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Simulation and correction of geometric distortions in scanning Kelvin probe microscopy

Anton Efimov and Sidney R. Cohen

J. Vac. Sci. Technol. A 18, 1051 (2000); http://dx.doi.org/10.1116/1.582472 (5 pages) | Cited 23 times

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Capacitance due to geometric influence of the finite tip shape and influence of distant surface points can lead to artifacts in scanning Kelvin probe microscopy (SKPM) images. These artifacts appear as features in the SKPM image which are due only to tip/surface geometry and not to true surface potential variations. They can also cause blurring of real features. Such effects are most prominent for samples with rich topography. We present here a method for identifying and removing these artifacts, and demonstrate it for a gold sample with rich topography relative to the nearly flat surface potential fluctuations. © 2000 American Vacuum Society.

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68.37.Ef	Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps	Atomic force microscopy (AFM)
68.37.Rt	Magnetic force microscopy (MFM)
68.37.Uv	Near-field scanning microscopy and spectroscopy
68.35.B-	Structure of clean surfaces (and surface reconstruction)

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Secondary ion mass spectrometry and x-ray photoelectron spectroscopy correlation study of nitrided gate oxide

C. A. Bradbury and C. Blackmer

J. Vac. Sci. Technol. A 18, 1056 (2000); http://dx.doi.org/10.1116/1.582299 (5 pages) | Cited 4 times

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Reliability of dielectric films such as silicon dioxide in the metal–oxide semiconductor gate insulator has become a key issue as devices shrink in size. Many of the problems associated with reduction in both the width and thickness of the gate oxide can be controlled with the addition of nitrogen. Nitrogen incorporation into the oxide has been shown to have significantly better charge trapping properties, less interface state generation, and more resistance to continued oxidation and incorporation of impurities. The nitrogen also acts as a barrier to diffusion of dopants from the silicon substrate. The amount of nitrogen present and its location in the oxide control the extent to which each of these properties is exhibited. The concentration and distribution of nitrogen in gate oxides was studied using secondary ion mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS). The SIMS analysis used Cs ion bombardment and detection of the CsN⁺ cluster to reduce the matrix effects associated with profiling from silicon oxide into silicon. A procedure was developed for XPS to provide the necessary signal to noise required for these low nitrogen concentrations. In addition to comparing the concentrations and spatial resolution of the nitrogen in the gate oxide, repeatability studies were also performed for each technique. © 2000 American Vacuum Society.

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81.65.Lp	Surface hardening: nitridation, carburization, carbonitridation
73.40.Qv	Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ng	Insulators
79.20.Rf	Atomic, molecular, and ion beam impact and interactions with surfaces
79.60.Bm	Clean metal, semiconductor, and insulator surfaces

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Channeling effects during focused-ion-beam micromachining of copper

J. R. Phillips, D. P. Griffis, and P. E. Russell

J. Vac. Sci. Technol. A 18, 1061 (2000); http://dx.doi.org/10.1116/1.582300 (5 pages) | Cited 4 times

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The rapid introduction of copper metallization for semiconductor devices has prompted increased research into focused-ion-beam micromachining of copper. Studies with the aim of increasing the material removal rate of Cu by focused-ion-beam micromachining have been complicated by variable micromachining behavior apparently resulting from differing Cu film morphologies produced by the various Cu deposition procedures. This work examined the micromachining behavior of thin copper films produced by physical-vapor deposition (PVD) and electroplating, as well as single-crystal copper samples. PVD copper films were found to be preferentially textured along 〈111〉, with a columnar grain structure. Channeling effects within this type of grain structure provide a geometric enhancement of the material removal rate of 30% when the sample normal is tilted 12° from the incident ion beam, regardless of sample rotation. Single-crystal (111) copper was found to exhibit similar material removal rate enhancement (averaged over 360° rotation) when tilted 12°, verifying that the etching enhancement observed in the PVD films is directly related to their 〈111〉 texture. Compared to the PVD film, electroplated (EP) copper thin films contained a significantly more random grain orientation. Consequently, the EP films did not exhibit any appreciable variation in material removal rate beyond the expected cosine dependence when tilted with respect to the incident Ga⁺ beam normal. Micromachining of the electroplated films, which have larger randomly oriented grains, results in grain decoration due to preferential etching producing severe micromachining-induced topography. © 2000 American Vacuum Society.

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81.65.Cf	Surface cleaning, etching, patterning
81.05.Bx	Metals, semimetals, and alloys
85.40.Ls	Metallization, contacts, interconnects; device isolation
61.85.+p	Channeling phenomena (blocking, energy loss, etc.)
06.60.Vz	Workshop procedures (welding, machining, lubrication, bearings, etc.)
81.20.Wk	Machining, milling
68.55.-a	Thin film structure and morphology
68.35.B-	Structure of clean surfaces (and surface reconstruction)

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Oxide-free phosphate films on copper probed by core and valence-band x-ray photoelectron spectroscopic studies in an anaerobic cell

John A. Rotole and Peter M. A. Sherwood

J. Vac. Sci. Technol. A 18, 1066 (2000); http://dx.doi.org/10.1116/1.582301 (6 pages) | Cited 8 times

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This article reports the results of a study of the formation of phosphate films formed directly on the surface of metallic copper without the presence of an oxide layer. The experiments were performed using aqueous electrochemical treatment in an anaerobic electrochemical cell designed to allow an oxide-free metal surface to be exposed to electrochemical treatment without having to expose the electrode to the atmosphere. The electrochemical treatment was performed using negative voltages (versus a saturated calomel electrode) in 5 M orthophosphoric acid. When the experiments were performed outside the anaerobic cell with as-received metallic copper, the treatment leads to the removal of oxide to leave a metallic surface with negligible amounts of oxide. In the anaerobic cell, however, a film consisting of a mixture of Cu(I) metalphosphate and orthophosphate is formed directly bonded to the metal. When this film is exposed to air for ten days, the surface film, still directly bonded to the metal, is oxidized to Cu(II) orthophosphate, this film remaining in a stable condition. The surface chemistries were identified by valence-band photoemission interpreted by cluster calculations. The work illustrates how, by starting with an oxide-free metal surface and performing the treatment in an inert environment in an anaerobic electrochemical cell, one can achieve unusual surface chemistries. © 2000 American Vacuum Society.

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79.60.Bm	Clean metal, semiconductor, and insulator surfaces
73.20.At	Surface states, band structure, electron density of states
82.65.+r	Surface and interface chemistry; heterogeneous catalysis at surfaces

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Core-level satellites and outer core-level multiplet splitting in Mn model compounds

A. J. Nelson, John G. Reynolds, and Joseph W. Roos

J. Vac. Sci. Technol. A 18, 1072 (2000); http://dx.doi.org/10.1116/1.582302 (5 pages) | Cited 21 times

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We report a systematic study of the Mn 2p, 3s, and 3p core-level photoemission and satellite structures for Mn model compounds. Charge transfer from the ligand state to the 3d metal state is observed and is distinguished by prominent shake-up satellites. We also observe that the Mn 3s multiplet splitting becomes smaller as the Mn oxidation state increases, and that 3s–3d electron correlation reduces the branching ratio of the ⁷S:⁵S states in the Mn 3s spectra. In addition, as the ligand electronegativity decreases, the spin-state purity is lost in the 3s spectra, as evidenced by peak broadening. Our results are best understood in terms of the configuration–interaction model including intrashell electron correlation, charge transfer, and final-state screening. © 2000 American Vacuum Society.

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79.60.Bm	Clean metal, semiconductor, and insulator surfaces
73.20.At	Surface states, band structure, electron density of states

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X-ray photoemission spectroscopy and scanning tunneling spectroscopy study on the thermal stability of WO₃ thin films

S. Santucci, C. Cantalini, M. Crivellari, L. Lozzi, L. Ottaviano, and M. Passacantando

J. Vac. Sci. Technol. A 18, 1077 (2000); http://dx.doi.org/10.1116/1.582303 (6 pages) | Cited 22 times

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In this work the surface electronic and structural properties of about 150 nm thick WO₃ films, deposited in high vacuum by thermal evaporation onto Si substrates, have been studied in ultrahigh vacuum (UHV) by means of x-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM)/spectroscopy. After deposition these films have been annealed in atmospheric oven for 24 h at different temperatures (300 and 500 °C) to stabilize the film morphology. XPS measurements to follow W 4f, O 1s peaks and the valence band, have been performed on these samples both as prepared and after a re-annealing in UHV at temperatures ranging from 50 to 350 °C. The UHV re-annealing procedure strongly modifies the W 4f peak of both the as deposited and the 300 °C/24 h treated samples, and produces an increase of metallic states at the Fermi edge. Instead, the 500 °C/24 h sample, after heating in UHV shows substantial stability of the nearly stoichiometric WO₃ phase. Using STM in UHV we have investigated the morphology of the samples at room temperature and after the annealing at elevated temperatures up to 350 °C. In particular, we have taken I–V curves on typical grains of the polycrystalline sample. Our findings on the electronic structure of samples close to the Fermi level are in agreement and allow a clearer understanding of the findings from the parallel XPS study. © 2000 American Vacuum Society.

