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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)

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)

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)

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)

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 3 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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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 1 time

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)

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)

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 1 time

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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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Extreme ultraviolet lithography (EUVL) is the leading candidate for lithography beyond the 22 nm half-pitch device manufacturing node. These geometries impose tighter requirements for standard critical dimension metrology and call for new strategies able to quantify and monitor extreme ultraviolet (EUV) specific parameters. In this paper, the approaches to measure two key EUV imaging parameters, namely flare and out-of-band (OoB) radiation, are discussed. EUV sources are known to emit a broad spectrum of wavelengths ranging from EUV to deep ultraviolet (DUV) and beyond. As the DUV can contribute to the photoresist exposure and degrade imaging performance, it is critical to accurately determine the amount of DUV OoB in EUVL exposure tools at the wafer level. In this paper, a methodology using an aluminum-coated reticle to measure the DUV/EUV ratio in resist is discussed. Such a mask is able to provide quantitative in situ information on the scanner DUV content thanks to its ability to transmit DUV and absorb EUV. The experimental OoB results for two EUVL tools are reported and compared with modeling predictions. Flare in EUVL is caused by light scattered by the surface roughness of the optical elements and has a larger impact as compared to optical lithography. As a consequence, a precise and accurate flare metrology is essential to guarantee a proper qualification of the effect, as well as to implement an effective compensation strategy. However, the flare level estimate has been historically based on operator and tool-dependent procedures that are unable to meet the requirements for accuracy and precision dictated by EUVL. A robust in-line approach to flare metrology is developed and qualified. As in the case of OoB, experimental flare results for two EUVL tools are reported. The experimental data are compared to full-chip simulations using the point spread function of the tool’s optical system.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
back to top Electron or Ion Sources and Systems

Defined emission area and custom thermal electron sources

William A. Mackie and Gerald G. Magera

J. Vac. Sci. Technol. B 29, 06F601 (2011); http://dx.doi.org/10.1116/1.3656350 (4 pages)

Online Publication Date: 27 October 2011

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The authors report on electron emission defining and stability techniques use for specialized thermionic cathodes. Primarily lanthanum hexaboride and cerium hexaboride have been used for cathode materials but we also use hafnium carbide for cases where background atmospheres preclude the use of hexaborides. A common form of emission suppression is to embed an oriented single crystal in graphite to suppress side emission and to help shape the electric field. Single planar discs 50 μm in diameter have been tested for use as high brightness, stable, and long life thermal sources. Line sources have also been developed with linewidth/lengths to 10/500 μm. Emission tests performed have shown that long-term drift and short-term instabilities can originate from boride and carbon interactions respectively. Improved mounting techniques are shown to yield emission with short-term beam current stability <0.05%.
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79.40.+z Thermionic emission

Review Article: Rare-earth monosulfides as durable and efficient cold cathodes

Marc Cahay, Punit Boolchand, Steven B. Fairchild, Larry Grazulis, Paul T. Murray, Tyson C. Back, Vincent Semet, Vu Thien Binh, Xiaohua Wu, Daniel Poitras, David J. Lockwood, Fei Yu, and Vikram Kuppa

J. Vac. Sci. Technol. B 29, 06F602 (2011); http://dx.doi.org/10.1116/1.3653275 (14 pages)

Online Publication Date: 28 October 2011

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In their rocksalt structure, rare-earth monosulfides offer a more stable alternative to alkali metals to attain low or negative electron affinity when deposited on various III-V and II-VI semiconductor surfaces. In this article, the authors first describe the successful deposition of lanthanum monosulfide via pulsed laser deposition on Si and MgO substrates. These thin films have been characterized by x-ray diffraction, atomic force microscopy, high resolution transmission electron microscopy, ellipsometry, Raman spectroscopy, ultraviolet photoelectron spectroscopy, and Kelvin probe measurements. For both LaS/Si and LaS/MgO thin films, the effective work function of the submicron thick thin films was determined to be about 1 eV from field emission measurements using the scanning anode field emission microscopy technique. The physical reasons for these highly desirable low work function properties were explained using a patchwork field emission model of the emitting surface. In this model, nanocrystals of low work function materials having a 〈100〉 orientation perpendicular to the surface and outcropping it are surrounded by a matrix of amorphous materials with a higher work function. To date, LaS thin films have been used successfully as cold cathode emitters with measured emitted current densities as high as 50 A/cm2. Finally, we describe the successful growth of LaS thin films on InP substrates and, more recently, the production of LaS nanoballs and nanoclusters using pulsed laser ablation.
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82.45.Fk Electrodes
78.66.Nk Insulators
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
73.30.+y Surface double layers, Schottky barriers, and work functions

Ion beams in SEM: An experiment towards a high brightness low energy spread electron impact gas ion source

David S. Jun, Vladimir G. Kutchoukov, and Pieter Kruit

J. Vac. Sci. Technol. B 29, 06F603 (2011); http://dx.doi.org/10.1116/1.3660390 (7 pages)

Online Publication Date: 15 November 2011

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A next generation ion source suitable for both high resolution focused ion beam milling and imaging applications is currently being developed. The new ion source relies on a method of which positively charged ions are extracted from a miniaturized gas chamber where neutral gas atoms become ionized by direct electron impact. The use of a very small gas chamber and a very narrow electron beam (<100 nm) allows for a very small ionization volume, which, in turn, yields a small virtual source size and low energy spread. The authors estimate that using a high current density electron beam from a Schottky electron gun the reduced brightness of this source can exceed that of the Gallium Liquid Metal Ion Sources and the energy spread can be well below 1 eV at an optimal gas pressure and gas chamber spacing while producing more than 1 nA of usable ion beam current. In a proof-of-concept study, the authors have produced ions of helium, argon, xenon, and air from a prototype gas chamber using an electron probe inside a scanning electron microscope. Using micro-channel plates and a phosphor screen, ion beam patterns have been acquired demonstrating that a beam of ions can be produced from a miniaturized gas chamber. The authors have measured up to several hundreds of pico-amperes of ion current in a Faraday cup using an input electron probe current of ∼14 nA with 1 keV incident energy. The authors have also verified that the ion beam current is dependent on the incident electron beam energy, gas chamber bias voltage, and the gas pressure inside the ionization chamber.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Nanomachining with a focused neon beam: A preliminary investigation for semiconductor circuit editing and failure analysis

Shida Tan, Richard Livengood, Paul Hack, Roy Hallstein, Darryl Shima, John Notte, and Shawn McVey

J. Vac. Sci. Technol. B 29, 06F604 (2011); http://dx.doi.org/10.1116/1.3660797 (6 pages)

Online Publication Date: 17 November 2011

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As the semiconductor device scaling trend continues, advancement in both focused ion beam source development and application innovations are needed to retain failure analysis and nanomachining application capabilities. In this work, a neon gas field ionization source was studied for its nanomachining properties. The authors have analyzed neon’s nanomachining precision at 10 and 20 keV on blank Cu and SiO2 thin films. Subsurface material amorphization from neon and its correlation with beam current distribution are characterized by TEM. In addition, some preliminary nanomachining work was performed on a 32 nm test chip and successfully demonstrated end-pointing on various device layers.
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.35.-p Nanoelectronic devices

Influence of gun design on Coulomb interactions in a field emission gun

T. Verduin, B. Cook, and P. Kruit

J. Vac. Sci. Technol. B 29, 06F605 (2011); http://dx.doi.org/10.1116/1.3660798 (4 pages)

Online Publication Date: 2 December 2011

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The authors investigate by simulation the Coulomb effects on brightness and energy spread for cold field emitters. At first, we show that brightness is ultimately limited by Coulomb interactions. The authors analyze the maximum attainable brightness for tip radii ranging from 1 nm to 1 μm. Remarkably, the brightness of a tip of 1 nm is comparable to a tip of 1 μm. Higher brightness can be achieved by adding a plate at the base of the field emitter, and therefore decreasing the shank length. However, the brightness enhancement due to the protrusion is ultimately limited by large extractor voltages and increased energy spread. In particular, the energy spread for larger tip radii grows faster with brightness. The authors conclude that performance enhancement due to the protrusion works best for smaller tip radii.
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84.47.+w Vacuum tubes
back to top Microfluidics

Fabrication of fluidic devices with 30 nm nanochannels by direct imprinting

Irene Fernandez-Cuesta, Anna Laura Palmarelli, Xiaogan Liang, Jingyu Zhang, Scott Dhuey, Deirdre Olynick, and Stefano Cabrini

J. Vac. Sci. Technol. B 29, 06F801 (2011); http://dx.doi.org/10.1116/1.3662886 (7 pages)

Online Publication Date: 23 November 2011

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In this work, we propose an innovative approach to the fabrication of a complete micro/nano fluidic system, based on direct nanoimprint lithography. The fabricated device consists of nanochannels connected to U-shaped microchannels by triangular tapered inlets, and has four large reservoirs for liquid input. A master silicon stamp with the multilevel structures is fabricated first, and then a negative replica is made, to be used as a stamp for ultraviolet nanoimprint lithography (UV-NIL). Afterwards, just one single UV-NIL step is necessary for patterning all the the micro and nanostructures. Furthermore, the devices are made of all-transparent materials, and the method allows flexibility for the type of substrates used. The active material (an inorganic-organic hybrid polymer) used for the fabrication of the device has been carefully chosen, so it has adequate surface properties (inert and hydrophilic) for its direct use for biological applications. Devices having 30 nm wide, 30 nm deep nanochannels have been fabricated, and the successful performance of the fluidic system and the continuity of the nanochannels have been proven by flow tests.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
back to top Simulation and Modeling

Modeling of charging effect on ion induced secondary electron emission from nanostructured materials

Kaoru Ohya, Daiki Takami, and Takuya Yamanaka

J. Vac. Sci. Technol. B 29, 06F901 (2011); http://dx.doi.org/10.1116/1.3643752 (6 pages)

Online Publication Date: 29 September 2011

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Charging effects caused by secondary electron (SE) emission of a nanostructured material during ion beam irradiation are investigated by simulation. The materials simulated are a 100-nm-high SiO2 step on an Si substrate, and a 100-nm-deep trench through an SiO2 film to the Si substrate. Each position on the surface is irradiated with a 30 keV Ga ion beam. A Monte Carlo based model for SE emission from SiO2 and Si is used for simulation in which the charging of SiO2 induced by ion beam irradiation is taken into account. Dynamic and self-consistent calculations are performed to model the transport of the ions and SEs, the charge accumulation in SiO2, and the electric field in the SiO2 and in the vacuum. The calculated charging characteristics are compared with those calculated for a 1 keV electron beam. For Ga ion incidence; as a result of successive positive charging, the SE yield of the SiO2 layer decreases more strongly than for electron incidence, eventually vanishing, and the surface voltage progressively increases. The SE yield increases when the Ga ion incidence occurs at the position near the step edge on the layer, in a similar way to that observed for the electron incidence. The increase in the yield is more localized than for electron incidence. When the trench is irradiated with the Ga ion beam, the sidewall of the trench becomes negatively charged from reentrance of SEs emitted from the bottom of the trench. This negative charging increases the SE yield at the bottom of the trench (an effect also observed in the simulations of electron beam irradiation), because it assists SEs, which may be reabsorbed by the sidewall if they are not charged, to exit the trench. As the width of the trench decreases, the increase in the electron yield is enhanced. This enhancement is stronger for the incident ion beam than for the electron beam.
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79.20.Hx Electron impact: secondary emission
61.80.Jh Ion radiation effects

