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Jul 2011

Volume 29, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Vac. Sci. Technol. A 29, 041510 (2011); http://dx.doi.org/10.1116/1.3597636 (5 pages)

Liangmin Wang, Dexing Li, Yuanyuan Hu, and Chao Jiang
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Organic thin film induced substrate restructuring: An STM study of the interaction of naphtho[2,3-a]pyrene Au(111) herringbone reconstruction

Erin V. Iski, April D. Jewell, Heather L. Tierney, Georgios Kyriakou, and E. Charles H. Sykes

J. Vac. Sci. Technol. A 29, 040601 (2011); http://dx.doi.org/10.1116/1.3602072 (5 pages) | Cited 4 times

Online Publication Date: 1 July 2011

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The structural properties and the interaction strength of naphtho[2,3-a]pyrene (NP), a promising multifunctional organic material for optoelectronic devices, has been studied on Au(111) by means of scanning tunnelling microscopy. The perturbation of the native herringbone reconstruction of the pristine Au(111) surface was used to assess the interaction strength of the organic film with the surface. It was found that a moderate temperature treatment (500 K) of the NP film led to a new equilibrium structure, which dramatically perturbed the herringbone reconstruction. Our data suggest that organic-metal interfaces studied at room temperature or lower do not necessarily reflect the true equilibrium structures of the organic films, which are important in understanding the associated properties of organic thin film electronic devices. Interpretation of the self-assembled NP structure on Au(111) is discussed in conjunction with STM tip induced imaging effects which appear prevalent on these complex organic/metal interfaces.
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68.35.bd Metals and alloys
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments
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Comparison of methods to determine bandgaps of ultrathin HfO2 films using spectroscopic ellipsometry

Ming Di, Eric Bersch, Alain C. Diebold, Steven Consiglio, Robert D. Clark, Gert J. Leusink, and Torsten Kaack

J. Vac. Sci. Technol. A 29, 041001 (2011); http://dx.doi.org/10.1116/1.3597838 (8 pages) | Cited 1 time

Online Publication Date: 23 June 2011

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With the replacement of SiO2 by high-k Hf-based dielectrics in complementary metal–oxide–semiconductor technology, the measurement of the high-k oxide bandgap is a high priority. Spectroscopic ellipsometry (SE) is one of the methods to measure the bandgap, but it is prone to ambiguity because there are several methods that can be used to extract a bandgap value. This paper describes seven methods of determining the bandgap of HfO2 using SE. Five of these methods are based on direct data inversion (point-by-point fitting) combined with a linear extrapolation, while two of the methods involve a dispersion model-based bandgap extraction. The authors performed all of these methods on a single set of data from a 40 Å HfO2 film, as well as on data from 20 and 30 Å HfO2 films. It was observed that the bandgap values for the 40 Å film vary by 0.69 eV. In comparing these methods, the reasons for this variation are discussed. The authors also observed that, for each of these methods, there was a trend of increasing bandgap with decreasing film thickness, which is attributed to quantum confinement. Finally, the authors observed a greater variation in bandgap values among the methods for the 40 Å films than among the methods for the 30 and 20 Å films. This is attributed to the larger tail in the extinction coefficient k curve for the 40 Å film.
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71.20.Ps Other inorganic compounds
77.55.D- High-permittivity gate dielectric films
78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Structural and electrical characterization of HBr/O2 plasma damage to Si substrate

Masanaga Fukasawa, Yoshinori Nakakubo, Asahiko Matsuda, Yoshinori Takao, Koji Eriguchi, Kouichi Ono, Masaki Minami, Fumikatsu Uesawa, and Tetsuya Tatsumi

J. Vac. Sci. Technol. A 29, 041301 (2011); http://dx.doi.org/10.1116/1.3596606 (7 pages) | Cited 1 time

Online Publication Date: 23 June 2011

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Silicon substrate damage caused by HBr/O2 plasma exposure was investigated by spectroscopic ellipsometry (SE), high-resolution Rutherford backscattering spectroscopy, and transmission electron microscopy. The damage caused by H2, Ar, and O2 plasma exposure was also compared to clarify the ion-species dependence. Although the damage basically consists of a surface oxidized layer and underlying dislocated Si, the damage structure strongly depends on the incident ion species, ion energy, and oxidation during air and plasma exposure. In the case of HBr/O2 plasma exposure, hydrogen generated the deep damaged layer (∼10 nm), whereas ion-enhanced diffusion of oxygen, supplied simultaneously by the plasma, caused the thick surface oxidation. In-line monitoring of damage thicknesses by SE, developed with an optimized optical model, showed that the SE can be used to precisely monitor damage thicknesses in mass production. Capacitance–voltage (C–V) characteristics of a damaged layer were studied before and after diluted-HF (DHF) treatment. Results showed that a positive charge is generated at the surface oxide–dislocated Si interface and/or in the bulk oxide after plasma exposure. After DHF treatment, most of the positive charges were removed, while the thickness of the “Si recess” was increased by removing the thick surface oxidized layer. As both the Si recess and remaining dislocated Si, including positive charges, cause the degradation of electrical performance, precise monitoring of the surface structure and understanding its effect on device performance is indispensable for creating advanced devices.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.77.-j Plasma applications
85.30.-z Semiconductor devices
61.05.Np Atom, molecule, and ion scattering (for structure determination only)