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68.60.Dv	Thermal stability; thermal effects
68.55.-a	Thin film structure and morphology
79.60.Bm	Clean metal, semiconductor, and insulator surfaces
73.20.At	Surface states, band structure, electron density of states
68.35.B-	Structure of clean surfaces (and surface reconstruction)
81.40.Gh	Other heat and thermomechanical treatments

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Consistent, combined quantitative Auger electron spectroscopy and x-ray photoelectron spectroscopy digital databases: Convergence of theory and experiment

M. P. Seah, I. S. Gilmore, and S. J. Spencer

J. Vac. Sci. Technol. A 18, 1083 (2000); http://dx.doi.org/10.1116/1.582304 (6 pages) | Cited 2 times

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Auger Electron Spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) have many aspects in common. Therefore, tests of aspects for one spectroscopy, applicable to the other, should be validated for both. Digital databases of elemental spectra for both AES and XPS have thus been measured using an electron spectrometer that has been fully calibrated for its intensity and energy axes. These databases of true spectra give absolute Auger electron yields and relative photoelectron yields. The AES data are measured for both 5 and 10 keV electron beam energies, whereas the XPS data are measured for both Al and Mg unmonochromated x rays at the magic angle. In addition to these we have measured reflected electron energy loss spectroscopy (REELS) data to provide a third database. The combination of these databases allows a refinement of the theories to obtain an overall convergence between theory and experiment. Improvements to the theory have been obtained by identifying three classes of parameter, those (i) for both AES and XPS, such as electron transport, the methodology of evaluation of peak areas, and the spectrometer response function, (ii) for AES only, such as the electron ionization cross section, backscattering, and specific electron backgrounds, and (iii) for XPS only, such as the photon-ionization cross section. Additionally, the use of REELS data for background subtraction seems significantly better than the use of any one single Tougaard universal cross section in the determination of the AES and XPS intensities in the databases. The formalism for quantitative analysis in AES and XPS, using relative sensitivity factors, has been revised to develop an accurate matrix-less formalism that is very simple for use by the analyst. This formalism, involving “average matrix sensitivity factors” rather than “pure element sensitivity factors,” has the same accuracy as the matrix formalism but its simplicity permits ready extension to systems beyond binary.

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07.81.+a	Electron and ion spectrometers
79.20.Fv	Electron impact: Auger emission
82.80.Pv	Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.-i	Photoemission and photoelectron spectra

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Adsorption probabilities of CO on O–ZnO: A molecular beam study

Th. Becker, Ch. Boas, U. Burghaus, and Ch. Wöll

J. Vac. Sci. Technol. A 18, 1089 (2000); http://dx.doi.org/10.1116/1.582475 (4 pages) | Cited 3 times

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We present measurements of initial adsorption probabilities, S₀, as well as its coverage dependence, S(Θ_CO), of CO on oxygen terminated ZnO(0001). The impact energies of the CO (48 meV<E_i<750 meV) and surfaces temperature (75 K<T_S< 220 K) have been varied. The shape of the coverage dependent adsorption probability curves indicates the presence of precursor mediated adsorption. The heat of adsorption has been determined to (7–2 Θ_CO) kcal/mol by assuming a pre-exponential factor of 1×10¹³ l/s. © 2000 American Vacuum Society.

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68.03.Fg	Evaporation and condensation of liquids
68.43.Mn	Adsorption kinetics
79.20.Rf	Atomic, molecular, and ion beam impact and interactions with surfaces
79.60.Dp	Adsorbed layers and thin films

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Compositional heterogeneity in ceria-based mixed oxides observed by x-ray photoelectron spectroscopy

G. W. Graham, C. L. Roe, L. P. Haack, and A. M. Straccia

J. Vac. Sci. Technol. A 18, 1093 (2000); http://dx.doi.org/10.1116/1.582305 (3 pages) | Cited 3 times

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It is argued that compositional heterogeneity in certain reducible mixed oxides, like Ce_1−xZr_xO₂, can be inferred from a variation in the metals ratio, as measured by x-ray photoelectron spectroscopy, between fully oxidized and partially reduced states of the oxide, provided that the characteristic linear dimension of the heterogeneity is at least as large as the typical electron inelastic mean-free path. The argument is supported by experimental results from two examples involving mixed phases, one in which the length scale is 100 nm and the other in which the domains are too small for detection by standard x-ray diffraction. © 2000 American Vacuum Society.

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61.66.Bi	Elemental solids
61.66.Dk	Alloys
79.60.Bm	Clean metal, semiconductor, and insulator surfaces

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Characterization of zirconia coatings deposited by inductively coupled plasma assisted chemical vapor deposition

P. Colpo, G. Ceccone, P. Sauvageot, M. Baker, and F. Rossi

J. Vac. Sci. Technol. A 18, 1096 (2000); http://dx.doi.org/10.1116/1.582306 (6 pages) | Cited 5 times

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Thin films of zirconia have been deposited by an inductively coupled plasma assisted chemical vapor deposition reactor from a tetra (tert-butoxy)–zircon precursor diluted in Ar and O₂ gas mixture. An independent rf generator is used to carefully control the substrate negative bias voltage during the deposition. Zirconia thin films, with thickness up to 10 μm were deposited on Si(100) polished wafers under different plasma conditions. Correlation between deposition parameters and microstructure has been established showing that the ion bombardment has a large influence on the coating characteristics. In particular, the possibility of tailoring mechanical properties of the films by controlling the applied dc bias voltage is discussed. © 2000 American Vacuum Society.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
62.20.Qp	Friction, tribology, and hardness
81.40.Pq	Friction, lubrication, and wear
81.65.-b	Surface treatments
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
68.55.-a	Thin film structure and morphology
81.05.Je	Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

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Adhesion effect of polyimide passivation layer on lead-on-chip die attachment

T. Tom Jiang, Cynthia A. Bradbury, and Michael Canavan

J. Vac. Sci. Technol. A 18, 1102 (2000); http://dx.doi.org/10.1116/1.582307 (5 pages)

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Adequate die-to-lead frame adhesion is necessary for lead-on-chip (LOC) package integrity during and after the manufacturing process. Inadequate adhesion may result in a variety of defects such as die adhesion failure, marginal wire bond, broken wire, and bent leads, which ultimately lead to electrical failure [Mallik, US Patent No. 4,835,120 (May 1989); M. Amagai and E. Kawasaki, Mater. Res. Symp. Proc. 338, 185 (1994)]. Adhesion between the LOC tape and the polyimide passivation is affected by the surface properties of both materials. Understanding the relationships between these properties helps engineers eliminate inadequate adhesion at die attach and continuously improve the manufacturing process. To this end, die that exhibit inadequate adhesion at die attach are analyzed and compared with die that exhibit adequate adhesion characteristics. To focus on the surface chemistry and physical properties of the passivation layer, x-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, atomic force microscopy (AFM), and surface energy are used. Molecular concentrations and orientations are investigated and related to inadequate adhesion at die attach. © 2000 American Vacuum Society.

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81.65.Rv	Passivation
68.35.Gy	Mechanical properties; surface strains
46.55.+d	Tribology and mechanical contacts
85.40.Ls	Metallization, contacts, interconnects; device isolation

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Identification of surface chemical functional groups correlated to failure of reverse osmosis polymeric membranes

Sharon Beverly, Sudipta Seal, and Seungkwan Hong

J. Vac. Sci. Technol. A 18, 1107 (2000); http://dx.doi.org/10.1116/1.582308 (7 pages) | Cited 12 times

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The goal of this study is to identify the causes of membrane failure observed during a 15-month operation of a low pressure reverse osmosis (RO) membrane pilot plant to treat a highly organic surface water from the Hillsborough River in Tampa, Florida, using various surface analytical techniques. Three different commercial RO membranes, made of cellulose acetate or polyamide, were used in this pilot study, and all of these membranes showed performance deterioration presumably due to membrane fouling and degradation at given experimental conditions. In order to elucidate the mechanisms of membrane failure, scanning electron microscopy with energy dispersive spectrometry (SEM/EDS), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) were performed on the surface of the polymeric RO membranes used. More specifically, molecular composition including surface functional groups were identified from XPS analysis, confirmed by FTIR, and correlated to membrane failure. In addition, surface morphology and fouling layer composition were determined by SEM/EDS. The results indicated that the cellulose acetate membrane was biologically damaged, while the polyamide membrane was compromised by chlorine oxidation. The biodegradation of cellulose acetate was evidenced by the presence of nitrogen on XPS and FTIR scans. Chlorine uptake shown in XPS and FTIR scans of used polyamide membranes was a good indicator of chemical degradation. This study demonstrated that XPS, combined with FTIR and SEM/EDS, is a valuable diagnostic tool for failure analysis of polymeric RO membranes and provides valuable information to aid the manufacturers in designing better membranes for reverse osmosis. © 2000 American Vacuum Society.

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82.39.Wj	Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes
87.16.D-	Membranes, bilayers, and vesicles
79.60.Fr	Polymers; organic compounds
68.35.Dv	Composition, segregation; defects and impurities
78.30.Jw	Organic compounds, polymers

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Self-assembled monolayers for polymer and protein cationization with time-of-flight secondary ion mass spectrometry

Roger Michel, Reto Luginbühl, Daniel J. Graham, and Buddy D. Ratner

J. Vac. Sci. Technol. A 18, 1114 (2000); http://dx.doi.org/10.1116/1.582309 (5 pages) | Cited 4 times

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Detection of cationized polymers and proteins with time-of-flight secondary ion mass spectrometry has been achieved using novel substrates consisting of carboxylic acid terminated self-assembled monolayers (SAMs) with silver ion substituted headgroups. However, other metal ions (Na, Cu, Tl, or Li) as SAM headgroups can be used as well. Polymers were deposited on the metal ion derivatized SAMs by spin coating while proteins were adsorbed onto the substrates. Control experiments carried out on nonsubstituted and methyl-terminated SAMs suggest that only metal ions in close proximity to the polymer can cationize the molecules and their fragments. Both cationized fragments and whole molecular species were observed for 1 kD polyethyleneoxide and low molecular weight proteins (<2 kD). © 2000 American Vacuum Society.

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82.35.-x	Polymers: properties; reactions; polymerization
87.14.E-	Proteins
87.15.K-	Molecular interactions; membrane-protein interactions
68.18.-g	Langmuir-Blodgett films on liquids
68.43.-h	Chemisorption/physisorption: adsorbates on surfaces
82.80.Ms	Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

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Sputter deposition and annealing of Ta, TaSi_x and TaB_x composite films and their application in next generation lithography masks

Kenneth Racette, Cameron Brooks, C. Richard Guarnieri, and Dennis Hendy

J. Vac. Sci. Technol. A 18, 1119 (2000); http://dx.doi.org/10.1116/1.582310 (6 pages) | Cited 2 times

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Ta and Ta composites with other elements have been developed as low stress absorbers for x-ray mask technology. These thin films are often produced in small quantities by sputter deposition from targets of pure Ta with chips of the minor elements placed on the target to create the composites. For membrane-mask manufacturing it is important that absorber films have uniform composition, thickness, and low, uniform stress to assure that image size and pattern placement errors are minimal. Since sputtered films containing Ta often have highly compressive stress, several methods have been used to reduce the final stress, including careful control of sputtering conditions, deposition of layered films with different stresses, and thermal annealing. Much data has been reported regarding the effects of thermal annealing of Ta films but less information is available on multiple element films such as TaSi_x and TaB_x. Previous reports on these materials have generally not discussed the behavior of these films under long term, higher volume manufacturing conditions. During the last several years IBM has been engaged in development and fabrication of refractory x-ray membrane masks using Ta composites as absorber materials. Films were sputter deposited from hot isostatically pressed powder targets of Ta, Si, and B using an S-gun magnetron cluster deposition system. This article reports on the deposition and annealing of these films and their application to membrane-mask fabrication in a manufacturing environment. The effects of deposition parameters such as dc power, argon gas pressure, and substrate composition on film stress, composition, and density are discussed. The results of nitrogen annealing on TaSi_x and TaB_x films are presented. Absorber film quality data and its impact on image size, image placement, and defect density of some x-ray masks is presented. © 2000 American Vacuum Society.

