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Nov 2008

Volume 26, Issue 6, pp. L45-2635

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Fabrication of thin-film silicon on insulator by separation by implanted oxygen layer transfer

Xing Wei, Ai Min Wu, Meng Chen, Jing Chen, Miao Zhang, Xi Wang, and Cheng Lu Lin

J. Vac. Sci. Technol. B 26, L45 (2008); http://dx.doi.org/10.1116/1.2990785 (3 pages) | Cited 3 times

Online Publication Date: 14 November 2008

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In this article, the authors propose an improved approach—separation by implanted oxygen (SIMOX) layer transfer process—to fabricate thin-film silicon on insulator (SOI). The top Si layer, a low-dose SIMOX wafer, was transferred upside down onto a thermally oxidized Si handle wafer by a bonding technique and etch-stop thinning process. Spectroscopic ellipsometry indicated a thin-film SOI with the device layer of 147.5±3.1 nm. An atomic-scale sharp interface between the device layer and buried oxide layer was observed by high-resolution transmission electron microscopy.
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68.55.ag Semiconductors
61.72.uf Ge and Si
68.37.Og High-resolution transmission electron microscopy (HRTEM)

Fabrication of Ag-tetracyanoquinodimethane nanostructures using ink-jet printing/vapor-solid chemical reaction process

Ravi Aggarwal, Roger J. Narayan, Kai Xiao, and David B. Geohegan

J. Vac. Sci. Technol. B 26, L48 (2008); http://dx.doi.org/10.1116/1.3021027 (5 pages)

Online Publication Date: 14 November 2008

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In this study, microscale patterns of the charge-transfer organic compound silver-tetracyanoquinodimethane (Ag-TCNQ) were prepared using a novel two-step ink-jet printing/vapor-solid chemical reaction process. First, silver nanoparticles were patterned on silicon using a piezoelectric ink-jet printer. Ag-TCNQ nanostructures were then processed on these patterned surfaces using a vapor-solid chemical reaction growth process. Scanning electron microscopy revealed that 50–100 nm wide, ∼ 2 μm long Ag-TCNQ nanocones, crystallites, and ribbons were fabricated using this two-step process. Patterns with a higher number density of silver nanoparticles demonstrated a greater number of nanocone structures. Micro-Raman spectroscopy results confirmed charge transfer between silver and TCNQ in the Ag-TCNQ nanostructure. Patterned Ag-TCNQ nanostructures fabricated using this novel two-step ink-jet printing/vapor-solid chemical reaction process could find use in high density, high-speed optical memory devices, magnetic devices, field effect transistors, organic light emitting diodes, metal/insulator/metal photoswitches, biosensors, and other advanced devices.
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81.16.Rf Micro- and nanoscale pattern formation
81.07.Bc Nanocrystalline materials
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
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The transition mechanisms of a ten-period InAs/GaAs quantum-dot infrared photodetector

Chi-Che Tseng, Shu-Ting Chou, Shin-Yen Lin, Cheng-Nan Chen, Wei-Hsun Lin, Yi-Hao Chen, Tung-Hsun Chung, and Meng-Chyi Wu

J. Vac. Sci. Technol. B 26, 1831 (2008); http://dx.doi.org/10.1116/1.2990784 (3 pages) | Cited 3 times

Online Publication Date: 3 November 2008

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This study explores the growth and effects of a ten-period InAs/GaAs quantum-dot infrared photodetector (QDIP). With a uniform quantum-dot (QD) size distribution and a QD density of 2.8×1010 cm−2, this 10 K photoluminescence spectrum shows a peak energy at 1.07 eV and a narrow full width at half maximum of 31.7 meV. The QDIP exhibits an asymmetric response under different voltage polarities and a high responsivity of 1.7 A/W at −1.1 V. Another noticeable observation in the spectral response of the device is the 6 μm peak detection wavelength with a high spectral broadening Δλ/λ of 0.67. By analyses of the photoluminescence excitation spectrum and the temperature dependence of spectral response, the wide spectral response of the QDIP is attributed to the summation of transitions between QD excited states and the wetting layer states, instead of transitions between QD ground state and higher excited states.
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78.67.Hc Quantum dots
73.63.Kv Quantum dots

Fabrication and testing of through-silicon vias used in three-dimensional integration

I. U. Abhulimen, A. Kamto, Y. Liu, S. L. Burkett, and L. Schaper

J. Vac. Sci. Technol. B 26, 1834 (2008); http://dx.doi.org/10.1116/1.2993174 (7 pages) | Cited 3 times

Online Publication Date: 3 November 2008

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The formation of through-silicon vias (TSVs) provides a vertical interconnect scheme that can be used in three-dimensional stacking technologies. A sloped via sidewall is essential for conformal coverage of via lining materials deposited in subsequent steps that provide insulation (SiO2), barrier (TaN), and metal seed (Cu) layers. In this article, via sidewall angles in the range of 83°–90° are investigated resulting in variable degrees of conformal lining of the insulation, barrier, and seed layers. Via insulation is deposited by plasma enhanced chemical vapor deposition, while barrier and seed layers are deposited by sputtering. A modified Bosch process, using a deep reactive ion etch tool, allows formation of differing via profiles in silicon substrates. Cross-sectional views of via profiles showing the coverage of lining materials (SiO2, TaN, and Cu) are examined with a scanning electron microscope. For a constant via sidewall angle, variable aspect ratios allow us to determine the specific via profile that can be conformally lined and filled by Cu electroplating without the presence of voids. The aspect ratios of the vias under study are in the range of 2–4. Electrical performance of the fabricated TSVs is reported and is consistent with expected performance.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Sz Deposition technology
81.65.Cf Surface cleaning, etching, patterning
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Pq Electrodeposition, electroplating
81.15.Cd Deposition by sputtering

GaN nanowire and Ga2O3 nanowire and nanoribbon growth from ion implanted iron catalyst

Jason L. Johnson, Yongho Choi, and Ant Ural

J. Vac. Sci. Technol. B 26, 1841 (2008); http://dx.doi.org/10.1116/1.2993175 (7 pages) | Cited 2 times

Online Publication Date: 3 November 2008

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The authors experimentally demonstrate a simple and efficient approach for nucleating the catalytic chemical vapor deposition (CVD) growth of GaN nanowires, Ga2O3 nanowires, and Ga2O3 nanoribbons by using ion implantation of Fe+ into thermally grown SiO2 layers and subsequent annealing to form the catalyst nanoparticles. This work shows that ion implantation can be used as a versatile method to create catalyst nanoparticles for wide band gap nanowire/nanoribbon growth. They also demonstrate that ion implanted catalyst nanoparticles prepared under identical conditions can be used to grow different types of nanowires/nanoribbons containing Ga by simply changing the gas types and flow rates during CVD growth. Furthermore, they systematically characterize the structural properties of the as-grown nanomaterials, and find that the distance between the Ga source and the substrate, growth temperature, growth time, and flow rates are all critical parameters for nanowire growth. They explain the growth of single-crystal wurtzite GaN and monoclinic β-Ga2O3 nanowires by the vapor-liquid-solid (VLS) growth model, whereas the growth of monoclinic β-Ga2O3 nanoribbons by a combination of the VLS and vapor-solid (VS) mechanisms. This work opens up the possibility of controlling the origin of wide band gap nanowires/nanoribbons at the nanometer scale using the technique of catalyst ion implantation through a lithographically defined mask, of integrating nanowires/nanoribbons into nonplanar three-dimensional device structures, and of growing different Ga-based wide band gap semiconductor nanostructures on the same substrate by simply changing the gas types and flow rates.
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81.07.Vb Quantum wires
81.07.Bc Nanocrystalline materials
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors

Gigahertz surface acoustic wave generation on ZnO thin films deposited by radio frequency magnetron sputtering on III-V semiconductor substrates

Qi Jie Wang, Christian Pflügl, William F. Andress, Donhee Ham, Federico Capasso, and Masamichi Yamanishi

J. Vac. Sci. Technol. B 26, 1848 (2008); http://dx.doi.org/10.1116/1.2993176 (4 pages) | Cited 3 times

Online Publication Date: 3 November 2008

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The authors demonstrate 1.6 GHz surface acoustic wave (SAW) generation using interdigital transducers patterned by e-beam lithography on a thin ZnO piezoelectric film deposited on an InP substrate. The highly oriented, dense, and fine-grain ZnO film with high resistivity was deposited by radio frequency magnetron sputtering and was characterized by x-ray diffraction, scanning electron microscopy, atomic force microscopy, and a four-point probe station. The acoustic wavelength of the 1.6 GHz SAW generated by exciting the interdigital transducer on ZnO/InP with a microwave signal is 1.6 μm. This SAW filter device could be monolithically integrated with optoelectronic devices, opening new opportunities to use SAWs for applications such as gigahertz-frequency filters on optoelectronic devices and novel widely tunable quantum cascade lasers.
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77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.35.Iv Acoustical properties
81.15.Cd Deposition by sputtering
85.40.Hp Lithography, masks and pattern transfer
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
73.61.Ga II-VI semiconductors

Large-area dielectric and metallic freestanding gratings for midinfrared optical filtering applications

Grégory Vincent, Stéphane Collin, Nathalie Bardou, Jean-Luc Pelouard, and Riad Haïdar

J. Vac. Sci. Technol. B 26, 1852 (2008); http://dx.doi.org/10.1116/1.2998728 (4 pages) | Cited 7 times

Online Publication Date: 3 November 2008

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The authors present a fabrication process of large-area (1.7×1.7 mm2) dielectric and metal-coated lamellar freestanding gratings structured at the micrometer scale. Both the stress management and the drying problems have been carefully optimized for the fabrication of drilled membranes. Transmission spectra measurements of freestanding gold-coated gratings demonstrate the achievement of high quality, accurately controlled optical filters in the midinfrared wavelength range.
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42.79.Dj Gratings
42.79.Ci Filters, zone plates, and polarizers

