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Nov 2011

Volume 29, Issue 6, Articles (06xxxx)

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J. Vac. Sci. Technol. B 29, 060801 (2011); http://dx.doi.org/10.1116/1.3641913 (21 pages)

Jian Shi and Xudong Wang
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Large-area suspended graphene on GaN nanopillars

Chongmin Lee, Byung-Jae Kim, Fan Ren, S. J. Pearton, and Jihyun Kim

J. Vac. Sci. Technol. B 29, 060601 (2011); http://dx.doi.org/10.1116/1.3654042 (5 pages) | Cited 1 time

Online Publication Date: 26 October 2011

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The authors have demonstrated large-area suspended graphene on GaN nanopillars predefined by nanosphere lithography and inductively coupled plasma etching. The graphene was successfully suspended over large areas without ripples and corrugations. Scanning electron microscopy, atomic force microscopy and micro-Raman spectroscopy were used to characterize the properties of the suspended graphene on nanopillars. The thermal properties of the suspended and supported graphene were investigated by varying the underlying GaN nanopilllar geometries from flat-top to sharp-cone morphologies and heating the resulting structures via irradiation with laser powers of 1.53 mW, 8.03 mW, and 16.19 mW. The heat transfer was effective even when the contact area between the suspended graphene and the supporting substrate was small, due to the high thermal conductivities of graphene and GaN. The extremely high thermal conductivity of the graphene can improve the thermal management in GaN-based high power electronic and optoelectronics devices, a critical factor for their long-term reliability.
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81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.46.-w Structure of nanoscale materials
68.37.Ps Atomic force microscopy (AFM)
78.30.Fs III-V and II-VI semiconductors

Recessed area patterning via nanoimprint lithography

Karen S. L. Chong, Yeong-Yuh Lee, and Hong Yee Low

J. Vac. Sci. Technol. B 29, 060602 (2011); http://dx.doi.org/10.1116/1.3660393 (5 pages)

Online Publication Date: 11 November 2011

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Three-dimensional structures in the channels of a patterned substrate are typically fabricated via a variety of approaches that include a combination of soft lithography and multiple photolithographic steps which can be complex and time consuming. Moreover, the design of a three-dimensional hierarchical template to carry out the direct recessed imprinting of polymers at the recessed area would be complicated and costly. To overcome this shortcoming, we report a method to fabricate a three-dimensional template that is capable of carrying out a direct recessed area imprint via the use of a polymer material. A sequential nanoimprinting process was used to first fabricate the template. A primary imprint was carried out to emboss micron-sized primary features onto a polymer template after which a secondary imprinting process was then carried out to imprint smaller nanoscale features onto the primary features thereby creating three-dimensional or hierarchical features on the polymer template. The template with three-dimensional features was then used to directly pattern other polymers creating patterns with micron features and nanoscale features in the channels via a one step imprinting process.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography

Investigating the effect of off-state stress on trap densities in AlGaN/GaN high electron mobility transistors

L. Liu, F. Ren, S. J. Pearton, R. C. Fitch, D. E. Walker, K. D. Chabak, J. K. Gillespie, M. Kossler, M. Trejo, David Via, and A. Crespo

J. Vac. Sci. Technol. B 29, 060603 (2011); http://dx.doi.org/10.1116/1.3660396 (5 pages) | Cited 3 times

Online Publication Date: 17 November 2011

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The temperature dependence of sub-threshold drain current versus gate voltage at a constant drain bias voltage were used to determine the trap densities in AlGaN/GaN high electron mobility transistors (HEMTs) before and after the off-state stress. Two different trap densities were obtained for the measurements conducted at 300–493 K and 493–573 K, respectively. The trap density at the lower temperature range almost doubled from 1.64 × 1012 to 3.3 × 1012/cm2–eV after a critical voltage for degradation of HEMTs was reached during the off-state drain voltage step-stress. The trap density at the higher temperature range only slightly increased from 8.1 × 1012 and 9.2× 1012/cm2–eV after the device stress. The trap densities were also strongly dependent on drain bias voltage; measurements conducted at higher drain bias voltages exhibited larger trap density due to more hot electrons generated at these conditions.
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85.30.Tv Field effect devices

Temperature mapping using single wavelength pyrometry during epitaxial growth

Bernard Paquette, Badii Gsib, and Richard Arès

J. Vac. Sci. Technol. B 29, 060604 (2011); http://dx.doi.org/10.1116/1.3660395 (5 pages) | Cited 1 time

Online Publication Date: 21 November 2011

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Epitaxial substrate temperature remains one of the most important parameters to control during deposition for the production of heterostructures with a high level of quality and uniformity. To this end, full wafer temperature measurement offers a powerful way to obtain information on the epitaxial process. This article presents a simple method to obtain in situ temperature mappings over a 4 in. wafer using a low-cost commercially available CCD camera as a single wavelength pyrometer in the near-infrared wavelength range. By correlating this pyrometric measurement with an independent temperature measurement, the emissivity at a single point can be extracted during epitaxial growth and is then used to correct temperature mappings under certain conditions.
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07.20.Dt Thermometers
07.20.Ka High-temperature instrumentation; pyrometers
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Functional semiconductor nanowires via vapor deposition

Jian Shi and Xudong Wang

J. Vac. Sci. Technol. B 29, 060801 (2011); http://dx.doi.org/10.1116/1.3641913 (21 pages) | Cited 3 times

Online Publication Date: 27 September 2011

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More than a decade’s worth of research has led to significant progress toward an understanding of the growth behavior of nanowires (NWs). Among all of the different bottom-up and top-down strategies, vapor deposition has unique advantages in producing high quality NW structures. This paper reviews the current understandings of the thermodynamics and kinetics of NW nucleation and growth behaviors using a vapor deposition approach. NW deposition from the vapor phase is divided into two general categories: that with and that without foreign metal catalysts. The distinct crystal nucleation and growth mechanisms, NW morphologies, and controlling parameters of these two categories are presented in detail and compared. In addition, ways to apply these strategies in order to realize complex NW structures such as NW heterojunctions and 3D NW networks are also discussed. The information about NW vapor deposition reviewed in this paper provides a comprehensive background for understanding NW growth phenomena, ways of achieving morphology and property control, and how to eventually pave the road toward industrial-level NW manufacturing.
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68.65.La Quantum wires (patterned in quantum wells)
81.07.Gf Nanowires
81.07.Vb Quantum wires
65.40.G- Other thermodynamical quantities
81.10.Bk Growth from vapor
82.60.Nh Thermodynamics of nucleation
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Effects of proton irradiation on dc characteristics of InAlN/GaN high electron mobility transistors

C. F. Lo, L. Liu, F. Ren, H.-Y. Kim, J. Kim, S. J. Pearton, O. Laboutin, Yu Cao, J. W. Johnson, and I. I. Kravchenko

J. Vac. Sci. Technol. B 29, 061201 (2011); http://dx.doi.org/10.1116/1.3644480 (6 pages) | Cited 7 times

Online Publication Date: 29 September 2011

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The effects of proton irradiation on the dc characteristics of InAlN/GaN high electron mobility transistors were investigated. In this study we used 5 MeV protons with doses varying from 2 × 1011 to 2 × 1015 cm−2. The transfer resistance and contact resistivity suffered more degradation as compared to the sheet resistance. With irradiation at the highest dose of 2 × 1015 cm−2, both forward- and reverse-bias gate currents were increased after proton irradiation. A negative threshold-shift and reduction of the saturation drain current were also observed as a result of radiation-induced carrier scattering and carrier removal. Devices irradiated with doses of 2 × 1011 to 2 × 1015 cm−2 exhibited minimal degradation of the saturation drain current and extrinsic transconductance. These results show that InAlN/GaN high electron mobility transistors are attractive for space-based applications when high-energy proton fluxes are present.
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85.30.Tv Field effect devices
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Graphitic carbon film formation under Ni templates by radio-frequency sputtering for transparent electrode applications

Meng-Yu Lin, Yung-Shuan Sheng, Shu-Han Chen, Ching-Yuan Su, Lain-Jong Li, and Shih-Yen Lin

J. Vac. Sci. Technol. B 29, 061202 (2011); http://dx.doi.org/10.1116/1.3646481 (3 pages)

Online Publication Date: 7 October 2011

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An alternate approach to the preparation of transfer-free graphitic carbon films is proposed in this paper. Using a standard radio-frequency sputtering system and a high-temperature annealing procedure, graphitic carbon films are prepared under Ni templates. The results demonstrate that carbon precipitation occurs at both Ni template interfaces. With repeated annealing procedures at 1100 °C, a sheet resistance of 1.36 × 104 Ω/□ can be achieved. Selective carbon film deposition has also been developed via pattern formation on the Ni templates. The results indicate the potential application of this method to transparent electrode formation.
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68.55.aj Insulators
81.15.Cd Deposition by sputtering
81.40.Gh Other heat and thermomechanical treatments
73.61.Ng Insulators

Pulsed-laser atom probe tomography of p-type field effect transistors on Si-on-insulator substrates