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81.15.Cd	Deposition by sputtering
85.40.Hp	Lithography, masks and pattern transfer
61.72.Cc	Kinetics of defect formation and annealing

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Model for detection of immobilized superparamagnetic nanosphere assay labels using giant magnetoresistive sensors

Mark Tondra, Marc Porter, and Robert J. Lipert

J. Vac. Sci. Technol. A 18, 1125 (2000); http://dx.doi.org/10.1116/1.582476 (5 pages) | Cited 39 times

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Commercially available superparamagnetic nanospheres are commonly used in a wide range of biological applications, particularly in magnetically assisted separations. A new and potentially significant technology involves the use of these particles as labels in magnetoresistive assay applications. In these assays, magnetic bead labels are used like fluorescent labels except that the beads are excited and detected with magnetic fields rather than with photons. A major advantage of this technique is that the means for excitation and detection are easily integrable on a silicon circuit. A preliminary study of this technique demonstrated its basic feasibility, and projected a sensitivity of better than 10⁻¹² molar [Baselt et al., Biosensors Bioelectronic 13, 731 (1998)]. In this article we examine the theoretical signal to noise ratio of this type of assay for the special case of a single magnetic bead being detected by a single giant magnetoresistive (GMR) detector. Assuming experimentally observed and reasonable parameters for the magnetic label and the sensitivity of the GMR detector, the signal to noise ratio is calculated to be greater than 5000:1 for detection of a single 1 μm diameter magnetic microsphere immobilized on the surface of a 1 μm×1 μm GMR sensor. Based on this large signal to noise ratio, the detection format should be applicable to more complicated assays where linear quantification is required or to assays requiring significantly smaller beads. Detection of microsphere labels approaching 10 nm may be possible upon further technological advances. © 2000 American Vacuum Society.

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75.50.Tt	Fine-particle systems; nanocrystalline materials
75.47.De	Giant magnetoresistance
75.50.Kj	Amorphous and quasicrystalline magnetic materials
07.55.-w	Magnetic instruments and components
87.80.-y	Biophysical techniques (research methods)

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Selective area growth of GaN on Si(111) by chemical beam epitaxy

Esther Kim, A. Tempez, N. Medelci, I. Berishev, and A. Bensaoula

J. Vac. Sci. Technol. A 18, 1130 (2000); http://dx.doi.org/10.1116/1.582311 (5 pages)

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We demonstrate the selective area growth of GaN on SiO₂-masked AlN/Si(111) and GaN/AlN/Si(111) wafers by chemical beam epitaxy (CBE) using triethyl gallium and ammonia. We investigated the selective nucleation process on Si wafers with oxide and nitride masks. The selectivity of the nucleation process was monitored in real time using time-of-flight mass spectroscopy of recoiled ions (TOF-MSRI). Our results show that TOF-MSRI peaks from mask-corresponding elements (Si and O or N) remain unchanged during GaN regrowth on continuous SiO₂ layers or nitridated Si(111) within the condition range we explored. The selective growth was confirmed by ex situ scanning electron microscopy analysis. We also found that, depending on the growth conditions, CBE can be used for selective growth of both microcolumnar and planar GaN films. Room temperature photoluminescence studies revealed that both types of films are optically active, which could potentially lead to novel device concepts and applications. © 2000 American Vacuum Society.

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81.05.Ea	III-V semiconductors
68.55.-a	Thin film structure and morphology
81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy

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High breakdown voltage Au/Pt/GaN Schottky diodes

G. T. Dang, A. P. Zhang, M. M. Mshewa, F. Ren, J.-I. Chyi, C.-M. Lee, C. C. Chuo, G. C. Chi, J. Han, S. N. G. Chu, R. G. Wilson, X. A. Cao, and S. J. Pearton

J. Vac. Sci. Technol. A 18, 1135 (2000); http://dx.doi.org/10.1116/1.582312 (4 pages) | Cited 7 times

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Au/Pt/GaN Schottky diode rectifiers were fabricated with reverse breakdown voltage (V_RB) up to 550 V on vertically depleting structures and >2000 V on lateral devices. The figure-of-merit (V_RB)²/R_ON, where R_ON is the on-state resistance, had values between 4.2 and 4.8 MW cm⁻². The reverse leakage currents and forward on-voltages were still somewhat higher than the theoretical minimum values, but were comparable to SiC Schottky rectifiers reported in the literature. These devices show promise for use in ultrahigh-power switches. © 2000 American Vacuum Society.

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85.30.Hi	Surface barrier, boundary, and point contact devices
85.30.Kk	Junction diodes
81.05.Ea	III-V semiconductors
84.70.+p	High-current and high-voltage technology: power systems; power transmission lines and cables

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Inductively coupled plasma-induced etch damage of GaN p-n junctions

R. J. Shul, L. Zhang, A. G. Baca, C. G. Willison, J. Han, S. J. Pearton, and F. Ren

J. Vac. Sci. Technol. A 18, 1139 (2000); http://dx.doi.org/10.1116/1.582313 (5 pages) | Cited 17 times

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Plasma-induced etch damage can degrade the electrical and optical performance of III–V nitride electronic and photonic devices. We have investigated the etch-induced damage of an inductively coupled plasma (ICP) etch system on the electrical performance of mesa-isolated GaN pn-junction diodes. GaN positive-insulating-negative mesa diodes were formed by Cl₂/BCl₃/Ar ICP etching under different plasma conditions. The reverse leakage current in the mesa diodes showed a strong relationship to chamber pressure, ion energy, and plasma flux. Plasma induced damage was minimized at moderate flux conditions (⩽500 W), pressures ⩾2 mTorr, and at ion energies below approximately −275 V. © 2000 American Vacuum Society.

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81.05.Ea	III-V semiconductors
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
81.65.Cf	Surface cleaning, etching, patterning
79.20.Rf	Atomic, molecular, and ion beam impact and interactions with surfaces

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Schottky diode measurements of dry etch damage in n- and p-type GaN

X. A. Cao, A. P. Zhang, G. T. Dang, F. Ren, S. J. Pearton, R. J. Shul, and L. Zhang

J. Vac. Sci. Technol. A 18, 1144 (2000); http://dx.doi.org/10.1116/1.582314 (5 pages) | Cited 16 times

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n- and p-type GaN was exposed to inductively coupled plasma of N₂, H₂, Ar, or Cl₂/Ar, as a function of source power (0–1000 W) and rf chuck power (20–250 W). For n-GaN, there was a strong reduction in diode reverse breakdown voltage and an increase in forward and reverse currents, while for p-GaN the reverse breakdown voltage increased. These results are consistent with creation of point defects with shallow donor nature that increase the conductivity of initially n-type GaN or decrease the conductivity of p-type GaN. Annealing at 750 °C under N₂ produced significant recovery of the electrical properties, while wet etch removal of 500–600 Å of the surface produced a full recovery. For completed n-type mesa diodes exposed to Ar or Cl₂/Ar discharges, the low bias forward currents increased by several orders of magnitude. The exposed surfaces became N₂ deficient in all cases. © 2000 American Vacuum Society.

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81.65.Cf	Surface cleaning, etching, patterning
81.05.Ea	III-V semiconductors
85.30.Hi	Surface barrier, boundary, and point contact devices
85.30.Kk	Junction diodes
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition

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Effect of N₂ discharge treatment on AlGaN/GaN high electron mobility transistor ohmic contacts using inductively coupled plasma

A. P. Zhang, G. T. Dang, F. Ren, J. M. Van Hove, J. J. Klaassen, P. P. Chow, X. A. Cao, and S. J. Pearton

J. Vac. Sci. Technol. A 18, 1149 (2000); http://dx.doi.org/10.1116/1.582315 (4 pages) | Cited 6 times

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The contact resistance of Ti/Al/Pt/Au metallization on AlGaN/GaN high electron mobility transistors was measured as a function of plasma exposure conditions prior to metal deposition. Inductively coupled plasma N₂ discharges were used to create nitrogen-deficient near-surface regions in the AlGaN/GaN structures. At modest ion fluxes (∼4×10¹⁶ cm² s⁻¹) and low ion energies (125 eV), there was no detectable surface roughening of the AlGaN. Under optimized conditions, the plasma treatment reduces the ohmic contact resistance by a factor of approximately 3. © 2000 American Vacuum Society.

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85.30.Tv	Field effect devices
73.40.Ns	Metal-nonmetal contacts
81.65.Cf	Surface cleaning, etching, patterning
73.61.Ey	III-V semiconductors
81.05.Ea	III-V semiconductors
73.40.Cg	Contact resistance, contact potential
85.40.Ls	Metallization, contacts, interconnects; device isolation
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
79.20.Rf	Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.Cc	Kinetics of defect formation and annealing

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Scanning tunneling microscopy study of surface morphology of Si(111) after synchrotron radiation stimulated desorption of SiO₂

Y. Gao, H. Mekaru, T. Miyamae, and T. Urisu

J. Vac. Sci. Technol. A 18, 1153 (2000); http://dx.doi.org/10.1116/1.582316 (5 pages) | Cited 3 times

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The surface morphology of Si(111) was investigated using scanning tunneling microscopy after desorption of surface SiO₂ by synchrotron radiation illumination. The surface shows large regions of an atomically flat Si(111)-7×7 structure, and is characterized by the formation of single bilayer steps nicely registered to the crystal structure. This is in sharp contrast to Si(111) surfaces after thermal desorption of SiO₂ at temperatures of 880 °C and above, where the surface steps are much more irregular. X-ray photoemission spectroscopy is also used to investigate the process of synchrotron radiation stimulated desorption. © 2000 American Vacuum Society.

