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Jul 2006

Volume 24, Issue 4, pp. 895-1689

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Thermal conductivity of AlN-diamond particulate composite films on silicon

K. Jagannadham

J. Vac. Sci. Technol. A 24, 895 (2006); http://dx.doi.org/10.1116/1.2198862 (5 pages) | Cited 1 time

Online Publication Date: 22 May 2006

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The thermal conductivity of a particulate composite film of diamond in AlN deposited on silicon was measured using 3ω technique in the temperature range of 205–300 K. The experimental results of increase in the temperature of heater line were analyzed using a model of film on semi-infinite substrate. The results of modeling are found to conform to the expected temperature dependence of the thermal conductivity of silicon, AlN, and diamond. Oxygen introduced during the deposition of the AlN-diamond composite film on silicon is found to reduce the thermal conductivity of the film and the substrate. Low cost AlN-diamond particulate composite films are found to offer good heat spreader characteristics for high power semiconductor devices.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Effects of N2 remote plasma nitridation on the structural and electrical characteristics of the HfO2 gate dielectrics grown using remote plasma atomic layer deposition methods

Jihoon Choi, Seokhoon Kim, Jinwoo Kim, Hyunseok Kang, Hyeongtag Jeon, and Choelhwyi Bae

J. Vac. Sci. Technol. A 24, 900 (2006); http://dx.doi.org/10.1116/1.2198865 (8 pages) | Cited 5 times

Online Publication Date: 22 May 2006

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The characteristics of remote plasma atomic layer deposited HfO2 on Si, which has a very thin SiO2 interlayer with and without remote plasma nitridation (RPN), have been investigated. Small amounts of N atoms were successfully incorporated by RPN pretreatment, in which the dominant emission species were excited atomic nitrogen (N*) and excited molecular nitrogen (N2*), into a very thin SiO2 interlayer for the growth of HfO2 thin film. The thin ( ∼ 1.5 nm) intermediate layer containing nitrogen, which was prepared by sequential O2 and N2 remote plasma treatment of the Si substrate, can effectively suppress growth of the unintentional interface layer. In addition, it enhances the thermal stability and the resistance to oxygen diffusion during rapid thermal annealing. The HfO2 film containing the remote plasma nitrided SiO2 interlayer annealed at 800 °C showed a lower equivalent oxide thickness of ∼ 1.89 nm and a lower leakage current density (3.78×10−7 A cm−2 at ∣VG−VFB∣ = 2 V) compared to a non-nitrided sample of the same physical thickness. Also, we compared the characteristics of HfO2 films annealed in two different ambient environments, N2 and O2.
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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.)
52.77.-j Plasma applications
66.30.J- Diffusion of impurities

Modeling of dc magnetron plasma for sputtering: Transport of sputtered copper atoms

T. Yagisawa and T. Makabe

J. Vac. Sci. Technol. A 24, 908 (2006); http://dx.doi.org/10.1116/1.2198866 (6 pages) | Cited 2 times

Online Publication Date: 22 May 2006

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A self-consistent modeling of two-dimensional structures of a dc magnetron plasma with a copper target is performed at 5 mTorr in Ar by using a hybrid model consisting of a particle-in-cell/Monte Carlo simulation for electrons and relaxation continuum model for ions. The erosion profile of the copper target is estimated by the flux velocity distribution of ions incident on the target. In the case of a dc magnetron, the discharge is mainly sustained by an E×B drift motion of energetic electrons near the position Bz ∼ 0 with a static doughnutlike magnetic field. Then, a strongly localized profile appears in the plasma structures. The position of a maximum erosion on the copper target exactly coincides with the position where the incident Ar+ ion flux is maximum. Under the system between the light ion and the heavy target atom, the energy of the sputtered Cu atom is low (<10 eV) despite the high-energy ion injection ( ∼ 200 eV) to the target surface. In particular, we have developed a technique to predict the transport of sputtered particles in the gas phase within a reasonable computational time. The spatial distribution of the sputtered particles is divided into two components: “directional” fast-moving particles that do not collide with Ar feed gas in the gas phase and “random” slow-moving particles whose energy is relaxed by collision. The sputtered Cu atoms are widely dispersed from the doughnutlike region on the target. At 5 mTorr, the flux of sputtered Cu atoms at the substrate is mainly affected by the random particles with relaxed energy by collision.
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52.25.Fi Transport properties
52.50.Dg Plasma sources
52.65.Pp Monte Carlo methods
52.65.Rr Particle-in-cell method
52.40.Hf Plasma-material interactions; boundary layer effects
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Investigation of room temperature electrical resistivities of LaNiO3−δ thin films deposited by rf magnetron sputtering and high oxygen-pressure processing

X. D. Zhang, X. J. Meng, J. L. Sun, G. S. Wang, T. Lin, and J. H. Chu

J. Vac. Sci. Technol. A 24, 914 (2006); http://dx.doi.org/10.1116/1.2198867 (5 pages) | Cited 9 times

Online Publication Date: 22 May 2006

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Highly (100)-oriented electrically conductive LaNiO3−δ (LNO) thin film with perovskite-type structure was deposited on Si(100) substrates by rf magnetron sputtering at substrate temperatures of 200, 300, 450, and 600 °C with a series of 0%, 20%, 40%, and 60% oxygen partial pressures, respectively. The room temperature (RT) resistivity of LNO films decreases with decreasing substrate temperature at a fixed oxygen partial pressure and with increasing oxygen partial pressure at a fixed substrate temperature. The lowest RT resistivity of as-sputtered LNO thin films was about 5.3×10−4 Ω cm. This value could be as low as ∼ 1.55×10−4 Ω cm by postprocessing called high oxygen-pressure processing at 8 MPa and is comparable to the lowest one, 1.5×10−4 Ω cm, of epitaxial LNO thin film deposited on lattice-matched SrTiO3, LaAlO3, or sapphire single-crystal substrates.
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73.61.Ng Insulators
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering

X-ray photoelectron spectroscopy study of the nucleation processes and chemistry of CdS thin films deposited by sublimation on different solar cell substrate materials

J. P. Espinós, A. I. Martín-Concepción, C. Mansilla, F. Yubero, and A. R. González-Elipe

J. Vac. Sci. Technol. A 24, 919 (2006); http://dx.doi.org/10.1116/1.2198868 (10 pages) | Cited 6 times

Online Publication Date: 22 May 2006

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Cadmium sulfide has been deposited by evaporation on five different substrates: CdTe, ZnO, Ag, TiO2, and partially reduced titanium oxide (i.e., TiO1.73). The deposition rate and the evolution of the Cd/S ratio on the different substrates have been determined by x-ray photoelectron spectroscopy. The growth mode of the films has been also studied by analyzing the shape of the backgrounds behind the photoemission peaks (peak shape analysis). It has been found that, under completely equivalent conditions, the deposition efficiency (i.e., sticking coefficient) is large on CdTe and TiO1.73, but very small on ZnO and TiO2. Silver constitutes an intermediate situation characterized by a long induction period where the deposition rate is small and a later increase in deposition efficiency comparable to that on CdTe. For the initial stages of deposition, below an equivalent monolayer, it has been also found that the Cd/S ratio is smaller than unity on TiO1.73 and ZnO but larger than unity on CdTe and Ag substrates. For sufficiently long deposition times the Cd/S ratio on the surface reaches unity. Except for silver substrate, cadmium appears as Cd2+ and sulfur as S−2 species at the initial stages of deposition. On the silver surface, cadmium adsorbs as Cd0 at low coverage. Peak shape analysis has shown that cadmium sulfide grows according to layer-by-layer mechanism (Frank–van de Merwe model) when the substrates are CdTe and TiO1.73, but large particles are formed that do not cover the surface for ZnO and Ag substrates (Volmer-Weber growth model). These results are consistent with the different chemical affinities of the substrate towards the atoms of cadmium and sulfur produced during the evaporation of the cadmium sulfide.
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81.05.Dz II-VI semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Dp Adsorbed layers and thin films
68.43.Mn Adsorption kinetics

Phase separation of a Ge2Sb2Te5 alloy in the transition from an amorphous structure to crystalline structures

YoungKuk Kim, S. A. Park, J. H. Baeck, M. K. Noh, K. Jeong, M.-H. Cho, H. M. Park, M. K. Lee, E. J. Jeong, D.-H. Ko, and H. J. Shin

J. Vac. Sci. Technol. A 24, 929 (2006); http://dx.doi.org/10.1116/1.2198869 (5 pages) | Cited 8 times

Online Publication Date: 22 May 2006

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Changes in the structural and electrical properties of a Ge2Sb2Te5 alloy thin film induced by phase transition were investigated using various analytical techniques. X-ray diffraction and scanning photoelectron microscopy showed that the phase separation occurred in a local area of the film during a phase transition when the amorphous structure was being transformed into crystalline structures. It was found that the heterogeneous distribution of Sb atoms that diffused during the phase transition accompanied the phase separation. Atomic force microscopy was used to examine the changes in surface morphology and roughness. The electrical conductance of the film was dramatically improved after the phase transition from an amorphous structure to crystalline structures as evidenced by the sheet resistance measurements. The sheet resistance changed from ∼ 109 to  ∼ 102 Ω/sq. during the phase transition. Differential scanning calorimetry was used to determine the exact phase transition temperature (160–170 °C) and the effective activation energy for the phase transition (2.5±0.11 eV) on the basis of Kissinger’s equation.
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64.75.-g Phase equilibria
61.43.Fs Glasses
73.61.Jc Amorphous semiconductors; glasses
68.55.-a Thin film structure and morphology
64.70.K- Solid-solid transitions
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Hysteresis behavior during reactive magnetron sputtering of Al2O3 using a rotating cylindrical magnetron

D. Depla, J. Haemers, G. Buyle, and R. De Gryse

J. Vac. Sci. Technol. A 24, 934 (2006); http://dx.doi.org/10.1116/1.2198870 (5 pages) | Cited 14 times

Online Publication Date: 22 May 2006

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Rotating cylindrical magnetrons are used intensively on industrial scale. A rotating cylindrical magnetron on laboratory scale makes it possible to study this deposition technique in detail and under well controlled conditions. Therefore, a small scale rotating cylindrical magnetron was designed and used to study the influence of the rotation speed on the hysteresis behavior during reactive magnetron sputtering of aluminum in Ar/O2 in dc mode. This study reveals that the hysteresis shifts towards lower oxygen flows when the rotation speed of the target is increased, i.e., target poisoning occurs more readily when the rotation speed is increased. The shift is more pronounced for the lower branch of the hysteresis loop than for the upper branch of the hysteresis. This behavior can be understood qualitatively. The results also show that the oxidation mechanism inside the race track is different from the oxidation mechanism outside the race track. Indeed, outside the race track the oxidation mechanism is only defined by chemisorption while inside the race track reactive ion implantation will also influence the oxidation mechanism.
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81.15.Cd Deposition by sputtering
81.65.Mq Oxidation
61.72.up Other materials

Reactive vacuum vapor deposition of aluminum oxide thin films by an air-to-air metallizer

T. Kobayashi, Y. Itoh, Y. Nakano, E. Hirai, R. Hashimoto, and S. Kamikawa

J. Vac. Sci. Technol. A 24, 939 (2006); http://dx.doi.org/10.1116/1.2198871 (7 pages)

Online Publication Date: 22 May 2006

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Reactive vacuum vapor deposition of aluminum oxide thin films by an air-to-air metallizer was examined via the direct simulation Monte Carlo method and experiments. Comparison of the calculated results with the measurements of the Al oxide thin film’s thickness showed (a) that the empirical flux of Al atoms arriving at the substrate is lower than the calculated result, probably due to the formation of Al oxide on the evaporation surface and (b) that the amount of oxygen calculated from the thickness of the film is twice the amount corresponding to the calculated flux, probably due to the effects of the decreased sticking coefficient of oxygen on the evaporating surface and sidewall, underestimated gas phase reaction, large mesh size overestimated film density, and formation of substoichiometric oxide. Aluminum oxide thin films deposited on plastic film substrates by this metallizer under strictly controlled O2 supply conditions have good transparency, an oxygen transmission rate of 2.7 cc/m2 day, and an electrical resistivity of 4.4×106 Ω2 m. Furthermore it was found that the oxygen transmission rate was reduced greatly to 1.0 cc/m2 day or less when the Al oxide coating film was laminated with another plastic film using an adhesive.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.61.Ng Insulators
78.66.Nk Insulators

Process optimization for the sputter deposition of molybdenum thin films as electrode for AlN thin films

F. Martin, P. Muralt, and M.-A. Dubois

J. Vac. Sci. Technol. A 24, 946 (2006); http://dx.doi.org/10.1116/1.2201042 (7 pages) | Cited 9 times

Online Publication Date: 22 May 2006

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Molybdenum thin films have been deposited on Ti/(100) Si substrates by dc sputtering. For process optimization, a design of experiments method was used with three input factors (target power, substrate temperature, and process gas flow). Deposition rate, resistivity, roughness, diffraction angle, and rocking curve width were analyzed as output responses using statistical analysis method. Subsequently, a process allowing the deposition of highly crystalline, smooth, and low resistivity Mo film was selected and tested against film thickness. The as-optimized sputtered molybdenum thin film was used as seeding electrode for the growth of highly c-axis textured AlN film by dc pulsed reactive sputtering.
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81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.61.At Metal and metallic alloys
81.05.Ea III-V semiconductors

Alternative method of using an electron beam for charge compensation during ultralow energy secondary-ion-mass spectroscopy experiments

B. Guzmán de la Mata, M. G. Dowsett, and R. J. H. Morris

J. Vac. Sci. Technol. A 24, 953 (2006); http://dx.doi.org/10.1116/1.2201044 (4 pages) | Cited 3 times

Online Publication Date: 22 May 2006

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Secondary-ion-mass spectroscopy (SIMS) analysis of insulators using positive primary beams is routinely performed by compensating the induced charge with a coincident electron beam. In the case of SIMS depth profiling, the established method consists of focusing an electron beam into the SIMS crater with a current well in excess of that of the primary ion beam. In this article we used both caesium and oxygen beams to bombard float glass, and intrinsic and doped diamond samples while varying the electron beam current and the area bombarded by electrons. We have studied how the electron beam to primary ion current density ratio modifies the charging conditions. We demonstrate that, for certain insulating and highly resistive materials, defocusing of the electron beam so as to cover the whole of the sample surface and part of the sample holder is extremely effective. It is also observed that the defocused electron beam works efficiently for an electron to primary ion current density ratio less than 1. We attribute this to the enhancement of surface conductivity through the creation of carriers in the conduction band, and observe similar effects when irradiating the surface with a laser diode. The ability to use a defocused electron beam will significantly aid profiling of insulating and highly resistive materials where alignment of the coincident electron and ion beams is problematic. Defocusing of the electron beam also offers the possible advantage of reducing or eliminating localized electron beam damage of certain material surfaces prior to and during profiling.
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61.80.Fe Electron and positron radiation effects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.25.+i Surface conductivity and carrier phenomena

Effects of pulsing parameters on production and distribution of macroparticles in cathodic vacuum arc deposition

Yawei Hu, Liuhe Li, Hua Dai, Xiaoling Li, Xun Cai, and Paul K. Chu

J. Vac. Sci. Technol. A 24, 957 (2006); http://dx.doi.org/10.1116/1.2201046 (5 pages)

Online Publication Date: 22 May 2006

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The effects of pulsing parameters such as the duty cycles, frequencies, and arc currents on the production and distribution of macroparticles (MPs) were studied. A tunable pulsed arc power supply that could provide either direct current (dc) or pulsed current plus dc was used in the experiments. Copper and titanium were used as the cathodes, and glasses were used as the substrate. Optical microscopy, scanning electron microscopy, and special image processing were utilized to investigate the MPs deposited onto the substrate. Our results illustrate the general trend that the MP density increases with higher dc but decreases with increasing pulsing frequency. There is no obvious relationship between the MP density and the duty cycle at high dc but the MP density obviously increases with the duty cycle at low dc.
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81.05.Bx Metals, semimetals, and alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Influence of layer thickness and compositional variations on the electrorefractive properties of a quantum well polarization-conversion modulator

Sasa Ristic and Nicolas A. F. Jaeger

J. Vac. Sci. Technol. A 24, 962 (2006); http://dx.doi.org/10.1116/1.2201051 (4 pages) | Cited 2 times

Online Publication Date: 22 May 2006

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We present our work done towards the development of a quantum well polarization-conversion modulator. This modulator will consist of multiple repetitions of quantum well structures exhibiting large electrorefractive effects. In them, a channel waveguide supporting only the fundamental TE-like and TM-like modes will be subjected to an applied electric field. Changes in this applied field cause the effective refractive index of one of the modes to increase and that of the other to decrease. Using these structures shows that short ( ∼ 2–3 mm) modulators, with 90° polarization rotation, low chirp ( ∼ ±0.1), and low drive electric fields ( ∼ 10 kV/cm) can be achieved. In this article, numerical simulations based on the effective-mass envelope-function approximation are used to study the influence of layer thickness and compositional variations on the electrorefractive properties of these quantum well structures.
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78.67.De Quantum wells
78.20.Jq Electro-optical effects
42.79.Hp Optical processors, correlators, and modulators
42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Working pressure induced structural and mechanical properties of nanoscale ZrN/W2N multilayered coatings

D. J. Li, M. X. Wang, J. J. Zhang, and J. Yang

J. Vac. Sci. Technol. A 24, 966 (2006); http://dx.doi.org/10.1116/1.2202124 (4 pages) | Cited 9 times

Online Publication Date: 22 May 2006

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This article reports the synthesis of ZrN/W2N multilayered coatings with nanoscale bilayer period using rf magnetron sputtering. X-ray diffraction, Auger electron spectroscopy, scanning electron microscope, nanoindenter, and profiler were employed to investigate the influence of working pressure on microstructural and mechanical properties of the coatings. Well-defined composition modulation and layer structure of the multilayered coating are indicated directly. A mixed polycrystalline of ZrN(111), W2N(111), W2N(200) and W2N(311) textures appeared in the multilayered structures. All multilayered coatings revealed higher nanohardness, elastic modulus, critical load, and lower residual stress than the rule-of-mixture value of monolithic ZrN and W2N coatings, especially for one prepared at 0.8 Pa working pressure.
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62.25.-g Mechanical properties of nanoscale systems
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.65.Ac Multilayers
79.20.Fv Electron impact: Auger emission
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.55.-a Thin film structure and morphology

Low-voltage resistive switching of polycrystalline SrZrO3:Cr thin films grown on Si substrates by off-axis rf sputtering

Jae-Wan Park, Jong-Wan Park, Min Kyu Yang, Kyooho Jung, Dal-Young Kim, and Jeon-Kook Lee

J. Vac. Sci. Technol. A 24, 970 (2006); http://dx.doi.org/10.1116/1.2202126 (4 pages) | Cited 3 times

Online Publication Date: 22 May 2006

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A polycrystalline Cr-doped SrZrO3/SrRuO3 layered structure showing a reproducible resistive switching behavior with a resistive switching voltage of ±2.5 V was successfully fabricated on commercial Si (100) substrate by off-axis rf sputtering. Typical resistance values of high- and low-resistance states were about 100 and 5 kΩ, respectively, so that the ratio of high- to low-resistance value is about 20. These values are appropriate for memory applications, and the resistive switching voltage of ±2.5 V is the lowest value among the switching voltages of Cr-doped SrZrO3 films on Si substrates reported in recent literature. We suggest that the low-voltage resistive switching of the polycrystalline Cr-doped SrZrO3 thin film is attributed to the reduction of resputtering effects and the formation of a clean interface between the Cr-doped SrZrO3 thin film and the SrRuO3 bottom electrode layer by the use of 90° off-axis sputtering.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Effect of oxygen incorporation on structural and properties of Ti–Si–N nanocomposite coatings deposited by reactive unbalanced magnetron sputtering

X. Z. Ding, X. T. Zeng, Y. C. Liu, and L. R. Zhao

J. Vac. Sci. Technol. A 24, 974 (2006); http://dx.doi.org/10.1116/1.2202128 (4 pages) | Cited 2 times

Online Publication Date: 22 May 2006

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Ti–Si–N–O nanocomposite coatings with different contents of oxygen were deposited by a combined dc/rf reactive unbalanced magnetron sputtering process in an Ar+N2+O2 mixture atmosphere. The composition, structure, mechanical, and tribological properties of the as-deposited coatings were analyzed by energy dispersive analysis of x-rays, x-ray diffraction (XRD), nanoindentation, and pin-on-disk tribometer experiments, respectively. It was found that in the range of lower oxygen content with atomic ratio of O/N ⩽ 0.72, the tribological properties of the Ti–Si–N–O coatings are evidently improved, in comparison with the coating without oxygen incorporation. At O/N = 0.72, the friction coefficient and wear rate of the as-deposited coatings are reduced to 20% and 45%, respectively. Meanwhile, however, their hardness was not reduced, but, on the contrary, slightly increased. With increasing oxygen content further to O/N ≥ 0.72, coating hardness decreased significantly. The friction coefficient of the as-deposited coatings decreased monotonously with the increase of oxygen content in the whole composition range investigated. The wear rate of the coatings exhibited a minimum value at around O/N = 0.72. In the lower range of O/N, wear rate decreased significantly due to the lubricant effect of oxygen incorporation, while in the higher range of O/N, wear rate increased gradually due to the weakening of coating hardness. XRD patterns revealed that the as-deposited coatings were mainly crystallized in cubic TiN phase, accompanied with minority of rutile structure titania in the case of higher oxygen incorporation.
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81.40.Pq Friction, lubrication, and wear
61.72.S- Impurities in crystals
62.20.Qp Friction, tribology, and hardness
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Direct observations of rapid diffusion of Cu in Au thin films using in situ x-ray diffraction

J. W. Elmer, T. A. Palmer, and E. D. Specht

J. Vac. Sci. Technol. A 24, 978 (2006); http://dx.doi.org/10.1116/1.2204926 (10 pages) | Cited 4 times

Online Publication Date: 22 May 2006

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In situ x-ray diffraction was performed while annealing thin film Au/Cu binary diffusion couples to directly observe diffusion at elevated temperatures. The temperature dependence of the interdiffusion coefficient was determined from isothermal measurements at 700, 800, and 900 °C, where Cu and Au form a disordered continuous face centered cubic solid solution. Large differences in the lattice parameters of Au and Cu allowed the initial diffraction peaks to be easily identified, and later tracked as they merged into one diffraction peak with increased diffusion time. Initial diffusion kinetics were studied by measuring the time required for the Cu to diffuse through the Au thin film of known thickness. The activation energy for interdiffusion was measured to be 65.4 kJ/mole during this initial stage, which is approximately 0.4× that for bulk diffusion and 0.8× that for grain boundary diffusion. The low activation energy is attributed to the high density of columnar grain boundaries combined with other defects in the sputter deposited thin film coatings. As interdiffusion continues, the two layers homogenize with an activation energy of 111 kJ/mole during the latter stages of diffusion. This higher activation energy falls between the reported values for grain boundary and bulk diffusion, and may be related to grain growth occurring at these temperatures which accounts for the decreasing importance of grain boundaries on diffusion.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
61.72.Mm Grain and twin boundaries

Type of precursor and synthesis of silicon oxycarbide (SiOxCyH) thin films with a surfatron microwave oxygen/argon plasma

Agnieszka Walkiewicz-Pietrzykowska, J. P. Espinós, and Agustin R. González-Elipe

J. Vac. Sci. Technol. A 24, 988 (2006); http://dx.doi.org/10.1116/1.2204927 (7 pages) | Cited 3 times

Online Publication Date: 22 May 2006

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Siliconelike thin films (i.e., SiOxCyHz) were prepared in a microwave plasma enhanced chemical vapor deposition reactor from structurally different organosilicon precursors [i.e., hexamethyldisiloxane (HMDSO), dimethylsilane (DMS), and tetramethylsilane (TMS)]. The films were deposited at room temperature by using different oxygen/argon ratios in the plasma gas. By changing the type of precursor and the relative concentration of oxygen in the plasma, thin films with different compositions (i.e., O/C ratio) and properties are obtained. In general, raising the oxygen concentration in the plasma produces the progressive removal of the organic moieties from the films whose composition and structure then approach those of silicon dioxide. The deposition rate was highly dependent on the type of precursor, following the order HMDSO⪢DMS>TMS. The polarizabilities, optical band gaps, and surface free energy of the films also depended on the thin film composition and structure. It is proposed that the Si–O bonds existing in HMDSO is the main factor controlling the distinct reactivity of this precursor and is also responsible for the different compositions and properties of the SiOxCyHz thin films prepared with very low or no oxygen in the plasma gas.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.66.Nk Insulators

Understanding ion-milling damage in Hg1−xCdxTe epilayers

Changzhen Wang, David J. Smith, Steve Tobin, Themis Parodos, Jun Zhao, Yong Chang, and Sivalingam Sivananthan