S. Jin, K. S. Jones, P. A. Ronsheim, and M. Hatzistergos

J. Vac. Sci. Technol. B 29, 061203 (2011); http://dx.doi.org/10.1116/1.3647879 (4 pages) | Cited 1 time

Online Publication Date: 7 October 2011

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Forty-five nanometer gate length p-type field effect transistors fabricated on Si-on-insulator substrates were analyzed using three-dimensional pulsed laser atom probe tomography. An optimized sample preparation methodology involving spacer etching and a change in sample orientation to align the Si/buried-SiO2 interface with the analysis direction was developed to overcome the inherent difficulties in field evaporation of insulating materials present in the device structure. Atom probe tomography analysis of samples prepared in this cross-sectional orientation was used to observe B segregation to the gate SiO2 at 5 nm from the edge of the gate, from both the poly-Si gate doping as well as the source–drain extension ion-implantation following rapid thermal annealing at 900 °C for 16 or 32 s.
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85.30.Tv Field effect devices

Comparison of passivation layers for AlGaN/GaN high electron mobility transistors

R. C. Fitch, D. E. Walker, Jr., K. D. Chabak, J. K. Gillespie, M. Kossler, M. Trejo, A. Crespo, L. Liu, T. S. Kang, C.-F. Lo, F. Ren, D. J. Cheney, and S. J. Pearton

J. Vac. Sci. Technol. B 29, 061204 (2011); http://dx.doi.org/10.1116/1.3656390 (6 pages) | Cited 3 times

Online Publication Date: 27 October 2011

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AlGaN/GaN high electron mobility transistors require surface passivation layers to reduce the effects of surface traps between the gate and drain contacts. These traps lead to the creation of a virtual gate and the associated collapse of drain current under rf conditions. The authors have investigated three different materials for passivation layers, namely thin (7.5 nm) Al2O3 and HfO2 deposited with an atomic layer deposition system and conventional, thick (200 nm) plasma enhanced chemically vapor deposited SiNX. The latter is found to be the most effective in reducing drain current loss during gate lag measurements in both single and double pulse mode, but also reduces fT and fMAX through additional parasitic capacitance.
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85.30.Tv Field effect devices
81.65.Rv Passivation
84.32.Dd Connectors, relays, and switches

Investigation of polarity effects on the degradation of Pd/Ti/Pt ohmic contacts to p-type SiC under current stress

B. P. Downey, J. R. Flemish, and S. E. Mohney

J. Vac. Sci. Technol. B 29, 061205 (2011); http://dx.doi.org/10.1116/1.3659730 (7 pages)

Online Publication Date: 10 November 2011

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Degradation of low resistance Pd/Ti/Pt ohmic contacts to p-SiC under high current density stressing and the effects of polarity are presented. The Pd/Ti/Pt contact is compared to the conventional Ti/Al contact and provides a lower contact resistance, smoother surface morphology, lower required annealing temperature, and better stability under current stressing. A thick Au overlayer is added to both metallizations for continuous direct current (dc) and pulsed dc stressing. A 31% increase in total resistance is measured for the Ti/Al contacts after 20 h of continuous dc stressing at 200 mA for 5 μm radius contacts, compared to an increase of only 2.5% for the Pd/Ti/Pt contacts. Degradation of the entire anode and cathode was observed for the Ti/Al contacts, whereas damage to only the leading edge of the cathode of the Pd/Ti/Pt contacts was found. The degradation behavior of the Pd/Ti/Pt contacts is explained by a polarity effect, where the cathode reached a higher temperature than the anode under continuous dc stressing. When the contacts were instead pulsed with a dc current of 200 mA using 5 μs pulses and a 10% duty cycle, both contact schemes were electrically stable, probably due to the reduced temperature during testing. However, chemical instability of the Ti/Al contacts was still evident, and although the Pd/Ti/Pt ohmic contacts appeared unaltered, voiding between the Au bond pad and the Pd/Ti/Pt metallization occurred.
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73.40.Ns Metal-nonmetal contacts
84.32.Dd Connectors, relays, and switches
85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Cg Contact resistance, contact potential
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PEN/Si3N4 bilayer film for dc bus capacitors in power converters in hybrid electric vehicles

Chen Zou, Qiming Zhang, Shihai Zhang, Douglas Kushner, Xin Zhou, Richard Bernard, and Raymond J. Orchard, Jr.

J. Vac. Sci. Technol. B 29, 061401 (2011); http://dx.doi.org/10.1116/1.3646479 (4 pages) | Cited 1 time

Online Publication Date: 7 October 2011

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High performance hybrid bilayer capacitor film has been developed by controlled deposition of silicon nitride (Si3N4) on polyethylene naphthalate (PEN). It was found that silicon nitride prepared with plasma-enhanced chemical vapor deposition can significantly increase the dielectric constant (K) and energy density of PEN by more than 20% and 50%, respectively. Moreover, the PEN/Si3N4 bilayer hybrid film also exhibits appropriate mechanical and thermal properties for capacitor winding. The high operating temperature and energy density of the PEN/Si3N4 bilayer dielectric film are very attractive for dc bus capacitors used in power inverters or converters found in hybrid electric vehicles, wind turbine generators, grid-tied photovoltaics, and smart grid, as well as pulsed power systems.
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68.55.aj Insulators
77.22.Ch Permittivity (dielectric function)
68.60.Bs Mechanical and acoustical properties
84.32.Tt Capacitors
77.55.-g Dielectric thin films
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Fabrication of two-dimensional tungsten photonic crystals for high-temperature applications

M. Araghchini, Y. X. Yeng, N. Jovanovic, P. Bermel, L. A. Kolodziejski, M. Soljacic, I. Celanovic, and J. D. Joannopoulos

J. Vac. Sci. Technol. B 29, 061402 (2011); http://dx.doi.org/10.1116/1.3646475 (4 pages) | Cited 4 times

Online Publication Date: 24 October 2011

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This article details microfabrication of two-dimensional tungsten photonic crystals (2D W PhCs) for high-temperature applications such as selective thermal emitters for thermophotovoltaic energy conversion. In particular, interference lithography and reactive ion etching are used to produce large area single crystal tungsten 2D PhCs. For this investigation, we fabricated a 2D W PhC sample consisting of an array of cylindrical cavities with 800 nm diameter, 1.2 μm depth, and 1.2 μm period. Extensive characterization and calibration of all microfabrication steps are presented. Experimentally obtained thermal emissivity spectrum is shown to match well with numerical simulations.
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42.70.Qs Photonic bandgap materials
81.16.Nd Micro- and nanolithography
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
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Integration of moth-eye structures into a poly(dimethylsiloxane) stamp for the replication of functionalized microlenses using UV-nanoimprint lithography

Tobias Senn, Oliver Kutz, Christian Weniger, Junming Li, Max Schoengen, Heike Löchel, Johannes Wolf, Philipp Göttert, and Bernd Löchel

J. Vac. Sci. Technol. B 29, 061601 (2011); http://dx.doi.org/10.1116/1.3644474 (5 pages) | Cited 2 times

Online Publication Date: 3 October 2011

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The increasing demand for low cost camera modules for mobile devices requires technological solutions for the manufacturing process. One of the most promising fabrication processes for microlenses for camera modules is UV-nanoimprint lithography. In a typical fabrication process, an elastomer stamp is used to replicate microlenses. In this work, a method is presented to integrate moth-eye structures as an antireflective layer into a poly(dimethylsiloxane) (PDMS) stamp containing a microlens array. The integration of these structures is done by a thermoforming process. Due to the integration of the moth-eye structures into the PDMS stamp, the optical performance of the replicated microlenses can be improved and no additional processing steps are necessary after the replication process.
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42.82.Et Waveguides, couplers, and arrays
81.16.Nd Micro- and nanolithography
81.10.Fq Growth from melts; zone melting and refining
42.79.Bh Lenses, prisms and mirrors
42.82.Cr Fabrication techniques; lithography, pattern transfer

Fabrication of ultra-high-density nanodot array patterns (∼3 Tbits/in.2) using electron-beam lithography

Min-Hyun Lee, Hyun-Mi Kim, Seong-Yong Cho, Kipil Lim, Soo-Yeon Park, Jae Jong Lee, and Ki-Bum Kim

J. Vac. Sci. Technol. B 29, 061602 (2011); http://dx.doi.org/10.1116/1.3646469 (5 pages)

Online Publication Date: 12 October 2011

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The authors fabricated 15 nm pitch scale high-density dot patterns on a Si substrate using a hydrogen silsesquioxane electron-beam (e-beam) resist, vacuum treatment as a prebake, and vertical sidewall etching. The e-beam lithography was performed at 100 keV. The dot density fabricated was close to 3 Tbits/in.,2 which is one of the highest density patterns reported thus far. The process window was quite wide and the result can be easily and routinely duplicated.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning

Development of an experimental technique for testing rheological properties of ultrathin polymer films used in nanoimprint lithography

Dariusz M. Jarzabek, Zygmunt Rymuza, Akira Horiba, and Yoshihiko Hirai

J. Vac. Sci. Technol. B 29, 061603 (2011); http://dx.doi.org/10.1116/1.3656377 (6 pages)

Online Publication Date: 3 November 2011

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A new method for the measurement of rheological properties (complex viscosity, viscosity and elasticity) of thin polymeric films is presented. The probe, which is placed on the end of an arm of a mini tuning fork, is caused to oscillate and then is put into poly(methyl methacrylate) films, whose thickness ranges from 30 nm to 1080 nm. All measured properties depend on temperature, thickness of the films, indentation depth and the molecular weight of PMMA. Complex viscosity, viscosity and elasticity are found to be lower at higher temperatures and higher with greater molecular weight. They are also lower for thicker films. The results gained from this experiment may be useful in the development of nanoimprint lithography and many other branches of nanotechnology. Furthermore, the method allows for the measurement of the rheological properties of many different thin films (nanoimprint polymers, oils, lubricants) at different temperatures.
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07.10.-h Mechanical instruments and equipment
68.60.Bs Mechanical and acoustical properties
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.dq Other elastic constants
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.16.Nd Micro- and nanolithography