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68.35.B-	Structure of clean surfaces (and surface reconstruction)
81.05.Cy	Elemental semiconductors
68.03.Fg	Evaporation and condensation of liquids
68.43.Mn	Adsorption kinetics
79.20.La	Photon- and electron-stimulated desorption
79.60.Dp	Adsorbed layers and thin films

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Investigation of titanium nitride gates for tantalum pentoxide and titanium dioxide dielectrics

D. Gilmer, C. Hobbs, R. Hegde, L. La, O. Adetutu, J. Conner, M. Tiner, L. Prabhu, S. Bagchi, and P. Tobin

J. Vac. Sci. Technol. A 18, 1158 (2000); http://dx.doi.org/10.1116/1.582317 (5 pages) | Cited 4 times

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The compatibility of metallic titanium nitride (TiN) as a gate electrode on TiO₂ and Ta₂O₅ gate dielectrics is investigated by rapid thermal annealing (RTA). The electrical and physical properties are characterized using I–V measurements and transmission electron microscopy. TiN/TiO₂ capacitors are electrically stable up to at least 800 °C for 90 s. However, the leakage density for TiN/Ta₂O₅ capacitors is increased by an 850 °C, 60 s RTA. Both TiN/TiO₂ and TiN/Ta₂O₅ capacitors display a large increase in leakage density after a 1025 °C, 20 s RTA. © 2000 American Vacuum Society.

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77.55.-g	Dielectric thin films
61.72.Cc	Kinetics of defect formation and annealing
73.40.Qv	Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt	Capacitors
61.80.Ba	Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Fv	Electron impact: Auger emission

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Separate and independent reductions in direct tunneling in oxide/nitride stacks with monolayer interface nitridation associated with the (i) interface nitridation and (ii) increased physical thickness

G. Lucovsky, Y. Wu, H. Niimi, H. Yang, J. Keister, and J. E. Rowe

J. Vac. Sci. Technol. A 18, 1163 (2000); http://dx.doi.org/10.1116/1.582318 (6 pages) | Cited 17 times

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Direct tunneling limits aggressive scaling of thermally grown oxides to about 1.6 nm, a thickness at which the tunneling current density J_g at 1 V is ∼1 A/cm². This article demonstrates that stacked gate dielectrics prepared by remote plasma processing and including (i) ultrathin nitrided SiO₂ interfacial layers and (ii) either silicon nitride or oxynitride bulk dielectrics can extend the equivalent oxide thickness to 1.1–1.0 nm before J_g exceeds 1 A/cm². Significant reductions in direct tunneling are derived from (i) interface nitridation at the monolayer level and (ii) the increased physical thickness of the nitride or oxynitride alloy layers. The “portability” of the interface contribution is demonstrated by combining the nitrided SiO₂ interface layers with transition-metal oxides, e.g., Ta₂O₅, in stacked gate dielectric structures and obtaining essentially the same reductions in tunneling current on n- and p-type substrates with respect to non-nitrided plasma-grown interface layers. © 2000 American Vacuum Society.

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73.61.Ng	Insulators
73.40.Gk	Tunneling

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Comparison of plasma chemistries for dry etching of Ta₂O₅

K. P. Lee, K. B. Jung, R. K. Singh, S. J. Pearton, C. Hobbs, and P. Tobin

J. Vac. Sci. Technol. A 18, 1169 (2000); http://dx.doi.org/10.1116/1.582319 (4 pages) | Cited 3 times

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Inductively coupled plasma etching of Ta₂O₅ was performed in a variety of different chemistries, including SF₆ with additions of O₂, Ar, CH₄ or H₂; Cl₂/Ar; N₂/Ar; and CH₄/H₂/Ar. Etch rates up to ∼1200 Å min⁻¹ were achieved with either SF₆- or Cl₂-based chemistries. Under these conditions the etch rates for Si were approximately four to seven times faster, although equirate etching was achieved at low source powers and low halogen gas percentages in the plasma chemistry. The etched Ta₂O₅ surfaces were smooth (root mean square roughness ⩽0.5 nm) over a broad range of conditions of source power, chuck power, and process pressure. The etch rates with N₂/Ar and CH₄/H₂/Ar were an order of magnitude lower than with SF₆ or Cl₂. There was no effect of postdeposition annealing on the Ta₂O₅ etch rates, at least up to 800 °C. © 2000 American Vacuum Society.

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82.33.Xj	Plasma reactions (including flowing afterglow and electric discharges)
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
81.65.Cf	Surface cleaning, etching, patterning
82.20.Pm	Rate constants, reaction cross sections, and activation energies
68.35.B-	Structure of clean surfaces (and surface reconstruction)

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Study of the impact of the time-delay effect on the critical dimension of a tungsten silicide/polysilicon gate after reactive ion etching

Shih-Po Lin, Chen-Hsien Ou, Szetsen Lee, Yu-Chung Tien, and Chin-Fa Hsu

J. Vac. Sci. Technol. A 18, 1173 (2000); http://dx.doi.org/10.1116/1.582320 (3 pages)

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The addition of HBr has been used with oxygen and chlorine-based chemistries to improve selectivity of polysilicon to gate oxide in gate-stack etching. As a consequence of high selectivity, polymer residues become a major factor in critical-dimension (CD) control. It is believed that the presence of HBr in the plasma is responsible for polymer formation. HBr and its polymer residues may induce surface reactions to form thin oxide layers. Such a phenomenon has been observed if the wafers are not treated with HF vapor immediately after reactive ion etching (RIE) of the gate. The magnitude of the oxide film growth is proportional to the delayed time between RIE and HF vapor treatment. The sidewall thickness of the gate is also affected by the time-delay effect. The growth of the oxide film on the sidewalls can eventually affect the gate CD, and thus the device performance. A simple reaction model for the growth of the oxide film is proposed to explain the correlation between delayed time and CD bias. © 2000 American Vacuum Society.

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81.65.Cf	Surface cleaning, etching, patterning
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
85.40.Ls	Metallization, contacts, interconnects; device isolation
68.35.Dv	Composition, segregation; defects and impurities
73.20.Mf	Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
82.33.Xj	Plasma reactions (including flowing afterglow and electric discharges)
82.20.Wt	Computational modeling; simulation

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Formation of Ni silicides on (001)Si with a thin interposing Pt layer

L. W. Cheng, S. L. Cheng, L. J. Chen, H. C. Chien, H. L. Lee, and F. M. Pan

J. Vac. Sci. Technol. A 18, 1176 (2000); http://dx.doi.org/10.1116/1.582321 (4 pages) | Cited 12 times

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The formation of Ni silicides on (001)Si with a thin interposing Pt layer has been investigated. NiSi was observed to be the only silicide phase for the samples annealed at 500–800 °C with a thin interposing Pt layer. The sheet resistance maintained the same low level in a wide temperature range. Pt addition was found to retard significantly the formation of nickel silicides and enhance the thermal stability of NiSi thin films on (001)Si. For Ni(30 nm)/Pt(1.5 nm)/(001)Si, the process window of NiSi was extended to 500–800 °C. The effects of a thin interposing Pt layer on the formation of Ni silicides on (001)Si are discussed. © 2000 American Vacuum Society.

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68.35.Fx	Diffusion; interface formation
61.72.Cc	Kinetics of defect formation and annealing
79.20.Fv	Electron impact: Auger emission

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Silicon nanodots fabricated on a Si(100) surface via thermal nitridation and oxygen etching reactions

Jeong Sook Ha, Kang-Ho Park, and Wan Soo Yun

J. Vac. Sci. Technol. A 18, 1180 (2000); http://dx.doi.org/10.1116/1.582322 (4 pages) | Cited 1 time

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Silicon nanodots with very uniform sizes have been fabricated on a Si(100) surface via a thermal nitridation followed by oxygen etching reaction. N₂ gas was exposed to a clean Si(100) surface at 800 °C and this surface was subsequently reacted with O₂ gas at 700 °C. Scanning tunneling microscope measurement of surface morphology showed that silicon nanodots with an average size of 5 nm were formed as a result of selective oxygen etching of the silicon surface. Silicon nitride islands of a few nanometers acted successfully as masks against oxygen etching at high temperatures. The number density of silicon nanodots is estimated to be 1×10¹²/cm². The lowering of nitridation temperature to 700 °C resulted in similar silicon nanodots with a little bit smaller sizes, indicating that silicon nitride islands formed even at this temperature can be successfully used as masks for oxygen exposure. Owing to the relatively low thermal mobility of nitrogen species, Si nanodots with uniform sizes could be obtained on the Si(100) substrate. © 2000 American Vacuum Society.

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81.05.Cy	Elemental semiconductors
81.07.-b	Nanoscale materials and structures: fabrication and characterization
68.37.Ef	Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps	Atomic force microscopy (AFM)
68.37.Rt	Magnetic force microscopy (MFM)
68.37.Uv	Near-field scanning microscopy and spectroscopy
68.65.-k	Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w	Structure of nanoscale materials

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Real-time optical characterization of heteroepitaxy by organometallic chemical vapor deposition

K. A. Bell, M. Ebert, S. D. Yoo, K. Flock, and D. E. Aspnes

J. Vac. Sci. Technol. A 18, 1184 (2000); http://dx.doi.org/10.1116/1.582323 (6 pages) | Cited 9 times

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Heteroepitaxy of GaP on Si(100) and GaAs(100) is investigated under organometallic chemical vapor deposition conditions using combined spectroscopic ellipsometry (SE) and non-normal-incidence reflectance-difference (-anisotropy) spectroscopy. Real-time monitoring greatly assists in identifying optimum starting surfaces for heteroepitaxy since prolonged exposure to PH₃ results in roughening of Si(100) and GaAs(100) surfaces, in agreement with previous work. Real-time SE data of GaP on Si indicate that under our conditions GaP and Si interpenetrate as optically identifiable materials over the first 75 Å, suggesting that either trimethylgallium or a reaction by-product can act as a catalyst for the formation of Si{111} facets. © 2000 American Vacuum Society.