J. Vac. Sci. Technol. A 24, 995 (2006); http://dx.doi.org/10.1116/1.2207148 (6 pages) | Cited 6 times

Online Publication Date: 22 May 2006

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Transmission electron microscopy (TEM) is widely used for the characterization of the microstructure of Hg1−xCdxTe epilayers. Traditional TEM sample preparation methods, which usually involve argon ion milling, can easily cause damage to the material, and the size and density of the induced defects depend on the milling conditions. In this work, the structural damage caused by argon ion milling of Hg1−xCdxTe epilayers has been investigated. Multilayer samples with different Hg concentrations, as grown by molecular beam epitaxy, and p-n heterojunctions, as grown by liquid-phase epitaxy, have been examined. It is shown that, in addition to the milling conditions, the extent of the ion-induced damage depends sensitively on the Hg concentration of the Hg1−xCdxTe alloy as well as the epilayer growth conditions (i.e., Hg rich or Te rich). A possible mechanism that explains these results is briefly discussed.
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68.65.Ac Multilayers
61.80.Jh Ion radiation effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

InGaN/GaN blue light emitting diodes with modulation-doped AlGaN/GaN heterostructure layers

Chin-Hsiang Chen

J. Vac. Sci. Technol. A 24, 1001 (2006); http://dx.doi.org/10.1116/1.2201048 (4 pages)

Online Publication Date: 9 June 2006

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The modulation-doped AlGaN/GaN heterostructure layers were used to improve the output power and efficiency of nitride-based blue light emitting diodes (LEDs). It was found that the output power of LEDs with the modulation-doped AlGaN/GaN layers measured at 20 mA injection current was increased from 4.8 to 6 mW. It was also found that the modulation-doped AlGaN/GaN layers can effectively spread pulse current. Nitride-based blue LEDs with the modulation-doped AlGaN/GaN layer can even endure a 3000 V reverse electrostatic discharge pulse voltage.
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85.60.Jb Light-emitting devices

Tunable hydrophilicity on a hydrophobic fluorocarbon polymer coating on silicon

K. Kolari and A. Hokkanen

J. Vac. Sci. Technol. A 24, 1005 (2006); http://dx.doi.org/10.1116/1.2207149 (7 pages) | Cited 1 time

Online Publication Date: 9 June 2006

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An efficient, economic, reliable, and repeatable patterning procedure of hydrophobic surfaces was developed. A fluorocarbon polymer derived from the C4F8 gas in an inductively coupled plasma etcher was used as the hydrophobic coating. For a subsequent patterning of hydrophilic apertures on the polymer, a short O2 plasma exposure through a silicon shadow mask was utilized. The overall hydrophilicity of the patterned surface can be tuned by the duration of the O2 plasma exposure, and also by the density and the size of the hydrophilic apertures. The laborious photolithography and tricky lift-off procedures are avoided. Optimization of the whole patterning process is explained thoroughly and supported with experimental data. The hydrophilic adhesion of the patterned polymer was evaluated with aqueous droplets, which were studied on matrices of the hydrophilic apertures of different sizes. The deposition parameters of the fluorocarbon polymer, the size of the droplet required to enable rolling on the patterned surface, and the duration of the O2 plasma exposure were considered as the main parameters. To determine the achievable resolution of the patterning procedure, the subsurface etching beneath the shadow mask was evaluated. The results show that a resolution of less than 10 μm can be achieved. The simple hydrophilic patterning procedure described here can be used for the production of on-plane microfluidics, where a controlled adhesion or decohesion of 8–50 μl droplets on the surface with a variable hydrophilicity from one location to another can be achieved.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.55.A- Nucleation and growth
81.15.Jj Ion and electron beam-assisted deposition; ion plating

Plasma etching of proton-exchanged lithium niobate

H. Hu, A. P. Milenin, R. B. Wehrspohn, H. Hermann, and W. Sohler

J. Vac. Sci. Technol. A 24, 1012 (2006); http://dx.doi.org/10.1116/1.2207150 (4 pages) | Cited 17 times

Online Publication Date: 9 June 2006

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Plasma etching of lithium niobate with fluorine gases is limited by the redeposition LiF. This results in a low etch rate and nonvertically etched walls. Etching of proton-exchanged lithium niobate can prevent the LiF deposition to a large extent because of the greatly reduced lithium concentration in lithium niobate. We performed different inductively coupled plasma etching processes using SF6 or CHF3/Ar on proton-exchanged lithium niobate. Negligible underetching and nearly vertically etched walls on proton-exchanged lithium niobate samples were obtained by CHF3/Ar gas at chamber pressure of 6 mTorr and 130 V dc bias.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
61.66.Fn Inorganic compounds

Observations of electrical and luminescence anomalies in InGaN/GaN blue light-emitting diodes

Tzer-En Nee, Jen-Cheng Wang, Hui-Tang Shen, Chung-Han Lin, and Ya-Fen Wu

J. Vac. Sci. Technol. A 24, 1016 (2006); http://dx.doi.org/10.1116/1.2207152 (4 pages) | Cited 3 times

Online Publication Date: 9 June 2006

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Unique correlations between the electrical and optical characteristics of InGaN/(In)GaN multiple quantum-well light-emitting diodes (LEDs) were investigated over a broad range of temperatures. The dependence of nonunity ideality factors extracted from the current-voltage analysis on temperature determines the carrier-transport mechanisms in the heterodevices. The pseudotemperatures To for the LEDs with multiquantum barriers and with GaN barriers were found to be 945 and 1385 K, respectively, at temperatures of 180–300 K while having values of 1195 and 2720 K below about 180 K. Correspondingly, the temperature-dependent electroluminescence observations suggest that the To anomaly caused the spectral intensity to deteriorate.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Layer structure of ultrathin Ag films on Ni/Pt(111)

H. Y. Ho, Y. J. Chen, C. W. Su, R. H. Chen, and C. S. Shern

J. Vac. Sci. Technol. A 24, 1020 (2006); http://dx.doi.org/10.1116/1.2208993 (4 pages)

Online Publication Date: 9 June 2006

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The layer structure of Ag on a Ni/Pt(111) surface after high temperature annealing was studied by Auger electron spectroscopy, depth profile of Ar ion sputtering, and low-energy electron diffraction (LEED). A structural phase p(2×2) LEED pattern was observed in one atomic monolayer (ML) on 1 ML Ni/Pt(111) surface after annealing at 800 K. Based on observations of the change of ion sputtering rates for the Ag overlayers, the LEED pattern, and minimum strain energy, we propose a layer structure of Ag for 1 ML Ag/1 ML Ni/Pt(111) after the 800 K annealing. The compositions in the subsurface region are 0.25 ML Ag in p(2×2) structure on the topmost layer, Ag75Ni25 alloy in the second layer, and Ni–Pt alloy in the remaining layers of the subsurface regions.
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68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments
79.20.Fv Electron impact: Auger emission
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.47.De Metallic surfaces

Evaluation of the shapes of Auger- and secondary-electron line scans across interfaces with the logistic function

S. A. Wight and C. J. Powell

J. Vac. Sci. Technol. A 24, 1024 (2006); http://dx.doi.org/10.1116/1.2209651 (7 pages) | Cited 1 time

Online Publication Date: 12 June 2006

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We report on the use of the extended logistic function for fitting Auger-electron (AE) and secondary-electron (SE) line scans. Such fits provide convenient and objective measures of parameters describing the interface width and possible asymmetry of a line scan. We show examples of fits to AE and SE line scans for three types of samples. Fits to AE and SE data for a gold island on a carbon substrate gave useful measures of the lateral resolution of a scanning Auger microscope and “tails” present in the line scans showed evidence of imperfect alignment of the microscope. Fits to AE spectra obtained as the primary beam was scanned across an edge of Cr/Cr2O3 lines on an indium tin oxide substrate showed similar tails due to the effect of backscattered electrons on the generation of Auger electrons for primary energies between 15 and 25 keV. Fits with the logistic function to SE line scans across a fractured Ni/Cr multilayer sample and to AE and SE line scans across a sputtered crater of this sample provided useful measures of the interface width.
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79.20.Fv Electron impact: Auger emission
79.20.Hx Electron impact: secondary emission

Dependence of the electrical properties of the ZnO thin films grown by atomic layer epitaxy on the reactant feed sequence

Chongmu Lee and Jongmin Lim

J. Vac. Sci. Technol. A 24, 1031 (2006); http://dx.doi.org/10.1116/1.2209653 (5 pages) | Cited 1 time

Online Publication Date: 12 June 2006

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Nitrogen-doped, p-type ZnO films have been grown successfully on sapphire (0001) substrates by atomic layer epitaxy (ALE) using Zn(C2H5)2 [diethylzinc (DEZn)], H2O, and NH3 as a precursor for zinc, an oxidant, and a doping source gas, respectively. The main process parameters for the growth of p-type ZnO were the NH3 flux and the reactant feed sequence in ALE. An annealing process was performed after the ALE process. The lowest electrical resistivity of the p-type ZnO films grown by ALE was 17.9 Ω cm with a hole concentration of 1.59×1017 cm−3. The results indicated that the carrier concentrations and carrier mobilities in the as-grown and annealed ZnO thin films depend strongly on the NH3 pulse time and on which step of an ALE cycle the NH3 doping is conducted. For both reactant feed sequences of DEZn–NH3–H2O and H2O–NH3–DEZn, n-type ZnO was changed to p-type ZnO by annealing, but the latter led to p-type ZnO with a carrier concentration after annealing higher than that in sequence 1 for the same NH3 flow rate. In addition, a model is proposed which can explain the difference between the two feed sequences in carrier concentration and carrier mobility before and after annealing. Time-dependent Hall effect measurement results also support that the nitrogen-doped ZnO film grown by ALE and then annealed at 1000 °C for 1 h is a p-type semiconductor.
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81.05.Dz II-VI semiconductors
73.61.Ga II-VI semiconductors
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.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Cc Kinetics of defect formation and annealing

Spectroellipsometric analysis of CHF3 plasma-polymerized fluorocarbon films

T. Easwarakhanthan, D. Beyssen, L. Le Brizoual, and J. Bougdira

J. Vac. Sci. Technol. A 24, 1036 (2006); http://dx.doi.org/10.1116/1.2209654 (8 pages) | Cited 6 times

Online Publication Date: 12 June 2006

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Optical and morphological properties of fluorocarbon films (CFx) deposited on Si substrates from CHF3 in a reactive ion etcher were studied by spectroscopic ellipsometry (SE). The study has led for 0.3–1.5 μm thick films to a thickness-independent, roughnessless, apparently nongraded two-layer model that requires the Cauchy dispersion and the Gaussian absorption for the film refractive index and extinction coefficient, and to an interface mixture of CFx, Si, and voids. The Si native oxide removal was ascertained from films formed on SiO2-sputtered Si substrate. The sample SE results were further verified by x-ray diffraction, atomic force microscopy, Fourier transform infrared, x-ray photoelectron and Auger electron spectroscopies, and capacitance studies. The film microstructure may thus be considered isotropic and homogeneous resulting from a random addition of CFx fragments including cross-links along the film depth. The films have low-dielectric constant(k ≈ 2.2) quality index of 1.38(615 nm) and are noticeably absorbent in UV while exhibiting strong transparency in visible. These films growing at a rate of 0.033 μm/min have 2%–3% thickness nonuniformity. The SE model decision making steps are described and the degree of confidence on the SE results are discussed with the support of literature results and those from and the above studies.
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77.55.-g Dielectric thin films
78.66.Qn Polymers; organic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Jw Organic compounds, polymers
79.60.Fr Polymers; organic compounds
77.22.Ch Permittivity (dielectric function)

Characterization of a methyl radical source for ultrahigh vacuum thin film growth studies

J. S. Gold, J. M. Lannon, K. S. Ziemer, M. Guntu, V. L. Tolani, and C. D. Stinespring

J. Vac. Sci. Technol. A 24, 1044 (2006); http://dx.doi.org/10.1116/1.2209655 (7 pages)

Online Publication Date: 12 June 2006

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An ultrahigh vacuum compatible methyl radical source has been developed and characterized. The methyl radicals were generated by passing a dilute mixture of methane in argon through a microwave discharge and sampling the discharge products using a molecular beam skimmer. The resulting molecular beam was characterized using a differentially pumped mass spectrometer. In addition to methyl radicals, other species observed in the beam included methane and higher hydrocarbons whose relative amounts were affected by source operating conditions. Radical fluxes as high as 8.4×1014 cm−2 s−1 were produced.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth

Effect of thermal annealing on the metastable optical properties of GaN thin films

Y. C. Chang, R. M. Kolbas, Z. J. Reitmeier, and R. F. Davis

J. Vac. Sci. Technol. A 24, 1051 (2006); http://dx.doi.org/10.1116/1.2209656 (4 pages)

Online Publication Date: 12 June 2006

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The optical metastability in unintentionally doped GaN (0001) films grown on AlN/SiC substrates has been investigated as a function of thermal annealing conditions using photoluminescence and optical microscopy. Annealing at 800 °C for 48 h in 1 atm of flowing nitrogen produced no change in the metastability. Annealing at 800 °C in ultrahigh vacuum for 48 h eliminated the phenomenon. Exposure of the sample to ultraviolet light during the latter anneal reduced the time to eliminate the metastability. This phenomenon was restored by subsequently annealing in ammonia at 775 °C for 3 h. These results suggest that the presence and elimination of the optical metastability are related to the presence in and the elimination of hydrogen from the GaN.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing

Low energy focused ion beam system design

Michael Rauscher and Erich Plies

J. Vac. Sci. Technol. A 24, 1055 (2006); http://dx.doi.org/10.1116/1.2208989 (12 pages) | Cited 1 time

Online Publication Date: 14 June 2006

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Focused ion beam (FIB) systems operated at typically 30 keV energy have now reached a remarkable level of sophistication in terms of optical performance. Not unlike the much earlier developments in scanning electron microscopy, there now seems to be a fairly recent trend towards also enhancing the low energy performance of these systems—mainly driven by their possible utilization in transmission electron microscopy sample preparation. However, low energy operation indeed appears to have already been an issue in the very early days of FIB development—although then against the background of potential applications in direct semiconductor device fabrication. In this study, different approaches for generating low energy ion probes are discussed on the basis of previous and existing FIB systems for which experimental data have been made available. Subsequently, a dedicated low energy focused ion beam column design is introduced, which operates similarly to many modern field emission scanning electron microscopes. The performance of the system is assessed by means of standard aberration-optical calculations as well as by using data from direct ray tracing. The latter also allows the consideration of the impact of mutual Coulomb interactions.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
06.60.Ei Sample preparation (including design of sample holders)

Reactive ion beam etching of HfO2 film and removal of sidewall redeposition

Xudi Wang, Ying Liu, Xiangdong Xu, Shaojun Fu, and Zheng Cui

J. Vac. Sci. Technol. A 24, 1067 (2006); http://dx.doi.org/10.1116/1.2209657 (6 pages) | Cited 2 times

Online Publication Date: 14 June 2006

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Comparative studies on ion beam etching (IBE) and reactive ion beam etching (RIBE) of HfO2 film have been carried out using photoresist as the masking layer. The etching rates of HfO2 film and photoresist mask in pure Ar and Ar/CHF3 mixture plasmas were measured as a function of ion energy, plasma composition, and ion beam incident angle. It has been found that the RIBE with Ar/CHF3 plasma is capable of lowering the threshold energy of ion beam and increasing sputtering yield, compared to the IBE with pure Ar. The redeposition of photoresist sidewall is a major issue, due to the formation of nonvolatile etching products during sputtering of HfO2 film in both IBE and RIBE. However, the sidewall redeposition can be easily removed in HCl solutions with assistance of ultrasonic wave for RIBE with Ar/CHF3 plasma. Alternatively, the sidewall redeposition can be eliminated by controlling the slope of photoresist sidewall or combined with ion incident angle.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
81.15.Cd Deposition by sputtering
77.55.-g Dielectric thin films
62.65.+k Acoustical properties of solids

Oxidation threshold in silicon etching at cryogenic temperatures

T. Tillocher, R. Dussart, X. Mellhaoui, P. Lefaucheux, N. Mekkakia Maaza, P. Ranson, M. Boufnichel, and L. J. Overzet

J. Vac. Sci. Technol. A 24, 1073 (2006); http://dx.doi.org/10.1116/1.2210946 (10 pages) | Cited 10 times

Online Publication Date: 14 June 2006

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In silicon etching in SF6/O2 plasmas, an oxidation threshold appears when the oxygen content is large enough. A SiOxFy passivation layer is formed under such conditions. This threshold is reached at lower oxygen proportions if the substrate is cooled down to cryogenic temperatures. In this article, we present a mass spectrometry study of this oxidation threshold in different experimental conditions (temperature, source rf power, self-bias) on bare silicon wafers. The presence of the threshold is clearly evident in the signals of many ions, for example, SiF3+, F+, and SOF2+. This helps us to determine the main reactions which can occur in the SF6/O2 plasma in our experimental conditions. This threshold appears for higher oxygen proportions when either the source power or the chuck self-bias is increased. The ion bombardment transfers energy to the surface and makes the film desorb. A model, describing the oxygen coverage as a function of the parameters mentioned above, is proposed to interpret these results. Data presented in this article give another point of view of the cryogenic etching process. They contribute to explain how anisotropic profiles can be achieved at low temperature. Surfaces subjected to ion bombardment (the bottom of the structures) are below the oxidation threshold while the structures sidewalls, not subjected to ion bombardment, are in passivating regime.
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81.05.Cy Elemental semiconductors
68.47.Fg Semiconductor surfaces
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
81.65.Mq Oxidation

Evolution of film temperature during magnetron sputtering

L. R. Shaginyan, J. G. Han, V. R. Shaginyan, and J. Musil

J. Vac. Sci. Technol. A 24, 1083 (2006); http://dx.doi.org/10.1116/1.2210947 (8 pages) | Cited 7 times

Online Publication Date: 14 June 2006

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We report on the results of measurements of the temperature TFsurf which developed on the surface of films deposited by magnetron sputtering of chromium and copper targets on cooling and non-cooling silicon substrates. The TFsurf and substrate temperature (Ts) were simultaneously measured using high-resolution IR camera and thermocouple, respectively. We revealed that the TFsurf steeply grows, keeps constant when it achieves saturation level, and rapidly drops to the value of the Ts after stopping the deposition. At the same time, the Ts either does not change for the case of cooling substrate or increases to a certain level for noncooling substrate. However, in both cases the Ts remains several times lower than the TFsurf. The TFsurf is proportional to the flux of energy delivered to the growth surface by sputtered atoms and other fast particles, weakly depends on the depositing metal and can achieve several hundreds of °C. This phenomenon is explained by a model assuming formation of a hot thin surface layer (HTSL) on the top of the growing film, which exists only during film deposition and exhibits extremely low thermal conductivity. Due to this unique property the temperature TFsurf of HTSL is several times higher than the Ts. Variations in the TFsurf fairly correlate with structure changes of Cr films along thickness investigated in detail previously.
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81.05.Bx Metals, semimetals, and alloys
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Stress evolution as a function of substrate bias in rf magnetron sputtered yttria-stabilized zirconia films

Jeffrey R. Piascik, Jeffrey Y. Thompson, Christopher A. Bower, and Brian R. Stoner

J. Vac. Sci. Technol. A 24, 1091 (2006); http://dx.doi.org/10.1116/1.2210949 (5 pages) | Cited 4 times

Online Publication Date: 14 June 2006

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An increase in compressive stress was observed in rf magnetron sputtered yttria-stabilized zirconia thin films upon exposure to ambient conditions (25 °C and 75% relative humidity). This increase was attributed to absorption of water molecules into intergranular pores. It was shown that increasing substrate bias power disrupted columnar grain growth and reduced the percent change in compressive stress when exposed to ambient environments. Transmission electron microscopy confirmed a reduction in intergranular porosity for substrate bias depositions but an increase in lateral defects. These defects are hypothesized to be stress-induced microcracks caused by a tetragonal to monoclinic phase transformation.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
77.55.-g Dielectric thin films
68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
64.70.K- Solid-solid transitions

Gallium nitride thin films deposited by radio-frequency magnetron sputtering

Toshiro Maruyama and Hidetomo Miyake

J. Vac. Sci. Technol. A 24, 1096 (2006); http://dx.doi.org/10.1116/1.2208988 (4 pages) | Cited 3 times

Online Publication Date: 15 June 2006

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Effects of self-induced negative bias in radio-frequency (rf) sputtering on the structure of the deposited film are discussed on the basis of the measured characteristics of the gallium nitride (GaN) films. A powdered GaN target was sputtered by either argon (Ar) or nitrogen (N2) gas to investigate the effects of the sputtering. When sputtering with Ar gas, the resputtering due to the ion bombardments produces a film deficient in nitrogen with poor crystallinity. The ion bombardment eventually destroys the crystal structure producing a black amorphous film caused by gallium atoms forming clusters. Alternatively, when sputtering with N2 gas, the activated nitrogen atmosphere enhances nitrogen incorporation and prevents the destruction of the crystal structure, making the film stoichiometric. To obtain high crystallinity, the effect of the self-induced negative bias should be minimized by decreasing the rf power and increasing the total pressure.
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81.05.Ea III-V semiconductors
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
61.66.Bi Elemental solids
61.66.Dk Alloys

Integrated active transient thermography for rapid nondestructive analysis of sputtering target bond integrity

C. E. Wickersham

J. Vac. Sci. Technol. A 24, 1100 (2006); http://dx.doi.org/10.1116/1.2210950 (7 pages) | Cited 1 time

Online Publication Date: 15 June 2006

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Integrated active transient thermography is described and used to evaluate bond integrity of sputtering targets. In integrated active transient thermography one surface of a bonded target-backing plate assembly is rapidly heated while an infrared camera captures the time dependence of the surface temperature distribution on the opposite side. Bond defects inhibit heat transfer between the backing plate and the target, causing a slower rate of surface temperature rise in areas with poor bond integrity. Finite element models of the heat flow in the target assembly are used to establish the expected temperature rise for a perfectly bonded target assembly. A bond integrity map that is independent of the target assembly geometry, analysis time, applied power, and material is obtained by dividing the difference between the integrated finite element model generated map and the integrated experimental bond integrity map by the integrated finite element map. Measurement time for a commercial sized sputtering target assembly is only 50 s.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.70.Fy Nondestructive testing: optical methods

Effect of grain orientation on tantalum magnetron sputtering yield

Z. Zhang, Ling Kho, and C. E. Wickersham

J. Vac. Sci. Technol. A 24, 1107 (2006); http://dx.doi.org/10.1116/1.2212436 (5 pages)

Online Publication Date: 15 June 2006

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The differential sputter yields of tantalum grains during argon ion magnetron sputtering were measured and found to correlate with the atomic packing density in the uppermost atomic layer. Grains with their (110) planes aligned within 15° of the sputtering surface had the highest sputtering yield (0.95 at./ion at 400 eV). Simultaneously, grains oriented so that their (111) planes were within 15° of the sputtering surface had sputtering yields of around two times lower (0.47 at./ion at 400 eV). These results are consistent with the surface sputtering rather than the channeling model. A correlation was found between the number of free atoms on the surface as determined using a facetted surface model and the measured sputtering yield.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.47.De Metallic surfaces
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Physical-vapor deposition flux-distribution calculations for static and rotating substrates: Derivation of the deposition geometry for optimal film-thickness uniformity

Glenn Teeter

J. Vac. Sci. Technol. A 24, 1112 (2006); http://dx.doi.org/10.1116/1.2208990 (7 pages) | Cited 1 time

Online Publication Date: 16 June 2006

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Flux-distribution formulas are applied to physical-vapor deposition from open-boat-type sources onto static and rotating substrates. A relation is derived for the dependence of flux variation at the substrate on source-substrate separation for the static-substrate case. For the rotating-substrate case, the deposition geometry that yields optimal film-thickness uniformity for different source-substrate separations is derived empirically. For rotating substrates, both the percentage flux variation and the magnitude of the net deposition flux obey power-law dependences with respect to the source-substrate separation. Finally, a formula is derived for the percentage of source material deposited on the substrate as a function of source position.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth

Conceptual design of a deposition system for uniform and combinatorial synthesis of multinary thin-film materials via open-boat physical-vapor deposition

Glenn Teeter

J. Vac. Sci. Technol. A 24, 1119 (2006); http://dx.doi.org/10.1116/1.2208991 (9 pages)

Online Publication Date: 16 June 2006

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Conventional flux-distribution formulas for rotating and static substrates are used to develop a method for combinatorial physical-vapor deposition. With this method, a single deposition system may be used, without modification, to deposit either highly uniform or graded-composition thin-film materials. This is accomplished through appropriate automated sequencing of source shuttersand substrate rotation. A constrained-composition parametrization is introduced, whichdetermines relative deposition times for the film constituents with and without substraterotation. The combinatorial deposition scheme developed here is applicable to binary, ternary,or quaternary phase systems. Examples are considered for the pseudoquaternary CuInSe2–AgInSe2–CuGaSe2–AgGaSe2 chalcopyrite materials system, which has relevance to thin-film photovoltaics.
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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
68.55.A- Nucleation and growth

Structural and electrochromic characterizations of pulsed laser deposited TaxW1−xO3−x/2 films