Method to pattern etch masks in two inclined planes for three-dimensional nano- and microfabrication

R. Willem Tjerkstra, Léon A. Woldering, Johanna M. van den Broek, Fred Roozeboom, Irwan D. Setija, and Willem L. Vos

J. Vac. Sci. Technol. B 29, 061604 (2011); http://dx.doi.org/10.1116/1.3662000 (8 pages) | Cited 1 time

Online Publication Date: 5 December 2011

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The authors present a method to pattern etch masks for arbitrary nano- and microstructures on different, inclined planes of a sample. Our method allows standard CMOS fabrication techniques to be used in different inclined planes; thus yielding three-dimensional structures with a network topology. The method involves processing of the sample in a first plane, followed by mounting the prepared sample in a specially designed silicon holder wafer such that the second, inclined plane is exposed to continued processing. As a proof of principle we demonstrate the fabrication of a patterned chromium etch mask for three-dimensional photonic crystals in silicon. The etch mask is made on the 90° inclined plane of a silicon sample that already contains high aspect ratio nanopores. The etch mask is carefully aligned with respect to these pores, with a high translational accuracy of <30 nm along the y-axis and a high rotational accuracy of 0.71° around the z-axis of the crystal. Such high alignment precisions are crucial for nanophotonics and for sub-micrometer applications in general. Although we limit ourselves to processing on two planes of a sample, it is in principle possible to repeat the presented method on more planes. The authors foresee potential applications of this technique in, e.g., microfluidics, photonics, and three-dimensional silicon electronics.
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81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
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Growth mechanism of multilayer-graphene-capped, vertically aligned multiwalled carbon nanotube arrays

Yuki Matsuoka, Ian T. Clark, and Masamichi Yoshimura

J. Vac. Sci. Technol. B 29, 061801 (2011); http://dx.doi.org/10.1116/1.3644494 (7 pages)

Online Publication Date: 7 October 2011

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The authors describe a rigorous investigation of the growth mechanism of composite structures consisting of graphene multilayers supported by vertically aligned multiwalled carbon nanotubes (VA-MWCNTs). The synthesis was performed via chemical vapor deposition with ethanol as a carbon source and iron films ranging in thickness from 1 to 9 nm as the catalyst. The morphology of grown films was investigated using scanning electron microscopy and transmission electron microscopy (TEM), and the crystallinity was studied using TEM and Raman spectroscopy. Thicker Fe films (8 or 9 nm) yielded composite structures, thin Fe films (1 to 4 nm) produced pure VA-MWCNTs, and Fe layers between 5 and 7 nm produced an intermediate structure composed of bundles of VA-MWCNTs fused together at their tips. The authors present growth mechanisms for all three structures. The authors attribute the change from VA-MWCNT to intermediate/composite with higher Fe film thicknesses to the formation of graphitic layers at the initial growth stage.
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81.16.Be Chemical synthesis methods
81.16.Hc Catalytic methods
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.55.J- Morphology of films
81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Fabrication of nanogaps by a progressive electromigration technique using wires of various thicknesses

Swatilekha Saha, Guoguang Qian, and Kim M. Lewis

J. Vac. Sci. Technol. B 29, 061802 (2011); http://dx.doi.org/10.1116/1.3647908 (4 pages)

Online Publication Date: 18 October 2011

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The authors report the fabrication of nanogaps formed by electromigration from gold wires of various widths (25–80 nm). This technique is a reliable and consistent method to create quality gaps without the need of very thin gold wires. The gaps are fabricated at room temperature and ambient atmosphere in contrast to the method of performing electromigration at liquid helium temperatures and in high vacuum environments. The authors observed that every nanogap formed using this technique was free of residual particles left over from the electromigration process.
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81.16.-c Methods of micro- and nanofabrication and processing
66.30.Qa Electromigration

Laser nitriding of niobium for application to superconducting radio-frequency accelerator cavities

S. Singaravelu, J. M. Klopf, G. Krafft, and M. J. Kelley

J. Vac. Sci. Technol. B 29, 061803 (2011); http://dx.doi.org/10.1116/1.3656380 (6 pages) | Cited 2 times

Online Publication Date: 1 November 2011

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Particle accelerators are a key tool for scientific research ranging from fundamental studies of matter to analytical studies at light sources. Cost-for-performance is critical, both in terms of initial capital outlay and ongoing operating expense, especially for electricity. The major factor is the niobium superconducting radio frequency (SRF) accelerator cavities at the heart of many of these machines. Presently, niobium SRF cavities operate near 1.9 K, well below the 4.2 K atmospheric boiling point of liquid helium to obtain sufficient performance. The consequent electric power costs are the most significant limit to operate the SRF cavities at 1.9 K. Transforming the cavity interior surface from niobium to δ niobium nitride (δNbN) with a critical temperature (Tc) ≅ 17 K instead of 9.2 K, appears to be a promising approach to raising the operating temperature. The traditional furnace method has nitrided niobium, but apparently have not been able to obtain δNbN.1 Moreover, furnace nitriding requires exposing the complete SRF cavity to an aggressive time-temperature history, risking mechanical distortion. As an alternative, laser gas nitriding has been applied successfully to a number of metals.2 A very recent review is available.3 The beam dimensions and thermal diffusion length permit modeling in one dimension to predict the time course of the surface temperature for a range of per-pulse energy densities. As with the earlier work,2 we chose conditions just sufficient for boiling of the niobium surface as a reference point. The treated materials were examined by scanning electron microscopy (SEM), electron probe microanalysis and x ray diffraction (XRD). The SEM images show a sharp transition with fluence from a smooth, undulating topography to significant roughening, interpreted here as the onset of ablation. Electron probe microanalysis measurements found a constant value of the nitrogen/niobium atom ratio to depths greater than the SRF active layer thickness. Certain irradiation conditions resulted in atomic ratio values consistent with formation of δNbN, and XRD data indicated only δNbN on top of the niobium metal.
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85.25.-j Superconducting devices
84.40.Az Waveguides, transmission lines, striplines
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation

High temperature focused ion beam response of graphite resulting in spontaneous nanosheet formation

Rupert Langegger, Alois Lugstein, Markus Glaser, Emmerich Bertagnolli, and Andreas Steiger-Thirsfeld

J. Vac. Sci. Technol. B 29, 061804 (2011); http://dx.doi.org/10.1116/1.3661994 (5 pages)

Online Publication Date: 16 November 2011

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This work presents an experimental study of a novel combination of a focused ion beam (FIB) with a heating stage to produce real-time microstructural imaging at elevated substrate temperatures from FIB exposed highly ordered pyrolytic graphite (HOPG). The surface modifications achieved by different angles of ion beam incidence and various substrate temperatures were investigated in situ by field emission scanning electron microscopy and afterwards by atomic force microscopy. The authors studied the formation and self-organization of ripples, porous structures, and graphite nanosheets (GNS), which appear spontaneously during FIB irradiation of HOPG. Here the evolution of pseudoperiodical ripples from small amplitudes to nanospikes with increasing ion fluences and the transformation into disorganized porous structures at higher temperatures was observed and further investigated. Moreover, the authors were able to induce the spontaneous formation of sheet like carbon nanostructures at substrate temperatures above T = 500 °C by controlling the scan speed and the ion fluence. These high aspect ratio crystalline GNS, several micrometers high and thinner than 60 nm, can be formed at predefined sites on the HOPG surface.
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81.16.-c Methods of micro- and nanofabrication and processing
81.40.Gh Other heat and thermomechanical treatments
81.05.uf Graphite
61.43.Gt Powders, porous materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.-b Nanoscale materials and structures: fabrication and characterization

Morphology of the Au-Si interface formed during solidification of liquid Au/Si(111) islands

Nick Jungwirth, Eric Dailey, Prashanth Madras, and Jeff Drucker

J. Vac. Sci. Technol. B 29, 061805 (2011); http://dx.doi.org/10.1116/1.3661996 (6 pages) | Cited 1 time

Online Publication Date: 17 November 2011

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Au islands grown on Si(111) substrates at substrate temperatures of 500 and 600 °C, both of which are greater than the bulk Au-Si eutectic temperature of 363 °C, are characterized using atomic force (AFM) and electron microscopy. Specific islands are imaged using AFM before and after Au dissolution using aqua regia to characterize the Au-Si interface formed as the islands solidify from the liquid phase while cooling from the growth temperature. Subsequent to Au dissolution, the islands present a craterlike morphology with a pit that may extend below the substrate surface depending on growth and annealing conditions. Craters formed beneath islands grown at a substrate temperature of 600 °C exhibit pits that penetrate below the substrate surface to a depth that is proportional to the area of the island footprint and possess a well-developed (111) facet at their base. Facets are also sometimes observed in the crater sidewalls and are more prevalent in samples slowly cooled through the solidus temperature than those that are radiatively quenched. Transmission electron micrographs of etched islands indicate the presence of segregated Au nanocrystals entrained in the crater lip.
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61.46.Hk Nanocrystals
81.30.Fb Solidification
81.40.Gh Other heat and thermomechanical treatments
81.65.Cf Surface cleaning, etching, patterning
64.70.D- Solid-liquid transitions
64.75.Bc Solubility

