percentage affects the film microstructure, and incorporating >13% P resulted in amorphous Ru(P) films. While codosing P(CH3)3 with Ru3(CO)12 improves film step coverage, the most conformal Ru(P) film is obtained with cis-RuH2(P(CH3)3)4. A fully continuous 5 nm Ru(P) film is formed within 1 μm deep, 8:1 aspect ratio trenches. The barrier performance is tested using Cu/Ru/Si(100) stacks annealed at 575 K, and sheet resistance was used as a measure of barrier failure. Cu diffusivity in physical vapor deposition (PVD) Ru is approximated to be 6.6×10−17 cm2/s at 575 K, which indicates fast Cu diffusion along the grain boundaries. While 26 nm polycrystalline PVD Ru failed after 6 h annealing by Cu penetration, 28 nm amorphous Ru(P) survived after 67 h annealing. First principles density functional calculations suggest 16.7% P degraded the adhesion strength by 12% when compared to crystalline Cu/Ru, by the presence of P at the interface. However, due to the strong Ru-Cu bonds, amorphous Ru(P) still forms a stronger interface with Cu than do Ta and TaN to Cu, as observed when annealing 10 nm Cu films on these surfaces at 675 K.
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68.55.-a Thin film structure and morphology
61.72.Mm Grain and twin boundaries
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Gh Other heat and thermomechanical treatments

Study on the amorphous Ta–Zr films as diffusion barrier in Cu metallization

Chuan Li, J. H. Hsieh, and Z. Z. Tang

J. Vac. Sci. Technol. A 26, 980 (2008); http://dx.doi.org/10.1116/1.2889441 (5 pages)

Online Publication Date: 1 July 2008

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An amorphous Ta–Zr binary alloy diffusion barrier was studied in the Cu metallization. A Cu/Ta50Zr50/Si stack with 50 nm thick amorphous film was prepared by cosputtering can effectively suppress the penetration of Cu atoms into substrate upon annealing up to 650 °C. Examining the thermal stability of the barrier revealed that the crystallization of these amorphous Ta50Zr50 films occurred at 800 °C, higher than its failure temperature. The results show that the existence of Cu layer first induced the formation of TaSi2 and ZrSi2 crystalline phases at 650 °C, followed by the formation of Cu3Si. A failure mechanism of the diffusion barrier is proposed based on the relation between the thermal stress and the activation energy of barrier/substrate interface reaction.
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68.35.Fx Diffusion; interface formation
81.40.Gh Other heat and thermomechanical treatments
81.15.Cd Deposition by sputtering

Ferroelectric properties of Pb(Mn1/3Nb2/3)O3−Pb(Zr,Ti)O3 thin films epitaxially grown on (001)MgO substrates

Tao Zhang, Kiyotaka Wasa, Isaku Kanno, and Shu-Yi Zhang

J. Vac. Sci. Technol. A 26, 985 (2008); http://dx.doi.org/10.1116/1.2900659 (6 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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Ferroelectric ternary perovskite thin films of 0.06Pb(Mn1/3,Nb2/3)O3 (PMnN)−0.42PbZrO3 (PZ)−0.52PbTiO3 (PT) [0.06PMnN–0.94PZT(45/55)] have been grown on the (001)MgO substrates by radio frequency-magnetron sputtering with quenching processing. The deposition conditions, microstructures, piezoelectric, and ferroelectric properties of the ternary perovskite thin films are described in comparison with the binary compounds of PZ–PT (PZT). The out-plane x-ray diffraction (XRD) measurements for the ternary PMnN–PZT perovskite thin films of 1 to 1−3 μm in film thickness show strong single (001) orientation. The in-plane Φ-scan XRD curve verified the ternary thin films are single crystals of perovskite structure. Their lattice parameters are almost the same as bulk values and the ternary thin films are almost stress free. The PMnN–PZT thin films show high density without columnar structure. The PZT-based ternary perovskite thin films with the small addition of PMnN, i.e., 6 mole % PMnN, exhibit a strong hard ferroelectric response, i.e., Ps = 60 μC/cm2 and 2Ec = 230 kV/cm. Their effective piezoelectric constants are typically e31,eff = −7.7 C/m2. These values are slightly higher than those of binary perovskite PZT thin films.
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77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
81.15.Cd Deposition by sputtering
77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Ion beam deposition of tantalum pentoxide thin film at room temperature