Optimization of antireflection structures of polymer based on nanoimprinting using anodic porous alumina

Takashi Yanagishita, Toshiaki Kondo, Kazuyuki Nishio, and Hideki Masuda

J. Vac. Sci. Technol. B 26, 1856 (2008); http://dx.doi.org/10.1116/1.2998731 (4 pages) | Cited 6 times

Online Publication Date: 3 November 2008

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The optimization of antireflection (AR) structures of polymer composed of an ordered array of tapered pillars was studied. An anodic porous alumina mold with precisely controlled tapered holes was prepared and used for photoimprinting of the polymer. The reflectance of the obtained AR polymer structures with conical pillars was evaluated through the measurement of transmittance. Among the AR structures with pillars with various slopes, those with a gradually changing slope exhibited the lowest reflectance. The fabrication process will be effective for the formation of an AR surface with minimized reflectance over a large sample area.
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42.70.Jk Polymers and organics
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Wc Optical coatings

A new approach to fabricating high density nanoarrays by nanocontact printing

Jian Gu, Xiaoyin Xiao, Bharath R. Takulapalli, Michael E. Morrison, Peiming Zhang, and Frederic Zenhausern

J. Vac. Sci. Technol. B 26, 1860 (2008); http://dx.doi.org/10.1116/1.2998754 (6 pages) | Cited 4 times

Online Publication Date: 3 November 2008

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The authors introduce a new scheme of nanocontact printing that fabricates nanoarrays using stamps generated by ultraviolet nanoimprint lithography. Array patterns can be generated by this printing technique in a high density (number of features per unit area) fashion with a feature size as low as 30 nm and period of 100 nm. Sub-500 nm alignment accuracy for multilayer printing has been obtained using a traditional contact mask aligner. They also demonstrate that they can image a nanoarray labeled by streptavidin by atomic force microscope.
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81.16.Nd Micro- and nanolithography
87.85.Rs Nanotechnologies-applications
87.14.gk DNA
85.40.Hp Lithography, masks and pattern transfer
81.16.Ta Atom manipulation
87.15.B- Structure of biomolecules

Neutral particle proximity lithography: Noncontact nanoscale printing without charge-related artifacts

Barry Craver, Hatem Nounu, James Wasson, and John C. Wolfe

J. Vac. Sci. Technol. B 26, 1866 (2008); http://dx.doi.org/10.1116/1.2998765 (5 pages) | Cited 1 time

Online Publication Date: 3 November 2008

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The authors present neutral particle proximity lithography, a high resolution, parallel exposure technique where a broad beam of energetic neutral particles floods a stencil mask and transmitted beamlets transfer the mask pattern to resist on a substrate. It preserves the advantages of nanoscale penumbra, diffraction, and resist scattering of ion beam lithography (IBL) yet is intrinsically immune to charge accumulation on the mask and substrate. In a series of direct comparisons, involving insulating substrates, large proximity gaps, and ultrasmall features, the authors show that the use of neutral particles provides a simple method for completely eliminating the charging artifacts of IBL. They demonstrate the ability to print 8 nm mask features with 5 nm pattern fidelity. Exposure times are about 200 s in poly(methyl methacrylate) resist.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Epitaxial cubic HfN diffusion barriers deposited on Si (001) by using a TiN buffer layer

Roy A. Araujo, Xinghang Zhang, and Haiyan Wang

J. Vac. Sci. Technol. B 26, 1871 (2008); http://dx.doi.org/10.1116/1.3002391 (4 pages) | Cited 1 time

Online Publication Date: 3 November 2008

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Cubic HfN (B1-NaCl) thin films were grown epitaxially on Si(001) substrates by using a TiN (B1-NaCl) buffer layer as thin as ∼ 10 nm. The HfN/TiN stacks were deposited by pulsed laser deposition with an overall thickness below 60 nm. Detailed microstructural characterizations include x-ray diffraction, transmission electron microscopy (TEM), and high resolution TEM. The electrical resistivity measured by four-point probe is as low as 70 μΩ cm at room temperature. Preliminary Cu diffusion tests show a good diffusion barrier property with a diffusion depth (2math) of 2–3 nm after annealing at 500 °C for 30 min in vacuum.
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68.55.aj Insulators
81.15.Fg Pulsed laser ablation deposition
66.30.-h Diffusion in solids
61.72.-y Defects and impurities in crystals; microstructure
73.61.Ng Insulators
81.40.Gh Other heat and thermomechanical treatments

Tungsten metal gate etching in Cl2/O2 inductively coupled high density plasmas

T. Morel, S. Bamola, R. Ramos, A. Beaurain, E. Pargon, and O. Joubert

J. Vac. Sci. Technol. B 26, 1875 (2008); http://dx.doi.org/10.1116/1.3002392 (8 pages) | Cited 4 times

Online Publication Date: 3 November 2008

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Plasma etching of W in a poly-Si/TiN/W/HfO2 gate stack is investigated in Cl2/O2 based plasmas. Preliminary studies have illustrated the issues induced with the introduction of a metal layer in the gate stack. Based on scanning electron microscopy observations, the authors first show that a mixture of Cl2, O2, and NF3 is required to successfully pattern the W layer without damaging the HfO2, poly-Si, and TiN profiles. For a better understanding of etch mechanisms, W etching is studied on blanket wafers and etch rates are presented and discussed with respect to the plasma parameters. The evolution of the etch rates as a function of O2 ratio in Cl2/O2 and Cl2/O2/NF3 plasmas is interpreted. X-ray photoelectron spectroscopy analyses demonstrate that the introduction of O2 in Cl2 leads to the creation of a thick WOClx deposit on the gate sidewalls. However, the WOCl deposition can be controlled and eliminated by adding fluorine in the plasma during W etching.
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81.05.Bx Metals, semimetals, and alloys
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
79.60.Bm Clean metal, semiconductor, and insulator surfaces

High and low temperature behavior of Ohmic contacts to AlGaN/GaN heterostructures with a thin GaN cap

M. A. Miller and S. E. Mohney

J. Vac. Sci. Technol. B 26, 1883 (2008); http://dx.doi.org/10.1116/1.3006018 (4 pages) | Cited 2 times

Online Publication Date: 3 November 2008

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V/Al/V/Ag contacts that provide low specific contact resistances as well as smooth surfaces and contact edges on AlGaN/GaN heterostructures were recently introduced. In the present study, the contacts are examined in greater detail, including an evaluation of their high temperature stability and their specific contact resistance as a function of measurement temperature. The contacts provide a low specific contact resistance of 5.2×10−7 Ω cm2 and contact resistance of 0.15 Ω mm after aging for 10 h at 500 °C in flowing N2. Furthermore, cross-sectional transmission electron microscopy (TEM) of the aged V/Al/V/Ag contacts shows little change in phase formation compared to the annealed contacts that were not aged. Beneath the annealed V/Al/V/Ag metallization, the AlGaN layer is left intact. On the other hand, cross-sectional TEM images of previously reported V/Al/V/Au and Ti/Al/Ti/Au contacts reveal that both of the Au-bearing metallizations react through a portion of the AlGaN layer and directly contact the underlying GaN. By comparing these TEM images with the observed temperature dependence of the specific contact resistance of all of the contacts measured from 77 to 573 K, conclusions regarding current transport mechanisms were drawn.
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73.40.Cg Contact resistance, contact potential
61.72.Cc Kinetics of defect formation and annealing
81.05.Ea III-V semiconductors
85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Characterization of a sol-gel based high-k dielectric field effect transistor for cryogenic operation

M. Ziaur Rahman Khan, D. G. Hasko, M. S. M. Saifullah, and M. E. Welland

J. Vac. Sci. Technol. B 26, 1887 (2008); http://dx.doi.org/10.1116/1.3006019 (5 pages) | Cited 4 times

Online Publication Date: 3 November 2008

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A silicon on insulator field effect transistor for cryogenic operation has been fabricated using a sol-gel derived TiO2 electron beam resist as a high-k gate dielectric and characterized over a range of temperatures. The TiO2 dielectric layer allows too large a gate leakage current for good device operation at room temperature, but the leakage current is strongly suppressed at cryogenic temperatures and good transistor characteristics were observed. The temperature dependence of the gate leakage current suggests that Frenkel-Poole and trap-assisted tunneling dominates the conduction in the dielectric layer. The drain current shows peaks at certain frequencies under continuous wave microwave irradiation, which may be caused by the resonance of electrons trapped in defects at the TiO2/SiO2 interface. These resonances offer the possibility to manipulate single electrons for nonclassical information processing.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.55.-g Dielectric thin films
85.30.Tv Field effect devices
73.50.Fq High-field and nonlinear effects

Improved field emission properties from polycrystalline indium oxide-coated single-walled carbon nanotubes

Jungwoo Lee, Wonjoo Lee, Kijo Sim, Sung-Hwan Han, and Whikun Yi

J. Vac. Sci. Technol. B 26, 1892 (2008); http://dx.doi.org/10.1116/1.3006020 (4 pages) | Cited 3 times

Online Publication Date: 3 November 2008

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The field emission (FE) characteristics of indium oxide (In2O3)-coated single-walled carbon nanotubes (SWCNTs) were studied. Scanning electron microscopy, x-ray diffractometer, and UV/visible spectroscopy confirmed that In2O3 exists as a polycrystalline cubic bixbyite structure on the surface of SWCNTs. The turn-on field of pristine SWCNTs decreased from 3.82 to 3.27 V/μm for In2O3-coated SWCNTs with optimal coating thickness. The maximum emission current density reached 3.5 mA/cm2, five times higher than that of pristine SWCNTs (0.68 mA/cm2) at an electric field of 7 V/μm. To explain the higher FE current density of In2O3-coated SWCNTs, Fowler–Nordheim plots were used with some assumptions.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.Fg Nanotubes
78.40.Ri Fullerenes and related materials
78.67.Ch Nanotubes