Dongfang Yang

J. Vac. Sci. Technol. A 24, 1128 (2006); http://dx.doi.org/10.1116/1.2209652 (8 pages) | Cited 2 times

Online Publication Date: 16 June 2006

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Structural and electrochromic property studies of mixed oxide TaxW1−xO3−x/2 films grown on indium tin oxide coated glass substrates by the reactive pulsed laser deposition in 5.32 Pa oxygen atmospheres are presented in this article. The crystallization temperatures of TaxW1−xO3−x/2 increase with the Ta content in the films: When x = 0, TaxW1−xO3−x/2 (i.e., WO3) films crystallized to a monoclinic phase at substrate temperatures as low as 400 °C; when x = 0.1, TaxW1−xO3−x/2 (i.e., Ta0.1W0.9O2.95) films crystallized mainly to a tetragonal phase at substrate temperatures ≥ 600 °C, and when x = 0.3, TaxW1−xO3−x/2 (i.e., Ta0.3W0.7O2.85) films crystallized to a cubic crystal structure at substrate temperatures ≥ 700 °C. As the Ta content increases, the degree of symmetry of crystallized TaxW1−xO3−x/2 films increases resulting in shortening the metal oxygen bond length and forming more rigid structure. Electrochromic properties of amorphous TaxW1−xO3−x/2 films with different Ta contents were evaluated in 0.1M H3PO4 solution. Under H+ intercalation at negative electrical potentials, WO3 (x = 0) film changes its color from light pink to midnight blue, Ta0.1W0.9O2.95 (x = 0.1) from light pink to cadet blue, and Ta0.3W0.7O2.85 (x = 0.3) from light green to light brown green. The colors of all TaxW1−xO3−x/2 films at colored state disappeared immediately after the H+ ions were extracted from the film at position electrical potentials showing excellent reversibility. With similar film thickness the change in optical density between colored state and bleached state for the WO3 is about 2 times higher than that of Ta0.1W0.9O2.95 and about 14 times higher than that of Ta0.3W0.7O2.85. The coloration efficiencies at wavelength λ = 633 nm for WO3, Ta0.1W0.9O2.95, and Ta0.3W0.7O2.85 films are 132, 122, and 65 cm2 C−1, respectively. The durability of TaxW1−xO3−x/2 films increases with the increase of the Ta content in the acidic environments: in 0.1M H3PO4 solution the etching rate of WO3 is about 4.6 times higher than that of Ta0.1W0.9O2.95, while Ta0.3W0.7O2.85 has not shown any noticeable degradation after 55 coloring/bleaching cycles (1.5 h). The excellent reversibility of ion intercalation/deintercalation, relatively high coloration efficiency, and improved chemical stability and cyclic durability suggest that Ta0.1W0.9O2.95 and Ta0.3W0.7O2.85 are good candidates as the electrochromic cathodic layer for electrochromic devices, especially for proton conducting liquid-gel-type devices. The results have also demonstrated that addition of one metal oxide (e.g., Ta2O5) into another (e.g., WO3) is an effective way to alter the electrochromic properties of the individual constituents and provides a convenient method for tailoring electrochromic properties of materials.
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68.55.-a Thin film structure and morphology
78.66.Nk Insulators
78.20.Jq Electro-optical effects
81.15.Fg Pulsed laser ablation deposition
64.70.K- Solid-solid transitions
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption

Extreme ultraviolet binary phase gratings: Fabrication and application to diffractive optics

F. Salmassi, P. P. Naulleau, E. M. Gullikson, D. L. Olynick, and J. A. Liddle

J. Vac. Sci. Technol. A 24, 1136 (2006); http://dx.doi.org/10.1116/1.2212435 (5 pages) | Cited 3 times

Online Publication Date: 16 June 2006

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Diffractive optics play an important role in a variety of fields such as astronomy, microscopy, and lithography. In the extreme ultraviolet region of the spectrum they have been difficult to make due to the extremely precise control required of their surface structure. We have developed a robust fabrication technique that achieves the required topographic control through the deposition of a thin film of Si on a Cr etch stop. We have fabricated binary phase gratings using this approach that have an efficiency of 80% of the theoretical maximum. This technique could be applicable to similar binary phase structures requiring precise topography control.
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81.05.Cy Elemental semiconductors
42.79.Dj Gratings
81.15.Cd Deposition by sputtering
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer
68.55.A- Nucleation and growth

High efficiency SiO2–TiO2 hybrid sol-gel antireflective coating for infrared applications

E. Brinley, S. Seal, R. Folks, E. Braunstein, L. Kramer, and S. Seal

J. Vac. Sci. Technol. A 24, 1141 (2006); http://dx.doi.org/10.1116/1.2210007 (6 pages) | Cited 3 times

Online Publication Date: 20 June 2006

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Sol-gel derived antireflective thin films were created for chalcogenide glass substrates in the 1.5–5 μm wavelength range of infrared region. Presented herein is a preparation and characterization of the hybrid sol-gel created including particle size, refractive index, pH, and Fourier transform infrared FTIR transmission spectra. It is shown that an increase of not less than 8% and up to 25.1% transmission is achieved using sol-gel derived antireflective coatings.
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42.79.Wc Optical coatings
42.70.-a Optical materials
78.66.Nk Insulators
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
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Comment on “Nanoscale fatigue and fracture toughness measurement of multilayered thin film structures for digital micromirror devices” [ J. Vac. Sci. Technol. A 22, 1397 (2004) ]

Jürgen Malzbender

J. Vac. Sci. Technol. A 24, 1147 (2006); http://dx.doi.org/10.1116/1.2207151 (1 page)

Online Publication Date: 20 June 2006

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Abstract Unavailable
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
68.60.Bs Mechanical and acoustical properties

Performance of a hot-cathode-ionization-gauge head with correcting electrode and shield tube, operated with an automated-pressure-compensating circuit in a synchrotron radiation environment

Hiroshi Saeki, Tamotsu Magome, and Yoshihiko Shoji

J. Vac. Sci. Technol. A 24, 1148 (2006); http://dx.doi.org/10.1116/1.2208992 (3 pages) | Cited 2 times

Online Publication Date: 20 June 2006

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07.30.Dz Vacuum gauges
84.47.+w Vacuum tubes
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Erratum: “Surface roughness in XeF2 etching of a-Si/c-Si(100) [ J. Vac. Sci. Technol. A 23, 126 (2005) ]”

A. A. E. Stevens and H. C. W. Beijerinck

J. Vac. Sci. Technol. A 24, 1151 (2006); http://dx.doi.org/10.1116/1.2209658 (1 page)

Online Publication Date: 20 June 2006

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Abstract Unavailable
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99.10.Cd Errata
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning
68.47.Fg Semiconductor surfaces
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back to top Applied Surface Science

Effect of nitrogen on the photocatalytic activity of TiOxNy thin films

K. Prabakar, T. Takahashi, T. Nezuka, T. Nakashima, Y. Kubota, and A. Fujishima

J. Vac. Sci. Technol. A 24, 1156 (2006); http://dx.doi.org/10.1116/1.2174018 (5 pages) | Cited 6 times

Online Publication Date: 21 June 2006

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Visible light active nitrogen doped titanium oxide (TiOxNy) thin films were deposited by dc reactive magnetron sputtering on glass substrates at different nitrogen flow rates and sputtering pressures. All the deposited films consist of composite of TiOxNy and TiO2 phases of anatase and a small portion of the rutile (R) phase was embedded in the polycrystalline films. X-ray diffraction and optical studies confirmed that the prepared films had nitrogen substituted at some of the oxygen sites in TiO2, which formed narrow N 2p band above the valence band. The surface roughness of the films varied between 5 and 25 nm for the films deposited at nitrogen flow of 0.5–5 SCCM (standard cubic centimeter per minute), respectively. The photocatalytic decomposition of methanol was investigated using fourier transform infrared as a function of irradiation time. The formaldehyde and CO species are the main intermediates by increasing the irradiation time in the presence of pure methanol and CO2 is produced after the complete decomposition. The properties of the films, including the crystallinity, surface morphology, and light absorption capability, are influenced by the nitrogen flow rate while the photocatalytic reaction on TiOxNy thin films is very sensitive to oxygen vacancy and its surface structure.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.50.-m Photochemistry
71.20.Nr Semiconductor compounds
61.72.up Other materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.66.Li Other semiconductors

Sputtering pressure dependent photocatalytic properties of TiO2 thin films

T. Takahashi, K. Prabakar, T. Nezuka, T. Yamazaki, T. Nakashima, Y. Kubota, and A. Fujishima

J. Vac. Sci. Technol. A 24, 1161 (2006); http://dx.doi.org/10.1116/1.2187984 (5 pages) | Cited 8 times

Online Publication Date: 21 June 2006

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The TiO2 films were deposited on glass substrate by direct current reactive magnetron sputtering under various total sputtering gas pressures (PTot) of 0.2, 0.5, 0.8, and 5 Pa and at the target to substrate distances (DT-S) of 40 and 70 mm. Argon and oxygen gas mixtures (Ar:O2 = 80:20) were used to deposit the films. The optimum conditions to deposit the films with high photocatalytic activities were investigated in detail using in situ Fourier transform infrared spectra in relation to the sputter deposition processes. The band gap energy was found to decrease from 3.25 to 3.13 eV for the TiO2 films deposited at PTot of 5–0.2 Pa and DT-S of 40 mm. For the films deposited at DT-S of 70 mm, the band gap varied between 3.3 and 3.2 eV. The rate of decomposition of methanol is rapid for the films deposited at PTot of 0.2 Pa and DT-S of 40 mm and as the DT-S and PTot increase, the photo-oxidation of methanol by TiO2 decreases. The formaldehyde and CO species are the main intermediates by increasing the irradiation time and CO2 is produced after the complete decomposition.
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81.05.Hd Other semiconductors
81.15.Cd Deposition by sputtering
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.50.-m Photochemistry
78.30.Hv Other nonmetallic inorganics
71.20.Nr Semiconductor compounds

Role of low-level impurities and intercalated molecular gases in the α particle radiolysis of polytetrafluoroethylene examined by static time-of-flight secondary-ion-mass spectrometery

Gregory L. Fisher, Christopher Szakal, Christopher J. Wetteland, and Nicholas Winograd

J. Vac. Sci. Technol. A 24, 1166 (2006); http://dx.doi.org/10.1116/1.2167982 (6 pages) | Cited 2 times

Online Publication Date: 21 June 2006

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The structural degradation of polytetrafluoroethylene (PTFE) upon irradiation with MeV alpha (α) particles is accompanied by the proliferation of hydrogenated and oxygen-functionalized fluorocarbon species. In this article, we explore the origin of monoxide- and dioxide-functionalized fluorocarbon species that emerge upon α particle irradiation of PTFE. Samples of neat PTFE were irradiated to α doses in the range of 107–5×1010 rad using 5.5 MeV math ions produced in a tandem accelerator. Static time-of-flight secondary-ion-mass spectrometry (TOF-SIMS), using a 20 keV C60+ source, was employed to probe chemical changes as a function of α particle irradiation. Chemical images and high-resolution mass spectra were collected in both the positive and negative polarities. Residual gas analysis, utilized to monitor the liberation of molecular gases during α particle irradiation of the PTFE in vacuum, is discussed in relationship to the TOF-SIMS data.
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61.82.Pv Polymers, organic compounds
61.80.Jh Ion radiation effects
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)

Time-of-flight secondary ion mass spectrometry measurements of a fluorocarbon-based self-assembled monolayer on Si

J. A. Ohlhausen and K. R. Zavadil

J. Vac. Sci. Technol. A 24, 1172 (2006); http://dx.doi.org/10.1116/1.2188412 (7 pages) | Cited 5 times

Online Publication Date: 21 June 2006

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Low surface energy coatings and films are needed to minimize stiction, high friction, and wear of the oxide-terminated silicon-based microelectromechanical systems (MEMSs) to ensure reliable device function. One common approach is to deposit self-assembled monolayer (SAM) films of molecules possessing a reactive silane head group and low energy pendant chain to cover the complex structures used in MEMS devices. The composition of these films is difficult to characterize and quantify. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is an excellent tool for characterizing these types of films because of its ability to detect small quantities of surface species at high spatial resolution and surface sensitivity; however, interpretation of the spectral data generated is complex and challenging. We are using the combination of x-ray Photoelectron Spectrometry and ToF-SIMS to detect and quantify a fluorocarbon-based SAM on Si coupons and on MEMS devices. Unexpected fragmentation caused by the interaction of the primary ion beam with the fluorocarbon chain in contact with the Si surface creates ions whose presence is not intuitive. We can account for these ion fragments and use them to aid in quantifying the film composition. Our methods include the use of coverage-dependent fragmentation signatures along with the application of multivariate statistical techniques to establish the covariance in these signatures.
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81.05.Cy Elemental semiconductors
81.65.-b Surface treatments
68.47.Fg Semiconductor surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.Gy Mechanical properties; surface strains

Thin oxide-free phosphate films of composition formed on the surface of vanadium metal and characterized by x-ray photoelectron spectroscopy

D. J. Asunskis and P. M. A. Sherwood

J. Vac. Sci. Technol. A 24, 1179 (2006); http://dx.doi.org/10.1116/1.2204924 (6 pages) | Cited 2 times

Online Publication Date: 21 June 2006

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This article reports the preparation of thin (less than 100 Å) oxide-free phosphate films of various compositions on vanadium metal. These films are interesting because of their potential for corrosion inhibition, adhesion promotion, and biocompatibility. Valence and core-level x-ray photoelectron spectroscopy (XPS) were used to characterize the films. The valence band spectra obtained were compared with spectra generated from band structure calculations for various vanadium phosphates and from previously reported spectra of vanadium phosphates. Vanadium phosphate coatings were created by the reaction of vanadium metal and different phosphorus-oxygen containing acids: H3PO4, H3PO3, H3PO2, and H2P2O7. This article focuses upon the valence band region which shows significant differences between the four vanadium phosphate films formed as well as clear differences between the these phosphates and vanadium oxides. The valence band spectra are effectively interpreted by band structure calculations.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
73.20.At Surface states, band structure, electron density of states

Effect of probe tip size on atomic force microscopy roughness values for very smooth samples

Carolyn F. H. Gondran and Diane K. Michelson

J. Vac. Sci. Technol. A 24, 1185 (2006); http://dx.doi.org/10.1116/1.2172936 (6 pages) | Cited 3 times

Online Publication Date: 21 June 2006

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Two-dimensional geometric models and experimental data are used to evaluate the effect of tip shape artifacts on atomic force microscopy images, roughness values, and power spectra. The effects of tip size are studied as a function of the surface feature height, spacing, and width. The models demonstrate that the need for sharp tips is dictated by the sample roughness and the size and spacing of surface features. In addition, the magnitude and direction of the error in the measured roughness parameters are related to artifact-induced changes in the skew in the distribution of the data points about the surface mean. Significantly, it is shown that either higher or lower roughness values can be measured using a smaller sized tip, depending on the surface character. These model results are supported by sample data obtained with 2 and 10 nm radii of curvature tipped probes on films used in semiconductor research and development. Sharp-tipped probes are clearly beneficial for imaging the surface microstructure of low-k materials. Tip size has a marked impact on the roughness values obtained on a somewhat smoother metal film sample. However, the high-k sample studied was smooth enough that no benefit was realized with the use of a sharper-tipped probe.
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68.37.Ps Atomic force microscopy (AFM)
07.79.Lh Atomic force microscopes
68.35.B- Structure of clean surfaces (and surface reconstruction)
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
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Exploring the collective dynamics of lipid membranes with inelastic neutron scattering

Maikel C. Rheinstädter, Tilo Seydel, Wolfgang Häußler, and Tim Salditt

J. Vac. Sci. Technol. A 24, 1191 (2006); http://dx.doi.org/10.1116/1.2167979 (6 pages) | Cited 3 times

Online Publication Date: 21 June 2006

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While most spectroscopic techniques, as e.g., nuclear magnetic resonance or dielectric spectroscopy, probe macroscopic responses, neutron and within some restrictions also x-ray scattering experiments give the unique access to microscopic dynamics at length scales of intermolecular or atomic distances. Only recently, it has become possible to study collective dynamics of planar lipid bilayers using neutron spectroscopy techniques [ M. Rheinstädter, C. Ollinger, G. Fragneto, F. Demmel, and T. Salditt, Phys. Rev. Lett. 93, 108107 (2004) ]. We determined the dispersion relation of the coherent fast picosecond density fluctuations on nearest-neighbor distances of the phospholipid acyl chains in the gel and in the fluid phases of a dimyristoylphoshatidylcholine bilayer. The experiments shed light on the evolution of structure and dynamics, and the relation between them, in the range of the gel-fluid main phase transition. The scattering volume restriction for inelastic neutron experiments was overcome by stacking several thousands of highly aligned membrane bilayers. By combining different neutron-scattering techniques, namely, three-axis, backscattering, and spin-echo spectroscopies, we present measurements of short- and long-wavelength collective fluctuations in biomimetic and biological membranes in a large range in momentum and energy transfer, covering time scales from about 0.1 ps to almost 1 μs and length scales from 3 Å to about 0.1 μm. The neutron-backscattering technique gives information about slow molecular dynamics of lipid acyl chains and the “membrane-water,” i.e., the water molecules in between the stacked bilayers in the nanosecond time range [ M. C. Rheinstädter, T. Seydel, F. Demmel, and T. Salditt, Phys. Rev. E 71, 061908 (2005) ]. The dispersion relations of the long-wavelength undulation modes in lipid bilayers with nanosecond relaxation times can be determined by quasielastic reflectometry on spin-echo spectrometers and give direct access to the elasticity parameters of the membranes.
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87.14.Cc Lipids
87.16.D- Membranes, bilayers, and vesicles
83.85.Hf X-ray and neutron scattering

Surface modification of silicon and polydimethylsiloxane surfaces with vapor-phase-deposited ultrathin fluorosilane films for biomedical nanodevices

Bharat Bhushan, Derek Hansford, and Kang Kug Lee

J. Vac. Sci. Technol. A 24, 1197 (2006); http://dx.doi.org/10.1116/1.2167077 (6 pages) | Cited 22 times

Online Publication Date: 21 June 2006

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Ultrathin coatings of fluorosilane films for silicon and polydimethylsiloxane (PDMS) nanochannels are desirable to control the hydrophobicity of the surface and reduce or prevent undesired protein adsorption or cell interactions critical for the performance of most biomedical micro/nanodevices. Surface modifications using vapor-phase deposition become increasingly important for some biomedical nanodevices and have advantages over liquid-phase deposition since the vapor phase can permeate more efficiently into silicon nanochannels. In this study, vapor-phase deposition was used to deposit ultrathin films of four fluorosilanes on silicon and PDMS and identify deposition conditions for an optimal process. The films were characterized by means of a contact angle analyzer for hydrophobicity, an ellipsometer for film thickness, and an atomic force microscope for surface roughness of these films. Results of this study and relevant mechanisms are the subject of this article.
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68.47.Fg Semiconductor surfaces
68.47.Mn Polymer surfaces
81.05.Cy Elemental semiconductors
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
87.80.-y Biophysical techniques (research methods)
87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications

Time-of-flight secondary ion mass spectrometry chemical imaging analysis of micropatterns of streptavidin and cells without labeling

Tae Geol Lee, Hyun Kyong Shon, Kyung-Bok Lee, Jinmo Kim, Insung S. Choi, and Dae Won Moon

J. Vac. Sci. Technol. A 24, 1203 (2006); http://dx.doi.org/10.1116/1.2206191 (5 pages) | Cited 6 times

Online Publication Date: 21 June 2006

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A bismuth cluster ion-beam-based time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been successfully used to image micropatterns of streptavidin and Chinese hamster ovary (CHO-k1) cells, as received and without any labeling. Three different analysis ion beams (Bi+, Bi3+, and Bi32+) were compared to obtain label-free TOF-SIMS chemical images of micropatterns of streptavidin, which were subsequently used for generating biotinylated cell patterns. Unlike using a Bi+ ion beam, using a Bi3+ or Bi32+ primary analysis ion beam yielded well-contrasted-TOF-SIMS images of streptavidin characteristic secondary ions. A principal component analysis of TOF-SIMS data was performed to generate a chemical image of the streptavidin itself. A chemical specific TOF-SIMS image analysis gave us a better understanding of the localization of cells at the outer boundaries of the streptavidin-patterned circles. Our work suggests that using cluster-ion analysis beams together with multivariate data analysis for TOF-SIMS chemical imaging would be an effectual method for producing label-free chemical images of micropatterns of biomolecules, including proteins and cells.
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87.80.-y Biophysical techniques (research methods)
87.15.-v Biomolecules: structure and physical properties
87.14.E- Proteins
back to top Electronc Materials and Devices

Metal organic chemical vapor deposition of ZrO2 thin films using the single precursor zirconium 3-methyl-3-pentoxide, Zr(mp)4

Wontae Cho, Hong Suk Jang, Ki-Seok An, Young Kuk Lee, Taek-Mo Chung, Chang Gyoun Kim, Yunsoo Kim, Byung-Soo So, Jin-Ha Hwang, and Donggeun Jung

J. Vac. Sci. Technol. A 24, 1208 (2006); http://dx.doi.org/10.1116/1.2172935 (5 pages) | Cited 3 times

Online Publication Date: 21 June 2006

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Thin films of zirconium dioxide, ZrO2, have been deposited on silicon substrates by metal organic chemical vapor deposition using the single precursor zirconium 3-methyl-3-pentoxide, {Zr[OC(CH3)(C2H5)2]4, Zr(mp)4}, with no additional oxygen source, and the chemical vapor deposition reaction mechanism was also investigated. Zr(mp)4 is a liquid at room temperature and shows an excellent one-step weight loss and a low residual weight less than 3% in its thermogravimetric analysis. The deposition rate was found to be ∼ 13 Å/min at the substrate temperature of 300 °C with the activation energy of 33.5 kJ/mol, which was obtained at the moderate precursor temperature of 70 °C and 50 sccm of the N2 carrier gas. By gas chromatography/mass spectrometry and nuclear magnetic resonance analyses of the thermally decomposed vapor phase products collected during the deposition of ZrO2 films, it was clearly found that the ZrO2 films are grown via β-hydrogen elimination processes of the Zr(mp)4 single precursor. An x-ray photoelectron spectroscopy investigation of the ZrO2 films revealed an almost negligible carbon incorporation, which indicates that, except for the β-hydrogen elimination processes, no additional decomposition and/or recombination processes contributed to the growth of the ZrO2 films. The morphology, crystallinity, and electrical properties of the ZrO2 films were characterized by x-ray diffraction, scanning electron microscopy, and capacitance-voltage measurements.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
76.60.-k Nuclear magnetic resonance and relaxation
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Unintentional doping and compensation effects of carbon in metal-organic chemical-vapor deposition fabricated ZnO thin films

Xiaonan Li, Sally E. Asher, Sukit Limpijumnong, S. B. Zhang, Su-Huai Wei, Teresa M. Barnes, Timothy J. Coutts, and Rommel Noufi

J. Vac. Sci. Technol. A 24, 1213 (2006); http://dx.doi.org/10.1116/1.2167981 (5 pages) | Cited 10 times

Online Publication Date: 21 June 2006

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Carbon is a typical impurity in thin films fabricated by metal-organic chemical-vapor deposition (MOCVD). The role of carbon in undoped and nitrogen-doped ZnO thin films was studied experimentally and theoretically to understand the possible compensation effects. ZnO thin films are fabricated by low-pressure MOCVD using diethylzinc, nitric oxide (for nitrogen-doped films), or oxygen precursors (for undoped films). Compared with sputtering-fabricated ZnO film, the carbon concentration in the MOCVD-fabricated ZnO film is very high. Furthermore, the MOCVD-fabricated ZnO:N film has an even higher carbon concentration than the undoped ZnO. Considering the signal observed previously by Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy, it is possible that the incorporated carbon has formed complexes with doped nitrogen. The first-principles calculations predict that the formation energy for carbon interstitial (Ci) is relatively high. However, due to the large binding energy between Ci and NO (nitrogen substitute on oxygen site), the formation energy of the carbon-nitrogen (CN) defect complex is lower than that of the Ci. As a result, with nitrogen doping, the carbon-impurity concentration would be high. In the insulator or p-type ZnO films, the CN defect complexes have 1+ charge state. Therefore, the existence of carbon in the ZnO:N film could be another possible passivation factor to the nitrogen acceptor, in addition to hydrogen.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.30.Fs III-V and II-VI semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Production of a hafnium silicate dielectric layer for use as a gate oxide by solid-state reaction

H. T. Johnson-Steigelman, A. V. Brinck, J. P. Chang, and P. F. Lyman

J. Vac. Sci. Technol. A 24, 1218 (2006); http://dx.doi.org/10.1116/1.2180274 (5 pages) | Cited 1 time

Online Publication Date: 21 June 2006

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The formation of hafnium silicate films (HfSixOy) for use as gate oxides with a large dielectric constant by solid-state reaction of Hf metal and SiO2 was investigated. Thin, fully reacted silicate films could be formed, and were thermally stable in vacuum to temperatures in excess of 800 °C. Evidence was found that the interface between a hafnium silicate layer and the silicon substrate is stable against SiO2 formation.
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77.55.-g Dielectric thin films
68.35.Ct Interface structure and roughness
68.60.Dv Thermal stability; thermal effects

Effect of nitrogen contents on the temperature dependence of photoluminescence in InGaAsN/GaAs single quantum wells

Fang-I Lai, S. Y. Kuo, J. S. Wang, H. C. Kuo, S. C. Wang, H. S. Wang, C. T. Liang, and Y. F. Chen

