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Elaboration of high aspect ratio monocrystalline silicon suspended nanobridges by low temperature alkaline treatment of dry etched trenches

Thomas Defforge, Gaël Gautier, Thomas Tillocher, Rémi Dussart, and François Tran-Van

J. Vac. Sci. Technol. A 30, 010601 (2012); http://dx.doi.org/10.1116/1.3665217 (3 pages)

Online Publication Date: 2 December 2011

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This paper describes the elaboration of high aspect ratio (250), high linear density (500 cm⁻¹) suspended silicon nanobridges into low concentrated alkaline solutions. Trenches were first etched into silicon using the deep reactive ion etching STiGer process. These structures were immersed into low concentrated potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) solutions. The behaviors of KOH and TMAH as silicon trenches etching agents (kinetic and quality of etching) were studied to optimize the silicon nanowires (SiNWs) formation and the elaboration of the suspended structures. The limits of the SiNWs thickness in these conditions were also discussed.

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81.65.Cf	Surface cleaning, etching, patterning
61.46.Km	Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
81.07.Gf	Nanowires
81.05.Cy	Elemental semiconductors

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Atomic layer deposition for nanostructured Li-ion batteries

H. C. M. Knoops, M. E. Donders, M. C. M. van de Sanden, P. H. L. Notten, and W. M. M. Kessels

J. Vac. Sci. Technol. A 30, 010801 (2012); http://dx.doi.org/10.1116/1.3660699 (10 pages) | Cited 8 times

Online Publication Date: 21 November 2011

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Nanostructuring is targeted as a solution to achieve the improvements required for implementing Li-ion batteries in a wide range of applications. These applications range in size from electrical vehicles down to microsystems. Atomic layer deposition (ALD) could be an enabling technology for nanostructured Li-ion batteries as it is capable of depositing ultrathin films (1–100 nm) in complex structures with precise growth control. The potential of ALD is reviewed for three battery concepts that can be distinguished, i.e., particle-based electrodes, 3D-structured electrodes, and 3D all-solid-state microbatteries. It is discussed that a large range of materials can be deposited by ALD and recent demonstrations of battery improvements by ALD are used to exemplify its large potential.

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82.47.Aa

Lithium-ion batteries

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Spatial atomic layer deposition: A route towards further industrialization of atomic layer deposition

Paul Poodt, David C. Cameron, Eric Dickey, Steven M. George, Vladimir Kuznetsov, Gregory N. Parsons, Fred Roozeboom, Ganesh Sundaram, and Ad Vermeer

J. Vac. Sci. Technol. A 30, 010802 (2012); http://dx.doi.org/10.1116/1.3670745 (11 pages) | Cited 14 times

Online Publication Date: 14 December 2011

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Atomic layer deposition (ALD) is a technique capable of producing ultrathin conformal films with atomic level control over thickness. A major drawback of ALD is its low deposition rate, making ALD less attractive for applications that require high throughput processing. An approach to overcome this drawback is spatial ALD, i.e., an ALD mode where the half-reactions are separated spatially instead of through the use of purge steps. This allows for high deposition rate and high throughput ALD without compromising the typical ALD assets. This paper gives a perspective of past and current developments in spatial ALD. The technology is discussed and the main players are identified. Furthermore, this overview highlights current as well as new applications for spatial ALD, with a focus on photovoltaics and flexible electronics.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.60.-q	Optoelectronic devices

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Atomic layer deposition for electrochemical energy generation and storage systems

Qing Peng, Jay S. Lewis, Paul G. Hoertz, Jeffrey T. Glass, and Gregory N. Parsons

J. Vac. Sci. Technol. A 30, 010803 (2012); http://dx.doi.org/10.1116/1.3672027 (14 pages) | Cited 7 times

Online Publication Date: 27 December 2011

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Clean renewable energy sources (e.g., solar, wind, and hydro) offers the most promising solution to energy and environmental sustainability. On the other hand, owing to the spatial and temporal variations of renewable energy sources, and transportation and mobility needs, high density energy storage and efficient energy distribution to points of use is also critical. Moreover, it is challenging to scale up those processes in a cost-effective way. Electrochemical processes, including photoelectrochemical devices, batteries, fuel cells, super capacitors, and others, have shown promise for addressing many of the abovementioned challenges. Materials with designer properties, especially the interfacial properties, play critical role for the performance of those devices. Atomic layer deposition is capable of precise engineering material properties on atomic scale. In this review, we focus on the current state of knowledge of the applications, perspective and challenges of atomic layer deposition process on the electrochemical energy generation and storage devices and processes.

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84.60.Ve	Energy storage systems, including capacitor banks
88.80.ff	Batteries
82.47.Jk	Photoelectrochemical cells, photoelectrochromic and other hybrid electrochemical energy storage devices

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Impact of CdSe/ZnS quantum dot spectrum converters on InGaP/GaAs/Ge multi-junction solar cells

Chun-Yuan Huang

J. Vac. Sci. Technol. A 30, 011201 (2012); http://dx.doi.org/10.1116/1.3673784 (3 pages)

Online Publication Date: 28 December 2011

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Multijunction solar cells (MJSCs) with a quantum dot (QD) spectrum converter have been proposed and studied to boost the device performance. Our QD spectrum converter consisted of a thin double side-polished sapphire substrate coated with a blue-emitting (λ_PL = 480 nm) CdSe/ZnS core/shell QD layer. To evaluate the effect of emission/re-absorption, the thickness of QD layer was modulated by adjusting the concentration of QD-toluene solution in spin-coat process. The quantum yield of the QD-toluene solution was about 88%. Considering the influence of QD concentration on the absorption/re-emission of incident light, the MJSCs could have better performance with the QD spectrum converter attached. With a 15-nm-thick QD spectrum converter attached, the short-circuit current density and power conversion efficiency of the MJSC were improved from 10.69 to 11.22 mA/cm² and from 22.29 to 23.41%, respectively. The possible reasons for the limited improvement were also proposed.

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88.40.jp	Multijunction solar cells
88.40.hj	Efficiency and performance of solar cells
88.40.jm	Thin film III-V and II-VI based solar cells

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Spatially resolved study of primary electron transport in magnetic cusps

Aimee A. Hubble and John E. Foster

J. Vac. Sci. Technol. A 30, 011301 (2012); http://dx.doi.org/10.1116/1.3656742 (9 pages)

Online Publication Date: 3 November 2011

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Spatially resolved primary electron current density profiles were measured using a planar Langmuir probe in the region above a magnetic cusp in a small ion thruster discharge chamber. The probe current maps obtained were used to study the electron collection mechanics in the cusp region in the limit of zero gas flow and no plasma production, and they allowed for the visualization of primary electron transport through the cusp. Attenuation coefficients and loss widths were calculated as a function of probe distance above the anode at various operating conditions. Finally, the collection mechanics between two magnetic cusps were studied and compared. It was found that primary electron collection was dominated by the upstream magnet ring.

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52.50.Dg	Plasma sources
52.70.Ds	Electric and magnetic measurements
51.50.+v	Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
52.80.-s	Electric discharges
05.60.-k	Transport processes

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Power effect of ZnO:Al film as back reflector on the performance of thin-film solar cells

Yang-Shih Lin, Shui-Yang Lien, Chao-Chun Wang, Chueh-Yang Liu, Asheesh Nautiyal, Dong-Sing Wuu, Pi-Chuen Tsai, Chia-Fu Chen, and Shuo-Jen Lee

J. Vac. Sci. Technol. A 30, 011302 (2012); http://dx.doi.org/10.1116/1.3667109 (5 pages)

Online Publication Date: 9 December 2011

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Aluminum-doped zinc oxide (AZO) is attracting interest as a potential transparent conducting oxide material for use in amorphous silicon (a-Si) thin-film solar cells. The absorption loss in the n-a-Si:H/Ag interface of the p-i-n thin film solar is high because the extinction coefficient of the Ag that is used as a back reflector is high. In this work, transparent conducting AZO films with a power in the range 500 W to 900 W prepared under Ar-ambient at a substrate temperature of 25 °C by RF-magnetron in-line sputtering. To minimize the absorption loss at longer wavelengths, an AZO layer we inserted at the n-a-Si:H/Ag interface of a solar cell with a glass/SnO₂:F/p-a-SiC:H/buffer-layer/i-a-Si:H/n-a-Si:H/Ag structure and the performance of the cell with AZO/Ag deposited instead of Ag on the back contact, was investigated. The effects of the RF-magnetron sputtering deposition parameters on the optical, electrical and structural properties of the AZO films were analyzed. Optimized AZO films with high transmittance (> 80%) and low resistivity (1.47 × 10⁻³ Ω-cm) in the wavelength range 400–800 nm were obtained under the sputtering conditions. The p-i-n a-Si solar cell with the AZO/Ag back contact had a conversion efficiency of 9.42%, which was higher than that (7.36%) of the cell without the AZO/Ag back contact. Light-soaking of these cells for 1000 h at 60 °C led to stabilization at 8.32% for the best cell. The relative typical efficiency degradation of about 10% for single-junction cells demonstrates that this treatment does not negatively influence stability.

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68.55.ag	Semiconductors
78.30.Fs	III-V and II-VI semiconductors
78.66.Hf	II-VI semiconductors
88.40.jj	Silicon solar cells
73.61.Ga	II-VI semiconductors
81.05.Dz	II-VI semiconductors

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Substrate grain size and orientation of Cu and Cu–Ni foils used for the growth of graphene films

Zachary R. Robinson, Parul Tyagi, Thomas M. Murray, Carl A. Ventrice, Jr., Shanshan Chen, Andrew Munson, Carl W. Magnuson, and Rodney S. Ruoff

J. Vac. Sci. Technol. A 30, 011401 (2012); http://dx.doi.org/10.1116/1.3663877 (7 pages) | Cited 6 times

Online Publication Date: 2 December 2011

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Graphene growth on Cu foils by catalytic decomposition of methane forms predominantly single-layer graphene films due to the low solubility of carbon in Cu. On the other hand, graphene growth on Cu–Ni foils can result in the controlled growth of few-layer graphene films because of the higher solubility of carbon in Ni. One of the key issues for the use of graphene grown by chemical vapor deposition for device applications is the influence of defects on the transport properties of the graphene. For instance, growth on metal foil substrates is expected to result in multidomain graphene growth because of the presence of grains within the foil that exhibit a variety of surface terminations. Therefore, the size and orientation of the grains within the metal foil should influence the defect density of the graphene. For this reason, we have studied the effect of total anneal time and temperature on the orientation and size of grains within Cu foils and Cu–Ni alloy foils with a nominal concentration of 90/10 by weight. The graphene growth procedure involves preannealing the foil in a H₂ background followed by the graphene growth in a CH₄/H₂ atmosphere. Measurements of the substrate grain size have been performed with optical microscopy and scanning electron microscopy. These results show typical lateral dimensions ranging from a few millimeters up to approximately a centimeter for Cu foils annealed at 1030 °C for 35 min and from tens of microns up to a few hundred microns for the 90/10 Cu–Ni foils annealed at 1050 °C for times ranging from 45 to 90 min. The smaller grains within the Cu–Ni foils are attributed to the higher melting point of the Cu–Ni alloy. The crystallographic orientation within each substrate grain was studied with electron backscatter diffraction, and shows that the preferred orientation for the Cu foil is primarily toward the (100) surface plane. For the 90/10 Cu–Ni foils, the orientation of the surface of the grains is initially toward the (110) plane and shifts into an orientation midway between the (100) and (111) planes as the anneal time is increased.