W. Kulisch, D. Gilliland, G. Ceccone, H. Rauscher, L. Sirghi, P. Colpo, and F. Rossi

J. Vac. Sci. Technol. A 26, 991 (2008); http://dx.doi.org/10.1116/1.2832407 (5 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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Tantalum pentoxide (Ta2O5) thin films have been deposited by reactive ion beam sputtering at room temperature. The films have been characterized by scanning electron microscopy, atomic force microscopy, x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), variable angle ellipsometry, and UV-VIS spectroscopy. The main parameter varied was the oxygen partial pressure. Stoichiometry is reached for pO ≥ 3×10−2 Pa; within the limit of XPS ( ∼ 1%) the films are free of contaminations. They are extremely smooth with a surface roughness of 0.14 nm only. From FTIR, it can be concluded that they are amorphous. For stoichiometric Ta2O5 films, the refractive index at 532 nm is in the range from 2.05 to 2.2, while the extinction coefficient is below the detection limit of our ellipsometer. UV-VIS spectra show stoichiometric films to possess a high transmission in a wide wavelength range with an absorption edge below 300 nm.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
77.55.-g Dielectric thin films
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps Atomic force microscopy (AFM)
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
78.40.Ha Other nonmetallic inorganics
78.30.Hv Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Effects of manganese oxide–mixed abrasive slurry on the tetraethyl orthosilicate oxide chemical mechanical polishing for planarization of interlayer dielectric film in the multilevel interconnection

Yong-Jin Seo, Sung-Woo Park, and Woo-Sun Lee

J. Vac. Sci. Technol. A 26, 996 (2008); http://dx.doi.org/10.1116/1.2936225 (6 pages)

Online Publication Date: 1 July 2008

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In this article, the authors have studied the chemical mechanical polishing (CMP) characteristics of mixed abrasive slurry (MAS) retreated by adding of manganese oxide (MnO2) abrasives within 1:10 diluted silica slurry. The slurry designed for optimal performance should produce reasonable removal rates, acceptable polishing selectivity with respect to the underlying layer, low surface defects after polishing, and good slurry stability. The modified abrasives in MAS are evaluated with respect to their particle size distribution, surface morphology, and CMP performances such as removal rate and nonuniformity. As an experimental result, the authors obtained the comparable slurry characteristics compared to original silica slurry in the viewpoint of high removal rate and low nonuniformity.
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81.65.Ps Polishing, grinding, surface finishing
85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.B- Structure of clean surfaces (and surface reconstruction)

Comparative study of photocatalytic activity in CdS–TiO2 thin films prepared by two different techniques

S. Biswas, M. F. Hossain, T. Takahashi, Y. Kubota, and A. Fujishima

J. Vac. Sci. Technol. A 26, 1002 (2008); http://dx.doi.org/10.1116/1.2938392 (5 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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In this study, CdS layer in CdS–TiO2 bilayer films was fabricated by two different chemical bath deposition techniques: one with an ammonium complex as complexing agent and the other with sodium citrate as a substitute for the ammonium complex. The TiO2 upper layer was deposited by dc magnetron sputtering technique for both the CdS underlayers. The effect of postdeposition vacuum annealing was studied for both samples. The photocatalytic activity was evaluated by measuring the decomposition of methanol in gas phase under ultraviolet-visible irradiation. The CdS thin films, prepared by both techniques, show a highly oriented hexagonal structure. The optical transmission edge of the CdS thin films deposited by the ammonia-free technique is in lower wavelength than that of the other technique. For both techniques, vacuum annealing extends the absorption edge to higher wavelength, but this effect is more pronounced for the ammonia-content technique. The decomposition efficiency of the as-deposited CdS–TiO2 thin film prepared by the ammonia-free technique is much higher than the as-deposited CdS–TiO2 prepared by ammonia-content technique. In case of the ammonia-content technique, high-vacuum annealing improves the photocatalytic activity but it has minimal influence in the other technique. The surface morphology of all the CdS thin films was studied by field emission scanning electron microscopy and atomic force microscopy in order to find out the possible inherent reason that leads to a huge difference in the photocatalytic decomposition activity of CdS–TiO2 thin films.
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82.50.Hp Processes caused by visible and UV light
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.15.Cd Deposition by sputtering
68.55.at Other materials
61.72.Cc Kinetics of defect formation and annealing