J. Vac. Sci. Technol. A 24, 1223 (2006); http://dx.doi.org/10.1116/1.2208996 (5 pages) | Cited 3 times

Online Publication Date: 21 June 2006

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A series of InGaAsN/GaAs single-quantum wells (SQWs) with N contents varied from 0% to 5.3% were grown by molecular-beam epitaxy using a solid As and a nitrogen plasma sources. The impact of nitrogen concentration on the optical properties, as determined by the temperature dependence of photoluminescence (PL), of a 6 nm SQW was investigated. In the low-temperature region, a pronounced temperature-dependent S-shaped peak position was observed in PL spectra while increasing the nitrogen concentration. Quenching behavior reveals that the defect-related nonradiative processes might be enhanced in the highly nitrogen incorporated samples and thus influence the recombination dynamics. In addition, the evolution of the peak position of the InGaAsN/GaAs samples was in agreement with the empirical Varshni model in the high-temperature region. A significant reduction in the temperature dependence of the emission peak position is analyzed as well, and further confirms the prediction of proposed band anticrossing model of the electronic structure of III-N-V alloys.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Effect of poly (3-hexylthiophene) film thickness on organic thin film transistor properties

Huiping Jia, Srinivas Gowrisanker, Gaurang K. Pant, Robert M. Wallace, and Bruce E. Gnade

J. Vac. Sci. Technol. A 24, 1228 (2006); http://dx.doi.org/10.1116/1.2202858 (5 pages) | Cited 16 times

Online Publication Date: 21 June 2006

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We present the effect of poly (3-hexylthiophene) (P3HT) thickness on the performance of organic thin film transistors (OTFTs). The P3HT film thickness varies from 11 to 186 nm. The devices have channel lengths of 5, 10, 20, 40, and 80 μm and a channel width of 500 μm. The mobility and on/off ratio are up to 0.08 cm2/V s and 7×103, respectively. The drain current and the mobility increase with thickness. At the same P3HT thickness, the drain current and mobility become higher when the channel length is reduced. The on/off ratio decreases quickly and then saturates for thickness >64 nm. Short channel devices have higher on/off ratio than long channel devices. For short channel devices (5 μm), the on/off ratio does not change significantly with thickness. The devices with shorter channel length and thicker P3HT films tend to have smaller threshold voltages. The threshold voltage saturates for long channel (20–80 μm) devices, for films thicker than 110 nm. The gate leakage (ID offset) is higher for thicker film devices. The performance dependence as a function of P3HT film thickness can be explained by the bulk conductance model and the SiO2 surface potential change. Our results suggest that the performance of P3HT OTFTs should be optimized based on the specific application.
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85.30.Tv Field effect devices
back to top Electronic Materials and Processing I

Role of defects at nanoscale ZnO and Cu(In,Ga)Se2 semiconductor interfaces

Y. M. Strzhemechny

J. Vac. Sci. Technol. A 24, 1233 (2006); http://dx.doi.org/10.1116/1.2167079 (5 pages)

Online Publication Date: 22 June 2006

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Current understanding and control of semiconductor contacts increasingly require measurements sensitive to defects and chemical changes at nanoscale interfaces. We offer examples illustrating dramatic macroscopic effects occurring in semiconductor systems as a result of nanoscale interface phenomena. In some cases, there is interplay of several competing defect-driven mechanisms. Elucidating them and finding the leading ones require careful experimental approach. For single-crystalline ZnO, we study the role of near-surface defects on the formation of Au Schottky contacts. Among the factors degrading the rectifying characteristics of such contacts one should consider the following. High concentrations of shallow donors in the surface and subsurface regions lead to barrier thinning, resulting in increased tunneling. Alternatively, the presence of deep defects near contact interface promotes tunneling by defect-assisted hopping. Nanoscale electronic and chemical studies show that independent reduction of both shallow donors and deep defects significantly improves the rectifying performance of the Au/ZnO contacts. We find that processing of ZnO with remote O and H plasmas allows for controllable tailoring of chemical and physical properties of the surface. By the same token, nanoscale compositional and electrostatic variations between grain boundaries and grain interiors in thin polycrystalline films of Cu(In,Ga)Se2, absorber layers in record-setting solar cells, show how nanoscale arrangement of near-surface stoichiometric defects may improve the overall photovoltaic efficiency. Confirming the theory, we find a 50% reduction in Cu composition from grain interior to boundary and a p-type potential barrier that acts to reduce majority-carrier hole recombination. These examples emphasize the practical significance of nanoscale chemical and electronic features at electronic material interfaces.
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68.35.Ct Interface structure and roughness
68.47.Fg Semiconductor surfaces
61.72.Mm Grain and twin boundaries
73.40.Gk Tunneling
72.40.+w Photoconduction and photovoltaic effects
61.66.Bi Elemental solids
61.66.Dk Alloys

Interstitial oxygen-related defects and current leakage in trench metal-oxide-semiconductor field-effect transistor on epi/As++ structure

Q. Wang, Manmohan Daggubati, Hossein Paravi, Rong Yu, and Xiao Feng Zhang

J. Vac. Sci. Technol. A 24, 1238 (2006); http://dx.doi.org/10.1116/1.2167075 (5 pages)

Online Publication Date: 22 June 2006

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Interstitial oxygen (Oi) related defect and reverse current leakage have been investigated on test trench metal-oxide-semiconductor field-effect transistors fabricated on epilayers over heavily arsenic-doped wafers (As++). The devices on the wafers sealed with polysilicon at backside exhibited an increased yield loss in reverse current leakage with increasing Oi concentration. The Oi concentration depth profiles indicate that Oi did precipitate out at the interface between the polysilicon layer and bulk silicon. This precipitation may consume the polylayer and reduce its gettering efficiency, which leads to an Oi-dependent current leakage. Similar experiments carried out with damaged backside As++ wafers show an overall low and Oi-independent current leakage yield loss. This reduced leakage yield loss is due to the intrinsic gettering effect of the Oi precipitates in these wafers close to the back surface. Transmission electron microscopy study revealed, in the junction region, the existence of intrinsic stacking faults and punch-out dislocation loop, characteristic of oxygen precipitation. The reverse current-voltage curves related to these defects have been quantitatively analyzed using the Shockley-Read-Hall model. The effective generation lifetimes of intrinsic stacking fault and punch-out dislocation loop are about 4.3 ps and 50 ns, respectively, and are significantly shorter than 2.5 μs in defect-free area.
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85.30.Tv Field effect devices
61.72.J- Point defects and defect clusters
61.72.uf Ge and Si
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Effects of molecular environments on the electrical switching with memory of nitro-containing OPEs

N. Gergel-Hackett, N. Majumdar, Z. Martin, N. Swami, L. R. Harriott, J. C. Bean, G. Pattanaik, G Zangari, Y. Zhu, I. Pu, Y. Yao, and J. M. Tour

J. Vac. Sci. Technol. A 24, 1243 (2006); http://dx.doi.org/10.1116/1.2208994 (6 pages) | Cited 6 times

Online Publication Date: 22 June 2006

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An oligo(phenylene ethynylene) (OPE) molecule with a nitro side group has exhibited electrical switching with memory and thus has potential for use in molecular electronic devices. However, different research groups have reported different electrical behaviors for this molecule. In addition to variations among test structures, differences in local molecular environments could be partially responsible for the differences in the reported results. Thus, we tested four variations of a nitro-OPE/dodecanethiol monolayer in the same type of nanowell test device to study how the environment of the nitro-OPE affects the observed electrical behavior. We found that the density of the nitro-containing molecules in the device altered the observed electrical switching behavior. Further, we found a positive correlation between the disorder of the monolayer and the observed electrical switching behavior. This correlation is consistent with suggestions that nitro molecule switching may depend on a conformational change of the molecule, which may be possible only in a disordered monolayer.
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85.65.+h Molecular electronic devices
84.30.Sk Pulse and digital circuits
back to top Electronic Materials and Processing II

Modeling of InAs/GaAs self-assembled heterostructures: Quantum dot to quantum ring transformation

I. Filikhin, B. Vlahovic, and E. Deyneka

J. Vac. Sci. Technol. A 24, 1249 (2006); http://dx.doi.org/10.1116/1.2174019 (3 pages)

Online Publication Date: 22 June 2006

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A single subband model for InAs/GaAs quantum dots (QDs) and quantum rings (QRs), where the energy dependence of the electron effective mass is defined by the Kane formula, is used. Model assumptions lead to the nonlinear Schrödinger equation in a three-dimensional space. Geometrical parameters of the model are based on the fabrication of QRs from a QD procedure for which the experimental capacitance-gate voltage (CV) data are available. The confinement state energies of QDs (QRs) are calculated. Obtained results for single electron energy levels reveal a good agreement with the CV spectroscopy experiments.
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73.21.La Quantum dots
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
03.65.Ge Solutions of wave equations: bound states

Comparison of a dominant electron trap in n-type and p-type GaNAs using deep-level transient spectroscopy

S. W. Johnston and S. R. Kurtz

J. Vac. Sci. Technol. A 24, 1252 (2006); http://dx.doi.org/10.1116/1.2167081 (6 pages) | Cited 6 times

Online Publication Date: 22 June 2006

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Both p-type and n-type dilute-nitrogen GaNAs epitaxial layers grown by metal-organic chemical vapor deposition were characterized by deep-level transient spectroscopy (DLTS). For each case, the dominant DLTS signal corresponds to an electron trap having an activation energy of about 0.2–0.3 eV for p-type GaNAs and about 0.3–0.4 eV for n-type GaNAs. In p-type GaNAs, the electron traps fill slowly, as the DLTS signal reaches saturation using zero-bias filling pulses with widths of 1 s. The electron traps fill quickly in the n-type GaNAs, as the DLTS signal does not typically increase after the shortest fill time of 10 μs. The electron-trap densities are calculated using modeling that accounts for the spatial region where traps fill and emit during DLTS measurement. A set of p-type samples with mid-1016 cm−3 net acceptors has N content ranging from 0.02% to 1.2%, and the resulting electron-trap concentrations range from 1.4×1017 to 4.3×1017 cm−3. A set of n-type samples with mid-1017 cm−3 doping has N content ranging from 0.011% to 0.45%, and the resulting electron-trap concentrations range from 7.6×1014 to 3.6×1016 cm−3. Additionally, a set of p-type samples with ∼ 0.25% N content has hole concentrations ranging from 4.3×1016 to 1.3×1017 cm−3, and the resulting electron-trap concentrations increase with acceptor doping ranging from 3.1×1017 to 7.2×1017 cm−3. A set of n-type samples with ∼ 0.25% N content has electron concentrations ranging from 4.5×1016 to 7.8×1017 cm−3. The resulting electron-trap concentrations also increase with donor concentration from 5.7×1015 to 3.5×1016 cm−3. The modeling of the Poole-Frenkel effect predicts that the trap may be about 100 meV deeper than implied by the measured activation energies.
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71.55.Eq III-V semiconductors
72.20.Ht High-field and nonlinear effects
back to top MEMS and NEMS

Surface characterization of human hair using tapping mode atomic force microscopy and measurement of conditioner thickness distribution

Richard A. Lodge and Bharat Bhushan

J. Vac. Sci. Technol. A 24, 1258 (2006); http://dx.doi.org/10.1116/1.2180275 (12 pages) | Cited 11 times

Online Publication Date: 22 June 2006

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The ways in which common hair care products, such as conditioner, deposit onto hair and change hair properties are of interest in beauty care science, since these properties are closely tied to product performance. In this study, tapping mode atomic force microscopy (AFM) is used to generate surface height maps of hair, which are then compared to maps generated using contact mode AFM. The frequency spectra of both data sets are also compared. This comparison is made to determine the most appropriate method for imaging compliant biological samples that may be subject to damage from interaction with the AFM tip during contact mode. Additionally, force calibration mode of AFM is used to obtain the local conditioner thickness distribution and adhesive force mapping of various hair surfaces. The conditioner thickness is extracted by measuring the forces on the AFM tip as it approaches, contacts, and pushes through the conditioner layer. Because the interaction of hair with skin is one of the most common in the real world, and clean skin is hydrophobic, a Si3N4 tip is coated with Z-TETRAOL to create a hydrophobic tip to measure friction and adhesion. These values are compared with those measured with the more common hydrophilic tips. Both chemically damaged and virgin (undamaged) hair samples as well as samples both treated with a commercial conditioner and those left untreated are compared. The location and thickness of the conditioner deposits are determined using this technique and relevant mechanisms driving the deposition are discussed. The effect of material contact angle on the tribological properties is also thoroughly discussed.
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87.64.Dz Scanning tunneling and atomic force microscopy
87.17.-d Cell processes

Replication-based fabrication for an optical device that incorporates vertically curved structures

M. W. Lee, K. J. Lim, C. H. Choi, S. B. Jo, S. G. Lee, E. H. Lee, S. G. Park, and B. H. O

J. Vac. Sci. Technol. A 24, 1270 (2006); http://dx.doi.org/10.1116/1.2201545 (7 pages)

Online Publication Date: 22 June 2006

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The replication process is a good method to fabricate passive optical devices. Silicon-based fabrication technology provides an efficient way to fabricate a replication master with an optically smooth surface roughness. As silicon-based technologies are often two-dimensional processes, the replication requires sophisticated fabrication steps for a master structure. For this, a vertically curved structure, which is essential for a passive optical device, is hard to fabricate. Special processes, such as x-ray lithography, laser ablation, and gray-scale lithography, can overcome the conventional two-dimensional fabrication process challenges. But these processes need additional steps, machines, and masks. This study demonstrates an easy way for fabricating a silicon master structure for vertically curved mirrors. This fabrication method is roughly divided into two steps. During the first step, a silicon wafer is etched using an inductively coupled plasma system to form optical waveguide structures in the master structure (45 μm depth and ∼ 5 nm surface roughness). During the second step, the vertically curved mirror structures at each end of the waveguides are formed by using photoresist reflow process. After the master fabrication, the master shape was transferred to a PDMS mold. The replication process was carried out by using UV curable polymers, and a successful vertical redirection of light by the curved structure was observed with a charge-coupled device. The measured propagation loss of the fabricated waveguide structure was 0.13 dB/cm, and the curved mirror loss was 0.35 dB.
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42.79.Gn Optical waveguides and couplers
42.79.Bh Lenses, prisms and mirrors
42.82.Cr Fabrication techniques; lithography, pattern transfer

Copper electroplating to fill blind vias for three-dimensional integration

S. Spiesshoefer, J. Patel, T. Lam, L. Cai, S. Polamreddy, R. F. Figueroa, S. L. Burkett, L. Schaper, R. Geil, and B. Rogers

J. Vac. Sci. Technol. A 24, 1277 (2006); http://dx.doi.org/10.1116/1.2206193 (6 pages) | Cited 12 times

Online Publication Date: 22 June 2006

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The continued demand for electronic products with decreased size, higher performance, and increased functionality requires improvements in the system level integration of logic, memory, and other functional integrated circuits. The formation of vertical interconnects in silicon may be one approach to provide this integration. This method involves stacking of individual die to form a highly interconnected three-dimensional structure by placing electrically conductive vias through the body of the silicon to bring the connections from top to bottom. Copper is the metal used to fill the through silicon via structure because of its high conductivity and common use in multilevel wiring. A process will be described in this article to electroplate copper into small diameter (5–10 μm) vias of aspect ratio >3. The objective of this project is to develop an electroplating process to obtain a void-free copper filled blind via; a via that does not go through the silicon substrate but terminates inside the silicon. Prior to plating, vias are formed by both reactive ion etch (RIE) and deep RIE processes and are then lined with insulation, barrier, and seed films. The insulation layer, SiO2, is deposited by plasma enhanced chemical vapor deposition while the barrier (TaN) and Cu seed layers are deposited by sputtering. A combination of three electroplating techniques is used in this study to fill the vias. They consist of optimized bath composition (additive control), fountain plating, and reverse pulse plating. The goal during electroplating is to achieve a bottom-up fill, also referred to as “a superfill.” This article describes the process that results in void-free electroplating to fill an array of blind vias as well as the related processing issues.
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85.40.Sz Deposition technology
85.40.Ls Metallization, contacts, interconnects; device isolation

Aspect ratio dependent etching lag reduction in deep silicon etch processes

S. L. Lai, D. Johnson, and R. Westerman

J. Vac. Sci. Technol. A 24, 1283 (2006); http://dx.doi.org/10.1116/1.2172944 (6 pages) | Cited 13 times

Online Publication Date: 22 June 2006

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Microelectromechanical system (MEMS) device fabrication often involves three dimensional structures with high aspect ratios. Moreover, MEMS designs require structures with different dimensions and aspect ratios to coexist on a single microchip. There is a well-documented aspect ratio dependent etching (ARDE) effect in deep silicon etching processes. For features with different dimensions etched simultaneously, the ARDE effect causes bigger features to be etched at faster rates. In practice, ARDE effect has many undesired complications to MEMS device fabrication. This article presents a physical model to describe the time division multiplex (TDM) plasma etch processes and thereafter the experimental results on ARDE lag reduction. The model breaks individual plasma etch cycles in the TDM plasma etch processes into polymer deposition, polymer removal, and spontaneous silicon etching stages. With the insights gained from the model and control over the passivation and etch steps, it has been demonstrated that ARDE lag can be controlled effectively. Experiments have shown that a normal ARDE lag can be changed to an inverse ARDE lag. Under optimized conditions, the ARDE lag is reduced to below 2%–3% for trenches with widths ranging from 2.5 to 100 μm, while maintaining good etch profile in trenches with different dimensions. Such results are achieved at etch rates exceeding 2 μm/min.
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81.65.Cf Surface cleaning, etching, patterning
68.47.Fg Semiconductor surfaces
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
52.77.Bn Etching and cleaning
81.65.Rv Passivation
back to top Manufacturing Science and Technology

Dependence of power trench metal-oxide-semiconductor field-effect transistor processes on wafer thickness

M. Daggubati, G. Sim, D. Long, H. Paravi, and Q. Wang

J. Vac. Sci. Technol. A 24, 1289 (2006); http://dx.doi.org/10.1116/1.2170093 (4 pages)

Online Publication Date: 22 June 2006

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The dependence of trench metal-oxide-semiconductor field-effect transistor processes on wafer thickness has been studied. In the photolithography process, it was found that the photoresist thickness decreased with the decrease of wafer thicknesses. This is due to the fact that thinner wafer has less thermal mass and hence less dissipation time. Unless compensated for, this change in resist thickness adds to critical dimension and trench depth variations. After the rapid thermal processing, the thinner wafers exhibited a lower resistivity and higher silicide stress (i.e., 3.23E+10 dyn/cm2 for 508 μm wafers and 4.60E+09 dyn/cm2 for 675 μm wafers). Also, the stress is more uniform across the thinner wafers, possibly due to uniform Si-rich TixSiy (x<y) phase. Both Z-contrast transmission electron microscopy imaging and energy dispersive x-ray profiling on the silicide layers of the thicker wafers revealed a Ti-rich layer (possibly TiSi) on the top of TixSiy (x<y) layer and at the Si-silicide interface; whereas only scattered regions of Ti-enriched regions were observed in thinner wafers. Higher temperature in thinner wafers seems to assist in the removal of this Ti-rich layer.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Fabrication of high precision demultiplexer using embossing technique with thermal curable polymers

C.-H. Choi, M.-W. Lee, B.-H. O, S.-G. Lee, S.-G. Park, and E.-H. Lee

J. Vac. Sci. Technol. A 24, 1293 (2006); http://dx.doi.org/10.1116/1.2197505 (4 pages)

Online Publication Date: 22 June 2006

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Photonic devices based on polymer materials have been fabricated mainly by using conventional lithography and etch processes. However, the fabrication method through these processes is complex and expensive. We fabricated 1310/1550 nm demultiplexer using an embossing technique, which was able to reduce the fabrication cost. The mold is an elastomeric polydimethylsiloxane (PDMS) and resists used as the core and the cladding layers are ZP 51 (ChemOptics) and ZP 49 (ChemOptics), respectively, which are thermal curable polymers. The fabrication process is summarized as follows: (1) manufacturing the photoresist master by lithography process, (2) forming the PDMS mold from the master, and (3) replicating the device using the mold. There is no observation of any noticeable pattern difference between the master and the replica in microscaled dimension. In this work, we also investigated the durability of a PDMS mold for mass production and successfully fabricated the 50th replica with the same mold. The replicated device was measured by the laser source and the charge-coupled device camera.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.86.+b Optical workshop techniques
42.70.Jk Polymers and organics
81.65.Cf Surface cleaning, etching, patterning

Effects of various oxidizers on chemical mechanical polishing performance of nickel for microelectromechanical system applications

Nam-Hoon Kim, Gwon-Woo Choi, Yong-Jin Seo, and Woo-Sun Lee

J. Vac. Sci. Technol. A 24, 1297 (2006); http://dx.doi.org/10.1116/1.2194926 (5 pages) | Cited 5 times

Online Publication Date: 22 June 2006

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Nickel and nickel-based alloys are known candidates to realize movable structures for microelectromechanical system (MEMS) application. Chemical mechanical polishing (CMP) has found extensive application in the fabrication of MEMS. In this study, the CMP of nickel was performed using the commercial slurry with the various ratios of different oxidizers and alumina particle as an abrasive. Moreover, the potentiodynamic polarization behaviors were discussed to evaluate the effects of nickel-CMP performance and electrochemical characteristics between nickel and the various oxidizers. As an experimental result, the removal rate of nickel reached a maximum at 1.0 vol % of H2O2 concentration. An addition of 5.0 wt % alumina (Al2O3) abrasive could improve the removal rate of nickel; however, many scratches were observed. For the case of Fe(NO3)3 addition as an oxidizer, both the removal rate and the surface topography were insufficient for MEMS applications. The potentiodynamic polarization results indicated that the surface chemistry and electrochemical characteristics of nickel play an important role in controlling the polishing behavior of nickel.
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81.65.Ps Polishing, grinding, surface finishing
82.70.Kj Emulsions and suspensions
07.10.Cm Micromechanical devices and systems
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Cross-sectional transmission electron microscopy method and studies of implant damage in single crystal diamond

D. P. Hickey, E. Kuryliw, K. Siebein, K. S. Jones, R. Chodelka, and R. Elliman

J. Vac. Sci. Technol. A 24, 1302 (2006); http://dx.doi.org/10.1116/1.2209659 (6 pages) | Cited 6 times

Online Publication Date: 22 June 2006

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Few transmission electron microscopy (TEM) studies of single crystal diamond have been reported, most likely due to the time and difficulty involved in sample preparation. A method is described for creating a TEM cross section of single crystal diamond using a focused ion beam and in situ lift-out. The method results in samples approximately 10 μm long by 3 μm deep with an average thickness of 100–300 nm. The total time to prepare a cross-sectional TEM sample of diamond is less than 5 h. The method also allows for additional thinning to facilitate high resolution TEM imaging, and can be applied to oddly shaped diamond samples. This sample preparation technique has been applied to the study of ion implantation damage in single crystal diamond and its evolution upon annealing. High-pressure–high-temperature diamonds were implanted with Si+ at an energy of 1 MeV and a temperature of 30 °C. One sample, with a (110) surface, was implanted with a dose of 1×1014 Si cm−2 and annealed at 950 °C for 10 and 40 min. No significant defect formation or evolution was discernible by cross-sectional transmission electron microscopy. Another sample, with a (100) orientation, was implanted with 1 MeV at 1×1015 Si cm−2 and annealed at 1050 °C for 10 min. Prior to annealing, a heavily damaged but still crystalline region was observed. Upon annealing, the sample showed no signs of conversion either to an amorphous form of carbon or to graphite. This is unexpected as the energy and dose are above the previously reported graphitization threshold for diamond. Higher annealing temperatures and possibly a high vacuum will be required for future study of defect formation, evolution, and phase transformations in ion-implanted single crystal diamond.
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61.80.Jh Ion radiation effects
61.72.up Other materials
61.72.Cc Kinetics of defect formation and annealing

End-pointing chamber clean by calorimetric probing of process effluent

Ing-Shin Chen, Jeffrey W. Neuner, James J. Welch, Philip S. H. Chen, and Frank DiMeo

J. Vac. Sci. Technol. A 24, 1308 (2006); http://dx.doi.org/10.1116/1.2167073 (6 pages)

Online Publication Date: 22 June 2006

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The semiconductor industry employs gas-phase cleaning widely to remove materials deposited on the chamber walls during thin-film deposition processes. Chamber clean end-pointing—i.e., terminating the process when the chamber is clean—is desirable to manage cost of ownership and environmental impact. Existing end-pointing methods tend to rely on changes of plasma characteristics as the in situ plasma removes the deposit in time. Chamber clean technology is moving towards remote generation of plasma species for cleaning. In this arrangement, the chamber is located downstream from the plasma source. Because the etching reaction occurs ex situ, there are no relevant changes occurring in the plasma characteristics, and the effectiveness of many existing methods decreases. We report the development of a calorimetric probe for chamber clean end-pointing. The probe has an all solid-state construction and is engineered to be immersed in the process effluent during end-pointing operation. When the probe is operated at constant temperature, the probe power is closely related to the energy flux carried by the effluent, which in turn correlates with chamber conditioning. We examine probe response to NF3 plasma and etching of silicon specimens in a laboratory setting, and demonstrate successful end-pointing for both in situ and remote chamber clean on production tools. The probe results compare favorably with other coinstalled end-pointing solutions.
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81.65.Cf Surface cleaning, etching, patterning
back to top Nanometer Structures