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68.55.ag	Semiconductors
61.48.Gh	Structure of graphene
81.05.ue	Graphene
68.55.A-	Nucleation and growth
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Ln	Defects and impurities: doping, implantation, distribution, concentration, etc.

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Energy calibrations in the x-ray absorption spectroscopy of uranium dioxide

Sung Woo Yu, J. G. Tobin, Paul Olalde-Velasco, Wan Li Yang, and Wigbert J. Siekhaus

J. Vac. Sci. Technol. A 30, 011402 (2012); http://dx.doi.org/10.1116/1.3670402 (8 pages) | Cited 4 times

Online Publication Date: 21 December 2011

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Proper and accurate placement of the components of the unoccupied density of states in uranium dioxide requires a careful calibration of the energy scales in the spectroscopic investigations. Here, the energy scale calibrations and corresponding spectroscopic measurements are described in detail, including photoelectron spectroscopy, inverse photoelectron spectroscopy and, most important, x-ray absorption spectroscopy.

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82.80.Ej	X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
82.80.Pv	Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm	Clean metal, semiconductor, and insulator surfaces
78.70.Dm	X-ray absorption spectra

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Probing compositional disorder in vanadium oxide thin films grown on atomic layer deposited hafnia on silicon by capacitance spectroscopy

Changhyun Ko, You Zhou, and Shriram Ramanathan

J. Vac. Sci. Technol. A 30, 011501 (2012); http://dx.doi.org/10.1116/1.3659020 (7 pages)

Online Publication Date: 10 November 2011

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The authors investigate capacitance-voltage characteristics of HfO₂/VO_x/HfO₂/n-Si metal-oxide semiconductor devices that include vanadium oxide (VO_x) films of different composition. Temperature dependent capacitance-voltage measurements are reported spanning the metal-insulator transition boundary of VO_x films. The measured trends in dielectric properties are cross-correlated with resistance ratio change and oxidation state in identical films. The results could be of relevance to advancing synthesis of correlated oxide films on dielectric layers and further utilizing capacitance spectroscopy as a way to probe oxide stoichiometry in gated heterostructures.

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85.30.Tv

Field effect devices

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Deposition of novel nanocomposite films by a newly developed differential pumping co-sputtering system

Masateru Nose, Takeshi Kurimoto, Atsushi Saiki, Kenji Matsuda, and Kiyoshi Terayama

J. Vac. Sci. Technol. A 30, 011502 (2012); http://dx.doi.org/10.1116/1.3659704 (7 pages)

Online Publication Date: 10 November 2011

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A differential pumping co-sputtering system was developed to facilitate a controlled, but flexible fabrication of multifunctional nanocomposite films with compositions not limited by thermodynamic restrictions. This system features a multichamber design with a differential pumping system. Dividing atmospheres with this set up greatly reduced the cross-contamination between chambers, and each material could be co-deposited by rapid rotation of the substrate. The clearance between the substrate holder and the chamber was set at 1–2 mm, and the conductance of the clearance was examined roughly using conductance equations for typical types of orifices. It was found that the potential difference (PD) value of the clearance between the two chambers was less than 0.01; the gas flow between the two chambers through the clearance thus appears to be a practical molecular flow. The PD value, where P is a pressure (Pa) and D is a diameter of an orifice or a pipe (m), is a gas flow indicator or parameter obtained from an equation of Knudsen number. The changes in the oxygen partial pressure and glow discharge plasma in the left chamber were investigated using a process gas monitor (PGM) and optical emission spectroscope (OES) by introducing different gases to each chamber. The PGM results revealed that the cross-contamination of oxygen from the other chamber was suppressed to 10 ± 3% of the original. In addition, the OES measurement for glow discharge plasma did not detect substantial oxygen contamination from the other chamber. Using the newly developed system, an AlN/SiO_x nanocomposite film consisting of B4-type AlN and amorphous SiO_x was obtained successfully.

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81.07.Bc	Nanocrystalline materials
81.15.Cd	Deposition by sputtering
52.80.Hc	Glow; corona
68.55.-a	Thin film structure and morphology

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Compact tool for deposition of composition spread alloy films

Deepika Priyadarshini, Petro Kondratyuk, James B. Miller, and Andrew J. Gellman

J. Vac. Sci. Technol. A 30, 011503 (2012); http://dx.doi.org/10.1116/1.3664078 (8 pages) | Cited 4 times

Online Publication Date: 29 November 2011

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Composition spread alloy films (CSAFs) are combinatorial materials libraries that contain broad, continuous composition ranges of binary or higher-order alloys on a single, compact substrate. When characterized for composition and functional properties using spatially resolved methods, CSAF libraries enable rapid determination of composition-property relationships across broad continuous regions of alloy composition space. In this report, we describe the design and operation of a novel offset filament deposition tool for preparation of CSAFs. The spatial distribution of individual alloy component fluxes to the substrate surface, and thus the film composition across the substrate, is controlled by the location and temperature of chemically distinct evaporative line sources. The tool can be used for quantitative deposition of thin (≤100 nm) CSAFs with up to four components. The authors demonstrate the performance of the tool by applying it to preparation of 100 nm thick Pd-Cu CSAFs, with lateral composition gradients that span the range Cu_0.05Pd_0.95 to Cu_0.95Pd_0.05, on a 12 mm diameter Mo(110) substrate.

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81.10.Bk	Growth from vapor
81.15.-z	Methods of deposition of films and coatings; film growth and epitaxy
82.80.-d	Chemical analysis and related physical methods of analysis
68.55.A-	Nucleation and growth
68.55.-a	Thin film structure and morphology

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Plasma etch characteristics of aluminum nitride mask layers grown by low-temperature plasma enhanced atomic layer deposition in SF₆ based plasmas

Alexander Perros, Markus Bosund, Timo Sajavaara, Mikko Laitinen, Lauri Sainiemi, Teppo Huhtio, and Harri Lipsanen

J. Vac. Sci. Technol. A 30, 011504 (2012); http://dx.doi.org/10.1116/1.3664306 (5 pages)

Online Publication Date: 5 December 2011

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The plasma etch characteristics of aluminum nitride (AlN) deposited by low-temperature, 200 °C, plasma enhanced atomic layer deposition (PEALD) was investigated for reactive ion etch (RIE) and inductively coupled plasma-reactive ion etch (ICP-RIE) systems using various mixtures of SF₆ and O₂ under different etch conditions. During RIE, the film exhibits good mask properties with etch rates below 10r nm/min. For ICP-RIE processes, the film exhibits exceptionally low etch rates in the subnanometer region with lower platen power. The AlN film’s removal occurred through physical mechanisms; consequently, rf power and chamber pressure were the most significant parameters in PEALD AlN film removal because the film was inert to the SFx+ and O⁺ chemistries. The etch experiments showed the film to be a resilient masking material. This makes it an attractive candidate for use as an etch mask in demanding SF₆ based plasma etch applications, such as through-wafer etching, or when oxide films are not suitable.

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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.ag	Semiconductors
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

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Comparison of wet and dry etching of zinc indium oxide for thin film transistors with an inverted gate structure

Michael A. Marrs, Bryan D. Vogt, and Gregory B. Raupp

J. Vac. Sci. Technol. A 30, 011505 (2012); http://dx.doi.org/10.1116/1.3668090 (6 pages)

Online Publication Date: 9 December 2011

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Not only are amorphous oxide semiconductor thin film transistors (TFTs) extremely sensitive to the processing of the active layer, but subsequent layer processing can also impact the performance. Due to this sensitivity, many surface treatments and passivation techniques for the active layer have been developed, but the influence of the etching of the active layer itself has not been explored extensively. These etch steps are especially critical in the manufacture of flexible microelectronics, for which process conditions are inherently limited by thermal stability of the plastic (<200 °C) and incompatibility of the plastic substrate with highly oxidizing chemical environments. Here, a novel dry etch process is compared to typical wet etch process in the context of flexible zinc indium oxide TFT array fabrication on plastic. The dry etch process provides superior control of the sidewall profile and the etch selectivity. These improvements using a dry etch approach decrease the off current of the TFT by 3 orders of magnitude from 2.65 nA for the wet etch process to 0.71 pA using the dry etch with a concurrent improvement in the device yield to 100% (for 120 transistors) with the dry etch. Additionally, the subthreshold slope improves from 1.9 to 1.0 V/decade, while the saturation mobility (6.5 cm²/V s) is not impacted by the etch process.

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85.30.Tv	Field effect devices
81.65.Cf	Surface cleaning, etching, patterning

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Transparent polycrystalline monoclinic HfO₂ dielectrics prepared by plasma assisted pulsed laser deposition

Zhifeng Ying, Jian Sun, Zhigao Hu, Wenlei Yu, Ning Xu, and Jiada Wu

J. Vac. Sci. Technol. A 30, 011506 (2012); http://dx.doi.org/10.1116/1.3673783 (6 pages)

Online Publication Date: 28 December 2011

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The electrical properties of transparent polycrystalline monoclinic HfO₂ dielectrics prepared by plasma assisted pulsed laser deposition were studied. The capacitance-voltage and leakage current-voltage characteristics of the capacitors incorporating HfO₂ dielectrics were examined in terms of the structural, optical properties of the HfO₂ layers. The interfacial properties between the HfO₂ layer and the Si substrate were also examined. The HfO₂ layers showed excellent thermal stability both in the HfO₂ structure and in the HfO₂/Si interface. The capacitance-voltage characteristics showed improvements through thermal annealing with a slight increase of leakage current. With an equivalent oxide thickness of 4.7 nm, the 700 °C annealed HfO₂ dielectrics had a dielectric constant of 16.5 and leakage current densities of 9.8 × 10⁻⁸ and 9.2 × 10⁻⁷ A/cm² at dielectric fields of +0.75 and −0.75 MV/cm, respectively.

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77.22.Ch	Permittivity (dielectric function)
81.15.Fg	Pulsed laser ablation deposition
81.40.Gh	Other heat and thermomechanical treatments
78.20.Ci	Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

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Effects of B₁₈H_x⁺ and B₁₈H_x dimer ion implantations on crystallinity and retained B dose in silicon

Yoji Kawasaki and Kentaro Shibahara

J. Vac. Sci. Technol. A 30, 011601 (2012); http://dx.doi.org/10.1116/1.3655892 (8 pages)

Online Publication Date: 27 October 2011

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The effects of B₁₈H_x⁺ and B₁₈H_x dimer ion (B₃₆H_y⁺) implantations on Si crystallinity and the retained B dose in Si were investigated using B₁₈H_x bombardment and compared with the effects of B⁺ implantation. Crystallinity was estimated for the implantation dose using molecular dynamic simulations (MDSs) and was quantified using the optical thickness obtained from spectroscopic ellipsometry. The authors focused on the crystallinity at a low B dose and compared the amorphized zones predicted by MDS for B₁₈H_x⁺ implantation with those measured using transmission electron microscopy; the predicted and measured results were in reasonable agreement. The authors then used their understanding of B₁₈H_x bombardment to discuss the process for the generation of larger amorphized zones and thicker amorphized layers, as observed in B₃₆H_y⁺ implantation. The retained B dose and the sputtering were examined with secondary ion mass spectroscopy, focusing on a comparison of the retained B and the sputtering of Si and SiO₂ surfaces. The retained B dose was lower for B₁₈H_x⁺ and B₃₆H_y⁺ implantations, with and without surface SiO₂, than for B⁺ implantation, although no sputtering was observed. The reduction of the retained B dose was more severe in the samples with SiO₂. The origin of the differences between Si and SiO₂ surfaces was considered to be Si melting; this was predicted by the MDSs, and observed indirectly as flat B profiles in the Si region. To examine the effects of both crystallinity and retained B dose on the electrical characteristics, the sheet resistance (R_S) was measured. The R_S for B₁₈H_x⁺ implantation was lower than that for B⁺ implantation at both B doses studied. Additionally, the B₃₆H_y⁺ implantation under conditions that produced a thicker amorphized layer led to lower R_S than B₁₈H_x⁺ implantation. These results indicate that both the amorphized layer and the amorphized zone contribute to the activation of more B atoms.