Effect of structure and surface morphology of sol-gel derived TiO2 photoelectrode on the performance of dye-sensitized solar cells

M. F. Hossain, S. Biswas, T. Takahashi, Y. Kubota, and A. Fujishima

J. Vac. Sci. Technol. A 26, 1007 (2008); http://dx.doi.org/10.1116/1.2832410 (5 pages) | Cited 1 time

Online Publication Date: 1 July 2008

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Nanocrystalline TiO2 photoelectrodes were successfully deposited on SnO2:F coated glass substrate by sol-gel technique with different polyethylene glycol (PEG) concentrations. Low cost chlorophyllin based dye was used along with carbon paste on SnO2:F glass as a counterelectrode. All the TiO2 electrodes show good crystallinity. The x-ray diffraction result indicates that the TiO2 thin film without PEG has more compact structure with high density of crystallite. For TiO2 film with the same number of coatings, introduction of PEG induces porous structure with less number of crystallites. The amount of dye incorporation was found to be highly dependent on the microstructure of electrodes, as apparent from optical measurements. The result shows that the photoelectric conversion efficiency increases with PEG concentration, but the fill factor decreases monotonically. The variation of photoelectric conversion efficiency of the solar cells with different TiO2 electrodes prepared with various PEG concentrations is discussed with the analysis of different microstructures of the TiO2 photoelectrodes and the corresponding dye incorporation.
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84.60.Jt Photoelectric conversion
68.55.J- Morphology of films
61.46.Hk Nanocrystals
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.35.bg Semiconductors

Effect of substrate temperature on the facing target sputter deposited TiO2 photoelectrode of dye-sensitized solar cells

M. F. Hossain, S. Biswas, T. Takahashi, Y. Kubota, and A. Fujishima

J. Vac. Sci. Technol. A 26, 1012 (2008); http://dx.doi.org/10.1116/1.2834686 (6 pages) | Cited 5 times

Online Publication Date: 1 July 2008

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Nanocrystalline TiO2 photoelectrodes were successfully deposited on SnO2:F coated glass substrate by facing target reactive sputtering technique with different substrate temperatures ranging from room temperature to 400 °C. Low cost chlorophylline based dye was used along with carbon paste on SnO2:F glass as a counterelectrode. All the TiO2 electrodes show good crystallinity. It has been observed that increase of substrate temperature not only alters the ratio of anatase and rutile phase but it also markedly changes the crystal orientation. The amount of dye incorporation was found to be highly dependent on the microstructure of electrodes, as apparent from optical measurements. The dye-sensitized solar cells, comprised of TiO2 photoelectrode, deposited at substrate temperature of 200 °C, show maximum photoelectric conversion efficiency; however, further enhancement of sputtering temperature drastically reduces the efficiency. The variation of photoelectric conversion efficiency of the solar cells with TiO2 electrodes deposited at different substrate temperatures is discussed with the analysis of different microstructures of the TiO2 photoelectrodes and the corresponding dye incorporation. Moreover, all the dye-sensitized solar cells of this present investigation exhibit reasonably good fill factor value.
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84.60.Jt Photoelectric conversion
82.45.Fk Electrodes
81.15.Cd Deposition by sputtering

Silicon carbonitrides: On the attainability of stable compounds with high nitrogen content