Enhancement of spatial resolution in generating point spread functions by Monte Carlo simulation in electron-beam lithography

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

J. Vac. Sci. Technol. B 29, 06F902 (2011); http://dx.doi.org/10.1116/1.3650696 (7 pages)

Online Publication Date: 17 October 2011

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The point spread function (PSF) plays an important role in electron beam lithography, e.g., for the estimation of the resist profile, proximity effect correction, etc. The conventional approach often derives PSFs directly from the Monte Carlo simulation, which might have a limitation in the spatial resolution under a certain size of memory available on a computer. A novel method is proposed to enhance the spatial resolution of PSFs generated from the Monte Carlo simulation without increasing the memory size or changing the simulation software. It exploits the fact that the PSF is radially symmetric and utilizes the concept of integrating the PSF. The integrated PSF is generated by the Monte Carlo simulation, and then the PSF is mathematically derived from its integration. Simulation results show that the proposed method has good potential for providing a practical way to enhance the spatial resolution of the PSF.
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85.40.Hp Lithography, masks and pattern transfer
05.10.Ln Monte Carlo methods

Process window modeling using focus balancing technique

Artak Isoyan, Ebo Croffie, and Lawrence S. Melvin, III

J. Vac. Sci. Technol. B 29, 06F903 (2011); http://dx.doi.org/10.1116/1.3662407 (7 pages)

Online Publication Date: 21 November 2011

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In this work, we present a methodology for process window capable optical proximity correction (OPC) compact model building which requires only one nominal process condition empirical data for model calibration, and enables full and predictable extrapolation to any process condition within focus-exposure matrix. In order to ensure modeling success, a focus and dose balancing techniques are used during model calibration. The model optimization method is based on a stepwise fitting methodology where staged optimization of the OPC model components is used. Model components are added during the OPC model calibration starting with more physical components, such as mask and optics, followed by resist components. In each optimization stage, a component is optimized using global regression methods. The optimized parameters regressed in a small range about their optimal values during subsequent model component optimization. The effectiveness of this approach in terms of accurate correction, process window interpolation and extrapolation were compared with conventional fitting methods through computational experiments. Prediction of measured verification patterns were used to assess the calibrated model quality.
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85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography
back to top Nanobiology and Cell Guidance

Suspended, micron-scale corner cube retroreflectors as ultra-bright optical labels

Tim Sherlock, Azeem Nasrullah, Julia Litvinov, Eliedonna Cacao, Jennifer Knoop, Steven Kemper, Katerina Kourentzi, Archana Kar, Paul Ruchhoeft, and Richard Willson

J. Vac. Sci. Technol. B 29, 06FA01 (2011); http://dx.doi.org/10.1116/1.3656801 (5 pages)

Online Publication Date: 3 November 2011

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Corner cube retroreflectors are objects with three mutually perpendicular reflective surfaces that return light directly to its source and are therefore extremely bright and easy to detect. In this work, we have fabricated suspended corner cube retroreflectors, 5 microns in size, consisting of a transparent epoxy core and three surfaces coated with gold as ultra-bright labels for use in a rapid, low-labor diagnostic platform. The authors have demonstrated that individual cubes are easily imaged using low-cost, low numerical aperture objectives in suspension and that they remain suspended over long periods of time. Moreover, we have demonstrated that the gold outer surfaces can be decorated with proteins, and that individual cubes can be bound to magnetic sample preparation particles bearing antibodies which recognize these proteins. The bound cubes can be imaged and tracked as they move through solution in response to an external magnetic field, and we have, as such, demonstrated the principle of the new biosensing approach.
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42.79.Fm Reflectors, beam splitters, and deflectors
42.82.Cr Fabrication techniques; lithography, pattern transfer

New approach for measuring protrusive forces in cells

A. Mathur, P. Roca-Cusachs, O. M. Rossier, S. J. Wind, M. P. Sheetz, and J. Hone

J. Vac. Sci. Technol. B 29, 06FA02 (2011); http://dx.doi.org/10.1116/1.3655580 (4 pages)

Online Publication Date: 11 November 2011

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Forces experienced by cells internally and externally can alter cellular signaling and function. The authors have developed an elastomeric device for the measurement of protrusive forces generated by cells, in which cells spreading on a planar surface encounter an array of pillars. The protrusive force can be calculated from the deflection of the pillar using simple mechanical considerations. The advantage of this approach is that multiple sensors can be integrated into a single device. Theaverage protrusive force was calculated as 800 pN for NIH 3T3 fibroblasts. The correct quantification of protrusive forces potentially can be used in the development of novel cancer therapies and diagnostic tools.
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87.85.gp Mechanical systems
87.17.-d Cell processes

Influence of surface patterning on bacterial growth behavior

Peter Nill, Dieter P. Kern, Nadine Goehring, and Andreas Peschel

J. Vac. Sci. Technol. B 29, 06FA03 (2011); http://dx.doi.org/10.1116/1.3662084 (5 pages)

Online Publication Date: 18 November 2011

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When cells colonize artificial materials, their growth behavior is undoubtedly influenced by physicochemical surface properties. In order to successfully untangle the numerous factors contributing to cell-surface interaction methods and tools are needed to reliably determine the significance of a single surface parameter without disturbing other influential factors. Especially studying the influence of purely physical properties, e.g., surface topography, in a microbiological in vitro assay is rather challenging. In an approach to provide microbiologists with a method suitable for this task, we demonstrate the fabrication of multiple, precisely defined microtopographies on a single elastomeric substrate that is designed to facilitate in vitro measurements. The applicability of these substrates is demonstrated by investigating the influence of microtopography on Staphylococcus aureus. Our findings suggest that microbial growth patterns are influenced by the underlying surface topography.
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87.17.Ee Growth and division
back to top Nanoelectronics

Novel method for fabrication of nanoscale single-electron transistors: Electron beam induced deposition of Pt and atomic layer deposition of tunnel barriers

Hubert C. George, Tatyana A. Orlova, Alexei O. Orlov, and Gregory L. Snider

J. Vac. Sci. Technol. B 29, 06FB01 (2011); http://dx.doi.org/10.1116/1.3640752 (4 pages)

Online Publication Date: 20 September 2011

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A novel method for fabricating metal-based single-electron transistors (SETs) is reported that combines a nanoscale island produced via electron beam induced deposition (EBID) of Pt metal with a tunnel barrier dielectric produced via atomic layer deposition (ALD) of alumina (Al2O3). A characteristic nonlinearity in Ids-Vds and Coulomb blockade oscillations of the SET are observed at 300 mK. The versatility of the EBID method provides a way to fabricate 3D structures that could be particularly useful in a number of charge sensing applications and which, combined with the accuracy and precise control that ALD provides for the SET’s tunnel barriers, greatly expands the choice of techniques suitable for SET fabrication.
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85.35.Gv Single electron devices
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Fabrication of hybrid metal island/silicon single electron transistor

Yen-Chun Lee, Alexei O. Orlov, and Gregory L. Snider

J. Vac. Sci. Technol. B 29, 06FB02 (2011); http://dx.doi.org/10.1116/1.3644340 (4 pages)

Online Publication Date: 3 October 2011

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A novel process for silicon single electron transistors (Si-SET) is presented, combining chemical mechanical polishing (CMP) with the advantages of silicon processing. To eliminate effects caused by random distribution of dopants in the island, The Si-SET’s doped-Si island is replaced with an aluminum or tantalum island by integrating a metal CMP technique with our nano-encapsulation process. The fabricated hybrid Al-island Si-SET has ∼10 nm silicon on insulator lines as the source and drain leads. It shows characteristic Coulomb blockade oscillations with a charging energy of ∼4 meV. The fabrication results demonstrate the scalability of the SET island and the tunnel junction size in a manufacturable top-down approach.
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85.35.Gv Single electron devices
81.05.Cy Elemental semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
81.65.Ps Polishing, grinding, surface finishing
85.35.Ds Quantum interference devices

Local, direct-write, damage-free thinning of germanium nanowires

Peter Roediger, Mario Mijic, Clemens Zeiner, Alois Lugstein, Heinz D. Wanzenboeck, and Emmerich Bertagnolli

J. Vac. Sci. Technol. B 29, 06FB03 (2011); http://dx.doi.org/10.1116/1.3660388 (6 pages)

Online Publication Date: 11 November 2011

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A crystallinity-retaining, implantation-free focused electron beam induced etching (FEBIE) process has been exploited to modify germanium nanowires. This technique shows a high selectivity to the metal contacts applied to the nanowires as well as to the substrate which did not exhibit significant etching. Raman-spectroscopic as well as electrical measurements have been performed on the FEBIE-modified nanowires. Experimental data obtained in this study suggest than unintentional stress is often applied to the nanowires by the defined electrical contacts. Electrical measurements indicate that the electronic properties of the as-grown Ge nanowires can be significantly altered already by a slight surface modification, resulting in an increased conductivity of more than two orders of magnitude.
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81.16.-c Methods of micro- and nanofabrication and processing
78.30.Am Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors
81.07.Gf Nanowires
78.67.Uh Nanowires
81.65.Cf Surface cleaning, etching, patterning
back to top Nanoimprint Lithography

Combining nanoimprint lithography and a molecular weight selective thermal reflow for the generation of mixed 3D structures

Arne Schleunitz, Christian Spreu, Marko Vogler, Hakan Atasoy, and Helmut Schift

J. Vac. Sci. Technol. B 29, 06FC01 (2011); http://dx.doi.org/10.1116/1.3643761 (4 pages)

Online Publication Date: 27 September 2011

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Sloped and stepped 3D structures were added to surface-patterned resists using grey-scale electron beam lithography and thermal reflow. A poly(methyl methacrylate) resist with moderate initial molecular weight of 120 kg/mol was chosen, which enabled processing with both nanoimprint and electron beam lithography. Using proper exposure doses, a molecular weight distribution was generated that allowed a selective thermal postprocessing of the exposed steps while the imprinted gratings on top of the resist were preserved. This allows fabricating mixed structures of microprisms surrounded by large-area nanogratings in the same resist layer. Working stamps were casted from the template pattern and subsequently replicated using thermal nanoimprint. As a possible application, backlight devices with arrays of light outcoupling prisms can be seen.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

Macro-optical inspection method for deterioration evaluation of release-coated mold surfaces for nanoimprint lithography