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61.72.U-	Doping and impurity implantation
07.60.Fs	Polarimeters and ellipsometers
07.75.+h	Mass spectrometers
61.43.Bn	Structural modeling: serial-addition models, computer simulation
79.20.Rf	Atomic, molecular, and ion beam impact and interactions with surfaces
85.40.Ry	Impurity doping, diffusion and ion implantation technology

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Thin-film electronics by atomic layer deposition

David H. Levy and Shelby F. Nelson

J. Vac. Sci. Technol. A 30, 018501 (2012); http://dx.doi.org/10.1116/1.3670748 (9 pages) | Cited 7 times

Online Publication Date: 14 December 2011

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Atomic layer deposition (ALD) produces conformal films with low defects and a high degree of thickness control. Many applications leverage these properties to yield excellent dielectrics and barrier layers. In recent years, ALD has been exploited to produce thin-film transistors, in which the technique is capable of producing all of the layers required, including the semiconductor. This perspective will examine the state-of-the-art use of ALD to produce thin-film electronics, notably the zinc oxide-based thin-film transistor. It is critical that the ZnO-based semiconductor material have sufficiently high resistivity in order to yield transistors with low off current and good switching characteristics. The nature of this problem and the approaches used to address it will be discussed. The use of rapid deposition technologies, such as spatial ALD, also has a strong impact on the quality of the ZnO semiconductor. Finally, demonstrations of various thin film electronics devices and systems produced by ALD will be reviewed.

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85.30.Tv	Field effect devices
85.40.Sz	Deposition technology

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Reaction mechanisms of atomic layer deposition of TaN_x from Ta(NMe₂)₅ precursor and H₂-based plasmas

H. C. M. Knoops, E. Langereis, M. C. M. van de Sanden, and W. M. M. Kessels

J. Vac. Sci. Technol. A 30, 01A101 (2012); http://dx.doi.org/10.1116/1.3625565 (10 pages) | Cited 1 time

Online Publication Date: 26 August 2011

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The reaction mechanisms of plasma-assisted atomic layer deposition (ALD) of TaN_x using Ta(NMe₂)₅ were studied using quadrupole mass spectrometry (QMS). The fact that molecule dissociation and formation in the plasma have to be considered for such ALD processes was illustrated by the observation of 4% NH₃ in a H₂-N₂ (1:1) plasma. Using QMS measurements the reaction products during growth of conductive TaN_x using a H₂ plasma were determined. During the Ta(NMe₂)₅ exposure the reaction product HNMe₂ was detected. The amount of adsorbed Ta(NMe₂)₅ and the amount of HNMe₂ released were found to depend on the number of surface groups generated during the plasma step. At the beginning of the plasma exposure step the molecules HNMe₂, CH₄, HCN, and C₂H₂ were measured. After an extended period of plasma exposure, the reaction products CH₄ and C₂H₂ were still present in the plasma. This change in the composition of the reaction products can be explained by an interplay of aspects including the plasma-surface interaction, the ALD surface reactions, and the reactions of products within the plasma. The species formed in the plasma (e.g., CH_x radicals) can re-deposit on the surface and influence to a large extent the TaN_x material composition and properties.

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68.55.ag	Semiconductors
52.77.-j	Plasma applications
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

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Nucleation delay in atomic layer deposition on a thin organic layer and the role of reaction thermochemistry

Kevin J. Hughes and James R. Engstrom

J. Vac. Sci. Technol. A 30, 01A102 (2012); http://dx.doi.org/10.1116/1.3625564 (14 pages) | Cited 1 time

Online Publication Date: 1 September 2011

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The atomic layer deposition (ALD) of a series of inorganic thin films on an interfacial organic layer has been examined, focusing on the existence of a delay in thin film nucleation and its dependence on the chemistry of each ALD reaction. The inorganic thin films examined were Al₂O₃, HfO₂, Ta₂O₅, and TaN_x, while the organic layer was a thin (∼5 Å thick) film of poly(ethylene imine), or PEI, on SiO₂. The early stages (<50 ALD cycles) of inorganic thin film growth in each case have been characterized using a combination of surface-sensitive techniques including ellipsometry, x-ray photoelectron spectroscopy, and atomic force microscopy. PEI has the effect of attenuating growth to different degrees depending on the subsequently grown ALD thin film, leading to no attenuation of growth for Al₂O₃, but significant incubation periods, in increasing order, for Ta₂O₅, HfO₂ and TaN_x. Angle-resolved x-ray photoelectron spectroscopy of an Al₂O₃ thin film deposited on PEI|SiO₂ demonstrates that, in this case, the PEI thin film is buried between the Al₂O₃ thin film and the SiO₂ substrate, with no significant decrease in the density of nitrogen from the as deposited PEI film. Results from the HfO₂ and the Ta-containing thin films indicate that the processes that lead to the attenuation of growth are associated mostly with the second half-cycle of ALD (H₂O or NH₃ exposure). The length of the incubation time is found to correlate with both the total enthalpy change of the overall ALD reaction, as well as the net internal energy change of a single ligand exchange reaction representative of the second half of the ALD reaction. These results suggest that the reaction thermochemistry, and activation barriers for the reactions involved the ALD process play a key role in determining the length of the incubation period caused by PEI.

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68.55.aj	Insulators
79.60.Dp	Adsorbed layers and thin films
81.15.-z	Methods of deposition of films and coatings; film growth and epitaxy
82.60.Cx	Enthalpies of combustion, reaction, and formation
68.35.B-	Structure of clean surfaces (and surface reconstruction)

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Scalability of plasma enhanced atomic layer deposited ruthenium films for interconnect applications

J. Swerts, S. Armini, L. Carbonell, A. Delabie, A. Franquet, S. Mertens, M. Popovici, M. Schaekers, T. Witters, Z. Tökei, G. Beyer, S. Van Elshocht, V. Gravey, A. Cockburn, K. Shah, et al.

J. Vac. Sci. Technol. A 30, 01A103 (2012); http://dx.doi.org/10.1116/1.3625566 (6 pages) | Cited 2 times

Online Publication Date: 2 September 2011

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Ru thin films were deposited by plasma enhanced atomic layer deposition using MethylCyclopentadienylPyrrolylRuthenium (MeCpPy)Ru and N₂/NH₃ plasma. The growth characteristics have been studied on titanium nitride or tantalum nitride substrates of various thicknesses. On SiO₂, a large incubation period has been observed, which can be resolved by the use of a metal nitride layer of ∼ 0.8 nm. The growth characteristics of Ru layers deposited on ultra-thin metal nitride layers are similar to those on thick metal nitride substrates despite the fact that the metal nitride layers are not fully closed. Scaled Ru/metal nitride stacks were deposited in narrow lines down to 25 nm width. Thinning of the metal nitride does not impact the conformality of the Ru layer in the narrow lines. For the thinnest lines the Ru deposited on the side wall showed a more granular structure when compared to the bottom of the trench, which is attributed to the plasma directionality during the deposition process.

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81.05.Bx	Metals, semimetals, and alloys
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq	Plasma-based ion implantation and deposition

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Charge trapping characteristics of Au nanocrystals embedded in remote plasma atomic layer-deposited Al₂O₃ film as the tunnel and blocking oxides for nonvolatile memory applications

Jaesang Lee, Hyungchul Kim, Taeyong Park, Youngbin Ko, Jaehun Ryu, Heeyoung Jeon, Jingyu Park, and Hyeongtag Jeon

J. Vac. Sci. Technol. A 30, 01A104 (2012); http://dx.doi.org/10.1116/1.3639131 (6 pages) | Cited 1 time

Online Publication Date: 16 September 2011

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Remote plasma atomic layer deposited (RPALD) Al₂O₃ films were investigated to apply as tunnel and blocking layers in the metal-oxide-semiconductor capacitor memory utilizing Au nanocrystals (NCs) for nonvolatile memory applications. The interface stability of an Al₂O₃ film deposited by RPALD was studied to observe the effects of remote plasma on the interface. The interface formed during RPALD process has high oxidation states such as Si⁺³ and Si⁺⁴, indicating that RPALD process can grow more stable interface which has a small amount of fixed oxide trap charge. The significant memory characteristics were also observed in this memory device through the electrical measurement. The memory device exhibited a relatively large memory window of 5.6 V under a 10/−10 V program/erase voltage and also showed the relatively fast programming/erasing speed and a competitive retention characteristic after 10⁴ s. These results indicate that Al₂O₃ films deposited via RPALD can be applied as the tunnel and blocking oxides for next-generation flash memory devices.

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81.07.Bc	Nanocrystalline materials
68.55.aj	Insulators
52.77.Dq	Plasma-based ion implantation and deposition
73.40.Gk	Tunneling
73.61.Ng	Insulators

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Wetting properties induced in nano-composite POSS-MA polymer films by atomic layer deposited oxides

Kyle A. Vasquez, Anita J. Vincent-Johnson, W. Christopher Hughes, Brian H. Augustine, Kyoungmi Lee, Gregory N. Parsons, and Giovanna Scarel

J. Vac. Sci. Technol. A 30, 01A105 (2012); http://dx.doi.org/10.1116/1.3639134 (6 pages) | Cited 2 times

Online Publication Date: 20 September 2011

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Due to their unique properties, nano-composite polyhedral oligomeric silsequioxane (POSS) copolymer films are attractive for various applications. Here we show that their natural hydrophobic character can become hydrophilic when the films are modified by a thin oxide layer, up to 8 nm thick, prepared using atomic layer deposition. A proper choice of the deposition temperature and thickness of the oxide layer are required to achieve this goal. Unlike other polymeric systems, a marked transition to a hydrophilic state is observed with oxide layers deposited at increasing temperatures up to the glass transition temperature (∼110 °C) of the POSS copolymer film. The hydrophilic state is monitored through the water contact angle of the POSS film. Infrared absorbance spectra indicate that, in hydrophilic samples, the integral of peaks corresponding to surface Al–O (hydrophilic) is significantly larger than that of peaks linked to hydrophobic species.