Measurement and simulation of spreading current in interlayer dielectric film deposition by plasma-enhanced chemical vapor deposition

Noriaki Matsunaga, Hirokatsu Okumura, Butsurin Jinnai, and Seiji Samukawa

J. Vac. Sci. Technol. A 29, 041302 (2011); http://dx.doi.org/10.1116/1.3596617 (6 pages)

Online Publication Date: 23 June 2011

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A serious issue affecting metal–oxide–semiconductor field-effect transistors is plasma-induced charging damage caused by the spreading current during plasma-enhanced chemical vapor deposition of dielectric films. This current is studied in detail by direct measurement of the plasma-induced vacuum ultraviolet photocurrent through a deposited SiO2 film. The current increased with increasing antenna-wiring spacing, which spreads the electric field over a greater area. Furthermore, the photocurrent showed a parabolic dependence on film thickness. A finite element method simulation demonstrated that the current through a deposited SiO2 film increased when the spreading effect was dominant and decreased when the resistance increase was dominant.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
79.60.Dp Adsorbed layers and thin films
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
77.55.-g Dielectric thin films
73.61.Ng Insulators

Modeling of plasma-induced damage and its impacts on parameter variations in advanced electronic devices

Koji Eriguchi, Yoshinori Takao, and Kouichi Ono

J. Vac. Sci. Technol. A 29, 041303 (2011); http://dx.doi.org/10.1116/1.3598382 (8 pages)

Online Publication Date: 23 June 2011

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A comprehensive model predicting the effects of plasma-induced damage (PID) on parameter variations in advanced metal–oxide–semiconductor field-effect transistors (MOSFETs) is proposed. The model focuses on the silicon recess structure (Si loss) in the source/drain extension region formed by high-energy ion bombardment during plasma etching. The model includes the following mechanisms: (1) damaged layer formation by ion impact and penetration, (2) Si recess structure formation by a subsequent wet etch, (3) MOSFET performance degradation, and (4) MOSFET parameter variation. Based on a range theory for plasma-etch damage, the thickness of the damaged layer exhibits a power-law dependence on the energy of the ion incident on the surface of Si substrate. Assuming that the damaged layer was formed during a gate or an offset spacer etch process, the depth of Si recess (dR) is a function of the depth profile of the created defect site (ndam), the wet-etch stripping time (tw), and the energy of the incident ion. It was found that dR also showed a power-law dependence on the average ion energy mathion estimated from applied self-dc-bias voltage for various tw. As for MOSFET performance degradation, the threshold voltage (Vth) shifted and the shift (ΔVth) increased with an increase in mathion and a decrease in gate length. This induces an increase in subthreshold leakage current (Ioff) for MOSFET. Technology computer-aided-design simulations were performed to confirm these results. By integrating the presented PID models, parameter variations could be predicted: Using a Monte Carlo method, it was demonstrated that PID increases parameter variations such as Vth and Ioff. It also was found that the variation in mathion induces Vth and Ioff variations, comparable to that induced by other process parameter fluctuations such as dopant fluctuation and gate length. In summary, considering the effects of PID on parameter variations is vital for designing future ultralarge-scale-integrated circuits with billions of built-in MOSFETs.
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85.30.Tv Field effect devices
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Surfaces of mixed formulation solder alloys at melting

M. J. Bozack, J. C. Suhling, Y. Zhang, Z. Cai, and P. Lall

J. Vac. Sci. Technol. A 29, 041401 (2011); http://dx.doi.org/10.1116/1.3584821 (9 pages)

Online Publication Date: 24 May 2011

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Mixed formulation solder alloys refer to specific combinations of Sn-37Pb and SAC305 (96.5Sn–3.0Ag–0.5Cu). They present a solution for the interim period before Pb-free electronic assemblies are universally accepted. In this work, the surfaces of mixed formulation solder alloys have been studied by in situ and real-time Auger electron spectroscopy as a function of temperature as the alloys are raised above the melting point. With increasing temperature, there is a growing fraction of low-level, bulk contaminants that segregate to the alloy surfaces. In particular, the amount of surface C is nearly ∼50–60 at. % C at the melting point. The segregating impurities inhibit solderability by providing a blocking layer to reaction between the alloy and substrate. A similar phenomenon has been observed over a wide range of (SAC and non-SAC) alloys synthesized by a variety of techniques. That solder alloy surfaces at melting have a radically different composition from the bulk uncovers a key variable that helps to explain the wide variability in contact angles reported in previous studies of wetting and adhesion.
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64.70.dj Melting of specific substances
64.75.-g Phase equilibria
68.08.Bc Wetting
79.20.Fv Electron impact: Auger emission

