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Sep 2008

Volume 26, Issue 5, pp. 1101-1363

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Magnetron sputtered Si–B–C–N films with high oxidation resistance and thermal stability in air at temperatures above 1500 °C

Jaroslav Vlček, Stanislav Hřeben, Jiří Kalaš, Jiří Čapek, Petr Zeman, Radomír Čerstvý, Vratislav Peřina, and Yuichi Setsuhara

J. Vac. Sci. Technol. A 26, 1101 (2008); http://dx.doi.org/10.1116/1.2949232 (8 pages) | Cited 1 time

Online Publication Date: 30 July 2008

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Novel quaternary Si–B–C–N materials are becoming increasingly attractive because of their possible high-temperature and harsh-environment applications. In the present work, amorphous Si–B–C–N films were deposited on Si and SiC substrates by reactive dc magnetron cosputtering using a single C–Si–B or B4C–Si target in nitrogen-argon gas mixtures. A fixed 75% Si fraction in the target erosion areas, a rf induced negative substrate bias voltage of −100 V, a substrate temperature of 350 °C, and a total pressure of 0.5 Pa were used in the depositions. The corresponding discharge and deposition characteristics (such as the ion-to-film-forming particle flux ratio, ion energy per deposited atom, and deposition rate) are presented to understand complex relationships between process parameters and film characteristics. Films deposited under optimized conditions (B4C–Si target, 50% N2+50% Ar gas mixture), possessing a composition (in at. %) Si32–34B9–10C2–4N49–51 with a low (less than 5 at. %) total content of hydrogen and oxygen, exhibited extremely high oxidation resistance in air at elevated temperatures (even above 1500 °C). Formation of protective surface layers (mainly composed of Si and O) was proved by high-resolution transmission electron microscopy, Rutherford backscattering spectrometry, and x-ray diffraction measurements after oxidization. Amorphous structure of the Si–B–C–N films was maintained under the oxidized surface layers after annealing in air up to 1700 °C (a limit imposed by thermogravimetric analysis in oxidative atmospheres).
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
81.65.Mq Oxidation
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
61.43.-j Disordered solids

Investigation of the suppression effect of polyethylene glycol on copper electroplating by electrochemical impedance spectroscopy

Chi-Cheng Hung, Wen-Hsi Lee, Ying-Lang Wang, Din-Yuen Chan, and Gwo-Jen Hwang

J. Vac. Sci. Technol. A 26, 1109 (2008); http://dx.doi.org/10.1116/1.2949233 (6 pages) | Cited 1 time

Online Publication Date: 30 July 2008

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Polyethylene glycol (PEG) is an additive that is commonly used as a suppressor in the semiconductor copper (Cu)-electroplating process. In this study, electrochemical impedance spectroscopy (EIS) was used to analyze the electrochemical behavior of PEG in the Cu-electroplating process. Polarization analysis, cyclic-voltammetry stripping, and cell voltage versus plating time were examined to clarify the suppression behavior of PEG. The equivalent circuit simulated from the EIS data shows that PEG inhibited the Cu-electroplating rate by increasing the charge-transfer resistance as well as the resistance of the adsorption layer. The presence of a large inductance demonstrated the strong adsorption of cuprous-PEG-chloride complexes on the Cu surface during the Cu-electroplating process. Increasing the PEG concentration appears to increase the resistances of charge transfer, the adsorption layer, and the inductance of the electroplating system.
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85.40.Ls Metallization, contacts, interconnects; device isolation
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution
82.80.Fk Electrochemical methods
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Silane injection in a high-density low-pressure plasma system and its influence on the deposition kinetics and material properties of SiO2

R. Botha, B. Haj Ibrahim, P. Bulkin, and B. Drévillon

J. Vac. Sci. Technol. A 26, 1115 (2008); http://dx.doi.org/10.1116/1.2949234 (5 pages) | Cited 1 time

Online Publication Date: 30 July 2008

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High-rate, low temperature deposition is an essential requirement for industrial fabrication technology to be suitable for the deposition of optical and protective coatings. High-density, low-pressure plasmas have received significant attention for such applications due to their ability to create large and controllable ion fluxes onto the substrate. In this study, the high-rate deposition of silica films from a silane and oxygen gas mixture in a high-density plasma system based on a matrix distributed electron cyclotron resonance (MDECR) plasma source is investigated using directional jet injection of undiluted silane. The influence of process parameters such as the microwave power, radio frequency biasing of the substrate holder, and gas flows on the OH content of the oxide films is studied using phase-modulated spectroscopic ellipsometry (SE), Fourier transform infrared (FTIR) spectroscopy, and transmission measurements. The results of the measurements, taken at various points across the wafer, show a decrease in the thickness-normalized OH concentration in the areas of higher deposition rates. The corresponding gas phase composition is investigated using optical emission spectroscopy and compared to the FTIR, transmission and SE measurement results in order to validate our findings and ultimately optimize the deposition process. It is found that the primary silane flux onto the surface, which depends on the positioning of the jet injection point and gas flow rate, plays an important role not only on the deposition rate but also on the OH content of the films. The authors conclude that high-density plasma deposition systems such as the MDECR plasma enhanced chemical vapor deposition system cannot be considered as well mixed for gases with dissociation products that have high sticking coefficients, contrary to the accepted paradigm.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
52.77.Dq Plasma-based ion implantation and deposition
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators
82.80.Dx Analytical methods involving electronic spectroscopy

Low energy secondary ion mass spectrometry with sub-keV O2+ beams at glancing incidence

Z. X. Jiang, K. Kim, T. Guenther, B. Robichaud, J. Benavides, L. Contreras, and D. D. Sieloff

J. Vac. Sci. Technol. A 26, 1120 (2008); http://dx.doi.org/10.1116/1.2952449 (8 pages)

Online Publication Date: 30 July 2008

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The ever increasing interest in surface analysis techniques with excellent depth resolution, great detection sensitivity, and good throughput has been a driving force for development of dynamic secondary ion mass spectrometry using low energy primary beams. This work investigated sputtering erosion of Si and emission of secondary ions from Si bombarded by sub-keV O2+ beams at glancing incidence. It was demonstrated that surface roughening remained minimal for 250 and 500 eV O2+ beams at an angle of incidence above 80° but developed rapidly at angles between 60° and 80°. The depth resolution for B and Ge appeared very different at the glancing incidence and changed dramatically in opposite ways as the angle of incidence decreased. The difference in the depth resolution was explained by the different diffusion/segregation behavior between B and Ge during O2+ bombardment. In general, the use of sub-keV O2+ beams at the glancing incidence (above 80°) favored a thinner altered layer, a short surface transient, a minimal apparent shift in depth profiles, a better depth resolution (not for B in Si), a good sputter rate, but a poor yield of the positive secondary ions. To address the issues with the low ion yield, we identified optimal cluster ions for common dopant such as boron and nitrogen. Good sensitivity was achieved for analyses of boron in Si by detecting BO2− as the characteristic secondary ion. A parallel study published elsewhere suggested SiN− as an ideal candidate for detection of nitrogen in ultrathin oxynitride [ Z. X. Jiang et al., Surf. Interface Anal. (in press) ]. For analyses of thin SiGe films in Si at glancing incidence, detection of Ge+ provided fairly good sensitivity. Applications of an O2+ beam at 250 eV 83° for analyses of shallow boron implant demonstrated superior accuracy in the measured near-surface boron distribution. Also the characterization of thin SiGe films exhibited excellent depth resolving power for Ge in Si although the ion yield of Ge+ was low.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.bg Semiconductors
66.30.J- Diffusion of impurities

