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Nov 2012

Volume 30, Issue 6, Articles (06xxxx)

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J. Vac. Sci. Technol. A 30, 060801 (2012); http://dx.doi.org/10.1116/1.4759260 (11 pages)

Sangmoo Jeong, Shuang Wang, and Yi Cui
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Degassing a vacuum system with in-situ UV radiation

Sean R. Koebley, Ronald A. Outlaw, and Randy R. Dellwo

J. Vac. Sci. Technol. A 30, 060601 (2012); http://dx.doi.org/10.1116/1.4754292 (3 pages)

Online Publication Date: 21 September 2012

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Photon-stimulated desorption (PSD) from a high-powered ultraviolet source was investigated as a technique to degas a vacuum system. A stainless steel vacuum system was pumped down from atmosphere with different time doses of 185 nm light, and the resulting outgassing rates were compared to that of a control pumpdown without UV assistance. PSD was found to provide a factor of 2 advantage in pumpdown pressure after only 30 min of UV exposure, with no additional advantage observed for longer irradiation times. Specifically, an outgassing rate of 3 × 10−10 Torr L s−1 cm−2 was reached 3 h sooner in pumpdowns with UV assistance compared to those without UV, while a rate of 1.2 × 10−10 Torr L s−1 cm−2 was reached 16 h sooner in UV runs. The authors calculated that about 22 monolayers of water were desorbed after 30 min of UV exposure. The results indicate that PSD by a 40 W 185 nm UV source can serve as a nonthermal technique to significantly speed the pumpdown of a vacuum system from atmosphere after only 30 min.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.43.Tj Photon stimulated desorption
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Nanoscale photon management in silicon solar cells

Sangmoo Jeong, Shuang Wang, and Yi Cui

J. Vac. Sci. Technol. A 30, 060801 (2012); http://dx.doi.org/10.1116/1.4759260 (11 pages) | Cited 1 time

Online Publication Date: 18 October 2012

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Light absorption in a photovoltaic device becomes critical as the thickness of an absorber layer is decreased to reduce cost. To enhance light absorption, photon management at the nanoscale has been studied because conventional methods, which are based on micrometer-sized structure, do not work well for thinner solar cells. This article reviews recent progress in photon management on the nanoscale for increasing light absorption in Si solar cells. The methodology for the absorption enhancement will be discussed, followed by advances in nanofabrication techniques that make the methodology a scalable and viable solution. The authors conclude with a discussion of the challenge of photon management schemes and future directions for light trapping in ultra-thin Si solar cells.
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88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells
81.16.-c Methods of micro- and nanofabrication and processing
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Frequency and electrode shape effects on etch rate uniformity in a dual-frequency capacitive reactor

Dougyong Sung, Vladimir Volynets, Wonsub Hwang, Yumi Sung, Seokhwan Lee, Myungsun Choi, and Gon-Ho Kim

J. Vac. Sci. Technol. A 30, 061301 (2012); http://dx.doi.org/10.1116/1.4754695 (4 pages)

Online Publication Date: 25 September 2012

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SiO2 was etched on 300 mm wafers in a dual-frequency capacitive plasma reactor to study etch rate nonuniformity as a function of driving frequency and power. It is shown that the etch rate profile shape varies significantly with the driving frequency. It also is shown that for different driving frequencies, the behavior of etch rate profile shape with the power is quite different, namely: (i) for lower frequency (27 MHz), the shape almost does not change with the power; (ii) for higher frequency (100 MHz), the shape considerably varies with the power. These results clearly indicate that the main reason for the etch rate nonuniformity in high-frequency capacitive reactors is the plasma nonuniformity caused by electromagnetic (standing wave and skin) effects. Using a specially shaped top electrode rather than the traditional flat one is shown to considerably improve the etch rate uniformity.
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81.65.Cf Surface cleaning, etching, patterning
72.30.+q High-frequency effects; plasma effects

Reaction mechanisms of oxygen plasma interaction with organosilicate low-k materials containing organic crosslinking groups

Mrunalkumar Chaudhari and Jincheng Du

J. Vac. Sci. Technol. A 30, 061302 (2012); http://dx.doi.org/10.1116/1.4755898 (7 pages) | Cited 1 time

Online Publication Date: 1 October 2012

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Integration of low dielectric constant (k) materials such as organosilicate glasses (OSG) into microelectronic processing demands a better of understanding the plasma/OSG interactions during plasma etching and ashing of these materials, based on which low-k materials with higher radiation resistance and better mechanical behaviors can be developed and optimized plasma processing conditions can be introduced to ensure continued miniaturization of semiconductor devices. Introducing organic crosslinking (e.g., –CH2–) in OSG has been shown to be an effective measure to improve the mechanical properties but their effect on plasma interaction is still not fully understood. In this paper, ab initio based molecular dynamics simulations have been employed to investigate the effect of the oxygen plasma on the carbon-bridged silicate networks in the OSG material. The results show that organic crosslinking in the Si–O–Si network leads to lower energy reaction pathways with atomic oxygen radicals that result in breakage of Si–CH2–Si linkages instead of Si–CH3 bonds and, consequently, a decrease in carbon removal. The incorporation of organic crosslinking groups can thus improve the resistance to oxygen plasma damage of OSG and, together with better mechanical properties, can lead to the design of stronger low-k dielectric films.
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52.77.Bn Etching and cleaning
81.05.Kf Glasses (including metallic glasses)
82.20.Hf Product distribution
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
77.55.Bh Low-permittivity dielectric films

Comparison endpoint study of process plasma and secondary electron beam exciter optical emission spectroscopy