Observation of NH2 species on tilted InN (01math1) facets

A. R. Acharya, M. Buegler, R. Atalay, N. Dietz, B. D. Thoms, J. S. Tweedie, and R. Collazo

J. Vac. Sci. Technol. A 29, 041402 (2011); http://dx.doi.org/10.1116/1.3596619 (5 pages) | Cited 2 times

Online Publication Date: 15 June 2011

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The structural properties and surface bonding configuration of InN layers grown by high-pressure chemical vapor deposition have been characterized using Raman spectroscopy, x-ray diffraction (XRD), and high resolution electron energy loss spectroscopy. The appearance of the A1(TO) mode at 447 cm−1 in unpolarized z(·)math Raman spectrum indicates distortions in the crystal lattice due to the growth of tilted plane crystallites. A Bragg reflex in the x-ray diffraction spectrum at 2Θ ≈ 33° has been assigned to tilted InN facets in the polycrystalline InN layer. The high resolution electron energy loss spectrum for this InN layer features vibration modes assigned to NH2 species indicating a surface orientation consistent with the crystalline properties observed in Raman spectroscopy and XRD. The appearance of tilted planes is suggested to be due to the effects of high V–III ratio and lattice mismatch on the growth mechanism.
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68.55.A- Nucleation and growth
68.55.J- Morphology of films
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Aging mechanism of the native oxide on silicon (100) following atmospheric oxygen plasma cleaning

Thomas S. Williams and Robert F. Hicks

J. Vac. Sci. Technol. A 29, 041403 (2011); http://dx.doi.org/10.1116/1.3597436 (7 pages) | Cited 4 times

Online Publication Date: 23 June 2011

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Silicon native oxide surfaces were cleaned with a radio frequency, atmospheric pressure helium and oxygen plasma and with an RCA standard clean-1. Both processes create a hydrophilic state with water contact angles of <5° and 16.2° ± 1.7°, respectively. During subsequent storage in a chamber purged with boil off from a liquid nitrogen tank, the water contact angle increased over time at a rate dependent on the cleaning method used. Internal reflection infrared spectroscopy revealed that the change in water contact angle was due to the adsorption of organic molecules with an average hydrocarbon chain length of 10 ± 2. The rate of the adsorption process decreased with the fraction of hydrogen-bonded hydroxyl groups on the surface relative to those groups that were isolated. On Si (100) surfaces that were cleaned by RCA standard clean-1 and then the plasma, 95.8% of the silanol groups were hydrogen bonded. The first-order rate constant for adsorption of the organic contaminant on this surface was 0.182 ± 0.008 h−1.
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81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
82.20.Pm Rate constants, reaction cross sections, and activation energies
68.43.Mn Adsorption kinetics
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Plasma enhanced atomic layer deposition of SiNx:H and SiO2

Sean W. King

J. Vac. Sci. Technol. A 29, 041501 (2011); http://dx.doi.org/10.1116/1.3584790 (9 pages) | Cited 2 times

Online Publication Date: 24 May 2011

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As the nanoelectronics industry looks to transition to both three dimensional transistor and interconnect technologies at the <22 nm node, highly conformal dielectric coatings with precise thickness control are increasingly being demanded. Plasma enhanced chemical vapor deposition (PECVD) currently fills this role for most applications requiring low temperature processing but does not always meet step coverage and thickness precision requirements. The authors present results for a hybrid technique, plasma enhanced atomic layer deposition (PEALD), which utilizes typical PECVD process gases and tooling while delivering improved topography coverage and thickness control. Specifically, the authors show that alternating SiH4 gas/N2 plasma exposures applied in an atomic layer deposition sequence can be used to deposit SiNx:H films in a self-limiting fashion with improved conformality and superior performance as a moisture barrier. PEALD of SiO2 using alternating SiH4 and CO2 plasma exposures is further demonstrated.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.55.aj Insulators
68.55.jd Thickness

Substrate effects on metal-insulator transition characteristics of rf-sputtered epitaxial VO2 thin films