Jun Taniguchi, Junki Takahashi, Mitsuru Uda, Atushi Kohayase, and Kenichi Kotaki

J. Vac. Sci. Technol. B 29, 06FC02 (2011); http://dx.doi.org/10.1116/1.3646885 (4 pages)

Online Publication Date: 14 October 2011

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Nanoimprint lithography (NIL) is a very useful technique for the fabrication of nanopatterns, and it is used in some practical applications. The key issue for mass production is the understanding of the lifetime and deterioration of the release coating on the mold surface, because the adhesion of polymer materials on the mold surface results in defective products. However, a method for inspecting the durability and evaluating the release layer on the mold surface has not yet been established. This paper describes a method for inspecting the deterioration of the release-coated mold surface using the macro-optical inspection method, which is based on the detection method using edge-reflected light. This macroinspection enables the evaluation of the nonuniformity of the surface and local defects on the macroscale (from 0.1 to several millimeters), because the edge-reflected light is very sensitive to undulations in the surface morphology. In order to examine the deterioration of the release-coated mold surface, a silicon mold with 220 nm diameter holes and a fluorine release agent were used. For the release agent treatment, the mold was first dipped into 0.1% release agent for 30 min. Then, the mold was removed from the release agent and baked at 100 °C for 3 min on a hot plate, after which several undulations were observed. After three such treatments, the overcoating of the release agent caused a lot of defects such as water marks, stripes, and coating nonuniformities. Thus, the macroinspection method enables a facile understanding of the differences in such surface undulations. In order to evaluate the lifetime and deterioration, the UV-NIL process was carried out 100 times. The results showed that the macroinspection method reveals the thin-release-layer behavior during the UV-NIL process and the deterioration and undulation of the release layer.
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81.16.Nd Micro- and nanolithography
68.35.bg Semiconductors
61.46.-w Structure of nanoscale materials

Room temperature nanoimprinting using spin-coated hydrogen silsesquioxane with high boiling point solvent

Yuji Kang, Makoto Okada, Shinya Omoto, Yuichi Haruyama, Kazuhiro Kanda, and Shinji Matsui

J. Vac. Sci. Technol. B 29, 06FC03 (2011); http://dx.doi.org/10.1116/1.3653227 (3 pages)

Online Publication Date: 25 October 2011

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The authors have previously used two methods for nanoimprinting hydrogen silsesquioxane (HSQ) patterns. In the casting method, the HSQ pattern was replicated at a low imprinting pressure of less than 1 MPa, however, the imprinting produced an uneven residue. On the contrary, in the spin-coating method, an evenly distributed HSQ film was produced. However, the HSQ pattern required a high imprinting pressure of about 40 MPa. To achieve imprinting at a low pressure with the spin-coating method, we propose a new room temperature nanoimprinting method using spin-coated HSQ and a poly(dimethylsiloxane) mold. The authors used high boiling point solvent, with a boiling point of greater than 200 °C, in place of the previously used solvent that had a boiling point of 96 °C. This method produced an evenly coated film in the liquid-phase.
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81.16.Rf Micro- and nanoscale pattern formation
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.41.+e Polymers, elastomers, and plastics

Evaluation of fluorine additive effect on cationic UV-nanoimprint resin

Makoto Okada, Yuichi Haruyama, Shinji Matsui, Hiroto Miyake, Shuso Iyoshi, Takao Yukawa, and Hidekazu Takeuchi

J. Vac. Sci. Technol. B 29, 06FC04 (2011); http://dx.doi.org/10.1116/1.3653513 (4 pages) | Cited 1 time

Online Publication Date: 26 October 2011

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Ultraviolet (UV) nanoimprint lithography is used to fabricate nanostructured devices with high-throughput, low cost, and high resolution. The nanoimprint mold is coated with an antisticking layer to enable easy separation of the mold from the UV nanoimprint resins. An important issue is finding a way to prevent the deterioration of the antisticking layer which results from repeated UV nanoimprinting. To do this, a UV nanoimprint resin with release properties is required. The authors evaluated the effect of a fluorine additive on a cationic UV-curable resin by x-ray photoelectron spectroscopy (XPS), scanning probe microscopy, and contact angle measurement. The authors confirmed from the XPS results that fluorine was present on the surface of the cured UV-curable resin with the fluorine additive. Furthermore, the adhesion and frictional forces of the UV-curable resin with the fluorine additive were lower than those of the UV-curable resin without the additive.
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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
81.16.Rf Micro- and nanoscale pattern formation
82.35.-x Polymers: properties; reactions; polymerization
42.82.Cr Fabrication techniques; lithography, pattern transfer
68.35.Np Adhesion

Evaluation of the curing process of UV resins in a 1,1,1,3,3-pentafluoropropane gas environment by photo differential scanning calorimetry and Fourier transform infrared spectroscopy

Yohei Sawada, Yuichi Haruyama, Kazuhiro Kanda, Shinji Matsui, Makoto Okada, Hiroto Miyake, Takeshi Ohsaki, Yoshihiko Hirai, and Hiroshi Hiroshima

J. Vac. Sci. Technol. B 29, 06FC05 (2011); http://dx.doi.org/10.1116/1.3656022 (4 pages)

Online Publication Date: 26 October 2011

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The formation of bubble defects during UV-nanoimprinting can be prevented by carrying out the process in a 1,1,1,3,3-pentafluoropropane (PFP) gas environment. The authors therefore evaluated the curing time and the calorific value of UV-curable resins in a PFP gas environment by photo differential scanning calorimetry and their polymerization degree by Fourier transform infrared spectroscopy. The authors found that UV-curable resins polymerized more efficiently in PFP than in air because PFP dissolves in the resins.
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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
82.35.-x Polymers: properties; reactions; polymerization
78.30.Jw Organic compounds, polymers

Fabrication of a seamless roll mold using inorganic electron beam resist with postexposure bake

Noriyuki Unno, Jun Taniguchi, and Kiyoshi Ishikawa

J. Vac. Sci. Technol. B 29, 06FC06 (2011); http://dx.doi.org/10.1116/1.3656052 (4 pages)

Online Publication Date: 26 October 2011

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The fabrication of next-generation devices via roll-to-roll (RTR) nanoimprinting has received considerable attention due to the high throughput and resolution associated with the process. In particular, RTR nanoimprinting with ultraviolet (UV)-curable resin is expected to be useful for the fabrication of large-area devices such as nonreflective films, transparent conductive sheets, and organic solar cells. In order to improve the resolution of such devices, the roll mold must be able to produce seamless fine patterns. Generally, a roll mold for nanoimprinting is made by attaching a planar mold replicated from the master mold via a nickel electroforming technique. However, this method produces seams, which reduces the product yield. In order to resolve these issues, the authors have developed a direct writing method using electron beam (EB) lithography on a rotating cylindrical substrate. In this study, the authors examined the potential for fabricating a seamless roll mold using high-resolution inorganic EB resist and the pattern shrink effect from postexposure bake (PEB). The authors used the dip-and-pull method to form the EB resist layer on the roll mold substrate (32 mm diameter, made of brass). The cleaned roll mold was dipped in the inorganic EB resist and then pulled out at a constant speed. The resulting sample was cured at 300 °C for 1 h. Next, the sample was mounted on rotating equipment and placed in a scanning electron microscope (SEM) equipped with an EB writing system, and the roll substrate was exposed to 10 kV EB while rotating at a constant speed. The revolution speed was set to ten turns per line pattern. Subsequently, PEB was carried out at 200 °C for 10 min in air. After the sample was cooled to room temperature, the EB-exposed area of the EB resist layer was developed using buffered HF. The obtained pattern on the roll mold was examined with the same SEM used for writing. Finally, RTR nanoimprinting using the obtained roll mold was carried out using UV-photocurable resin. At that time, the sample was coated with an antisticking layer of fluorinated silane coupling agent. As a result, a seamless line pattern 190 nm wide was obtained on a polyethylene terephthalate film over a length of 10 cm.
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81.16.Nd Micro- and nanolithography
81.10.Fq Growth from melts; zone melting and refining
82.45.-h Electrochemistry and electrophoresis
85.40.Hp Lithography, masks and pattern transfer
61.41.+e Polymers, elastomers, and plastics

Soft patterning on cylindrical surface of plastic optical fiber

Harutaka Mekaru, Hideki Takagi, Akihiro Ohtomo, Mitsunori Kokubo, and Hiroshi Goto

J. Vac. Sci. Technol. B 29, 06FC07 (2011); http://dx.doi.org/10.1116/1.3656802 (7 pages)

Online Publication Date: 27 October 2011

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The authors have developed a novel thermal imprinting method to fabricate microstructures on the surface of plastic optical fibers (POFs) without causing any damage to them. In conventional thermal nanoimprinting using a planar mold, the shape of the molding material is in the form of a film spread on a planar substrate, or the molding material is used in its bulk form. In the case of any 3-dimensional shaped molding material such as in the case of a fiber, the shape becomes susceptible to a certain degree of damage caused by the planar mold. In order to address this problem, we have designed a thermal imprinting method using sliding planar molds. A fiber tightly stretched between two reel stations (for sending and winding of the fiber) is sandwiched between two planar molds facing each other. The fiber is then rolled against the pattern sides of the two planar molds while the rolling motion of the fiber remains synchronized with the sliding motion of the planar molds. The problem of twists in the fiber caused by the sliding planar molds was solved by dynamically rotating the two reel stations to match the rotation of the fiber. To demonstrate this technology, we employed a special electroformed-Ni mold with a mirror image of a string of characters forming the word “MACROBEANS” engraved in the form of a lattice, where the individual characters were composed of diffraction grating structures with 1 and 2 μm of linewidths. Using this mold, the cylindrical surface of a POF made of a 240-μm-diameter polymethyl methacrylate core with a coating of a 5-μm-thick fluoroplastic cladding was thermal-imprinted. From the observation of the imprinted patterns on the POFs, it was verified that the cylindrical surface was patterned without causing any damage to the POF. The height of the convex mold pattern was 1.1 μm, and the depth of the concave imprinted pattern was approximately 1.0 μm.
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42.81.Bm Fabrication, cladding, and splicing
61.72.-y Defects and impurities in crystals; microstructure
81.16.Rf Micro- and nanoscale pattern formation
82.45.-h Electrochemistry and electrophoresis
42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings

Large-diameter roll mold fabrication method using a small-diameter quartz roll mold and UV nanoimprint lithography