P. L. Stephan Thamban, Stuart Yun, Gabriel Padron-Wells, Jimmy W. Hosch, and Matthew J. Goeckner

J. Vac. Sci. Technol. A 30, 061303 (2012); http://dx.doi.org/10.1116/1.4756694 (8 pages)

Online Publication Date: 3 October 2012

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Traditionally process plasmas are often studied and monitored by optical emission spectroscopy. Here, the authors compare experimental measurements from a secondary electron beam excitation and direct process plasma excitation to discuss and illustrate its distinctiveness in the study of process plasmas. They present results that show excitations of etch process effluents in a SF6 discharge and endpoint detection capabilities in dark plasma process conditions. In SF6 discharges, a band around 300 nm, not visible in process emission, is observed and it can serve as a good indicator of etch product emission during polysilicon etches. Based on prior work reported in literature the authors believe this band is due to SiF4 gas phase species.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.-s Electric discharges

Study on breathing mode oscillation suppression of self-excited Hall thrusters

Wei Liqiu, Han Ke, Wang Chunsheng, Li Hong, Zhang ChaoHai, and Yu Daren

J. Vac. Sci. Technol. A 30, 061304 (2012); http://dx.doi.org/10.1116/1.4758788 (5 pages)

Online Publication Date: 17 October 2012

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It is found that the breathing mode oscillation of the discharge current is suppressed notably in a Hall thruster operating with the electromagnets driven in series by the discharge current. In order to study the physical mechanism of this suppression, the ionization distribution is measured experimentally and the spatiotemporal features of the ionization front motion are studied numerically with a one-dimensional quasineutrality hydrodynamic model. Results show that the ionization front motion is restricted in a small range due to the closed-loop feedback control of the magnetic field. The steady-state ionization distribution is narrow and condensed when the electromagnetic coils connect in series with the discharge circuit. The different magnetic field excitation accompanied by different ionization characteristics is the main reason for the suppression of the discharge-current low-frequency breathing mode oscillation.
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41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
87.19.Wx Pneumodyamics, respiration
02.60.-x Numerical approximation and analysis

Study on the oxidation and reduction of tungsten surface for sub-50 nm patterning process

Jong Kyu Kim, Seok Woo Nam, Sung Il Cho, Myung S. Jhon, Kyung Suk Min, Chan Kyu Kim, Ho Bum Jung, and Geun Young Yeom

J. Vac. Sci. Technol. A 30, 061305 (2012); http://dx.doi.org/10.1116/1.4758790 (8 pages)

Online Publication Date: 19 October 2012

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The oxidation characteristics of tungsten line pattern during the carbon-based mask-layer removal process using oxygen plasmas have been investigated for sub-50 nm patterning processes, in addition to the reduction characteristics of the WOx layer formed on the tungsten line surface using hydrogen plasmas. The surface oxidation of tungsten lines during the mask layer removal process could be minimized by using low-temperature (300 K) plasma processing for the removal of the carbon-based material. Using this technique, the thickness of WOx on the tungsten line could be decreased to 25% compared to results from high-temperature processing. The WOx layer could also be completely removed at a low temperature of 300 K using a hydrogen plasma by supplying bias power to the tungsten substrate to provide a activation energy for the reduction. When this oxidation and reduction technique was applied to actual 40-nm-CD device processing, the complete removal of WOx formed on the sidewall of tungsten line could be observed.
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81.65.Mq Oxidation
81.16.Pr Micro- and nano-oxidation
82.30.-b Specific chemical reactions; reaction mechanisms
81.16.Rf Micro- and nanoscale pattern formation
52.77.-j Plasma applications

Negative oxygen ion formation in reactive magnetron sputtering processes for transparent conductive oxides

Thomas Welzel and Klaus Ellmer

J. Vac. Sci. Technol. A 30, 061306 (2012); http://dx.doi.org/10.1116/1.4762815 (12 pages) | Cited 1 time

Online Publication Date: 25 October 2012

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Reactive d.c. magnetron sputtering in Ar/O2 gas mixtures has been investigated with energy-resolved mass spectrometry. Different metal targets (Mg, Ti, Zn, In, InSn, and Sn), which are of importance for transparent conductive oxide thin film deposition, have been used to study the formation of negative ions, mainly high-energetic O−, which are supposed to induce radiation damage in thin films. Besides their energy distribution, the ions have been particularly investigated with respect to their intensity in comparison of the different target materials. To realize the comparability, various calibration factors had to be introduced. After their application, major differences in the negative ion production have been observed for the target materials. The intensity, especially of O−, differs by about two orders of magnitude. It is shown that this difference results almost exclusively from ions that gain their energy in the target sheath. Those may gain additional energy from the sputtering process or reflection at the target. Low-energetic negative ions are, however, less affected by changes of the target material. The results concerning O− formation are discussed in term of the sputtering rate from the target and are compared to models for negative ion formation.
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81.15.Cd Deposition by sputtering
61.80.Jh Ion radiation effects
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.55.A- Nucleation and growth
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New method of calculating adsorption and scattering for Xe-Pt(111) using Direct Simulation Monte Carlo techniques

Brook I. Bentley and Robert B. Greendyke

J. Vac. Sci. Technol. A 30, 061401 (2012); http://dx.doi.org/10.1116/1.4748801 (8 pages)

Online Publication Date: 31 August 2012

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A new scheme is presented for calculating adsorption and scattering for a gas–surface system in the thermal scattering regime using Direct Simulation Monte Carlo techniques. Results are compared with experimental data for the Xe-Pt(111) gas–surface system at surface temperatures of 95 K (adsorption) and 800 K (scattering). Fair agreement is found for the initial adsorption probability, while good agreement is found for the adsorption probability versus coverage. When implemented with the Cercignani–Lampis–Lord scattering kernel, the new scheme was found to improve scattering properties. Any scattering kernel or method amenable to Direct Simulation Monte Carlo techniques may be applied with the new scheme. Optimal values of accommodation coefficients were also found for the surface (αn = 0.74, αt = 0.60) and the adlayer (αn,ad = 0.89, αt,ad = 0.60).
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.49.Bc Atom scattering from surfaces (diffraction and energy transfer)
68.43.Mn Adsorption kinetics