Synthesis and purification of single-walled carbon nanotubes by methane decomposition over iron-supported catalysts

Jong-Sik Kim, Gwan-Ha Kim, and Chang-Il Kim

J. Vac. Sci. Technol. A 24, 1314 (2006); http://dx.doi.org/10.1116/1.2210943 (4 pages) | Cited 1 time

Online Publication Date: 22 June 2006

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This article describes the synthesis and the purification of carbon nanotubes. Large quantities of single-walled carbon nanotubes (SWNTs) with few defects and very small amount of amorphous carbon coating have been synthesized by catalytic decomposition of methane over well-dispersed iron particles supported on MgO at the temperature range from 800 to 1000 °C. It was found that the quality of carbon nanotubes was slightly increased as increasing growth temperature while the yield was decreased to some degree. It was also found that the as-grown SWNTs can be separated easily from the support by a simple acidic treatment rather than thermal oxidation to obtain a product with high yields of SWNTs. Above 94 wt % high purity SWNTs were obtained by combining two-step processes of thermal oxidation in air and acid treatment without multistep filtration. The as-grown and purified SWNTs were also characterized by field emission scanning electron microscopy, x-ray diffraction, and Raman spectroscopy.
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81.07.De Nanotubes
81.20.Ym Purification
61.46.Fg Nanotubes
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.16.Pr Micro- and nano-oxidation

Growth of carbon nanotube bundle arrays on silicon surfaces

Michael J. Bronikowski, Harish M. Manohara, and Brian D. Hunt

J. Vac. Sci. Technol. A 24, 1318 (2006); http://dx.doi.org/10.1116/1.2172943 (5 pages) | Cited 5 times

Online Publication Date: 22 June 2006

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The growth on silicon substrates of arrayed bundles of multiwalled carbon nanotubes (CNTs) by metal catalyzed chemical vapor deposition of carbon from ethylene has been characterized and optimized. We find that, while CNTs can grow on bare Si substrates, the growth is substantially more reproducible if a thin ( ∼ 3 nm) barrier layer of aluminum oxide is used between the Si surface and iron catalyst. Optimum Fe thickness and growth temperature are 3.0 nm and 650 °C, respectively. We find that the CNT length increases linearly with time at a rate of 3–4 μm/min for up to 2 h of CNT growth, after which the growth ceases. The length of the resulting CNT can thus be controlled up to a maximum length of ∼ 500 μm. Such control over CNT bundle length will be crucial in the incorporation of these bundle arrays into high-intensity electron field emission devices.
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81.07.De Nanotubes
81.05.U- Carbon/carbon-based materials
81.16.Hc Catalytic methods
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.46.Fg Nanotubes

Temperature-induced control of aspect ratio of gold nanorods

Hyung Ju Park, Chil Seong Ah, Wan-Joong Kim, Insung S. Choi, Kwang-Pil Lee, and Wan Soo Yun

J. Vac. Sci. Technol. A 24, 1323 (2006); http://dx.doi.org/10.1116/1.2198864 (4 pages) | Cited 9 times

Online Publication Date: 22 June 2006

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Aspect ratio of gold nanorods can be controlled by simply adjusting the reaction temperature in the seed-mediated synthesis of the nanorods. The gold nanorods were synthesized by the injection of gold nanoparticle seeds of around 4 nm in diameter into a reaction mixture containing hydrogen tetrachloroaurate, hexadecyltrimethylammonium bromide, and ascorbic acid. Average aspect ratio of the resulting nanorod increases from 1 to about 40 with decreasing the reaction temperature from 315 to 276 K, which can be attributed to the temperature-induced change in the shape of the micellar templates. For further understanding of the growth mechanism, silver nanoparticles were also used as seeds in the preparation of the gold nanorod.
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81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials

Controlled gold nanoparticle assembly on DNA molecule as template for nanowire formation

Hyung Jin Kim, Yonghan Roh, and Byungyou Hong

J. Vac. Sci. Technol. A 24, 1327 (2006); http://dx.doi.org/10.1116/1.2191859 (5 pages) | Cited 4 times

Online Publication Date: 22 June 2006

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A reducer was used to construct Au nanowires (AuNWs) by the conjugation of 2-aminoethanthiol-capped gold nanoparticles (AET-AuNPs) and the immobilized DNA molecules on 3-aminopropyltriethoxysilane-coated Si wafer. The AuNPs coated with AET monolayer seem to be electrostatically assembled along DNA molecules by careful control of the relative molar quantities of AuNPs and AET. A variety of AuNP sizes (2, 5, and 10 nm) was used and also the ratio of AET to AuNP solution was varied to control the interparticle spacing and finally to form the nanowire based on DNA template. The formation of long-range AuNWs and the interparticle spacing were observed with atomic force microscopy.
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81.16.Dn Self-assembly
81.07.Bc Nanocrystalline materials

Observation of strong red photoluminescence with broadband in indium oxynitride nanoparticles

T. S. Ko, C. P. Chu, H. G. Chen, T. C. Lu, H. C. Kuo, and S. C. Wang

J. Vac. Sci. Technol. A 24, 1332 (2006); http://dx.doi.org/10.1116/1.2198863 (4 pages) | Cited 4 times

Online Publication Date: 22 June 2006

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Indium oxynitride nanoparticles were synthesized on a silicon substrate in nitrogen atmosphere using the method involving thermal evaporation of pure indium in a two-zone reactor. Nanoscale compositional analysis by energy dispersion spectrum showed the existence of indium oxynitride compound. X-ray diffraction analysis further confirmed high crystallization and nitrogen atom existence within the nanoparticles. Scanning electron microscopy investigations showed shape transformation from amorphous sphere to well-shaped octahedron with an average nanoparticle size ranging from 50 nm to 1 μm when the growth temperature of the substrate was increased from 600 to 900 °C. Photoluminescence study was performed on the indium oxynitride nanoparticle samples grown at different temperatures. It was found that with increasing growth temperatures there was not only the formation of high quality indium oxynitride nanoparticles but also an increase in the intensities of emissions. These nanoparticles grown at 900 °C could emit a strong photoluminescence spectrum centered around 700 nm with a broad full width at half maximum of about 250 nm, spanning the whole red segment.
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78.55.Hx Other solid inorganic materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Synthesis of Au nanotubes with SiOx nanowires as sacrificial templates

M. Y. Lu, Y. C. Chang, and L. J. Chen

J. Vac. Sci. Technol. A 24, 1336 (2006); http://dx.doi.org/10.1116/1.2172942 (4 pages) | Cited 5 times

Online Publication Date: 22 June 2006

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Gold nanotubes with SiOx nanowires as sacrificial templates have been synthesized. SiOx nanowires were functionalized by 3-aminopropyl trimethoxysilane that generates a charged surface. The attachment of negatively charged Au nanoparticles was followed. The coverage of Au nanoparticles was initially less than 30%. Further coverage was achieved by the reduction of gold hydroxide to grow the continuous nanoshell on Au nanoparticles, which serve as nucleation sites. The final coverage of Au nanoshells on SiOx nanowires depends strongly on the relative amount of SiOx nanowires in gold hydroxide solution. Both transmission electron microscope and scanning electron microscope images revealed the formation of Au nanotubes with the removal of SiOx nanowires by etching in a dilute HF solution.
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81.07.Bc Nanocrystalline materials
81.05.Bx Metals, semimetals, and alloys
81.16.-c Methods of micro- and nanofabrication and processing
81.65.Cf Surface cleaning, etching, patterning

High-voltage parallel writing on iron nitride thin films

N. Farkas, J. D. Ehrman, E. A. Evans, R. D. Ramsier, and J. A. Dagata

J. Vac. Sci. Technol. A 24, 1340 (2006); http://dx.doi.org/10.1116/1.2167074 (4 pages)

Online Publication Date: 22 June 2006

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We report large area patterning of sputter-deposited FeN thin films by a high-voltage parallel writing technique that was recently developed to modify ZrN surfaces. Systematically patterned 15–100-nm-thick FeN films consisting of features with well-defined sizes and shapes are obtained by applying high dc voltages between a stamp and the samples. During the process the oxide dissolves, exposing the substrate beneath. This controlled breakdown eliminates the need for any postexposure etching. The single-step imprinting method presented here provides an emerging route to fabricate isolated FeN geometrical structures on silicon substrates for magnetic applications.
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81.65.-b Surface treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Cd Deposition by sputtering
64.75.-g Phase equilibria

Formation of large-area nanostructures on Si and Ge surfaces during low energy ion beam erosion

B. Ziberi, F. Frost, and B. Rauschenbach

J. Vac. Sci. Technol. A 24, 1344 (2006); http://dx.doi.org/10.1116/1.2188415 (5 pages) | Cited 14 times

Online Publication Date: 22 June 2006

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In this contribution results on self-organized patterns formed during low energy Xe+ ion beam erosion on Si and Ge surfaces are presented. It was found that the evolution of surface patterns depends on ion incidence angle, erosion time, and ion energy. In the case without sample rotation ripple patterns form on the Si and Ge surfaces with a wavelength λ<100 nm, for ion energies Eion ⩽ 2000 eV at near normal ion incidence (αion ∼ 5°) and at room temperature. The experimental results of a decreasing ripple wavelength with ion incidence angle on Si coincide with the Bradley-Harper [J. Vac. Sci. Technol. A 6, 2390 (1988). ] theory of ripple formation. While the independency of λ from the ion flux suggests that thermally activated surface diffusion can be ruled out as the dominant relaxation mechanism. Experiments reveal that the wavelength of ripples increases with ion energy. With sample rotation at 75° ion incidence angle dot patterns form on the surface with a mean size λ<50 nm.
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81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
61.80.Jh Ion radiation effects
61.46.-w Structure of nanoscale materials
68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)

Quantum-dot nanodevices with carbon nanotubes

K. Ishibashi, S. Moriyama, D. Tsuya, T. Fuse, and M. Suzuki

J. Vac. Sci. Technol. A 24, 1349 (2006); http://dx.doi.org/10.1116/1.2201054 (7 pages) | Cited 14 times

Online Publication Date: 22 June 2006

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We review our recent work on quantum-dot devices with carbon nanotubes. We conclude that the single-wall carbon nanotube quantum dot is an artificial atom with two- or four-electron shell structures. Zeeman splitting of single particle levels was observed, which is advantageous for the spin based quantum computing device (spin qubit) because the single spin is generated by putting one electron in the shell. Single-electron devices such as single-electron inverter and single-electron exclusive-OR gates have been fabricated, and their performance has been demonstrated at liquid-helium temperature. Despite the expected room-temperature operation from the single-electron charging energy, the operation temperature of our devices was limited to ∼ 10 K because of the low height of the tunnel barrier.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.35.Kt Nanotube devices
01.30.Rr Surveys and tutorial papers; resource letters
03.67.Lx Quantum computation architectures and implementations
85.35.Gv Single electron devices
84.30.Sk Pulse and digital circuits
back to top Nanometer-Scale Science and Technology II

Optical activation of implanted impurities in ZnS nanowires

D. Stichtenoth, D. Schwen, S. Müller, C. Borchers, and C. Ronning

J. Vac. Sci. Technol. A 24, 1356 (2006); http://dx.doi.org/10.1116/1.2167078 (4 pages) | Cited 4 times

Online Publication Date: 22 June 2006

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Nanostructures of zinc sulfide (ZnS), a II-VI compound semiconductor with a direct band gap of 3.66 eV in the cubic phase and 3.74 eV in the wurtzite phase, show interesting optical properties, making it a promising candidate for optoelectronic devices. Single-crystalline nanobelts and nanowires were synthesized in a computer-controlled process according to the vapor-liquid-solid-mechanism. We investigated the morphology, structure, and composition by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The optical properties were studied by low-temperature photoluminescence (PL) and cathodoluminescence. The synthesized ZnS nanowires were implanted with nitrogen and boron as potential donor and acceptor, respectively. The implanted nanowires were investigated directly after ion implantation and showed a high quantity of defects resulting in nonluminescent material. Annealing procedures recovered the crystal structure and the luminescence, and we found emerging and varying PL lines indicating the activation of the implanted impurities.
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78.55.Et II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
68.65.La Quantum wires (patterned in quantum wells)
61.72.up Other materials
back to top Plasma Science and Technology

Some aspects of dissipation mechanisms in chlorine containing capacitively coupled discharges

Gerhard Franz

J. Vac. Sci. Technol. A 24, 1360 (2006); http://dx.doi.org/10.1116/1.2198861 (6 pages)

Online Publication Date: 22 June 2006

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The temperature of gaseous neutrals in capacitively coupled discharges of chlorine, argon, and hydrogen has been measured using optical emission spectroscopy. This has been accomplished by adding small amounts of nitrogen to the ambient. The temperature can then be obtained by fitting the unresolved second rotational positive band of nitrogen. It has been found that the gaseous temperature in argon saturates for higher pressures logarithmically, whereas in chlorine, a linear behavior is observed up to the highest pressures and power inputs. Highest temperatures in chlorine have been found to be about 1100 °C, whereas in hydrogen, temperatures higher than 500 °C are rarely observed. Likewise, the effective collision frequency in chlorine increases significantly in the medium pressure range indicating a change in excitation/dissipation from the regime of stochastic heating to Ohmic heating, whereas the discharge in the inert gas still remains in the regime of stochastic heating. The experimental data for the collision frequency of the electrons with neutrals can be perfectly modeled for chlorine with these reduced gaseous densities.
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52.80.-s Electric discharges
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.50.Nr Plasma heating by DC fields; ohmic heating, arcs
52.25.-b Plasma properties

Particle-in-cell simulations of planar and cylindrical Langmuir probes: Floating potential and ion saturation current

Felipe Iza and Jae Koo Lee

J. Vac. Sci. Technol. A 24, 1366 (2006); http://dx.doi.org/10.1116/1.2187991 (7 pages) | Cited 8 times

Online Publication Date: 22 June 2006

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Particle-in-cell and hybrid electron-Boltzmann simulations of planar and cylindrical Langmuir probes are compared with various probe theories. Floating potentials for planar and cylindrical probes are calculated and significant deviations from the typical approximation used for argon discharges of ∼ 5Te are shown. The interpretation of simulated ion saturation currents by the orbital motion limited and the Laframboise theories result in an overestimation of the ion density. On the other hand, the cold-ion theory underestimates the ion density. These deviations are related to the overestimation and underestimation, respectively, of the ion orbital motion around cylindrical probes. The best agreement is obtained when the probe theory suggested by Tichy et al. is used. This theory incorporates ion orbital motion as in the Laframboise theory, collisional orbital motion destruction as suggested by Zakrzewski and Kopiczynski, and ion scattering as given by Chouet al.
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52.70.Ds Electric and magnetic measurements
52.65.Rr Particle-in-cell method
52.25.Fi Transport properties
52.80.-s Electric discharges
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Dry etching of TaN/HfO2 gate-stack structure in BCl3/Ar/O2 inductively coupled plasmas

M. H. Shin, M. S. Park, N.-E. Lee, Jiyoung Kim, Chung Ywong Kim, and Jinho Ahn

J. Vac. Sci. Technol. A 24, 1373 (2006); http://dx.doi.org/10.1116/1.2210944 (7 pages) | Cited 15 times

Online Publication Date: 22 June 2006

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In this work, etching characteristics of TaN(200 nm)/HfO2(80 nm) gate-stack structures on Si substrate were investigated by varying the process parameters such as BCl3/(BCl3+Ar+O2) gas mixing ratio (Q), top-electrode power, dc self-bias voltage (Vdc), and overetch time in an inductively coupled plasma etcher. To understand the role of the etch gas chemistry, we measure the relative changes in the optical emission intensity of ions and radicals in the plasma as well as in the chemical binding states of the etched TaN surfaces. We used optical emission spectroscopy and x-ray photoelectron spectroscopy respectively. The results showed that BCl3/Ar/O2 plasma is more effective in etching the oxidized TaN than Cl2/Ar/O2 or HBr/Ar/O2 plasma. It is believed that the B radical species removes the oxygen atoms on the oxidized TaN surface more effectively by forming volatile boron-oxygen-chlorine compounds, such as trichloroboroxin (BOCl)3), boron oxychloride (BOCl), and boron dioxide. The measurement data also indicated that high etch selectivities of the TaN to the HfO2 layer could be obtained at the low Vdc, high top-electrode power, and shorter overetch time.
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81.07.Bc Nanocrystalline materials
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
79.60.Bm Clean metal, semiconductor, and insulator surfaces
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Effects of N2 addition on chemical dry etching of silicon oxide layers in F2/N2/Ar remote plasmas

J. Y. Hwang, D. J. Kim, N.-E. Lee, Y. C. Jang, and G. H. Bae

J. Vac. Sci. Technol. A 24, 1380 (2006); http://dx.doi.org/10.1116/1.2206190 (6 pages) | Cited 5 times

Online Publication Date: 22 June 2006

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In this study, chemical dry etching characteristics of silicon oxide layers were investigated in the F2/N2/Ar remote plasmas. A toroidal-type remote plasma source was used for the generation of remote plasmas. The effects of additive N2 gas on the etch rates of various silicon oxide layers deposited using different deposition techniques and precursors were investigated by varying the various process parameters, such as the F2 flow rate, the additive N2 flow rate, and the substrate temperature. The etch rates of the various silicon oxide layers at room temperature were initially increased and then decreased with the N2 flow increased, which indicates an existence of the maximum etch rates. Increase in the oxide etch rates under the decreased optical emission intensity of the F radicals with the N2 flow increased implies that the chemical etching reaction is in the chemical reaction-limited regime, where the etch rate is governed by the surface chemical reaction rather than the F radical density. The etch rates of the silicon oxide layers were also significantly increased with the substrate temperature increased. In the present experiments, the F2 gas flow, the additive N2 flow rate, and the substrate temperature were found to be the critical parameters in determining the etch rate of the silicon oxide layers.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
78.55.Hx Other solid inorganic materials

Effect of different frequency combination on ArF photoresist deformation and silicon dioxide etching in the dual frequency superimposed capacitively coupled plasmas

C. H. Lee, D. H. Kim, N.-E. Lee, and G. C. Kwon

J. Vac. Sci. Technol. A 24, 1386 (2006); http://dx.doi.org/10.1116/1.2201059 (9 pages) | Cited 8 times

Online Publication Date: 22 June 2006

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This study investigated the deformation of ArF photoresist (PR) and the etch characteristics of ArF PR and SiO2 layers in a dual frequency superimposed capacitively coupled plasma (DFS-CCP) etcher with multiple frequency sources under different frequency combinations in C4F8/CH2F2/O2/Ar capacitively coupled plasma. In the DFS-CCP etcher, the high-frequency (fHF) power (13.56, 27, and 60 MHz) was varied to control the plasma density while a fixed low frequency (fLF) of 2 MHz was used to control the ion bombardment energy to the wafer. The morphology of the blanket ArF PR surfaces and line patterns of the ArF PR after etching showed a significant increase in the level of surface roughening and deformation with increasing HF source frequency (fHF) from 13.56 to 60 MHz under the same Vdc and gas flow conditions. This was attributed to the increased F radical flux and possibly ion flux on the surface. The Vdc also played an important role in increasing the surface roughness and ArF PR deformation, which was presumably due to the increased ion flux and ion-bombardment energy, respectively. The etch rates of the ArF PR and silicon oxide layers increased significantly with increasing ∣Vdc∣ and fHF possibly due to the increased ion energy and ion/radical flux density, respectively. The etch selectivity of the SiO2 layer to the ArF PR was enhanced most significantly by the increase in CH2F2 flow rate due to the formation of a thicker and C-rich CFx polymer on the oxide and PR surfaces.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
85.40.Hp Lithography, masks and pattern transfer

Surface etching mechanism of Bi4−xLaxTi3O12 thin films using quadrupole mass spectroscopy

Jong-Gyu Kim, Gwan-Ha Kim, and Chang-Il Kim

J. Vac. Sci. Technol. A 24, 1395 (2006); http://dx.doi.org/10.1116/1.2187985 (4 pages) | Cited 1 time

Online Publication Date: 22 June 2006

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The etching mechanism of (Bi4−xLax)Ti3O12 (BLT) thin films in Ar/Cl2 inductively coupled plasma (ICP) was investigated as a function of gas mixing ratios, process pressure, and ICP powers at fixed other conditions. Etch rates were measured by using an α-step surface profiler. The maximum etch rate of BLT thin films was 117 nm at 0.8 Ar/(Ar+Cl2) gas mixing ratios with following conditions: process pressure of 15 mTorr, gas flow rate of 20 sccm, ICP power of 700 W, and dc bias of −150 V. The etch rate was increased as decreasing the process pressure. For a detailed investigation of etching mechanisms of BLT thin films, the ion energy distributions of each positive species were measured using quadrupole mass spectrometer and analyzed those data. Also the electron energy distribution was measured as a function of Ar/Cl2 gas mixing ratios.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.65.Cf Surface cleaning, etching, patterning
77.80.-e Ferroelectricity and antiferroelectricity

Etching characteristics of LaNiO3 thin films in BCl3/Ar gas chemistry

Gwan-Ha Kim and Chang-Il Kim

J. Vac. Sci. Technol. A 24, 1399 (2006); http://dx.doi.org/10.1116/1.2201543 (5 pages) | Cited 1 time

Online Publication Date: 22 June 2006

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LaNiO3 (LNO) electrode was intensively studied as electrodes because LNO has a pseudocubic perovskite crystal structure with a lattice parameter of 3.84 Å. But the etching process of LNO thin films must be developed in order to realize highly integrated ferroelectric random access memories. In this work, we investigated etching characteristics and mechanisms of LNO thin films using inductively coupled BCl3/Ar plasma (ICP) system. The maximum etch rate of LNO thin films was 41.1 nm/min at a BCl3(20)/Ar(80) gas mixing ratio. The positive ions and the ion energy distributions were measured with a quadrupole mass spectrometer (QMS). As rf power and dc bias voltage increased and working pressure decreased, the ion energy and etch rates of LNO thin films were increased. A chemically assisted physical etch of LNO was experimentally confirmed by ICP system and QMS measurements.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Wafer level microarcing model in 90 nm chemical-vapor deposition low-k via etch on 300 mm silicon-on-insulator substrate

Hai Cong, Chun Hui Low, Yelehanka Ramachandramurthy Pradeep, Xin Zhang, Perera Chandima, Wu Ping Liu, Juan Boon Tan, and Liang Choo Hsia

J. Vac. Sci. Technol. A 24, 1404 (2006); http://dx.doi.org/10.1116/1.2187990 (6 pages)

Online Publication Date: 22 June 2006

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In SiOCH (C-doped SiO2) via etch application, high polymer deposition chemistry is needed for better selectivity to both photoresist and underlying barrier materials. To prevent etch stop, high ion energy plasma is required to achieve a good process window. C4F6/CH3F, etc., was used as via main etch chemistry for better selectivity and striation performance. However, wafer level microarcing (WLMA) was observed at the wafer edge around the guard ring. This WLMA phenomenon is different from that of the magnetically enhanced reactive ion etching or capacitively coupled plasma low-gap reactor. By process optimization, we managed to develop a process that is production-ramp worthy. We have also compared the rf parameters during via etch process on both silicon-on-insulator and bulk Si substrates, which shows no significant difference. The electrical and defect scan results suggest that it is free from WLMA.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Bn Etching and cleaning

Cold atmospheric plasma in nitrogen and air generated by the hybrid plasma source

H. Baránková, L. Bárdoš, and D. Söderström

J. Vac. Sci. Technol. A 24, 1410 (2006); http://dx.doi.org/10.1116/1.2174017 (4 pages)

Online Publication Date: 22 June 2006

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Generation of long plumes of cold atmospheric plasma in nitrogen and air has been successfully performed by the hybrid hollow electrode activated discharge (H-HEAD) source. The source with a simple cylindrical electrode terminated by a gas nozzle combines the microwave antenna plasma with the hollow cathode plasma generated inside the gas nozzle by pulsed dc power. The H-HEAD source is capable of generating up to 10 cm long plumes in air at microwave powers below 500 W and at air flow rates as low as 100 sccm (standard cubic centimeter per minute). The corresponding flow rates in the nitrogen plasma are even less than 80 sccm. The discharges in air and nitrogen have similar shapes and are comparable with the corresponding plasma columns in argon. A comparison of the optical emission spectra of the plasma in nitrogen and air is presented. The temperatures generated on steel substrates by interaction with nitrogen and air plasma columns at different microwaves and dc powers are compared with the corresponding effects in argon plasma.
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52.50.Dg Plasma sources
52.80.Hc Glow; corona
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.40.Hf Plasma-material interactions; boundary layer effects

Damage-free metal-oxide-semiconductor gate electrode patterning on thin HfSiON film using neutral beam etching