Oxide nanotube analogues: CuO nanobarrels

H. H. Farrell and Ruben D. Parra

J. Vac. Sci. Technol. B 29, 061806 (2011); http://dx.doi.org/10.1116/1.3661990 (5 pages)

Online Publication Date: 29 November 2011

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Recently, CuO “rings” on the order of 100 nm diameter have been observed experimentally by El-Azab and Liang [A. El-Azab and Y. Liang, Philos. Mag. 83, 3847 (2003)]. In a separate effort, we have used first principles density functional calculations to investigate smaller, single walled CuO structures that appear to be nanotubes or nanobarrels with a square unit mesh rather than the hexagonal mesh of carbon nanotubes. These CuO nanobarrels are novel and unique. They are metallic or semimetallic in nature having unoccupied energy levels just above the Fermi Level. Different nanobarrels have a different spins, depending on their size and geometry. Those with an even number of CuO units may have spin zero, or be ferrimagnetic. Those with an odd number of CuO units are always ferrimagnetic with a residual spin. The authors anticipate that these nanostructures will almost certainly yield intriguing results when studied experimentally.
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71.20.Ps Other inorganic compounds
75.50.Gg Ferrimagnetics
61.46.Hk Nanocrystals
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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Semiconductor nanopores formed by chemical vapor deposition of heteroepitaxial SiC films on SOI(100) substrates

Yoshifumi Ikoma, Hafizal Yahaya, Keiji Kuriyama, Hirofumi Sakita, Yuta Nishino, and Teruaki Motooka

J. Vac. Sci. Technol. B 29, 062001 (2011); http://dx.doi.org/10.1116/1.3646471 (5 pages)

Online Publication Date: 7 October 2011

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The authors investigated the formation of nanometer-scale pore (nanopore) arrays by chemical vapor deposition (CVD) of heteroepitaxial SiC films on Si(100) membranes prepared by anisotropic etching of silicon on insulator substrates from the back-side surfaces. SiC heteroepitaxial films with thicknesses of ∼10 nm were grown by pulse jet CVD of CH3SiH3 gas. During the SiC growth, inverted pyramidal pits with {111} facets grew into the Si membranes due to the surface diffusion of Si atoms outward from the bulk Si. Nanopores were formed at the tips of the inverted pyramidal pits. The pore sizes were found to be dependent on the existence of the buried oxide layers under the Si membranes. It is suggested that maintaining the {111} facets during the SiC growth on the Si membrane is essential for smaller size (∼nm) pore formation.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
66.30.Pa Diffusion in nanoscale solids
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
81.65.Cf Surface cleaning, etching, patterning
68.35.Fx Diffusion; interface formation
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Suppression of boron diffusion in deep submicron devices

Michael A. Gribelyuk, Phil Oldiges, Paul A. Ronsheim, Jun Yuan, and Leon Kimball

J. Vac. Sci. Technol. B 29, 062201 (2011); http://dx.doi.org/10.1116/1.3656376 (4 pages)

Online Publication Date: 16 November 2011

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Two-dimensional electrostatic potential of 45 nm technology semiconductor devices was mapped by electron holography with 2 nm resolution. The 2-D active dopant distribution was reconstructed by the inverse modeling of the electrostatic potential. Identically manufactured devices with and without a carbon co-implant were compared. The authors show that in the presence of the carbon co-implant, the two-dimensional diffusion of the boron halo implant during thermal processing is reduced. It is demonstrated that the carbon co-implant improves the control of the device short channel effects.
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85.40.Ry Impurity doping, diffusion and ion implantation technology

Interface and electrical properties of Tm2O3 gate dielectrics for gate oxide scaling in MOS devices

M. Kouda, T. Kawanago, P. Ahmet, K. Natori, T. Hattori, H. Iwai, K. Kakushima, A. Nishiyama, N. Sugii, and K. Tsutsui

J. Vac. Sci. Technol. B 29, 062202 (2011); http://dx.doi.org/10.1116/1.3660800 (4 pages) | Cited 2 times

Online Publication Date: 17 November 2011

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The authors analyzed the electrical properties of MOS capacitors with thulium oxide (Tm2O3) gate dielectrics and evaluated the thickness-dependent properties. The authors observed that a thin silicate layer (instead of an SiO2 layer) with a thickness of less than 1 nm had formed between the Tm2O3 and Si substrate after an annealing process at 500 °C. The authors obtained an effective oxide thickness of 0.55 nm with dielectric constants of 18 and 12 for Tm2O3 and its silicate, respectively. The leakage current properties with different thicknesses have revealed sufficient suppression by 2 orders of magnitude from the required levels. However, conduction mechanism analyses and a model to explain the flatband voltage (Vfb) behavior on different thicknesses showed the presence of charged defects in the oxides, which were mostly located at the Tm2O3 and silicate interface. The effective mobility of nFET showed degraded properties by Coulomb scatterings, which were consistent with the Vfb shift. The less reactive properties of Tm2O3 are advantageous for gate oxide scaling in future MOS devices.
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84.32.Tt Capacitors
85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing
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Fabrication of a blue organic light-emitting diode with a novel thermal deposition boat

Sangmin Lee and Ching W. Tang

J. Vac. Sci. Technol. B 29, 062401 (2011); http://dx.doi.org/10.1116/1.3656392 (4 pages) | Cited 4 times

Online Publication Date: 27 October 2011

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A highly efficient blue phosphorescent organic light emitting diode (PhOLED) is fabricated by using a novel thermal deposition boat. The boat has two unique features: indirect deposition rate control and fast rate response. With these features, a compact combinatorial evaporation source module is constructed, which utilizes only limited space and enables the fabrication of OLED devices of complex architectures. The deposition rate using this newly designed boat can be controlled within 5% accuracy and the rate response is sufficiently fast that it is particularly useful for producing emitting layers with a linearly graded composition. Two blue PhOLED devices with different architecture in the emitting layer are fabricated with the new boat. The device with a linearly graded mixed host shows higher efficiency than the device with a uniformly mixed one, indicating the advantage of gradual interface change.
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85.60.Jb Light-emitting devices
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Surface plasmon waveguide devices with Tg-bonded Cytop claddings

Charles Chiu, Ewa Lisicka-Skrzek, R. Niall Tait, and Pierre Berini

J. Vac. Sci. Technol. B 29, 062601 (2011); http://dx.doi.org/10.1116/1.3660801 (7 pages) | Cited 1 time

Online Publication Date: 21 November 2011

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Surface plasmon waveguide devices were fabricated in symmetric Cytop claddings by bonding the claddings with Au waveguides and microfluidic channels at the interface. Au features were patterned and deposited on the bottom wafer and microfluidic channels were patterned and etched into the top wafer. Aligned wafer bonding and annealing were performed at temperatures slightly above the glass transition temperature (Tg) of Cytop. The bond strength is high, allowing dicing, ultrasonic cleaning, and polishing of facets. The bond is also of good hermiticity as assessed by fluid injection, and of reasonable optical quality as verified by measurements of long-range surface plasmon propagation at λ = 1310 and 1550 nm.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
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back to top Directed Assembly

Patterned atomic layer epitaxy of Si/Si(001):H

James H. G. Owen, Joshua Ballard, John N. Randall, Justin Alexander, and James R. Von Ehr

J. Vac. Sci. Technol. B 29, 06F201 (2011); http://dx.doi.org/10.1116/1.3628673 (6 pages) | Cited 3 times

Online Publication Date: 29 August 2011

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We aim to develop techniques for the building of atomically precise structures. On the H-terminated Si(001) surface, H atoms can be selectively removed using an STM tip with appropriate lithography conditions, creating arbitrary patterns of reactive dangling bonds with atomic precision. The exposed patterns are used as templates for the growth of Si and Ge by gas-source epitaxy, using disilane and digermane as the precursor gases. The quality of the epitaxy, in terms of island size and defect density of the second and subsequent monolayer (ML), is dependent upon the electron exposure. Good-quality growth of the second and following MLs requires a multiple of the exposure required for good-quality growth of the first ML. This is interpreted in terms of remanent hydrogen in island sites in the first ML.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Modeling the power spectrum of thermal line edge roughness in a lamellar diblock copolymer mesophase

August W. Bosse

J. Vac. Sci. Technol. B 29, 06F202 (2011); http://dx.doi.org/10.1116/1.3644338 (4 pages) | Cited 1 time

Online Publication Date: 17 October 2011

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The authors examines a phenomenological expression for the thermal line edge roughness (LER) power spectrum in a lamellar diblock copolymer (DCP) that includes explicit contributions from interfacial fluctuations and bulk composition fluctuations. The author compares this equation to stochastic simulations of LER in a lamellar DCP, and it is demonstrated that the equation approximately fits the simulation data for weakly to moderately segregated DCPs. This equation will facilitate LER modeling in block copolymer directed self-assembly applications, and it can serve as the LER power spectrum model in a scattering-based LER metrology framework.
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61.41.+e Polymers, elastomers, and plastics
64.75.Va Phase separation and segregation in polymer blends/polymeric solutions

Towards an all-track 300 mm process for directed self-assembly

Chi-Chun Liu, Christopher J. Thode, Paulina A. Rincon Delgadillo, Gordon S. W. Craig, Paul F. Nealey, and Roel Gronheid