Friction and counterface wear influenced by surface profiles of plasma electrolytic oxidation coatings on an aluminum A356 alloy

Jun Feng Su, Xueyuan Nie, Henry Hu, and Jimi Tjong

J. Vac. Sci. Technol. A 30, 061402 (2012); http://dx.doi.org/10.1116/1.4750474 (11 pages)

Online Publication Date: 7 September 2012

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To reduce the fuel consumption and emission of passenger vehicles, aluminum engines have been increasingly used throughout the last 30 years. Since most conventional aluminum alloys have poor wear resistance, various technical solutions have been developed to generate a wear-resistant cylinder bore surface against the sliding piston ring. In this work, the plasma electrolytic oxidation (PEO) process was employed to produce oxide coatings on an Al alloy A356 for Al engine blocks, to protect against the wear attack. The surface morphology and coating thicknesses were tailored by polishing two PEO coatings. A reciprocating sliding tribometer was used to investigate the tribological and wear behavior of the PEO coatings, counterface materials, and that of a state-of-the-art plasma transferred wire arc coating (as a benchmark) under two lubricated conditions. The results show that the PEO coatings have a low coefficient of friction and minimal wear. The variation in tribological behavior and counterface wear among the tested materials was likely due to different topographic features such as skewness and kurtosis caused by microbump distribution, porosity, and valleys on as-prepared, sanded, and polished coating surfaces.
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89.20.Kk Engineering
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear
81.65.Ps Polishing, grinding, surface finishing

Symmetric–asymmetric transformation of an image on GaAs(001)-c(4 × 4)α surface using scanning tunneling microscopy

Kazuma Yagyu, Shigeru Kaku, and Junji Yoshino

J. Vac. Sci. Technol. A 30, 061403 (2012); http://dx.doi.org/10.1116/1.4754804 (4 pages)

Online Publication Date: 3 October 2012

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Many studies have observed a clean GaAs(001)-c(4 × 4) surface using scanning tunneling microscopy. These studies have reported the observation of an asymmetric pattern formed from three asymmetric Ga–As dimers. In this study, however, a symmetric pattern was also observed depending on the applied bias voltage. These symmetric (asymmetric) patterns were observed at positive (negative) sample biases.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.bg Semiconductors

Dielectric function of LaAlO3 from 0.8 to 6 eV between 77 and 700 K

Cayla Marie Nelson, Maria Spies, Lina S. Abdallah, Stefan Zollner, Yun Xu, and Hongmei Luo

J. Vac. Sci. Technol. A 30, 061404 (2012); http://dx.doi.org/10.1116/1.4754811 (6 pages) | Cited 2 times

Online Publication Date: 4 October 2012

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The authors used spectroscopic ellipsometry to determine the dielectric function and the refractive index of LaAlO3 as a function of photon energy from 0.8 to 6 eV between 77 and 700 K. The ellipsometric angles were acquired over a broad range of incidence angles with a computer-controlled Berek waveplate compensator and with zone-averaging of the adjustable polarizer. The data were corrected for surface effects, such as surface roughness or adsorbed overlayers. The authors report Tauc–Lorentz model parameters for LaAlO3 at 300 K. After annealing in UHV for 20 h, the surface layer thickness decreased from 15 Å to less than 1 Å. They speculate that the anneal causes surface modifications, such as the evaporation of adsorbed molecular layers (hydrocarbons or water) or surface vacancies, and that surface diffusion leads to a reduction of surface roughness. They have also measured the temperature-dependence of the refractive index at 1.96 eV between 77 and 700 K and given a theoretical explanation of its origin.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Gh Other heat and thermomechanical treatments
61.72.jd Vacancies
68.35.bt Other materials
68.35.Fx Diffusion; interface formation
68.43.Mn Adsorption kinetics

Reflection high-energy electron diffraction evaluation of thermal deoxidation of chemically cleaned Si, SiGe, and Ge layers for solid-source molecular beam epitaxy

Dyan Ali and Christopher J. K. Richardson

J. Vac. Sci. Technol. A 30, 061405 (2012); http://dx.doi.org/10.1116/1.4757594 (7 pages)

Online Publication Date: 8 October 2012

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The authors present a study on the thermal evolution of the reflection high-energy electron diffraction pattern of chemically cleaned (001)-oriented Si, Ge, and SiGe surfaces, associating observed changes in the reconstructions with the desorption of known residual contaminants for Si and Ge surfaces. The implications of residual oxides prior to epitaxy on stacking fault densities in the grown films are presented. Further evidence for the two-phase nature of oxides on SiGe surfaces is provided, demonstrating that it is necessary to heat a SiGe surface up to the thermal deoxidation temperature of a Si surface to obtain stacking fault-free growth.
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81.65.Mq Oxidation
68.35.bg Semiconductors
68.43.Nr Desorption kinetics
68.55.ag Semiconductors
68.47.Fg Semiconductor surfaces
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Direct observation of hopping and merging of single Au adatoms to form dimers on Si(111)-(7 × 7)

Lei Zhang, Yujin Jeon, Hyungjoon Shim, and Geunseop Lee

J. Vac. Sci. Technol. A 30, 061406 (2012); http://dx.doi.org/10.1116/1.4758134 (5 pages)

Online Publication Date: 11 October 2012

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Au single adatoms and dimers were imaged on Si(111)-(7 × 7) at different temperatures and bias voltages using a variable-temperature scanning tunneling microscope. At room temperature (RT), a single Au adatom induces sharp highlighted triangular features in the half unit cells (HUCs) of Si(111)-(7 × 7). These triangular features become fuzzy at temperatures lower than 225 K, as a result of the reduced moving speed of the single Au adatoms inside the HUCs. The formation of an Au adatom dimer was directly observed at RT when a single Au adatom in a HUC jumped into a neighboring HUC that already contained a single Au adatom. The Au adatom dimer appears either as a noisy feature in the central area of the HUC defined by three Si center adatoms or as a bright protrusion located close to a corner Si adatom site at RT. It was observed that a noisy feature also can change into a bright protrusion, inducing charge redistribution in the nearby Si adatoms in both the occupied and neighboring HUCs.
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68.55.-a Thin film structure and morphology
66.30.-h Diffusion in solids
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.43.Mn Adsorption kinetics