HBr-based inductively coupled plasma etching of high aspect ratio nanoscale trenches in GaInAsP/InP

Wei Zhou, N. Sultana, and D. L. MacFarlane

J. Vac. Sci. Technol. B 26, 1896 (2008); http://dx.doi.org/10.1116/1.3010711 (7 pages) | Cited 5 times

Online Publication Date: 3 November 2008

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The authors report inductively coupled plasma (ICP) dry etching of nanoscale trenches with feature sizes of approximately 140 nm wide by 20 μm long by 3 μm deep in InP with and without quantum wells, based on HBr chemistry. Both focused ion beam and electron beam lithography nanopatterned features are presented with high aspect ratios in excess of 30:1. Importantly, with HBr, hybrid GaInAsP/InP heterostructures can be anisotropically and vertically etched through with reasonable smoothness at 165 °C, which is comparatively lower than what chlorine-based chemistry requires and is therefore beneficial for achieving reliable InP devices. The phenomenon of aspect ratio dependent etching, or reactive ion etch lag, begins to manifest itself when the etch aspect ratio of InP approaches 30:1 using this ICP technique. The application of interest is a novel coupler for integrated photonics.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
81.16.Nd Micro- and nanolithography
68.65.Fg Quantum wells
81.16.Rf Micro- and nanoscale pattern formation

Spatial scaling metrics of mask-induced line-edge roughness

Patrick P. Naulleau and Gregg Gallatin

J. Vac. Sci. Technol. B 26, 1903 (2008); http://dx.doi.org/10.1116/1.3010712 (8 pages) | Cited 16 times

Online Publication Date: 3 November 2008

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Mask contributors to line-edge roughness (LER) have recently been shown to be an issue of concern for both the accuracy of current resist evaluation tests as well the ultimate LER requirements for the 22 nm production node. Problems arise from mask absorber LER as well as mask multilayer roughness leading to random phase variations in the reflected beam. Not only do these mask contributors effect the total measured LER in resist but they also have an impact on LER spatial scaling characteristics such as power spectral density and the related descriptors of correlation length and roughness exponent. Understanding how these metrics respond to mask effects may lead to an experimental mechanism for evaluating the importance of mask contributors to observed LER in resist. Here the authors present a detailed study of mask-induced LER spatial characteristics. The authors further describe the influence of illumination conditions and defocus on the metrics and compare the results to those expected from intrinsic resist LER. The results show power spectral density analysis to be a promising technique for distinguishing mask and resist contributors to LER.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Feature profile evolution during shallow trench isolation etch in chlorine-based plasmas. I. Feature scale modeling

John Hoang, Cheng-Che Hsu, and Jane P. Chang

J. Vac. Sci. Technol. B 26, 1911 (2008); http://dx.doi.org/10.1116/1.2998756 (8 pages) | Cited 4 times

Online Publication Date: 10 November 2008

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The authors developed a cellular based Monte Carlo (MC) feature scale model capable of direct coupling to the dominant plasma species ratios from a reactor scale model in order to simulate the profile evolution of shallow trench isolation etch in chlorine-based plasmas and its variation from the center to the edge of the wafer. Carefully planned experiments along with scanning electron microscopy (SEM) were used to calibrate the MC model, where one to two plasma parameters were systematically varied. Simulated feature profiles were found to agree well with experimental observations, capturing details such as microtrenching, faceting, tapering, and bowing. The particle counts used to achieve these fits agreed well with those estimated from SEM, corroborating the chemistry and physics used in the feature scale model. In addition, the feature scale model uses a novel surface representation that eliminates the artificial flux fluctuations originating from the discrete cells used in the simulation and enables a much more precise calculation of the surface normal, which dictates the trajectory of reflected species.
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52.65.Pp Monte Carlo methods
05.10.Ln Monte Carlo methods

Feature profile evolution during shallow trench isolation etch in chlorine-based plasmas. II. Coupling reactor and feature scale models

Cheng-Che Hsu, John Hoang, Vu Le, and Jane P. Chang

J. Vac. Sci. Technol. B 26, 1919 (2008); http://dx.doi.org/10.1116/1.2998759 (7 pages) | Cited 3 times

Online Publication Date: 10 November 2008

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A two-dimensional numerical fluid model was developed to investigate the effects of reactor design on the radial profiles of plasma species, namely, etch products and positive ions, during shallow trench isolation etching in Cl2/O2/Ar inductively coupled plasmas. Specifically, the dual-coil and dual gas-feed designs of the reactor were examined. The former parameter was determined to be effective in tailoring the radial ion flux profile at pressures higher than 20 mT, while the latter parameter was shown to alter the etch product transport in the convection-dominant flow regime. Coupling of the reactor scale model to a feature scale model allowed investigation of minor center to edge variations in the etched feature profile. This hybrid model suggests that the general radial decrease in the etch depth seen from a set of design of experiments is caused by an inherent decrease in the spatial distribution of chlorine radicals. In addition, the increase in the silicon sidewall angle from center to edge can be qualitatively explained by the radial profile of the etch products.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning

Damage mechanism in low-dielectric (low-k) films during plasma processes

Butsurin Jinnai, Toshihisa Nozawa, and Seiji Samukawa

J. Vac. Sci. Technol. B 26, 1926 (2008); http://dx.doi.org/10.1116/1.3010721 (7 pages) | Cited 15 times

Online Publication Date: 10 November 2008

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Plasma is extensively used for the etching/ashing of low-dielectric (low-k) films. However, since low-k films, such as SiOC films, are vulnerable to plasma irradiation, they are severely damaged during plasma processes, such as the extraction of methyl groups from low-k films. As a result, plasma irradiation increases the dielectric constant of low-k films and reduces the reliability of Cu/low-k interconnects. In previous work, the authors achieved highly selective and low-damage etching processes for low-k films by using their developed neutral beam process instead of the conventional plasma process. They have now investigated the damage mechanism in low-k films (porous SiOC films) during plasma processes by clarifying the effects of ions, radicals, and photons in plasma. First, they compared the damage in SiOC films etched by the conventional plasma process and the neutral beam process. Their results show that plasma processes change the structure of the SiOC film deeply within the film (over 100 nm in depth) and increase the film’s dielectric constant, whereas the neutral beam process maintains the structure of the SiOC film. Additionally, they found that when a combination of the neutral beam process and a 172 nm excimer lamp is used, photon irradiation enhances the extraction of methyl groups from the SiOC film by breaking Si–C bonds in the film. These results show that photon irradiation plays a very important role in the damage mechanism in low-k films during plasma processes.
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77.55.-g Dielectric thin films
52.77.Bn Etching and cleaning
77.22.Ch Permittivity (dielectric function)
85.40.Ls Metallization, contacts, interconnects; device isolation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Photoconductivity of vertically aligned ZnO nanoneedle array

Dongseok Park and Kijung Yong

J. Vac. Sci. Technol. B 26, 1933 (2008); http://dx.doi.org/10.1116/1.2998730 (4 pages) | Cited 8 times

Online Publication Date: 14 November 2008

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A high-density vertically well-aligned ZnO nanoneedle array was fabricated on a ZnO-buffer film on silicon substrates by metal-organic chemical vapor deposition at a growth temperature of 480–500 °C. Highly crystalline ZnO nanoneedle arrays showed a strong near-bandedge emission at 380 nm in room-temperature photoluminescence. A simple ultraviolet (UV) sensor was fabricated by evaporating a Ag electrode on the ZnO nanoneedle array. The photoresponse results showed very high photocurrent ( ∼ 10−4 A) from ZnO nanoneedles compared to a single-nanowire sensor ( ∼ 10−8 A), indicating high sensitivity of the photosensor. It also showed fast rise and decay times in UV-on/off switching measurements.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Improved crystalline quality nonpolar a-GaN films grown by hydride vapor phase epitaxy

A. A. Donskov, L. I. D’yakonov, A. V. Govorkov, Y. P. Kozlova, S. S. Malakhov, A. V. Markov, M. V. Mezhennyi, V. F. Pavlov, A. Y. Polyakov, N. B. Smirnov, T. G. Yugova, and S. J. Pearton

J. Vac. Sci. Technol. B 26, 1937 (2008); http://dx.doi.org/10.1116/1.3021367 (5 pages) | Cited 2 times

Online Publication Date: 14 November 2008

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Nonpolar a-GaN films were grown by hydride vapor phase epitaxy on r-sapphire. As the thickness of the grown films was increased from 50 to over 250 μm, the width of the double-crystal rocking curve for the (11–20) reflection decreased from 2000 to 500 arc sec, indicating a strong decrease in the dislocation density. Microcathodoluminescence mapping of the thick films suggests that the dislocation density is ∼ 102 cm−2, which is more than two orders of magnitude lower than for thin films. The authors also observe a corresponding decrease in the density of residual donors from 1020 to 1018 cm−3, with respective mobility increase from (10–20) to 150 cm2/V s. The luminescence spectra of the thin films show the presence of intense defect bands attributed in literature to stacking faults. These bands are very strongly suppressed in thick films, which also show about an order of magnitude higher band edge luminescence intensity.
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68.55.ag Semiconductors
81.05.Ea III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.66.Fd III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Solid-phase growth mechanism of tungsten oxide nanowires synthesized on sputtered tungsten film

Y. Kojima, K. Kasuya, K. Nagato, T. Hamaguchi, and M. Nakao

J. Vac. Sci. Technol. B 26, 1942 (2008); http://dx.doi.org/10.1116/1.2990783 (6 pages) | Cited 5 times

Online Publication Date: 18 November 2008

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The authors have proposed a solid-phase growth mechanism of tungsten oxide nanowires synthesized on sputtered tungsten films. Transmission electron microscopy observation, x-ray diffraction analyses, and some ex situ experiments were performed to verify the growth model. The nanowire nuclei are generated at irregular points on the W surface. An amorphous oxidized layer is formed on the W surface by annealing, and tungsten oxide molecules migrate on the W surface into the nuclei, thus contributing to the nanowire growth.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.43.Er Other amorphous solids
81.40.Gh Other heat and thermomechanical treatments