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68.08.Bc	Wetting
78.30.Jw	Organic compounds, polymers
78.66.Qn	Polymers; organic compounds
78.66.Sq	Composite materials
64.70.pj	Polymers
68.55.am	Polymers and organics

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Study of amorphous lithium silicate thin films grown by atomic layer deposition

Jani Hämäläinen, Frans Munnik, Timo Hatanpää, Jani Holopainen, Mikko Ritala, and Markku Leskelä

J. Vac. Sci. Technol. A 30, 01A106 (2012); http://dx.doi.org/10.1116/1.3643349 (5 pages) | Cited 4 times

Online Publication Date: 27 September 2011

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Lithium silicate thin films, which are interesting materials for example in lithium ion batteries, were grown by the atomic layer deposition technique from lithium hexamethyldisilazide [LiHMDS, Li(N(SiMe₃)₂)] and ozone precursors. Films were obtained at a wide deposition temperature range between 150 and 400 °C. All the films were amorphous except at 400 °C, where partial decomposition of LiHMDS was also observed. The growth behavior was examined in detail at 250 °C, and saturation of growth rates and refractive indices with precursor doses was confirmed, thereby verifying self-limiting surface reactions. Likewise, the linear thickness dependence of the films with the number of deposition cycles was verified. Strong dependence of growth rate and film composition on deposition temperature was also seen. Overall, the amorphous films grown at 250 °C had a stoichiometry close to lithium metasilicate (Li_2.0SiO_2.9) with 0.7 at. % carbon and 4.6 at. % hydrogen impurities. The corresponding growth rate and refractive index (n₅₈₀) were 0.8 Å/cycle and about 1.55.

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68.55.aj	Insulators
68.55.Nq	Composition and phase identification
78.20.Ci	Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Nk	Insulators
61.66.Bi	Elemental solids
61.66.Dk	Alloys
82.65.+r	Surface and interface chemistry; heterogeneous catalysis at surfaces

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Combination of characterization techniques for atomic layer deposition MoO₃ coatings: From the amorphous to the orthorhombic α-MoO₃ crystalline phase

Madeleine Diskus, Ola Nilsen, Helmer Fjellvåg, Spyros Diplas, Pablo Beato, Clare Harvey, Evelien van Schrojenstein Lantman, and Bert M. Weckhuysen

J. Vac. Sci. Technol. A 30, 01A107 (2012); http://dx.doi.org/10.1116/1.3643350 (6 pages)

Online Publication Date: 29 September 2011

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Thin films of MoO₃ deposited on Si(111) and Al₂O₃(001) substrates by atomic layer deposition have been investigated by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and Raman spectroscopy for detailed characterization of composition and morphology. Comparison of angle resolved x-ray photoelectron spectroscopy (ARXPS) and XPS depth profiles based on Ar⁺ sputtering is reported. Sputtering induces a reduction of molybdenum in MoO₃ from +IV to metallic Mo as the interface toward Si is approached, whereas ARXPS on a 10 nm thin film shows that Mo(VI) remains outside the interface toward Si where lower valent molybdenum compounds are formed. Upon annealing, the as-deposited amorphous thin films of MoO₃ crystallize into β- or α-MoO₃ as identified by x-ray diffraction. The current study provides a convenient route toward formation of metastable β-MoO₃ and a full crystallization pathway from amorphous to crystalline α-MoO₃. Combined AFM and Raman analysis have been performed on thin films of α-MoO₃ deposited on Al₂O₃(001) and prove that the crystallization proceeds via island growth at 600 °C. The Raman intensity ratios between different bands depend strongly on morphology and size of crystalites.

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64.70.K-	Solid-solid transitions
68.55.aj	Insulators
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Xy	Scanning Auger microscopy, photoelectron microscopy
78.30.Hv	Other nonmetallic inorganics
81.30.Hd	Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

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Nanocoating zinc alkoxide (zincone) hybrid polymer films on particles using a fluidized bed reactor

Xinhua Liang, Ying-Bing Jiang, and Alan W. Weimer

J. Vac. Sci. Technol. A 30, 01A108 (2012); http://dx.doi.org/10.1116/1.3644952 (6 pages) | Cited 2 times

Online Publication Date: 3 October 2011

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Ultrathin zinc alkoxide (zincone) hybrid polymer films were coated on large quantities of primary titania nanoparticles using molecular layer deposition (MLD) in a fluidized bed reactor. Diethyl zincand ethylene glycol were used as reactants at a reaction temperature of 80 or 120 °C. The composition and conformal zincone films were confirmed by x-ray photoelectron spectroscopy and TEM, respectively. The growth rate was higher at a lower reaction temperature. Primary nanoparticles were coated individually despite their strong tendency to aggregate during fluidization. Porous zinc oxide was formed by the oxidation of the hybrid zincone films in air at 400 °C. The surface area of the porous film itself was ∼40 m²/g for the MLD films after oxidation at 250 °C, and 31 m²/g for the films after oxidation at 400 °C. Methylene blue oxidation tests indicated that the zincone MLD film can reduce the photoactivity of TiO₂ particles, but the passivation effect of the aged zincone films decreased due to the decomposition of zincone in the presence of water at room temperature to form a more stable composite containing zinc. The passivation effect of the oxidized zincone films further decreased due to the nonuniformity of the zinc oxide films after crystallization during the oxidation process.

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68.55.A-	Nucleation and growth
61.41.+e	Polymers, elastomers, and plastics
68.55.am	Polymers and organics
61.46.Df	Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.35.Np	Nanoparticles in polymers
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

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Plasma and vacuum ultraviolet induced charging of SiO₂ and HfO₂ patterned structures

J. L. Lauer, G. S. Upadhyaya, H. Sinha, J. B. Kruger, Y. Nishi, and J. L. Shohet

J. Vac. Sci. Technol. A 30, 01A109 (2012); http://dx.doi.org/10.1116/1.3654012 (6 pages) | Cited 1 time

Online Publication Date: 25 October 2011

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The authors compare the effects of plasma charging and vacuum ultraviolet (VUV) irradiation on oxidized patterned Si structures with and without atomic-layer-deposited HfO₂. It was found that, unlike planar oxidized Si wafers, oxidized patterned Si wafers charge up significantly after exposure in an electron-cyclotron resonance plasma. The charging is dependent on the aspect ratio of the patterned structures. This is attributed to electron and/or ion shading during plasma exposure. The addition of a 10 nm thick HfO₂ layer deposited on top of the oxidized silicon structures increases the photoemission yield during VUV irradiation, resulting in more trapped positive charge compared to patterns without the HfO₂ dielectric.

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61.80.Ba	Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms	Insulators
76.40.+b	Diamagnetic and cyclotron resonances
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.25.Os	Emission, absorption, and scattering of electromagnetic radiation

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Use of a high-flow diaphragm valve in the exhaust line of atomic layer deposition reactors

Neil P. Dasgupta, Orlando Trejo, and Fritz B. Prinz

J. Vac. Sci. Technol. A 30, 01A110 (2012); http://dx.doi.org/10.1116/1.3656945 (5 pages) | Cited 2 times

Online Publication Date: 25 October 2011

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In many atomic layer deposition (ALD) reactors, a stop valve is placed between the reaction chamber and the vacuum pump to allow for long precursor exposure times. This valve can lead to a reduction in conductance to the pump, lowering pumping efficiency and increasing the required purging time. In this study, a prototype high-flow (flow coefficient C_v = 1.7) diaphragm valve designed for ALD compatibility was inserted into the exhaust line of an ALD reactor and compared to a standard ALD diaphragm valve (C_v = 0.62). The results show that the chamber base pressure was reduced by 66% with the high-flow valve, which has implications for precursor delivery and mass transport. Furthermore, ZnO films were deposited via ALD, and the variation in thickness across a 100 mm diameter Si wafer was shown to be lower for the high-flow valve, especially with short purging times. These results suggest that the use of a high-flow ALD valve in the exhaust line can be beneficial when attempting to reduce the purging time and improve uniformity in research-scale reactors, and it could eventually be utilized in larger production-scale reactors.

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07.30.Cy	Vacuum pumps
81.05.Dz	II-VI semiconductors
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

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Temperature induced changes in a AgPt nanofilm on Ru(0001)

Jens Onsgaard, P. Jan Godowski, and Zhe Shen Li

J. Vac. Sci. Technol. A 30, 01A111 (2012); http://dx.doi.org/10.1116/1.3653986 (7 pages)

Online Publication Date: 27 October 2011

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Nanometer thick AgPt films deposited in a layer-by-layer fashion onto Ru(0001) at room temperature (RT) were investigated using high-resolution photoelectron spectroscopy. A four layer film, Pt(1)Ag(1)Pt(1)Ag(1)/Ru(0001), with one monolayer of Ag as the first deposited material on Ru(0001), shows a small intermixing of Ag and Pt during deposition at RT. The Pt4f_7/2 spectra exhibit the most pronounced core level shifts during heating; an effect caused by clustering of Pt inside the film. No alloying of Ag and Pt is observed. This behavior is in contrast to that of analog AgPd films on Ru(0001) where alloying takes place. Annealing of the layered AgPt film in the temperature interval of RT to 625 °C results in the segregation of Ag at the surface and a complete desorption of Ag takes place at 625 °C.

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68.55.-a	Thin film structure and morphology
79.60.Jv	Interfaces; heterostructures; nanostructures
81.40.Gh	Other heat and thermomechanical treatments
68.43.Nr	Desorption kinetics
61.46.-w	Structure of nanoscale materials
68.47.Pe	Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

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Thermal chemistry of Mn₂(CO)₁₀ during deposition of thin manganese films on silicon oxide and on copper surfaces

Xiangdong Qin, Huaxing Sun, and Francisco Zaera

J. Vac. Sci. Technol. A 30, 01A112 (2012); http://dx.doi.org/10.1116/1.3658373 (10 pages) | Cited 7 times

Online Publication Date: 3 November 2011

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The surface chemistry of dimanganese decacarbonyl on the native oxide of Si(100) wafers was characterized with the aid of x-ray photoelectron spectroscopy. Initial experiments in a small stainless-steel reactor identified a narrow range of temperatures, between approximately 445 and 465 K, in which the deposition of manganese could be achieved in a self-limiting fashion, as is desirable for atomic layer deposition. Deposition at higher temperatures leads to multilayer growth, but the extent of this Mn deposition reverses at even higher temperatures (about 625 K), and also ifhydrogen is added to the reaction mixture. Extensive decarbonylation takes place below room temperature, but limited C–O bond dissociation and carbon deposition are still seen after high exposures at 625 K. The films deposited at low (∼450 K) temperatures are mostly in the form of MnO, but at 625 K that converts to a manganese silicate, and upon higher doses a manganese silicide forms at the SiO₂/Si(100) interface as well. No metallic manganese could be deposited with this precursor on either silicon dioxide or copper surfaces.

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82.65.+r	Surface and interface chemistry; heterogeneous catalysis at surfaces
82.80.Pv	Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Dp	Adsorbed layers and thin films
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

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Impact of electrode roughness on metal-insulator-metal tunnel diodes with atomic layer deposited Al₂O₃ tunnel barriers

Nasir Alimardani, E. William Cowell, III, John F. Wager, John F. Conley, Jr., David R. Evans, Matthew Chin, Stephen J. Kilpatrick, and Madan Dubey

J. Vac. Sci. Technol. A 30, 01A113 (2012); http://dx.doi.org/10.1116/1.3658380 (5 pages) | Cited 3 times

Online Publication Date: 3 November 2011

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Metal-insulator-metal (MIM) tunnel diodes on a variety of high and low work function metals with various levels of root-mean-square roughness are fabricated using high quality atomic layer deposited Al₂O₃ as the insulating tunnel barrier. It is found that electrode surface roughness can dominate the current versus voltage characteristics of MIM diodes, even overwhelming the impact of metal work function. Devices with smoother bottom electrodes are found to produce current versus voltage behavior with higher asymmetry and better agreement with Fowler-Nordheim tunneling theory, as well as a greater percentage of functioning devices.