Jun Taniguchi, Noriyuki Unno, and Hiroki Maruyama

J. Vac. Sci. Technol. B 29, 06FC08 (2011); http://dx.doi.org/10.1116/1.3657524 (5 pages)

Online Publication Date: 2 November 2011

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The roll-to-roll (RTR) technique is a high-throughput method for nanoimprint lithography (NIL); however, the fabrication of the roll mold for RTR NIL is difficult because of the cylindrical shape of the mold. Roll molds are usually fabricated by rolling up a nickel-plated foil imprinted with a nanopattern, but this method generates a seam. To produce a seamless nanoscale mold, we have previously developed a technique for direct writing with an electron beam (EB) onto a rotating cylindrical substrate. The method uses a cylindrical substrate (the roll mold substrate) coated with a resist that is written upon directly by an EB while the roll mold substrate is rotated in a vacuum. However, the throughput of this technique is very low. In an attempt to overcome this problem, we investigated a roll diameter amplification method using direct transfer from a patterned small mold. The roll mold was made of synthetic quartz, and its diameter was 30 mm. This roll mold was dipped in hydrogen silsesquioxane, which acts as high-resolution negative-type EB resist. The mold coated with the EB resist was subjected to EB lithography at an acceleration voltage of 30 kV and an EB current of 100 nA. After development, 520 nm line patterns were obtained on the quartz roll mold. The transparent roll mold was subsequently used to transfer the pattern directly onto a large mold at a rotation speed of 0.2 rpm, a nip force of 60 N, and a UV dose of 60 mW/cm2. The diameter of the large mold was 150 mm, and the mold was covered with a UV-curable film. The width of the transfer lines was 510 nm. By using a large mold made of the resulting patterned polymer, RTR UV-NIL was carried out at a feed speed of 1 mm/s, a nip pressure of 0.25 MPa, and a UV dose of 87 mW/cm2. The transfer film was the same UV-curable film. The replicated lines widths were 590 nm; this large value was caused by deformation of the polymer mold during the RTR NIL process. The roll diameter amplification method is therefore very effective for RTR UV-NIL, because a small-diameter roll can be used as the master mold.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
42.70.Ce Glasses, quartz
42.82.Cr Fabrication techniques; lithography, pattern transfer

Suitability of thin poly(dimethylsiloxane) as an antisticking layer for UV nanoimprinting

Makoto Okada, Yuichi Haruyama, Kazuhiro Kanda, and Shinji Matsui

J. Vac. Sci. Technol. B 29, 06FC09 (2011); http://dx.doi.org/10.1116/1.3653226 (5 pages)

Online Publication Date: 3 November 2011

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The antisticking capabilities and durability of thin poly(dimethylsiloxane) (PDMS) were compared to a fluorinated antisticking layer (F-ASL) to assess its suitability for use in UV nanoimprint lithography (UV-NIL). Typically, UV-NIL is used to fabricate high-throughput, low-cost, high-resolution nanostructure devices. The nanoimprint mold is typically coated with an antisticking layer to ensure easy separation of the mold from the UV nanoimprint resins. This layer must be highly durable to meet the demands of a manufacturing environment, and F-ASL is the standard type used. In PS-b-PDMS block copolymer lithography, the template is coated with a thin layer of PDMS. In this study, we focused on using PDMS as the antisticking layer for nanoimprinting and examined its antisticking capabilities and durability by step and repeat (S&R) UV nanoimprinting. Experimental results showed that the thin PDMS layer functions comparably to the F-ASL as an antisticking layer.
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81.16.Nd Micro- and nanolithography
68.55.am Polymers and organics

Mechanical characteristics of imprinted nanostructures fabricated with a poly(dimethylsiloxane) mold

Yuji Kang, Makoto Okada, Yasuki Nakai, Yuichi Haruyama, Kazuhiro Kanda, and Shinji Matsui

J. Vac. Sci. Technol. B 29, 06FC10 (2011); http://dx.doi.org/10.1116/1.3657520 (6 pages)

Online Publication Date: 3 November 2011

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Nanoscale imprinted pillars were fabricated with three resin systems and characterized by measuring the spring constant using a scanning probe microscopy cantilever manipulated with a three-axis actuator. The functional dependence of the spring constant on the height and diameter of the pillar was then used to determine the Young’s modulus. Nanoindentation was used to determine the Young’s modulus of the base film. Before high temperature annealing, the Young’s modulus of the imprinted pillar was nearly the same as that of film. After the annealing, the Young’s modulus of the imprinted pillar was lower than that of the film.
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81.16.Nd Micro- and nanolithography
81.40.Jj Elasticity and anelasticity, stress-strain relations
85.40.Hp Lithography, masks and pattern transfer
62.20.de Elastic moduli
61.72.Cc Kinetics of defect formation and annealing

Atomic step patterning in nanoimprint lithography: Molecular dynamics study

Kazuhiro Tada, Masaaki Yasuda, Geng Tan, Yumiko Miyake, Hiroaki Kawata, Mamoru Yoshimoto, and Yoshihiko Hirai

J. Vac. Sci. Technol. B 29, 06FC11 (2011); http://dx.doi.org/10.1116/1.3659712 (6 pages)

Online Publication Date: 8 November 2011

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Atomic-scale formability of nanoimprint lithography using an atomically stepped mold is investigated in a molecular dynamics simulation for inorganic SiO2 glass material. Fast Fourier transformation analysis of the surface height of the glass is performed to confirm the periodicity of the atomic-step pattern. From the analysis, the resolution of glass nanoimprint lithography is found to be 0.2 nm for the atomically stepped mold. This theoretical resolution agrees with the experimental resolution.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

Liquid transfer imprint lithography: A new route to residual layer thickness control

Namil Koo, Jung Wuk Kim, Martin Otto, Christian Moormann, and Heinrich Kurz

J. Vac. Sci. Technol. B 29, 06FC12 (2011); http://dx.doi.org/10.1116/1.3660792 (4 pages)

Online Publication Date: 10 November 2011

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In this study, an extension of the soft UV nanoimprint process is presented with improved control of the residual layer thickness and significant reduction of the nanoimprint proximity effect. The process is based on the consecutive halving of the liquid resist layer by a liquid transfer process. In the initial stage, this liquid transfer process uses a thick initial resist layer to ensure complete filling of the stamp cavities. The thick residual layer is then thinned down to about half by peeling off the applied imprint stamp, a process that can be repeated until the desired residual layer thickness is achieved. The information carrying layer remaining on the stamp can be transferred conformally to any substrate even with nonplanar surfaces. The fabrication of silicon photonic waveguides and photovoltaic antireflection textures are two applications where the advantage of this process becomes particularly clear.
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81.16.Nd Micro- and nanolithography
42.79.Gn Optical waveguides and couplers

Mechanical characterization of a piezo-operated thermal imprint system

Andre Mayer, Sakia Moellenbeck, Khalid Dhima, Si Wang, and Hella-Christin Scheer

J. Vac. Sci. Technol. B 29, 06FC13 (2011); http://dx.doi.org/10.1116/1.3656048 (4 pages)

Online Publication Date: 14 November 2011

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Dynamic agitation during imprint is investigated as a means to reduce the imprint temperature of thermoplastic materials. The imprint system used consists of a stepping motor and a piezo unit as the main components. The motor controls the working point of the system, and a sinusoidal motion of the piezo unit (3 piezos at 120° with respect to each other) superimposes an additional dynamic excitation. The system was characterized with respect to its mechanical behavior by exploiting analogies between mechanical and electrical quantities. The results show that the system can be operated at a frequency of up to about 60 Hz and that the piezos act as a dynamic motion source in the system. First imprint experiments with polystyrene at 100 °C indicate the potential of this frequency-assisted imprint technique.
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85.40.Hp Lithography, masks and pattern transfer
61.41.+e Polymers, elastomers, and plastics
81.16.Nd Micro- and nanolithography

Experimental analysis for process control in hybrid lithography

Khalid Dhima, Christian Steinberg, Saskia Möllenbeck, Andre Mayer, Si Wang, and Hella-Christin Sheer

J. Vac. Sci. Technol. B 29, 06FC14 (2011); http://dx.doi.org/10.1116/1.3659717 (7 pages) | Cited 1 time

Online Publication Date: 14 November 2011

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The positive tone resist AZ 1505 is characterized with respect to hybrid lithography that uses thermal nanoimprint lithography to define the nanometric part of a lithography pattern in a first step, followed by optical lithography to define the micron-scaled patterns in the same resist layer in a second step. The parameters investigated are glass temperature and sensitivity (dose curves), both after thermal loading in a typical imprint sequence. The glass transition of the multicomponent resist formulation is derived from stress measurements and the dose curves are evaluated from development rate monitoring via laser interferometry at 532 nm. The results show that both parameters are affected by thermal loading, but adequate choice of the processing parameters makes it possible to compensate for the thermal degradation of the photoresist as long as the imprint temperature chosen does not exceed 130 °C. Based on the characterization results, successful hybrid lithography and lift-off has been demonstrated with AZ 1505.
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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

High aspect ratio fine pattern transfer using a novel mold by nanoimprint lithography

J. Sakamoto, N. Fujikawa, N. Nishikura, H. Kawata, M. Yasuda, and Y. Hirai

J. Vac. Sci. Technol. B 29, 06FC15 (2011); http://dx.doi.org/10.1116/1.3662080 (5 pages)

Online Publication Date: 18 November 2011

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To conduct our research, a Si mold with a high aspect nano trench pattern was fabricated using a new edge lithography process, and the pattern was replicated into PMMA films on Si wafer by thermal nanoimprint lithography. By using edge lithography, a SiO2 circular line pattern of 35 nm width and 3.5 μm height was obtained and the aspect ratio became 100. The Cr patterns were fabricated by a lift-off process by using the high aspect SiO2 nano patterns, and the Si substrate was etched by the advanced plasma etching of the gas switching process. A Si trench pattern of 25 nm width and 1.0 μm depth was obtained, and these Si trench patterns were used for nanoimprint molds. The aspect ratios of the nano trench patterns were about 10. The nano trench patterns were replicated into PMMA films with various molecular weights by thermal nanoimprint lithography. The pattern replication failed when the PMMA resins of 50 and 120 k molecular weights were used. It is found that the PMMA pattern was often broken during the demolding process and its strength was very important for the successful pattern replication of the high aspect pattern. A PMMA line pattern of 30 nm width and 230 nm height was successfully fabricated when the PMMA resin of 996 k molecular weight was used.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning

Fabrication of silicon template with smooth tapered sidewall for nanoimprint lithography

Jian He, K. Richter, J. W. Bartha, and S. Howitz

J. Vac. Sci. Technol. B 29, 06FC16 (2011); http://dx.doi.org/10.1116/1.3662094 (5 pages)

Online Publication Date: 21 November 2011

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In this work, the authors developed reactive-ion etching processes to fabricate silicon templates with smooth tapered sidewalls for nanoimprint lithography. In these etching processes a dual-layer etching mask system was used to avoid the mask undercut. Electron beam lithography was used to define the patterns in the nanometer range. The etched structures have slightly tapered sidewalls and a surface roughness of less than 5 nm. The sidewall angle can be controlled from 90° down to 85° by varying the flow rate ratio of the etching and the passivation gas and the mask undercut is totally avoided. Using these etching processes, the authors successfully fabricated silicon templates with lateral dimensions down to 50 nm and aspect ratios up to 10 and with an etching rate above 100 nm/min. Using these silicon templates the demolding force in nanoimprint lithography can be significantly reduced.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
68.35.bg Semiconductors
61.46.-w Structure of nanoscale materials