Shuichi Noda, Takuya Ozaki, and Seiji Samukawa

J. Vac. Sci. Technol. A 24, 1414 (2006); http://dx.doi.org/10.1116/1.2189264 (7 pages) | Cited 4 times

Online Publication Date: 22 June 2006

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The charging damage of metal-oxide-semiconductor (MOS) capacitors and the degradation of HfSiON dielectric films during gate electrode etching were compared with neutral beam etching and conventional plasma etching. Furthermore, residual flux of charged particles (positive/negative ions and electrons) in the neutral beam was analyzed and the relationship between the residual charge flux and the charging damage induced in SiO2 and/or HfSiON gate dielectrics was investigated. Although the residual charge flux and its composition varied depending on the neutral beam acceleration method (dc or rf biasing), the amounts were noticeably lower than that with the plasma etching system. The gate leakage currents of the MOS capacitors etched using the neutral beam were sufficiently lower than those in the plasma etching, which was consistent with the charge flux during the gate electrode etching. On the neutral beam irradiated surface of the HfSiON film, there were no changes in the x-ray photoelectron spectrometry spectra, while large decreases in Hf composition were observed on the plasma-irradiated surface.
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84.32.Tt Capacitors
85.30.Tv Field effect devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Characteristics of large-diameter plasma using a radial-line slot antenna

C. Tian, T. Nozawa, K. Ishibasi, H. Kameyama, and T. Morimoto

J. Vac. Sci. Technol. A 24, 1421 (2006); http://dx.doi.org/10.1116/1.2167983 (4 pages) | Cited 6 times

Online Publication Date: 22 June 2006

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Characteristics of the surface-wave plasma generated by a radial-line slot antenna (RLSA) have been studied by both direct plasma probe measurements and numerical simulations. Some unique characteristics have been found, including excellent critical radial plasma uniformity, low electron temperature under various pressure conditions, the main plasma generation area of RLSA being limited in the plasma surface, and few high-energy electrons existing in the wafer region. Numerical simulations are implemented to reveal the more essential difference in plasma generation between the RLSA and the other plasma sources, where the superiority of RLSA plasma has been confirmed. The features of high plasma uniformity and low electron temperature lead to free plasma damage in our associated etching process.
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52.50.Dg Plasma sources
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.70.Ds Electric and magnetic measurements
52.65.-y Plasma simulation
52.25.-b Plasma properties
52.77.Bn Etching and cleaning

Application of the shaped electrode technique to a large area rectangular capacitively coupled plasma reactor to suppress standing wave nonuniformity

L. Sansonnens, H. Schmidt, A. A. Howling, Ch. Hollenstein, Ch. Ellert, and A. Buechel

J. Vac. Sci. Technol. A 24, 1425 (2006); http://dx.doi.org/10.1116/1.2189266 (6 pages) | Cited 6 times

Online Publication Date: 22 June 2006

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The electromagnetic standing wave effect can become the main source of nonuniformity limiting the use of very high frequency in large area reactors exceeding 1 m2 required for industrial applications. Recently, it has been proposed and shown experimentally in a cylindrical reactor that a shaped electrode in place of the conventional flat electrode can be used in order to suppress the electromagnetic standing wave nonuniformity. In this study, we show experimental measurements demonstrating that the shaped electrode technique can also be applied in large area rectangular reactors. We also present results of electromagnetic screening by a conducting substrate which has important consequences for industrial application of the shaped electrode technique.
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52.50.Dg Plasma sources
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.40.Hf Plasma-material interactions; boundary layer effects
back to top Plasma Science and Technology I

Mechanism for difference in etched depth between isolated and dense via holes of SiOCH film

Yoshinori Momonoi, Kazumasa Yonekura, and Masaru Izawa

J. Vac. Sci. Technol. A 24, 1431 (2006); http://dx.doi.org/10.1116/1.2206194 (10 pages)

Online Publication Date: 23 June 2006

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We investigated the mechanism for differences in etched depth between isolated and dense via holes of a damascene structure using a SiOCH film (k = 2.8). In Ar/CHF3/N2 and Ar/C4F6/N2 plasmas, the depth of an isolated (4.8 μm pitch) hole was more than 40% varied from a dense (200 nm pitch) hole. The difference between dense and isolated holes was found to become larger with increasing air exposure time of the wafer. The amount of H2O in the SiOCH film also increased with increasing air exposure time based on thermal desorption spectroscopy (TDS) analysis. Therefore, we investigated the effects of H2O addition to the plasmas. The investigation revealed that the etched depths of dense holes became similar to those of isolated holes with H2O addition. Based on these results, we concluded that the mechanism for the difference between isolated and dense holes was as follows. When the capping layer on SiOCH is etched, the H2O contained in SiOCH desorbs in etched holes and affects etching reactions. The etching characteristics of isolated holes are significantly affected, since the amount of desorbed H2O in isolated holes is larger than that in dense holes.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
77.55.-g Dielectric thin films
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
68.43.Vx Thermal desorption
85.40.Ls Metallization, contacts, interconnects; device isolation
back to top Surface Engineering

Reactive magnetron sputtering deposition and columnar growth of nc‐TiC/a‐C:H nanocomposite coatings

D. Galvan, Y. T. Pei, and J. Th. M. De Hosson

J. Vac. Sci. Technol. A 24, 1441 (2006); http://dx.doi.org/10.1116/1.2188411 (7 pages) | Cited 3 times

Online Publication Date: 23 June 2006

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TiC/a‐C:H coatings were deposited using closed-field unbalanced reactive magnetron sputtering deposition from Ti targets. Different acetylene gas flow and substrate bias values were employed to vary the coatings’ compositions and microstructures. The application of an external negative substrate bias increased the deposition rate of the plasma-enhanced chemical vapor deposition process from the reactive atmosphere. The sputtering of carbonaceous species from the poisoned targets surface was a minor source of C flux to the substrates. The application of an external substrate bias during deposition yielded films with a featureless cross-sectional structure, but the dominant parameter controlling the columnar growth was the chemical composition of the films. An explanation of this effect was formulated based on the microstructures observed and the deposition technique employed.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
61.43.Er Other amorphous solids

Tribological behavior and thermal stability of TiC/a-C:H nanocomposite coatings

Y. T. Pei, D. Galvan, and J. Th. M. De Hosson

J. Vac. Sci. Technol. A 24, 1448 (2006); http://dx.doi.org/10.1116/1.2194927 (6 pages) | Cited 8 times

Online Publication Date: 23 June 2006

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Advanced TiC/a-C:H nanocomposite coatings have been produced via reactive deposition in a closed-field unbalanced magnetron sputtering system (Hauzer HTC-1200). These wear-resistant coatings are targeted for automotive applications where high load-bearing capacity and thermal stability, low friction, and wear resistance are the primary requirements. In this article the tribological behavior of the nanocomposite coatings is scrutinized by means of ball-on-disk tribotests at elevated temperature or after annealing in the temperature range of 150–400 °C. The thermal stability of the coatings in terms of critical temperatures, at which the degradation of wear resistance and friction of the coatings starts, is monitored with depth profiling of oxygen content using Auger spectroscopy in conjunction with detailed examinations of the mechanical properties of the annealed coatings. A striking result is that a coating thermally stable up to 350 °C may fail at much lower temperatures during elevated-temperature tribotests. The origin of failure is attributed to the interfacial delamination due to the discontinuity in mechanical properties between the coatings and substrates at elevated temperatures. It indicates a stringent requirement to optimize the interlayer of advanced tribological coatings developed for high temperature applications.
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62.25.-g Mechanical properties of nanoscale systems
68.35.Gy Mechanical properties; surface strains
81.40.Pq Friction, lubrication, and wear
81.40.Gh Other heat and thermomechanical treatments
62.20.Qp Friction, tribology, and hardness
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
back to top Surface Science

Hot electrons at metal-organic interface: Time-resolved two-photon photoemission study of phenol on Ag(111)

Sunmin Ryu, Jinyoung Chang, Hyuksang Kwon, and Seong Keun Kim

J. Vac. Sci. Technol. A 24, 1454 (2006); http://dx.doi.org/10.1116/1.2167076 (6 pages) | Cited 3 times

Online Publication Date: 23 June 2006

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We used time-resolved two-photon photoemission (2PPE) spectroscopy to investigate the excitation mechanism and dynamical behavior of the anionic molecular resonance (MR) state of phenol weakly interacting with Ag(111). The photoexcited MR state of phenol was found at 3.1 eV above the Fermi level at 1 ML (monolayer) coverage, and the binding energy of this state remained rather constant at 0.74±0.05 eV for all coverages. The polarization angle dependence of the 2PPE signal clearly showed that the MR state is populated by an indirect excitation process involving scattering of photoexcited hot electrons rather than direct electronic transition from a bulk band. The lifetime of the MR state was found to increase from 33 to 60 fs upon increasing the coverage from 1 to 9 ML, implying that the MR state becomes further decoupled from the bulk at a higher coverage. These results constitute the first time-resolved 2PPE study that clearly demonstrates the hot-electron-mediated mechanism operating for molecules that are potentially active photochemically but weakly interacting with a metal surface.
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72.30.+q High-frequency effects; plasma effects
72.20.Ht High-field and nonlinear effects
78.47.-p Spectroscopy of solid state dynamics
79.60.Jv Interfaces; heterostructures; nanostructures
73.20.At Surface states, band structure, electron density of states
71.20.Rv Polymers and organic compounds

Adsorption of sulfur dioxide on Zircaloy-4 at 300 K

N. Stojilovic, J. D. Ehrman, and R. D. Ramsier

J. Vac. Sci. Technol. A 24, 1460 (2006); http://dx.doi.org/10.1116/1.2180272 (4 pages)

Online Publication Date: 23 June 2006

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We investigate the interaction of sulfur dioxide (SO2) with Zircaloy-4 (Zry-4) surfaces after adsorption at 300 K. A shift in the Zr(MNN) feature toward lower energies of about 3 eV is observed following saturation exposures, indicating oxidation of Zr by dissociated oxygen. Temperature programed desorption experiments indicate irreversible adsorption. Relatively short Ar-ion sputtering removes sulfur from the near-surface region without significantly affecting the oxygen Auger signal. Annealing of the SO2/Zry-4 system results in dissolution of oxygen into the bulk, leaving sulfur in the near-surface region.
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68.43.Mn Adsorption kinetics
68.43.Vx Thermal desorption
81.65.Mq Oxidation
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
79.20.Fv Electron impact: Auger emission

Surface and bulk electronic structures of Heusler-type Fe2VAl

Hidetoshi Miyazaki, Kazuo Soda, Sinya Yagi, Masahiko Kato, Tsunehiro Takeuchi, Uichiro Mizutani, and Yoichi Nishino

J. Vac. Sci. Technol. A 24, 1464 (2006); http://dx.doi.org/10.1116/1.2191858 (4 pages) | Cited 3 times

Online Publication Date: 23 June 2006

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Surface and bulk electronic structures of Heusler-type (L21 type) Fe2VAl have been investigated by photoelectron spectroscopy, in particular, for the valence band and V 2p core level regions, in order to elucidate the changes in the valence band electronic structures for the surface and bulk regions. In the valence band spectrum, the intensity at the Fermi level EF is increased for the surface-sensitive low photon energy excitation in comparison to the bulk-sensitive high photon energy excitation. It is also found that the intensity around a binding energy of 0.4 eV is enhanced for large photoelectron takeoff angles for the bulk-sensitive photoelectron spectrum. The V 2p core level spectrum shows a surface-derived shoulder structure on the low binding energy side of the main feature, which suggests that the valence electron concentration around V may be large in the surface layers in comparison to the bulk. These facts suggest that a pseudogap is formed around EF in the bulk electronic structure, as predicted by band calculations, and that it is destroyed in the surface layers by the V 3d states as well as the Fe 3d states emerging in midpseudogap of the bulk electronic structure.
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71.20.Gj Other metals and alloys
73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Formation of nickel silicide and germanosilicide layers on Si(001), relaxed SiGe/Si(001), and strained Si/relaxed SiGe/Si(001) and effect of postthermal annealing

J. H. Ko, C. H. Jang, S. H. Kim, Y.-J. Song, and N. E. Lee

J. Vac. Sci. Technol. A 24, 1468 (2006); http://dx.doi.org/10.1116/1.2210942 (6 pages) | Cited 2 times

Online Publication Date: 23 June 2006

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This study compared the formation of nickel silicide or germanosilicide layers on various SiGe based heterostructures as well as the effects of the different annealing schemes (one-step versus two-step annealing) on the morphological, structural, and electrical properties. Uniform nickel silicide or germanosilicide layers were first formed by rapid thermal annealing of various heterostructures. The two-step annealing process of the samples first at 400 °C (TA1) and subsequently at between 600 and 800 °C (TA2) led to an increase in the sheet resistance, which was attributed to the formation of a high-resistivity NiSi2 phase, the agglomeration of the silicide or germanosilicide layers, and the formation of an amorphous interlayer between the silicide or germanosilicide layers. The lower sheet resistance of the silicide or germanosilicide layers formed on the relaxed-Si1−xGex (x = 0.15)/Si(001) substrates by two-step annealing compared with that of the samples formed on the strained Si/relaxed SiGe/Si(001) and Si(001) was attributed to the suppression of the high-resistivity NiSi2 phase as well as the superior thermal stability of the germanosilicide layer formed on the relaxed Si1−xGex (x = 0.15)/Si(001). The amorphous interlayers formed in the samples annealed using two-step procedure appeared to suppress interface roughening between the silicide or germanosilicide and the SiGe layer presumably due to the reduced Ni and Ge diffusion rate. Here, an amorphous interlayer was formed, which was attributed to the large negative heat of mixing in Ni–Si–Ge systems during the phase transformation and grain growth.
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68.55.A- Nucleation and growth
73.61.Ng Insulators
61.72.Cc Kinetics of defect formation and annealing
61.82.Ms Insulators
68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
64.75.-g Phase equilibria

Laser assisted and wet chemical etching of silicon nanostructures

Kurt W. Kolasinski, David Mills, and Mona Nahidi

J. Vac. Sci. Technol. A 24, 1474 (2006); http://dx.doi.org/10.1116/1.2188414 (6 pages) | Cited 3 times

Online Publication Date: 23 June 2006

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Etching of silicon can be accomplished in a number of ways: in aqueous solutions of fluoride or KOH, or by simultaneous exposure to a gas such as SF6 or HCl and high power laser irradiation. Here we review how laser assisted etching, chemically enhanced laser ablation, and stain etching can be used to create pillars, pores, porosified pillars, and macropores. Pillar dimensions can range from 10 μm tall with ∼ 200 nm tips to >100 μm high with 10 μm tips. Ordered arrays can be produced and sharpening can lead to aspect ratio approaching 104. Porous silicon with a visibly photoluminescent nanocrystalline structure can be made by etching in fluoride solutions. Acidic fluoride+oxidant solutions (stain etchants) allow us to form porous silicon on substrates of arbitrary topology. Moreover, these etchants can be used to control the photoluminescence spectrum of the resulting film, presumably through control of the size distribution of the nanocrystalline structures that are responsible for photoluminescence.
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81.05.Cy Elemental semiconductors
81.05.Rm Porous materials; granular materials
61.46.Hk Nanocrystals
81.65.Cf Surface cleaning, etching, patterning
61.43.Gt Powders, porous materials
79.20.Ds Laser-beam impact phenomena
back to top Surface Science I

Ostwald ripening of manganese silicide islands on Si(001)

M. R. Krause, A. Stollenwerk, M. Licurse, and V. P. LaBella

J. Vac. Sci. Technol. A 24, 1480 (2006); http://dx.doi.org/10.1116/1.2167070 (4 pages) | Cited 10 times

Online Publication Date: 23 June 2006

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The deposition of Mn onto Si(001) in the submonolayer regime has been studied with scanning tunneling microscopy to gain insight into the bonding and energetics of Mn with Si. The as-deposited Mn films at room temperature are unstructured. Upon annealing to 300–700 °C three-dimensional islands of Mn or MnxSiy form while between the islands the Si(001)-(2×1) reconstruction becomes visible. With increasing annealing time the density of islands per surface area decreases while the average height of the remaining islands increases. The large islands grow in size at the expense of the small ones, which can be understood in the context of Ostwald [Z. Phys. Chem. 34, 495 (1900) ] ripening theory. The average island height shows a time dependence of H ∼ t1/4, indicating that surface diffusion is the growth limiting process.
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68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.55.-a Thin film structure and morphology
back to top Surface Science II

Effect of self-assembled monolayer film order on nanofriction

Sharadha Sambasivan, Shuchen Hsieh, Daniel A. Fischer, and Stephen M. Hsu

J. Vac. Sci. Technol. A 24, 1484 (2006); http://dx.doi.org/10.1116/1.2204920 (5 pages) | Cited 9 times

Online Publication Date: 23 June 2006

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Self-assembled monolayers have increasingly been explored as potential protective films in devices against friction and adhesion. However, detailed characterization of the monolayer film structure is difficult. This article utilizes a combination of near edge x-ray absorption fine structure (NEXAFS) spectroscopy and Fourier transform infrared (FTIR) spectroscopy to determine the film structure in order to explain the observed nanofriction measurement results. A series of n-alkyltrichlorosilane self-assembled monolayer films with various chain lengths (C5–C30) was prepared on silicon (100) surfaces. Nanofriction measurements were conducted using an atomic force microscope. Results showed that the lowest friction was obtained with a C12 film with higher friction values observed for C5 and C30 films. To explain these observations, the x-ray absorption technique NEXAFS was used to quantitatively measure the surface molecular orientation (order) of these films. It was observed that C12, C16, and C18 films were highly ordered with a molecular orientation of the carbon backbone nearly perpendicular to the surface. C5 and C30 films were less oriented and C10 film showed partial orientation. FTIR spectra suggested that these films possessed different degrees of order. This combination of molecular orientation and order supports and confirms that nanofriction results were heavily influenced by the order and structure of these films.
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68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
78.70.Dm X-ray absorption spectra
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
78.30.-j Infrared and Raman spectra
back to top Thin Films

Irradiation effect of nitrogen ion beam on hydrogenated amorphous carbon films

Yoshihisa Watanabe, Satoru Katoh, and Nobuaki Kitazawa

J. Vac. Sci. Technol. A 24, 1489 (2006); http://dx.doi.org/10.1116/1.2204922 (5 pages)

Online Publication Date: 23 June 2006

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Hydrogenated amorphous carbon (a-C:H) thin films were deposited on silicon single crystal substrates from toluene vapor using rf plasma at room temperature. After deposition, the a-C:H films were irradiated with a nitrogen ion beam and effects of nitrogen ion beam irradiation on surface morphology and composition were studied. Nitrogen ion irradiation was performed using nitrogen ion beams of 0.2 and 1.5 keV for 10 min under the constant ion current density at room temperature. Surface morphology was observed by atomic force microscopy (AFM). Changes in composition and carbon-nitrogen bonding states were analyzed by x-ray photoelectron spectroscopy (XPS). Carbon structures were examined by Raman spectroscopy. AFM observations revealed that the film surface became smooth after nitrogen ion beam irradiation and a notable difference in surface roughness is hardly observed between 0.2 and 1.5 keV ion irradiation. XPS studies showed that nitrogen was implanted near the surface of the a-C:H films after nitrogen ion irradiation and combined with carbon, resulting in carbon nitride formation. Depth profiles obtained by XPS showed that nitrogen ions were implanted in the a-C:H films more deeply after 1.5 keV ion irradiation than 0.2 keV ion irradiation. The implanted nitrogen ion behavior inside the films has been clarified, which is useful to judge the effectiveness for the formation of carbon nitride layers. Carbon structures did not change remarkably after nitrogen ion irradiation except the surface region, where carbon nitride layers are formed.
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61.80.Jh Ion radiation effects
61.82.Ms Insulators
52.77.Dq Plasma-based ion implantation and deposition
81.15.Jj Ion and electron beam-assisted deposition; ion plating
61.43.Er Other amorphous solids
79.60.Ht Disordered structures

Fabrication of micropatterned mesoporous silica film on a flexible polymer substrate through pattern transfer and subsequent photocalcination

Atsushi Hozumi, Takashi Kizuki, Masahiko Inagaki, and Naoto Shirahata

J. Vac. Sci. Technol. A 24, 1494 (2006); http://dx.doi.org/10.1116/1.2187986 (6 pages) | Cited 2 times

Online Publication Date: 23 June 2006

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A microfabrication method for mesoporous silica (MPS) film on a flexible polymer substrate is proposed. The method consists of three processes. First, by using a spatially defined microtemplate consisting of dual self-assembled monolayers (SAMs) with alternating trifluorocarbon (CF3) and amino (NH2) groups, a mesostructured silica/surfactant composite (MSSC) film was site-selectively deposited on the CF3-terminated SAM regions through hydrophobic and van der Waals interactions between the surfactant molecules and the hydrophobic SAM surface. Next, in order to transfer these prefabricated MSSC micropatterns to a poly(ethyleneterephthalate) (PET) substrate, the sample was pressed firmly against the PET surface for 60 min at 90 °C under a pressure of 4 MPa. Due to the weak adhesion between the MSSC film and the CF3-terminated SAM surface, the deposited MSSC micropatterns readily peeled off the SAM surface and were transferred to the PET substrate while preserving both the morphology and the nanostructures of the micropatterns, as evidenced by atomic force microscopy (AFM), scanning electron microscopy, energy dispersion x-ray spectroscopy, and x-ray diffractometry (XRD). Finally, to remove the surfactant molecules and obtain well-defined nanopores, a photochemical approach, known as “photocalcination,” using UV light of 185 and 254 nm wavelengths was employed. Fourier transform infrared spectroscopy XRD, and AFM confirmed that the surfactant molecules were completely eliminated from the MSSC micropatterns without distorting either their finely patterned microstructures or their well-ordered periodic nanostructures. Through this technique, well-shaped 5 μm wide MPS micropatterns were fabricated on the flexible PET substrates. These embedded MPS micropatterns adhered tightly to the PET substrates and no peeling was observed in a Scotch® tape peeling test.
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81.05.Rm Porous materials; granular materials
61.43.Gt Powders, porous materials
81.40.Gh Other heat and thermomechanical treatments
78.30.-j Infrared and Raman spectra
82.50.-m Photochemistry
68.55.A- Nucleation and growth

X-ray photoemission spectroscopy and Fourier transform infrared characterizations of C60 states in C60 doped conducting polymers

H. Kato, S. Takemura, K. Iwasaki, Y. Watanabe, N. Nanba, T. Hiramatsu, O. Nishikawa, and M. Taniguchi

J. Vac. Sci. Technol. A 24, 1500 (2006); http://dx.doi.org/10.1116/1.2210945 (5 pages) | Cited 1 time

Online Publication Date: 23 June 2006

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Conducting polymer polythiophene (PT) film incorporated with C60 was prepared by electrochemical doping and diffusing injection methods. Charge transfer and the molecule-chain interaction were investigated by x-ray photoemission spectroscopy (XPS). Vibration states of the doped C60 and polymer backbone in the hybrid films were also investigated by fourier transform infrared (FTIR) reflaction absorption spectroscopy and FTIR transmission. The XPS spectral profile of the electrochemically doped sample was different from that of the casting sample, which reflects the different dopant-chain interactions in polymer films. The higher binding peaks appearing in the C 1s spectra correspond to C60 and its charged states doped in the polymer, which are closely connected with threefold t1u lowest unoccupied molecular orbital and fivefold hu higest occupied molecular orbital. FTIR transmission measurements clarified that C60 molecules were doped in the polymer film using both electrochemical doping and casting, as characteristic peaks due to the vibration modes of C60 were observed. The C60 peaks observed in the spectra for electrochemical doping and casting samples differed, which reflects the different doping states of C60. The results of XPS and FTIR suggest the conductive state of PT may be controlled by changing the ionic states of C60.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.35.+c Brillouin and Rayleigh scattering; other light scattering
61.72.up Other materials
61.72.S- Impurities in crystals
66.30.J- Diffusion of impurities
71.55.Ht Other nonmetals

X-ray photoemission spectroscopy characterization of electrochemical growth of conducting polymer on oxidized Si surface

H. Kato, S. Takemura, N. Takakuwa, K. Ninomiya, T. Watanabe, Y. Watanabe, N. Nanba, and T. Hiramatsu

J. Vac. Sci. Technol. A 24, 1505 (2006); http://dx.doi.org/10.1116/1.2208995 (4 pages) | Cited 2 times

Online Publication Date: 23 June 2006

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Electrochemical growth of conducting polymer polythiophene (PT) film on an oxidized Si(100) wafer was closely investigated by x-ray photoemission spectroscopy (XPS). The initial stage of polymer growth was investigated by analyzing the core-level energies and spectral profiles of the atomic components. The oxidized Si surface was also closely characterized by XPS using curve fitting of Si 2p and Si 2s core-level spectra to determine precisely covalent states of Si at surface layers. The XPS spectra of Si 2p and Si 2s of the oxidized substrate surface was composed of five peaks which correspond with Si valence values, such as Si, Si+, Si2+, Si3+, and SiO2. The core-level energy positions of those different states were determined by XPS. The Si wafer was prepared through several stages of a wet cleansing process. Scanning tunneling microscopy image of nanoscale ordered native oxide surface was obtained. The native SiO2 layers remained and was probed by Fourier transform infrared spectroscopy reflection absorption spectroscopy and XPS measurements. Electrochemical PT growth at the initial stage was implemented on the oxidized SiO2 surface on Si(100) substrate. The obtained XPS spectra of Si 2p showed that the Si2+ and Si3+ peaks associated with polymer deposition shrank. This experimental result reflects the interface linkage between the organic polymer chain and the Si oxidized layer such as S–O–Si. The bonds between organic and inorganic species such as S–Si are also suggested by analysis of the S 2p3/2,1/2 core-level profile.
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82.45.Qr Electrodeposition and electrodissolution
81.15.Pq Electrodeposition, electroplating
68.55.A- Nucleation and growth
79.60.Fr Polymers; organic compounds
78.66.Qn Polymers; organic compounds
78.30.Jw Organic compounds, polymers