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85.30.Mn	Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.Tv	Field effect devices
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

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Thermal chemistry of copper(I)-N,N ′-di-sec-butylacetamidinate on Cu(110) single-crystal surfaces

Qiang Ma, Francisco Zaera, and Roy G. Gordon

J. Vac. Sci. Technol. A 30, 01A114 (2012); http://dx.doi.org/10.1116/1.3658381 (10 pages) | Cited 4 times

Online Publication Date: 3 November 2011

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The surface chemistry of copper(I)-N,N′-di-sec-butylacetamidinate on Cu(110) single-crystal surfaces has been characterized under ultrahigh vacuum by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy. A series of thermal stepwise conversions were identified, starting with the partial dissociative adsorption of the copper acetamidinate dimers into a mixture of monomers and dimers on the surface. An early dissociation of a C–N bond leads to the production of N-sec-butylacetamidine, which is detected in TPD experiments in three temperature regimes, the last one centered around 480 K. Butene, and a small amount of butane, is also detected above approximately 500 K, and hydrogen production, an indication of dehydrogenation of surface fragments, is observed at 460, 550 and 670 K. In total, only about 10% of the initial copper(I)-N,N′-di-sec-butylacetamidinate adsorbed monolayer decomposes, and only about ∼3% of carbon is left behind on the surface after heating to high temperatures. The implications of this surface chemistry to the design of chemical film growth processes using copper acetamidinates as precursors are discussed.

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68.43.Vx	Thermal desorption
79.60.Dp	Adsorbed layers and thin films
82.30.Lp	Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.80.Pv	Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
88.30.E-	Hydrogen production with renewable energy
68.43.Mn	Adsorption kinetics

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Conformality of remote plasma-enhanced atomic layer deposition processes: An experimental study

Maarit Kariniemi, Jaakko Niinistö, Marko Vehkamäki, Marianna Kemell, Mikko Ritala, Markku Leskelä, and Matti Putkonen

J. Vac. Sci. Technol. A 30, 01A115 (2012); http://dx.doi.org/10.1116/1.3659699 (5 pages)

Online Publication Date: 11 November 2011

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In total, five metal oxide and one metal plasma-enhanced atomic layer deposition (PEALD) processes were studied with respect to the conformality of the coatings. The study reveals that also high aspect ratio structures (up to 60:1) can be coated conformally with remote PEALD. Oxides could relatively easily be deposited into demanding 3D structures with rather short cycle times but not the silver metal. The key factor in achieving excellent conformality seems to be that sufficient radical density is required to overcome the loss of radicals by recombination. In the case of metals where hydrogen plasma is applied the recombination of hydrogen radicals causes major difficulties in obtaining perfect conformality.

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52.77.Dq	Plasma-based ion implantation and deposition
81.15.Jj	Ion and electron beam-assisted deposition; ion plating
81.15.Kk	Vapor phase epitaxy; growth from vapor phase
68.55.at	Other materials

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Core-shell nanowire arrays of metal oxides fabricated by atomic layer deposition

M. A. Thomas and J. B. Cui

J. Vac. Sci. Technol. A 30, 01A116 (2012); http://dx.doi.org/10.1116/1.3660389 (7 pages) | Cited 3 times

Online Publication Date: 11 November 2011

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Atomic layer deposition (ALD) has proven to be an excellent candidate for the deposition of thin layers onto various nanostructures to create core-shell structures with new functionalities and improved device application potential. The authors have used ALD to fabricate metal oxide core-shell nanowires based on electrodeposited ZnO nanowire arrays and Al₂O₃, ZnO, and TiO₂ shells. The authors observe distinctive features of the core-shell nanowires induced by the shell coatings. Most notably, the photoluminescence of the nanowire cores can be enhanced or depleted by the shell, depending on the choice of shell material. Specifically, ZnO–Al₂O₃ core-shell nanowires display improved optical characteristics over their bare ZnO nanowire core equivalents. These results have important implications for related optoelectronics based on ZnO nanowires or their core-shell nanostructures.

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81.07.Gf	Nanowires
81.16.-c	Methods of micro- and nanofabrication and processing
78.55.Et	II-VI semiconductors
81.15.Pq	Electrodeposition, electroplating
82.45.Qr	Electrodeposition and electrodissolution
78.67.Uh	Nanowires

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Paper deacidification and UV protection using ZnO atomic layer deposition

C. A. Hanson, C. J. Oldham, and G. N. Parsons

J. Vac. Sci. Technol. A 30, 01A117 (2012); http://dx.doi.org/10.1116/1.3656251 (5 pages) | Cited 1 time

Online Publication Date: 15 November 2011

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Acid degradation of cellulosic paper in archival books, periodicals, and historic documents is a serious and widespread problem. Using acidic page samples from ∼40 year old books, we demonstrate that atomic layer deposition (ALD) ZnO can adjust and controllably neutralize the paper acid content. The paper samples were collected and analyzed in accordance with recognized Technical Association of the Pulp and Paper Industry (TAPPI) test standards. The average pH of the starting paper was 3.7 ± 0.4 and 4.4 ± 0.1 as determined using the TAPPI surface probe and cold water extraction methods, respectively. After 50 ALD ZnO cycles, the same tests on the coated paper produced an average pH of 7.39 ± 0.08 and 7.3 ± 0.4, respectively. Scanning electron microscopy confirmed that the cellulose structure remained intact during ALD. Additional tests of recently printed newspaper samples coated with ALD ZnO also show that ALD can effectively prevent paper discoloration and embrittlement caused by UV sunlight photoexposure. While there are many known methods for paper preservation, including others using diethyl zinc, the control afforded by ALD provides attractive advantages over other known approaches for preservation of archival paper and other natural fibrous materials.

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89.20.Kk

Engineering

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Effect of pulsed deposition of Al₂O₃ for native oxides reduction of GaAs by atomic layer deposition technique

R. B. Konda, R. Mundle, O. Bamiduro, H. Dondapati, M. Bahoura, A. K. Pradhan, and C. Donley

J. Vac. Sci. Technol. A 30, 01A118 (2012); http://dx.doi.org/10.1116/1.3662862 (4 pages) | Cited 1 time

Online Publication Date: 21 November 2011

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The reduction of native oxides on GaAs substrates is studied by predeposition cleaning as well as by short time pulsing of the metal precursor for the self-cleaning mechanism using atomic layer deposition (ALD) of trimethyl aluminum (TMA). The role of the predeposition cleaning followed by ALD application has significant effects in restraining the regrowth of native oxides. The short time pulsing of the TMA is effective for the self-cleaning mechanism to reduce the intensity of GaAs native oxides. The reduction in native oxides on GaAs surface during ALD of TMA was investigated using x-ray photoelectron spectroscopy. X-ray photoelectron studies demonstrated that the pulsed deposition of TMA in the range of 2 to 4 s is the most effective way of cleaning the GaAs native oxides. Our studies demonstrate a full proof self-cleaning process for GaAs wafers for any potential applications.

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81.65.Cf	Surface cleaning, etching, patterning
68.55.ag	Semiconductors
79.60.Bm	Clean metal, semiconductor, and insulator surfaces
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

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Evaluation of high thermal stability cyclopentadienyl Hf precursors with H₂O as a co-reactant for advanced gate logic applications

Steven Consiglio, Robert D. Clark, Genji Nakamura, Cory S. Wajda, and Gert J. Leusink

J. Vac. Sci. Technol. A 30, 01A119 (2012); http://dx.doi.org/10.1116/1.3664106 (5 pages) | Cited 1 time

Online Publication Date: 22 November 2011

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For the purpose of extending the upper temperature limit of metallorganic atomic layer deposition, mixed ligand precursors containing cyclopentadienyl (Cp, C₅H₅) ligands have been shown to exhibitsuperior thermal stability compared to the widely adopted tetrakis(ethylmethylamino)hafnium (TEMAH) precursor while also possessing adequate vapor pressure characteristics for use in atomic layer deposition (ALD) processing. In order to prevent the deleterious oxidation of the underlying Si from O₃ the use of a milder oxidant such as H₂O is preferred. Accordingly in this study, we investigated ALD using the liquid precursors CpHf(NMe₂)₃ and (CpMe)₂Hf(OMe)Me in the temperature range 305 – 410 °C with H₂O as a co-reactant and compared the film growth and electrical properties with films deposited using a conventional TEMAH/H₂O process at 305 °C as well as the same process with an optimized annealing scheme. The CpHf(NMe₂)₃/H₂O process was observed toexhibit a growth-per-cycle (GPC) in the range 0.23 – 0.36 Å/cycle which is roughly half that of the TEMAH/H₂O process (∼0.6 Å/cycle). In the 340 – 375 °C range this process is comparable toTEMAH/H₂O in terms of equivalent oxide thickness but with slightly higher leakage. Even thoughthis process allows for higher processing temperatures it is not able to scale to the level of theTEMAH/H₂O process using an optimized annealing scheme. For (CpMe)₂Hf(OMe)Me withH₂O,in the process space investigated in this study this process was unable to afford a viable growth rate (<0.03 Å/cycle) for device testing although a GPC of 0.33 Å/cycle was obtained using O₃.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Gh	Other heat and thermomechanical treatments
84.30.Sk	Pulse and digital circuits
68.55.aj	Insulators
68.60.Dv	Thermal stability; thermal effects

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Impact of precursor chemistry on atomic layer deposition of lutetium aluminates

Laura Nyns, Xiaoping Shi, Hilde Tielens, Sven Van Elshocht, Lucien Date, and Robert Schreutelkamp

J. Vac. Sci. Technol. A 30, 01A120 (2012); http://dx.doi.org/10.1116/1.3662838 (6 pages)

Online Publication Date: 23 November 2011

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Rare earth-based oxides are of interest for their potential application in future logic high-performance technologies where Germanium is the channel material. In addition, their aluminates are considered as promising high-k dielectrics for nonvolatile memory technologies. However, it has been found that the dielectric quality of these materials is highly dependent on the method of preparation. The authors have therefore examined the atomic layer deposition (ALD) of Lu_xAl_2−xO₃ layers by means of Tris(isopropyl cyclopentadienyl) Lutetium (Lu(ⁱPrCp)₃), Tris(diethyl-amido)aluminum and H₂O or O₃ in a nanolaminate approach. This manuscript covers the impact of the oxidizer on both the ALD process characteristics and Lu_xAl_2−xO₃ layer properties. Because of the hygroscopic nature of rare earth oxides, the O₃-based ALD of Lu_xAl_2−xO₃ is well controlled compared to the H₂O-based process. On the other hand, Lu_xAl_2−xO₃ dielectrics grown with H₂O as the oxidizer show better electrical properties in terms of Equivalent Oxide Thickness (EOT) and leakage current density because of lower C impurities, especially in case of Lu-rich compositions.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.55.D-	High-permittivity gate dielectric films

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Molecular layer deposition of polyethylene terephthalate thin films

Tatyana V. Ivanova, Philipp S. Maydannik, and David C. Cameron

J. Vac. Sci. Technol. A 30, 01A121 (2012); http://dx.doi.org/10.1116/1.3662846 (5 pages) | Cited 3 times

Online Publication Date: 23 November 2011

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Thin films of polyethylene terephthalate (PET) have been grown using sequential surface chemical reactions on silicon substrates. The surface has been sequentially exposed to terephthaloyl chloride (TC) and ethylene glycol (EG) in an ASM F-120 atomic layer deposition reactor. Precursor pulses were alternated with 30 s of N₂ purge. The process has been studied as a function of temperature, precursor pulsing time, and number of cycles. The films were deposited in the temperature range 145–175 °C and the precursors were held at 130 °C (TC) and 70 °C (EG). Before deposition the silicon surface was functionalized using 3-aminopropyltriethoxysilane to ensure nucleation of the film. The film growth exhibits self-limiting behavior and linear growth rate dependence that confirms its molecular layer deposition nature. The deposited films have been identified as PET by means of attenuated total reflectance FTIR which reveals the presence of characteristic carbonyl and aromatic groups. Film thickness was measured by spectroscopic ellipsometry. The maximum deposition rate of 3.3Å/cycle was obtained. Surface morphology was investigated using AFM showing average roughness (Ra) of 3.5 nm.