M. Rudolphi, H. Baumann, U. Geckle, and M. Bruns

J. Vac. Sci. Technol. A 26, 1018 (2008); http://dx.doi.org/10.1116/1.2924331 (5 pages) | Cited 3 times

Online Publication Date: 1 July 2008

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Thin stoichiometric SiCN thin films and layers along selected tie lines of the phase diagram have been synthesized from the elements by means of ion implantation of carbon and nitrogen ions into silicon wafer substrates as well as rf magnetron cosputtering of targets with different Si/C area ratios by using Ar/N2 sputter gas with successive variation of the N2 content. After synthesis, the samples were heat treated under high vacuum conditions utilizing an electron beam annealing system. Resonant nuclear reaction analysis, non-Rutherford backscattering spectrometry and Auger electron spectroscopy have been used to perform an elemental analysis of the films and layers, respectively. The chemical binding states were investigated with x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.
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81.15.Cd Deposition by sputtering
61.72.Cc Kinetics of defect formation and annealing
78.30.Hv Other nonmetallic inorganics
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.80.Jh Ion radiation effects
68.55.-a Thin film structure and morphology
81.30.Dz Phase diagrams of other materials
back to top Thin Films I

Optical characterization of InN layers grown by high-pressure chemical vapor deposition

M. Alevli, R. Atalay, G. Durkaya, A. Weesekara, A. G. U. Perera, N. Dietz, R. Kirste, and A. Hoffmann

J. Vac. Sci. Technol. A 26, 1023 (2008); http://dx.doi.org/10.1116/1.2908736 (4 pages) | Cited 1 time

Online Publication Date: 1 July 2008

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The optical properties of InN layers grown by high-pressure chemical vapor deposition have been studied. Raman, infrared reflection, and transmission spectroscopy studies have been carried out to investigate the structural and optical properties of InN films grown on sapphire and GaN/sapphire templates. Results obtained from Raman and IR reflectance measurements are used to estimate the free carrier concentrations, which were found to be varying from mid 1018 to low 1020 cm−3. The values for free carrier concentrations are compared to optical absorption edge estimates obtained from optical transmission spectra analysis. The analysis shows that optical absorption edge for InN shifts below 1.1 eV as the free carrier concentration decreases to low 1018 cm−3.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors

Structural study of TiO2-based transparent conducting films

T. Hitosugi, N. Yamada, S. Nakao, K. Hatabayashi, T. Shimada, and T. Hasegawa

J. Vac. Sci. Technol. A 26, 1027 (2008); http://dx.doi.org/10.1116/1.2944260 (3 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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We have investigated microscopic structures of sputter and pulsed laser deposited (PLD) anatase Nb-doped TiO2 transparent conducting films, and discuss what causes the degradation of resistivity in sputter-deposited films. Cross-sectional transmission electron microscope and polarized optical microscope images show inhomogeneous intragrain structures and small grains of ∼ 10 μm in sputter-deposited films. From comparison with PLD films, these results suggest that homogeneous film growth is the important factor to obtain highly conducting sputter-deposited film.
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68.55.J- Morphology of films
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.61.Le Other inorganic semiconductors
81.15.Fg Pulsed laser ablation deposition
81.15.Cd Deposition by sputtering
68.55.ag Semiconductors
back to top Thin Films II

A model for calculating resputter rates in codeposition

J. M. Gregoire and R. B. van Dover

J. Vac. Sci. Technol. A 26, 1030 (2008); http://dx.doi.org/10.1116/1.2885213 (7 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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The ability to calculate composition in composition spread thin films is a powerful tool in combinatorial research. This ability is pivotal in high-throughput studies, where the time and effort required to determine elemental compositions using standard techniques can be prohibitive. Calculating codeposited film composition from single-source deposition profiles requires a model for film growth in codeposition. In dc magnetron sputtering, modeling film growth as the simple addition of individual rates can lead to significant errors, primarily due to resputtering of film atoms by energetically reflected gas atoms. We develop a model which includes the definition of a resputter coefficient that is used to calculate resputtering rates in the codeposition of an arbitrary number of sources. The accuracy of the model is demonstrated for the codeposition of Pt and Pb. In the development of the model, useful parametrizations of fundamental quantities of sputter dynamics are presented, and the authors also present tabulated values of the resputter coefficient for 27 commonly sputtered elements at select sputter voltages.
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68.55.Nq Composition and phase identification
81.15.Cd Deposition by sputtering
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Efficient combining of ion pumps and getter-palladium thin films