Fe(001) thin films for x-ray diffraction and terahertz emission studies

C. A. Meserole, G. L. Fisher, D. J. Hilton, Q. X. Jia, R. D. Averitt, D. J. Funk, and A. J. Taylor

J. Vac. Sci. Technol. A 24, 1509 (2006); http://dx.doi.org/10.1116/1.2187988 (5 pages)

Online Publication Date: 23 June 2006

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Our interests in growing thin films of iron (Fe) are twofold. First, Fe(001) films are ideal targets for an ultrafast x-ray diffraction instrument designed to understand complex behavior, such as melting or solid-solid phase transitions, in shock-loaded materials. Second, we have discovered that thin iron films generate picosecond, broadband terahertz frequencies after intense femtosecond pulse excitation by a Ti:sapphire laser. Excluding film thickness, the criteria for samples used in both experiments are identical due to the similarities of the experiments. Iron films are grown in ultrahigh vacuum (UHV) conditions on (001)-oriented magnesium oxide (MgO) substrates. We have investigated the effects of substrate preparation on the film quality and have found that films grown in UHV on UV/ozone-cleaned and annealed MgO(001) have a better crystal quality than films grown on as-received MgO(001). However, both substrate preparation methods produce continuous, (001)-oriented thin films of iron.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.40.Gh Other heat and thermomechanical treatments
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Effect of Cl2/Ar gas mixing ratio on (Pb,Sr)TiO3 thin film etching behavior in inductively coupled plasma

Gwan-Ha Kim and Chang-Il Kim

J. Vac. Sci. Technol. A 24, 1514 (2006); http://dx.doi.org/10.1116/1.2187989 (4 pages)

Online Publication Date: 23 June 2006

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The development of anisotropic etching process for (Pb,Sr)TiO3 (PST) thin films is an important task to provide a small feature size and an accurate pattern transfer. Etching characteristics of PST thin films were investigated using inductively coupled plasma etching system as functions of Cl2/Ar gas mixing ratio. The PST etch rate increased with the increase of chlorine radical and ion energy intensity. It was found that the increasing of Ar content in gas mixture lead to sufficient increasing of etch rate. The maximum etch rate of PST film is 56.2 nm/min at Cl2/(Cl2+Ar) of 0.2. It was proposed that the sputter etching is a dominant etching mechanism while the contribution of chemical reaction is relatively low due to low volatility of etching products.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

Thermochromic La1−xSrxMnO3 (x = 0.1, 0.175, and 0.3) smart coatings grown by reactive pulsed laser deposition

M. Soltani, M. Chaker, X. X. Jiang, D. Nikanpour, and J. Margot

J. Vac. Sci. Technol. A 24, 1518 (2006); http://dx.doi.org/10.1116/1.2204923 (6 pages) | Cited 8 times

Online Publication Date: 23 June 2006

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Thermochromic La1−xSrxMnO3 (x = 0.1, 0.175, and 0.3) (LSMO) smart coatings were synthesized on (100) silicon and (0001) sapphire substrates by means of reactive pulsed laser deposition process at relatively low substrate temperature (500 °C) and without postannealing. X-ray diffraction patterns indicated that all deposited LSMO films have polycrystalline structures. The energy dispersive x-ray spectroscopy analysis indicated approximately the same La/Sr ratio in the formed LSMO coatings as in their corresponding targets. While, the x-ray photoelectron spectroscopy analysis of the LSMO/sapphire revealed that the strontium segregate at the film surface. The thermochromism of LSMO coatings was investigated by measuring their infrared reflectance as a function of temperature (up to 160 °C). It was observed that the reflectance decreased as the temperature increased. Reflectance switching of about 25% was achieved in La0.7Sr0.3MnO3/Si at a wavelength of 5 μm. The sheet electrical resistivity as a function of temperature (up to 130 °C) of LSMO/sapphire was investigated by means of the standard four-point probe technique. The resistivity decreased with increasing the temperature and no metallic-to-insulator transition was observed. However, it is found that the resistivity is very sensitive to the concentration level of Sr dopant: the resistivity decreased as the concentration of Sr increased. In addition, at room temperature, a higher temperature coefficient of resistance of −2.30%/°C was achieved in La0.9Sr0.1MnO3 thin films. Finally, these LSMO smart coatings are promising materials for optical switching and IR uncooled bolometer devices.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.30.Hv Other nonmetallic inorganics
72.80.Sk Insulators
68.35.Dv Composition, segregation; defects and impurities
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

TiN and TiO2:Nb thin film preparation using hollow cathode sputtering with application to solar cells

S. Y. Guo, W. N. Shafarman, and A. E. Delahoy

J. Vac. Sci. Technol. A 24, 1524 (2006); http://dx.doi.org/10.1116/1.2180273 (6 pages) | Cited 4 times

Online Publication Date: 23 June 2006

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Titanium nitride (TiN) is well known for its excellent conductivity, inertness, and good optical reflectivity at long wavelengths. These properties make it a potential IR-reflective back contact material suitable for ultrathin Cu(In,Ga)Se2 (CIGS) solar cells. Using a pulsed power, 12 cm linear hollow cathode source fitted with Ti targets and with N2 as the reactive gas, TiN films were deposited on Mo-coated glass. The static deposition rate was 50 nm/min for a sputtering power of only 500 W. The high deposition rate indicates the advantage of the reactive environment, hollow cathode sputtering method, i.e., the reactive gas is excluded from the target. Electrical, optical, and physical properties of the films were measured. Resistivities in the range of 50–60 μΩ cm were achieved. Reflectance and x-ray diffraction measurements were conducted, and the effects of deposition parameters such as substrate bias and substrate temperature were studied. The optical emission from N and Ti atoms in the plasma was also studied. CIGS solar cells were successfully fabricated on TiN and a conversion efficiency of 12.3% was achieved. Transparent and moderately conductive TiO2 films doped with Nb were also prepared. The electrical and optical properties of these films are reported, and the reflectance of a-Si solar cells was reduced via incorporation of a TiO2:Nb layer.
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68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
84.60.Jt Photoelectric conversion

Inhomogeneous rarefaction of the process gas in a direct current magnetron sputtering system

F. Jimenez, S. D. Ekpe, and S. K. Dew

J. Vac. Sci. Technol. A 24, 1530 (2006); http://dx.doi.org/10.1116/1.2210005 (5 pages) | Cited 6 times

Online Publication Date: 23 June 2006

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The interactions between energetic particles and the sputter gas in a magnetron sputtering system have strong effects on the growth, structures, and properties of the film. These interactions result in inhomogeneous rarefaction of the gas in the space between target and substrate and affect both the transport of particles towards the substrate and the dynamics of the plasma. A hybrid Monte Carlo and fluid model is developed to simulate three-dimensional (3D) gas rarefaction due to the sputtering of metals in argon, neon, and krypton. The governing equations are solved iteratively in a 3D space with a nonuniform grid (octree). Collision events between the sputtered particles and the process gas are assumed as the dominant source of gas heating; however, the effect of the reflected neutrals is also included in the model. Gas rarefaction profiles have been predicted for different process conditions. Model results compare well with experimental ones. The extent of rarefaction depends on process conditions as well as the thermal conductivity of the gas. Materials with high sputtering yield, such as silver, show more rarefaction at a given cathode current than those with low sputtering yield, such as tungsten and aluminum. A higher sputtering yield means more sputtered atoms, thus more energy and momentum deposited in the gas. For a 75 mm target at 300 W and 10 mTorr, a rarefaction of about 65% is obtained for the sputtering of Al in Ar gas, with the substrate plane located 10 cm in front of the target.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
51.20.+d Viscosity, diffusion, and thermal conductivity

Characteristics of atomic layer deposited TiO2 films and their photocatalytic activity

Rodjana Pheamhom, Changshin Sunwoo, and Do-Heyoung Kim

J. Vac. Sci. Technol. A 24, 1535 (2006); http://dx.doi.org/10.1116/1.2172941 (5 pages) | Cited 13 times

Online Publication Date: 23 June 2006

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Titanium dioxide thin films were grown by atomic layer deposition (ALD) at 100–250 °C with tetrakis-dimethyl-amido titanium, using H2O2 as a counter-reactant. We have explored the effects of deposition temperature and the reactant pulse and purge times on the film growth rate to optimize the ALD process of TiO2. The film growth rate decreased with growth temperature below 175 °C, but was saturated to 0.28 Å/cycle at 175–250 °C. All the as-deposited films were highly pure, and the root-mean-square roughness was less than 2.5% of the film thickness. The films deposited at 150 °C and above were polycrystalline with an anatase structure, whereas those deposited at 125 ° C were amorphous. There was no change of crystal structure after annealing the crystalline films at temperatures of 450–650 °C. All the crystalline films were shown to have a photocatalytic activity in decomposing methylene blue in an aqueous solution. The films prepared at higher deposition temperatures were shown to have a better photocatalytic activity in decomposing methylene blue.
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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.-a Thin film structure and morphology
68.55.A- Nucleation and growth
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.40.Gh Other heat and thermomechanical treatments

Effects of TiOx physical vapor deposition parameters on the preferred orientation and adhesion of Pt films on γ-Al2O3

E. Derniaux, P. Kayser, C. Gageant, C. Sanchez, and D. Boivin

J. Vac. Sci. Technol. A 24, 1540 (2006); http://dx.doi.org/10.1116/1.2194925 (6 pages)

Online Publication Date: 23 June 2006

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TiOx physical vapor deposition (PVD) films were studied to improve the adhesion of Pt/AlN/Pt piezoelectric transducers on γ-Al2O3/NiCoCrAlY/superalloy components. Thick (1.7–3.8 μm) TiOx films deposited by rf reactive cathodic sputtering on α-Al2O3 substrates were analyzed by x-ray diffraction (XRD) and scanning electron microscopy equipped with energy dispersive x-ray spectroscopy. The influence of substrate temperature (Ts), oxygen mole fraction in the plasma gas and annealing (1050 °C, 1 h, in air) on structural properties, morphology, and chemical composition of the films was observed. Thin ( ⩽ 10 nm) TiOx adhesion layers and Pt films were sputtered on α-Al2O3. The effects of TiOx deposition parameters on the adhesion and the orientation of as-deposited and annealed Pt films were examined by tensile pull-off test and XRD, respectively. The results showed a (111) preferred orientation and good adhesion of Pt films. Finally, the selected TiOx deposition parameters were applied on γ-Al2O3/NiCoCrAlY/superalloy substrates. Adhesion properties of annealed Pt films on γ-Al2O3 and TiOx/γ-Al2O3 were evaluated. The results showed a drastic improvement of the pull-off force ( ≈ 0 to  ≈ 100 MPa) by using the TiOx “glue layer.” The adhesion layer also led to a pronounced (111) preferential orientation of the Pt films.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
68.43.Mn Adsorption kinetics
43.38.Fx Piezoelectric and ferroelectric transducers

Birefringent films for contrast enhancement of liquid crystal on silicon projection systems

Karen Hendrix, Kim Tan, Markus Duelli, David Shemo, and Markus Tilsch

J. Vac. Sci. Technol. A 24, 1546 (2006); http://dx.doi.org/10.1116/1.2189263 (6 pages)

Online Publication Date: 23 June 2006

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High-performance projection displays based on liquid crystal on silicon (LCoS) panel technology have the potential to deliver very high contrast and performance at an attractive price. These systems use polarization-based light engines that utilize wire grid polarizers (WGP) and vertical-aligned nematic LCoS panels. To achieve high contrast, the linear polarization state created by the WGP must be maintained in the dark state to prevent light leakage to the screen. However, the LCoS panel has a residual retardance, and without compensation, this leakage degrades the system contrast. We describe the design and contrast measurement results of a birefringent contrast enhancing component that compensates this residual retardance and improves the overall system contrast ratio to 6000:1. The component is comprised of birefringent films with individually controllable A-plate and C-plate compensation, accurate retardance targeting, and excellent uniformity for both retardance magnitude and orientation. The component also has good environmental durability and low defects.
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85.60.Pg Display systems
42.79.Kr Display devices, liquid-crystal devices
42.79.Ci Filters, zone plates, and polarizers

Compliant system of polyimide microwires for cryogenic detector applications

C. A. Allen, D. E. Franz, and S. H. Moseley

J. Vac. Sci. Technol. A 24, 1552 (2006); http://dx.doi.org/10.1116/1.2194922 (4 pages) | Cited 1 time

Online Publication Date: 23 June 2006

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We have developed a system of highly compliant, low thermal conductance electrical interconnects for cryogenic detector applications. The arrays of microwires are metallic, thin-film electrical leads supported by a layer of polyimide, capable of spanning the thermally isolated gap between the detector array and the low temperature heat sink in cryogenic detector assemblies. The low thermal conductance of the microwires enables detector thermal isolation without the need for conventional hard wiring, such as soldered manganin (an alloy of nickel, manganese, aluminum, iron, and copper) or stainless steel. Designed for compactness, an array of 30 microwires can be designed to fit on a silicon chip less than one-half of 1 cm2 in total surface area. We describe techniques for fabrication of arrays of polyimide microwires with several different types of conductive traces, both superconducting and normal metals. Mechanical elongation of 20% beyond the design length resulted in an increase in aluminum microwire resistance of only 1%, and no stress to the polyimide. Cryogenic elongation yielded no change in electrical or mechanical properties. The thermal conductivity of a single, aluminum microwire is found to be 3.8×10−8 W/K at 4.4 K and 1.1×10−8 W/K at 2.2 K.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
85.40.Ls Metallization, contacts, interconnects; device isolation
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
back to top Vacuum Technology

Vacuum measurement by carbon nanotube field emission

In-Mook Choi, Sam-Yong Woo, and Seung-Soo Hong

J. Vac. Sci. Technol. A 24, 1556 (2006); http://dx.doi.org/10.1116/1.2167984 (4 pages) | Cited 3 times

Online Publication Date: 23 June 2006

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A vacuum measurement technology utilizing the carbon nanotube (CNT) field-emission effect has been developed and characterized. The fabricated pressure sensor is a triode type similar to a conventional ionization gauge, but has a planar structure similar to a field-emission display. Owing to the excellent field-emission characteristics of CNTs, it is possible to make a cost effective cold cathode-type ion gauge. The triode-type CNT sensor has been manufactured by a screen-printing method and by a thermal chemical-vapor deposition growth method. A modified structure with an electron filter has also been introduced and characterized so as to improve the performances, such as sensitivity and stability. A glass grid with Cr deposited by e-beam is placed on the cathode. By the voltage applied to the grid, electrons are emitted from the CNTs and they ionize gas molecules in the chamber. Two modes are available to detect the gas density in the chamber, an electron emission mode and an ionization mode. In the electron emission mode, the collector voltage is controlled to be slightly higher than the grid voltage, whereas in the ionization mode it is controlled to be lower than the grid voltage so as to obtain a large ionization ratio. The ionized molecules are gathered at the collector and the electrons return to the grid in the triode structure. The ionization ratio increases as a function of pressure in the electron emission mode. The ionization characteristics are dependent on the gas and the combination of the voltages applied to the grid and the collector. In this article, the various metrological characteristics of the developed pressure sensor utilizing CNTs are introduced.
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07.30.-t Vacuum apparatus
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
79.70.+q Field emission, ionization, evaporation, and desorption

Spallation Neutron Source ring vacuum systems

M. Mapes, H. C. Hseuh, J. Rank, L. Smart, R. Todd, and D. Weiss

J. Vac. Sci. Technol. A 24, 1560 (2006); http://dx.doi.org/10.1116/1.2206192 (8 pages)

Online Publication Date: 23 June 2006

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The Spallation Neutron Source ring, which is presently being commissioned at Oak Ridge National Laboratory, is designed to accumulate high-intensity protons. Ultrahigh vacuum of 10−9 torr is required in the accumulator ring to minimize beam-residual gas ionization. To reduce the secondary-electron yield and the associated electron cloud instability, the ring vacuum chambers are coated with titanium nitride (TiN). In order to minimize radiation exposure, quick-disconnect chain clamp flanges are used in some areas where radiation levels are expected to be high. This article describes the design, fabrication, assembly, and vacuum processing of the ring and beam transport vacuum systems, as well as the associated vacuum instrumentation.
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29.25.Dz Neutron sources
07.30.-t Vacuum apparatus

Improvement of materials surface properties by rf glow discharge treatment

T. B. Huang, X. Chen, X. Q. Tian, and L. Z. Cha

J. Vac. Sci. Technol. A 24, 1568 (2006); http://dx.doi.org/10.1116/1.2197507 (4 pages)

Online Publication Date: 23 June 2006

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Materials surface properties were improved by the application of a rf glow discharge treatment for vacuum and electronic applications. The surface morphology was studied under different glow discharge treatments and it could be shown by experiments that the roughness of materials surface varied due to the glow discharge treating process and that a clean and smooth surface could be obtained after the treatment. The experimental results revealed that the outgassing rates for different gases decreased and the evacuating properties for the materials improved following the application of the glow discharge treatment.
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81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
52.77.Bn Etching and cleaning
52.80.Hc Glow; corona

High temperature outgassing tests on materials used in the DIII-D tokamak

K. L. Holtrop and M. J. Hansink

J. Vac. Sci. Technol. A 24, 1572 (2006); http://dx.doi.org/10.1116/1.2178363 (6 pages)

Online Publication Date: 23 June 2006

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This article is a continuation of previous work on determining the outgassing characteristics of materials used in the DIII-D magnetic fusion tokamak [ K. L. Holtrop, J. Vac. Sci. Technol. A 17, 2064 (1999) ]. Achievement of high performance plasma discharges in the DIII-D tokamak requires careful control of impurity levels. Among the techniques used to control impurities are routine bakes of the vacuum vessel to an average temperature of 350 °C. Materials used in DIII-D must release only very small amounts of impurities (below 2×10−6 mole) at this temperature that could be transferred to the first wall materials and later contaminate plasma discharges. To better study the behavior of materials proposed for use in DIII-D at elevated temperatures, the initial outgassing test chamber was improved to include an independent heating control of the sample and a simple load lock chamber. The goal was to determine not only the total degassing rate of the material during baking, but to also determine the gas species composition and to obtain a quantitative estimate of the degassing rate of each species by the use of a residual gas analyzer. Initial results for aluminum anodized using three different processes, stainless steel plated with black oxide and black chrome, and a commercially available fiber optic feedthrough will be presented.
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07.30.Bx Degasification, residual gas
52.55.Fa Tokamaks, spherical tokamaks
81.65.-b Surface treatments
28.52.Fa Materials
28.52.Av Theory, design, and computerized simulation

Pressure dependence of laminar-turbulent transition in gases

L. D. Hinkle, A. Muriel, and S. A. Novopashin

J. Vac. Sci. Technol. A 24, 1578 (2006); http://dx.doi.org/10.1116/1.2197506 (6 pages) | Cited 3 times

Online Publication Date: 23 June 2006

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The transition between the laminar and turbulent flow regimes is traditionally addressed using the continuum formulation of the Navier-Stokes equations and dimensionless parameters such as the Reynolds number. However, a detailed understanding of the transition mechanisms has remained elusive. Theoretical approaches based on molecular and quantum mechanical models have been proposed but have yet to be thoroughly tested experimentally. In an effort to test a quantum-based model, specific apparatus and experiments have been designed to evaluate particular features of the laminar-turbulent transition. Hysteresis plots of flow versus differential pressure are used to examine the flow transition that occurs inside a tube with a divergent entrance. The hysteresis plots generated in these tests show several notable features and quantitative trends. The primary focus of this article is on the observed dependence of the laminar-turbulent transition behavior on the absolute pressure. Whereas the continuum-based model does not predict a pressure dependence of the laminar-turbulent transition, a molecular-based model indicates a pressure effect on the transition to turbulent flow.
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47.27.Cn Transition to turbulence
47.10.ad Navier-Stokes equations

Computational fluid dynamic model of a tapered Holweck vacuum pump operating in the viscous and transition regimes. I. Vacuum performance

S. Giors, E. Colombo, F. Inzoli, F. Subba, and R. Zanino

J. Vac. Sci. Technol. A 24, 1584 (2006); http://dx.doi.org/10.1116/1.2178362 (8 pages) | Cited 1 time

Online Publication Date: 23 June 2006

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Holweck molecular drag pumps are used as high-pressure stages in hybrid turbomolecular vacuum pumps, where they can operate in the transition and the viscous regime. In this article we develop a Navier-Stokes model of a Holweck pump with tapered pumping channels, applying slip-flow boundary conditions, to predict vacuum performances with and without gas flow. The commercial computational fluid dynamic code FLUENT is used to solve the model equations and to predict the pressure profile along the grooves. A specifically designed experiment is presented, whose arrangement provides the boundary conditions as input to the model and whose results are used to validate it.
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07.30.Cy Vacuum pumps
47.45.Gx Slip flows and accommodation
47.10.ad Navier-Stokes equations
47.11.-j Computational methods in fluid dynamics

Selective water vapor cryopumping through argon

A. P. Kryukov, O. Podcherniaev, P. H. Hall, D. J. Plumley, V. Yu. Levashov, and I. N. Shishkova

J. Vac. Sci. Technol. A 24, 1592 (2006); http://dx.doi.org/10.1116/1.2194928 (5 pages) | Cited 1 time

Online Publication Date: 23 June 2006

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A selective cryopumping process for water vapor control takes place in vacuum systems for web coating or plasma operations, such as sputter deposition, etching, etc. Excessive water vapor content will affect the quality of the processes and final products. These vacuum systems typically operate at pressures corresponding to transitional or viscous flow regimes, and water vapor cryopumping is highly limited by diffusion of water vapor molecules through a noncondensable process gas (argon, air). An analytical model was created to describe water vapor condensing process through a noncondensable gas diffusion barrier. The model accounts for the collisions of different molecules by means of Boltzmann kinetic equations for two-component rarefied gas. It was assumed that water vapor content is about three orders of magnitude lower than that of the noncondensable gas (argon). Cryopumping process was analyzed for two simplified cases when water vapor source and cryosurface are parallel plates and coaxial cylinders. The calculations were conducted for different water vapor outgassing rates and argon pressures ranging from 0.5×10−3 to 20.0×10−3 torr. At certain parameters a strongly nonlinear distribution of water vapor pressure and density versus distance between source and cryosurface was obtained. At high argon pressures an increase of water vapor pressure was observed near an outgassing surface. The results were used for calculation of water vapor cryopumping rates.
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51.10.+y Kinetic and transport theory of gases
47.45.-n Rarefied gas dynamics
07.30.Cy Vacuum pumps

Effect of heat on the pumping performance of cryopump

H.-P. Cheng and Y.-H. Shen

J. Vac. Sci. Technol. A 24, 1597 (2006); http://dx.doi.org/10.1116/1.2201055 (4 pages)

Online Publication Date: 23 June 2006

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This study used quartz lamp and the small disk heaters as the heating sources to investigate the pumping performance of the two-stage Gifford-McMahon (G-M) closed-loop gaseous helium cryopump with heat transfer effect. In the experiment, the heat was applied by two means, for the first-stage array by thermal radiation and for the second-stage array by applying directly. The test system was constructed in accordance to the single-dome flow-meter pumping measuring apparatus recommended by Welch et al. [J. Vac. Sci. Technol. A 17, 3081 (1999) ]. The experiment applied varied levels of electrical power to the heaters, introduced Ar to the test dome, and measured the corresponding dome pressure, gas throughput, and temperatures of the different arrays inside the cryopump. The results showed that the temperature of the introduced gas heated by the heater in the test dome would influence the measured pumping speed of cryopump. When the thermal load is applied primarily on the first-stage array, the temperature of the second-stage array varies significantly as the temperature of the first-stage array changes; when applied directly to the second-stage array, the temperature of the first-stage array varies little as the temperature of the second-stage array changes. The pumping speed of cryopump and temperature of the two-stage arrays increase gradually as gas throughput rises, and sharply when the gas in the test dome is nonmolecular flow. The measured refrigeration capacity of second-stage cooling station is approximate to the data provided by ULVAC.
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07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
07.30.Cy Vacuum pumps
44.40.+a Thermal radiation

ISAC target vacuum system

Dimo Yosifov and Igor Sekachev

J. Vac. Sci. Technol. A 24, 1601 (2006); http://dx.doi.org/10.1116/1.2172940 (4 pages)

Online Publication Date: 23 June 2006

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The Isotope Separator and Accelerator (ISAC) facility at TRIUMF has been in full operation since 1999. The ISAC east and west targets use proton beam from the cyclotron to produce various radioactive isotopes, which are then ionized and extracted. The ions are then passed through the mass separator and selected ions are transferred to the low energy experiments or injected into a radio frequency quadrupole accelerator. The accompanying radioactive contamination from the production of radioactive ions requires a complex vacuum system. The main target vacuum space consists of two semiseparate (primary and secondary) volumes pumped by turbo-molecular pumps. The primary volume uses four pumps while the secondary volume uses two pumps. Two hermetic rotary vane pumps are used as backing pumps. The nominal vacuum in both volumes is about 1.33×10−4 Pa (1.0×10−6 Torr). The pressure is monitored by two cold cathode and two hot filament ion gauges. The cold cathode gauges are used to interlock the system, which is critical during the bake out of the target and beam production. The exhaust gas from the vacuum pumps can be radioactive. Three gas storage tanks (decay tanks) are used for temporary storage of the radioactive exhaust and its controlled release to the atmosphere. Gas-species insensitive membrane gauges are used for monitoring the pressure in the storage tanks. This article describes the details of the ISAC target vacuum system as well as some procedures related to the handling of the exhaust gas with traces of radioactive contamination produced by the targets.
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07.77.Ka Charged-particle beam sources and detectors
29.27.Ac Beam injection and extraction
07.30.Cy Vacuum pumps
29.25.Ni Ion sources: positive and negative
29.20.dg Cyclotrons
back to top Applied Surface Science/Surface Characterization of Organic and Biological Systems