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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
68.55.-a	Thin film structure and morphology
81.05.Ea	III-V semiconductors
78.66.Fd	III-V semiconductors
07.60.Fs	Polarimeters and ellipsometers
78.20.Bh	Theory, models, and numerical simulation
68.35.B-	Structure of clean surfaces (and surface reconstruction)

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Real-time thickness and compositional control of Ga_1−xIn_xP growth using p-polarized reflectance

V. Woods, N. Dietz, K. Ito, and I. Lauko

J. Vac. Sci. Technol. A 18, 1190 (2000); http://dx.doi.org/10.1116/1.582469 (6 pages)

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Advances in the engineering and design of advanced electro-optical materials require sensors and control strategies that allow tight control over thickness and composition of multilayered structures. In response to this demand, we developed and applied p-polarized reflectance (PR) for real-time optical characterization and control of heteroepitaxial GaP/GaInP growth under pulsed chemical beam epitaxy conditions. For closed-loop control, we applied nonlinear control algorithms (based on nonlinear Kalman filtering) that utilizes the PR signals to adjust the source flows involved in the heteroepitaxial growth of Ga_1−xIn_xP on Si(001). A reduced order surface kinetics model has been formulated to establish the linkage between the surface reaction kinetic and its optical response. These data are linked to compute the compositional and thickness change per time unit, utilizing the monitored PR signals for validation. This allows the establishment of feedback control algorithms, able to control both the growth rate and composition of Ga_1−xIn_xP heterostructures. © 2000 American Vacuum Society.

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81.05.Ea	III-V semiconductors
81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd	III-V semiconductors

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Deposition of polycrystalline Si and SiGe by ultra-high vacuum chemical molecular epitaxy

K. M. Chen, H. J. Huang, C. Y. Chang, L. P. Chen, and G. W. Huang

J. Vac. Sci. Technol. A 18, 1196 (2000); http://dx.doi.org/10.1116/1.582324 (6 pages) | Cited 1 time

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The polycrystalline Si_1−xGe_x (poly-Si_1−xGe_x) films have better properties than poly-Si for device fabrications, such as lower proceeding temperature and process thermal budget. For these reasons, the poly-Si_1−xGe_x films have been utilized for low-temperature thin film transistor fabrications and gate electrodes of metal–oxide–semiconductor transistors. In this work, disilane and germane were used to grow poly-Si_1−xGe_x films at low temperature (<600 °C) by the cold-wall type ultrahigh vacuum chemical molecular epitaxy system. The poly-Si_1−xGe_x films were deposited on oxide and nitride surfaces. The Ge fraction x was evaluated from x-ray diffraction and Auger electron spectroscopy. It is observed that the Ge fraction increases with the increase of the GeH₄ flow rate. The result is only slightly related to the substrate type. The growth rate increases with the Ge fraction at lower values and then decreases with the Ge fraction in the higher composition range. This implies that the growth mechanism of poly-Si_1−xGe_x films is different from that of epitaxial Si_1−xGe_x on Si. The uniformity of poly-Si_1−xGe_x films depends on the Ge fraction, and it is improved by the addition of germanium. The result can be explained by the lower activation energy (<0.25 eV) of poly-Si_1−xGe_x deposition as compared to that of poly-Si (∼2.1 eV). From the x-ray diffraction and atomic force microscopy analyses, the crystallinity and surface roughness of films are suitable for device fabrications. © 2000 American Vacuum Society.

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81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
81.05.Hd	Other semiconductors
81.05.Cy	Elemental semiconductors
79.20.Fv	Electron impact: Auger emission
68.55.-a	Thin film structure and morphology
68.55.Nq	Composition and phase identification
68.35.B-	Structure of clean surfaces (and surface reconstruction)
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk	Vapor phase epitaxy; growth from vapor phase

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Strength of nanoscale copper under shear

P. Heino, P. Holloway, and E. Ristolainen

J. Vac. Sci. Technol. A 18, 1202 (2000); http://dx.doi.org/10.1116/1.582325 (5 pages) | Cited 1 time

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Properties and processing of copper have received much interest among the electronics community mainly because of its low electrical resistance. One of its important application fields is in electrical interconnections. Mechanical properties of such nanoscale copper connections are, however, not well known and understood. In this article we study the effects of shear strain and stress in several nanoscale copper systems consisting of about 200 000 atoms with the effective-medium theory and molecular dynamics method. The role of polycrystalline microstructure on the shear strength is analyzed. It seems that the strength decreases as the grain size decreases, in contrast to macroscopic systems. In single crystals we study dislocation initiation and propagation. The results indicate that both sub- and supersonic dislocations may be present in copper. The minimum stress and strain, at which a dislocation initiated in a single crystal was 1.2 GPa and 4.6%. These values can be much larger than the values for a large scale copper sample, since polycrystalline microstructure was seen to decrease the system strength. © 2000 American Vacuum Society.

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81.40.Jj	Elasticity and anelasticity, stress-strain relations
85.40.Ls	Metallization, contacts, interconnects; device isolation
62.20.F-	Deformation and plasticity
61.72.Bb	Theories and models of crystal defects
61.72.Lk	Linear defects: dislocations, disclinations
61.46.-w	Structure of nanoscale materials
81.07.-b	Nanoscale materials and structures: fabrication and characterization

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Effects of a new combination of additives in electroplating solution on the properties of Cu films in ULSI applications

J. C. Hu, T. C. Chang, C. W. Wu, L. J. Chen, C. S. Hsiung, W. Y. Hsieh, W. Lur, and T. R. Yew

J. Vac. Sci. Technol. A 18, 1207 (2000); http://dx.doi.org/10.1116/1.582326 (4 pages) | Cited 12 times

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Effects of a new combination of additives in acid electroplating solution on the properties of Cu thin films have been investigated. The electroplated Cu films exhibit an excellent superfilling behavior. 0.18 μm vias with an aspect ratio exceeding 5 were filled completely without any void or seam. Strong (111) texture was found for the electroplated Cu films. The resistivity of a 450-nm-thick Cu film was measured to be 1.84 μΩ cm. © 2000 American Vacuum Society.

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81.15.Pq	Electrodeposition, electroplating
85.40.Ls	Metallization, contacts, interconnects; device isolation
68.55.-a	Thin film structure and morphology

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Surface modification and cleaning enhancement of TaSi(N) films with dilute hydrofluoric acid

P. J. S. Mangat, W. J. Dauksher, R. Whig, and W. L. O’Brien

J. Vac. Sci. Technol. A 18, 1211 (2000); http://dx.doi.org/10.1116/1.582327 (5 pages) | Cited 3 times

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Amorphous TaSi(N) alloy films are of great interest for application in the fabrication of reticles for next generation lithography and for incorporation into semiconductor devices as barrier layers for Cu processing. The stress characteristics of TaSi(N) films are critical when used as an absorber on x-ray and extreme ultraviolet lithography masks, or as a scatterer for electron projection lithography masks. One little understood, but critical characteristic of these films, is that they undergo a stress change towards a less tensile or more compressive state upon interaction with a buffered oxide etch (BOE). We have investigated the cause of this behavior using synchrotron radiation based high-resolution core level (Ta 4f and Si 2p) photoemission spectroscopy. Our results indicate that, upon interaction with a BOE, the surface oxide undergoes a major reorganization and the Ta gets heavily oxidized, resulting in the formation of Ta₂O₅. Such a reaction would lead to a buildup of strain in the oxidized region, which we interpret as being the contributing factor for the observed stress changes in the TaSi(N) thin films. Furthermore, annealing the surface results in a significant reduction of the oxide desorbtion temperature from 650 to 450 °C due to the HF interaction. This can be attributed to a change in the bonding configuration by HF, wherein the Si–O bonds are broken and weak Ta–O bonds are formed, causing the loosely bonded oxide to desorb at lower temperatures. © 2000 American Vacuum Society.

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81.65.Cf	Surface cleaning, etching, patterning
85.40.Hp	Lithography, masks and pattern transfer
68.60.Bs	Mechanical and acoustical properties
79.60.Dp	Adsorbed layers and thin films
68.55.-a	Thin film structure and morphology
61.43.-j	Disordered solids
73.20.-r	Electron states at surfaces and interfaces
81.65.Mq	Oxidation
82.65.+r	Surface and interface chemistry; heterogeneous catalysis at surfaces
68.03.Fg	Evaporation and condensation of liquids
68.43.Mn	Adsorption kinetics
68.43.-h	Chemisorption/physisorption: adsorbates on surfaces

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Low-k Si–O–C–H composite films prepared by plasma-enhanced chemical vapor deposition using bis-trimethylsilylmethane precursor

Yoon-Hae Kim, Seok-Kiu Lee, and Hyeong Joon Kim

J. Vac. Sci. Technol. A 18, 1216 (2000); http://dx.doi.org/10.1116/1.582328 (4 pages) | Cited 59 times

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Low-k Si–O–C–H composite films were prepared using bis-trimethylsilylmethane as a precursor and oxygen in a rf plasma reactor. The growth rate of the Si–O–C–H composite film followed a second-order exponential decay function. This behavior could be explained by the formation of nanosized voids due to Si–CH₃ and OH-related bonds included in the film. OH-related bonds were detected in films deposited at 30 °C, but could not be observed for the films deposited above 60 °C. In contrast, Si–CH₃ bonds were also detected at 30 °C, but decreased monotonically up to 210 °C and were absent of higher temperatures. After postannealing the film deposited at 30 °C, the Si–CH₃ bonds were unchanged, but the OH-related bonds were easily removed. This film showed a low dielectric constant of 2.44 and leakage current density of 4.4×10⁻⁷ A/cm² at 1 MV/cm. © 2000 American Vacuum Society.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.55.-g	Dielectric thin films
61.72.Qq	Microscopic defects (voids, inclusions, etc.)
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
68.55.Ln	Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc	Kinetics of defect formation and annealing
81.40.Gh	Other heat and thermomechanical treatments
77.22.Ch	Permittivity (dielectric function)
73.61.Ng	Insulators