Hard stamp processes for the EVG 620 full field nanoimprint system

James Conway, James B. Kruger, Mahnaz Mansourpour, and Paul Rissman

J. Vac. Sci. Technol. B 29, 06FC17 (2011); http://dx.doi.org/10.1116/1.3662085 (6 pages)

Online Publication Date: 22 November 2011

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The EVG 620 nanoimprint system is a 4 in. full wafer system suitable for university and research environments (EV Group, A-4782 Sankt Florian am Inn, Austria). By limiting the area printed and by the use of hard masks, nanoimprint lithography resolution can be extended to well below the design resolution of the system. The EVG 620 has found application primarily with soft stamps, such as those made of polydimethylsiloxane [Plachetka et al., Microelectron. Eng. 73-74, 167 (2004)]. However, soft stamps can have limited resolution and are difficult to clean, meaning they should be disposed of after a single stamp. Hard stamps made from quartz wafers have ultimate resolution limited only by the e-beam exposure system used for definition and are easy to clean in sulfuric peroxide or oxygen plasma strippers. Hard stamps have been demonstrated on the EVG 620 instrument at Stanford Nanofabrication Facility with resolution down to 20 nm. Both positive tone (PMMA, ZEP-520) and negative tone templates [hydrogen silsequioxane (HSQ)] have been fabricated. The positive tone templates require a plasma etch step, while the HSQ templates [Mancini et al., J. Vac. Sci. Technol. B 20, 2896 (2002)] can be used directly for nanoimprint. A process for creation of daughter templates from silicon master e-beam exposures has been demonstrated on the EVG 620. The silicon master with HSQ patterns is placed on the wafer stage and a quartz wafer coated with nanoimprint polymer is mounted where the template is normally placed. The resultant image on the quartz wafer is then transferred into the substrate with plasma etching, and these daughter templates can then be used for image transfer. Minimal loss of resolution has been demonstrated with this process.
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81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning

Characterization of pentafluoropropane dissolved UV-nanoimprint resin

Mika Chinen, Yohei Sawada, Yuichi Haruyama, Shinji Matsui, Makoto Okada, and Hiroshi Hiroshima

J. Vac. Sci. Technol. B 29, 06FC18 (2011); http://dx.doi.org/10.1116/1.3662856 (5 pages)

Online Publication Date: 23 November 2011

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Bubble defects in ultraviolet (UV) nanoimprinting can be eliminated by carrying out the procedure in pentafluoropropane (PFP) gas ambient. Furthermore, the viscosity of the UV-nanoimprint resin is about one-fifth lower than that in air. The authors assume from these results that the PFP gas dissolves into the UV-nanoimprint resin, and the dissolved PFP might affect the characteristics of UV-nanoimprint resin. In this experiment, we analyzed the properties of PFP-dissolved UV-nanoimprint resin using a Fourier transform infrared (FT-IR) spectrometer and contact-angle meter. First, we measured the FT-IR spectrum. The results for resins in PFP gas ambient showed a peak due to the stretching vibration of the C–F bond before and after UV irradiation. Next, the sliding angles and speeds of resins were measured by measurement of the sliding angle in air and PFP gas ambient. The sliding speeds in PFP gas ambient were five times those in air and the sliding angles were one-fourth lower than those in air. The increase in sliding speeds and the decrease in sliding angles in PFP gas ambient were due to the PFP gas dissolving into the resin.
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81.16.Nd Micro- and nanolithography
64.75.Bc Solubility
78.30.Jw Organic compounds, polymers

Anisotropic filling phenomenon of cavities in UV nanoimprint lithography

Qing Wang and Hiroshi Hiroshima

J. Vac. Sci. Technol. B 29, 06FC19 (2011); http://dx.doi.org/10.1116/1.3662889 (5 pages)

Online Publication Date: 23 November 2011

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The authors investigated a resist-filling process using a capacity-equalized mold with complementary cavities added to line trenches. By tracking the bubble shrinking process in real time using a video monitoring system, we observed a filling phenomenon that differs from the well-reported isotropic filling. In this newly observed anisotropic filling, a bubble shrinks at different rates along its length and width directions of the rectangular complementary cavities, with a higher shrinkage rate along its length direction. The authors found that the resist-filling process had two phases. The first phase of the resist-filling process is anisotropic, and the second phase of the process is isotropic. Total complete filling time thus depends on the cavity dimensions, and the portion of filling time devoted to anisotropic filling depends linearly on the cavity length. Our findings suggest that the resist-filling process should exhibit similar two-phase behavior for other complex 3D patterns also.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
back to top Maskless Lithography

Charging effects during focused electron beam induced deposition of silicon oxide

Sanne K. de Boer, Willem F. van Dorp, and Jeff Th. M. De Hosson

J. Vac. Sci. Technol. B 29, 06FD01 (2011); http://dx.doi.org/10.1116/1.3659713 (4 pages)

Online Publication Date: 8 November 2011

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This paper concentrates on focused electron beam induced deposition of silicon oxide. Silicon oxide pillars are written using 2, 4, 6, 8, 10-pentamethyl-cyclopenta-siloxane (PMCPS) as precursor. It is observed that branching of the pillar occurs above a minimum pillar height. The branching is attributed to charging of the deposit by the electron beam. The branching can be suppressed by introducing water into the chamber together with PMCPS. At the same time, the cointroduction of water results in a higher growth rate, which is found to be specific to PMCPS.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.Dj E-beam and hot filament evaporation deposition

Scanning proximal probe lithography for sub-10 nm resolution on calix[4]resorcinarene

Marcus Kaestner and Ivo W. Rangelow

J. Vac. Sci. Technol. B 29, 06FD02 (2011); http://dx.doi.org/10.1116/1.3662092 (6 pages) | Cited 1 time

Online Publication Date: 18 November 2011

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The use of molecular resist in scanning proximal probe lithography (SPPL) offers a novel and promising maskless lithographic method with sub-10 nm resolution. Here, the authors present their investigation of the patterning capabilities of C-Methylcalix[4]resorcinarene at ambient conditions using SPPL. The STM-based setup operates in constant-current Fowler–Nordheim regime and results in positive-tone self-developing phenomena. The lithographic operation is performed at currents in the range of pico-ampere, writing speeds of 1–10 μm/s, and bias voltages ranging from 20 up to 70 V. Currently, the authors have achieved feature sizes from 7 nm to micrometers depending on the applied exposure parameters. The direct patterning process shows high reproducibility and reliability over this large feature range.
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68.55.am Polymers and organics

Multitip atomic force microscope lithography system for high throughput nanopatterning

Young Oh, Chulmin Choi, Kunbae Noh, Diana Villwock, Sungho Jin, Gwangmin Kwon, and Haiwon Lee

J. Vac. Sci. Technol. B 29, 06FD03 (2011); http://dx.doi.org/10.1116/1.3662396 (6 pages)

Online Publication Date: 22 November 2011

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An atomic force microscope (AFM) system with multiple parallel lithography probes of equal heights on a single cantilever was created in order to improve the throughput of AFM lithography. The multitip probe was fabricated by electron-beam (e-beam) lithography and a dry silicon etching process. Several carbon islands were made on a single cantilever in a straight line by e-beam lithography and were used as an etch mask, whereas the silicon pedestal structure of the multitip probe was fabricated by reactive ion etching (RIE). Finally the carbon islands were sharpened by a RIE process using oxygen gas. The multitip probe was successfully applied to form multidot pattern arrays on a negative resist film coated on silicon by low electric field induced AFM lithography. A pedestal nanopillar structure was utilized as a convenient support feature that enabled better control of multiple nanotip arrays for AFM writing. The authors fabricated such a nanopedestal array with extremely sharp nanoneedle tips.
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81.05.U- Carbon/carbon-based materials
52.77.Bn Etching and cleaning
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning

Lithography-patterning-fidelity-aware electron-optical system design optimization

Sheng-Yung Chen (陳勝勇), Hoi-Tou Ng (伍海濤), Shiau-Yi Ma (馬學億), Hsing-Hong Chen (陳信宏), Chun-Hung Liu (劉俊宏), and Kuen-Yu Tsai (蔡坤諭)

J. Vac. Sci. Technol. B 29, 06FD04 (2011); http://dx.doi.org/10.1116/1.3662402 (8 pages)

Online Publication Date: 7 December 2011

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Low-energy electron beam lithography is a promising patterning solution for the 21 nm half-pitch node and beyond due to its high resolution, low substrate damage, and increased resist sensitivities. To ensure a successful electron-optical system (EOS) design, many factors such as focusing properties (FPs) and patterning fidelity (PF) have to be considered. In traditional EOS optimization flow, FPs are typical performance indices selected when optimizing the EOS design parameters. In each numerical iteration, the EOS FP simulation results are compared with specified performance index values. The differences are reduced by adjusting the EOS design parameters until convergence. However, the performance indices related to FPs may have no direct relation to lithography PF, which is judged by the quality of the developed resist patterns. A new EOS design methodology which directly incorporates lithography PF metrics into the optimization flow is proposed. The EOS design parameters are first optimized while meeting the geometric constraints by using the traditional design flow to obtain acceptable FPs. In order to ensure lithography PF, writing patterns are selected and writing parameters are optimized. Then, constraints and cost functions related to PF are selected to further optimize the EOS design parameters to obtain acceptable PF. In each numerical iteration, the simulated lithography patterning results are compared against specified PF metric values. Their differences are reduced by adjusting the EOS design parameters until all constraints are met and PF cost functions are converged. The proposed method is applied to an EOS structure design for a 5 keV electron beam lithography system which includes a single-gate source and a focusing lens. Initial values of EOS design parameters and geometric constraints are selected based on previous studies. A drawn layout for a 22 nm isolated line pattern is used for verifying the lithography PF specifications based on the International Technology Roadmap of Semiconductors. The developed resist pattern after applying the proposed method clearly indicates that the PF is significantly improved from the value of corresponding critical dimension (CD) and the value of gate CD control.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
back to top Micro- and Nano-mechanics (MEMS, NEMS)

Investigation of graphene piezoresistors for use as strain gauge sensors

Xing Chen, Xiaohu Zheng, Ji-Kwan Kim, Xinxin Li, and Dong-Weon Lee

J. Vac. Sci. Technol. B 29, 06FE01 (2011); http://dx.doi.org/10.1116/1.3660784 (5 pages)

Online Publication Date: 10 November 2011

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The primary objective of this research is to fabricate a graphene-based piezoresistive strain gauge and characterize its sensitivity. The strain gauge consists of mechanically exfoliated graphene sheets and electrical electrodes located on a silicon wafer. Instead of using e-beam lithography, which is the most widely applied methods in experimental studies of graphene, a new fabrication method utilizing conventional photolithography was used to easily fabricate a new nanoelectromechanical system strain gauge. The proposed fabrication technique is easy and only requires a few types of microfabrication equipment, thereby opening up a new way to broadly spread and facilitate associated graphene research, especially for those laboratories with limited resources. To characterize the piezoresistive sensitivity of the graphene-based strain gauge, a strain-detection system built by an equivalent-stress macrocantilever was set up to generate mechanical bending strain where a calibrated commercial strain gauge was packaged to display the generated strain. Utilizing this measurement setup, the electrical properties of the graphene-based piezoresistive strain gauge were reliably investigated. A high gauge factor of ∼150 was experimentally measured with the graphene device, which promises a new strain gauge of high sensitivity.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
81.16.Nd Micro- and nanolithography
85.35.-p Nanoelectronic devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Quality factor enhancement on nanomechanical resonators utilizing stiction phenomena