J. Vac. Sci. Technol. B 29, 06F203 (2011); http://dx.doi.org/10.1116/1.3644341 (6 pages) | Cited 7 times

Online Publication Date: 18 October 2011

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This study modifies the authors’ previously reported directed self-assembly (DSA) process of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) in order to meet the throughput and material-related requirements of a semiconductor manufacturing environment. It is demonstrated that all of the bottleneck steps in the authors’ DSA process, including the deposition of the cross-linkable mat and the deposition of the brush layer, can be done in minutes on a hot plate in an N2 atmosphere, which simulates the processing environment of a lithography track module. A 25-nm-pitch pattern resulting from a 4:1 density multiplication was demonstrated with a manufacturing-compatible organic solvent. A preliminary uniformity study on 300 mm wafers was also presented. The modified DSA process presents a viable solution to some of the anticipated throughput-related challenges to DSA commercialization and thus, brings integration of DSA within reach of the semiconductor manufacturing industry.
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81.16.Dn Self-assembly
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Fabrication of chevron patterns for patterned media with block copolymer directed assembly

Guoliang Liu, Paul F. Nealey, Ricardo Ruiz, Elizabeth Dobisz, Kanaiyalal C. Patel, and Thomas R. Albrecht

J. Vac. Sci. Technol. B 29, 06F204 (2011); http://dx.doi.org/10.1116/1.3650697 (7 pages) | Cited 1 time

Online Publication Date: 18 October 2011

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Advances in block copolymer directed assembly have highlighted the potential of block copolymer lithography to define patterned templates for magnetic recording bit patterned media (BPM). The naturally periodic features found in block copolymer films display superior size uniformity at ultrahigh densities, making them ideal lithographic masks to define the highly periodic data bits in the data sector of hard disk drives. In addition to the data bits, BPM architecture requires additional features to encode servo information. Because of the nature of the information stored in servo sectors, the geometry and shape of servo features differ from those in the data sectors, potentially compromising their compatibility with the features that can be naturally formed by block copolymers. The authors investigated the compatibility of a block copolymer directed assembly with the formation of complex chevron structures for sector header servo patterns within the framework of a BPM design that uses rectangular bits as the storage units. In order to ensure proper registration between the data tracks and the chevron patterns, the authors propose a design that employs lamellae-forming block copolymers assembled on chemical patterns with density multiplication into sets of lines that define both the data tracks and the servo features simultaneously. Due to the high free energy penalty associated with bending the lamellar domains, the block copolymer formed defective structures at the apex of the chevrons, as well as in the junction areas between chevrons and periodic horizontal lines. Adding stripes to the design of the chemical patterns near these complex areas prevented defects from propagating into the periodic line areas. In addition, the predictable defective structure offered flexibility for subsequent signal processing such as track identification and head position correction.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.41.+e Polymers, elastomers, and plastics

Selective placement of DNA origami on substrates patterned by nanoimprint lithography

Erika Penzo, Risheng Wang, Matteo Palma, and Shalom J Wind

J. Vac. Sci. Technol. B 29, 06F205 (2011); http://dx.doi.org/10.1116/1.3646900 (5 pages) | Cited 1 time

Online Publication Date: 3 November 2011

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Self-assembled DNA nanostructures can be used as scaffolds to organize small functional nanocomponents. In order to build working devices—electronic circuits, biochips, optical/photonics devices—controlled placement of DNA nanostructures on substrates must be achieved. Here we present a nanoimprint lithography-based process to create chemically patterned templates, rendering them capable of selectively binding DNA origami. Hexamethyldisilazane (HMDS) is used as a passivating layer on silicon dioxide substrates, which prevents DNA attachment. Hydrophilic areas, patterned by nanoimprint lithography with the same size and shape of the origami, are formed by selective removal of the HMDS, enabling the assembly of the origami scaffolds in the patterned areas. The use of nanoimprint lithography, a low cost, high throughput patterning technique, enables high precision positioning and orientation of DNA nanostructures on a surface over large areas.
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85.65.+h Molecular electronic devices
87.14.gk DNA
87.80.Ek Mechanical and micromechanical techniques

Optimization of block copolymer self-assembly through graphoepitaxy: A defectivity study

Raluca Tiron, Xavier Chevalier, Christophe Couderc, Jonathan Pradelles, Jessy Bustos, Laurent Pain, Christophe Navarro, Stephanie Magnet, Guillaume Fleury, and Georges Hadziioannou

J. Vac. Sci. Technol. B 29, 06F206 (2011); http://dx.doi.org/10.1116/1.3659714 (8 pages) | Cited 2 times

Online Publication Date: 10 November 2011

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In this paper we report a synoptic methodology to evaluate and optimize the long-range order induced by graphoepitaxy of block copolymer (BCP) self-assembly. The authors focus the study on a BCP that produces hexagonally packed arrays of cylinders oriented perpendicular to the substrate with the copolymer film thickness greater than the trench depth. Prepatterned structures used in the graphoepitaxy approach have been generated by e-beam lithography on a commercial hydrogen silesquioxane resist. A suitable surface modification was accomplished by grafting a random polystyrene-r-poly(methyl methacrylate) copolymer on the prepatterned surfaces. The polystyrene-b-poly(methyl methacrylate) was spin-coated and annealed in order to generate the desired self-assembly. Since the self-assembly process is based on a thermodynamic mechanism, the induced defectivity needs to be reassessed with respect to the standard lithographic process. Using the cylinder center coordinates, a Delaunay triangulation is performed to find the nearest neighbors. This triangulation enables us to easily locate the disclinations which are characterized by having a number of nearest neighbors different from six. Thus, the number of defects can be quantified precisely. Additionally, this methodology affords an accurate evaluation of both the optimum mesa and trench critical dimensions yielding defect-free surfaces and may be extended to monitor the robustness of the BCP directed self-assembly process. Such diagnostics are critical in the implementation of large scale industrial processes.
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81.16.Dn Self-assembly
81.16.Nd Micro- and nanolithography
81.40.Gh Other heat and thermomechanical treatments
68.55.am Polymers and organics
61.41.+e Polymers, elastomers, and plastics
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Di-block copolymer directed anodization of hexagonally ordered nanoporous aluminum oxide

Kunbae Noh, Chulmin Choi, Hyunsu Kim, Young Oh, Jin-Yeol Kim, Se-Yeon Jung, Tae-Yeon Seong, and Sungho Jin

J. Vac. Sci. Technol. B 29, 06F207 (2011); http://dx.doi.org/10.1116/1.3659716 (6 pages)

Online Publication Date: 10 November 2011

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Porous anodized aluminum oxide (AAO) nanostructures have been extensively investigated as versatile templates for nanodots and nanowires for many applications. Such self-ordered AAO structures are often achieved by so-called two-step anodization. Ordered pore arrangements can be obtained in the second step after removing the AAO layer formed in the first anodizing step, during which hexagonally ordered, concave-pored Al surface is formed so as to serve as vertical pore nucleation sites for the subsequent anodization step. Although such a two-step anodization process has proven useful for bulk Al surface, the relatively large amount of Al material that needs to be used up to obtain a well ordered AAO template is an issue when the starting material is a thin film layer of Al rather than a bulk Al foil. In this paper, we demonstrate successful fabrications of ordered and vertically aligned AAO nanopore patterns directed by a hexagonally patterned poly(styrene-b-4-vinylpyridine) di-block copolymer layer placed on a thin Al film surface. In addition, a successful electrodeposition of Ni nanowires into the AAO nanopores is demonstrated and their magnetization properties are studied.
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81.16.Rf Micro- and nanoscale pattern formation
82.45.Qr Electrodeposition and electrodissolution
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)
75.75.Cd Fabrication of magnetic nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Pq Electrodeposition, electroplating

Direct top-down ordering of diblock copolymers through nanoimprint lithography

M. Salaün, N. Kehagias, B. Salhi, T. Baron, J. Boussey, C. M. Sotomayor Torres, and M. Zelsmann

J. Vac. Sci. Technol. B 29, 06F208 (2011); http://dx.doi.org/10.1116/1.3662399 (5 pages) | Cited 3 times

Online Publication Date: 18 November 2011

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In this work, thermal nanoimprint lithography (NIL) is used on full 8 in. silicon wafers to imprint a thin PS-b-PMMA block copolymer (BCP) layer. The authors show that the imprinted BCP layer can thermally self-organize after the NIL process or during the NIL process itself, depending on experimental conditions used. Self-organized imprinted features with good graphoepitaxy alignment are obtained with a cylindrical BCP. Nevertheless, a standard fluorinated silane mold treatment is shown not to be neutral to the BCP. Then, if the line features do not have a thickness exactly commensurable to the natural self-organizing period of the polymer l0, a surface wetting layer is observed.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Dn Self-assembly
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
68.08.Bc Wetting
back to top Electron or Ion Beam Lithography

3D Nanostructuring of hydrogen silsesquioxane resist by 100 keV electron beam lithography

Joan Vila-Comamala, Sergey Gorelick, Vitaliy A. Guzenko, and Christian David

J. Vac. Sci. Technol. B 29, 06F301 (2011); http://dx.doi.org/10.1116/1.3629811 (5 pages) | Cited 2 times

Online Publication Date: 29 August 2011

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The authors investigated the three-dimensional nanostructuring of hydrogen silsesquioxane (HSQ) resist by multiple-step 100 keV electron beam lithography. Consecutive overlay exposures were used to create two- and three-levels in high aspect ratio HSQ structures with lateral dimensions down to 30 nm and resist thicknesses of about 1 μm. The HSQ resist was developed by a high contrast solution and supercritically dried in a carbon dioxide environment after each exposure step. The three-dimensional HSQ patterning has potential applications in the fabrication of performance enhanced devices such as photonic crystals, nanoelectromechanical systems, and diffractive X-ray lenses.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer

Selective profile transformation of electron-beam exposed multilevel resist structures based on a molecular weight dependent thermal reflow