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Advanced selective dry etching of GaAs/AlGaAs in high density inductively coupled plasmas

J. W. Lee, M. W. Devre, B. H. Reelfs, D. Johnson, J. N. Sasserath, F. Clayton, D. Hays, and S. J. Pearton

J. Vac. Sci. Technol. A 18, 1220 (2000); http://dx.doi.org/10.1116/1.582329 (5 pages) | Cited 19 times

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We report a breakthrough for selective etching of GaAs over Al_xGa_1−xAs, x=0.2, layer with a high density plasma source. This result is particularly important for III–V devices such as heterojunction bipolar transistors (HBTs) or high electron mobility transistors (HEMTs). For example, fabrication of HBTs requires a process for selective etching of a GaAs contact layer while stopping on AlGaAs layer. Inductively coupled plasma (ICP) etching with BCl₃/SF₆/N₂/He chemistries showed extremely high selectivity of GaAs over AlGaAs (>200:1) and a photoresist (>10:1). This process also produced excellent sidewall passivation on GaAs with reasonably high rate (>1500 Å /min.). Both scanning electron microscope and atomic force microscope data showed AlGaAs etch stop layer was quite smooth after processing. We found that He played a key role in enhancing selectivity and obtaining smooth AlGaAs surfaces. When used with resist masks, addition of N₂ into BCl₃/SF₆ plasma helped formation of passivation on the sidewall and maintained high anisotropy. An optimized condition with BCl₃/SF₆/N₂/He ICP plasmas showed excellent pattern transfer into GaAs with high rate, anisotropy, and selectivity. © 2000 American Vacuum Society.

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81.05.Ea	III-V semiconductors
73.40.Kp	III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
81.65.Cf	Surface cleaning, etching, patterning

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Characterization of plasma enhanced chemical vapor deposited SiC and its application in advanced reticle technology–scattering with angular limitation in projection electron beam lithography membrane

S.-I. Han, P. J. S. Mangat, S. M. Smith, W. J. Dauksher, D. Convey, and R. B. Gregory

J. Vac. Sci. Technol. A 18, 1225 (2000); http://dx.doi.org/10.1116/1.582330 (5 pages) | Cited 1 time

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In scattering with angular limitation in projection electron beam lithography (SCALPEL) mask technology, the choice of membrane material is an important issue from the perspective of mask performance and manufacturing. Low-pressure chemical vapor deposition SiN has been widely employed for SCALPEL membranes because of its excellent manufacturability and other material properties. However, amorphous plasma enhanced chemical vapor deposition SiC:H has a good potential for the membrane material, and we have developed an optimized process to deposit the SiC films for mask fabrication. © 2000 American Vacuum Society.

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85.40.Hp	Lithography, masks and pattern transfer
81.05.Gc	Amorphous semiconductors
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

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New approach for the fabrication of device-quality Ge/GeO₂/SiO₂ interfaces using low temperature remote plasma processing

R. S. Johnson, H. Niimi, and G. Lucovsky

J. Vac. Sci. Technol. A 18, 1230 (2000); http://dx.doi.org/10.1116/1.582331 (4 pages) | Cited 17 times

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It has been shown that low temperature (300 °C) remote plasma enhanced processing can separately and independently control interface formation and bulk oxide deposition on silicon substrates. Plasma processing is followed by a low thermal budget thermal anneal, e.g., 30 s at 900 °C. In this article, this process has been modified and applied to germanium substrates to determine if it can provide a successful pathway to device-quality Ge–dielectric interfaces. The new process also employs a three-step process: (i) an O₂/He plasma-assisted, predeposition oxidation of the germanium surface to form a superficial germanium–oxide passivating film, (ii) deposition of a SiO₂ bulk film by remote plasma-enhanced chemical vapor deposition from SiH₄ and O₂, and (iii) a postdeposition anneal for chemical and structural relaxation. The resulting interfaces are improved by the predeposition, plasma-assisted oxidation step, but are still far too defective for device applications. © 2000 American Vacuum Society.

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81.65.Mq	Oxidation
81.05.Cy	Elemental semiconductors
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
68.35.Ct	Interface structure and roughness
61.72.Cc	Kinetics of defect formation and annealing
81.40.Gh	Other heat and thermomechanical treatments
81.65.Rv	Passivation
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

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Multicolor-emitting thin-film electroluminescent devices using Ga₂O₃ phosphors co-doped with Mn and Cr

Tadatsugu Minami, Toshikuni Nakatani, and Toshihiro Miyata

J. Vac. Sci. Technol. A 18, 1234 (2000); http://dx.doi.org/10.1116/1.582332 (5 pages) | Cited 7 times

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High-luminance multicolor-emitting thin-film electroluminescent (TFEL) devices have been developed using a new Mn- and Cr-co-doped Ga₂O₃ phosphor with variations of both Mn and Cr from 0 to a content of 20 at. %. Ga₂O₃:Mn,Cr TFEL devices driven at 1 kHz exhibited a change from green to red in emission color, maintaining luminances above 100 cd/m², when the co-doped Cr content was varied from 0 to 20 at. % under a constant Mn content of 0.3 at. % doping. In addition, the emission color of a Ga₂O₃:Mn,Cr TFEL device co-doped with a Mn content of 0.3 at. % and a Cr content of 3 at. % changed from green to red with an increase of the applied voltage. © 2000 American Vacuum Society.

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85.60.Jb	Light-emitting devices
78.60.Fi	Electroluminescence
78.66.Nk	Insulators

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Intrinsic and extrinsic magnetic properties of the naturally layered manganites

A. Berger, J. F. Mitchell, D. J. Miller, J. S. Jiang, and S. D. Bader

J. Vac. Sci. Technol. A 18, 1239 (2000); http://dx.doi.org/10.1116/1.582333 (8 pages) | Cited 3 times

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Structural and magnetic properties of the two-layered Ruddlesden–Popper phase SrO(La_1−xSr_xMnO₃)₂ with x=0.3–0.5 are highlighted. Intrinsic properties of these naturally layered manganites include a “colossal” magnetoresistance, a composition-dependent magnetic anisotropy, and almost no remanence. Above the Curie temperature there is a nonvanishing extrinsic magnetization attributed to intergrowths (stacking faults in the layered structure). These lattice imperfections consist of additional or missing manganite layers, as observed in transmission electron microscopy. Their role in influencing the properties of the host material is highlighted. © 2000 American Vacuum Society.

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75.50.Dd	Nonmetallic ferromagnetic materials
75.30.Gw	Magnetic anisotropy
61.66.Fn	Inorganic compounds
75.47.Gk	Colossal magnetoresistance
75.60.Ej	Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz	Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

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Ferromagnetic semiconductor heterostructures based on (GaMn)As

M. Tanaka, H. Shimizu, T. Hayashi, H. Shimada, and K. Ando

J. Vac. Sci. Technol. A 18, 1247 (2000); http://dx.doi.org/10.1116/1.582334 (7 pages) | Cited 9 times

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Growth, transport, magnetic, magneto-optical, and magnetotunneling properties of ferromagnetic semiconductor (GaMn)As and its quantum heterostructures, including superlattices and tunnel junctions, are presented. Spin-related phenomena in such III–V based ferromagnetic quantum heterostructures are shown to give a new degree of freedom in the band-gap engineering and wave function engineering for semiconductor electronics and photonics. © 2000 American Vacuum Society.

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75.50.Cc	Other ferromagnetic metals and alloys
73.40.Kp	III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Jt	Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
78.20.Ls	Magneto-optical effects
75.50.Pp	Magnetic semiconductors
73.40.Gk	Tunneling
78.66.Fd	III-V semiconductors

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Low-temperature gaseous nitriding and subsequent oxidation of epitaxial Ni/Fe bilayers

A. V. Mijiritskii and D. O. Boerma

J. Vac. Sci. Technol. A 18, 1254 (2000); http://dx.doi.org/10.1116/1.582335 (5 pages) | Cited 1 time

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Low-temperature gaseous nitriding was applied to epitaxial Ni/Fe bilayers deposited onto a MgO(001) substrate. The pore-free nitride layers produced were subsequently oxidized in oxygen. The samples were analyzed by conversion electron Mössbauer spectroscopy (CEMS), x-ray diffraction (XRD), and Rutherford backscattering spectroscopy in combination with channeling techniques. Nitriding in pure NH₃ gas at 300 °C led to the formation of a textured ϵ-Fe–nitride layer with a predominant composition of Fe_2.07N. The epitaxial relationship of the ϵ-Fe–nitride layer with the MgO substrate was found to be ϵ-Fe_2.07N{203}〈010〉‖MgO{001}〈110〉. The nitride layer produced was subsequently oxidized in p(O₂)=100 mbar at 275 °C. While the XRD spectra acquired on the oxidized samples revealed the formation of a Fe–oxide phase with a spinel structure, the CEMS spectral lines could not be interpreted in terms of any Fe–oxide or Fe–hydroxide phase know. It is suggested that the peculiarities in the CEMS data are caused by N atoms incorporated into the oxide lattice. © 2000 American Vacuum Society.

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81.65.Lp	Surface hardening: nitridation, carburization, carbonitridation
81.65.Mq	Oxidation
81.05.Bx	Metals, semimetals, and alloys
76.80.+y	Mössbauer effect; other γ-ray spectroscopy
82.80.Yc	Rutherford backscattering (RBS), and other methods of chemical analysis
61.85.+p	Channeling phenomena (blocking, energy loss, etc.)

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Surface-sensitive, element-specific magnetometry with x-ray linear dichroism

F. O. Schumann, R. F. Willis, and J. G. Tobin

J. Vac. Sci. Technol. A 18, 1259 (2000); http://dx.doi.org/10.1116/1.582336 (5 pages) | Cited 1 time

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It is shown that the x-ray magnetic linear dichroism (XMLD) in x-ray photoemission signal can be used to monitor the element specific magnetic moments in ultra thin alloy films. Comparison with recent superconducting quantum interference device data provides a quantitative check that demonstrates that the total magnetization derived from summing the constituent elemental moments changes with the composition of the alloy. This is illustrated by the contrasting behavior of FeNi and CoNi alloys. © 2000 American Vacuum Society.