Hiroki Ashiba, Reo Kometani, Shin’ichi Warisawa, and Sunao Ishihara

J. Vac. Sci. Technol. B 29, 06FE02 (2011); http://dx.doi.org/10.1116/1.3660384 (5 pages)

Online Publication Date: 14 November 2011

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A simple method of applying tensile stress to nanomechanical resonators was proposed and demonstrated. Two parallel beams were fabricated by wet etching. The beams then stuck to each other due to surface tension caused by the rinse solution and formed a stiction resonator. The stuck beams were stressed because of the deformation caused by the sticking. The stiction resonators were modeled to estimate the sticking length and evaluate the strain of the resonators. The maximum resonator strain obtained in this study was over 0.3%. The quality factors of the stiction resonators were then experimentally evaluated. Results showed that tensile stress had a significant effect on the quality factor enhancement. Using stiction is an effective, useful, and widely applicable method for the tensile stress application.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.07.Oj Nanoelectromechanical systems (NEMS)

Dynamic characteristics control of DLC nano-resonator fabricated by focused-ion-beam chemical vapor deposition

Reo Kometani, Shunjiro Nishi, Shin’ichi Warisawa, and Sunao Ishihara

J. Vac. Sci. Technol. B 29, 06FE03 (2011); http://dx.doi.org/10.1116/1.3662493 (4 pages)

Online Publication Date: 22 November 2011

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The authors fabricated a resonant frequency-tunable diamondlike carbon (DLC) resonator by focused-ion-beam chemical vapor deposition and a wet-etching process for fabrication of a functional resonant device. The resonant frequency of the DLC resonator with a cantilever shape was controlled electrically via the electrostatic attractive force generated by the opposite electrode. As a result, we achieved an extremely large resonant frequency tuning ratio of approximately 730%. This indicates that the electrostatic attractive force, when added to the restorative force of the DLC resonator, works effectively to change the resonant frequency.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.07.Oj Nanoelectromechanical systems (NEMS)
81.05.ug Diamond
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

MEMS process compatibility of multiwall carbon nanotubes

Eugene H. Cook and David J. D. Carter

J. Vac. Sci. Technol. B 29, 06FE04 (2011); http://dx.doi.org/10.1116/1.3662082 (12 pages)

Online Publication Date: 29 November 2011

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While carbon nanotubes (CNT) have been proposed and used as structural elements (e.g., cantilevers, bearings, nanofluidic channels, etc.) in microsystems, knowledge of the compatibility of CNTs with a broad range of standard microelectromechanical system (MEMS) fabrication processes is incomplete. This work investigates the effect of 23 common MEMS processes and chemicals on catalytically-grown and arc-discharge-produced multiwall nanotubes (MWNT) and compares the observed effects with those reported in the literature. Specific individual nanotubes are observed using scanning-electron microscopy (SEM) and transmission-electron microscopy (TEM) before and after the application of each process. This allows detection of process-induced changes to the nanotube from the bulk scale down to the nanometer and even atomic scales. Various thin-film deposition techniques are used to deposit common MEMS materials on MWNTs. A variety of wet chemicals and dry etching techniques are applied to MWNTs. Many processes prove compatible with the MWNTs, which suggests that they are robust for integration into MEMS devices.
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81.16.Hc Catalytic methods
81.65.Cf Surface cleaning, etching, patterning
07.10.Cm Micromechanical devices and systems
81.07.De Nanotubes

Low frequency tantalum electromechanical systems for biomimetical applications

Rhonira Latif, Enrico Mastropaolo, Andrew Bunting, Rebecca Cheung, Thomas Koickal, Alister Hamilton, Michael Newton, and Leslie Smith

J. Vac. Sci. Technol. B 29, 06FE05 (2011); http://dx.doi.org/10.1116/1.3662408 (6 pages)

Online Publication Date: 29 November 2011

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The integration of p-channel metal-oxide-semiconductor transistors and tantalum bridge structures for the fabrication of resonant gate transistors (RGTs) that operate in the audible frequency range has been developed. Resonant gate transistors with channel length of 15 μm and clamped-clamped tantalum bridges of 0.5 mm to 1.6 mm in length have been fabricated. The measured first modal frequency of the bridges has been found to be higher than the expected theoretical value. From the experimental and theoretical analysis of the first three modes, the stress in the bridges has been extracted and found to be tensile with values of 3 MPa – 10 MPa. Finite element simulation has validated the extracted stress and the mode shapes of the tantalum bridges. The modulation of conductance in the channel region between the source and drain by the tantalum bridge of the RGT has been demonstrated. The threshold voltage and transconductance of the fabricated p-channel RGT have been measured to be −37 V and 6.84 μS, respectively.
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85.30.Tv Field effect devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Carbon nanomechanical resonator fabrication from PMMA by FIB/electron-beam dual-beam lithography

Reo Kometani, Taiki Hatakeyama, Kouhei Kuroda, Shin’ichi Warisawa, and Sunao Ishihara

J. Vac. Sci. Technol. B 29, 06FE06 (2011); http://dx.doi.org/10.1116/1.3662083 (5 pages)

Online Publication Date: 2 December 2011

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An ultra-thin carbon nanomechanical resonator was fabricated from poly(methyl methacrylate) (PMMA) using focused-ion-beam (FIB) and electron-beam dual-beam lithography. A suspended PMMA structure was cured using an ion-beam modification technique using a 30-kV Ga+ FIB, and carbonized to a diamondlike carbon. In addition, we analyzed the vibrational properties of the cured PMMA nanowire to confirm that it functioned as a resonant structure.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.07.Oj Nanoelectromechanical systems (NEMS)
back to top Micro- and Nano-photonics, Plasmonics

Light trapping in plasmonic nanocavities on metal surfaces

Aleksandr Polyakov, Howard A. Padmore, Xiaogan Liang, Scott Dhuey, Bruce Harteneck, James P. Schuck, and Stefano Cabrini

J. Vac. Sci. Technol. B 29, 06FF01 (2011); http://dx.doi.org/10.1116/1.3634021 (4 pages)

Online Publication Date: 9 September 2011

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In this article we present a fabrication method for producing 15 nm wide 45 nm deep nanogrooves on the metal surface that provide for efficient light trapping. These grooves form a subwavelength grating that allows p-polarized light to efficiently cople to the surface plasmon polaritons modes inside the grooves producing complete absorption. A test-of-concept device showing 16 times increase in absorption compared to the plain metal is presented. The authors also present an alternative fabrication method for producing higher quality devices with sub-10 nm wide grooves.
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78.66.Bz Metals and metallic alloys
81.16.-c Methods of micro- and nanofabrication and processing
42.79.Dj Gratings
78.68.+m Optical properties of surfaces

Large area 3D helical photonic crystals

A. K. Raub and S. R. J. Brueck

J. Vac. Sci. Technol. B 29, 06FF02 (2011); http://dx.doi.org/10.1116/1.3640756 (6 pages)

Online Publication Date: 3 October 2011

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Three-dimensional helical photonic crystals are attractive for chiral metamaterial devices that mix electrical and magnetic responses. In chiral metamaterials, the refractive index for propagation of light along the axis of the helix is different as the handedness of the circular polarization is parallel or antiparallel to the chiral axis. The refractive index is increased for one circular polarization and reduced for the other, if the chirality is strong enough, negative refraction may occur. A novel interferometric lithography (IL) technique utilizing six separate two-beam exposures for fabricating three-dimensional helical photonic crystals is presented. In contrast to most previous demonstrations, which used a two-photon direct-write process, IL is a large-area process readily adaptable to realistic manufacturing constraints. This novel interferometric lithography uses only TE polarized light for maximum contrast and allows for independent dimensional control of the helix period along each lattice axis. Both mathematical models and experimentally realized three-dimensional helical photonic crystals (over a mm2 in area and up to 5 μm tall, with a helix spacing of 1.1 μm and a helix pitch of 1.9 μm on a hexagonal grid) are presented. The helical photonic crystals are formed as thick photoresist structures that can be subsequently used as mandrels for a sol-gel or metal electroforming processes, enabling a high index contrast chiral metamaterial. Optical transmission measurements of these helical photonic crystals are reported at the 1550 nm telecom wavelength.
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42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Gradually shifting surface plasmon resonance by controlling the diameter of a nanohole structure by self-assembly

Takamitsu Takagi, Reo Kometani, Sunao Ishihara, Shinichi Warisawa, Kazuma Kurihara, and Koichi Awazu

J. Vac. Sci. Technol. B 29, 06FF03 (2011); http://dx.doi.org/10.1116/1.3660387 (5 pages)

Online Publication Date: 10 November 2011

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A new fabrication method for a surface plasmon resonance (SPR) device with a gradual SPR shift—namely, using a nanostructure self-assembled by using a mixed block copolymer as a template—was developed. By this method, it was demonstrated that the diameter of a self-assembled nanohole can be controlled by changing the film thickness of a mixed block copolymer. It was also demonstrated that SPR wavelength shift can be controlled according to the nanohole structure (with diameter controlled according to film thickness). An actual SPR device with a gradually shifted SPR wavelength was fabricated, and it was confirmed that this SPR device can detect refractive-index change in its surroundings. This device has the potential to expand the application of SPR devices.
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81.16.Dn Self-assembly
68.55.jd Thickness
73.22.Lp Collective excitations
61.46.-w Structure of nanoscale materials

Multilayer infrared metamaterial fabrication using membrane projection lithography

D. Bruce Burckel, Joel R. Wendt, Sally Samora, Michael B. Sinclair, Igal Brener, and James C. Ginn

J. Vac. Sci. Technol. B 29, 06FF04 (2011); http://dx.doi.org/10.1116/1.3653258 (4 pages)

Online Publication Date: 11 November 2011

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Membrane projection lithography is extended from a single layer fabrication technique to a multilayer process, adding polymeric backfill and planarization after each layer is completed. Unaligned contact lithography is used as a rapid prototyping tool to aid in process development, patterning resist membranes in seconds without requiring long e-beam write times. The fabricated multilayer structures show good resistance to solvent attack from subsequent process steps and demonstrate in-plane and out of plane multilayer metallic inclusions in a dielectric host, which is a critical step in the path to develop bulklike metamaterials at optical frequencies.
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81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
85.40.Ls Metallization, contacts, interconnects; device isolation
81.16.Nd Micro- and nanolithography

Coexistence of guided mode resonance and extraordinary optical transmission in metal/dielectric/metal photonic crystal slab

Neil Ou, Jia-Hong Shyu, Huang-Ming Lee, and Jong-Ching Wu

J. Vac. Sci. Technol. B 29, 06FF05 (2011); http://dx.doi.org/10.1116/1.3662406 (4 pages)

Online Publication Date: 21 November 2011

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This study examines the optical properties of metal-dielectric-metal (MDM) photonic crystal slabs (PCS) which consist of a 100-nm freestanding silicon nitride membrane that is sandwiched on either side by a 20-nm-thick gold film with an array of hexagonal tapered holes. It shows the extraordinary optical transmission phenomenon that is generated from the coupling of internal surface plasmon polaritons that are excited by dual gold layers. In addition, the presence of transmission dips can be attributed to the guided mode resonance of silicon nitride based PCS. Numerical calculation of photonic band structure confirms this attribution. This coexistence of extraordinary optical transmission and the guided mode resonance in MDM PCS may contribute to the development of multifunctional optical devices.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.21.Ac Multilayers