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81.05.Lg	Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.bm	Polymers, organics
78.30.Jw	Organic compounds, polymers
78.66.Qn	Polymers; organic compounds

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Continuous atomic layer deposition: Explanation for anomalous growth rate effects

Philipp S. Maydannik, Tommi O. Kaariainen, and David. C. Cameron

J. Vac. Sci. Technol. A 30, 01A122 (2012); http://dx.doi.org/10.1116/1.3662861 (6 pages) | Cited 3 times

Online Publication Date: 29 November 2011

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Spatial atomic layer deposition (ALD) on moving substrates has recently been the subject of increasing interest and development. Recent results of deposition on flexible substrates in a cylindrical rotating continuous ALD system showed that in certain regions of operation, deviations from ideal ALD behavior occurred showing excess deposition during the trimethylaluminium (TMA)/water process for aluminum oxide. It was speculated that this was due to boundary layer gas entrainment at the surface of the moving substrate and consequent drag-through of precursors between the different precursor vapor zones. In this paper a study has been made of these gas entrainment effects by using helium as a tracer gas to determine how the transport between zones takes place. A simple model of the process based on physical principles has been constructed which replicates the observed helium transport behavior in the boundary layer. Based on this, it has been shown that gas entrainment is not the reason for the anomalous excess growth in this system. As an alternative explanation, adsorption of excess water molecules on the substrate surface and their carry over to the TMA zone has been proposed as the cause of the anomalous growth. A physical model for this process has been constructed and it has been shown that simulations based on this model reproduce the observed behavior over a range of substrate temperatures.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.43.Mn	Adsorption kinetics

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Atomic layer deposition of Al₂O₃ on V₂O₅ xerogel film for enhanced lithium-ion intercalation stability

Dawei Liu, Yanyi Liu, Stephanie L. Candelaria, Guozhong Cao, Jun Liu, and Yoon-Ha Jeong

J. Vac. Sci. Technol. A 30, 01A123 (2012); http://dx.doi.org/10.1116/1.3664115 (6 pages) | Cited 1 time

Online Publication Date: 29 November 2011

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V₂O₅ xerogel films were fabricated by casting V₂O₅ sols onto fluorine-doped tin oxide glass substrates at room temperature. Five, ten and twenty atomic layers of Al₂O₃ were grown onto as-fabricated films respectively. The bare film and Al₂O₃-deposited films all exhibited hydrous V₂O₅ phase only. Electrochemical impedance spectroscopy study revealed increased surface charge-transfer resistance of V₂O₅ films as more Al₂O₃ atomic layers were deposited. Lithium-ion intercalation tests at 600 mAg⁻¹ showed that bare V₂O₅ xerogel film possessed high initial discharge capacity of 219 mAhg⁻¹ but suffered from severe capacity degradation, i.e., having only 136 mAhg⁻¹ after 50 cycles. After deposition of ten atomic layers of Al₂O₃, the initial discharge capacity was 195 mAhg⁻¹ but increased over cycles before stabilizing; after 50 cycles, the discharge capacity was as high as 225 mAhg⁻¹. The noticeably improved cyclic stability of Al₂O₃-deposited V₂O₅ xerogel film could be attributed to the improved surface chemistry and enhanced mechanical strength. During repeated lithium-ion intercalation/de-intercalation, atomic layers of Al₂O₃ which were coated onto V₂O₅ surface could prevent V₂O₅ electrode dissolution into electrolyte by reducing direct contact between active electrode and electrolyte while at the same time acting as binder to maintain good mechanical contact between nanoparticles inside the film.

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68.15.+e	Liquid thin films
82.30.Fi	Ion-molecule, ion-ion, and charge-transfer reactions
82.45.Fk	Electrodes
82.45.Gj	Electrolytes
82.70.Gg	Gels and sols

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Atomic layer deposition of GaN at low temperatures

Cagla Ozgit, Inci Donmez, Mustafa Alevli, and Necmi Biyikli

J. Vac. Sci. Technol. A 30, 01A124 (2012); http://dx.doi.org/10.1116/1.3664102 (4 pages) | Cited 1 time

Online Publication Date: 1 December 2011

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The authors report on the self-limiting growth of GaN thin films at low temperatures. Films were deposited on Si substrates by plasma-enhanced atomic layer deposition using trimethylgallium (TMG) and ammonia (NH₃) as the group-III and -V precursors, respectively. GaN deposition rate saturated at 185 °C for NH₃ doses starting from 90 s. Atomic layer deposition temperature window was observed from 185 to ∼385 °C. Deposition rate, which is constant at ∼0.51 Å/cycle within the temperature range of 250 – 350 °C, increased slightly as the temperature decreased to 185 °C. In the bulk film, concentrations of Ga, N, and O were constant at ∼36.6, ∼43.9, and ∼19.5 at. %, respectively. C was detected only at the surface and no C impurities were found in the bulk film. High oxygen concentration in films was attributed to the oxygen impurities present in group-V precursor. High-resolution transmission electron microscopy studies revealed a microstructure consisting of small crystallites dispersed in an amorphous matrix.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.33.Xj	Plasma reactions (including flowing afterglow and electric discharges)
68.55.A-	Nucleation and growth
68.55.ag	Semiconductors
52.77.Dq	Plasma-based ion implantation and deposition
81.05.Ea	III-V semiconductors

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Atomic layer deposition fabricated substoichiometric TiO_x nanorods as fuel cell catalyst supports

Richard Phillips, Paul Hansen, and Eric Eisenbraun

J. Vac. Sci. Technol. A 30, 01A125 (2012); http://dx.doi.org/10.1116/1.3664111 (6 pages) | Cited 2 times

Online Publication Date: 1 December 2011

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Atomic layer deposition (ALD)-grown substoichiometric TiO_x (1< x <2) was investigated as a possible fuel cell catalyst support material. The Magneli or Ti₄O₇ phase in particular exhibits acombination of high conductivity, stability, and corrosion resistance, which makes this material a promising replacement support structure when considering the inferior corrosion resistance of carbon-based supports. The current work investigates a novel technique for manufacturing conductive high aspect ratio TiO_x nanorods using ALD over high aspect ratio anodic aluminum oxide templates and annealing to reduce the degree of oxidation and increase conductivity. The combination of optimized ALD parameters and the inclusion of a post deposition H₂ anneal enable the production of a conductive Magneli phase TiO_x film at temperatures below 450 °C.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.45.Bb	Corrosion and passivation
68.55.A-	Nucleation and growth
61.46.-w	Structure of nanoscale materials
61.72.Cc	Kinetics of defect formation and annealing
81.07.Bc	Nanocrystalline materials

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Growth and electrical properties of silicon oxide grown by atomic layer deposition using Bis(ethyl-methyl-amino)silane and ozone

Seok-Jun Won, Hyung-Suk Jung, Sungin Suh, Yu Jin Choi, Nae-In Lee, Cheol Seong Hwang, and Hyeong Joon Kim

J. Vac. Sci. Technol. A 30, 01A126 (2012); http://dx.doi.org/10.1116/1.3664122 (7 pages) | Cited 1 time

Online Publication Date: 1 December 2011

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Silicon oxide thin film grown at low temperatures (<300–500 °C) is essential for a range of applications in semiconductor devices. In this study, silicon oxide films were deposited at a substrate temperature of ∼300 °C by an atomic layer deposition (ALD) process using Bis(ethyl-methyl-amino)silane (BEMAS). BEMAS precursors adsorbed on the growing surface reacted with ozone but not with H₂O. This suggests that the Si–H bonds in the BEMAS precursors adsorbed on the surface are robust and could be cleaved only by ozone. The reaction using BEMAS and ozone exhibited ALD saturation behavior. The dielectric constant of the ALD-SiO₂ was measured to be ∼9, which is 2.3 times higher than that (∼3.9) of normal amorphous SiO₂. This was attributed to the existence of the ∼10% OH species in the film.

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81.05.Hd	Other semiconductors
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.43.Mn	Adsorption kinetics
77.22.Ch	Permittivity (dielectric function)

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Reaction mechanisms for atomic layer deposition of aluminum oxide on semiconductor substrates

Annelies Delabie, Sonja Sioncke, Jens Rip, Sven Van Elshocht, Geoffrey Pourtois, Matthias Mueller, Burkhard Beckhoff, and Kristine Pierloot

J. Vac. Sci. Technol. A 30, 01A127 (2012); http://dx.doi.org/10.1116/1.3664090 (10 pages) | Cited 6 times

Online Publication Date: 2 December 2011

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In this work, we have studied the TMA/H₂O (TMA = Al(CH₃)₃) atomic layer deposition (ALD) of Al₂O₃ on hydroxyl (OH) and thiol (SH) terminated semiconductor substrates. Total reflection x-ray fluorescence reveals a complex growth-per-cycle evolution during the early ALD reaction cycles. OH and SH terminated surfaces demonstrate growth inhibition from the second reaction cycle on. Theoretical calculations, based on density functional theory, are performed on cluster models to investigate the first TMA/H₂O reaction cycle. Based on the theoretical results, we discuss possible mechanisms for the growth inhibition from the second reaction cycle on. In addition, our calculations show that AlCH₃ groups are hydrolyzed by a H₂O molecule adsorbed on a neighboring Al atom, independent of the type of backbonds (Si-O, Ge-O, or Ge-S) of AlCH₃. The coordination of Al remains four-fold after the first TMA/H₂O reaction cycle.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.30.-b	Specific chemical reactions; reaction mechanisms
82.80.Ej	X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.55.A-	Nucleation and growth
68.43.Mn	Adsorption kinetics
71.15.Mb	Density functional theory, local density approximation, gradient and other corrections

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Selective atomic layer deposition with electron-beam patterned self-assembled monolayers

Jie Huang, Mingun Lee, and Jiyoung Kim

J. Vac. Sci. Technol. A 30, 01A128 (2012); http://dx.doi.org/10.1116/1.3664282 (5 pages) | Cited 1 time

Online Publication Date: 2 December 2011

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The authors selectively deposited nanolines of titanium oxide (TiO₂) through atomic layer deposition (ALD) using an octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) as a nucleation inhibition layer. Electron-beam (e-beam) patterning is used to prepare nanoline patterns in the OTS SAM on SiO₂/Si substrates suitable for selective ALD. The authors have investigated the effect of an e-beam dose on the pattern width of the selectively deposited TiO₂ lines. A high dose (e.g., 20 nC/cm) causes broadening of the linewidth possibly due to scattering, while a low dose (e.g., 5 nC/cm) results in a low TiO₂ deposition rate because of incomplete exposure of the OTS SAMs. The authors have confirmed that sub-30 nm isolated TiO₂ lines can be achieved by selective ALD combined with OTS patterned by EBL at an accelerating voltage of 2 kV and line dose of 10 nC/cm. This research offers a new approach for patterned gate dielectric layer fabrication, as well as potential applications for nanosensors and solar cells.