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75.70.Ak	Magnetic properties of monolayers and thin films
75.50.Bb	Fe and its alloys
75.50.Cc	Other ferromagnetic metals and alloys
75.70.Rf	Surface magnetism
79.60.Dp	Adsorbed layers and thin films
75.30.Cr	Saturation moments and magnetic susceptibilities
75.60.Ej	Magnetization curves, hysteresis, Barkhausen and related effects

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Exchange bias in Fe/Cr double superlattices

J. S. Jiang, G. P. Felcher, A. Inomata, R. Goyette, C. S. Nelson, and S. D. Bader

J. Vac. Sci. Technol. A 18, 1264 (2000); http://dx.doi.org/10.1116/1.582337 (5 pages) | Cited 2 times

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Utilizing the oscillatory interlayer exchange coupling in Fe/Cr superlattices, we have constructed “double superlattice” structures where a ferromagnetic (F) and an antiferromagnetic (AF) Fe/Cr superlattice are coupled through a Cr spacer. The minor hysteresis loops in the magnetization are shifted from zero field, i.e., the F superlattice is exchange biased by the AF one. The double superlattices are sputter deposited with (211) epitaxy and possess uniaxial in-plane magnetic anisotropy. The magnitude of the bias field is satisfactorily described by the classic formula for collinear spin structures. The coherent structure and insensitivity to atomic-scale roughness makes it possible to determine the spin distribution by polarized neutron reflectivity, which confirms that the spin structure is collinear. The magnetic reversal behavior of the double superlattices suggests that a realistic model of exchange bias needs to address the process of nucleating local reverse domains. © 2000 American Vacuum Society.

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75.70.Cn	Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb	Fe and its alloys
75.50.Ee	Antiferromagnetics
75.30.Et	Exchange and superexchange interactions
75.60.Ej	Magnetization curves, hysteresis, Barkhausen and related effects
75.25.-j	Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Gw	Magnetic anisotropy
75.60.Ch	Domain walls and domain structure
75.70.Kw	Domain structure (including magnetic bubbles and vortices)

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Magnetic stability of novel exchange coupled systems

A. Inomata, J. S. Jiang, C.-Y. You, J. E. Pearson, and S. D. Bader

J. Vac. Sci. Technol. A 18, 1269 (2000); http://dx.doi.org/10.1116/1.582338 (4 pages) | Cited 5 times

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The magnetic stability of two different interfacial exchange coupled systems is investigated using the magneto-optic Kerr effect during repeated reversal of the soft layer magnetization by field cycling up to 10⁷ times. For uniaxial Fe/Cr(211) exchange biased “double-superlattice” systems, small but rapid initial decay of exchange bias field H_E and the remanent magnetization is observed. Also the Sm–Co/Fe bilayers grown epitaxially with uniaxial in-plane anisotropy show similar decay. However, the H_E of biaxial and random in-plane bilayers shows gradual decay without large reduction of the magnetization. These different decay behaviors are explained by their different microstructure and interfacial spin configurations. © 2000 American Vacuum Society.

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75.30.Et	Exchange and superexchange interactions
78.20.Ls	Magneto-optical effects
75.60.Ej	Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb	Fe and its alloys
75.70.Cn	Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw	Magnetic anisotropy
75.50.Ee	Antiferromagnetics
78.66.Bz	Metals and metallic alloys

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Effects of ultraviolet illumination on dry etch rates of NiFe-based magnetic multilayers

H. Cho, K. P. Lee, Y. B. Hahn, E. S. Lambers, and S. J. Pearton

J. Vac. Sci. Technol. A 18, 1273 (2000); http://dx.doi.org/10.1116/1.582339 (5 pages) | Cited 6 times

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NiFe and NiFeCo were dry etched in inductively coupled plasma Cl₂/Ar and CO/NH₃ discharges, either with or without concurrent UV illumination from a Hg arc lamp. No enhancement was observed for CO/NH₃ etching of the two materials, or for Cl₂/Ar etching of NiFe. However, enhancements in etch rate of up to a factor of three were observed for Cl₂/Ar etching of NiFeCo when ultraviolet (uv) illumination was employed. The etched surface morphologies were similar both with and without the UV irradiation. The etch rates in Cl₂/Ar discharges were strongly correlated with the amount of chlorinated residues detected on the surface by Auger electron spectroscopy, indicating that the desorption of the metal chloride reaction products was the rate-limiting step in the etching. © 2000 American Vacuum Society.

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75.70.Cn	Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
81.05.Bx	Metals, semimetals, and alloys
79.20.Fv	Electron impact: Auger emission
68.35.B-	Structure of clean surfaces (and surface reconstruction)
61.80.Ba	Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg	Metals and alloys

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Growth of ultrathin Co/Cu/Si(110) films

S. Maat, C. Liu, W. Eads, M. T. Umlor, and G. J. Mankey

J. Vac. Sci. Technol. A 18, 1278 (2000); http://dx.doi.org/10.1116/1.582340 (4 pages) | Cited 2 times

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We report the results of a study of the structural properties of Co films deposited on Cu/H–Si(110). A Cu(111) buffer layer is formed by evaporation or ultrahigh vacuum sputter deposition on the H-terminated Si(110) surface. From consideration of bulk lattice constants, the Cu films undergo a 6% expansion along the [1, −1, 0] direction and a 13% compression along the [1, 1, −2] direction. The structure and annealing behavior of the Cu buffer layer was determined with a combination of low-energy electron diffraction (LEED) and Auger electron spectroscopy. The LEED patterns of Co films evaporated on this buffer layer are compared to Co films grown on a Cu(111) single crystal. © 2000 American Vacuum Society.

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81.15.Cd	Deposition by sputtering
81.15.-z	Methods of deposition of films and coatings; film growth and epitaxy
68.65.-k	Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a	Thin film structure and morphology
81.40.Gh	Other heat and thermomechanical treatments

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Generation of positively charged particles at an anode and transport to device wafers in a real radio frequency plasma etching chamber for tungsten etch-back process

Tsuyoshi Moriya, Natsuko Ito, Fumihiko Uesugi, Yuji Hayashi, and Koji Okamura

J. Vac. Sci. Technol. A 18, 1282 (2000); http://dx.doi.org/10.1116/1.582341 (5 pages) | Cited 11 times

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The transport path of particles, that have flaked off a grounded anode of a real parallel-plate radio frequency (rf) plasma etching equipment for tungsten etch-back processing to device wafers on the cathode, is measured by using an in situ monitoring system that measures laser light scattered by the particles. A few particles appear constantly only near the grounded anode while rf power is being supplied. These particles have parabolic trajectories that open upward. Few particles are observed near the wafer. On the other hand, at the timing of the turning off of rf power, many particles appear near the anode. Their trajectories from the anode to the chamber wall are sharply curved. Near the wafer, which has a negative self-bias voltage, almost all the particles’ trajectories are from the chamber wall to the wafer. Therefore, the particles move from the anode to the device wafer on the cathode and keep away from the after-glow plasma as well as from the bulk plasma. These particles are then attracted to the wafer by its negative self-bias voltage. These phenomena indicate that the particles generated at the anode have positive charges. © 2000 American Vacuum Society.

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52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
81.65.Cf	Surface cleaning, etching, patterning
52.25.Vy	Impurities in plasmas
52.80.Pi	High-frequency and RF discharges
52.25.Fi	Transport properties
52.70.Kz	Optical (ultraviolet, visible, infrared) measurements
42.62.Eh	Metrological applications; optical frequency synthesizers for precision spectroscopy
52.80.Hc	Glow; corona

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Multizone uniformity control of a chemical mechanical polishing process utilizing a pre- and postmeasurement strategy

Chadi El Chemali, James Moyne, Kareemullah Khan, Rock Nadeau, Paul Smith, John Colt, Jonathan Chapple-Sokol, and Tarun Parikh

J. Vac. Sci. Technol. A 18, 1287 (2000); http://dx.doi.org/10.1116/1.582342 (10 pages) | Cited 5 times

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Achieving good uniformity process control in chemical mechanical polishing (CMP) requires a representative uniformity metric and strong models relating this metric to process tunable inputs. Previous efforts in CMP uniformity control have yielded acceptable results utilizing a center-to-edge (CTE) first order nonuniformity metric. Closer analysis of post CMP process nonuniformity, however, reveals significant higher order nonuniformity components such as the center “dimple” and outer “doughnut” regions. These nonuniformity characteristics are due in part to upstream chemical vapor deposition (CVD) processing. Utilizing a multizone approach to uniformity modeling, a more accurate mathematical model of CMP uniformity has been identified. The model has been utilized to customize a thickness and uniformity multivariate run-to-run software control solution for the process. The controller is based on the generic cell controller structure, which is a proven enabler for run-to-run control for a number of processes including CMP, vapor phase epitaxy, and etch. The control algorithm is a zeroth order adjustable linear approximation two-stage algorithm with exponentially weighted moving average noise filtering. This algorithm, which supports first order linear and nonlinear models, has been demonstrated to be effective in CMP CTE and thickness multivariate control. The control solution has been enhanced to utilize both pre and post CMP process metrology along with process models to suggest process recipe modifications on a run-to-run basis. Results indicate improved control of CMP process nonuniformity qualities of interest. Further, the results quantify the significant benefit of utilizing premetrology (feedforward) information in addition to traditional postmetrology (feedback) in determining control recipe advice. © 2000 American Vacuum Society.

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81.65.Ps

Polishing, grinding, surface finishing

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Demonstration of broadband radio frequency sensing: Empirical polysilicon etch rate estimation in a Lam 9400 etch tool

Craig Garvin and J. W. Grizzle

J. Vac. Sci. Technol. A 18, 1297 (2000); http://dx.doi.org/10.1116/1.582343 (6 pages) | Cited 2 times

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The sensitivity of a novel broad frequency band (1–2.25 GHz) radio frequency sensing system to plasma etching process conditions is demonstrated. This is accomplished by using the sensing system to estimate polysilicon etch rate in a Lam 9400 etch tool. A designed experiment varying physical and chemical reactive ion etching regimes was performed with five repetitions at each experimental point. A model relating broadband sensor response to etch rate was regressed using four repetitions of the data and validated on the fifth. Two representations of the broadband data were considered separately when regressing the models, with subset selection used in each case to choose the best predictor variables. In one representation, the sensor data was considered as a vector of 402 real numbers corresponding to magnitude and phase of reflection coefficient at each of 201 frequencies, resulting in an R² of etch rate estimate of 0.997. In the other, the broadband response was parameterized on the basis of a multimodal cavity resonance model. The inferred parameters of natural frequency, quality factor and resistance were then used as the predictor variables for regression, resulting in an R² of 0.962. © 2000 American Vacuum Society.