Arne Schleunitz, Vitaliy A. Guzenko, Andreas Schander, Marko Vogler, and Helmut Schift

J. Vac. Sci. Technol. B 29, 06F302 (2011); http://dx.doi.org/10.1116/1.3634013 (4 pages) | Cited 2 times

Online Publication Date: 9 September 2011

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Novel 3D resist structures are generated with both smooth slopes and stepped resist profiles on the same substrate and in very close vicinity. By performing gray-scale electron-beam exposure and development steps twice with different dose ranges, a selective transformation of multilevel structures into continuous slopes upon thermal treatment was enabled. The molecular weight dependence was analyzed and related to the locally different ability of the resist to flow, which enables one to selectively address resist structures which should be altered while others stay unaffected. The technique has large potential for prototyping elements and devices and can be used to fabricate stamps with complex 3D surface patterns for fabrication using nanoimprint.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Developer-free direct patterning of PMMA/ZEP 520A by low voltage electron beam lithography

David Ai Zhi Zheng (鄭愛智), Mohammad Ali Mohammad, Steven Kelly Dew, and Maria Stepanova

J. Vac. Sci. Technol. B 29, 06F303 (2011); http://dx.doi.org/10.1116/1.3634017 (7 pages)

Online Publication Date: 9 September 2011

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The authors report an approach that has potential to fabricate dense structures without liquid development. Two kinds of positive tone electron beam resist, 950k PMMA and ZEP 520A (Nippon Zeon), were studied for their properties and behaviors while subjecting them to exposure, thermal development, and reactive ion etching. So far, we have successfully patterned 70 nm half-pitch gratings in both 950k PMMA and ZEP 520A without liquid development.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning

Nanopatterning of PMMA on insulating surfaces with various anticharging schemes using 30 keV electron beam lithography

Mustafa Muhammad, Steven C. Buswell, Steven K. Dew, and Maria Stepanova

J. Vac. Sci. Technol. B 29, 06F304 (2011); http://dx.doi.org/10.1116/1.3636367 (6 pages) | Cited 1 time

Online Publication Date: 14 September 2011

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As a low cost and high throughput method for nanoscale pattern replication, step and flash imprint lithography (SFIL) with UV transparent masters is gaining prominence for its potential in photonics and integrated-circuit fabrication. However, dielectric materials appropriate for fabricating nanostructured SFIL masters present a challenge when employing electron beam lithography (EBL) because insulator substrates covered by polymeric resists such as PMMA tend to accumulate charge during EBL exposures, thereby degrading the process. In this work we explore the performance of four different EBL anticharging schemes for nanofabrication of dense arrays of dots having diameters 16–30 nm in PMMA on UV transparent fused silica (FS) substrates. These include overlayers of aluminum or a water-soluble conducting polymer, as well as sandwiching of Al or Cr thin films between the substrate and PMMA. The quality of patterns transferred from PMMA into the underlying metallic layers was analyzed, and the grain size of the metal was found to be the limiting factor determining the edge roughness. The best resolution was attained employing the conducting polymer top-coating. This scheme also involves fewer processing steps. The authors have used this technique for lift-off of Cr and Au as well as Cr masked etch transfer of nanosized patterns into glass substrates for UV-transparent master mold fabrication.
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81.16.Rf Micro- and nanoscale pattern formation
68.35.bt Other materials
61.41.+e Polymers, elastomers, and plastics

Electron-beam-induced deposition of 3-nm-half-pitch patterns on bulk Si

J. C. van Oven, F. Berwald, K. K. Berggren, P. Kruit, and C. W. Hagen

J. Vac. Sci. Technol. B 29, 06F305 (2011); http://dx.doi.org/10.1116/1.3640743 (6 pages) | Cited 2 times

Online Publication Date: 20 September 2011

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This paper demonstrates electron-beam-induced deposition of few-nm-width dense features on bulk samples by using a scanning electron-beam lithography system. To optimize the resultant features, three steps were taken: (1) features were exposed in a repetitive sequence, so as to build up the deposited features gradually across the entire pattern, and thus avoid proximity effects; (2) an additional delay was added between exposures to permit diffusion of reactants into the exposed area; and (3) the exposures were phase-synchronized to the dominant noise source (the 50-Hz line voltage) to minimize the effect of noise. The reasons these steps led to significant improvements in patterning resolution are discussed.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
66.30.H- Self-diffusion and ionic conduction in nonmetals

Comparison between ZEP and PMMA resists for nanoscale electron beam lithography experimentally and by numerical modeling

Kirill Koshelev, Mohammad Ali Mohammad, Taras Fito, Kenneth L. Westra, Steven K. Dew, and Maria Stepanova

J. Vac. Sci. Technol. B 29, 06F306 (2011); http://dx.doi.org/10.1116/1.3640794 (9 pages) | Cited 2 times

Online Publication Date: 22 September 2011

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A modern alternative to the positive-tone PMMA resist is the ZEP 520A (Nippon Zeon) brand co-polymer resist, which offers a higher sensitivity and etch durability for electron beam lithography. However, the molecular mechanisms are not entirely understood, and the relative performance of two resists for various process conditions of nanofabrication is not readily predictable. The authors report a thorough experimental comparison of the performance of PMMA 950k and ZEP 520A resists in MIBK:IPA, ZED, and IPA:water developers. Interestingly, ZEP resist performance was found to depend significantly on the developer. ZED developer increases the sensitivity, whereas IPA:water optimizes line edge roughness and conceivably the resolution at the expense of sensitivity. The authors also describe two alternative numerical models, one assuming an enhancement of the main chain scission in ZEP as a result of electronic excitations in side groups, and another without such enhancement. In the second case, the differences in ZEP and PMMA resists performance are attributed to their different interaction with the developers. Using both approaches, the authors parameterize the respective models of ZEP development by fitting numerical results to the experimental resist morphologies, and analyze the outcomes.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.16.Nd Micro- and nanolithography

Comparison of hydrogen silsesquioxane development methods for sub-10 nm electron beam lithography using accurate linewidth inspection

D. S. Macintyre and S. Thoms

J. Vac. Sci. Technol. B 29, 06F307 (2011); http://dx.doi.org/10.1116/1.3634020 (6 pages)

Online Publication Date: 27 September 2011

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There is presently considerable interest in determining the resolution limits of hydrogen silsesquioxane as a negative tone electron beam resist. Various techniques for improving the resolution and contrast have been reported in the literature. These include the use of concentrated tetramethyl ammonium hydroxide, hot development, sodium hydroxide, salty development, and the use of dilute hydrofluoric acid dips. One difficulty in comparing the results from different research groups is that measurements are made using different electron microscopes working at various beam energies. Different groups frequently use different resist thickness and a variety of electron beam lithography tools operating at differing beam energies. These variations mean that useful comparisons at the nanometer scale are often not possible. This paper compares different development techniques using a unified inspection regime and a high contrast backscattered electron detector. The paper also considers important issues such as resist sensitivity, process latitude, and processing delay effects.
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81.16.Nd Micro- and nanolithography

Secondary-electron signal level measurements of self-assembled monolayers for spatial-phase-locked electron-beam lithography

Lin Lee Cheong, Jose M. Lobez, Euclid E. Moon, Jeffrey T. Hastings, and Henry I. Smith

J. Vac. Sci. Technol. B 29, 06F308 (2011); http://dx.doi.org/10.1116/1.3646897 (5 pages)

Online Publication Date: 7 October 2011

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The secondary-electron signal levels of eight thiophenol-based self-assembled monolayers (SAMs) on gold (Au) are measured and compared against the signal level from bare gold between energies 1 and 2 keV. To enable accurate comparison, scanning electron micrographs of SAMs are taken with a Faraday cup and a reference sample. Most SAMs-on-gold produce a lower signal level than that from bare gold, with the exception of 3-methylthiophenol. Highest occupied molecular orbital and lowest unoccupied molecular orbital levels of the thiophenol derivatives are calculated and compared against the signal levels. Signal levels from bis[3-(triethoxysilyl)propyl]tetrasulfide, (4-chlorophenyl)-triethoxysilane, and amino-propyl-triethoxy-silane on titanium (Ti) and aluminum (Al) are also measured. All three SAMs on aluminum have lower signal levels than bare Al but this effect is reversed for the case of Ti, where SAMs deposited on Ti result in a higher signal level. A hybrid Ti/Al fiducial grid is fabricated and the point-spread function at 2 keV in the underlying resist is investigated.
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81.16.Dn Self-assembly
81.16.Nd Micro- and nanolithography

Electron beam lithography writing strategies for low loss, high confinement silicon optical waveguides

Richard J. Bojko, Jing Li, Li He, Tom Baehr-Jones, Michael Hochberg, and Yukinori Aida

J. Vac. Sci. Technol. B 29, 06F309 (2011); http://dx.doi.org/10.1116/1.3653266 (6 pages) | Cited 5 times

Online Publication Date: 25 October 2011

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The authors present a robust process for fabricating passive silicon photonic components by direct-write electron beam lithography (EBL). Using waveguide transmission loss as a metric, we study the impact of EBL writing parameters on waveguide performance and writing time. As expected, write strategies that reduce sidewall roughness improve waveguide loss and yield. In particular, averaging techniques such as overlap or field shift writing reduce loss, however, the biggest improvement comes from writing using the smaller field-size option of our EBL system. The authors quantify the improvement for each variation and option, along with the tradeoff in writing time.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer

Parallel electron-beam-induced deposition using a multi-beam scanning electron microscope