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81.16.Rf	Micro- and nanoscale pattern formation
68.47.Pe	Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
81.15.Jj	Ion and electron beam-assisted deposition; ion plating

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Atomic layer deposition of Pt growth template for orienting PbZr_xTi₁₋_xO₃ thin films

Daniel M. Potrepka, Luz M. Sanchez, and Ronald G. Polcawich

J. Vac. Sci. Technol. A 30, 01A129 (2012); http://dx.doi.org/10.1116/1.3664766 (7 pages)

Online Publication Date: 2 December 2011

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Atomic layer deposition (ALD) offers a method for sidewall growth due to its ability to deposit isotropic thin films. As a first step to provide underlying growth templates on sidewalls, proof-of-principal depositions were made on flat wafer surfaces using ALD Pt thin films deposited on: ALD HfO₂, ALD Al₂O₃, and oxidized sputtered-Ti films. X-ray diffraction rocking curve full-width half maxima for 25 nm Pt films obtained after a rapid thermal anneal at 700 °C were 2.06°, 5.45°, and 7.84° on the TiO₂, Al₂O₃, and HfO₂ coatings, respectively. Sheet resistance decreased with Pt thickness (deposited onto TiO₂/SiO₂/Si): from 5 Ω/□ at 25 nm to 0.63 Ω/□ at 100 nm. A 500 ± 25 nm PbZr_0.52Ti_0.48O₃ film was deposited by a chemical solution deposition process onto 100 nm ALD Pt films deposited on the TiO₂/SiO₂/Si substrates. The 001 Lotgering factor derived from x-ray diffraction data was 0.56 for 001/100 oriented PbZr_0.52Ti_0.48O₃.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.84.Cg	PZT ceramics and other titanates
77.65.-j	Piezoelectricity and electromechanical effects

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Plasma-enhanced atomic layer deposition and etching of high-k gadolinium oxide

Steven A. Vitale, Peter W. Wyatt, and Chris J. Hodson

J. Vac. Sci. Technol. A 30, 01A130 (2012); http://dx.doi.org/10.1116/1.3664756 (7 pages) | Cited 1 time

Online Publication Date: 5 December 2011

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Atomic layer deposition (ALD) of high-quality gadolinium oxide thin films is achieved using Gd(iPrCp)₃ and O₂ plasma. Gd₂O₃ growth is observed from 150 to 350 °C, though the optical properties of the film improve at higher temperature. True layer-by-layer ALD growth of Gd₂O₃ occurred in a relatively narrow window of temperature and precursor dose. A saturated growth rate of 1.4 Å/cycle was observed at 250 °C. As the temperature increases, high-quality films are deposited, but the growth mechanism appears to become CVD-like, indicating the onset of precursor decomposition. At 250 °C, the refractive index of the film is stable at ∼1.80 regardless of other deposition conditions, and the measured dispersion characteristics are comparable to those of bulk Gd₂O₃. XPS data show that the O/Gd ratio is oxygen deficient at 1.3, and that it is also very hygroscopic. The plasma etching rate of the ALD Gd₂O₃ film in a high-density helicon reactor is very low. Little difference is observed in etching rate between Cl₂ and pure Ar plasmas, suggesting that physical sputtering dominates the etching. A threshold bias power exists below which etching does not occur; thus it may be possible to etch a metal gate material and stop easily on the Gd₂O₃ gate dielectric. The Gd₂O₃ film has a dielectric constant of about 16, exhibits low C–V hysteresis, and allows a 50 × reduction in gate leakage compared to SiO₂. However, the plasma enhanced atomic layer deposition (PE-ALD) process causes formation of an ∼1.8 nm SiO₂ interfacial layer, and generates a fixed charge of −1.21 × 10¹²cm⁻², both of which may limit use of PE-ALD Gd₂O₃ as a gate dielectric.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.80.Pv	Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Dp	Adsorbed layers and thin films
78.20.Ci	Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.55.D-	High-permittivity gate dielectric films
77.22.Ch	Permittivity (dielectric function)

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Cathode encapsulation of organic light emitting diodes by atomic layer deposited Al₂O₃ films and Al₂O₃/a-SiN_x:H stacks

W. Keuning, P. van de Weijer, H. Lifka, W. M. M. Kessels, and M. Creatore

J. Vac. Sci. Technol. A 30, 01A131 (2012); http://dx.doi.org/10.1116/1.3664762 (6 pages) | Cited 2 times

Online Publication Date: 5 December 2011

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Al₂O₃ thin films synthesized by plasma-enhanced atomic layer deposition (ALD) at room temperature (25 °C) have been tested as water vapor permeation barriers for organic light emitting diode devices. Silicon nitride films (a-SiN_x:H) deposited by plasma-enhanced chemical vapor deposition served as reference and were used to develop Al₂O₃/a-SiN_x:H stacks. On the basis of Ca test measurements, a very low intrinsic water vapor transmission rate of ≤ 2 × 10⁻⁶ g m⁻² day⁻¹ and 4 × 10⁻⁶ g m⁻² day⁻¹ (20 ^oC/50% relative humidity) were found for 20–40 nm Al₂O₃ and 300 nm a-SiN_x:H films, respectively. The cathode particle coverage was a factor of 4 better for the Al₂O₃ films compared to the a-SiN_x:H films and an average of 0.12 defects per cm² was obtained for a stack consisting of three barrier layers (Al₂O₃/a-SiN_x:H/Al₂O₃).

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85.60.Jb	Light-emitting devices
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq	Plasma-based ion implantation and deposition

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Nanoscratch testing of atomic layer deposition and magnetron sputtered TiO₂ and Al₂O₃ coatings on polymeric substrates

Tommi O. Kääriäinen, Peter J. Kelly, David C. Cameron, Ben Beake, Heqing Li, Paul M. Barker, and Carolin F. Struller

J. Vac. Sci. Technol. A 30, 01A132 (2012); http://dx.doi.org/10.1116/1.3665418 (9 pages)

Online Publication Date: 5 December 2011

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Titania and alumina thin films are commercially important materials, finding a wide variety of applications. These materials are commonly deposited onto glass substrates by reactive magnetron sputtering techniques, or more recently by atomic layer deposition (ALD). Such films have been well-characterized in terms of their structures and properties, including their nanomechnical and nanotribological properties. There is increasing demand, though, to deposit thin (<100 nm) functional films onto polymeric substrates, which can provide cost and weight savings and opens up the potential of deposition in large throughput roll-to-roll coating systems. However, polymeric substrates impose severe limitations due to both their thermal and mechanical properties. In the former case, production is restricted to low temperature processes and in the latter case, the substrate offers negligible load support for the thin ceramic coating. While nanoindentation and nanotribological testing of thin ceramic coatings on rigid substrates have become established techniques, the same cannot be said of testing similar “hard” coatings on “soft” flexible polymeric substrates. It is recognized that the coating/substrate system is very different in nature and the mechanisms of failure may also be very different. Sub-100 nm titania and alumina coatings have, therefore, been deposited onto a range of polymeric substrate materials by low temperature ALD and, for comparison purposes, magnetron sputtering techniques, including mid-frequency pulsed dc and high power impulse magnetron sputtering. Nanoscratch testing has been carried out on these coatings usingspherical indenters. Indenter radius and loading rate were varied and their influence on the elastoplastic properties of the film and the substrate are considered and comparisons are made withthesame coating materials deposited onto “rigid” substrates.

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81.65.-b	Surface treatments
68.55.aj	Insulators
62.20.Qp	Friction, tribology, and hardness
81.40.Pq	Friction, lubrication, and wear
81.40.Lm	Deformation, plasticity, and creep
62.20.fq	Plasticity and superplasticity

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Real-time spectroscopic ellipsometric investigation of adsorption and desorption in atomic layer deposition: A case study for the strontium bis(tri-isopropylcyclopentadienyl)/water process

Han Wang (王瀚), Xiaoqiang Jiang (蒋晓强), and Brian G. Willis

J. Vac. Sci. Technol. A 30, 01A133 (2012); http://dx.doi.org/10.1116/1.3664757 (5 pages) | Cited 2 times

Online Publication Date: 6 December 2011

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The atomic layer deposition (ALD) of SrO thin films from Sr(C5iPr₃H₂)₂ (g) and H₂O (g) was studied using real-time spectroscopic ellipsometry (SE) investigations of adsorption and desorption during each half cycle. Adsorption of Sr(C5iPr₃H₂)₂ was self-terminating at deposition temperatures of 150–350 °C and the saturated growth per cycle (GPC) highly depended on the deposition temperature, ranging from 0.05 to 0.33 nm/cycle at the lower and upper limits, respectively. Submonolayer sensitivity of SE was demonstrated by examining changes in the ellipsometric parameters and apparent thickness before and after precursor pulses. A comparison between experimental GPC and available theoretical models demonstrates that the deposition temperature has a marked effect on the reaction mechanism and indicates more than one operation regime for the ALD process of Sr(C5iPr₃H₂)₂ and H₂O.