Measurement of reactive and condensable gas permeation using a mass spectrometer

Xiao Dong Zhang, Jay S. Lewis, Charles B. Parker, Jeffrey T. Glass, and Scott D. Wolter

J. Vac. Sci. Technol. A 26, 1128 (2008); http://dx.doi.org/10.1116/1.2952453 (10 pages) | Cited 1 time

Online Publication Date: 30 July 2008

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Permeation of water vapor, oxygen, nitrogen, and carbon dioxide through polymer films is measured by the programed valving mass spectrometry (PVMS) method. The results are calibrated with a standard permeation rate for each gas to determine the detection sensitivity. The calibrated lower detection limits are 1.90×10−7 g/m2 day for water vapor, 2.81×10−2 cm3/m2 day for oxygen, 2.15×10−2 cm3/m2 day for nitrogen, and 3.29×10−2 cm3/m2 day for carbon dioxide. The lower detection limits presented here for water vapor, nitrogen, and carbon dioxide are more than two orders of magnitude lower than the corresponding values offered by the NIST-traceable standard techniques. In addition, the PVMS water vapor lower detection limit meets the sensitivity requirement for detecting “ultrabarrier” water vapor permeation rates, while the oxygen lower detection limit is higher than that offered by the standard technique. However, the results suggest a modified measurement protocol and/or system modifications to overcome this limitation. Effusivity through a flow orifice was also examined using the PVMS method for the above gases. The effusion results from the flow orifice, combined with the permeation results from polymer samples, provide insight into the factors that may influence gas detection sensitivities.
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07.75.+h Mass spectrometers
82.80.-d Chemical analysis and related physical methods of analysis

Identification and quantification of iron silicide phases in thin films

D. R. Miquita, J. C. González, M. I. N. da Silva, W. N. Rodrigues, M. V. B. Moreira, R. Paniago, R. Ribeiro-Andrade, R. Magalhães-Paniago, H.-D. Pfannes, and A. G. de Oliveira

J. Vac. Sci. Technol. A 26, 1138 (2008); http://dx.doi.org/10.1116/1.2953708 (11 pages)

Online Publication Date: 6 August 2008

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Iron silicide samples were grown on Si (111) substrates by solid phase epitaxy and reactive deposition epitaxy. The different iron silicide phases and their correlations with the growth parameters were analyzed by x-ray photoelectron spectroscopy, conversion electron Mössbauer spectroscopy, x-ray diffraction, atomic force microscopy, and magnetic force microscopy. The authors investigated the potential of each technique for identifying and quantifying of the phases. In particular, the authors used a semiquantitative analysis of magnetic force microscopy images to spatially resolve the semiconductor β-FeSi2 phase.
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64.70.kg Semiconductors
81.30.Dz Phase diagrams of other materials
81.15.Np Solid phase epitaxy; growth from solid phases
68.47.Fg Semiconductor surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Structure and mechanical properties of diamondlike carbon films produced by hollow-cathode plasma deposition

H. F. Jiang, X. B. Tian, S. Q. Yang, R. K. Y. Fu, and P. K. Chu

J. Vac. Sci. Technol. A 26, 1149 (2008); http://dx.doi.org/10.1116/1.2953711 (5 pages) | Cited 3 times

Online Publication Date: 6 August 2008

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Diamondlike carbon (DLC) films are deposited on AISI 304 stainless-steel substrates using hollow-cathode chemical vapor deposition. The effects of the substrate bias on the structural and mechanical properties of the films are studied. X-ray photoelectron spectroscopy reveals the existence of CC (sp2) and C–C (sp3) functional groups in the films, and Raman spectra show that the ratio of the G (graphite) peak to the D (disorder) peak depends on the sample bias. The DLC film deposited at −50 V bias has the highest sp3 content, and this is consistent with the G-band position and D-band full width at half maximum as a result of substrate biasing. The sample bias also has a critical influence on the thickness and hardness of the deposited films. The largest thickness (1700 nm) and highest hardness (HV1099) are achieved at a bias voltage of −50 V. All the films show low friction coefficients, and the sample treated at −200 V gives rise to the lowest friction coefficient.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
79.60.Dp Adsorbed layers and thin films
78.30.Hv Other nonmetallic inorganics

Wafer heating mechanisms in a molecular gas, inductively coupled plasma: in situ, real time wafer surface measurements and three-dimensional thermal modeling

M. J. Titus and D. B. Graves

J. Vac. Sci. Technol. A 26, 1154 (2008); http://dx.doi.org/10.1116/1.2953713 (7 pages) | Cited 1 time

Online Publication Date: 6 August 2008

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The authors report measurements and modeling of wafer heating mechanisms in an Ar/O2 inductively coupled plasma (ICP). The authors employed a commercially available on-wafer sensor system (PlasmaTemp™ developed by KLA-Tencor) consisting of an on-board electronics module housing battery power and data storage with 30 temperature sensors embedded onto the wafer at different radial positions. This system allows for real time, in situ wafer temperature measurements. Wafer heating mechanisms were investigated by combining temperature measurements from the PlasmaTemp™ sensor wafer with a three-dimensional heat transfer model of the wafer and a model of the ICP. Comparisons between pure Ar and Ar/O2 discharges demonstrated that two additional wafer heating mechanisms can be important in molecular gas plasmas compared to atomic gas discharges. The two mechanisms are heating from the gas phase and O-atom surface recombination. These mechanisms were shown to contribute as much as 60% to wafer heating under conditions of low bias power. This study demonstrated how the “on-wafer” temperature sensor not only yields a temperature profile distribution across the wafer, but can be used to help determine plasma characteristics, such as ion flux profiles or plasma processing temperatures.
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52.50.Dg Plasma sources
52.70.Ds Electric and magnetic measurements
52.25.Kn Thermodynamics of plasmas
52.80.-s Electric discharges

Capillary flow meter for calibrating spinning rotor gauges

Robert F. Berg

J. Vac. Sci. Technol. A 26, 1161 (2008); http://dx.doi.org/10.1116/1.2953715 (5 pages)

Online Publication Date: 6 August 2008

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This article describes a capillary flow meter whose maximum flow rate of 0.2 μmol/s ( ∼ 0.2 cm3/min at ambient conditions) covers the range that is useful for calibrating spinning rotor gauges. Knowing the input pressure, output pressure, and temperature of the capillary yields the gas flow rate with a relative standard uncertainty as small as 0.04%. The flow meter, which requires no moving parts aside from valves, comprises a ballast tank, a coil of quartz capillary with an inner diameter of 0.1 mm, and a commercial instrumentation package. Measurements near 0.1 μmol/s showed agreement with an independent primary flow meter to within 0.2%, comparable to the combined relative standard uncertainty of 0.11%. Additional measurements showed that operating the capillary flow meter with an exit pressure less than 1 kPa allowed the flow to stabilize within minutes. However, the small exit pressure caused an unexpected enhancement of the slip correction in the hydrodynamic model of the capillary.
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47.80.-v Instrumentation and measurement methods in fluid dynamics
06.20.Dk Measurement and error theory