Yanjie Cui and Shriram Ramanathan

J. Vac. Sci. Technol. A 29, 041502 (2011); http://dx.doi.org/10.1116/1.3584817 (7 pages) | Cited 5 times

Online Publication Date: 25 May 2011

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We report on synthesis and phase transition characteristics of VO2 films grown on various single crystal substrates Al2O3 (0001), TiO2 (101), TiO2 (001), and MgF2 (001). An epitaxial orientation relationship was established for films on Al2O3 and TiO2 from x-ray 2θ-ω coupled scans and φ scans. Films grown on these substrates exhibit a metal to insulator transition below that for bulk single crystals with accompanying resistance change of 3 to 4 orders of magnitude. Trends in phase transition characteristics with substrate physical properties are analyzed. Postdeposition treatment studies in oxygen and ozone at low temperatures demonstrate that epitaxial VO2 films on TiO2 can tolerate oxidation environment better than the films on Al2O3. The studies could be of relevance toward further advancing structure-functional property relations in this important material system.
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68.55.A- Nucleation and growth
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
68.55.J- Morphology of films
81.15.Cd Deposition by sputtering
68.55.ag Semiconductors

Glancing angle deposition of Ge nanorod arrays on Si patterned substrates

C. Khare, R. Fechner, J. Bauer, M. Weise, and B. Rauschenbach

J. Vac. Sci. Technol. A 29, 041503 (2011); http://dx.doi.org/10.1116/1.3589781 (7 pages) | Cited 2 times

Online Publication Date: 25 May 2011

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A periodic arrangement of Ge nanorods on a Si(111) substrate was realized by glancing angle deposition (GLAD) onto honeycomb-like arranged Au hillocks formed using a self-assembled monolayer of polystyrene nanospheres as an evaporation mask. Additionally, a honeycomb-like arrangement of Au dots was used as an etch mask in a reactive ion beam etching process for pattern transfer procedure. Resulting honeycomb patterns consisting of Si hillocks within the Si(111) substrates were utilized to deposit Ge nanorods. Effective morphological variations in shape and dimension of GLAD-grown nanorods on honeycomb-like patterned substrates with both Au dot and Si dot arrays are strongly influenced by interseed distances, seed heights, and consequently shadowing lengths. For a large pattern period, it was observed that the usual triangular shape of the nanorod changed to a hexagonal shape as an effect of additional particle flux that reached the growing nanorod from the direction of second and third-nearest neighbors due to inadequate shadowing lengths and increased interseed condensation.
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81.07.Bc Nanocrystalline materials
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
81.05.Cy Elemental semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
81.65.Cf Surface cleaning, etching, patterning
81.15.Jj Ion and electron beam-assisted deposition; ion plating

Optical and electrical properties of transparent conducting B-doped ZnO thin films prepared by various deposition methods

Jun-ichi Nomoto, Toshihiro Miyata, and Tadatsugu Minami

J. Vac. Sci. Technol. A 29, 041504 (2011); http://dx.doi.org/10.1116/1.3591348 (6 pages) | Cited 2 times

Online Publication Date: 27 May 2011

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B-doped ZnO (BZO) thin films were prepared with various thicknesses up to about 500 nm on glass substrates at 200 °C by dc or rf magnetron sputtering deposition, pulsed laser deposition (PLD), and vacuum arc plasma evaporation (VAPE) methods. Resistivities of 4–6 × 10−4 Ω cm were obtained in BZO thin films prepared with a B content [B/(B + Zn) atomic ratio] around 1 at. % by PLD and VAPE methods: Hall mobilities above 40 cm2/Vs and carrier concentrations on the order of 1020 cm−3. All 500-nm-thick-BZO thin films prepared with a resistivity on the order of 10−3–10−4 Ω cm exhibited an averaged transmittance above 80% in the wavelength range of 400–1100 nm. The resistivity in BZO thin films prepared with a thickness below about 500 nm was found to increase over time with exposure to various high humidity environments. In heat-resistance tests, the resistivity stability of BZO thin films was found to be nearly equal to that of Ga-doped ZnO thin films, so these films were judged suitable for use as a transparent electrode for thin-film solar cells.
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78.66.Hf II-VI semiconductors
68.55.ag Semiconductors
73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Cd Deposition by sputtering
81.15.Fg Pulsed laser ablation deposition

Simple self-gettering differential-pump for minimizing source oxidation in oxide-MBE environment