C. Paolini, M. Mura, and F. Ravelli

J. Vac. Sci. Technol. A 26, 1037 (2008); http://dx.doi.org/10.1116/1.2834685 (5 pages)

Online Publication Date: 1 July 2008

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Nonevaporable getters (NEGs) have been extensively studied in the last several years for their sorption properties toward many gases. In particular, an innovative alloy as a thin film by magnetron sputtering was developed and characterized at the European Organization for Nuclear Research. It is composed of Ti–Zr–V and protected by an overlayer of palladium (Pd), according to a technology for which the authors got the licence. NEG-Pd thin films used in combination with ion getter pumps is a simple, easy way to handle pumping devices for ultrahigh and extremely high vacuum applications. To show how to apply this coating technology to the internal surface of different types of ion pumps, the authors carried out several tests on pumps of various shapes, sizes (in terms of nominal pumping speed), and types (diode, noble diode, and triode). Special care was taken during the thermal cycle of baking and activation of the pumps to preserve the internal film from sources of contamination and/or from the sputtering of the titanium cathodes of the pump. Some important remarks will be made about the most appropriate conditions of pressure and temperature. The performance of the NEG-Pd-coated ion pumps was evaluated in terms of ultimate pressure and hydrogen pumping speed. The contribution of the thin film is particularly relevant for the pumping of this gas, due to its high sticking factor on palladium and the great sorption capacity of the underlying getter. Finally, the possibility of further improvement by substituting palladium with other Pd-based alloys will also be evaluated.
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07.30.Cy Vacuum pumps
81.65.Tx Gettering
68.43.Mn Adsorption kinetics
81.15.Cd Deposition by sputtering
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Recent advances to enhance low Earth orbit space simulation

Frank G. Collins

J. Vac. Sci. Technol. A 26, 1042 (2008); http://dx.doi.org/10.1116/1.2839696 (8 pages) | Cited 1 time

Online Publication Date: 1 July 2008

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Accurate ground-based simulation of low Earth orbit (LEO) conditions experienced by a satellite has proven to be a challenge. Recent progress that has been made toward the development of means for simulating portions of the LEO environment will be reviewed. A satellite in LEO has a speed relative to the atmosphere of approximately 8 km/s. The neutral atmospheric molecules exchange momentum upon collision with the surfaces of the satellite, leading to drag, lift, and moments, but ground facilities still have trouble simulating pure beams of ground state atmospheric gases at this speed. The most important atmospheric species, atomic oxygen, collides with ram-direction satellite surfaces with a relative energy of 5 eV. The solar UV spectrum in LEO is a composite of many emission lines and continuum, which must be simulated using special lamp systems. Thruster plumes and outgassing molecules result in a contamination atmosphere close to the spacecraft surface. Energetic atomic oxygen atoms in the presence of solar UV radiation and contamination gases can produce synergistic effects that result in many chemical reactions on or in the vicinity of the outer satellite surfaces. These reactions can lead to structural or operational damage to various satellite components, such as a reduction in the effectiveness of thermal control paints, cleanliness of optical lenses, and the reduction of the output of solar cells. Several techniques for generating beams of 5 eV atomic oxygen in the ground state will be reviewed as well as special diagnostic instrumentation developed to detect atomic oxygen. These are combined in space simulation chambers for a more complete study of materials degradation. Some electric thrusters exit directly to the vacuum of space. Their exhaust and plume simulation presents unique vacuum chamber pumping problems. Specially designed cryogenic pumps to simulate the conditions that these electric thrusters will experience in orbit will be described. Reference to inventories of space simulation chambers will be given.
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97.60.-s Late stages of stellar evolution (including black holes)
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back to top Electronic Material and Processing/Nanometer-Scale Science and Technology

Optical properties of organic and inorganic capped CdS nanoparticles and the effects of x-ray irradiation on organic capped CdS nanoparticles