Reduction in hydrogen outgassing from stainless steels by a medium-temperature heat treatment

C. D. Park, S. M. Chung, Xianghong Liu, and Yulin Li

J. Vac. Sci. Technol. A 26, 1166 (2008); http://dx.doi.org/10.1116/1.2956625 (6 pages) | Cited 2 times

Online Publication Date: 6 August 2008

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The authors carried out heat treatments, in-vacuum or in-air at 400 °C, to reduce the hydrogen outgassing rate from stainless steels. An outgassing rate as low as 2×10−14 Torr ℓ s−1 cm−2 was routinely achieved by a medium-temperature bakeout, but it took much longer time than reported to perform intensive thermal treatment. The result shows that the diffusion process governs degassing only at the early stage of degassing while the recombination limits outgassing at low concentrations. Air baked chambers had somewhat lower outgassing rates than in-vacuum baked chambers, suggesting that the surface oxide acts as a further barrier for H2 outgassing. However, the main effect may be attributed to the removal of mobile hydrogen through diffusion. The results showed that the ultralow outgassing rate can be reproducibly achieved for stainless steel chambers with the established heat treatment procedure. The study also showed that the ultralow outgassing property of a treated chamber can be restored by a low temperature (>150 °C) postbakeout, after exposure to ambient air.
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84.60.-h Direct energy conversion and storage
81.40.Gh Other heat and thermomechanical treatments
66.30.-h Diffusion in solids

Trench profile angle beveling

Hui Chen and Q. Wang

J. Vac. Sci. Technol. A 26, 1172 (2008); http://dx.doi.org/10.1116/1.2960554 (6 pages)

Online Publication Date: 6 August 2008

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A trench bevel etch process is developed as a method to produce trench profiles with a prerequired angle. This process depends on both surface reaction and gas conductance along the trench. To study the surface reaction probability, activation energies were measured for SF6 and CF4 chemistries and were found to be 6 and 140 meV, respectively. It has been demonstrated that CF4 etch chemistry is in surface-reaction-rate-limited regime and contributes little to the trench beveling. SF6 chemistry with its low activation energy is in reactant-transport-rate-limited regime and contributes significantly to the bevel process. The dependences of bevel etch on trench aspect ratio was also investigated in detail. It has been found that high aspect ratio trench produces larger bevel angle than that does for small aspect ratio. A phenomenological model was constructed by introducing reactant conduction loss L and sidewall reaction loss S to quantitatively describe the effects of both reactant transport and surface reaction. Through comparison of theoretical modeling and experiment, an S value between 0.8 and 1 is reached to explain the experimental results from SF6 chemistry. This result demonstrates the SF6 is a spontaneous surface reaction and is consistent with our activation energy measurement.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.20.Pm Rate constants, reaction cross sections, and activation energies

Ferroelectric properties of Bi3.25La0.75Ti3O12 films using HfO2 as buffer layers for nonvolatile-memory field-effect transistors

Kyoung-Tae Kim, Gwan-Ha Kim, Jong-Chang Woo, and Chang-II Kim

J. Vac. Sci. Technol. A 26, 1178 (2008); http://dx.doi.org/10.1116/1.2960555 (4 pages) | Cited 2 times

Online Publication Date: 6 August 2008

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The ferroelectric Bi3.25La0.75Ti3O12 (BLT) thin film and HfO2 layer were fabricated using both metal-organic decomposition and atomic-layer deposition methods. The HfO2 thin film was deposited as a buffer layer between Si substrate and BLT thin films. The electrical and structural properties of the metal-ferroelectric-insulator-semiconductor (MFIS) structure were investigated by varying the HfO2 layer thickness. Transmission electron microscopy showed no interdiffusion and reaction occurring when the HfO2 film is used as a buffer layer. The width of the memory window in the capacitance-voltage curves for the MFIS structure was decreased with increasing thickness of the HfO2 buffer layer. The experimental results showed that the BLT-based MFIS structure is suitable for nonvolatile-memory field-effect transistors with a large memory window.
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77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.65.Ac Multilayers

Cyclic, cryogenic, highly anisotropic plasma etching of silicon using SF6/O2

A. F. Isakovic, K. Evans-Lutterodt, D. Elliott, A. Stein, and J. B. Warren

J. Vac. Sci. Technol. A 26, 1182 (2008); http://dx.doi.org/10.1116/1.2960557 (6 pages) | Cited 4 times

Online Publication Date: 6 August 2008

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The authors report on the development and characterization of a plasma etching method that utilizes process steps common to both the well-known Bosch and the cryogenic deep reactive ion etching methods for silicon. This hybrid process uses cyclical etch steps that alternate between etching and passivating chemistries as in the Bosch process, while still maintaining sample temperatures at −100 °C on a cryogenically cooled stage. The advantages of this process are superior control of wall profiles for isolated features, minimization of grass formation, and the elimination of an expensive gas, c-C4F8, required in the Bosch passivation step. The authors show examples of x-ray optic elements deep etched to 100 μm depth with the cyclic cryogenic process.
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81.05.Cy Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning
81.65.Rv Passivation
52.77.Bn Etching and cleaning

Influence of N2 gas pressure and negative bias voltage on the microstructure and properties of Cr–Si–N films by a hybrid coating system

Qimin Wang, In-Wook Park, and Kwangho Kim

J. Vac. Sci. Technol. A 26, 1188 (2008); http://dx.doi.org/10.1116/1.2960558 (7 pages)

Online Publication Date: 6 August 2008

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Cr–Si–N films were deposited using a hybrid coating system combining arc ion plating and magnetron sputtering. The authors investigated the influence of N2 flux rate and negative bias voltage on the microstructure and properties of Cr–Si–N films, e.g., chemical composition, film morphology, phase structure, residual stress, and microhardness. The results showed that all the Cr–Si–N films were close to stoichiometry. The N2 flux rate had no important influence on the microstructure and properties of the Cr–Si–N films. Applying a negative bias voltage resulted in significant decrease in macroparticle densities and smoother film surface. Also the film microstructure transformed from apparent columnar to nanocomposite microstructure. The maximum microhardness obtained ranged from 45 to 50 GPa at a bias voltage ranging from −50 to −100 V. The microhardness enhancement could be ascribed to the mixed effect of grain size diminishment and residual compressive stress.
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68.60.Bs Mechanical and acoustical properties
82.80.-d Chemical analysis and related physical methods of analysis
81.15.Cd Deposition by sputtering
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.J- Morphology of films
68.55.Nq Composition and phase identification

Enhanced chemical immunity for negative electron affinity GaAs photoemitters

G. A. Mulhollan and J. C. Bierman

J. Vac. Sci. Technol. A 26, 1195 (2008); http://dx.doi.org/10.1116/1.2965816 (3 pages) | Cited 3 times

Online Publication Date: 6 August 2008

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Negative electron affinity GaAs photoemitters require ultrahigh vacuum conditions to achieve the best performance and to maintain the quantum yield. This limits their utility in applications where the background pressure is high. The authors have developed an activation procedure by which the reactivity to CO2, a principal cause of yield decay, is greatly reduced. The use of a second alkali in the activation process is responsible for the increased immunity of the activated surface. The best immunity was obtained by using a combination of Cs and Li without any loss in near band gap yield.
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85.60.Ha Photomultipliers; phototubes and photocathodes