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68.43.Mn	Adsorption kinetics
68.43.Nr	Desorption kinetics
68.55.aj	Insulators
68.47.Pe	Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

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Atomic layer deposition of titanium phosphate on silica nanoparticles

Monika K. Wiedmann, David H. K. Jackson, Yomaira J. Pagan-Torres, Eunkyung Cho, James A. Dumesic, and T. F. Kuech

J. Vac. Sci. Technol. A 30, 01A134 (2012); http://dx.doi.org/10.1116/1.3664097 (8 pages)

Online Publication Date: 9 December 2011

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Titanium phosphate was deposited on silica nanoparticles by atomic layer deposition (ALD). The precursors were titanium tetrachloride (TiCl₄), trimethylphosphate ((MeO)₃PO), and water. Depositions were done at 150–300 °C employing a variety of pulse sequences which altered the self-limiting deposition process. Using the pulse sequence TiCl₄-H₂O-(MeO)₃PO-H₂O, the process was self-limiting at 200 °C, and ≤0.3 at.% Cl was incorporated into the material. With the pulse sequence TiCl₄-H₂O-(MeO)₃PO, the process was not completely self-limiting at 200 °C and slightly more Cl incorporation occurred. Using the pulse sequence TiCl₄-(MeO)₃PO, the process was not self-limiting at 175 or 250 °C, and Cl incorporation was 0.2–2 at.%. The surface area of the material decreased from 300 m²/g for uncoated silica to 46 m²/g for silica coated with 60ALD cycles.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj	Insulators

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Growth characteristics, material properties, and optical properties of zinc oxysulfide films deposited by atomic layer deposition

Jonathan R. Bakke, Jukka T. Tanskanen, Carl Hägglund, Tapani A. Pakkanen, and Stacey F. Bent

J. Vac. Sci. Technol. A 30, 01A135 (2012); http://dx.doi.org/10.1116/1.3664758 (8 pages) | Cited 2 times

Online Publication Date: 9 December 2011

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Zinc oxysulfide—Zn(O,S)—is a wide bandgap semiconductor with tunable electronic and optical properties, making it of potential interest as a buffer layer for thin film photovoltaics. Atomic layer deposition (ALD) of ZnS, ZnO, and Zn(O,S) films from dimethylzinc, H₂O, and H₂S was performed, and the deposited films were characterized by means of x-ray diffraction, x-ray photoelectron spectroscopy, and spectroscopic ellipsometry. With focus on the investigation of Zn(O,S) film growth characteristics and material properties, the ZnO/(ZnO + ZnS) ALD cycle ratios were systematically varied from 0 (ZnS ALD) to 1 (ZnO ALD). Notably, a strong effect ofthematerial properties on the optical characteristics is confirmed for the ternary films. The Zn(O,S) ALD growth and crystal structure resemble those of ZnS up to a 0.6 cycle ratio, at whichpoint XPS indicates 10% oxygen is incorporated into the film. For higher cycle ratios thefilm structure becomes amorphous, which is confirmed with XRD patterns and also reflected inthe optical constants as determined by spectroscopic ellipsometry; in particular, the optical bandgap transforms from direct type for the (cubic) ZnS like phase to a more narrow bandgap withamorphous characteristics, causing bandgap bowing. A direct bandgap is recovered atyethigherZnO/(ZnO + ZnS) cycle ratios, whereproperties converge toward ZnO ALD in termsof film growth rate, crystallinity, and composition.

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68.55.ag	Semiconductors
79.60.Bm	Clean metal, semiconductor, and insulator surfaces
78.66.Jg	Amorphous semiconductors; glasses
81.05.Gc	Amorphous semiconductors
78.66.Hf	II-VI semiconductors
81.05.Dz	II-VI semiconductors

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Evaluating operating conditions for continuous atmospheric atomic layer deposition using a multiple slit gas source head

P. Ryan Fitzpatrick, Zachary M. Gibbs, and Steven M. George

J. Vac. Sci. Technol. A 30, 01A136 (2012); http://dx.doi.org/10.1116/1.3664765 (10 pages) | Cited 2 times

Online Publication Date: 9 December 2011

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Continuous atmospheric atomic layer deposition (ALD) is based on the separation of ALD reactants in space rather than in time. In this study, operating conditions for continuous atmospheric ALD were evaluated using a multiple slit gas source head. A test apparatus was constructed consisting of a gas source head that sits above a substrate that is driven by a programmable stepper motor. The gas source head was composed of a series of rectangular channels that spatially separate the ALD reactants. With Al₂O₃ ALD as the model system, the trimethylaluminum (TMA) reactant channel was positioned in the center and the H₂O reactant channels were located on both sides of the TMA channel. This design allowed for deposition of two Al₂O₃ ALD cycles during one complete back-and-forth translation of the substrate. The gap spacing between the gas source head and substrate was fixed and controlled using micrometers. A series of experiments was conducted using He as a tag gas to determine operating conditions that prevent reactant cross diffusion. There was a wider range of suitable exhaust pumping speeds at a 30 μm gap spacing than at a 100 μm gap spacing. However, mechanical tolerances were not sufficient to allow back-and-forth translation of the substrate at a gap spacing of 30 μm. For Al₂O₃ ALD at a 100 μm gap spacing, the best Al₂O₃ film uniformity was achieved when there was a slight vacuum of ∼−5 Torr beneath the gas source head relative to ambient. A larger vacuum beneath the gas source head occurred if the pumping speed of the exhaust channel was higher relative to the N₂ supplied to the gas source head. These conditions produced a smaller footprint of Al₂O₃ deposition resulting from an influx of N₂ from the higher pressure ambient. The gas source head had a higher pressure than ambient if the exhaust pumping speed was too low relative to the N₂ supply. Under these conditions, reactant gas leaked out the sides and formed Al₂O₃ powder around the perimeter of the gas source head resulting from the chemical vapor deposition reaction of TMA with ambient moisture. A response surface model was generated to predict the dependence of the pressure beneath the gas source head relative to ambient on the various operating conditions.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A-	Nucleation and growth

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Initiation of atomic layer deposition of metal oxides on polymer substrates by water plasma pretreatment

E. Steven Brandt and Jeremy M. Grace

J. Vac. Sci. Technol. A 30, 01A137 (2012); http://dx.doi.org/10.1116/1.3666026 (15 pages)

Online Publication Date: 9 December 2011

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The role of surface hydroxyl content in atomic layer deposition (ALD) of aluminum oxide (AO) on polymers is demonstrated by performing an atomic layer deposition of AO onto a variety of polymer types, before and after pretreatment in a plasma struck in water vapor. The treatment and deposition reactions are performed in situ in a high vacuum chamber that is interfaced to an x-ray photoelectron spectrometer to prevent adventitious exposure to atmospheric contaminants. X-ray photoelectron spectroscopy is used to follow the surface chemistries of the polymers, including theformation of surface hydroxyls and subsequent growth of AO by ALD. Using dimethyl aluminum isopropoxide and water as reactants, ALD is obtained for water-plasma-treated poly(styrene) (PS), poly(propylene) (PP), poly(vinyl alcohol) (PVA), and poly(ethylene naphthalate) (PEN). For PS, PP, and PEN, initial growth rates of AO on the native (untreated) polymers are at least an order of magnitude lower than on the same polymer surface following the plasma treatment. By contrast, native PVA is shown to initiate ALD of AO as a result of the presence of intrinsic surface hydroxyls that are derived from the repeat unit of this polymer.

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81.15.-z	Methods of deposition of films and coatings; film growth and epitaxy
68.55.aj	Insulators
52.77.-j	Plasma applications
79.60.Fr	Polymers; organic compounds

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Atomic layer deposition of Al-doped ZnO films using ozone as the oxygen source: A comparison of two methods to deliver aluminum

Hai Yuan, Bing Luo, Dan Yu, An-jen Cheng, Stephen A. Campbell, and Wayne L. Gladfelter

J. Vac. Sci. Technol. A 30, 01A138 (2012); http://dx.doi.org/10.1116/1.3666030 (8 pages) | Cited 4 times

Online Publication Date: 9 December 2011

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Aluminum-doped ZnO films were prepared by atomic layer deposition at 250 °C using diethylzinc (DEZ), trimethylaluminum (TMA), and ozone as the precursors. Two deposition methods were compared to assess their impact on the composition, structural, electrical, and optical properties as a function of Al concentration. The first method controlled the Al concentration by changing the relative number of Al to Zn deposition cycles; a process reported in the literature where water was used as the oxygen source. The second method involved coinjection of the DEZ and TMA during each cycle where the partial pressures of the precursors control the aluminum concentration. Depth profiles of the film composition using Auger electron spectroscopy confirmed a layered microstructure for the films prepared by the first method, whereas the second method led to a homogeneous distribution of the aluminum throughout the ZnO film. Beneath the surface layer the carbon concentrations for all of the films were below the detection limit. Comparison of their electrical and optical properties established that films deposited by coinjection of the precursors were superior.

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81.05.Dz	II-VI semiconductors
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.80.Pv	Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
73.61.Ga	II-VI semiconductors
78.66.Hf	II-VI semiconductors
79.20.Fv	Electron impact: Auger emission

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Effects of Ar plasma treatment for deposition of ruthenium film by remote plasma atomic layer deposition

Taeyong Park, Jaesang Lee, Jingyu Park, Heeyoung Jeon, Hyeongtag Jeon, Ki-Hoon Lee, Byung-Chul Cho, Moo-Sung Kim, and Heui-Bok Ahn

J. Vac. Sci. Technol. A 30, 01A139 (2012); http://dx.doi.org/10.1116/1.3666033 (5 pages) | Cited 1 time

Online Publication Date: 9 December 2011

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Ruthenium thin films were deposited on argon plasma-treated SiO₂ and untreated SiO₂ substrates by remote plasma atomic layer deposition using bis(ethylcyclopentadienyl)ruthenium [Ru(EtCp)₂] as a Ru precursor and ammonia plasma as a reactant. The results of in situ Auger electron spectroscopy (AES) analysis indicate that the initial transient region of Ru deposition was decreased by Ar plasma treatment at 400 °C, but did not change significantly at 300 °C. The deposition rate exhibited linearity after continuous film formation and the deposition rates were about 1.7 Å/cycle and 0.4 Å/cycle at 400 °C and 300 °C, respectively. Changes of surface energy and polar and dispersive components were measured by the sessile drop test. The quantity of surface amine groups was measured from the surface nitrogen concentration with AES. Furthermore, the Ar plasma-treated SiO₂ contained more amine groups and less hydroxyl groups on the surface than on untreated SiO₂. Auger spectra exhibited chemical shifts by Ru-O bonding, and larger shifts were observed on untreated substrates due to the strong adhesion of Ru films.

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81.15.Jj	Ion and electron beam-assisted deposition; ion plating
68.55.at	Other materials
52.77.Dq	Plasma-based ion implantation and deposition
68.35.Md	Surface thermodynamics, surface energies
79.20.Fv	Electron impact: Auger emission
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

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Process study of gadolinium aluminate atomic layer deposition fromthegadolinium tris-di-isopropylacetamidinate precursor

Leonard N. J. Rodriguez, A. Franquet, B. Brijs, H. Tielens, and C. Adelmann

J. Vac. Sci. Technol. A 30, 01A140 (2012); http://dx.doi.org/10.1116/1.3666037 (8 pages)

Online Publication Date: 9 December 2011

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The growth of gadolinium aluminate films by atomic layer deposition from gadolinium tris-di-isopropylacetamidinate and trimethylaluminium was studied. The consequences of using water versus ozone as the oxidant were studied. The effects of pulse lengths, metal source ratios, and temperature were noted. Depositing two cycles of gadolinium oxide per cycle of aluminum oxide was found to yield films with a stiochiometry of Gd_1.04AlO₃ and a growth rate of 2.2 Å in aggregate for each set of gadolinium and aluminum cycles. The deposition rate was found to be stable between 210 and 325 °C. The use of ozone instead of water as the oxygen source was found to reduce the film uniformity. The densities ranged from 3 to 6 g/cm³ depending on the Gd content of the films. The impurity contamination of the films was measured by secondary ion mass spectrometry and infrared absorption and found consistent with carboxylated species. Theextracted bandgap for the Gd_1.04AlO₃ films was 5.8 eV. The films were amorphous as deposited.

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68.55.aj	Insulators
77.55.D-	High-permittivity gate dielectric films
68.55.Ln	Defects and impurities: doping, implantation, distribution, concentration, etc.
78.30.Hv	Other nonmetallic inorganics
78.66.Nk	Insulators
79.20.Rf	Atomic, molecular, and ion beam impact and interactions with surfaces

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Jan 2012

Volume 30, Issue 1, Articles (01xxxx)