Study of surface cleaning methods and pyrolysis temperatures on nanostructured carbon films using x-ray photoelectron spectroscopy

Pranita Kerber, Lisa M. Porter, Lynne A. McCullough, Tomasz Kowalewski, Mark Engelhard, and Donald Baer

J. Vac. Sci. Technol. A 30, 061407 (2012); http://dx.doi.org/10.1116/1.4759238 (6 pages)

Online Publication Date: 12 October 2012

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Nanostructured carbon (ns-C) films fabricated by stabilization and pyrolysis of diblock copolymers are of interest for a variety of electrical/electronic applications due to their chemical inertness, high-temperature insensitivity, very high surface area, and tunable electrical resistivity over a wide range [Kulkarni et al., Synth. Met. 159, 177 (2009)]. Because of their high porosity and associated high specific surface area, controlled surface cleaning studies are important for fabricating electronic devices from these films. In this study, quantification of surface composition and surface cleaning studies on ns-C films synthesized by carbonization of diblock copolymers of polyacrylonitrile-b-poly(n-butyl acrylate) at two different temperatures were carried out. X-ray photoelectron spectroscopy was used for elemental analysis and to determine the efficacy of various surface cleaning methods for ns-C films and to examine the polymer residues in the films. The in-situ surface cleaning methods included HF vapor treatment, vacuum annealing, and exposure to UV-ozone. Quantitative analysis of high-resolution XPS scans showed 11 at. % nitrogen was present in the films pyrolyzed at 600 °C, suggesting incomplete denitrogenation of the copolymer films. The nitrogen atomic concentration decreased significantly for films pyrolyzed at 900 °C confirming extensive denitrogenation at that temperature. Furthermore, quantitative analysis of nitrogen subpeaks indicated higher loss of nitrogen atoms residing at the edge of graphitic clusters relative to that of nitrogen atoms within the graphitic clusters, suggesting higher graphitization with increasing pyrolysis temperature. Of the surface cleaning methods investigated, in-situ annealing of the films at 300 °C for 40 min was found to be the most efficacious in removing adventitious carbon and oxygen impurities from the surface.
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68.55.-a Thin film structure and morphology
81.16.-c Methods of micro- and nanofabrication and processing
81.07.Bc Nanocrystalline materials
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.41.+e Polymers, elastomers, and plastics
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Oxidation behavior of arc evaporated Al-Cr-Si-N thin films

Christian Tritremmel, Rostislav Daniel, Christian Mitterer, Paul H. Mayrhofer, Markus Lechthaler, and Peter Polcik

J. Vac. Sci. Technol. A 30, 061501 (2012); http://dx.doi.org/10.1116/1.4748802 (6 pages)

Online Publication Date: 24 August 2012

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The impact of Al and Si on the oxidation behavior of Al-Cr-(Si)-N thin films synthesized by arc evaporation of powder metallurgically prepared AlxCr1−x targets with x = Al/(Al + Cr) of 0.5, 0.6, and 0.7 and (Al0.5Cr0.5)1−zSiz targets with Si contents of z = 0.05, 0.1, and 0.2 in N2 atmosphere was studied in detail by means of differential scanning calorimetry, thermogravimetric analysis (TGA), x-ray diffraction, and Raman spectroscopy. Dynamical measurements in synthetic air (up to 1440 °C) revealed the highest onset temperature of pronounced oxidation for nitride coatings prepared from the Al0.4Cr0.4Si0.2 target. Isothermal TGA at 1100, 1200, 1250, and 1300 °C highlight the pronounced improvement of the oxidation resistance of AlxCr1−xN coatings by the addition of Si. The results show that Si promotes the formation of a dense coating morphology as well as a dense oxide scale when exposed to air.
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81.65.Mq Oxidation
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Bx Metals, semimetals, and alloys
68.55.A- Nucleation and growth
78.30.Er Solid metals and alloys
73.61.At Metal and metallic alloys

Mechanically robust silica-like coatings deposited by microwave plasmas for barrier applications

Anna Maria Coclite, François De Luca, and Karen K. Gleason

J. Vac. Sci. Technol. A 30, 061502 (2012); http://dx.doi.org/10.1116/1.4748804 (9 pages)

Online Publication Date: 29 August 2012

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Dense and flexible silicon dioxide-like barrier coatings were deposited by microwave postdischarge (downstream plasma). The optical transparency, recyclability, and compatibility with microwave usage are some of the advantages of SiOx offers as compared to thin metallic coatings. Generally, porous silicon dioxide coatings with poor barrier properties are obtained by microwave downstream plasmas, because of limited ion bombardment. Here, we demonstrate that by using very high powers, mechanically robust, barrier coatings deposit both by pulsed and continuous microwave downstream discharges. These SiOx coatings exhibit hardness comparable to Al2O3, but have higher elasticity. Thus, the SiOx have superior cohesion and the ability to recover after cracking. The high critical tensile and compression strain for crack formation demonstrates that these coatings are very resistant and flexible. Correspondingly, a two orders of magnitude barrier improvement is obtained with 100-nm-thick-coating deposited by continuous discharge. The films deposited by pulsed discharges show better elasticity and flexibility but slightly lower barrier performances compared to the coatings deposited by continuous discharges.
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52.80.Pi High-frequency and RF discharges
52.77.Dq Plasma-based ion implantation and deposition
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.55.-a Thin film structure and morphology
62.20.de Elastic moduli

New oxygen radical source using selective sputtering of oxygen atoms for high rate deposition of TiO2 films