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81.05.Cy	Elemental semiconductors
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
81.65.Cf	Surface cleaning, etching, patterning

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Real time control of plasma deposited optical filters by multiwavelength ellipsometry

T. Heitz, A. Hofrichter, P. Bulkin, and B. Drevillon

J. Vac. Sci. Technol. A 18, 1303 (2000); http://dx.doi.org/10.1116/1.582344 (5 pages) | Cited 5 times

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Real time control of optical filters by multiwavelength ellipsometry is presented. The filters consist of SiO₂/Si3N₄ multilayers deposited on transparent substrates by a microwave plasma technique at room temperature. Using four-wavelength kinetic ellipsometry measurements and standard dispersion laws, efficient algorithms have been developed to determine in real time the current refractive index (n) and deposition rate (R_d) of the different layers. The program is based on minimizing square differences between calculated and experimental ellipsometry data. From the (n, R_d) calculation, which takes less than 200 ms, a control process operating the gas flows has been implemented which allows the deposition of high quality optical filters. As an illustration, the growth of a 11-layer Bragg reflector has been controlled in real time. The deposited filter has been characterized by comparing experimental and target spectral response, both in ellipsometry and spectrophotometry modes. Transmission measurements show excellent agreement in peak position and bandwidth, with less than 2% error. © 2000 American Vacuum Society.

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42.79.Ci	Filters, zone plates, and polarizers
07.60.Fs	Polarimeters and ellipsometers
78.20.Ci	Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
42.86.+b	Optical workshop techniques

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Effects of trapped charges on Hg-Schottky capacitance–voltage measurements of n-type epitaxial silicon wafers

Q. Wang, D. Liu, J. T. Virgo, J. Yeh, and R. J. Hillard

J. Vac. Sci. Technol. A 18, 1308 (2000); http://dx.doi.org/10.1116/1.582345 (5 pages) | Cited 3 times

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The effects of surface charge in the oxide layer for Hg-Schottky capacitance–voltage (C–V) measurements have been discussed in detail. The accumulation of majority carriers at the Si surface has been identified as a major factor controlling the stability and accuracy of the Hg-Schottky C–V measurement. For n-type wafers, the fixed oxide charge in Si oxide layer induces electron accumulation at the oxide/Si interface. This electron accumulation cannot be dissipated until a depleting voltage as high as −5.0 V is applied depending on the preparation of the oxide layer. It has been found that introducing Cu during the growth of the oxide layer can produce a deep trap level in the oxide. Pre-electrical-field stress at 5 MV/cm for 5 s can fill these traps and eliminate electron accumulation, resulting in a stable and accurate C–V measurement. Our results on p-type wafers show that the fixed oxide charge in the oxide layer can establish a surface depletion condition and produce a stable and accurate C–V measurement. With these experimental results, we propose that Si oxide layer can improve the stability and accuracy of the Hg-Schottky C–V measurement for both n- and p-type wafers. For n-type wafers, pre-electrical stress and a Si oxide layer with deep electron trap level are necessary; for p-type wafers, only the fixed oxide charge is needed. © 2000 American Vacuum Society.

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73.40.Qv	Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.Hb	Impurity and defect levels; energy states of adsorbed species
72.20.Jv	Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr	Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.30.+y	Surface double layers, Schottky barriers, and work functions

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Plasma etch-back planarization coupled to chemical mechanical polishing for sub 0.18 μm shallow trench isolation technology

André Schiltz, Laëtitia Palatini, Maryse Paoli, Maurice Rivoire, and Alain Prola

J. Vac. Sci. Technol. A 18, 1313 (2000); http://dx.doi.org/10.1116/1.582346 (8 pages) | Cited 1 time

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A new plasma etch-back planarization technique is presented with countermasking to preplanarize shallow trench isolation (STI) substrates before chemical mechanical polishing (CMP). A preplanarization step is necessary since CMP alone cannot provide effective planarization for sub 0.18 technology due to the dishing effect. The preplanarization step uses the principle of two layer planarization technique which consists of spin coating a first photoresist layer, using a countermask for the lithographic step, flowing and curing the resist blocks in STI topographies, spin coating a second photoresist layer to planarize the residual topography, and transferring the final flat surface into the substrate using conventional plasma etch back. In difference with previous techniques, we used a special mask with oversizing and exclusion of all STI critical dimensions smaller than 1.55 μm, the zones with the smaller STI dimensions being masked using a special narrow lines grid. Such a masking strategy avoids any misalignment problem, where the resized first photoresist blocks are reflowed in STI topographies, leading to an easy planarization by the second resist layer. Additionally, the lithographic step is a noncritical step using conventional i-line resist. Using appropriate planarization model and simulation, the first layer thickness can be adjusted to get an effectively planarized topography. The final surface is then transferred into the oxide substrate using the plasma etch-back technique. Various gas mixtures were tested using LAM 4520 plasma etching equipment. The (Ar/CF₄/O₂) gas mixture was observed to fulfill etch-back requirements with better performance. Equality of etch rate in resist and in oxide can be adjusted by the O₂/CF₄ gas ratio. A design of experiment was used to determine the optimum conditions of plasma transfer of the planarized profile into the substrate. Finally, the preplanarized wafer is polished by CMP, resulting in an effectively planarized topography with residual topography smaller than 50 nm. The technique is a noncritical lithographic technique scaleable for technologies below 0.18 μm. © 2000 American Vacuum Society.

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81.65.Cf	Surface cleaning, etching, patterning
81.65.Ps	Polishing, grinding, surface finishing
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
85.40.Hp	Lithography, masks and pattern transfer

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Experimental and theoretical results of room-temperature single-electron transistor formed by the atomic force microscope nano-oxidation process

Y. Gotoh, K. Matsumoto, T. Maeda, E. B. Cooper, S. R. Manalis, H. Fang, S. C. Minne, T. Hunt, H. Dai, J. Harris, and C. F. Quate

J. Vac. Sci. Technol. A 18, 1321 (2000); http://dx.doi.org/10.1116/1.582347 (5 pages) | Cited 6 times

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The single-walled carbon-nanotube (SWNT) was grown directly onto the top of the conventional Si atomic force microscopy (AFM) cantilever. This SWNT AFM cantilever was introduced into the AFM nano-oxidation process, which oxidized the titanium (Ti) metal film on the atomically flat α-Al₂O₃ substrate and formed the ultranarrow oxidized titanium (TiO_x) line of 5 nm width. This TiO_x line was used as the tunnel junction of the single-electron transistor (SET), and the SET fabricated by this process showed room-temperature Coulomb oscillation with periods of 1 V. It was determined by three-dimensional simulation that the tunnel-junction capacitance shows only weak dependence on the tunnel-junction width. © 2000 American Vacuum Society.

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81.07.-b	Nanoscale materials and structures: fabrication and characterization
81.16.-c	Methods of micro- and nanofabrication and processing
85.35.-p	Nanoelectronic devices
73.23.Hk	Coulomb blockade; single-electron tunneling
85.35.Gv	Single electron devices
81.65.Mq	Oxidation
85.35.Ds	Quantum interference devices

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Fabrication of bismuth nanowires with a silver nanocrystal shadowmask

S. H. Choi, K. L. Wang, M. S. Leung, G. W. Stupian, N. Presser, B. A. Morgan, R. E. Robertson, M. Abraham, E. E. King, M. B. Tueling, S. W. Chung, J. R. Heath, S. L. Cho, and J. B. Ketterson

J. Vac. Sci. Technol. A 18, 1326 (2000); http://dx.doi.org/10.1116/1.582348 (3 pages) | Cited 7 times

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We fabricated bismuth (Bi) nanowires with low energy electron beam lithography using silver (Ag) nanocrystal shadowmasks and a subsequent chlorine reactive ion etching. Submicron-size metal contacts on the single Bi nanowire were successfully prepared by in situ focused ion beam metal deposition for transport measurements. The temperature dependent resistance measurements on the 50 nm wide Bi nanowires showed that the resistance increased with decreasing temperature, which is characteristic of semiconductors and insulators.© 2000 American Vacuum Society.

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68.65.-k	Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.07.-b	Nanoscale materials and structures: fabrication and characterization
73.61.At	Metal and metallic alloys
61.46.-w	Structure of nanoscale materials
81.65.Cf	Surface cleaning, etching, patterning
81.16.-c	Methods of micro- and nanofabrication and processing
85.35.-p	Nanoelectronic devices
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
81.15.Jj	Ion and electron beam-assisted deposition; ion plating

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Fabrication of metal nanowire using carbon nanotube as a mask

Wan Soo Yun, Jinhee Kim, Kang-Ho Park, Jeong Sook Ha, Young-Jo Ko, Kyoungwan Park, Seong Keun Kim, Yong-Joo Doh, Hu-Jong Lee, Jean-Paul Salvetat, and László Forró

J. Vac. Sci. Technol. A 18, 1329 (2000); http://dx.doi.org/10.1116/1.582349 (4 pages) | Cited 26 times

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We report on the fabrication of metal nanowires on an insulating substrate using carbon nanotubes as a new kind of mask material. By irradiating Ar⁺ ions of 300 eV energy on a nanotube-coated Au/Ti thin layer on a SiO₂ substrate, Au/Ti nanowires were successfully formed just underneath the nanotube, indicating that the carbon nanotubes had acted as a good mask against the argon ion bombardment. The Au/Ti wire of a few nanometers in width was frequently observed among the wires of various widths. After the formation of the Au/Ti nanowires, the carbon nanotube on the metal nanowire could be removed by atomic force microscope. © 2000 American Vacuum Society.

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BROWSE VOLUMES

Jul 2000

Volume 18, Issue 4, pp. 1051-2038