Study of fluorocarbon plasma in 60 and 100 MHz capacitively coupled discharges using mass spectrometry

Andrey Ushakov, Vladimir Volynets, Sangmin Jeong, Dougyong Sung, Yongho Ihm, Jehun Woo, and Moonhyeong Han

J. Vac. Sci. Technol. A 26, 1198 (2008); http://dx.doi.org/10.1116/1.2965812 (10 pages)

Online Publication Date: 6 August 2008

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The signals of positive ions and radicals formed in the fluorocarbon plasma of the capacitively coupled plasma reactor were measured using a quadrupole mass spectrometry and optical emission actinometry. The plasma was produced at 60 and 100 MHz frequencies for the same reactor configuration and gas mixtures. Experiments were performed at 25 mTorr with a SiO2 wafer on the grounded electrode. Mass spectra of ions were measured in C4F8/O2/Ar and C4F6/O2/Ar gas mixtures at 500–1500 W generator powers. For 60 and 100 MHz discharges production of fluorocarbon ions and radicals is discussed. It was found that the production of heavy species increases with frequency. The high mass signals such as C3F3+, C2F4+, C2F5+, C3F5+, C4F7+ decrease when CHF3 is added to the gas mixture. However, the signals of CFx+ (x = 1,2,3) do not change significantly. These results are compared to the results of polymer film deposition on the wafer. It was suggested to control the polymerization film formation by adding small amount of CHF3 to the process mixture.
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52.50.-b Plasma production and heating
52.80.Pi High-frequency and RF discharges
52.25.Fi Transport properties
52.25.Tx Emission, absorption, and scattering of particles
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.35.-x Polymers: properties; reactions; polymerization

On the phase identification of dc magnetron sputtered Pt–Ru alloy thin films

A. P. Warren, R. M. Todi, B. Yao, K. Barmak, K. B. Sundaram, and K. R. Coffey

J. Vac. Sci. Technol. A 26, 1208 (2008); http://dx.doi.org/10.1116/1.2966422 (5 pages)

Online Publication Date: 6 August 2008

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The microstructure and the electronic work function of Pt–Ru alloy thin films spanning the compositional range from pure Pt to pure Ru were investigated. Nominally 50 nm thick films were cosputtered from elemental targets in an ultrahigh vacuum chamber. X-ray reflectivity and Rutherford backscattering spectroscopy were used to determine the film thicknesses and compositions. The electronic work function of the alloy film samples was determined by analysis of the capacitance-voltage characteristics of films deposited as part of a metal-oxide-semiconductor capacitor structure and found to range from 4.8 eV for pure Ru to 5.2 eV for pure Pt. To better understand the variation in work function for the intermediate compositions, the films were characterized by transmission electron microscopy and x-ray and electron diffractions. A notable increase in the compositional range of the hexagonal close packed (hcp) phase was observed, suggesting a metastable extension of the hcp phase stability as compared to bulk Pt–Ru alloys. The steepest change in the electronic work function for the intermediate alloy compositions coincided with a rapid change in the c/a ratio of the hcp phase.
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68.55.Nq Composition and phase identification
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.37.Og High-resolution transmission electron microscopy (HRTEM)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.40.Cg Contact resistance, contact potential
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Enhancement of metal oxide deposition rate and quality using pulsed plasma-enhanced chemical vapor deposition at low frequency

Michael T. Seman, David N. Richards, Pieter C. Rowlette, Nicholas G. Kubala, and Colin A. Wolden

J. Vac. Sci. Technol. A 26, 1213 (2008); http://dx.doi.org/10.1116/1.2966425 (5 pages) | Cited 3 times

Online Publication Date: 6 August 2008

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The deposition rate and quality of alumina thin films fabricated by plasma-enhanced chemical vapor deposition (PECVD) increased significantly when square wave power modulation was applied at low frequency ( ∼ 1 Hz). The pulsed PECVD rate was enhanced by a factor of ∼ 3 relative to continuous wave operation, and the quantity of impurities was dramatically attenuated. Deposition experiments on trenches with aspect ratios ranging from 4 to infinity demonstrated that the technique achieves a high degree of conformality. Important reactor design and operating considerations are described. Pulsed PECVD produced similar quality improvements for Ta2O5, TiO2, and ZnO, suggesting that the approach has widespread potential for metal oxide synthesis.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth

Origin of hydrogen desorption during friction of stainless steel by alumina in ultrahigh vacuum

R. A. Nevshupa, E. Roman, and J. L. de Segovia

J. Vac. Sci. Technol. A 26, 1218 (2008); http://dx.doi.org/10.1116/1.2968682 (6 pages)

Online Publication Date: 20 August 2008

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A study of the tribodesorption of hydrogen stimulated by the friction of an alumina pin on stainless steel in ultrahigh vacuum at room temperature is presented. A special two-chamber ultrahigh-vacuum system separated by a well-defined orifice of low conductance is used to determine minute amounts of desorbed gases. The friction cell allows the control of the normal force of the alumina pin on the stainless-steel surface, the frequency of sweeping, as well as the dwell, i.e., the time between consecutive strokes. The profile of the p(H2)-t desorption curve shows a near-exponential increase in pressure to a stable value; then, after the friction cessation, the pressure decreases back to the initial value. The desorption curve presents an oscillating signal over the continuous one that corresponds with the sweeping frequency. An important aspect of the present research has been to elucidate the origin of the desorbed hydrogen: bulk or surface of materials. In this respect, the amount of tribodesorbed hydrogen is compared with the amount of adsorbed hydrogen at dwell times from 0.5 to 4 s. This adsorption is 50 and 5 times lower than the desorbed hydrogen at normal forces of 0.072 and 0.218 N, respectively, and a dwell time of 4 s. An important finding is that the amount of desorbed hydrogen is irrespective of the dwell time, and the desorption rate increases linearly with sweeping frequency. The authors conclude that the origin of the desorbed hydrogen is in the bulk.
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68.43.Nr Desorption kinetics
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness

Two-silane chemical vapor deposition treatment of polymer (nylon) and oxide surfaces that yields hydrophobic (and superhydrophobic), abrasion-resistant thin films

Gaurav Saini, Ken Sautter, Frank E. Hild, Jerry Pauley, and Matthew R. Linford

J. Vac. Sci. Technol. A 26, 1224 (2008); http://dx.doi.org/10.1116/1.2953699 (11 pages)

Online Publication Date: 20 August 2008

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This article describes a two-silane, chemical vapor deposition (CVD) approach to creating hydrophobic (or even superhydrophobic), abrasion-resistant coatings on silicon oxide and polymer (nylon) substrates. This multistep approach employs only reagents delivered in the gas phase, as follows: (i) plasma cleaning/oxidation of the substrate, (ii) CVD of 3-isocyanatopropyltriethoxysilane, which is used as an adhesion promoter for the substrate, (iii) hydrolysis with water vapor, and (iv) CVD of (tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane (the “Rf-Cl silane”). Surfaces are characterized by wetting, spectroscopic ellipsometry, x-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). This work has the following unique features. First, the authors explore an all gas phase deposition of a new silane coating that is scientifically interesting and technologically useful. Second, the authors show that the presence of an adhesion promoter in the process leads to thinner films that are more robust in abrasion testing. Third, results obtained using plasma/deposition equipment that is relatively inexpensive and/or available in most laboratories are compared to those obtained with a much more sophisticated, commercially available plasma/CVD system (the YES-1224P). The entire deposition process can be completed in only ∼ 1 h using the industrial equipment (the 1224P). It is of significance that the polymer surfaces modified using the 1224P are superhydrophobic. Fourth, the thickness of the Rf-Cl silane layer deposited by CVD correlates well with the thickness of the underlying spin coated nylon surface, suggesting that the nylon film acts as a reservoir of water for the hydrolysis and condensation of the Rf-Cl silane.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.-j Plasma applications
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Growth and interface of HfO2 films on H-terminated Si from a TDMAH and H2O atomic layer deposition process