Yoji Yasuda, Hao Lei, and Yoichi Hoshi

J. Vac. Sci. Technol. A 30, 061503 (2012); http://dx.doi.org/10.1116/1.4748803 (6 pages)

Online Publication Date: 4 September 2012

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We have developed a new oxygen radical source based on the reactive sputtering phenomena of a titanium target for high rate deposition of TiO2 films. In this oxygen radical source, oxygen radicals are mainly produced by two mechanisms: selective sputter-emission of oxygen atoms from the target surface covered with a titanium oxide layer, and production of high-density oxygen plasma in the space near the magnetron-sputtering cathode. Compared with molecular oxygen ions, the amount of atomic oxygen radicals increased significantly with an increase in discharge current so that atomic oxygen radicals were mainly produced by this radical source. It should be noted that oxygen atoms were selectively sputtered from the target surface, and titanium atoms sputter-emitted from the target cathode were negligibly small. The amount of oxygen radicals supplied from this radical source increased linearly with increasing discharge current, and oxygen radicals of 1 × 1015 atoms/s/cm2 were supplied to the substrate surface at a discharge current of 1.2 A. We conclude that our newly developed oxygen radical source can be a good tool to achieve high rate deposition and to control the structure of TiO2 films for many industrial design applications.
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81.15.Cd Deposition by sputtering
52.77.Dq Plasma-based ion implantation and deposition

Metal versus rare-gas ion irradiation during Ti1−xAlxN film growth by hybrid high power pulsed magnetron/dc magnetron co-sputtering using synchronized pulsed substrate bias

Grzegorz Greczynski, Jun Lu, Jens Jensen, Ivan Petrov, Joseph E. Greene, Stephan Bolz, Werner Kölker, Christoph Schiffers, Oliver Lemmer, and Lars Hultman

J. Vac. Sci. Technol. A 30, 061504 (2012); http://dx.doi.org/10.1116/1.4750485 (8 pages)

Online Publication Date: 7 September 2012

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Metastable NaCl-structure Ti1 − xAlxN is employed as a model system to probe the effects of metal versus rare-gas ion irradiation during film growth using reactive high-power pulsed magnetron sputtering (HIPIMS) of Al and dc magnetron sputtering of Ti. The alloy film composition is chosen to be x = 0.61, near the kinetic solubility limit at the growth temperature of 500  °C. Three sets of experiments are carried out: a −60 V substrate bias is applied either continuously, in synchronous with the full HIPIMS pulse, or in synchronous only with the metal-rich-plasma portion of the HIPIMS pulse. Alloy films grown under continuous dc bias exhibit a thickness-invariant small-grain, two-phase nanostructure (wurtzite AlN and cubic Ti1−xAlxN) with random orientation, due primarily to intense Ar+ irradiation leading to Ar incorporation (0.2 at. %), high compressive stress (−4.6 GPa), and material loss by resputtering. Synchronizing the bias with the full HIPIMS pulse results in films that exhibit much lower stress levels (−1.8 GPa) with no measureable Ar incorporation, larger grains elongated in the growth direction, a very small volume fraction of wurtzite AlN, and random orientation. By synchronizing the bias with the metal-plasma phase of the HIPIMS pulses, energetic Ar+ ion bombardment is greatly reduced in favor of irradiation predominantly by Al+ ions. The resulting films are single phase with a dense competitive columnar structure, strong 111 orientation, no measureable trapped Ar concentration, and even lower stress (−0.9 GPa). Thus, switching from Ar+ to Al+ bombardment, while maintaining the same integrated incident ion/metal ratio, eliminates phase separation, minimizes renucleation during growth, and reduces the high concentration of residual point defects, which give rise to compressive stress.
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68.55.aj Insulators
61.80.Jh Ion radiation effects
61.82.Rx Nanocrystalline materials
68.60.Bs Mechanical and acoustical properties
81.15.Cd Deposition by sputtering
64.75.Bc Solubility

Microstructure and electrical properties of LaNiO3 thin films by RF sputtering for the growth of (Pb,La)(Zr,Ti)O3 films on silicon and nickel substrates

Shanshan Liu, Beihai Ma, Manoj Narayanan, Sheng Tong, Rachel Koritala, and Uthamalingam Balachandran

J. Vac. Sci. Technol. A 30, 061505 (2012); http://dx.doi.org/10.1116/1.4752084 (8 pages)

Online Publication Date: 13 September 2012

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Conductive LaNiO3 (LNO) thin films were deposited on Si substrates by RF sputtering at room temperature to 600 °C. X-ray diffraction of the LNO films showed that preferred orientation varied from (100) below 500 °C to (110) at 600 °C at deposition temperature of 200–600 °C. The room temperature resistivity was 2250–3400 μΩ-cm at the range of 200 °C ∼500 °C. The LNO films, deposited at room temperature, were postannealed in air from 500 to 800 °C, and the resistivity value was 280 μΩ-cm at a postannealing temperature of 600 °C. Subsequently, sol–gel derived (Pb,La)(Zr,Ti)O3 thin films were deposited on LNO-buffered nickel substrates and characterized, the results were compared to those of the same films on silicon substrates. The comparison demonstrated that the performance characteristics of the LNO-buffered nickel foils are similar to those of LNO-buffered silicon substrates. Thus, LNO films prepared by the sputtering method can act as an effective barrier layer on nickel substrates for embedded microelectronic devices.
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77.55.F- High-permittivity capacitive films
77.80.-e Ferroelectricity and antiferroelectricity
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.55.-a Thin film structure and morphology