The coexistence of surface reconstruction domains on strained heteroepitaxial films

Lee E. Sears, Joanna Mirecki Millunchick, and Chris Pearson

J. Vac. Sci. Technol. B 26, 1948 (2008); http://dx.doi.org/10.1116/1.2993173 (4 pages)

Online Publication Date: 18 November 2008

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Thin films of In0.81Ga0.19As/InP, grown by molecular beam epitaxy and imaged by in vacuo scanning tunneling microscopy, are observed to possess surfaces that consist of multiple reconstruction domains; small anisotropic regions of β2(2×4) in a matrix of a disordered (n×3) reconstruction. The shape and size distribution of these domains is consistent with anisotropic elastic relaxation at the domain boundaries. The boundary energy anisotropy varies with the growth temperature, indicating that the configurational entropy along the [1math0] direction is higher than for the [110].
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
65.40.gd Entropy

Ge1−ySny photoconductor structures at 1.55 μm: From advanced materials to prototype devices

R. Roucka, J. Xie, J. Kouvetakis, J. Mathews, V. D’Costa, J. Menéndez, J. Tolle, and S.-Q. Yu

J. Vac. Sci. Technol. B 26, 1952 (2008); http://dx.doi.org/10.1116/1.3021024 (8 pages) | Cited 5 times

Online Publication Date: 18 November 2008

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Prototype detector structures were fabricated on Si substrates using Ge1−ySny as active material for the first time. This alloy system covers the entire near-IR telecommunication spectrum and grows at a low temperature of 350 °C, compatible with complementary metal-oxide-semiconductor (CMOS) Si technology. Processing protocols were developed for photolithography-based patterning and subsequent etching, CMOS compatible metallization, and for the formation of low-resistivity Ohmic contacts. A first generation of devices based on as-grown Ge1−ySny layers was followed by a second generation incorporating ex situ rapid thermal annealing for defect reduction, as well as additional growth and processing improvements, leading to enhanced mobilities and simultaneous reduction in intrinsic carrier concentrations. While both device generations show a significant photoconductive response at 1.55 μm, the thicker second-generation samples yield improved performance due to better confinement of deleterious defects near the interface, which increases the optically active fraction of the film.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation
73.50.Dn Low-field transport and mobility; piezoresistance

Growth of Si nanowires on micropillars for the study of their dopant distribution by atom probe tomography

T. Xu, J. P. Nys, B. Grandidier, D. Stiévenard, Y. Coffinier, R. Boukherroub, R. Larde, E. Cadel, and P. Pareige

J. Vac. Sci. Technol. B 26, 1960 (2008); http://dx.doi.org/10.1116/1.3021371 (4 pages) | Cited 9 times

Online Publication Date: 18 November 2008

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This article reports on the growth of Au islands on the Si(111) surface as a function of the Au evaporation rate and the temperature of the surface in ultrahigh vacuum. By controlling the density of the Au islands and their size, it is possible to subsequently grow single vertically oriented Si nanowires on top of (111)-oriented silicon micropillar and analyze their chemical composition at the atomic scale with the femtosecond laser assisted tomographic atom probe. Three-dimensional images of the atom distribution in the nanowire, in particular, the distribution of boron impurities, are obtained and compared to the intended impurity concentration.
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68.65.La Quantum wires (patterned in quantum wells)
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.35.B- Structure of clean surfaces (and surface reconstruction)
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)
78.47.-p Spectroscopy of solid state dynamics
61.72.uf Ge and Si

Modifications of dielectric films induced by plasma ashing processes: Hybrid versus porous SiOCH materials

M. Darnon, T. Chevolleau, T. David, N. Posseme, J. Ducote, C. Licitra, L. Vallier, O. Joubert, and J. Torres

J. Vac. Sci. Technol. B 26, 1964 (2008); http://dx.doi.org/10.1116/1.3006021 (7 pages) | Cited 9 times

Online Publication Date: 20 November 2008

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This work focuses on the impact of oxidizing (O2) and reducing plasma ashing chemistries (NH3, CH4) on the modifications of dielectric materials in a porous or an hybrid state (SiOCH matrix+porogen). The plasma ashing processes have been performed on blanket wafers using O2, NH3, and CH4 based plasmas. The modifications of the remaining film after plasma exposures have been investigated using different analysis techniques such as x-ray photoelectron spectroscopy, infrared spectroscopy, x-ray reflectometry, and porosimetric ellipsometry. For the porous material the authors have shown that NH3 and O2 plasmas induce carbon depletion and moisture uptake while the CH4 plasma only leads to important carbon depletion without moisture uptake and to the formation of a thin carbon layer on the surface. For the hybrid material, no significant material modification is evidenced with the O2 plasma while an important methyl depletion and porogen degradation are observed with reducing chemistries such as CH4 and NH3 plasmas. The impact of the porogen on the film modification and the value of the dielectric constant will be presented and discussed.
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77.55.-g Dielectric thin films
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
77.22.Ch Permittivity (dielectric function)
61.43.Gt Powders, porous materials
78.66.Qn Polymers; organic compounds
79.60.Fr Polymers; organic compounds

Formation and stability of NiSi in the presence of Co and Fe alloying elements

D. Deduytsche, C. Detavernier, R. L. Van Meirhaeghe, J. L. Jordan-Sweet, and C. Lavoie

J. Vac. Sci. Technol. B 26, 1971 (2008); http://dx.doi.org/10.1116/1.3010719 (7 pages)

Online Publication Date: 20 November 2008

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The formation and degradation of NiSi in the presence of Co and Fe alloying elements have been investigated. Alloyed Ni layers were characterized with in situ techniques to determine the stability of the NiSi phase on single crystalline and on polycrystalline Si substrates. It is shown that the phase stability is decreased with the addition of Co or Fe. The formation of the NiSi2 phase on Si(100) is initiated at a temperature that is more than 200 °C lower for the Ni alloys than for a reference Ni layer. Thereby a few percent of Co or Fe results in the formation of a polycrystalline NiSi2 phase on a single crystalline substrate. The low formation temperature of the NiSi2 phase in the presence of Co or Fe can be attributed to a mixing entropy effect. The morphological stability of the silicide films on Si(100) and on polycrystalline Si is improved due to the early formation of NiSi2 and is related to an increased film thickness and also to a higher deformation temperature for the poly-Si.
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68.55.at Other materials
65.40.gd Entropy
81.05.Bx Metals, semimetals, and alloys
68.55.jd Thickness

Study of 193 nm photoresist degradation during short time fluorocarbon plasma exposure III. Effect of fluorocarbon film and initial surface condition on photoresist degradation

M. Sumiya, R. Bruce, S. Engelmann, F. Weilnboeck, and G. S. Oehrlein

J. Vac. Sci. Technol. B 26, 1978 (2008); http://dx.doi.org/10.1116/1.3021037 (9 pages) | Cited 2 times

Online Publication Date: 20 November 2008

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The effect of fluorocarbon film and surface pretreatments on roughness formation of 193 nm photoresist (PR) during short time fluorocarbon plasma exposure was investigated. The present work complements two earlier reports by this group on surface modifications of 193 nm PR during plasma etching. The authors employed a shutter approach to minimize initial plasma transient effects on processing of PR surfaces. Surface chemical conditions after plasma etching were observed by x-ray photoelectron spectroscopy. The authors investigated the effect of deposited fluorocarbon film and pretreatments using several gas chemistries on PR roughening. Pretreated samples exhibited smaller roughness after plasma etching as compared to specimens processed without pretreatment. Three main mechanisms were identified for surface roughness reduction after pretreatment: (a) the formation of a fluorinated surface layer—having a large amount of fluorine on the PR surface at the beginning of the etch reduces PR surface roughening, (b) the improvement of durability of the PR under plasma exposure by removal of the ester group, and (c) a rapid fluorination and a reduction in the PR etch rate during the initial etch period due to the formation of a protective film on the top of the PR. The authors conclude from this work that the initial surface chemical state is an important factor that determines the degree of surface roughness formation for 193 nm PR during the initial etch period.
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85.40.Hp Lithography, masks and pattern transfer
52.77.Bn Etching and cleaning

Interface states mediated reverse leakage through metal/AlxGa1−xN/GaN Schottky diodes

Changzhi Lu, Xiaoling Zhang, Xuesong Xie, Shiwei Feng, Ibrahima Diagne, Arif Khan, and S. Noor Mohammad

J. Vac. Sci. Technol. B 26, 1987 (2008); http://dx.doi.org/10.1116/1.3002393 (6 pages) | Cited 6 times

Online Publication Date: 24 November 2008

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Interface states modulated reverse leakage current through metal/AlxGa1−xN/GaN diodes has been studied. Reverse leakage current and breakdown voltage have been measured over wide temperature ranges. The investigation suggests that the piezoelectric polarization and the spontaneous polarization at the AlxGa1−xN/GaN heterostructure create polarization induced charges in AlxGa1−xN, and influence the two-dimensional electron gas at the GaN/AlxGa1−xN interface. Both of them dictate the barrier height of the strained AlxGa1−xN Schottky contact. High density of defect states at the metal/AlxGa1−xN interface leads to high reverse leakage current via Fowler-Nordheim emission and/or Frankel-Poole emission. The most notable finding is the reduction in the leakage current almost to zero at high temperatures due to strain relaxation, reduction in defect states, and barrier height enhancement at the metal/AlxGa1−xN interface. Such finding may have significant impact on the way we design high-power microwave devices.
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85.30.Kk Junction diodes
77.22.Ej Polarization and depolarization
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.30.+y Surface double layers, Schottky barriers, and work functions