Nanofabrication of photonic crystal-based devices using electron beam spot lithography

A. S. Jugessur, M. Yagnyukova, and J. S. Aitchison

J. Vac. Sci. Technol. B 29, 06FF06 (2011); http://dx.doi.org/10.1116/1.3662088 (5 pages)

Online Publication Date: 23 November 2011

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This paper reports on photonic crystal-based devices fabricated via the electron beam spot lithography technique. This technique produces uniform, submicron, and nanometer scale periodic holes over large areas in the millimeter range and the write time is a factor of over 120 times faster than the conventional direct-write technique. Generic design guidelines of this technique are established and the patterning of photonic crystal holes’ arrays in the square and hexagonal lattice configurations are investigated. The single spot lithography technique could potentially be useful as a mass fabrication approach, particularly for very large areas of 2D photonic crystal-based devices and possibly for other device fabrication, for a wide range of scientific and technological applications.
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42.70.Qs Photonic bandgap materials
42.79.-e Optical elements, devices, and systems
back to top Nanostructures and Pattern Transfer

Etch properties of resists modified by sequential infiltration synthesis

Yu-Chih Tseng, Qing Peng, Leonidas E. Ocola, David A. Czaplewski, Jeffrey W. Elam, and Seth B. Darling

J. Vac. Sci. Technol. B 29, 06FG01 (2011); http://dx.doi.org/10.1116/1.3640758 (4 pages)

Online Publication Date: 27 September 2011

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The etch resistance of electron-beam lithography resists, poly(methyl methacrylate) (PMMA) and ZEP520A, is increased significantly by sequential infiltration synthesis (SIS). This process infiltrates the bulk of the resist film with alumina, rendering it resistant to plasma etching. The enhanced etch resistance eliminates the need for an intermediate hard mask and the associated process costs and pattern fidelity losses. Furthermore, the improvement is realized with no degradation to the line-edge roughness of lithographically defined patterns. The enhancement in etch resistance is especially strong at the edges of the printed lines, owing to diffusion of the SIS precursors from the resist sidewalls. These improvements enable the anisotropic transfer of sub-100 nm patterns deeply into silicon without the need for an intermediate hard mask.
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81.65.Cf Surface cleaning, etching, patterning
81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography

Twelve nanometer half-pitch W–Cr–HSQ trilayer process for soft x-ray tungsten zone plates

Julia Reinspach, Fredrik Uhlén, Hans M. Hertz, and Anders Holmberg

J. Vac. Sci. Technol. B 29, 06FG02 (2011); http://dx.doi.org/10.1116/1.3643760 (4 pages)

Online Publication Date: 29 September 2011

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The authors describe a new W–Cr–HSQ trilayer nanofabrication process for high-resolution and high-diffraction-efficiency soft x-ray W zone-plate lenses. High-resolution HSQ gratings were first fabricated by electron-beam lithography and high-contrast development in a NaCl/NaOH solution. The HSQ pattern was then transferred to the Cr layer by RIE with Cl2/O2, and subsequently to the W layer by cryogenic RIE with SF6/O2. The anisotropy of the W etch as a function of substrate temperature was investigated, and the best etch profile was achieved at −50 °C. Using this optimized process, W gratings with half-pitches down to 12 nm and a height of 90 nm were fabricated. For a zone plate with corresponding parameters, this would result in a theoretical diffraction efficiency of 9.6% (at λ = 2.48 nm), twice as high as has been reported previously.
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68.65.Ac Multilayers
81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning

New diamond nanofabrication process for hard x-ray zone plates

Fredrik Uhlén, Sandra Lindqvist, Daniel Nilsson, Julia Reinspach, Ulrich Vogt, Hans M. Hertz, Anders Holmberg, and Ray Barrett

J. Vac. Sci. Technol. B 29, 06FG03 (2011); http://dx.doi.org/10.1116/1.3656055 (4 pages)

Online Publication Date: 28 October 2011

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The authors report on a new tungsten-hardmask-based diamond dry-etch process for fabricating diamond zone plate lenses with a high aspect ratio. The tungsten hardmask is structured by electron-beam lithography, together with Cl2/O2 and SF6/O2 reactive ion etching in a trilayer resist-chromium-tungsten stack. The underlying diamond is then etched in an O2 plasma. The authors demonstrate excellent-quality diamond gratings with half-pitch down to 80 nm and a height of 2.6 μm, as well as zone plates with a 75 μm diameter and 100 nm outermost zone width. The diffraction efficiency of the zone plates is measured to 14.5% at an 8 keV x-ray energy, and the imaging properties were investigated in a scanning microscope arrangement showing sub-100-nm resolution. The imaging and thermal properties of these lenses make them suitable for use with high-brightness x-ray free-electron laser sources.
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81.05.ug Diamond
42.79.Ci Filters, zone plates, and polarizers
81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning

Selective graphene growth from DLC thin film patterned by focused-ion-beam chemical vapor deposition

Taiki Hatakeyama, Reo Kometani, Shin’ichi Warisawa, and Sunao Ishihara

J. Vac. Sci. Technol. B 29, 06FG04 (2011); http://dx.doi.org/10.1116/1.3655581 (5 pages) | Cited 1 time

Online Publication Date: 2 November 2011

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The authors were able to grow a few-layer graphene film on a SiO2 substrate directly and selectively by using focused-ion-beam chemical vapor deposition (FIB-CVD) and a Ga evaporation process. FIB-CVD can control the thickness of the diamondlike carbon (DLC) film and potentially control the number of graphene layers, and Ga evaporation causes the direct transformation of patterned DLC into graphene. DLC was graphitized by annealing with a Ga film at 1000 °C and 1100 °C. Increasing the thickness of the Ga film resulted in a graphitized pattern that had a strong Raman 2D band. The formation of graphene above and around a dimple on the SiO2 layer indicates that Ga dissolved the DLC and graphene precipitated not between the liquid Ga and the SiO2 substrate but, rather, on the small droplets of Ga. This behavior is different than that reported in previous studies of graphitization at the interface between a carbon layer and liquid Ga.
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81.05.ue Graphene
81.05.ug Diamond
78.30.Am Elemental semiconductors and insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors

Pulsed helium ion beam induced deposition: A means to high growth rates

Paul F. A. Alkemade, Hozanna Miro, Emile van Veldhoven, Diederik J. Maas, Daryl A. Smith, and Philip D. Rack

J. Vac. Sci. Technol. B 29, 06FG05 (2011); http://dx.doi.org/10.1116/1.3656347 (6 pages)

Online Publication Date: 3 November 2011

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The sub-nanometer beam of a helium ion microscope was used to study and optimize helium-ion beam induced deposition of PtC nanopillars with the (CH3)3Pt(CPCH3) precursor. The beam current, beam dwell time, precursor refresh time, and beam focus have been independently varied. Continuous beam exposure resulted in narrow but short pillars, while pulsed exposure resulted in thinner and higher ones. Furthermore, at short dwell times the deposition efficiency was very high, especially for a defocused beam. Efficiencies were measured up to 20 times the value for continuous exposure conditions. The interpretation of the experimental data was aided by a Monte Carlo simulation of the deposition. The results indicate that two regimes are operational in ion beam induced deposition (IBID). In the first one, the adsorbed precursor molecules originally present in the beam interaction region decompose. After the original precursor layer is consumed, further depletion is averted and growth continues by the supply of molecules via adsorption and surface diffusion. Depletion around the beam impact site can be distinguished from depletion on the flanges of the growing pillars. The Monte Carlo simulations for low precursor surface coverage reproduce measured growth rates, but predict considerably narrower pillars, especially at short dwell times. Both the experiments and the simulations show that the pillar width rapidly increases with increasing beam diameter. Optimal writing strategy, good beam focusing, and rapid beam positioning are needed for efficient and precise fabrication of extended and complex nanostructures by He-IBID.
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81.07.Bc Nanocrystalline materials
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.16.-c Methods of micro- and nanofabrication and processing

Technology platform for the fabrication of titanium nanostructures

Serge Ecoffey, Marc Guilmain, Jean-François Morissette, Frédéric Bourque, Jérémy Pont, Bruno Lee Sang, and Dominique Drouin

J. Vac. Sci. Technol. B 29, 06FG06 (2011); http://dx.doi.org/10.1116/1.3657517 (4 pages)

Online Publication Date: 3 November 2011

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This paper presents two approaches for the fabrication of top-down titanium nanostructures. The first approach involves electron beam lithography followed by a tailored titanium plasma etching. The two main challenges of this process lie in the optimization of the negative tone Ma–N electroresist resolution and in the definition of a controlled titanium etching process for titanium patterns less than 20 nm thick and wide. The second proposed approach is a damascene process where the titanium nanostructures are buried in the oxide. Very shallow and narrow (20 nm × 20 nm) trenches are first patterned in the oxide and nanostructures are obtained by planarization of an evaporated titanium film. The dimensions of the structures are defined by the electron beam lithography resolution and the etching recipe. The third dimension is given by the titanium or any other metal thickness and can be controlled down to few nanometers thanks to the planarization step.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.65.Mq Oxidation
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Nanofabrication down to 10 nm on a plastic substrate

Li Tao, Jongho Lee, and Deji Akinwande

J. Vac. Sci. Technol. B 29, 06FG07 (2011); http://dx.doi.org/10.1116/1.3662081 (6 pages) | Cited 1 time

Online Publication Date: 17 November 2011

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In this work, we proved the feasibility of nanofabrication down to 10 nm on a plastic substrate with varied fabrication techniques. Durable polyimide sheets (25–200 μm thick), commercially available as Kapton® film, was selected as substrate material with smoothened surface for enhanced resolution and registration in the fabrication process. E-beam lithography at 30 kV of 10 nm grooves and 25 nm metal lift-off were demonstrated for the first time on polyimide. Step-flash imprint of sub 100 nm dense gratings (1:1 ratio) was successfully performed on 2′′ wafer-size polyimide substrate. Directed self-assembly yield gratings of di-block copolymer with 10 nm half-pitch on polyimide. These techniques enable á la carte platforms that can be integrated with traditional semiconductor or flexible electronic processing. As an example, graphene field effect transistor with channel length of 200 nm was fabricated on polyimide with performance comparable to reported high mobility graphene flexible electronics on polyethylene terephthalate plastics. The capability of nano-fabrication down to 10 nm on polyimide paves the way for fundamental studies and scalable fabrication of novel nano-scale materials and devices on plastic substrates.
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81.16.Dn Self-assembly
61.41.+e Polymers, elastomers, and plastics
61.46.-w Structure of nanoscale materials

Fabrication of complex nanostructures of Poly(vinylidenefluoride-trifluoroethylene) by dual step hot-embossing

Juan-juan Wen, Zhen-kui Shen, Zhi-jun Qiu, An-quan Jiang, Ran Liu, and Yifang Chen