Justin C. Hackley, J. Derek Demaree, and Theodosia Gougousi

J. Vac. Sci. Technol. A 26, 1235 (2008); http://dx.doi.org/10.1116/1.2965813 (6 pages) | Cited 4 times

Online Publication Date: 20 August 2008

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HfO2 thin films have been deposited by an atomic layer deposition (ALD) process using alternating pulses of tetrakis(dimethyl)amino hafnium and H2O precursors at a substrate temperature of 200–325 °C. The initial stage of film growth on OH- and H-terminated Si(100) surfaces is investigated using Rutherford backscattering spectrometry (RBS), x-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). The authors observe an initial growth barrier on the Si–H surface for the first approximately four process cycles, where film growth is more efficient on the OH-terminated surface. Both starting surfaces require about 15 cycles to reach a steady growth rate per cycle, with the OH-terminated surface displaying a slightly higher growth rate of 2.7×1014 Hf/cm2 compared to 2.4×1014 Hf/cm2 for Si–H. Combining the RBS and SE data we conclude that the films deposited on the OH-terminated surface are denser than those deposited on the Si–H surface. Angle-resolved XPS measurements reveal the formation of an ∼ 8 Å interfacial layer after four ALD cycles on the H-terminated surface for a deposition temperature of 250 °C, and transmission electron microscopy verifies that the thickness of the interfacial layer does not change substantially between the 4th and the 25th process cycles. The interfacial layer appears to depend weakly on the deposition temperature from 200 to 325 °C, ranging from 6.9 to 8.4 Å.
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77.55.-g Dielectric thin films
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Unique lack of chemical reactivity for 2,3-dimethyl-2-butene on a Si(100)-2×1 surface

Mark R. Madachik and Andrew V. Teplyakov

J. Vac. Sci. Technol. A 26, 1241 (2008); http://dx.doi.org/10.1116/1.2966427 (7 pages)

Online Publication Date: 20 August 2008

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Adsorption of 2,3-dimethyl-2-butene on Si(100)-2×1 has been studied by a combination of multiple internal reflection Fourier transform infrared spectroscopy and computational investigations implementing density functional theory (DFT). Since the previously studied olefins have been shown to form a di-σ product on this surface following [2+2] cycloaddition, it was also initially expected for 2,3-dimethyl-2-butene. Infrared spectra taken at 100 K show that 2,3-dimethyl-2-butene adsorbs on the surface molecularly at this temperature. Heating the surface to room temperature left no indication of a chemisorbed product. Large doses at room temperature did not produce any observable absorption bands in the infrared spectrum, indicating that [2+2] cycloaddition of 2,3-dimethyl-2-butene does not occur. This assessment was verified by the Auger electron spectroscopy studies confirming that neither room temperature exposure nor annealing to 800 K produced any carbon remaining on this surface. These experimental observations of the absence of a chemical reaction between an olefin and a very reactive silicon surface were substantiated by DFT investigation of the adsorption kinetics. The formation of two possible π-bonded precursors was considered, and the energies required to form the di-σ-bonded product from either one of these precursors were predicted to be substantially higher than the desorption barrier. Thus, 2,3-dimethyl-2-butene is a unique olefin that is very inert with respect to the Si(100)-2×1 surface, making it a desirable carrier gas or a ligand in the precursor molecules in a number of deposition processes involving silicon substrates.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.43.Mn Adsorption kinetics
82.80.Dx Analytical methods involving electronic spectroscopy
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.20.At Surface states, band structure, electron density of states
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

The effectiveness of HCl and HF cleaning of Si0.85Ge0.15 surface

Yun Sun, Zhi Liu, Shiyu Sun, and Piero Pianetta

J. Vac. Sci. Technol. A 26, 1248 (2008); http://dx.doi.org/10.1116/1.2966428 (3 pages) | Cited 1 time

Online Publication Date: 20 August 2008

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The cleaning of Si0.85Ge0.15 surfaces using HCl and HF solutions is studied using synchrotron radiation photoelectron spectroscopy. The HF solution is found to be effective in removing both the Si oxide and the Ge oxide while the HCl solution can only remove part of the Ge oxide. For samples treated with HF, four spectral components are needed to fit the Ge 3d photoemission spectra. One is the bulk component and the other three are attributed to the surface Ge atoms with monohydride, dihydride, and trihydride terminations, respectively.
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81.65.Cf Surface cleaning, etching, patterning
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Characteristics of Hf-silicate thin films synthesized by plasma enhanced atomic layer deposition

Jiurong Liu, Ryan M. Martin, and Jane P. Chang

J. Vac. Sci. Technol. A 26, 1251 (2008); http://dx.doi.org/10.1116/1.2966430 (7 pages) | Cited 1 time

Online Publication Date: 20 August 2008

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Hafnium silicate films were grown by alternating the deposition cycles of hafnium oxide and silicon oxide using a plasma enhanced atomic layer deposition process. The as-deposited and 900 °C annealed hafnium silicate films were determined to be amorphous using grazing incidence x-ray diffraction. This suggested that the formation of hafnium silicate suppressed the crystallization of HfO2 at high temperatures. The dielectric constants increased from ∼ 5 to ∼ 17 as the hafnium content increased from 9 to 17 at. % in the hafnium silicate films. The leakage currents through the Hf-rich Hf-silicate films were two to three orders of magnitude lower than that of SiO2 with the same equivalent oxide thickness in the range of 1.6–2.3 nm. The estimated band gap of Hf-silicate films from the O 1s plasma loss spectra increased with the increasing Si content due to the higher band gap of SiO2 than that of HfO2.
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77.55.-g Dielectric thin films
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
52.77.Dq Plasma-based ion implantation and deposition
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Effect of negative bias voltage on CrN films deposited by arc ion plating. I. Macroparticles filtration and film-growth characteristics

Qi Min Wang and Kwang Ho Kim

J. Vac. Sci. Technol. A 26, 1258 (2008); http://dx.doi.org/10.1116/1.2966432 (9 pages)

Online Publication Date: 20 August 2008

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Chromium nitride (CrN) films were deposited on Si wafers by arc ion plating (AIP) at various negative bias voltages and several groups of N2/Ar gas flux ratios and chamber gas pressures. The authors systematically investigated the influence of negative bias voltage on the synthesis, composition, microstructure, and properties of the AIP CrN films. In this part (Part I), the investigations were mainly focused on the macroparticle distributions and film-growth characteristics. The results showed that macroparticle densities on the film surfaces decreased greatly by applying negative bias voltage, which can be affected by partial pressure of N2 and Ar gases. From the statistical analysis of the experimental results, they proposed a new hybrid mechanism of ion bombardment and electrical repulsion. Also, the growth of the AIP CrN films was greatly altered by applying negative bias voltage. By increasing the bias voltage, the film surfaces became much smoother and the films evolved from apparent columnar microstructures to an equiaxed microstructure. The impinging high-energy Cr ions accelerated by negative bias voltages were deemed the inherent reason for the evolution of growth characteristics.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.at Other materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Effect of negative bias voltage on CrN films deposited by arc ion plating. II. Film composition, structure, and properties