Investigation of the oxide-assisted growth mechanism for nanowire growth and a model for this mechanism

S. Noor Mohammad

J. Vac. Sci. Technol. B 26, 1993 (2008); http://dx.doi.org/10.1116/1.3002486 (15 pages) | Cited 3 times

Online Publication Date: 24 November 2008

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Oxide-assisted growth (OAG) mechanism produces high-density nonowires (NWs). Salient features of the existing models for this OAG mechanism and the fundamentals underlying this mechanism have been investigated in some detail. A simple, novel, malleable model for the OAG mechanism has been developed, and the concept of droplet used to develop this model has been articulated. The concept takes into consideration the size-dependent melting temperature depression. Two important elements of the model are (1) the attraction between the vapor-phase NW species and the droplet species, which leads to landing of the NW species on the droplet surface, and (2) the diffusion of the NW species through the droplet species to the liquid/solid interface, which leads to supersaturation and nucleation. The present investigation, together with our model, indicates that the assistance of a suitable oxide, the formation of nanoclusters/seeds, and the creation of droplets are all central to the OAG mechanism, which is essentially self-catalytic in nature. Various chemical reactions taking place on the droplet surface and the temperature range for these reactions are also important. The formation of a core and sheath during nucleation are the inevitable results of the use of oxide. The role of the droplet surface tension and the electrostatic forces between the droplet and the reactive (source) NW vapor species are crucial for OAG. Possible participation of a foreign element catalytic agent (FECA) in the NW growth by OAG mechanism has been examined. Based on these investigations, the present model appears to explain many of the OAG-grown NW characteristics. The experimentally observed oxide sheath has been addressed. Also, the basic causes of higher growth rates of the NWs grown by the OAG and FECA-mediated OAG mechanisms have been explained.
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81.16.-c Methods of micro- and nanofabrication and processing
81.05.-t Specific materials: fabrication, treatment, testing, and analysis

Bias power dependence of reactive ion etching lag in contact hole etching using inductively coupled fluorocarbon plasma

Shin-ichi Imai

J. Vac. Sci. Technol. B 26, 2008 (2008); http://dx.doi.org/10.1116/1.3021031 (5 pages) | Cited 4 times

Online Publication Date: 24 November 2008

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This article describes the bias power dependence of reactive ion etching (RIE) lag from 1300 to 700 W bias power in contact hole etching using inductively coupled C2F6 fluorocarbon plasma without additive gases at 2600 W source power, 5 mTorr operational pressure, and a total gas flow of 40 SCCM (SCCM denotes cubic centimeter per minute at STP). RIE lag is estimated by etching multiple feature sizes on one wafer. In the discussion of the bias power dependence of RIE lag, the authors used an RIE lag model based on a solid angle model modified by a specular reflection on the wall of a contact hole. The RIE lag model indicates that the RIE lag characteristic is caused by the three-dimensional structure of the contact hole. The etched depth relates to a term of a cubic root of etch time. Moreover, a decrease in bias power slows the etch rates, but the maximum etched depth increases in contact hole etching. By decreasing the bias power from 1300 to 700 W, the RIE lag characteristic can be dramatically improved in a limitation aspect ratio from 27 to 133.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
85.40.Ls Metallization, contacts, interconnects; device isolation
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Erratum: “Spherical field emission cathode based on carbon nanotube paste and its application in luminescent bulbs” [ J. Vac. Sci. Technol. B 26, 1404 (2008) ]

Weiqi Fu, Peng Liu, Jie Tang, Liang Liu, and Shoushan Fan

J. Vac. Sci. Technol. B 26, 2013 (2008); http://dx.doi.org/10.1116/1.3006022 (1 page)

Online Publication Date: 24 November 2008

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Abstract Unavailable
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99.10.Cd Errata
78.67.Ch Nanotubes
79.70.+q Field emission, ionization, evaporation, and desorption
82.45.Fk Electrodes
85.45.-w Vacuum microelectronics
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back to top Line Edge Roughness/Resists

Preface

Cynthia Hanson

J. Vac. Sci. Technol. B 26, 2024 (2008); http://dx.doi.org/10.1116/1.3043663 (1 page)

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Abstract Unavailable
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81.16.-c Methods of micro- and nanofabrication and processing
01.10.Fv Conferences, lectures, and institutes
back to top E-Beam Maskless Lithography

Electron beams in individual column cells of multicolumn cell system

Akio Yamada, Hiroshi Yasuda, and Masaki Yamabe

J. Vac. Sci. Technol. B 26, 2025 (2008); http://dx.doi.org/10.1116/1.2976603 (7 pages) | Cited 7 times

Online Publication Date: 1 December 2008

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In the Mask D2I project at ASET, the authors designed a novel electron beam exposure system having the concepts of multicolumn cell (MCC), character projection, and variable shaped beam to improve the throughput of electron beam exposure systems. They presented the electron optical structure of an individual column cell in the MCC and have shown shaped beam performances in the column cell. They evaluated the impacts on beam position in one column cell caused by deflections of major and minor deflectors in other column cell, which were less than 2.5 nm for both averaged and transitional impacts between +full and −full deflections. They will improve the evaluation accuracy to analyze the origin of the impacts and decrease the impacts from other column cell.
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41.75.Fr Electron and positron beams

Process variation-aware three-dimensional proximity effect correction for electron beam direct writing at 45 nm node and beyond

Kozo Ogino, Hiromi Hoshino, and Yasuhide Machida

J. Vac. Sci. Technol. B 26, 2032 (2008); http://dx.doi.org/10.1116/1.3013861 (7 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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The simplified electron energy flux (SEEF)model by which the backscattered energy distribution in the multilayered structure is calculated has been applied to the analysis of critical dimension (CD) variations caused by the thickness variations in copper interconnect. The SEEF model defines the reflection, downward transmission, and upward transmission of electron energy fluxes in each layer. Parameters of the SEEF model are expressed as functions of the depth from the substrate surface and are modified by the approximation in regard to the thickness variation. Using this approach, the process window for the dose and thickness variation has been analyzed quantitatively and the necessity of improving the process window has been confirmed especially at 45 nm node and beyond. Moreover, a variation-aware proximity effect correction method, in which CD variations caused by process variations are reduced and dose margins for various patterns with the same linewidth are equalized, is proposed. The correction method improves the process window for isolated line pattern and 1:1 line-and-space pattern when the sixth wiring layer is fabricated.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation

Charging and error budgets in electron beam lithography tools

John G. Hartley and Adam Lyons

J. Vac. Sci. Technol. B 26, 2039 (2008); http://dx.doi.org/10.1116/1.3021373 (4 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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Given a set of end user requirements that establish the overall performance goals of a system, the error budget allows a system architect to seek an optimum balance between various subsystems to achieve the most efficient design. When factors that contribute to the overall error budget are poorly understood the result is likely a suboptimal design that relies on the designer’s knowledge of the “art” as opposed to the desired but absent scientific understanding. This typically leads to overengineering of other subsystems to compensate. One factor not strongly quantified is drift due to charging. In this article, the authors explicitly examine contributions due to particle contamination, voids in conductive coatings that expose insulating material, and contamination induced insulating films on conductors in the electron optic subsystem.
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85.40.Hp Lithography, masks and pattern transfer
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

An innovative design of wafer height and tilt sensor for lithography systems

Junru Ruan and John Hartley

J. Vac. Sci. Technol. B 26, 2043 (2008); http://dx.doi.org/10.1116/1.3013318 (6 pages)

Online Publication Date: 1 December 2008

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Since lithography systems have limited depth of focus, precise and real-time measurement of wafer height is important for the image quality control. The traditional grazing incidence height sensor for lithography system consists of two basic components: a light source to illuminate the wafer surface and a detection surface to receive the reflected light beam from the wafer. Mathematical study of this type of height sensor shows that they will fail to differentiate the height difference of the wafer from the tilt of the wafer. In order to obtain the tilt information, height sensors with more complicated designs are used, and examples of these designs are briefly reviewed. A new design for a wafer height sensor is proposed here. By adding an independent detection surface, the new design is able to obtain wafer height and tilt information without using a complicated optical design, which results in easy alignment and calibration.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
81.16.Nd Micro- and nanolithography

Influence of hydrogen silsesquioxane resist exposure temperature on ultrahigh resolution electron beam lithography

Vadim Sidorkin, Emile van der Drift, and Huub Salemink

J. Vac. Sci. Technol. B 26, 2049 (2008); http://dx.doi.org/10.1116/1.2987965 (5 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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Performance of hydrogen silsesquioxane (HSQ) resist material with respect to the temperature during electron beam exposure was investigated. Electron beam exposure at elevated temperatures up to 90 °C shows sensitivity rise and slight contrast (γ) degradation compared to lower temperature cases. Ultrahigh resolution structures formed at elevated temperatures manifest better uniformity together with aspect ratio improvement and less linewidth broadening with overdose. Potential mechanisms for observed phenomena are proposed.
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85.40.Hp Lithography, masks and pattern transfer

Dynamic stencil lithography on full wafer scale

Veronica Savu, Marc A. F. van den Boogaart, Juergen Brugger, Julien Arcamone, Marc Sansa, and Francesc Perez-Murano

J. Vac. Sci. Technol. B 26, 2054 (2008); http://dx.doi.org/10.1116/1.2987953 (5 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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In this paper, the authors present a breakthrough extension of the stencil lithography tool and method. In the standard stencil lithography static mode, material is deposited through apertures in a membrane (stencil) on a substrate which is clamped to the stencil. In the novel dynamic mode, the stencil is repositioned with respect to the substrate inside the vacuum chamber and its motion is synchronized with the material deposition. This can be done either in a step-and-repeat or in a continuous mode. The authors present the first results proving the accurate x-y-z in situ positioning and movement of our stages during and in between patterning.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography

Projection maskless patterning for nanotechnology applications

Elmar Platzgummer, Hans Loeschner, and Gerhard Gross

J. Vac. Sci. Technol. B 26, 2059 (2008); http://dx.doi.org/10.1116/1.2993260 (5 pages) | Cited 8 times

Online Publication Date: 1 December 2008

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Projection maskless patterning (PMLP) is based on a programmable aperture plate system and on charged particle projection optics with 200× reduction, providing thousands of electron or ion (H+, He+, Ar+, Xe+, C60−) beams working in parallel on the substrate. As part of the European CHARPAN project a PMLP proof-of-concept tool has been realized. Using resolution templates, with 10 keV H+ multibeams a resolution of 16 nm lines and spaces was achieved in HSQ resist across the proof-of-concept tool 25×25 μm2 exposure field at an exposure dose of 25 μC/cm2. Enhancing the dose by 10% there was <1 nm increase in linewidth. With 10 keV Ar+ multibeams resistless nanopatterning of various materials was accomplished. Inserting a wired programmable aperture plate system providing ∼ 4000 beams, first HSQ resist exposure and patterning results have been accomplished, implementing gray scale exposure techniques. The system is being upgraded to a PMLP engineering tool integrating an aperture plate system with complementary metal oxide semiconductor electronics providing ∼ 40 000 programmable beams, a precursor gas injection system for in situ ion multibeam induced etching and deposition, and a laser-interferometer controlled high-precision vacuum stage. Industrial PMLP nanotechnology applications are discussed.
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81.16.Rf Micro- and nanoscale pattern formation
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.Cd Deposition by sputtering
42.82.Cr Fabrication techniques; lithography, pattern transfer
back to top Electron Beam Sources

Sub-50 nm resolution surface electron emission lithography using nano-Si ballistic electron emitter

A. Kojima, H. Ohyi, and N. Koshida

J. Vac. Sci. Technol. B 26, 2064 (2008); http://dx.doi.org/10.1116/1.2981068 (5 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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It is demonstrated that parallel electron beam lithography using a nano-Si planar ballistic electron emitter (PBE) provided the resolution below 30 nm even in a low accelerating voltage. This high resolving power is explained by the nature of ballistic electron transport in nanocrystalline silicon. The parallel EB lithography was performed on a 1:1 electron imaging system. The system was composed of the PBE as a patterned surface electron source, a target wafer parallel to the surface electron source, and vertical electromagnetic fields. The PBE projected a patterned electron image on the target. A replica of the pattern was transferred into a resist on the target wafer within less than 1 s. The experimental exposure was performed over 10 mm2 area. The PBE was composed of a thin metal surface electrode, nanosilicon layer, and semiconductor substrate. The electrons injected from semiconductor substrate were accelerated via cascade tunneling through the nanosilicon layer and reached the outer surface as ballistic or quasiballistic electrons. As a result, the chromatic aberration limiting resolution is expected to be quite small. The 1:1 electron imaging system based on the PBE provides promising solution for high resolution and high throughput lithography with low cost system with the simple electron optics for the next generation device fabrication in the sub-30 nm scale.
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81.16.Nd Micro- and nanolithography
72.80.Cw Elemental semiconductors
72.20.Ht High-field and nonlinear effects
73.23.Ad Ballistic transport

Multilevel visualization of local electric field at probe apex using scanning electron microscopy

Jun-ichi Fujita, Yuta Ikeda, and Ikumi Suzuki

J. Vac. Sci. Technol. B 26, 2069 (2008); http://dx.doi.org/10.1116/1.2991517 (4 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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The authors have found that the locally enhanced field at a probe apex can be visualized using conventional scanning electron microscopy (SEM) under a low accelerating voltage. The local electric field deflects the primary electrons in the vicinity of the apex. They placed a gold grid detector just beside the beam axis to detect these deflected primary electrons. The secondary electrons thus generated from the grid simultaneously created a concentric contour ring around the probe apex in the SEM image. Thus, a simple Rutherford scattering model could be adopted to analyze the local electric field distribution at the tip apex.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Effect of the electric field on the form stability of a Schottky electron emitter: A step model

M. S. Bronsgeest and P. Kruit

J. Vac. Sci. Technol. B 26, 2073 (2008); http://dx.doi.org/10.1116/1.3010732 (7 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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The stability of the physical shape of an electron emitter (co)determines the stability of the performance of electron-beam equipment. A typical short-term instability of the Schottky electron source is the instability of the (100) facet at the tip end known as “collapsing rings.” This instability causes probe instabilities, but it is known from experiments that this can be prevented by applying high enough extraction voltages. The phenomenon of collapsing rings can be explained with a step-flow model, which is based on variations in equilibrium concentrations of adatoms on the surface. The effect of the extraction voltage can be incorporated by acknowledging the redistribution of the surface charge associated with adatom formation. For operation at constant extraction voltages the adatom formation energy becomes a function of the local charge density. The charge-density distribution on the emitter surface as a function of the applied extraction voltage can be calculated with boundary-element methods. It is shown that, provided the relevant material properties are known, it can be predicted if, for a given tip shape, a collapse is to be expected.
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73.30.+y Surface double layers, Schottky barriers, and work functions
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Range of validity of field emission equations

A. S. Bahm, G. A. Schwind, and L. W. Swanson

J. Vac. Sci. Technol. B 26, 2080 (2008); http://dx.doi.org/10.1116/1.2978403 (5 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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The analytical equations for field emission current density and total energy distribution are compared with a rigorous numerical solution of the fundamental emission equations over a wide range of electric field, work function, and temperature. In particular, the range of the latter parameters where agreement occurs between the analytical and numerical results is established. Some interesting periodic deviations with applied electric field are observed for the numerically calculated current density and total energy distributions.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.30.+y Surface double layers, Schottky barriers, and work functions

Evaluation of electron energy spread in CsBr based photocathodes

Juan R. Maldonado, Yun Sun, Zhi Liu, Xuefeng Liu, Sayaka Tanimoto, Piero Pianetta, and Fabian Pease

J. Vac. Sci. Technol. B 26, 2085 (2008); http://dx.doi.org/10.1116/1.2976572 (6 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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Photocathodes with relatively low energy spread (<0.5 eV) are required for electron sources in several applications including single and multiple electron beam inspection and lithography tools and free electron lasers. CsBr based photocathodes have been shown to be very robust and capable of operation at high current density (>150 A/cm2) with very long lifetime (approximately hundreds of hours/spot). Experimental results of the photoelectron energy spread obtained in CsBr films deposited on both metal and InGaN substrates will be presented in this paper.
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85.60.Ha Photomultipliers; phototubes and photocathodes
back to top Ion Beam Technology

Brightness measurements of a gallium liquid metal ion source

C. W. Hagen, E. Fokkema, and P. Kruit

J. Vac. Sci. Technol. B 26, 2091 (2008); http://dx.doi.org/10.1116/1.2987958 (6 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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The virtual source size of a liquid metal ion source is an order of magnitude larger than the size of the region from which the ions are emitted at the source. This source size has a direct effect on the reduced brightness and, hence, on the performance of these sources. The variation of the virtual source size of a gallium liquid metal ion source as a function of the angular current density at the source has been measured. This was done by measuring the source image size from images of a pencil lead sample taken with an FEI focused ion beam system. The measurements indicate that the virtual source size grows from about 50–80 nm when the emission current increases from 1 to 10 μA. The experimental data on the virtual source size are compared with the theory on stochastic Coulomb interactions in the source region. On the basis of these measurements the authors show that the reduced brightness deteriorates with an increasing angular current density. The maximum reduced brightness measured was 1×106 A/(m2 sr V).
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07.77.Ka Charged-particle beam sources and detectors
29.25.Ni Ion sources: positive and negative

The use of ionic liquid ion sources in focused ion beam applications

Anthony N. Zorzos and Paulo C. Lozano

J. Vac. Sci. Technol. B 26, 2097 (2008); http://dx.doi.org/10.1116/1.2991619 (6 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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A new monoenergetic, high-brightness ion source can be constructed using an arrangement similar to liquid metal ion sources by substituting the liquid metal with an ionic liquid or room-temperature molten salt. Ion beams produced by these ionic liquid ion sources (ILISs) have energy deficits and distributions that closely resemble their metallic counterparts, with the exception that they can be stably operated at current levels as low as a few nanoamperes if needed. ILISs are here presented as having two further key advantages: (1) the ability to obtain both positive and negative ion beams and (2) the ability to produce very diverse molecular ions in terms of their masses, compositions, and properties due to the fact that the number of available ionic liquids is large. In this article an overview of ILISs is presented, as well as preliminary results of their performance in a focused ion beam column.
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29.25.Lg Ion sources: polarized
29.25.Ni Ion sources: positive and negative
07.77.Ka Charged-particle beam sources and detectors

Elemental analysis with the helium ion microscope

Sybren Sijbrandij, Bill Thompson, John Notte, Bill W. Ward, and Nicholas P. Economou

J. Vac. Sci. Technol. B 26, 2103 (2008); http://dx.doi.org/10.1116/1.2993262 (4 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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The newly developed helium ion microscope is an instrument well suited to high resolution surface specific imaging with several unique contrast mechanisms. In addition to its imaging capabilities, the focused helium ion beam (subnanometer in size) has recently been used for elemental analysis. The scattering probability, angular distribution, and recoil energy combine to provide valuable information about the specimen being analyzed.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
68.37.-d Microscopy of surfaces, interfaces, and thin films
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Sputtering limits versus signal-to-noise limits in the observation of Sn balls in a Ga+ microscope