Decomposition and phase transformation in TiCrAlN thin coatings

Rikard Forsén, Mats Johansson, Magnus Odén, and Naureen Ghafoor

J. Vac. Sci. Technol. A 30, 061506 (2012); http://dx.doi.org/10.1116/1.4757953 (8 pages) | Cited 3 times

Online Publication Date: 9 October 2012

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Metastable solid solutions of cubic (c)-(TixCryAlz)N coatings were grown by a reactive arc evaporation technique to investigate the phase transformations and mechanisms that yield enhanced high-temperature mechanical properties. Metal composition ranges of y < 17 at. % and 45 < z < 62 at. % were studied and compared with the parent TiAlN material system. The coatings exhibited age hardening up to 1000 °C, higher than the temperature observed for TiAlN. In addition, the coatings showed a less pronounced decrease in hardness when hexagonal (h)-AlN was formed compared to TiAlN. The improved thermal stability is attributed to lowered coherency stress and lowered enthalpy of mixing due to the addition of Cr, which results in improved functionality in the temperature range of 850–1000 °C. Upon annealing up to 1400 °C, the coatings decompose into c-TiN, bcc-Cr, and h-AlN. The decomposition takes place via several intermediate phases: c-CrAlN, c-TiCrN, and hexagonal (β)-Cr2N. The evolution in microstructure observed across different stages of spinodal decomposition and phase transformation can be correlated to the thermal response and mechanical hardness of the coatings.
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81.65.-b Surface treatments
82.60.-s Chemical thermodynamics
64.75.Bc Solubility
62.20.Qp Friction, tribology, and hardness
81.40.Gh Other heat and thermomechanical treatments
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Effect of MoO3 doping power on the electrical, optical, and structural properties of MoO3-doped In2O3 anodes for organic solar cells

Yong-Hee Shin, Han-Ki Kim, and Seok-In Na

J. Vac. Sci. Technol. A 30, 061507 (2012); http://dx.doi.org/10.1116/1.4758789 (7 pages) | Cited 2 times

Online Publication Date: 15 October 2012

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The authors investigated the effects of MoO3 doping power on the electrical, optical, and structural properties of MoO3-doped In2O3 (IMO) films for use as transparent electrodes in organic solar cells (OSCs). By optimizing the RF power of the MoO3 target (30 W), they obtained IMO films with sheet resistance of 24.57 Ω/sq and optical transmittance of 81.57%, comparable to conventional Sn-doped In2O3 (ITO) electrodes. In particular, the IMO film exhibited a high optical transmittance in the near-infrared (NIR) wavelength region due to the effects of Mo dopant with high Lewis acid strength and high mobility. In addition, strongly oriented (222) grains led to a smooth surface of the IMO electrode with root mean square roughness of 2.344 nm. The OSC fabricated on the optimized IMO electrode showed cell performances with a fill factor of 64.66%, a short circuit current of 8.058 mA/cm2, an open circuit voltage of 0.611 V, and a power conversion efficiency of 3.186%, which are nearly identical to OSCs with an ITO reference. This indicates that the IMO film is a promising alternative to the ITO electrode for the tandem OSC absorbing NIR wavelength region.
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78.66.Nk Insulators
73.61.Ng Insulators
82.45.-h Electrochemistry and electrophoresis
88.40.H- Solar cells (photovoltaics)
61.72.U- Doping and impurity implantation
68.55.-a Thin film structure and morphology

Transparent conductive indium zinc oxide films prepared by pulsed plasma deposition

Runlai Wan, Ming Yang, Qianfei Zhou, and Qun Zhang

J. Vac. Sci. Technol. A 30, 061508 (2012); http://dx.doi.org/10.1116/1.4762800 (5 pages)

Online Publication Date: 23 October 2012

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Transparent conductive indium zinc oxide films were prepared by pulsed plasma deposition from a ceramic target (90 wt. % In2O3 and 10 wt. % ZnO). The dependences of film properties upon the substrate temperature was investigated using characterization methods including x-ray diffraction, atomic force microscope, Hall measurement, ultraviolet-visible spectroscopy, and x-ray photoelectron spectroscopy. The films grown at room temperature had a rather smooth surface due to the amorphous structure, with a root mean square roughness of less than 1 nm. The atomic ratio of Zn/(Zn + In) in these films is 15.3 at. %, which is close to that in the target, and the chemical states of indium and zinc atoms were In3+ and Zn2+, respectively. The films deposited on a substrate with a temperature of 200 °C exhibited polycrystalline structure and a preferred growth orientation along the (222) plane. Here the electrical properties were improved due to the better crystallinity, with the films exhibiting a minimum resistivity value of 4.2 × 10−4 Ω cm, a maximum carrier mobility of 45 cm2 V−1 s−1, and an optical transmittance over 80% in the visible region.
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68.55.-a Thin film structure and morphology
78.66.-w Optical properties of specific thin films
73.61.-r Electrical properties of specific thin films
81.15.Fg Pulsed laser ablation deposition
78.40.Ha Other nonmetallic inorganics
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Characterization of epitaxially grown indium islands on Si(111)

Chad Lunceford and Jeff Drucker

J. Vac. Sci. Technol. A 30, 061509 (2012); http://dx.doi.org/10.1116/1.4764049 (6 pages)

Online Publication Date: 26 October 2012

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Indium deposition onto on-axis Si(111) substrates and those miscut by 2.5° toward [11math] was investigated. The Si substrates were held at temperatures ranging from room temperature up to 475 °C and the In deposition rate was varied by a factor of ∼20. All depositions were performed under ultrahigh vacuum conditions onto surfaces that were cleaned in situ. For growth at 100 °C and room temperature, the In films organize into three-dimensional islands. This result suggests that In deposition onto on-axis or miscut Si(111) substrates at temperatures lower than the In melting point of 157 °C is a viable route to form In seeds for epitaxial Si or Ge nanowire growth using the vapor–liquid–solid method. The morphology of the resultant island ensembles and their formation mechanisms are discussed.
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68.55.at Other materials
81.15.Kk Vapor phase epitaxy; growth from vapor phase

MnP nanoclusters embedded in GaP epitaxial films grown by organometallic vapor-phase epitaxy: A reciprocal space mapping and transmission electron microscopy study

Samuel Lambert-Milot, Simon Gaudet, Christian Lacroix, David Ménard, Remo A. Masut, Christian Lavoie, and Patrick Desjardins