Qi Min Wang and Kwang Ho Kim

J. Vac. Sci. Technol. A 26, 1267 (2008); http://dx.doi.org/10.1116/1.2966434 (10 pages) | Cited 1 time

Online Publication Date: 20 August 2008

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Chromium nitride (CrN) films were deposited on Si wafers by arc ion plating at various negative bias voltages and several groups of N2/Ar gas flux ratios and chamber gas pressures. The authors systematically investigated the influence of negative bias voltage on the synthesis, composition, microstructure, and properties of the arc ion plating (AIP) CrN films. In this article, the authors investigated the influence of negative bias voltage on the chemical composition, structure, and mechanical properties of the CrN films. The results showed that the chemical composition and phase structure of the AIP CrN films were greatly altered by application of negative bias voltage. Due to the selective resputtering effect, substoichiometric CrN films were obtained. With increase in bias voltages, the main phases in the films transformed from Cr+CrN to Cr2N at low N2/Ar flow ratios, whereas the films at high N2/Ar flow ratios retained the CrN phase structure. The CrN films experienced texture transformation from CrN (200) to CrN (220), and Cr2N (300) to Cr2N(300)+Cr2N(110). Increase in negative bias voltage also resulted in microstructure evolution of coarse columnar grains→fine columnar grains→quasiamorphous microstructure→recrystallized structures. From the experimental results, the authors proposed a new structure zone model based on enhanced bombardment of incident ions by application of negative bias voltage. The influence of negative bias voltage on the microhardness and residual stresses of the films and the inherent mechanisms were also explored.
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68.55.jm Texture
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
68.35.Gy Mechanical properties; surface strains
68.60.Bs Mechanical and acoustical properties
81.15.Jj Ion and electron beam-assisted deposition; ion plating
82.80.-d Chemical analysis and related physical methods of analysis

Pulsed dc self-sustained magnetron sputtering

A. Wiatrowski, W. M. Posadowski, and Z. J. Radzimski

J. Vac. Sci. Technol. A 26, 1277 (2008); http://dx.doi.org/10.1116/1.2966436 (5 pages) | Cited 3 times

Online Publication Date: 20 August 2008

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The magnetron sputtering has become one of the commonly used techniques for industrial deposition of thin films and coatings due to its simplicity and reliability. At standard magnetron sputtering conditions (argon pressure of ∼ 0.5 Pa) inert gas particles (necessary to sustain discharge) are often entrapped in the deposited films. Inert gas contamination can be eliminated during the self-sustained magnetron sputtering (SSS) process, where the presence of the inert gas is not a necessary requirement. Moreover the SSS process that is possible due to the high degree of ionization of the sputtered material also gives a unique condition during the transport of sputtered particles to the substrate. So far it has been shown that the self-sustained mode of magnetron operation can be obtained using dc powering (dc-SSS) only. The main disadvantage of the dc-SSS process is its instability related to random arc formation. In such case the discharge has to be temporarily extinguished to prevent damaging both the magnetron source and power supply. The authors postulate that pulsed powering could protect the SSS process against arcs, similarly to reactive pulsed magnetron deposition processes of insulating thin films. To put this concept into practice, (i) the high enough plasma density has to be achieved and (ii) the type of pulsed powering has to be chosen taking plasma dynamics into account. In this article results of pulsed dc self-sustained magnetron sputtering (pulsed dc-SSS) are presented. The planar magnetron equipped with a 50 mm diameter and 6 mm thick copper target was used during the experiments. The maximum target power was about 11 kW, which corresponded to the target power density of ∼ 560 W/cm2. The magnetron operation was investigated as a function of pulse frequency (20–100 kHz) and pulse duty factor (50%–90%). The discharge (argon) extinction pressure level was determined for these conditions. The plasma emission spectra (400–410 nm range) and deposition rates were observed for both dc and pulsed dc self-sustained sputtering processes. The pulse characteristics of the voltage and current of the magnetron source during pulsed dc-SSS operation are shown. The presented results illustrate that a stable pulsed dc-SSS process can be obtained at a pulsing frequency in the range of 60–90 kHz and duty factor of 80%–90%.
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81.15.Cd Deposition by sputtering
52.77.-j Plasma applications
81.65.-b Surface treatments

Feedback control of HfO2 etch processing in inductively coupled Cl2/N2/Ar plasmas

Chaung Lin, Keh-Chyang Leou, Ting-Chieh Li, Lurng-Shehng Lee, and Pei-Jer Tzeng

J. Vac. Sci. Technol. A 26, 1282 (2008); http://dx.doi.org/10.1116/1.2966438 (5 pages) | Cited 2 times

Online Publication Date: 20 August 2008

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The etch rate of HfO2 etch processing has been feedback controlled in inductively coupled Cl2/N2/Ar plasmas. The ion current and the root mean square rf voltage on the wafer stage, which are measured using a commercial impedance meter connected to the wafer stage, are chosen as controlled variables because the positive-ion flux and ion energy incident upon the wafer surface are the key factors that determine the etch rate. Two 13.56 MHz rf generators are used to adjust the inductively coupled plasma power and bias power which control ion density and ion energy, respectively. The adopted HfO2 etch processing used rather low rf voltage. The ion-current value obtained by the power/voltage method is underestimated, so the neural-network model was developed to assist estimating the correct ion-current value. The experimental results show that the etch-rate variation of the closed-loop control is smaller than that of the open-loop control. However, the first wafer effect cannot be eliminated using closed-loop control and thus to achieve a constant etch rate, the chamber-conditioning procedure is required in this etch processing.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning

Growth and ellipsometric characterizations of highly (111)-oriented Bi2Ti2O7 films on platinized silicon by metal organic decomposition method

Z. G. Hu, Y. W. Li, M. Zhu, F. Y. Yue, Z. Q. Zhu, and J. H. Chu

J. Vac. Sci. Technol. A 26, 1287 (2008); http://dx.doi.org/10.1116/1.2970142 (6 pages)

Online Publication Date: 20 August 2008

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Optical properties and electronic structure of Bi2Ti2O7 (BTO) films on platinized silicon substrates have been investigated using near-infrared-ultraviolet spectroscopic ellipsometry. The optical dispersion in the photon energy range of 0.73–5.8 eV has been extracted by fitting the experimental data with a four-phase layered model. The Tauc–Lorentz dispersion function has been fundamentally applied and describes the optical response of the BTO films well. The refractive index in the transparent region can be reasonably fitted by a single oscillator function and the maximum electronic transition occurs near 4.2 eV for the BTO material. The long wavelength refractive index n(0) can be estimated to about 1.7 at zero point. The fundamental band gap energy was determined to be about 3.2 eV, which was supported by different theoretical evaluation methods. The present results can be important for future applications of BTO-based electro-optics and optoelectronic devices.
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71.20.Ps Other inorganic compounds

Deterioration of seal reliability due to noncoaxial arrangement of ConFlat type flanges and gasket