V. Castaldo, C. W. Hagen, B. Rieger, and P. Kruit

J. Vac. Sci. Technol. B 26, 2107 (2008); http://dx.doi.org/10.1116/1.3013306 (9 pages) | Cited 6 times

Online Publication Date: 1 December 2008

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In principle, a scanning ion microscope can produce smaller probe sizes than a scanning electron microscope because the diffraction contribution is smaller. However, the imaging resolution is often severely limited by the sputtering damage. In this article, an experimental procedure to establish the limit of a focused ion beam system for imaging purposes is proposed. The procedure is based on the observation of the change in geometry (i.e., shrinking) of the features in a Sn-ball sample imaged with a Ga+ beam. Plots of the balls’ diameter versus the irradiation time give a straightforward visual evaluation of the time allowed for the observation of a single feature before the removal of material due to the ion bombardment becomes unacceptable. For each particle, the curve, together with the error band connected with the imaging process, gives the values of uncertainty/resolution due to the two competing processes, collecting of information (for example, from secondary electrons) and damaging of the target. A plot of the uncertainty that is derived from these two processes for different sampling times allows the determination of the limiting factor of the imaging mode in use, and, ultimately, the highest possible resolution obtainable with a given machine for the observation of a certain sample. Together with simulations and theoretical studies, the described procedure will be able to confirm the effectiveness of the new ion sources that are currently being developed.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
61.80.Jh Ion radiation effects
back to top Photon Beam Technology

Enhancement in hyper-numerical-aperture imaging through selective TM polarization

Bruce Smith, Jianming Zhou, and Peng Xie

J. Vac. Sci. Technol. B 26, 2116 (2008); http://dx.doi.org/10.1116/1.3002565 (5 pages)

Online Publication Date: 1 December 2008

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The degradation of projected images using TM polarization is not intrinsic because losses in image contrast can be recoverable. By controlling the photoresist/substrate interface reflectivity, high modulation for TM polarization can be maintained for angles approaching 90° in a photoresist. Although there is calculated loss of image contrast with increasing polarization angle using suppressed reflection (i.e., with an antireflection coating), the loss is not nearly as large when imaging over a reflective substrate. These results can potentially impact the design of illumination, possibly away from most recent TE-only schemes for oblique imaging angles and high numerical apertures (NA). Several cases of TM illumination are presented combined with tuned substrate reflectivity for 0.93 NA, 1.20 NA, and 1.35 NA and compared to results using TE illumination. Additionally, a scheme for frequency doubling with a single TM polarized exposure is presented. Using a single exposure and selective TM polarization, the reflective component produced at the photoresist/substrate interface is utilized for a four-beam imaging scenario. In doing so, patterns deposited into a photoresist film with double density are made possible.
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85.40.Hp Lithography, masks and pattern transfer

Image quality improvement in focused ion beam photomask repair system

Anto Yasaka, Fumio Aramaki, Masashi Muramatsu, Tomokazu Kozakai, Osamu Matsuda, Yasuhiko Sugiyama, Toshio Doi, Osamu Takaoka, Ryoji Hagiwara, and Koji Nakamae

J. Vac. Sci. Technol. B 26, 2121 (2008); http://dx.doi.org/10.1116/1.2981071 (3 pages)

Online Publication Date: 1 December 2008

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Focused ion beam (FIB) technology has widely been adopted as a defect repair tool on photomasks for semiconductor manufacturing. In the FIB mask repair process, scanning ion image (FIB image) is used for the defect area recognition. Quality of the FIB images is one of the most important factors in order to improve the repair accuracy. Precise imaging of the small features on the photomasks, however, is a challenging subject due to the surface charge buildup induced by FIB scanning, even though simultaneous electron beam irradiation is used for the charge compensation. The authors have developed new method of the FIB scanning for better image quality. This method utilizes software accumulation of multiple images with different scan directions and results in higher peak-to-background ratio and higher contrast images with isolated mask patterns on the quartz substrate, compared to the images acquired from conventional single scanning. The images also show better uniformity and symmetry of the secondary electron intensity.
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85.40.Hp Lithography, masks and pattern transfer
61.80.Fe Electron and positron radiation effects
85.30.-z Semiconductor devices

High-speed optical beam-steering based on phase-arrayed waveguides

Mona Jarrahi, R. Fabian, W. Pease, David A. B. Miller, and Thomas H. Lee

J. Vac. Sci. Technol. B 26, 2124 (2008); http://dx.doi.org/10.1116/1.2978945 (3 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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The authors present a high-speed optical beam-steering system employing phase-arrayed waveguides. They demonstrate a 100 mrad deflection angle at the fastest ever reported instrument-limited deflection speed of 18 GHz and power consumption of 1.8 mW.
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42.82.Et Waveguides, couplers, and arrays
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Gn Optical waveguides and couplers
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Hp Optical processors, correlators, and modulators
85.60.-q Optoelectronic devices

Application of vector scanning in focused ion beam photomask repair system

Anto Yasaka, Fumio Aramaki, Masashi Muramatsu, Tomokazu Kozakai, Osamu Matsuda, Yasuhiko Sugiyama, Toshio Doi, Osamu Takaoka, Ryoji Hagiwara, and Koji Nakamae

J. Vac. Sci. Technol. B 26, 2127 (2008); http://dx.doi.org/10.1116/1.2976574 (4 pages)

Online Publication Date: 1 December 2008

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With continuous reduction in linewidth of the VLSI devices, the pattern integrity of photomasks becomes considerably more important than ever. Consequently, requirement for the defect repair technology on photomasks is more severe and strict. Focused ion beam (FIB) technology has been widely used for defect repairing in photomask industry. Therefore, the performance of the FIB mask repair tool has to be improved especially in repair accuracy and precision. The FIB repair processes are classified into two kinds; one is additive repair using FIB induced deposition for missing patterns, the other is subtractive repair using gas assisted FIB etching for extra patterns. In both processes, precursor gas is applied onto the processing area through a small nozzle. Thus, the repair processes are controlled by the FIB irradiation and the precursor gas supply. Important characteristics of the repairs, such as size, shape, and placement of the repair area, are defined by the FIB scanning control. As conventional FIB systems used raster type of beam scanning for the repair processes, the size, shape, and placement could be controlled with the unit of pixel size (typically about 6–12 nm). However, in order to satisfy the recent requirement, more precise beam control is needed. The authors have developed a vector scanning system to meet the requirement. The vector scanning system enables us to control ion beams more precisely and more arbitrarily. Furthermore, unicursal beam scanning can be applied to the repair processes, which minimizes beam blanking times. By adopting the vector scanning, repair precision is improved. Additionally, sidewall angle of the repair region is also improved because the repair shape is formed without beam blanking.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Linewidth uniformity in Lloyd’s mirror interference lithography systems

Thomas B. O’Reilly and Henry I. Smith

J. Vac. Sci. Technol. B 26, 2131 (2008); http://dx.doi.org/10.1116/1.3013391 (4 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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Control of linewidth in patterns written with interference lithography (IL) is an important part of process control for many applications, requiring an understanding of how exposure parameters, such as dose and dose modulation, vary across the exposed area, and how a given photoresist will respond to changes in those parameters. This article presents a model of linewidth variation in a common IL system, Lloyd’s mirror, along with some results derived from that model that relate to optimizing the linewidth uniformity that can be achieved for a given application. An extension to a previously reported resist-characterization method that makes it possible to directly measure how changes in dose modulation affect linewidth is also discussed.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
07.60.Ly Interferometers
42.79.Bh Lenses, prisms and mirrors

Spatial-frequency multiplication with multilevel interference lithography

Chih-Hao Chang, Y. Zhao, R. K. Heilmann, and M. L. Schattenburg

J. Vac. Sci. Technol. B 26, 2135 (2008); http://dx.doi.org/10.1116/1.2976604 (4 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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The authors present a large-area spatial-frequency multiplication fabrication process for patterning one-dimensional periodic structures using multilevel interference lithography. In this process, multiple grating levels with different phase offsets are overlaid by aligning to a reference grating. Each grating level is pattern transfered into a single hard mask layer, effectively reducing the grating period. The linewidth of the grating lines is controlled with nanometer repeatability by plasma etching and an image-reversal process. The authors demonstrate overlay accuracy of 0.6±1.9 nm over 16×12 mm2 for two levels of 200 nm period gratings. Using this process, a subdiffraction-limited resolution grating with 100 nm period is fabricated using light with λ = 351.1 nm. This process can also be used to fabricate more complex periodic geometries.
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42.79.Dj Gratings
42.86.+b Optical workshop techniques

Light modulation with nanopatterned diffractive microelectromechanical system pixels

Jack L. Skinner, A. Alec Talin, and David A. Horsley

J. Vac. Sci. Technol. B 26, 2139 (2008); http://dx.doi.org/10.1116/1.2998725 (6 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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The design, fabrication, and testing of a microelectromechanical system (MEMS) optical modulator is presented. Polarization effects of noncircular holes on reflectivity are examined. Thermal nanoimprint lithography is used to form an array of 150 nm diameter nanoholes in a 60 nm thick metal film on a silicon-on-insulator wafer. A quartz superstrate with an indium tin oxide electrode and a photoresist spacer is used to electrostatically actuate the MEMS pixel. The motion of the pixel in relation to the superstrate causes shifts in the wavelengths of optical interference from the periodic nanohole array. An optical modulation depth of over 67% is demonstrated with this modulation method. Dynamic modal analysis is also presented.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
42.79.Hp Optical processors, correlators, and modulators
85.40.Hp Lithography, masks and pattern transfer

Improving lithography pattern fidelity and line-edge roughness by reducing laser speckle

Oleg Kritsun, Ivan Lalovic, Slava Rokitski, Bill Partlo, Bruno La Fontaine, Nigel Farrar, and Harry Levinson