P. C. Post, A. Mohammadi-Gheidari, C. W. Hagen, and P. Kruit

J. Vac. Sci. Technol. B 29, 06F310 (2011); http://dx.doi.org/10.1116/1.3656027 (4 pages) | Cited 2 times

Online Publication Date: 26 October 2011

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Lithography techniques based on electron-beam-induced processes are inherently slow compared to light lithography techniques. The authors demonstrate here that the throughput can be enhanced by a factor of 196 by using a scanning electron microscope equipped with a multibeam electron source. Using electron-beam induced deposition with MeCpPtMe3 as a precursor gas, 14 × 14 arrays of Pt-containing dots were deposited on a W/Si3N4/W membrane, with each array of 196 dots deposited in a single exposure. The authors demonstrate that by shifting the array of beams over distances of several times the beam pitch, one can deposit rows of closely spaced dots that, although originating from different beams within the array, are positioned within 5 nm of a straight line.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes

Experimental evaluation method of point spread functions used for proximity effects correction in electron beam lithography

Bengt A. Nilsson

J. Vac. Sci. Technol. B 29, 06F311 (2011); http://dx.doi.org/10.1116/1.3656343 (6 pages) | Cited 2 times

Online Publication Date: 1 November 2011

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The accuracy of the proximity effect correction in electron beam lithography is very dependent on how well the point-spread function used in the correction matches the actual electron scattering effects. A fast and simple technique to evaluate and compare the medium and long-range accuracy of electron scattering point-spread functions is presented. The method is based on the evaluation of the thickness uniformity of partially developed resist inside the proximity corrected pattern by judging the interference color uniformity. It can be applied to almost any pattern design. As an example, three corrected exposures using point-spread functions for semi-insulating GaAs generated by commercial Monte Carlo simulation programs were experimentally evaluated.
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81.16.Nd Micro- and nanolithography
02.50.Ng Distribution theory and Monte Carlo studies

Density multiplication of nanostructures fabricated by ultralow voltage electron beam lithography using PMMA as positive- and negative-tone resist

Adegboyega P. Adeyenuwo, Maria Stepanova, and Steven K. Dew

J. Vac. Sci. Technol. B 29, 06F312 (2011); http://dx.doi.org/10.1116/1.3657512 (8 pages) | Cited 1 time

Online Publication Date: 2 November 2011

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The authors report a density multiplication process for nanoscale patterns composed of dots and lines using electron beam lithography with low voltage 1 keV exposures and cold development. The density doubling is achieved in a single exposure-development step using polymethylmethacrylate (PMMA) as the resist. PMMA exhibits a dual positive- and negative-tone behavior depending on the electron dose employed in this density multiplication process. Fabricated nanostructures are characterized via scanning electron microscopy and subsequent feature size measurements. After density doubling, the minimum dot diameter of an initially 80 nm pitch array of single pixel dots was measured as approximately 27 nm, and the minimum width in an initially 100 nm pitch array of lines was approximately 21 nm. Methodologies for controlling the dimensions of fabricated structures are discussed. Modeling of the electron beam exposure has been carried out using an original electron beam lithography simulator in order to understand the nominal yields of scission in PMMA required in order to achieve the density multiplication, and the results are discussed.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.16.Nd Micro- and nanolithography

Miniaturization of grayscale images

Joel K. W. Yang, Huigao Duan, Jaslyn B. K. Law, Hong Yee Low, and Bryan Cord

J. Vac. Sci. Technol. B 29, 06F313 (2011); http://dx.doi.org/10.1116/1.3660790 (5 pages) | Cited 1 time

Online Publication Date: 15 November 2011

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Printing of binary patterns onto substrates has been the strength of resist-based binary lithography that has advanced the semiconductor industry. When patterning grayscale structures however, grayscale-lithography processes that are often difficult to use are considered. Here, we describe a process using binary-lithography to create arbitrary grayscale patterns. Particularly, we demonstrate a novel algorithm for the miniaturization of grayscale images that preserves grayscale information when imaged in a scanning electron microscope (SEM). The brightness level of each pixel was adjusted by controlling the density of nanometer-scale pixel elements. Using 17 shades of gray, we demonstrate the electron-beam lithography patterning of an M.C. Escher mezzotint and the Lena image with pixel elements consisting of 10-nm-diameter nanoposts spaced by gaps as small as 10 nm. The patterned images were tens of microns in size and faithfully reproduce the original images under SEM inspection. The process described could find applications in the fabrication of deep sub-wavelength elements with gradually varying dimensions in nanophotonic devices, and in creating grayscale images as anti-counterfeit features on substrates.
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42.30.Va Image forming and processing

Three-dimensional proximity effect correction for large-scale uniform patterns

Q. Dai, S.-Y. Lee, S.-H. Lee, B.-G. Kim, and H.-K. Cho

J. Vac. Sci. Technol. B 29, 06F314 (2011); http://dx.doi.org/10.1116/1.3660785 (9 pages) | Cited 2 times

Online Publication Date: 18 November 2011

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One of the major limiting factors in electron beam (e-beam) lithography is the geometric distortion of written features due to electron scattering, which is known as the proximity effect. A conventional approach to the proximity effect correction (PEC) is, through 2D simulation, to determine the dose distribution and/or shape modification for each feature in a circuit pattern such that the written pattern is as close to the target pattern as possible. Earlier, it was shown that the 3D PEC, which considers the variation of exposure along the resist-depth dimension, would be necessary for the feature size well below 100 nm. Also, a feature-by-feature correction procedure is too time-consuming to be practical, especially for the 3D PEC of large-scale patterns. In this paper, a new method for the 3D PEC is proposed, which adopts 3D resist profile (instead of 2D exposure distribution) in optimization, but avoids the intensive computation by employing a critical-location-based correction procedure. The proposed method achieves 3D resist profiles closer to the target ones, compared to 2D PEC. The simulation results show that the proposed method has a potential to provide a practical and effective alternative to the conventional approach.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer

Model based hybrid proximity effect correction scheme combining dose modulation and shape adjustments

Thomas Klimpel, Martin Schulz, Rainer Zimmermann, Hans-Jürgen Stock, and Alex Zepka

J. Vac. Sci. Technol. B 29, 06F315 (2011); http://dx.doi.org/10.1116/1.3662879 (7 pages) | Cited 2 times

Online Publication Date: 29 November 2011

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The authors present a general approach to combine model-based dose modulations and shape modifications into a hybrid proximity effects correction (PEC) scheme for electron beam lithography. The authors simplify this scheme significantly by using an appropriate dose correction strategy. This allows us to use an existing optical proximity correction tool for the shape adjustments. This hybrid PEC scheme is demonstrated by computing corrections for simple test patterns as well as a more complex pattern. The model used corresponds to an electron multibeam tool with an acceleration voltage of 50 kV. It predicts resist contours from a written dose distribution. The authors evaluate the quality of the results both for nominal process conditions and in the presence of process variations. The results are compared against the corresponding results for a correction using only dose modulation. The authors also use the hybrid scheme to compensate intentional overexposure by shape adjustments and include these results in the comparison so that the impact of overexposure on robustness against process variations can be determined.
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85.40.Hp Lithography, masks and pattern transfer

Measurement of surface potential of insulating film on a conductive substrate in a scanning electron microscope specimen chamber

Masatoshi Kotera, Akira Osada, Masaru Otani, and Yasuhiro Ohara

J. Vac. Sci. Technol. B 29, 06F316 (2011); http://dx.doi.org/10.1116/1.3662079 (6 pages)

Online Publication Date: 1 December 2011

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An electrostatic force microscope system in a scanning electron microscope specimen chamber was developed to measure the surface potential of an insulator film on a conductive substrate irradiated by an electron beam. As the accelerating voltage varies with the constant beam current, the surface charges positively if the voltage is lower than 1 kV or higher than 3 kV but negatively if the voltage is between 1.1 and 2.7 kV. This positive-negative-positive potential alternation is explained by the relationship between the electron range and the film thickness, and verified by the Monte Carlo simulation of electron trajectories. By selecting the acceleration voltage as 30 kV to show less potential variation with time, the spatial potential distribution at the specimen surface is obtained, and a negative dip is observed around 50 μm from the edge of the irradiated area. The authors find that the depth of the dip increases with an increase in the electron dose, and the negative potential distribution spreads over 300 μm is obtained, which is almost 10 times larger than the primary electron range in the specimen. The characteristic variation in the distribution agrees with a hypothetically derived charge distribution obtained in a different experiment.
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73.61.Ng Insulators
02.70.Uu Applications of Monte Carlo methods
61.80.Fe Electron and positron radiation effects

Electron bombardment of films used for reducing spurious charge in electrostatic electron optics

Juan R. Maldonado, Fabian Pease, Charles J. Hitzman, Alan D. Brodie, Paul Petric, Chris Bevis, Mark McCord, William M. Tong, Francoise Kidwingira, Piero Pianetta, Matt Bibee, Apurva Mehta, and Ritwik Bhatia

J. Vac. Sci. Technol. B 29, 06F317 (2011); http://dx.doi.org/10.1116/1.3663957 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2011