Nilima V. Hullavarad and Shiva S. Hullavarad

J. Vac. Sci. Technol. A 26, 1050 (2008); http://dx.doi.org/10.1116/1.2940346 (8 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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In this article, the authors report synthesis of CdS nanoparticles using a simple, inexpensive and straightforward chemical colloidal method using organic and inorganic capping agents. 1-6 hexanedithiol, mercaptoethanol, thioglycerol, tetraethyl orthosilicate, and tetraethyl orthotitaniate are used as the capping agents. The optical absorption spectra of CdS nanoparticles synthesized using the same parameters are found to depend on the nature of capping agents. The infrared absorption measurements provided important information about the nature of bonding. The optical studies on effect of x-ray irradiation on thioglycerol-capped CdS nanoparticle are also discussed.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.80.Cb X-ray effects
78.30.Fs III-V and II-VI semiconductors

Characterization of electrospray ion-beam-deposited CdSe/ZnS quantum dot thin films from a colloidal solution

Yuki Tani, Satoshi Kobayashi, and Hiroshi Kawazoe

J. Vac. Sci. Technol. A 26, 1058 (2008); http://dx.doi.org/10.1116/1.2912072 (4 pages) | Cited 1 time

Online Publication Date: 1 July 2008

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Colloidal semiconductor quantum dot (QD) nanocrystals can be deposited in the form of inorganic thin films using the ion beam direct deposition method. To simultaneously preserve the nanocrystal configuration and remove the organics derived from the ligand and solvent, the authors used an electrospray technique and an ion beam technique. These techniques provided a soft-ionization process to obtain nanocrystalline ions and a collision process to attain a nonequilibrium state of the deposits, respectively. Because of the nature of the soft-ionization process, the electrospray phenomenon resulted in various forms of QD ions that depended on the preparation of the colloidal solution source and spraying conditions. The authors concentrated on finding operational conditions of the system that deposited thin films with reduced organics concentrations by examining the correlation between fast Fourier transform infrared absorption spectroscopy and photoluminescence intensity. The morphology of the deposited films was observed using an atomic force microscope.
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68.55.ag Semiconductors
78.67.Hc Quantum dots
78.66.Hf II-VI semiconductors
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.Rs Spray coating techniques

Programmable memory devices using gold nanoparticles capped with alkanethiols of different carbon chain lengths

Pei Ying Lai and J. S. Chen

J. Vac. Sci. Technol. A 26, 1062 (2008); http://dx.doi.org/10.1116/1.2836426 (6 pages)

Online Publication Date: 1 July 2008

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Electrical bistability is demonstrated in a polymer memory device using polystyrene containing an organic conjugated compound (8-hydroxyquinoline) and gold nanoparticles (Au NPs) capped with different alkanethiols of carbon chain lengths as the active layer between two metal electrodes. Au NPs capped with three different alkanethiols [1-octanethiol (C8), 1-dodecanethiol (C12), and 1-octadecanethiol (C18)] are investigated for the correlation with the memory performance. Above a threshold voltage, the as-fabricated device can transit from low conductivity state to high conductivity state. By applying a certain positive voltage, the high conductivity state can return to the low conductivity state. The switch-on voltages of thiol-derivatized Au NPs based organic memory devices are almost the same. Current fluctuations appeared in the static current–voltage characteristic of Au NPs capped with a 1-octadecanethiol (C18) based memory device. This feature is related to quantized charging and discharging of Au NPs because of the Coulomb repulsion between electrons confined in nanocrystals.
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84.30.Sk Pulse and digital circuits
back to top Renewable Energy Science & Technology Topical Conference/Thin Films/Surface Science