Yong-Seung Kim, Namrata Bansal, and Seongshik Oh

J. Vac. Sci. Technol. A 29, 041505 (2011); http://dx.doi.org/10.1116/1.3591384 (4 pages)

Online Publication Date: 27 May 2011

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Source oxidation of easily oxidizing elements such as Ca, Sr, Ba, and Ti in an oxidizing ambient leads to their flux instability and is one of the biggest problems in the multielemental oxide molecular beam epitaxy technique. Here, the authors report a new scheme that can completely eliminate the source oxidation problem: a self-gettering differential pump using the source itself as the pumping medium. The pump simply comprises a long collimator mounted in front of the source in extended port geometry. With this arrangement, the oxygen partial pressure near the source was easily maintained well below the source oxidation regime, resulting in a stabilized flux, comparable to that of an ultrahigh-vacuum environment. Moreover, this pump has a self-feedback mechanism that allows a stronger pumping effectiveness for more easily oxidizing elements, which is a desired property for eliminating the source oxidation problem.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Mq Oxidation

Effects of thermal annealing on the microstructure of sputtered Al2O3 coatings

V. Edlmayr, T. P. Harzer, R. Hoffmann, D. Kiener, C. Scheu, and C. Mitterer

J. Vac. Sci. Technol. A 29, 041506 (2011); http://dx.doi.org/10.1116/1.3584803 (8 pages) | Cited 2 times

Online Publication Date: 2 June 2011

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The morphology and microstructure of Al2O3 thin films deposited by pulsed direct current magnetron sputtering were studied in the as-grown state and after vacuum annealing at 1000 °C for 12 h using transmission electron microscopy. For the coating deposited under low ion bombardment conditions, the film consists of small γ- and/or δ-Al2O3 grains embedded in an amorphous matrix. The grain size at the region close to the interface to the substrate was much larger than that of the remaining layer. Growth of the γ-Al2O3 phase is promoted during annealing but no transformation to α-Al2O3 was detected. For high-energetic growth conditions, clear evidence for γ-Al2O3 formation was found in the upper part of the coating with grain size much larger than for low-energetic growth, but the film was predominately amorphous at the interface region. Annealing resulted in the transformation of γ-Al2O3 to α-Al2O3, while the mainly amorphous part crystallized to γ-Al2O3.
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68.55.A- Nucleation and growth
61.72.Cc Kinetics of defect formation and annealing
81.65.-b Surface treatments
68.55.J- Morphology of films
81.15.Cd Deposition by sputtering
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Comparative study of low dielectric constant material deposited using different precursors

Bor-Jou Wei, Yi-Lung Cheng, Fu-Hsing Lu, Tai-Jung Chiu, and Han-Chang Shih

J. Vac. Sci. Technol. A 29, 041507 (2011); http://dx.doi.org/10.1116/1.3592888 (7 pages)

Online Publication Date: 2 June 2011

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Two kinds of organosilicate precursors, trimethylsilane (3MS) and diethoxymethylsilane (DEMS), were used to produce low-k films by plasma-enhanced chemical vapor deposition in this work. The experimental results indicate that DEMS-based low-k films have superior electrical and reliability performances than 3MS-based low-k films. Furthermore, the DEMS-based low-k films exhibit a higher mechanical strength, chemical and thermal stability, and better adhesion strength on various barrier films. Therefore, the DEMS-based films are promising low-k materials, which can be integrated in a very large scale integration circuit as an interlayer dielectric material.
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77.55.Bh Low-permittivity dielectric films
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Sz Deposition technology
68.60.Dv Thermal stability; thermal effects
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Numerical ellipsometry: n-k plane analysis of transparent conducting films

D. Barton and F. K. Urban, III

J. Vac. Sci. Technol. A 29, 041508 (2011); http://dx.doi.org/10.1116/1.3589803 (8 pages)

Online Publication Date: 6 June 2011

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It is well known that across the optical spectrum, indium tin oxide (ITO) has a window of transparency and that it is optically opaque (has a high extinction coefficient, k) at energies outside of the window. Such a material presents a particular challenge to ellipsometry data analysis arising from these different optical behaviors. The purpose of this work is to apply n-k plane data analysis to such an ITO film. An ITO film grown on a silicon substrate was measured at 293 wavelengths, every 5 nm from 210 to 1700 nm, and at each of three incidence angles of 55°, 65°, and 75°. Thus at each wavelength, there are three measurements which result in a set of three solution curves. If measurements had no experimental uncertainty and if the film were “perfect,” the three curves would intersect at a point at the value of film n, k, and d. In actual fact, they come close to intersecting and have a region of closest approach. The key result is that the mathematics supports different approximating film models across wavelength, considering measurement error. In the transparent region from approximately 300–980 nm, the ITO matches a single layer film ideal model while additional layers do not result in improved modeling due to measurement error. On the other hand, due to the underlying mathematics, from 980 to 1000 nm a two-layer ideal model provides two well defined intersections and so there are six real number unknowns which may be determined. At longer wavelengths, the film corresponds to an absorbing layer which appears vertically inhomogeneous but which cannot be well characterized due to the different light interaction depths at the three incidence angles. Lorenz, Cauchy, Drude, generalized oscillator, and other models of optical properties as a function of light wavelength were not used. Additional measurements, for example during film growth, are needed to further refine the modeling.
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78.66.-w Optical properties of specific thin films
07.60.Fs Polarimeters and ellipsometers