J. Vac. Sci. Technol. A 30, 061510 (2012); http://dx.doi.org/10.1116/1.4758132 (22 pages) | Cited 2 times

Online Publication Date: 7 November 2012

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Full three dimensional x-ray diffraction reciprocal space maps combined with transmission electron microscopy measurements provide a systematic determination of the texture of GaP epilayers containing embedded MnP nanoclusters grown on GaP(001) by organometallic vapor phase epitaxy. This approach reveals that the texture of the MnP clusters depends on the growth surface morphology and bonding configuration and on the lattice mismatch at the cluster/matrix interfaces during growth. It demonstrates that the orthorhombic MnP nanoclusters are oriented along specific GaP crystallographic directions, forming six well defined families, whose population is influenced by the growth temperature and the film thickness. The clusters principally grow on GaP(001) and GaP{111} facets with a small fraction of clusters nucleating on higher-index GaP{hhl} facets. Most epitaxial alignments share a similar component: the MnP(001) plane (c-axis plane) is parallel to the GaP{110} plane family. Axiotaxial ordering between the MnP clusters and the GaP matrix is also observed. Furthermore, with this systematic approach, all phases present in these heterogeneous films can be identified. In particular, traces of hexagonal Mn2P precipitates have been observed while their formation can be avoided by lowering the growth temperature. Comparing the structural results presented here with magnetic measurement carried out on similar samples confirms that the effective magnetic properties of the heterogeneous layer can be tuned by controlling the texture of the ferromagnetic nanoclusters.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films

Apparatus for deposition of composition spread alloy films: The rotatable shadow mask

Benoit Fleutot, James B. Miller, and Andrew J. Gellman

J. Vac. Sci. Technol. A 30, 061511 (2012); http://dx.doi.org/10.1116/1.4766194 (10 pages) | Cited 1 time

Online Publication Date: 9 November 2012

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Composition spread alloy films (CSAFs) are materials libraries used for high throughput investigations of multicomponent materials such as alloys, AxByC1−x−y. CSAFs are prepared such that the alloy film has a lateral spatial gradient in its local composition; thus, they include a set of alloy samples with a distribution of compositions that spans a continuous region of composition space (x,y). A tool based on the shadow mask concept has been developed for generating composition gradients, but modified to allow rotation of the shadow mask during CSAF deposition. The tool allows deposition of CSAFs containing up to four elements with rotatable shadow masks between each of the four electron beam evaporation sources and the deposition substrate. This allows codeposition of any combination of up to four components. In the case of the ternary AxByC1−x−y CSAFs, the three components can be deposited such that the resulting CSAF spans the entire ternary alloy composition space (x = 0 → 1, y = 0 → 1 − x) and, furthermore, contains all three binary alloys AxB1−x, AxC1−x, and BxC1−x (x = 0 → 1) and all three pure components. The innovation of the rotatable shadow masks also allows preparation of CSAFs that magnify selected regions of the composition space (x = xmin → xmax, y = ymin → 1 − x). Herein, we describe the design and performance of this new CSAF deposition tool and assess its merits and limitations with respect to other methods for CSAF preparation.
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81.15.Dj E-beam and hot filament evaporation deposition
68.55.Nq Composition and phase identification

Ion-induced effects on grain boundaries and a-Si:H tissue quality in microcrystalline silicon films

A. C. Bronneberg, N. Cankoy, M. C. M. van de Sanden, and M. Creatore

J. Vac. Sci. Technol. A 30, 061512 (2012); http://dx.doi.org/10.1116/1.4766193 (10 pages)

Online Publication Date: 21 November 2012

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Microcrystalline silicon films have been deposited by means of the remote expanding thermal plasma. The effect of ion bombardment on the microcrystalline silicon film properties has been investigated by applying an RF bias to the deposition substrate. The application of the RF substrate bias resulted in the formation of an additional plasma in front of the substrate holder. Neither the SiH4 depletion nor the growth flux was significantly enhanced upon substrate biasing, which suggests that (the composition of) the growth precursor flux is unaffected and that the ion-film interaction mechanisms were responsible for the observed material changes. Moderate bias conditions (i.e., dc bias voltages up to ∼70 V) led to an improved grain boundary passivation and densification of the amorphous silicon tissue, as concluded from the analysis of the infrared Si-Hx stretching modes. These improvements have been ascribed to ion-induced Si surface atom displacement, which enhances the surface diffusion length of the growth precursors. More-energetic ion bombardment (i.e., under applied dc bias voltages of ∼60 V and higher) resulted in enhanced (di)vacancy incorporation via ion-induced Si bulk atom displacement. The film crystallinity was found not to be affected by the ion bombardment, although a reduced crystallite size was observed under ion bombardment conditions where Si bulk displacement had been sufficiently activated. The extent of the ion-film interaction mechanism has been enhanced by increasing the ion-to-Si deposition flux ratio. Under specific ion bombardment conditions, i.e., dc bias voltage in the range of 40–70 V and ion/Si arrival rate ∼0.20, microcrystalline silicon films have been obtained which, on the basis of the Si-Hx stretching modes, are qualified as solar-grade, i.e., the intergranular space is filled with a dense amorphous silicon tissue which completely passivates the crystalline grain boundaries.
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61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.ag Semiconductors
61.72.Mm Grain and twin boundaries
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Long-term stability of metal-envelope enclosed Bayard–Alpert ionization gauges