Electron backscatter diffraction of CdTe thin films: Effects of CdCl2 treatment

H. R. Moutinho, R. G. Dhere, M. J. Romero, C.-S. Jiang, B. To, and M. M. Al-Jassim

J. Vac. Sci. Technol. A 26, 1068 (2008); http://dx.doi.org/10.1116/1.2841523 (6 pages)

Online Publication Date: 1 July 2008

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In this work, the authors describe procedures to prepare the surface of close-spaced sublimation CdTe thin films necessary for producing good electron backscatter diffraction (EBSD) data. They found that polishing resulted in an amorphous layer on the surface and no Kikuchi pattern; however, ion-beam milling produced a relatively flat and good-quality surface, resulting in high-quality patterns and, consequently, excellent EBSD data. The authors used a combination of polishing and ion-beam milling or etching to study the crystalline structure of the CdTe film at different depths. They also used EBSD, in conjunction with other analytical techniques, to investigate the effects of the CdCl2 treatment, performed at different temperatures and times, on the recrystallization process of physical vapor deposition CdTe thin films. The authors found that the untreated films were 〈111〉 oriented, with grain sizes smaller than 1μm. The CdCl2 at 350 °C produced partially recrystallized films, whereas treatments at 400 °C or 420 °C produced completely recrystallized films, with no texture, and grains with grain sizes varying from about 1μm to more than 40μm. These films were so flat that good EBSD data could be obtained without any surface preparation. Atomic force microscopy and scanning electron microscopy showed that large grains had different morphologies than smaller grains, and EBSD showed that these large grains had 〈111〉 texture. These results indicate that the (111) surface is the lowest energy surface in these films and, consequently, 〈111〉-oriented grains grow at the expense of grains oriented in less-favorable directions. Regardless of the deposition method and treatment, the CdTe films have a high density of 60° 〈111〉 twin boundaries.
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79.20.Kz Other electron-impact emission phenomena
68.55.ag Semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.66.Fn Inorganic compounds
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.Mm Grain and twin boundaries
back to top Nanometer-Scale Science and Technology/Manufacturing Science and Technology

Study of characteristic fragmentation of nanocarbon by the scanning atom probe

Osamu Nishikawa, Masahiro Taniguchi, and Yahachi Saito

J. Vac. Sci. Technol. A 26, 1074 (2008); http://dx.doi.org/10.1116/1.2832364 (5 pages) | Cited 1 time

Online Publication Date: 1 July 2008

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Six nine purity graphite and single-walled carbon nanotube (SWCNT), double-walled carbon nanotube (DWCNT), multiple-walled carbon nanotube (MWCNT) are mass analyzed by the scanning atom probe. Surface atoms well exposed to the external field are field evaporated and individual evaporated fragment ions are detected. Each specimen exhibits a characteristic mass spectrum of fragmented cluster ions. The SWCNT exhibits the cleanest mass spectrum with a small amount of hydrogen. The commercially available DWCNT shows two types of mass spectra: one is fairly clean and the other with many C15(H2O)m clusters. The laboratory grown MWCNT shows various doubly and triply ionized cluster ions indicating strong bonding between the atoms forming the clusters. The sharper the mass peak is and the higher the multiplicity of charge is, the stronger the binding between atoms forming the clusters. The commercially available pure graphite shows three types of mass spectra, fairly clean spectra without large C–H clusters, spectra with various C–H clusters with a large mass peak of C28H4, and spectra with larger clusters such as C38Hn. The magic number forming the clusters is discussed.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.46.Fg Nanotubes
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
79.70.+q Field emission, ionization, evaporation, and desorption
back to top Plasma Science and Technology I/Thin Films

Self-limiting deposition of aluminum oxide thin films by pulsed plasma-enhanced chemical vapor deposition

Scott F. Szymanski, Pieter Rowlette, and Colin A. Wolden

J. Vac. Sci. Technol. A 26, 1079 (2008); http://dx.doi.org/10.1116/1.2891258 (6 pages) | Cited 6 times

Online Publication Date: 1 July 2008

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Self-limiting deposition of aluminum oxide (Al2O3) thin films was accomplished by pulsed plasma-enhanced chemical vapor deposition using a continuous delivery of trimethyl aluminum (TMA) and O2. Film characterization included spectroscopic ellipsometry and Fourier transform infrared (FTIR) spectroscopy. Deposition rates scaled with TMA exposure and could be controlled over a large range of 1–20 Å/pulse. For fixed conditions, digital control over film thickness is demonstrated. Deposition rates initially decreased with substrate temperature before becoming constant for Ts>100 °C. Higher growth rates at low temperature are attributed to the thermal reaction between H2O, produced during the plasma on step, with TMA during the plasma off step. Gas-phase analysis confirms the coexistence of these species, and their degree of overlap is a strong function of the chamber wall temperature. With both the substrate and chamber wall temperature elevated, impurities related to carbon and hydroxyl groups are attenuated below the detection limit of FTIR.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
52.77.Dq Plasma-based ion implantation and deposition
78.30.Hv Other nonmetallic inorganics
back to top Tribology 4/Advanced Surface Energy