Direct simulation Monte Carlo study of effects of thermal nonuniformities in electron-beam physical vapor deposition

A. Venkattraman and Alina A. Alexeenko

J. Vac. Sci. Technol. A 29, 041509 (2011); http://dx.doi.org/10.1116/1.3592890 (10 pages)

Online Publication Date: 10 June 2011

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In a typical electron-beam physical vapor deposition system, there is limited control over how the high-power electron beam heats the metal surface. This leads to thermal nonuniformities at the melt. Three-dimensional direct simulation Monte Carlo simulations were performed with the aim of quantifying the effect of such spatial variations of source temperature in thin film depositions using an electron-beam physical vapor deposition system. The source temperature distribution from a typical deposition process was used in the direct simulation Monte Carlo simulations performed for various mass flow rates. The use of an area-averaged temperature is insufficient for all mass flow rates due to the highly nonlinear relationship between temperature and saturation number density, and hence, the mass flux. The mass flow rate equivalent temperature was determined, and the simulations performed with this temperature were compared with those corresponding to the actual nonuniform temperature distribution. For low mass flow rates, the growth rates depend very weakly on the spatial variation of temperature as long as an equivalent temperature corresponding to the same mass flow rate was used. However, as the mass flow rate increases, the error associated with this approximation increases. For deposition processes with source Knudsen numbers less than 0.05, it is not possible to account for the spatial nonuniformities in temperature using the total mass flow rate without significant errors. For a given mass flow rate, the errors associated with using an equivalent temperature decrease with increasing collector plane distance since the flow is allowed to expand further, thereby decreasing the effects of slit temperature nonuniformities.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.A- Nucleation and growth

Realization of uniform large-area pentacene thin film transistor arrays by roller vacuum thermal evaporation

Liangmin Wang, Dexing Li, Yuanyuan Hu, and Chao Jiang

J. Vac. Sci. Technol. A 29, 041510 (2011); http://dx.doi.org/10.1116/1.3597636 (5 pages) | Cited 1 time

Online Publication Date: 17 June 2011

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A conventional vacuum thermal evaporation (VTE) system has been extended to a roller-VTE system with a moving substrate-holder to realize large-area organic film deposition. The multidimensional movement of the substrate-holder guarantees excellent uniformity of the large-area pentacene thin films. An 85-nm-thick pentacene film with a relative standard deviation as low as 2.7% is demonstrated within a 300 mm × 500 mm area. Thin film transistor arrays are then fabricated using the uniform pentacene films. The average transistor mobility is up to 0.85 cm2/V s with a relative standard deviation of 10%.
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81.05.Fb Organic semiconductors
81.15.Dj E-beam and hot filament evaporation deposition
85.30.Tv Field effect devices
68.55.ag Semiconductors

Optical transparency and electrical conductivity of nonstoichiometric ultrathin InxOy films

Shay Joseph and Shlomo Berger

J. Vac. Sci. Technol. A 29, 041511 (2011); http://dx.doi.org/10.1116/1.3599463 (10 pages)

Online Publication Date: 17 June 2011

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The effect of thickness and composition on the electrical conductivity and optical transparency, mainly in the infrared, of ultrathin InxOy films was studied. InxOy films 35–470 Å thick with oxygen atomic fractions of ∼0.3 and ∼0.5 were prepared via dc magnetron sputtering. All films were polycrystalline, consisting of only the cubic bixbiyte phase of In2O3. The average grain size of the films increased from 30 to 95 nm as the film thickness increased. The weak dependence of the electrical conductivity on the frequency and the low activation energies for conduction, a few hundredths of an eV, provided an indication that free band conduction was the primary electrical conduction mechanism in the case of all ultrathin InxOy films. It was found that introducing a high degree of nonstoichiometry in the form of oxygen deficiency did not help improve the electrical conductivity, since not all vacancies contributed two free electrons for conduction and due to impurity scattering. The optical nature of these films, studied mainly by ellipsometry, was found to be dependent on the film’s composition and thickness. In the infrared, the dielectric function of all InxOy films was consistent with the Drude model, inferring that the transparency loss in this region was a result of free charge carriers. In the visible however, InxOy films under 170 Å, which had an oxygen atomic fraction of ∼0.5, were modeled by extending the Drude model to the shorter wavelengths. Films over 170 Å, with the same composition, were modeled using the Cauchy dispersion model, meaning that no absorption was measured. These results indicate that, optically, under specific compositions, ultrathin InxOy films undergo a transition from metalliclike behavior to dielectric behavior with increasing film thickness. Using a figure of merit approach, it was determined that a nonstoichiometric 230 Å thick InxOy film, with an oxygen atomic fraction of ∼0.3, had the best combination of conductivity and transparency, namely, absorption of less than 20% in the infrared, about 10% in the visible, and electrical resistance of only 230 Ω at 20 kHz. Such a film may be classified as a highly conductive transparent oxide even in the infrared.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Nk Insulators
81.15.Cd Deposition by sputtering
61.72.jd Vacancies
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
73.61.Ng Insulators