James A. Fedchak and Dana R. Defibaugh

J. Vac. Sci. Technol. A 30, 061601 (2012); http://dx.doi.org/10.1116/1.4750482 (7 pages)

Online Publication Date: 12 September 2012

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Ionization vacuum gauges are used as secondary standards by calibration laboratories and as transfer standards in intercomparisons among metrology laboratories. A quantitative measurement of gauge stability with respect to the gauge calibration factor is critical for these applications. We report the long-term calibration stability of hot-filament metal-envelope enclosed ionization gauges based upon the analysis of repeat calibrations of nine gauges over a 15 year period. All of the gauges included in the study were of the same type: Bayard–Alpert type ionization gauges of an all-metal construction with an integral metal-envelope surrounding the hot-filament, grid, and collector. All were calibrated repeatedly at the National Institute of Standards and Technology (NIST) using the NIST high-vacuum standard but are owned by organizations external to NIST. The gauges were removed from the high-vacuum standard after calibration, shipped back to the gauge-owner, and were returned to NIST at a later date (more than 1 year) for recalibration. Gauge stability was determined using a pooled standard deviation (weighted root-mean-square average of individual gauge standard deviations) based on all calibration factors measured at NIST and was used to define the relative uncertainty component associated with long-term stability uLTS. We determined uLTS = 1.9% (k = 1) for gauges operated with 4 mA of emission current, and uLTS = 2.8% (k = 1) for gauges operated with 0.1 mA emission current.
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07.30.Dz Vacuum gauges
06.20.fb Standards and calibration

Characterization of alkali metal dispensers and non-evaporable getter pumps in ultrahigh vacuum systems for cold atomic sensors

David R. Scherer, David B. Fenner, and Joel M. Hensley

J. Vac. Sci. Technol. A 30, 061602 (2012); http://dx.doi.org/10.1116/1.4757950 (5 pages)

Online Publication Date: 9 October 2012

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A glass ultrahigh vacuum chamber with rubidium alkali metal dispensers and nonevaporable getter pumps has been developed and used to create a cold atomic sample in a chamber that operates with only passive vacuum pumps. The ion-mass spectrum of evaporated gases from the alkali metal dispenser has been recorded as a function of dispenser current. The efficacy of the nonevaporable getter pumps in promoting and maintaining vacuum has been characterized by observation of the Rb vapor optical absorption on the D2 transition at 780 nm and vacuum chamber pressure rate of rise tests. The authors have demonstrated a sample of laser-cooled Rb atoms in this chamber when isolated and operating without active vacuum pumps.
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07.30.Cy Vacuum pumps
32.10.Bi Atomic masses, mass spectra, abundances, and isotopes
32.30.Bv Radio-frequency, microwave, and infrared spectra

Comparison of beryllium oxide and pyrolytic graphite crucibles for boron doped silicon epitaxy

Dyan Ali and Christopher J. K. Richardson

J. Vac. Sci. Technol. A 30, 061603 (2012); http://dx.doi.org/10.1116/1.4764509 (4 pages)

Online Publication Date: 30 October 2012

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This article reports on the comparison of beryllium oxide and pyrolytic graphite as crucible liners in a high-temperature effusion cell used for boron doping in silicon grown by molecular beam epitaxy. Secondary ion mass spectroscopy analysis indicates decomposition of the beryllium oxide liner, leading to significant incorporation of beryllium and oxygen in the grown films. The resulting films are of poor crystal quality with rough surfaces and broad x-ray diffraction peaks. Alternatively, the use of pyrolytic graphite crucible liners results in higher quality films.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.35.bg Semiconductors
61.72.uf Ge and Si
68.55.ag Semiconductors
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Growth of Fe cubical particles on substrates during gas flow sputtering

Hiroshi Sakuma, Shinichi Sakamoto, Akimasa Naoi, Yusuke Saito, and Kiyoshi Ishii

J. Vac. Sci. Technol. A 30, 061604 (2012); http://dx.doi.org/10.1116/1.4764933 (6 pages)

Online Publication Date: 7 November 2012

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The shape of Fe fine particles formed during gas flow sputtering was examined. Simultaneous formation of truncated dodecahedron particles with an average size of 80 nm and small particles with an average size of 20 nm was observed in an Ar gas flow. Truncated dodecahedron particles deposited on a substrate were observed to grow and change their shape as a result of collisions with the small particles. Under conditions of short substrate-target separation or a high gas flow rate, particles with a novel shape and possessing {100} facets of a body-centered-cubic structure and a staircase-like structure on the edges of the cubes were formed. On the other hand, under conditions of long substrate-target separation and a low gas flow rate, aggregated particles, which were almost round particles covered with smaller particles, were formed. This behavior is explained by the kinetic energy of the small particles, termed “gas flow energy” in this paper, which is a function of the velocity of the small particles prior to colliding with the truncated dodecahedron particles on the substrate.
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75.75.Cd Fabrication of magnetic nanostructures
75.50.Mm Magnetic liquids
75.50.Tt Fine-particle systems; nanocrystalline materials
81.15.Cd Deposition by sputtering
81.16.-c Methods of micro- and nanofabrication and processing
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Design of an effective vibration isolation system for measurements sensitive to low-frequency vibrations

Katsuya Iwaya, Ryota Shimizu, Akira Teramura, Seiji Sasaki, Toru Itagaki, and Taro Hitosugi

J. Vac. Sci. Technol. A 30, 063201 (2012); http://dx.doi.org/10.1116/1.4754700 (5 pages)

Online Publication Date: 25 September 2012

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We constructed an effective vibration isolation system that employed an active vibration isolation system on top of a thick base-slab foundation and evaluated the performance by comparing the resultant vibration levels with the most stringent criterion of architectural standards (VC-E). The effect of the thick base slab on reducing vibrations was systematically investigated by comparing vibration levels at the bedrock with those at the base slab. The vibration spectra measured on the active vibration isolation table achieved an overall 1/100–1/200 of the VC-E in the range of 1–100 Hz, except at 5–25 Hz in the vertical direction. In addition, these vibration spectra were compared with those from another vibration isolation system based on a separate foundation. These comparative studies of vibration isolation, including details of the entire systems, can provide useful information for designing an effective vibration isolation system for various experiments that are highly sensitive to low-frequency vibration noise, such as scanning probe microscopy, electron microscopy, and ultrafine patterning.
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07.10.Fq Vibration isolation
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