Measuring the thickness of organic/polymer/biological films on glass substrates using spectroscopic ellipsometry

Harland G. Tompkins, Tom Tiwald, Corey Bungay, and Andrew E. Hooper

J. Vac. Sci. Technol. A 24, 1605 (2006); http://dx.doi.org/10.1116/1.2172945 (5 pages) | Cited 2 times

Online Publication Date: 23 June 2006

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In this work we discuss a method of determining film thickness for film/substrate combination where the index of refraction of the film and substrate in the transparent spectral regions is almost identical. Common examples of this situation are organic/polymer/biological films on glass substrates. Infrared ellipsometry is used and we use weight gain to provide some necessary additional information for determining the optical functions for the film material. The spectral regions of strong molecular vibrations are then used for determining film thickness.
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68.55.-a Thin film structure and morphology
61.41.+e Polymers, elastomers, and plastics
78.66.Qn Polymers; organic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Jk Polymers and organics
back to top Applied Surface Science/Thin Film Characterization

Hot electron transport across manganese silicide layers on the Si(001) surface

A. J. Stollenwerk, M. R. Krause, R. Moore, and V. P. LaBella

J. Vac. Sci. Technol. A 24, 1610 (2006); http://dx.doi.org/10.1116/1.2206195 (3 pages) | Cited 1 time

Online Publication Date: 23 June 2006

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Ballistic electron emission microscopy (BEEM) has been performed on MnSi/Si(001) Schottky diodes at 80 K to study the hot electron transport properties. The BEEM spectra best fit the thermally broadening 5/2 power law model with two threshold heights at 0.71 and 0.86 eV, indicating a complex interface band structure. In addition, the normalized BEEM current in the MnSi overlayer was found to be approximately seven times less than is observed in Au/Si(001) samples of similar thicknesses, indicating a larger amount of hot electron scattering in the MnSi/Si(001) samples.
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73.40.Ns Metal-nonmetal contacts
72.20.Ht High-field and nonlinear effects
73.20.At Surface states, band structure, electron density of states
85.30.Kk Junction diodes

Optimization and deposition of CdS thin films as applicable to TiO2/CdS composite catalysis

K. Prabakar, T. Takahashi, T. Nakashima, Y. Kubota, and A. Fujishima

J. Vac. Sci. Technol. A 24, 1613 (2006); http://dx.doi.org/10.1116/1.2167080 (5 pages) | Cited 8 times

Online Publication Date: 23 June 2006

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Methanol decomposition has been studied by in situ Fourier transform infrared spectroscopy on a CdS/TiO2 bilayer deposited on glass substrates. First CdS thin films were deposited by chemical bath deposition method using the CdSO4 and thiourea as the precursors and ammonia as the complexing agent and have the optical band gap of 2.2–2.29 eV for the different CdSO4 solution concentrations. The structure of the CdS films was found to have mixed cubic and hexagonal phases, while the TiO2 films were polycrystalline anatase structure with an optical band-gap energy of 3.2 eV deposited at a total sputtering pressure of 0.1 Pa in an argon and oxygen gas mixture (Ar:O2 = 80:20) at 200 W sputtering power. The visible light active photocatalytic degradation efficiency of methanol over a TiO2/CdS double layer is four times higher than that of a TiO2 single layer. The decomposition of methanol pathway proceeds via formaldehyde as the intermediate product.
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81.05.Dz II-VI semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
64.75.-g Phase equilibria
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
78.66.Hf II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
back to top Applied Surface Science/Thin Film Characterization II

Laser processing of polymer nanocomposite thin films

A. T. Sellinger, E. M. Leveugle, K. Gogick, L. V. Zhigilei, and J. M. Fitz-Gerald

J. Vac. Sci. Technol. A 24, 1618 (2006); http://dx.doi.org/10.1116/1.2167980 (5 pages) | Cited 11 times

Online Publication Date: 23 June 2006

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Current biotechnology and sensor research has enhanced the drive to establish viable methods for depositing high-quality polymer thin films. In this research, thin films of poly(methyl methacrylate) (PMMA) were prepared by matrix-assisted pulsed-laser evaporation (MAPLE). Up to 2 wt % of carbon nanotubes were subsequently added to MAPLE target systems for deposition of polymer nanocomposite films. Targets were ablated using a 248 nm (KrF) laser at fluences ranging from 0.045 to 0.75 J/cm2. In addition, polymer concentration in MAPLE targets was varied between 1 and 5 wt % relative to the matrix solvent, in this case toluene. Films were deposited on Si substrates at room temperature in an Ar atmosphere. Molecular-dynamics simulations of MAPLE were utilized for interpretation of experimental observations. Particularly, the ejection of large clusters consisting of both PMMA and toluene molecules was studied and related to the observed morphology of the deposited films.
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81.16.Mk Laser-assisted deposition
81.15.Fg Pulsed laser ablation deposition
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
42.62.-b Laser applications
68.47.Mn Polymer surfaces
81.07.-b Nanoscale materials and structures: fabrication and characterization

Surface and texture characterization of thin-film ZnTe formed with pulsed-laser deposition

Artur Erlacher, Alejandra R. Lukaszew, Herbert Jaeger, and Bruno Ullrich

J. Vac. Sci. Technol. A 24, 1623 (2006); http://dx.doi.org/10.1116/1.2167072 (4 pages) | Cited 4 times

Online Publication Date: 23 June 2006

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Using thin-film semiconductors as active photonic interfaces, an all-optical laser digitizer can be realized. Based on these results, zinc telluride (ZnTe) has attracted our interest since it is an appealing semiconductor for applications in photonics. Low-temperature pulsed-laser deposition (PLD), i.e., without substrate heater, was employed to deposit amorphous thin-film ZnTe on silicon (Si) and glass substrates using either the 1064 or 532 nm emission lines of a nanosecond-pulsed Nd:YAG laser. In spite of the predominantly amorphous sample textures, x-ray-diffraction experiments and analysis of the surface roughness including outgrowth distribution using atomic force microscopy reveal major differences in surface morphology and crystal textures between samples formed at these two laser wavelengths. This indicates wavelength-dependent ablation and wavelength-dependent PLD mechanisms with nanosecond pulses. Our observations contribute to a better understanding of PLD and provide tools to fine-tune and optimize the optoelectronic and photonic properties of ZnTe amorphous thin films as well as their incorporation into Si-based technologies in order to fabricate cost-effective and functional optoelectronic devices.
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81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
back to top Electronic Materials and Processing/Novel Approaches in Wide Bandgap Semiconductors

Quantitative assessment of diffusivity and specularity of surface-textured reflectors for light extraction in light-emitting diodes

Y. Xi, X. Li, J. K. Kim, F. Mont, Th. Gessmann, H. Luo, and E. F. Schubert

J. Vac. Sci. Technol. A 24, 1627 (2006); http://dx.doi.org/10.1116/1.2194924 (4 pages) | Cited 4 times

Online Publication Date: 23 June 2006

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Surface-textured reflectors fabricated by natural lithography and ion beam etching have a specular and a diffusive component of the reflectivity. The diffusely and specularly reflected powers of surface-textured reflectors are measured and analyzed quantitatively in terms of a theoretical model. The diffusive-power-to-total-power ratio is determined and shown to strongly depend on the surface texture. The light extraction efficiency from a waveguide clad by a partially diffuse reflector is analyzed and shown to be enhanced.
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85.60.Jb Light-emitting devices

Metal-organic chemical-vapor deposition of high-reflectance III-nitride distributed Bragg reflectors on Si substrates

M. A. Mastro, R. T. Holm, N. D. Bassim, D. K. Gaskill, J. C. Culbertson, M. Fatemi, C. R. Eddy, R. L. Henry, and M. E. Twigg

J. Vac. Sci. Technol. A 24, 1631 (2006); http://dx.doi.org/10.1116/1.2172937 (4 pages) | Cited 2 times

Online Publication Date: 23 June 2006

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High-reflectance group III-nitride distributed Bragg reflectors (DBRs) were deposited by metal-organic chemical-vapor deposition on Si(111) substrates. A reflectance greater than 96% was demonstrated for an AlN/GaN DBR with a stop band centered in the blue-green range of the visible spectrum. Crack-free GaN cap layers were grown on the DBR structures to demonstrate the opportunity to build III-nitride optoelectronic devices in this material. The DBR structure was under significant strain due to growth on a mismatched substrate, although the GaN cap layer was shown to be strain-free.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
42.79.Bh Lenses, prisms and mirrors
42.82.Gw Other integrated-optical elements and systems
78.40.Fy Semiconductors
68.60.Bs Mechanical and acoustical properties

Low-temperature synthesis of silica-enhanced gallium nitride nanowires on silicon substrate

Chin-Hua Hsieh, Li-Jen Chou, Yu-Lun Chueh, and Mu-Tung Chang

J. Vac. Sci. Technol. A 24, 1635 (2006); http://dx.doi.org/10.1116/1.2174016 (5 pages)

Online Publication Date: 23 June 2006

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Low-temperature synthesis of GaN nanowires is successfully achieved by silica-enhanced processes. GaN nanowires were synthesized by reaction of metal gallium vapor with ammonia and hydrogen gases at the temperature of 700 °C on the amorphous SiO2 substrate. From scanning electron microscopy images, the morphologies of GaN nanowires are wirelike with a length up to 5 μm and the average diameter of GaN nanowires measured by transmission electron microscopy (TEM) is about 25 nm. The x-ray diffraction analysis of as-synthesized products indicates that the nanowires have the hexagonal wurtzite structure of GaN crystal. The corresponding electron diffraction pattern also indicates that the as-synthesized GaN nanowires exhibited a single-crystal feature with uniform oxygen doping characterized by electron energy loss spectroscopy. The compositional line profile of TEM analysis reveals that GaN nanowires are terminated by Au nanoparticles, which infer an evidence that the vapor-liquid-solid model is the major growth mechanism.
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81.07.Bc Nanocrystalline materials
81.05.Ea III-V semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.46.Hk Nanocrystals
79.20.Uv Electron energy loss spectroscopy
back to top Magnetic Interfaces and Nanostructures/Magnetic Semiconductors

Manganese-induced long-range lattice disorder and vacancy formation in metal-organic chemical vapor deposition grown and ion-implanted Ga1−xMnxN

William E. Fenwick, Ali Asghar, Shalini Gupta, Hun Kang, Martin Strassburg, Nikolaus Dietz, Samuel Graham, Matthew H. Kane, and Ian T. Ferguson

J. Vac. Sci. Technol. A 24, 1640 (2006); http://dx.doi.org/10.1116/1.2201052 (4 pages) | Cited 2 times

Online Publication Date: 23 June 2006

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The structural properties and lattice dynamics of Ga1−xMnxN were studied for Mn concentrations from 0.0% to 1.5%. Ga1−xMnxN layers were fabricated by either Mn incorporation during the metal-organic chemical vapor deposition (MOCVD) growth process or by postgrowth ion implantation into MOCVD-grown GaN epilayers. The crystalline integrity and the absence of major second phase contributions were confirmed by high-resolution x-ray diffraction analysis. Raman spectroscopy showed that increased Mn incorporation in the epilayers significantly affected long-range lattice ordering, revealing a disorder-induced mode at 300 cm−1 and a local vibrational mode at 669 cm−1. The low intensities of both modes were shown to scale with Mn concentration. These observations support the formation of nitrogen vacancies, even under optimized MOCVD growth conditions. The slight excess of metal components in the growth process compared to undoped GaN growth and the incorporation of Mn deep acceptor levels favors the formation of nitrogen vacancies relative to undoped GaN. Such vacancies form shallow donor complexes and thus contribute to self-compensation. Electronic defects such as these may be detrimental to the ferromagnetic ordering process.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.J- Point defects and defect clusters
61.72.uj III-V and II-VI semiconductors

Observation of crystallite formation in ferromagnetic Mn-implanted Si

C. Awo-Affouda, M. Bolduc, M. B. Huang, F. Ramos, K. A. Dunn, B. Thiel, G. Agnello, and V. P. LaBella

J. Vac. Sci. Technol. A 24, 1644 (2006); http://dx.doi.org/10.1116/1.2189265 (4 pages) | Cited 17 times

Online Publication Date: 23 June 2006

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Mn-implanted Si was investigated using transmission electron microscopy to gain insight into the structure of the implanted region. Diffraction contrast images, selected area diffraction patterns, and high resolution images of the samples were acquired before and after postimplant annealing at 800 °C. The images of the annealed samples revealed the formation of nanometer size precipitates distributed throughout the implanted region. Analysis of the selected area diffraction pattern determined that the most prominent lattice spacing of the crystallites is 2.15 Å. This spacing indicates that the most probable phase of the crystallites is MnSi1.7 and this is consistent with the Mn:Si binary phase diagram. This phase is paramagnetic at room temperature with a Curie temperature of 47 K and cannot readily account for the high Curie temperature of the material.
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75.50.Pp Magnetic semiconductors
75.50.Cc Other ferromagnetic metals and alloys
75.20.En Metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Annealing temperature effects on the structure of ferromagnetic Mn-implanted Si

M. Bolduc, C. Awo-Affouda, F. Ramos, and V. P. LaBella

J. Vac. Sci. Technol. A 24, 1648 (2006); http://dx.doi.org/10.1116/1.2194921 (4 pages) | Cited 14 times

Online Publication Date: 23 June 2006

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The dependence of the magnetization of Mn-implanted Si on the postimplant annealing temperature is studied. p-type Si wafers were implanted with 300 keV Mn+ ions at 350 °C to a fluence of 1×1016 cm−2 and then annealed at 500–900 °C for 5 min. Ferromagnetic hysteresis loops were obtained at 10 K using a superconducting quantum interference device magnetometer. The saturation magnetization increases with the postimplant annealing temperature, reaching an optimum field strength of 0.2 emu/g at 800 °C. An out diffusion of Mn is observed at higher temperatures that coincides with a decrease in the saturation magnetization. The calculated point-defect profile that was generated by the implantation process peaks around the Mn-depleted region, suggesting that the residual implant damage may play a role in the ferromagnetic behavior of Mn-implanted Si.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Pp Magnetic semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.82.Fk Semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.uf Ge and Si
61.72.J- Point defects and defect clusters
back to top Magnetic Interfaces and Nanostructures/Advanced Magnetic Storage and Manufactoring Processes

Interface stability between amorphous ferromagnetic layer and Al oxide barrier in tunneling magnetoresistive films at elevated temperatures

Xilin Peng, Dick Kvitek, Augusto Morone, Steven H. Axdal, and Song Xue

J. Vac. Sci. Technol. A 24, 1652 (2006); http://dx.doi.org/10.1116/1.2198860 (3 pages)

Online Publication Date: 23 June 2006

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The interface stability and microstructure between amorphous and crystalline ferromagnetic (FM) layers Fe56Co24B20 and Co70Fe30 (at. %) and oxide barrier layers (AlO) deposited by physical vapor deposition, in both as-deposited and annealed states, have been studied using hysteresis loops for magnetic measurement, x-ray photoelectron spectroscopy for elemental depth profiling, and transmission electron microscopy for atomic-level microstructure. AlO was found to be amorphous on both amorphous Fe56Co24B20 and polycrystalline Fe30Co70 FM layers. Substantial Fe diffusion towards the AlO layer and Al diffusion towards the FM layer are clearly observed for the Fe56Co24B20/AlO system when annealed above 360 °C and will likely cause magnetic tunneling junction devices made from this system to fail.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
79.60.Jv Interfaces; heterostructures; nanostructures
66.30.J- Diffusion of impurities
75.50.Kj Amorphous and quasicrystalline magnetic materials
back to top Plasma Science and Technology/Emerging Plasma Applications

Effect of substrate material and bias on properties of TiN films deposited in the hybrid plasma reactor

L. Bárdos, H. Baránková, and L.-E. Gustavsson

J. Vac. Sci. Technol. A 24, 1655 (2006); http://dx.doi.org/10.1116/1.2167082 (5 pages) | Cited 1 time

Online Publication Date: 23 June 2006

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Parameters of TiN films deposited in the hybrid hollow cathode and microwave electron cyclotron resonance (ECR) plasma reactor can be strongly affected by the substrate material. Differences have been found between films grown on Si substrates and steel substrates, as well as between steel substrates from martensite and austenite steels. Temperature measurements by simple probes made from different materials with surfaces covered by wafers from Si or from steel confirmed substantial differences depending on individual materials. These differences can be explained by material-dependent absorptions of the microwave power as well as by enhanced particle bombardment of ferromagnetic substrates connected with deformation of the magnetic field in the hybrid plasma reactor. The effect of surface bombardment has been confirmed by voltage-current measurements using electrically biased probes. The results correspond well with properties of the obtained TiN films. Observed effects could be of more general importance, e.g., for microwave ECR plasmas, magnetron sputtering, as well as for most magnetized plasma systems.
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52.77.Dq Plasma-based ion implantation and deposition
68.55.-a Thin film structure and morphology
76.40.+b Diamagnetic and cyclotron resonances
68.47.Fg Semiconductor surfaces
75.50.Bb Fe and its alloys
73.61.-r Electrical properties of specific thin films
back to top Surface Science/Organic Film Growth and Characterization

Para-sexiphenyl thin films grown by hot wall epitaxy on KCl(001) substrates

A. Yu. Andreev, A. Montaigne, G. Hlawacek, H. Sitter, and C. Teichert

J. Vac. Sci. Technol. A 24, 1660 (2006); http://dx.doi.org/10.1116/1.2172933 (4 pages) | Cited 3 times

Online Publication Date: 23 June 2006

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Here, we use atomic force microscopy (AFM) to study the morphology and growth kinetics of para-sexiphenyl layers deposited by hot wall epitaxy on crystalline KCl(001) substrates. It is shown that the growth process is quite complex and can be divided preliminarily into two steps. The initial growth stage is characterized by the formation of long needlelike crystallites built of “lying” molecules and oriented mainly into the 〈110〉 directions in accordance with the substrate’s fourfold symmetry. If the coverage increases, terraced crystalline mounds composed of monolayers of upright standing molecules start to develop between the needles. The mound formation is due to repeated two-dimensional nucleation of para-sexiphenyl molecules. By means of phase imaging in the AFM tapping mode, it could be further demonstrated that both needlelike crystallites and flat terraced mounds grow directly on the substrate surface, i.e., there is no wetting layer formed during the deposition of para-sexiphenyl on KCl(001).
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68.55.A- Nucleation and growth
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.37.Ps Atomic force microscopy (AFM)
back to top Thin Films/Thin Films for Photovoltaic and Energy Applications

Preparation and characterization of transparent conducting ZnTe:Cu back contact interface layer for CdS/CdTe solar cell for photoelectrochemical application

Upendra S. Avachat and Neelkanth G. Dhere

J. Vac. Sci. Technol. A 24, 1664 (2006); http://dx.doi.org/10.1116/1.2201053 (4 pages) | Cited 1 time

Online Publication Date: 23 June 2006

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FSEC Photovoltaic Materials Laboratory has developed a photoelectrochemical (PEC) cell using multiple band gap tandem of thin-film photovoltaic (PV) cells and a photocatalyst for hydrogen production by water splitting. CdS/CdTe solar cell, a promising candidate for low-cost, thin-film PV cell, is used as one of the thin-film solar cells in a PEC cell. The back contact has been developed for a CdS/CdTe solar cell which involves the deposition of a primary p-type ZnTe:Cu back contact interface layer followed by the deposition of transparent and conducting ZnO:Al and Ni–Al outer metallization layer. This article presents preparation and characterization of ZnTe:Cu back contact interface layer deposited by hot wall vacuum evaporation (HWVE) technique. HWVE technique has produced highly stoichiometric ZnTe:Cu thin films with cubic phase having {111} texture orientation and produced better transparency in the near infrared region on a glass substrate.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.40.+w Photoconduction and photovoltaic effects
84.60.Jt Photoelectric conversion
85.40.Ls Metallization, contacts, interconnects; device isolation

CuPc:C60 blend film: A photoemission investigation

L. Lozzi, V. Granato, S. Picozzi, M. Simeoni, S. La Rosa, B. Delly, and S. Santucci

J. Vac. Sci. Technol. A 24, 1668 (2006); http://dx.doi.org/10.1116/1.2194923 (8 pages) | Cited 9 times

Online Publication Date: 23 June 2006

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The electronic structure of thin blend films composed of copper phthalocyanine (CuPc) and fullerene (C60) have been studied by x ray, soft-x-ray photoemission spectroscopy, and by theoretical simulations. Samples with different C60/CuPc concentration ratios were prepared by thermal evaporation in ultrahigh vacuum conditions. A strong shift of the highest occupied molecular orbital (HOMO) of CuPc towards the Fermi level and of the HOMO C60 states towards higher binding energy was observed. The comparison between valence band structures and core level line shape indicates that the central part of the CuPc molecule is lightly modified by the presence of the C60 molecule. The theoretical analysis, performed using density functional theory, confirms this small interaction between the two molecules, with a small charge density localized between the two molecules and a structural modification of the CuPc molecule.
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73.20.At Surface states, band structure, electron density of states
71.20.Rv Polymers and organic compounds
79.60.Fr Polymers; organic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
back to top Thin Films/In Situ/Ex Situ and Real-Time Monitoring

Real-time spectroscopic ellipsometry studies of the growth of amorphous and epitaxial silicon for photovoltaic applications

D. H. Levi, C. W. Teplin, E. Iwaniczko, Y. Yan, T. H. Wang, and H. M. Branz

J. Vac. Sci. Technol. A 24, 1676 (2006); http://dx.doi.org/10.1116/1.2167083 (8 pages) | Cited 5 times

Online Publication Date: 23 June 2006

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In situ monitoring of material properties during thin-film deposition provides researchers with a valuable tool for maximizing solar cell performance, while also enabling efficient exploration of deposition parameter space. This article describes how our research team has utilized in situ real-time spectroscopic ellipsometry (RTSE) to maximize our productivity in two related projects. We are using hot wire chemical vapor deposition (HWCVD) for low-temperature (90–235 °C) deposition of very thin films of amorphous hydrogenated silicon for amorphous Si/crystal-Si heterojunction (SHJ) solar cells. We are also using HWCVD for low-temperature (200–440 °C) deposition of epitaxial films of silicon on crystal-Si substrates. We utilize RTSE as both an in situ diagnostic and a postgrowth analysis tool for SHJ solar cells and epi-Si films grown by HWCVD. Using input from RTSE analysis we have achieved a photovoltaic energy conversion efficiency of 17.1% on an Al-backed p-type float-zone c-Si wafer. Epi-Si films have been grown as thick as 500 nm utilizing parameter optimization based on RTSE analysis.
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78.66.Db Elemental semiconductors and insulators
68.55.-a Thin film structure and morphology
84.60.Jt Photoelectric conversion
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
back to top Thin Films/Focused Beam Processing and Fabrication

Reduction of laser-induced roughness in a-Si:H surfaces for vacuum compatible lithography

R. N. Jacobs, E. W. Robinson, A. J. Stoltz, J. H. Dinan, and L. Salamanca-Riba

J. Vac. Sci. Technol. A 24, 1684 (2006); http://dx.doi.org/10.1116/1.2172938 (6 pages)

Online Publication Date: 23 June 2006

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A vacuum compatible lithography technique has recently been demonstrated, whereby amorphous hydrogenated silicon (a-Si:H) films are used as a resist. Following plasma deposition of the a-Si:H film, poly-Si patterns are generated on the surface by excimer laser exposure through a projection mask. Development is then carried out by hydrogen plasma etching for which etch selectivities of over 1000:1 have been achieved between a-Si:H and poly-Si regions. However, the roughness induced by excimer laser irradiation can be well over ten times that of the as-deposited a-Si:H surface. This is problematic because the roughness may be transferred to underlying device layers during subsequent pattern transfer plasma etching. We have developed a stepwise laser irradiation procedure that reduces the surface roughness by an order of magnitude to a level of ∼ 1 nm. This value is approximately equal to the surface roughness for the as-deposited a-Si:H film. The irradiation procedure uses multiple pulses with progressive increases in the energy density, in contrast to the single high energy density pulses previously used. Transmission electron microscopy and Fourier transform infrared spectroscopy are used to understand and confirm the mechanism behind this process. Our data suggest that the observed reduction in roughness is due both to smaller grain sizes and to a slow rate of H removal from the film surface. The results may also hold significance for other applications of laser processed a-Si:H, even where different film properties are desired.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
79.20.Ds Laser-beam impact phenomena
81.65.Cf Surface cleaning, etching, patterning
42.82.Cr Fabrication techniques; lithography, pattern transfer
78.30.Am Elemental semiconductors and insulators
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