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In electrostatic electron optics charging on the surfaces of insulators separating the electrodes can cause undesired beam fluctuation. In prior work, the authors showed that coating the insulators with a film deposited by atomic layer deposition (ALD) could lead to acceptably low charging effects in the reflection electron beam lithography system. However, the stability of the resistivity can also be affected by contaminants present in the vacuum environment of the electron beam tool. The mechanism of formation for carbon layers typically involves the cracking of hydrocarbon contaminants adsorbed on the film surface by photon, electrons, or heat. This work describes changes in resistivity of ALD films of zinc–zirconium oxide and tantalum–niobium oxide 40 nm thick under different operating conditions. In a vacuum system utilizing an oil rough pump and a turbo pump, <0.01 C/cm2 bombardment with 309 V electrons results in about 1 order of magnitude reduction in surface resistance. This effect was not observed in an ion-pumped system suggesting that carbon contamination is the culprit. XPS measurements confirmed this suspicion. Improved results on a new material under development are presented.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
41.85.-p Beam optics
73.25.+i Surface conductivity and carrier phenomena
back to top Emerging technologies

3D nanostructures by stacking pre-patterned fluid-supported single-crystal Si membranes

Shabnam Ghadarghadr, Corey P. Fucetola, Lin Lee Cheong, Euclid E. Moon, and Henry I. Smith

J. Vac. Sci. Technol. B 29, 06F401 (2011); http://dx.doi.org/10.1116/1.3628672 (3 pages) | Cited 4 times

Online Publication Date: 26 August 2011

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The fabrication of complex three-dimensional (3D) structures at sub-100 nm resolution presents a difficult challenge. 3D photonic crystals that contain waveguides, resonant cavities, filters or other devices, and require deep-sub-100 nm dimensional control, are a particular example of this challenge. Multilayer 3D structures can be formed by stacking and bonding thin membranes that have been patterned in advance. This approach enables the full panoply of 2D planar-fabrication techniques to be employed. Membranes containing patterns that are not perfectly regular will exhibit in-plane distortion unless their intrinsic stress is zero. To minimize the effects of intrinsic stress we float individual membranes on the surface of a liquid. Thin single-crystal Si membranes on an oxide substrate are first patterned and then removed by etching the oxide in hydrofluoric acid. The freed Si membranes readily float on the liquid surface, aided by the hydrophobic nature of H-terminated Si. The authors describe methods for cleaning, patterning, manipulating, bonding and stacking such freely floating membranes.
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81.16.Rf Micro- and nanoscale pattern formation
81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
68.65.Ac Multilayers
81.65.Cf Surface cleaning, etching, patterning

3D fabrication by stacking prepatterned, rigidly held membranes

Amil A. Patel, Corey P. Fucetola, Euclid E. Moon, and Henry I. Smith

J. Vac. Sci. Technol. B 29, 06F402 (2011); http://dx.doi.org/10.1116/1.3643762 (3 pages) | Cited 2 times

Online Publication Date: 29 September 2011

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The authors describe an approach to fabricating high resolution, complex 3D structures based on the stacking of thin membranes that have been patterned in advance. The membranes are attached to a rigid frame by means of tethers that are strong enough to permit normal handling but can be cleaved after bonding. The tether shape was designed using finite-element analysis to enable clean cleavage at a specific location so that fragments are avoided that would interfere with the bonding of subsequent layers. The authors used 12 × 12 mm SiNx membranes, 350 nm thick, patterned with a square array of holes at 600 nm pitch and demonstrate the stacking of three layers.
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81.16.Rf Micro- and nanoscale pattern formation

Probe field enhancement in photonic crystals by upconversion nanoparticles

Jingyu Zhang, Teresa E. Pick, Daniel Gargas, Scott Dhuey, Emory M. Chan, Ying Wu, Xiaogan Liang, P. James Schuck, Deirdre L. Olynick, Brett A. Helms, and Stefano Cabrini

J. Vac. Sci. Technol. B 29, 06F403 (2011); http://dx.doi.org/10.1116/1.3662086 (5 pages)

Online Publication Date: 18 November 2011

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Lanthanide-doped upconverting nanoparticles, converting low frequency light to high frequency light through a multiphoton process, have shown interesting properties for bioimaging. Here, the authors describe a method to deposit a thin layer of upconverting Er3+ doped NaYF4 nanoparticles (15 to 25-nm) on a quasi-zero-average-index crystal over a 2 × 4 mm area to observe light propagation through the structure. Assisted by the photoluminescence of the nanoparticles with upconverting three-photon process, the enhanced field intensity confined in photonic crystals at near infrared wavelength is detected in visible green light under conventional optical microscope. This new technique has distinct advantages over the typical near infrared setups with infrared camera or near-field scanning optical microscope setups.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials
back to top Extreme Ultraviolet lithography

Mask roughness challenges in extreme ultraviolet mask development

Patrick Naulleau, Brittany McClinton, Kenneth A. Goldberg, Iacopo Mochi, and Abbas Rastegar

J. Vac. Sci. Technol. B 29, 06F501 (2011); http://dx.doi.org/10.1116/1.3632989 (5 pages)

Online Publication Date: 3 October 2011

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Despite significant progress in the commercialization of extreme ultraviolet (EUV) lithography, many challenges remain. Although availability of a reliable high power source is arguably the most daunting of these challenges, important mask issues are also of major concern. The issue of EUV phase roughness that can arise from either multilayer or capping layer roughness has recently become of increasing concern. The problem with mask phase roughness is that it couples to image plane speckle and thus line-edge roughness (LER). The coupling; however, depends on many factors including roughness magnitude, roughness correlation length, illumination partial coherence, aberrations and defocus, and numerical aperture. Analysis shows that only on the order of 50 pm multilayer roughness may be tolerable at the 22 nm half-pitch node. The analysis; however, also shows that the difficulty does not scale with future node reductions. Moreover, it is found that ruthenium is a particularly bad choice for capping layer from the perspective of phase roughness and that cleaning damage in such a multilayer could lead to unacceptable image-plane LER.
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85.40.Hp Lithography, masks and pattern transfer

Actinic characterization of extreme ultraviolet bump-type phase defects

Kenneth A. Goldberg and Iacopo Mochi

J. Vac. Sci. Technol. B 29, 06F502 (2011); http://dx.doi.org/10.1116/1.3653257 (6 pages) | Cited 1 time

Online Publication Date: 25 October 2011

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Multilayer blank defects in extreme ultraviolet (EUV) lithography photomasks continue to be among the highest concerns impeding commercialization. The SEMATECH Berkeley Actinic Inspection Tool (AIT), an all-EUV, high-magnification microscope, is routinely used to investigate mask defects, including native and programmed defects on mask blanks. So-called phase defects, created by buried substrate bumps and pits, formed within or below the EUV-reflective multilayer coating, cause phase-shifts in the reflected light field. These small disturbances are difficult to detect, yet they can create critical defects in patterns arranged above them. The authors report the through-focus measurement of programmed defects with a range of sizes reaching below the optical resolution of the AIT, and below the detection capabilities of advanced deep ultraviolet mask blank inspection tools. Consistent with previous measurements of native phase defects, we find that the observed phase and intensity changes are much smaller than predicted by a simple phase-change model based on the measured top-surface profile. Through simulation, we investigate the dependence of defect detectability on the illumination partial coherence.
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85.40.Hp Lithography, masks and pattern transfer

Imaging of extreme-ultraviolet mask patterns using coherent extreme-ultraviolet scatterometry microscope based on coherent diffraction imaging

Tetsuo Harada, Masato Nakasuji, Teruhiko Kimura, Takeo Watanabe, Hiroo Kinoshita, and Yutaka Nagata

J. Vac. Sci. Technol. B 29, 06F503 (2011); http://dx.doi.org/10.1116/1.3657525 (7 pages) | Cited 2 times

Online Publication Date: 3 November 2011

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In extreme-ultraviolet (EUV) lithography, defect-free mask production is a critical issue for high-volume manufacturing. For mask inspection and metrology, we have developed a coherent EUV scatterometry microscope (CSM). It is a simple lensless system. An aerial image of the mask pattern is reconstructed with iterative calculation based on coherent diffraction imaging. Periodic patterns, aperiodic patterns, and phase structures were reconstructed well by the CSM. A defect in a line-and-space pattern was detected as a diffraction signal. The aerial image of the defect is also reconstructed. This paper demonstrates the capability of the CSM to observe complex diffraction amplitudes directly from the pattern and the defect.
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85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer

Analysis of a scheme for de-magnified Talbot lithography

L. Urbanski, M. C. Marconi, A. Isoyan, A. Stein, C. S. Menoni, and J. J. Rocca

J. Vac. Sci. Technol. B 29, 06F504 (2011); http://dx.doi.org/10.1116/1.3653507 (4 pages) | Cited 2 times

Online Publication Date: 10 November 2011

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The authors describe a photolithographic scheme based on the replication of a periodic transparent mask in a photoresist utilizing the coherent self-imaging Talbot effect. A periodic two-dimensional diffractive structure (or Talbot mask) composed of unit tiles distributed in a square matrix was illuminated by a coherent extreme ultraviolet (EUV) beam from a table top EUV laser. The illumination beam was reflected in a spherical mirror and the Talbot mask was placed in the path of the convergent beam. At designed locations determined by the Talbot distance, reduced replicas of the mask were obtained and used to print the slightly de-magnified copies of the mask on the surface of a photoresist. Experimental results showing the de-magnification effect are in good agreement with the diffraction theory. The limits of the technique are discussed.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

Metrology development for extreme ultraviolet lithography: Flare and out-of-band qualification

G. F. Lorusso, E. Hendrickx, N. Davydova, Y. Peng, M. Eurlings, K. Feenstra, and J. Jiang

J. Vac. Sci. Technol. B 29, 06F505 (2011); http://dx.doi.org/10.1116/1.3660385 (7 pages) | Cited 1 time

Online Publication Date: 17 November 2011

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