Satoshi Kurokouchi

J. Vac. Sci. Technol. A 26, 1293 (2008); http://dx.doi.org/10.1116/1.2970143 (7 pages)

Online Publication Date: 20 August 2008

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Certain combinations of commercially available ConFlat type flanges with a gasket can yield an excessively wide gap between the gasket’s outer rim and the flange’s gasket-retaining counter. (The present ISO Technical Specification for the ConFlat type sealing system allows a maximum gap of some 0.8 mm width.) Tightening this type of flange-and-gasket combination almost never results in a perfect coaxial arrangement; rather, it produces eccentric arrangements of the matching flanges and sandwiched gaskets. In a tightening test with coaxially arranged flanges and eccentrically arranged gaskets, seal performance was independent of the gap width, whether or not baking was included in the test conditions. The results indicate that the existing “capture model” lacks validity as a rationale for the seal mechanism of the ConFlat system. By contrast, the eccentric arrangement of matching flanges did prove to have a strong influence on seal reliability, particularly where the tightening test includes a baking process. The negative impact on seal reliability observed in eccentric arrangements can be ascribed to local bending that occurs on the tightened gasket and the consequent diminution of seal area and seal pressure. Annealing of the gasket material during the baking process lowers seal pressure further, thus increasing the probability of leaks.
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81.20.Vj Joining; welding
81.40.Gh Other heat and thermomechanical treatments

Plasma-assisted molecular beam epitaxy and characterization of SnO2 (101) on r-plane sapphire

M. E. White, M. Y. Tsai, F. Wu, and J. S. Speck

J. Vac. Sci. Technol. A 26, 1300 (2008); http://dx.doi.org/10.1116/1.2966423 (8 pages) | Cited 6 times

Online Publication Date: 25 August 2008

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Plasma-assisted molecular beam epitaxy has been shown to be a viable and practical method for producing high quality tin oxide, SnO2. Phase-pure epitaxial single crystalline SnO2 (101) thin films of 1 μm in thickness were reproducibly grown on r-plane sapphire Al2O3 (10math2) substrates. The SnO2 epitaxy progressed in the Volmer–Weber growth mode. A minimum on-axis ω-scan full width at half maximum of 0.22° for the SnO2 (101) peak was measured indicating relatively low film mosaic. An epitaxial relationship of [010]SnO2∥[math2math0]sapphire and [math01]SnO2∥[math011]sapphire was determined between the film and substrate. A SnO2 film tilt of 1.3° around the [010]SnO2 toward [0001]sapphire was measured. A dislocation density of 8×109 cm−2 was measured. Hall effect measurements quantified an unintentionally doped electron concentration for different samples in a range (0.3–3.0)×1017 cm−3 with a corresponding electron mobility range of 20–100 cm2/V s. The SnO2 growth behavior was determined to be in one of the two distinct growth regimes. An oxygen-rich regime was characterized by a linear increase in the film growth rate with increasing Sn flux; whereas, the films grown entirely in the Sn-rich regime showed a decrease in the growth rate with increased Sn flux.
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68.55.aj Insulators
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
73.50.Dn Low-field transport and mobility; piezoresistance

Increased O(math) metastable flux with Ar and Kr diluted oxygen plasmas and improved film properties of grown SiO2 film

Takeshi Kitajima, Toshiki Nakano, and Toshiaki Makabe

J. Vac. Sci. Technol. A 26, 1308 (2008); http://dx.doi.org/10.1116/1.2968684 (6 pages) | Cited 1 time

Online Publication Date: 25 August 2008

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Metastable O(math) atoms produced in rare gas diluted O2 plasmas are believed to be the key of high quality SiO2 film formation at low substrate temperatures. The authors diagnosed the behavior of the O(math) density in highly rare gas diluted O2 plasma and applied the increased O(math) flux to the formation of thin SiO2 films on Si(100) substrate. O(math) flux increases 4.5 times with Kr (97%) dilution of O2 plasma while it increases 2.8 times for the case of Ar (97%). X-ray photoelectron spectroscopy spectrum showed Si–Si bond in the grown film was decreased by rare gas diluted plasmas. The stoichiometry of the film is improved by Ar and Kr dilution and corresponds to the increase in O(math) flux to the surface. Electrical breakdown field measured by atomic force microscopy was 1.5 times higher for Kr/O2 plasma grown film compared to the pure O2 case and supports the quality of the film.
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34.35.+a Interactions of atoms and molecules with surfaces
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Pi High-frequency and RF discharges
52.40.Hf Plasma-material interactions; boundary layer effects
52.77.Dq Plasma-based ion implantation and deposition

Synthesis of nanoscale CNx/TiAlN multilayered coatings by ion-beam-assisted deposition

M. Cao, D. J. Li, X. Y. Deng, and X. Sun

J. Vac. Sci. Technol. A 26, 1314 (2008); http://dx.doi.org/10.1116/1.2956627 (5 pages)

Online Publication Date: 28 August 2008

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CNx/TiAlN multilayered coatings with different nanoscale modulation periods and ratio of CNx within each period were prepared by ion-beam-assisted deposition at room temperature. Auger electron spectroscopy (AES), x-ray diffraction (XRD), and nanoindenter and a profiler were used to characterize the microstructure and mechanical properties of the coatings. The low-angle XRD pattern and AES indicated a well-defined multilayered structure of the coating. Although monolithic CNx and TiAlN coatings formed amorphous and nanocrystalline structures, respectively, the CNx/TiAlN multilayers exhibited coherent epitaxial growth due to the mutual growth-promoting effect at small CNx layer thickness (<0.6 nm). At modulation period Λ = 2.83 nm and CNx thickness of 10% within each period, the multilayers exhibited strong TiAlN (111) and weak AlN (111) textures and showed the highest hardness (32 GPa), elastic modulus (409 GPa), and critical fracture load (65.7 mN).
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.65.Ac Multilayers
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.Qp Friction, tribology, and hardness

Test particle Monte Carlo study of the cryogenic pumping system of the Karlsruhe tritium neutrino experiment

X. Luo and Ch. Day

J. Vac. Sci. Technol. A 26, 1319 (2008); http://dx.doi.org/10.1116/1.2956628 (7 pages)

Online Publication Date: 28 August 2008

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The cryogenic pumping system (CPS) is the last active tritium pumping system of the Karlsruhe tritium neutrino (KATRIN) experiment, in which the neutrino mass will be directly measured from the tritium beta decay. The spectrometer systems downstream to the CPS are required to be tritium-free. The high pumping speed of the CPS is to be provided by condensed argon frost at 3–3.5 K on the surfaces of the beamline tubes. In this unique design the beta particles can be simultaneously guided to the spectrometers by the superconducting magnets around the beamline tubes. In addition, nonevaporable getter (NEG) strips or NEG coated tubes are to be used in the last two sections of the CPS to secure this tritium-free boundary in case of a cryogenic failure event. In this article, the properties of the CPS are studied by the test particle Monte Carlo method, in which the effects of the argon frost sticking coefficient, the geometry of the beamline tube and the bend angle between two beamline sections are addressed. The tritium flow rate reduction factor and the adsorption distribution profile are estimated. The performance of the NEG section at different geometries is also presented.
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07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
07.30.Cy Vacuum pumps

Contribution of statistical time delay and formative time to total electrical breakdown time delay in argon for different afterglow periods