J. Vac. Sci. Technol. B 29, 06FG08 (2011); http://dx.doi.org/10.1116/1.3662087 (4 pages)

Online Publication Date: 17 November 2011

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In this work, complex 3D ferroelectric nanostructures have been successfully fabricated on Poly(vinylidenefluoride-trifluoroethylene), P(VDF-TrFE), thin films using a special hot-embossing process with two sequential shots on the same site with a grating template and a rounded square array template at the same hot-embossing temperature. The nanostructures have been characterized with scanning electron microscopy, atomic force microscopy and piezoresponse force microscopy, respectively. It is shown that sequential hot-embossing offers an effective way to create complex structures for functional ferroelectric materials by conducting secondary or tertiary imprinting toward various applications, including mass production of ferroelectric devices such as nonvolatile memories, photonics, bionic structure and surface wetting.
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81.16.Nd Micro- and nanolithography
68.55.am Polymers and organics
61.46.-w Structure of nanoscale materials
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Jd Polymers; organic compounds

Computational study of electron-irradiation effects in carbon nanomaterials on substrates

Yoshinori Chihara, Masaaki Yasuda, Shinya Wakuda, Hiroaki Kawata, and Yoshihiko Hirai

J. Vac. Sci. Technol. B 29, 06FG09 (2011); http://dx.doi.org/10.1116/1.3662409 (5 pages) | Cited 1 time

Online Publication Date: 23 November 2011

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Molecular dynamics simulation is performed to study electron-irradiation effects in carbon nanomaterials on substrates. The interaction between an incident electron and a carbon atom in target nanomaterials is introduced by the Monte Carlo method. Collisions of the backscattered electrons from the substrate are also introduced. The distributions of energy and the exit angle of backscattered electrons are calculated using Monte Carlo simulation of electron scattering in the substrate. Structural changes become more remarkable when the carbon nanomaterials are on the substrates. The threshold energy and the characteristics of structural changes by backscattered electrons are also discussed.
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81.05.U- Carbon/carbon-based materials
61.80.Fe Electron and positron radiation effects
61.82.Rx Nanocrystalline materials
79.20.Kz Other electron-impact emission phenomena
81.07.-b Nanoscale materials and structures: fabrication and characterization

Injection compression molding of high-aspect-ratio nanostructures

Keisuke Nagato, Tetsuya Hamaguchi, and Masayuki Nakao

J. Vac. Sci. Technol. B 29, 06FG10 (2011); http://dx.doi.org/10.1116/1.3662405 (4 pages)

Online Publication Date: 1 December 2011

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High-aspect-ratio nanostructures were replicated by injection compression molding. The effects of the mold temperature and pattern shape on the degree of replication were investigated using a replication technique for optical disks (digital versatile disks) and a Ni stamper with patterns with a width and height of 200 and 400 nm. A higher mold temperature and a smaller area-duty ratio (hill area/unit area) of the Ni stamper, i.e., a larger area-duty ratio of the replica resulted in better replication because a Ni stamper with a smaller area-duty ratio suppresses the formation of a skin layer.
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81.16.-c Methods of micro- and nanofabrication and processing
81.10.Fq Growth from melts; zone melting and refining
42.79.Vb Optical storage systems, optical disks
back to top Optical Lithography, including Masks and Maskless

Evaluation of three exposure schemes for absorbance-modulated interference lithography

John E. Foulkes, Charles W. Holzwarth, and Richard J. Blaikie

J. Vac. Sci. Technol. B 29, 06FH01 (2011); http://dx.doi.org/10.1116/1.3640757 (6 pages)

Online Publication Date: 27 September 2011

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Using absorbance-modulated interference lithography (AMIL), subdiffraction-limited gratings can be patterned using a variety of configurations. Three main configurations are compared here using results from a finite-element modeling simulation study, with combinations of standing-wave interference illumination and/or flood illumination for the two wavelengths needed for AMIL. Flood illumination for the short-wavelength exposure combined with standing-wave exposure in the longer wavelength is the simplest configuration, but does not provide the best imaging performance. This is achieved for standing-wave illumination for both sources with matched periods in the standing waves. For 405 nm short-wavelength exposure and azobenzenelike material characteristics in the absorbance-modulation layer 133-nm period grating images are shown with image contrast of 0.58. The sensitivity to misalignment of the two standing wave periods has been studied, and no significant increase in linewidth is found for phase errors between the two interference patterns of up to 20% of the period.
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81.16.Rf Micro- and nanoscale pattern formation
42.40.Eq Holographic optical elements; holographic gratings
42.79.Dj Gratings
42.86.+b Optical workshop techniques
02.70.Dh Finite-element and Galerkin methods
81.16.Nd Micro- and nanolithography

Flexible poly(dimethyl siloxane) support layers for the evanescent characterization of near-field lithography systems

Ciaran P. Moore and Richard J. Blaikie

J. Vac. Sci. Technol. B 29, 06FH02 (2011); http://dx.doi.org/10.1116/1.3653511 (4 pages)

Online Publication Date: 24 October 2011

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The authors present an improved near-field contact lithography technique that facilitates the characterization of superlens-based imaging systems. Pattern transfer is realized by discrete mask and photoresist components, in combination with water-soluble metal-dielectric superlens layers. Damage to imaging components is prevented by the inclusion of a flexible poly(dimethyl siloxane) (PDMS) layer in the photoresist stack. The AFM micrographs of near-field exposures performed using this technique show good fidelity between the mask and image patterns, which is not the case when the PDMS layer is omitted. The increased robustness and fidelity offered by this technique pave the way towards a full spatial frequency-domain characterization of optical superlenses, based entirely on experimentally measured data.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.70.Jk Polymers and organics
42.79.Bh Lenses, prisms and mirrors
42.82.Cr Fabrication techniques; lithography, pattern transfer

Fast aerial image simulations using one basis mask pattern for optical proximity correction

Shiyuan Liu, Xiaofei Wu, Wei Liu, and Chuanwei Zhang

J. Vac. Sci. Technol. B 29, 06FH03 (2011); http://dx.doi.org/10.1116/1.3659718 (7 pages)

Online Publication Date: 10 November 2011

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Aerial image simulation is one of the key parts in the model-based optical proximity correction (OPC) technique, which has become a must have process to improve lithography performance with ever-decreasing feature sizes. In this paper, a fast aerial image simulation approach is proposed by using one basis mask pattern to generate a lookup table, where the convolutions of the basis pattern with the partially coherent kernels are precalculated and stored. A rectilinear polygon mask pattern used in integrated circuit layouts can be decomposed into several shifted basis patterns. Its convolutions with kernels for use in aerial image calculation can then be quickly obtained from the precalculated lookup table by applying the translation-invariant property of two-dimensional convolution. Simulations conducted by using the proposed approach have demonstrated that this approach yields a superior quality in the fields of aerial image calculation and OPC optimization, due to the advantage of dramatically decreasing the storage requirement. It is fully expected that this approach will be simple to implement and will provide a useful practical means for OPC systems.
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42.30.-d Imaging and optical processing

Computational lithography: Exhausting the resolution limits of 193-nm projection lithography systems

David O. S. Melville, Alan E. Rosenbluth, Andreas Waechter, Marc Millstone, Jaione Tirapu-Azpiroz, Kehan Tian, Kafai Lai, Tadanobu Inoue, Masaharu Sakamoto, Kostas Adam, and Alexander Tritchkov

J. Vac. Sci. Technol. B 29, 06FH04 (2011); http://dx.doi.org/10.1116/1.3662090 (14 pages)

Online Publication Date: 23 November 2011

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In the recent past, scaling of semiconductor fabrication systems has been dominated by wavelength and numerical aperture modifications. This is now no longer the case for 193-nm immersion projection lithography (193i) systems as there are no technical paths for continued benefit from the in these areas. Instead, a range of techniques including patterning processes and system optimization are being used to push the limits of the system. This paper will review the elements that are now driving scaling for a system of fixed wavelength and numerical aperture.
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85.40.Hp Lithography, masks and pattern transfer
back to top Resists

In situ study of hydrogen silsesquioxane dissolution rate in salty and electrochemical developers

Katherine J. Harry, Sebastian Strobel, Joel K. W. Yang, Huigao Duan, and Karl K. Berggren

J. Vac. Sci. Technol. B 29, 06FJ01 (2011); http://dx.doi.org/10.1116/1.3644339 (5 pages)

Online Publication Date: 29 September 2011

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In order to better characterize the development of the electron-beam resist hydrogen silsesquioxane (HSQ), the authors used a quartz crystal microbalance (QCM) to study its rate of dissolution in situ. The authors determined the effect of both salt concentration and applied electric potential on the development rate of HSQ. The development rates were measured by spinning HSQ directly onto a quartz crystal resonator, and then developing in a QCM microfluidic module. In order to more directly observe the effect of electric potentials on the HSQ development rate, a film of HSQ was partially cross-linked in an O2 plasma asher and then developed in the QCM flow module with a salt-free NaOH solution. As the partially cross-linked HSQ slowly developed, electric potentials were applied and removed from the crystal allowing the observation of how the development rate increased upon the application of a positive electric potential. The increased development rate caused by both the addition of salt ions and a positive electric potential suggests that the rate may be limited by a build-up of negative charge on the HSQ.
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81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
82.45.Qr Electrodeposition and electrodissolution
85.40.Hp Lithography, masks and pattern transfer
64.75.Bc Solubility
52.77.Bn Etching and cleaning

Improved time dependent performance of hydrogen silsesquioxane resist using a spin on top coat

Daron A. Westly, Donald M. Tennant, Yukinori Aida, Hirofumi Ohki, and Takashi Ohkubo

J. Vac. Sci. Technol. B 29, 06FJ02 (2011); http://dx.doi.org/10.1116/1.3660788 (7 pages)

Online Publication Date: 2 December 2011

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Hydrogen silsesquioxane (HSQ) is a high resolution negative tone electron beam (e-beam) resist with a resolution well below 10 nm. However, it is known that the time delay between spinning and e-beam exposure has an effect on the contrast and sensitivity. Significant effort has been placed on finding the best developer conditions (e.g., time, temperature, concentration, etc.) to maximize the performance of the resist. However, to date, little progress has been made to mitigate the problem of temporal dependence of optimal results. The authors report a significantly improved time dependent performance of HSQ by using a spin on top coat developed by Showa Denko. The material contains a conductive, water-soluble polymer (i.e., poly[isothianaphthene sulfonate]) and surfactants. Exposure delays from 0 to 12 h were performed in vacuum and the effect on sensitivity and ultimate resolution was compared to results without a top coat. Various bottom layers and top coats were also used and the change in performance was evaluated. In all cases a significant improvement is observed when a top coat is applied and little change occurs with other parameters. The time lag effect is shown to be the equivalent of a decrease in sensitivity over time with about 30% degradation from the optimal dose over the test period if no top coat is used. The use of the top coat reduces the effect to about 5% while also improving initial sensitivity. The authors believe this represents a widely applicable solution to the time lag issue common to HSQ processes.
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68.55.aj Insulators
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