Plasma treatment of HfO2-based metal–insulator–metal resistive memories

C. Vallée, P. Gonon, C. Mannequin, T. Chevolleau, M. Bonvalot, H. Grampeix, C. Licitra, N. Rochat, and V. Jousseaume

J. Vac. Sci. Technol. A 29, 041512 (2011); http://dx.doi.org/10.1116/1.3599825 (6 pages)

Online Publication Date: 23 June 2011

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This work focuses on Au/HfO2/TiN nonvolatile resistive memory [resistive random access memories (RRAMs)] stacks, where HfO2 is deposited by the atomic layer deposition technique on TiN electrodes. For as-grown RRAMs, no Reset is observed (the structure remains locked in a low resistive state). It is observed that an NH3 plasma treatment of the HfO2/TiN bilayer can restore a Reset stage. X-ray photoelectron spectroscopy analyses showed that the Reset recovery is related to a modification of the HfO2/TiN interface via transformation of the TiON interfacial layer. Thus, postdeposition plasma treatments of the oxide/electrode interface are identified as a valuable tool to improve the switching properties of oxide-based RRAMs.
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84.30.Sk Pulse and digital circuits
85.40.Sz Deposition technology

Study of stress in tensile nitrogen-plasma-treated multilayer silicon nitride films

Pierre Morin, Gaetan Raymond, Daniel Benoit, Denis Guiheux, Roland Pantel, Fabien Volpi, and Muriel Braccini

J. Vac. Sci. Technol. A 29, 041513 (2011); http://dx.doi.org/10.1116/1.3602082 (8 pages) | Cited 2 times

Online Publication Date: 1 July 2011

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The authors conducted a physico-chemical analysis of tensile sequential-nitrogen-plasma-treated silicon nitride films, which function as stressor liners in complementary metal oxide semiconductor (CMOS) technologies. These films are made of stacked nanometer-thick, plasma-enhanced, chemical vapor-deposited layers which were individually treated with N2-plasma, to increase stress. This study allowed us to monitor the evolution of the films’ chemical composition and stress as a function of process parameters such as deposition and post-N2-plasma duration. Consistent with secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM) and other physico-chemical analysis results, it was shown that the elementary component of the films can be modeled with a bi-layer consisting of an untreated slice at the bottom that is covered by a more tensile post-treated film. In addition, we observed that longer plasma treatments increase residual stress, SiN bond concentration and layer density, while reducing hydrogen content. The stress increase induced by the plasma treatment was shown to correlate with the increase in SiN bonds following a percolation mechanism that is linked to hydrogen dissociation. Kinetics laws describing both SiN bond generation and stress increase are proposed and it is demonstrated that stress increase follows first-order kinetics.
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68.65.Ac Multilayers
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
64.60.ah Percolation
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Improving the quality of barrier/seed interface by optimizing physical vapor deposition of Cu Film in hollow cathode magnetron

A. Dulkin, E. Ko, L. Wu, I. Karim, K. Leeser, K. J. Park, L. Meng, and D. N. Ruzic

J. Vac. Sci. Technol. A 29, 041514 (2011); http://dx.doi.org/10.1116/1.3602079 (6 pages)

Online Publication Date: 8 July 2011

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The quality of physical vapor deposition (PVD) grown barrier/seed interface in Cu interconnect metallization was significantly improved by enhancing Cu nucleation on the Ta barrier surface. This was accomplished through filtering of nonenergetic species from the deposition flux, increasing the fraction of Cu ions, improving metal ion flux uniformity, and minimizing gas ion bombardment of the growing film. The self-sputtering ability of Cu was combined with a magnetically confined high-density plasma in the Novellus hollow cathode magnetron (HCM®) PVD source. Spatial profiles of plasma density and temperature, as well as ion flux, metal ion fraction, and ion energy, were measured by planar Langmuir probes, quartz crystal microbalances, and gridded energy analyzers, all located at the wafer level. Multiple criteria, such as seed step coverage and roughness, the seed layer’s resistance to agglomeration, and its stability in the plating bath, have been used to evaluate interface quality. As a result, a new and improved Cu PVD process which demonstrates superior stability during subsequent process steps and ensures successful electrofill performance with a more than 50 % reduction in minimal requirement of field thickness as well as sidewall thickness has been developed.
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81.05.Bx Metals, semimetals, and alloys
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.35.Ct Interface structure and roughness
52.77.Dq Plasma-based ion implantation and deposition
52.70.Ds Electric and magnetic measurements
52.25.-b Plasma properties
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Experimental results and numerical modeling of a high-performance large-scale cryopump. I. Test particle Monte Carlo simulation