Momcilo M. Pejovic and Milic M. Pejovic

J. Vac. Sci. Technol. A 26, 1326 (2008); http://dx.doi.org/10.1116/1.2966435 (5 pages)

Online Publication Date: 28 August 2008

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The contribution of statistical time delay and formative time to total electrical breakdown time delay in an argon-filled tube at 4 mbar pressure for afterglow periods from 3 ms to 300 s has been analyzed. This contribution was analyzed on the basis of total electrical breakdown time-delay experimental data and their standard deviation. It was shown that for values of afterglow period from 3 to 70 ms, the contribution of statistical time delay to total electrical breakdown time delay can be neglected. For afterglow periods higher then 70 ms the experimental results of total electrical breakdown time delay can be described by Laue’s distribution, which was developed for statistical time delay. It shows that in this case the formative time is much smaller than the statistical time delay, so the total electrical breakdown time delay is approximately equal to the statistical time delay.
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51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
52.80.Hc Glow; corona

Local supply of gas in vacuum: Application to a field ion source

Marion Descoins, Zoubida Hammadi, and Roger Morin

J. Vac. Sci. Technol. A 26, 1331 (2008); http://dx.doi.org/10.1116/1.2968689 (5 pages) | Cited 1 time

Online Publication Date: 28 August 2008

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The flow of hydrogen, helium, and nitrogen through a millimeter long and micrometer size annulus capillary from a high pressure chamber to a low pressure chamber is measured in a wide pressure range. The corresponding gas conductance is deduced. Molecular, transition, and viscous regimes are observed. The local supply of gas strongly increases with pressure in the viscous regime up to a regime controlled by capillary exit loss. Based on such a geometry, the gas supply to a field ion source with a coaxial structure is shown to be increased by more than three orders of magnitude compared to a conventional supply.
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47.15.Rq Laminar flows in cavities, channels, ducts, and conduits
29.25.Ni Ion sources: positive and negative
29.25.Lg Ion sources: polarized

Real-time scanning tunneling microscopy observations of the oxidation of a Ti/Pt(111)-(2×2) surface alloy using O2 and NO2

Shuchen Hsieh, G. F. Liu, and Bruce E. Koel

J. Vac. Sci. Technol. A 26, 1336 (2008); http://dx.doi.org/10.1116/1.2969903 (7 pages)

Online Publication Date: 28 August 2008

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The authors have used scanning tunneling microscopy (STM), low energy electron diffraction (LEED), and Auger electron spectroscopy (AES) to study the nascent oxidation of an ordered Ti/Pt(111)-(2×2) surface alloy exposed to oxygen (O2) or nitrogen dioxide (NO2) under ultrahigh vacuum conditions. The Ti/Pt(111)-(2×2) surface alloy was formed by depositing an ultrathin Ti film on Pt(111) and annealing to 1050 K. This produces an alloy film in which the surface layer is pure Pt and the second layer contains Ti atoms in a (2×2) structure, which causes the pattern observed by STM and LEED. Real-time imaging of the surface at 300 K was carried out by continuously scanning with the STM while either O2 or NO2 was introduced into the chamber. O2 exposures did not cause any gross structural changes; however oxygen was detected on the surface afterward using AES. Annealing this surface to 950 K resulted in the formation of an ordered TiOx overlayer as characterized by both LEED and STM. In contrast, NO2 exposures caused definite changes in the surface morphology at 300 K, and the root-mean-square roughness increased from 3.5 to 7.1 Å after a large NO2 exposure. No ordered structures were produced by this treatment, but annealing the surface to 950 K formed an ordered pattern in LEED and corresponding clear, well-resolved structures in STM images. We account for these observations on the disruption or reconstruction of the Ti/Pt(111)-(2×2) surface alloy by arguments recalling that Ti oxidation is an activated process. The energetic barrier to TiOx formation cannot be surmounted at room temperature at low oxygen coverages, and annealing the surface was necessary to initiate this reaction. However, the higher oxygen coverages obtained using the more reactive oxidant NO2 lowered the chemical potential in the system sufficiently to overcome the activation barrier to extract Ti from the alloy at room temperature and form a disordered TiOx film. These results illustrate the importance of the surface oxygen coverage in nucleating the room temperature oxidation of the Pt–Ti surface alloys and further show the ability of NO2 in ultrahigh vacuum studies for probing the chemistry that will occur at higher O2 pressure.
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81.65.Mq Oxidation
79.20.Fv Electron impact: Auger emission
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
81.40.Gh Other heat and thermomechanical treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Ultralow k films by using a plasma-enhanced chemical vapor deposition porogen approach: Study of the precursor reaction mechanisms

A. Castex, V. Jousseaume, J. Deval, J. Bruat, L. Favennec, and G. Passemard

J. Vac. Sci. Technol. A 26, 1343 (2008); http://dx.doi.org/10.1116/1.2953704 (12 pages)

Online Publication Date: 28 August 2008

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As interconnects are scaled down, much effort is made to achieve ultralow k material with a dielectric constant lower than 2.5. Thus, many new precursors are investigated in plasma-enhanced chemical vapor deposition. This is particularly true with the porogen approach where two molecules are used: an organosilicon to create the silicon matrix and an organic molecule “porogen” that creates material porosity during a post-treatment such as annealing. In this article, the influence of the organosilicon molecular structure is investigated. Two “matrix precursors” with different structures are therefore compared. The first one, referred to as D5, has a ring structure (decamethyl pentacyclosiloxane); the second one, referred to as DEOMS, has a star structure (diethoxymethyl silane). The porogen organic molecule, referred to as CHO, is cyclohexen oxide. The fragmentation paths of the precursor molecules in the plasma are investigated by quadrupole mass spectroscopy and the film structure is studied by Fourier transform infrared spectroscopy. The mass spectroscopy analysis shows that the fragmentation in plasma is highest for DEOMS, intermediate for CHO, and lowest for D5 in comparable process conditions. At the maximum plasma power setting, the loss rate, which yields molecule consumption, is 43%–81% for the D5-CHO mixture, respectively, and 73%–37% for the DEOMS-CHO mixture, respectively. This is related to higher bond-dissociation energy for the siloxane (SiOSi) link in D5 than silane (SiH), silylethoxyde (SiOC2H5) in DEOMS, or CC and epoxy cycle in CHO. Indeed, a higher electron-energy relative threshold for dissociation under electron impact is measured for D5 (around 7 eV) than for DEOMS and CHO (around 4 eV). Moreover, the fragment structures differ from one precursor to another. Methyl groups are abstracted from D5 and a few polysiloxane chains are produced from pentacycle opening and fragmentation. In the case of DEOMS, many single silicon-atom-bearing species are produced. Consequently, the D5-based films have significant retention of siloxane cycles and a less diverse silicon environment than DEOMS-based films. The porogen incoporation (organic phase) was evidenced through alkyl group absorption and is more important with DEOMS than D5 as a matrix precursor. Moreover, the epoxy moiety of the porogen seems scavenged by the plasma and is not retained in the films. These results confirm other studies that discarded D5-CHO chemistry for porous dielectric achievement in an industrial reactor, whereas DEOMS-CHO leads to porous films with an ultralow dielectric constant. Eventually, this study shows that the usefulness of cyclosiloxane precursors is not straightforward.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ch Permittivity (dielectric function)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
68.55.aj Insulators
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