Microstructure and tribological behavior of tungsten-containing diamondlike carbon coated rubbers

Y. T. Pei, X. L. Bui, X. B. Zhou, and J. Th. M. De Hosson

J. Vac. Sci. Technol. A 26, 1085 (2008); http://dx.doi.org/10.1116/1.2889443 (8 pages) | Cited 3 times

Online Publication Date: 1 July 2008

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Tungsten-containing diamondlike carbon (W-DLC) coatings have been deposited on FKM (fluorocarbon), ACM (acrylate), and HNBR (hydrogenated nitrile butadiene) rubbers via unbalanced magnetron reactive sputtering from a WC target in C2H2/Ar plasma. The surface morphology and fracture cross sections of coated rubbers have been scrutinized by high resolution scanning electron microscopy (SEM). The random crack networks formed due to the large difference in the coefficients of thermal expansion break down the W-DLC coatings into segments of a couple of hundred micrometers in size, facilitating good flexibility if the interfacial adhesion between the coating and a rubber substrate is strong enough. The size and density of growth defects in the W-DLC coatings strongly depend on the surface roughness of the rubber sheets. The tribological behavior of uncoated and coated rubbers has been investigated with ball-on-disk tribotest under dry sliding condition against a 6 mm 100Cr6 ball. Uncoated rubbers exhibited a very high coefficient of friction (>0.9). W-DLC coated FKM did not considerably reduce the friction because the coating was damaged due to poor adhesion. W-DLC coated HNBR and ACM exhibited excellent tribological performance, and very low coefficients of friction (<0.24) were achieved even at high normal load of 5 N. After tribotests, the W-DLC coatings on HNBR and ACM were intact and no serious damage was observed on the wear tracks.
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68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.35.bt Other materials

Effects of annealing on antiwear and antibacteria behaviors of TaN–Cu nanocomposite thin films

J. H. Hsieh, M. K. Cheng, Y. K. Chang, C. Li, C. L. Chang, and P. C. Liu

J. Vac. Sci. Technol. A 26, 1093 (2008); http://dx.doi.org/10.1116/1.2900660 (5 pages) | Cited 1 time

Online Publication Date: 1 July 2008

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TaN–Cu nanocomposite films were deposited by reactive cosputtering on Si and tool steel substrates. The films were then annealed using rapid thermal annealing (RTA) at 400 °C for 2, 4, and 8 min, respectively, to induce the nucleation and growth of Cu particles in TaN matrix and on film surface. Field emission scanning electron microscopy was applied to characterize Cu nanoparticles emerged on the surface of TaN–Cu thin films. The effects of annealing on the antiwear and antibacterial properties of these films were studied. The results reveal that annealing by RTA can cause Cu nanoparticles to form on the TaN surface. Consequently, the tribological behaviors, as well as the antibacterial behavior may vary depending on particle size, particle distribution, and total exposed Cu amount. For the samples with large Cu particles, the reduction of averaged friction and wear rate is obvious. Apparently, it is due to the smeared Cu particles adhered onto the wear tracks. This Cu layer may act as a solid lubricant. From the antibacterial testing results, it is found that both Cu particle size and total exposed Cu amount are critical in making short-term antibacterial effect. Overall, all the annealed TaN–Cu samples can reach >99% antibacterial efficiency in 24 h, with respect to uncoated Si substrate.
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68.60.Bs Mechanical and acoustical properties
81.40.Pq Friction, lubrication, and wear
81.15.Cd Deposition by sputtering
68.55.at Other materials
62.20.Qp Friction, tribology, and hardness
81.16.-c Methods of micro- and nanofabrication and processing
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