Xueli Luo, Christian Day, Horst Haas, and Stylianos Varoutis

J. Vac. Sci. Technol. A 29, 041601 (2011); http://dx.doi.org/10.1116/1.3585665 (7 pages) | Cited 2 times

Online Publication Date: 13 May 2011

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For the torus of the nuclear fusion project ITER (originally the International Thermonuclear Experimental Reactor, but also Latin: the way), eight high-performance large-scale customized cryopumps must be designed and manufactured to accommodate the very high pumping speeds and throughputs of the fusion exhaust gas needed to maintain the plasma under stable vacuum conditions and comply with other criteria which cannot be met by standard commercial vacuum pumps. Under an earlier research and development program, a model pump of reduced scale based on active cryosorption on charcoal-coated panels at 4.5 K was manufactured and tested systematically. The present article focuses on the simulation of the true three-dimensional complex geometry of the model pump by the newly developed ProVac3D Monte Carlo code. It is shown for gas throughputs of up to 1000 sccm (∼1.69 Pa m3/s at T = 0° C) in the free molecular regime that the numerical simulation results are in good agreement with the pumping speeds measured. Meanwhile, the capture coefficient associated with the virtual region around the cryogenic panels and shields which holds for higher throughputs is calculated using this generic approach. This means that the test particle Monte Carlo simulations in free molecular flow can be used not only for the optimization of the pumping system but also for the supply of the input parameters necessary for the future direct simulation Monte Carlo in the full flow regime.
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28.52.-s Fusion reactors
07.30.Cy Vacuum pumps
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
02.70.Uu Applications of Monte Carlo methods

Influence of surface topography on in situ reflection electron energy loss spectroscopy plasmon spectra of AlN, GaN, and InN semiconductors

B. Strawbridge, N. Cernetic, J. Chapley, R. K. Singh, S. Mahajan, and N. Newman

J. Vac. Sci. Technol. A 29, 041602 (2011); http://dx.doi.org/10.1116/1.3584775 (5 pages) | Cited 1 time

Online Publication Date: 24 May 2011

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This study of III-N semiconductor surfaces demonstrates that concurrent application of in situ reflection high energy electron diffraction and glancing-angle reflection electron energy loss spectroscopy (REELS) can be used during reactive molecular beam epitaxy to provide a surface sensitive, real-time determination of the surface texture and film composition. REELS spectra of rough AlN, GaN, and InN surfaces are dominated by bulk plasmons. Nearly atomically smooth topographies are found to shift the energy of the maximum of the plasmon loss peak to lower values, presumably as a result of the additional contributions from the surface plasmons. This shift to lower energies correlates well with the fraction of the topmost surface, which lies within a few degrees from the sample surface plane.
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68.55.jm Texture
68.55.ag Semiconductors
81.05.Ea III-V semiconductors
68.37.-d Microscopy of surfaces, interfaces, and thin films
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
68.55.A- Nucleation and growth

Precision vacuum pumping speed measurement using sonic nozzles

Wan-Sup Cheung, Jin-Hyun Shin, Kyung-Am Park, and Jong-Yeon Lim

J. Vac. Sci. Technol. A 29, 041603 (2011); http://dx.doi.org/10.1116/1.3600200 (11 pages)

Online Publication Date: 23 June 2011

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Constant volume flow meter systems were developed for measuring pumping speeds of dry vacuum pumps. Their capability to measure throughput in the low vacuum region was exploited to calibrate 0.03, 0.2, and 1.6 mm throat diameter sonic nozzles. It was demonstrated that the calibrated sonic nozzles enabled the precise measurement of the pumping speed of a dry vacuum pump under test as the constant volume flow meter systems. To examine the measurement capability of both approaches considered in this study, the expanded measurement uncertainty, as well as the detailed measurement uncertainty budget, is presented. The proposed pumping speed measurement method has potential application for a new “in situ and portable” pumping speed tester or analyzer for the Korean semiconductor and flat display process industry.
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47.80.Cb Velocity measurements
47.85.-g Applied fluid mechanics
47.60.Kz Flows and jets through nozzles
07.30.Cy Vacuum pumps
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