J. Vac. Sci. Technol. B 26, 2145 (2008); http://dx.doi.org/10.1116/1.2992027 (6 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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In this article the authors discuss the impact of coherence, or laser speckle, of current generation 193 nm argon fluoride (ArF) excimer sources on lithographic patterning. They report a new metrology capability to characterize single-pulse speckle patterns at the exit of the laser aperture and quantify the speckle dependence on time integral square (TIS) pulse duration for different system configurations. The authors performed lithographic exposures on high-numerical-aperture immersion and dry ArF systems as a function of source pulse duration and have quantified the speckle impacts on measured photoresist line-edge roughness (LER) and linewidth roughness (LWR) using immersion and dry lithography processes. Measurements were obtained for multiple feature sizes, pitches, and illumination modes using both static and scanning exposures. They have compared the measured LWR due to laser speckle to results of a line-roughness image model, which accounts for the LER, LWR, and critical dimension uniformity due to the effective dose variation from laser speckle. Finally, the authors present measurements that demonstrate the proportionality between laser speckle contrast and the inverse root of the TIS pulse duration and find that the lithographic LWR exhibits a similar relationship with pulse duration.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
42.30.Ms Speckle and moiré patterns
back to top Nano-optical Devices

Fabrication of metallic nanoslit waveguides with sharp bends

M. Lu, L. E. Ocola, S. K. Gray, and G. P. Wiederrecht

J. Vac. Sci. Technol. B 26, 2151 (2008); http://dx.doi.org/10.1116/1.3013398 (5 pages)

Online Publication Date: 1 December 2008

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Metallic nanoslit waveguides are promising candidates for ultrahigh-density optical interconnections. A variety of devices based on metallic nanoslit waveguides have already been proposed that show a great superiority over conventional photonic devices for compactness. However very few two-dimensional devices have been experimentally demonstrated with in-plane geometries due to fabrication difficulties. In this article, a feasible process is presented using traditional semiconductor fabrication technologies such as mix-and-match lithography and electroplating, which is cable of fabricating complicated 100 nm wide, 800 nm deep gold slit waveguides with multiple sharp right-angle corners. The process can be extended to volume production manufacturing with minor modifications, thus enabling the fabrication of nanoslit photonic circuits and networks.
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42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Gn Optical waveguides and couplers

Optical antennas: A boost for infrared detection

Huifeng Li and Xing Cheng

J. Vac. Sci. Technol. B 26, 2156 (2008); http://dx.doi.org/10.1116/1.3013272 (4 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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Optical antennas that operate at infrared wavelengths are studied for their potential application in enhancing the sensitivity of infrared detectors. Huge enhancement of infrared intensity can be achieved at the gap region of dipole and bowtie aperture antennas. The intensity enhancement is found to increase monotonically with a narrower gap size. The infrared radiation is also found to be concentrated above and below the antenna plane at the gap region, which allows for easy integration of the optical antennas with infrared detectors. The advantages of the infrared antennas, such as strong field enhancement and easy fabrication, may present a viable solution toward achieving highly sensitive and highly compact uncooled infrared detectors to impact numerous infrared technologies.
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84.40.Ba Antennas: theory, components and accessories
85.60.Gz Photodetectors (including infrared and CCD detectors)

Fabrication of Fresnel zone plates by holography in the extreme ultraviolet region

Sankha S. Sarkar, Pratap K. Sahoo, Harun H. Solak, Christian David, and J. Friso Van der Veen

J. Vac. Sci. Technol. B 26, 2160 (2008); http://dx.doi.org/10.1116/1.2987960 (4 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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Fabrication of Fresnel zone plates (FZPs) with nanometer scale resolution is one of the major challenges in lithographic fabrication. The authors present a holographic approach to create FZPs where the interference pattern between a spherical beam and a plane wave is recorded to obtain the FZP structure. The spherical beam is obtained by diffraction from a circular aperture (pinhole) in a semiopaque membrane which is illuminated by a spatially coherent extreme ultraviolet beam. The beam transmitted by the membrane serves as the reference plane wave. The resulting pattern gives rise to a FZP with outermost zone width comparable to the dimension of the circular aperture. Fabrication and test results of a FZP obtained with this method are presented. The technique offers a solution to the pattern-placement problem encountered in serial ZP writing techniques as well as high resolution potential.
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42.79.Ci Filters, zone plates, and polarizers
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.86.+b Optical workshop techniques
42.82.Cr Fabrication techniques; lithography, pattern transfer

Fabrication strategies for filter banks based on microring resonators

C. W. Holzwarth, R. Amatya, M. Dahlem, A. Khilo, F. X. Kärtner, E. P. Ippen, R. J. Ram, and Henry I. Smith

J. Vac. Sci. Technol. B 26, 2164 (2008); http://dx.doi.org/10.1116/1.3021389 (4 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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Wavelength-division demultiplexers are a fundamental component needed for many proposed integrated photonic systems. By using filter banks based on microring resonators it is possible to create demultiplexers that are two orders of magnitude smaller and achieve better performance than the discrete component demultiplexers currently used. To create a filter bank out of microring resonators the resonant-frequency spacing must be controlled to within 1 GHz. This is achieved by controlling the electron-dose during scanning-electron-beam lithography in order to change the average ring waveguide width on the tens of picometer scale. Using this method a second-order twenty-channel dual filter bank (80 microrings) is fabricated with a average channel spacing of 83 GHz demonstrating the capability to make changes in the average ring waveguide width with an accuracy of 75 pm. It is shown that any frequency errors that remain after fabrication can be corrected using thermal tuning with integrated microheaters. The amount of power needed to correct for all frequency errors in the fabricated filter banks is 0.09 W, compared to the 2.4 W that is needed if no attempt is made to control the frequency spacing during fabrication. Also a temperature stabilization circuit is demonstrated that can stabilize the temperature of the filters to 80 mK (280 MHz).
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Ci Filters, zone plates, and polarizers

Focused ion beam fabrication of metallic nanostructures on end faces of optical fibers for chemical sensing applications

A. Dhawan, J. F. Muth, D. N. Leonard, M. D. Gerhold, J. Gleeson, T. Vo-Dinh, and P. E. Russell

J. Vac. Sci. Technol. B 26, 2168 (2008); http://dx.doi.org/10.1116/1.3013329 (6 pages) | Cited 8 times

Online Publication Date: 1 December 2008

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Focused ion beam (FIB) fabrication of fiber optic sensors, mainly chemical sensors, which are based on plasmonics-active nanostructures formed on the cleaved tips of optical fibers, is reported. The nanostructures fabricated included nanoholes in optically thick metallic films as well as metallic nanopillars and nanorods. The sensing mechanism is based on detecting shifts in surface plasmon resonances (SPRs) associated with nanoholes in metallic films and localized SPRs of metallic nanopillars and nanorods, when the refractive index of the medium surrounding the nanostructures is changed. These sensors can be employed for the detection of chemical agents in air as well as liquid media surrounding the sensors. FIB milling was employed to fabricate ordered arrays of nanoholes in optically thick (100–240 nm) metallic films deposited on cleaved end faces of multimode, four-mode, and single-mode optical fibers. Separately, metallic nanorods and nanopillars were formed by first depositing a metallic (gold or silver) film on tips of optical fibers, which was followed by FIB milling large area patterns to form freestanding nanorods and nanopillars. Utilizing FIB allows engineering nanostructure geometries, i.e., nanostructure shapes and sizes that are chosen based on the plasmon resonances associated with them. Formation of periodic arrays of nanoholes provides a means of tuning plasmon resonance peaks, associated with extraordinary transmission of light through the array of nanoholes in the metallic films, based on periodicity and shape of the nanoholes as well as on refractive index changes to form sensitive chemical sensors.
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42.81.Pa Sensors, gyros
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

NIL processes and material characterization on transparent substrates for optical applications

N. Chaix, C. Gourgon, C. Perret, S. Decossas, S. Landis, V. G. Lambertini, and N. Li Pira

J. Vac. Sci. Technol. B 26, 2174 (2008); http://dx.doi.org/10.1116/1.2998726 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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Several nanoimprint lithography polymers have been investigated for optical applications. The objective was to establish which materials can be used as a permanent polymer coated on top of a glass substrate to provide nanostructures imprinted by nanoimprint lithography. 400 and 600 nm dots were realized in polystyrene, polymethylmethacrylate (PMMA), mr-I T85, and mr-I6000. The adhesion study shows that PMMA and mr-I6000 materials are the best candidates for demolding issues. Scanning electron microscopy characterization confirmed that PMMA structures are well defined, whereas dots printed in other polymers exhibit defects due to sticking issues which lead to local pattern deformation. Finally, optical characterization showed that the nonperfect profiles are a benefit in terms of light extraction. Polycarbonate sheets were also imprinted on one or two sides in order to study the influence of a double side patterning. It was also concluded that a double side imprinted device leads to an increase in the external efficiency.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
61.41.+e Polymers, elastomers, and plastics
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Fabrication of 200 nm period blazed transmission gratings on silicon-on-insulator wafers

Minseung Ahn, Ralf K. Heilmann, and Mark L. Schattenburg

J. Vac. Sci. Technol. B 26, 2179 (2008); http://dx.doi.org/10.1116/1.2968613 (4 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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The authors report on the fabrication of 200 nm period blazed transmission gratings on silicon-on-insulator (SOI) wafers. These critical angle transmission (CAT) gratings require 3–5 μm tall freestanding grating bars with a very high aspect ratio (>100) and smooth sidewalls. In order to meet the challenging geometrical requirements, they modified and improved our previously reported process for the fabrication of a CAT grating prototype with 574 nm period. They have used potassium hydroxide (KOH) solutions to fabricate high aspect ratio gratings on ⟨110⟩ SOI wafers. The KOH etching process was improved to minimize the lateral undercut through precise grating alignment to ⟨111⟩ planes within ±0.05° and a room temperature etch process with 50 wt % KOH. In addition, an image-reversal technique with a high silicon content spin-on polymer was applied to increase process latitude with a high duty cycle nitride mask. A surfactant was also added to the KOH solution to promote hydrogen bubble release. With the improved process, they achieved a high etch anisotropy of above 300 on a ⟨110⟩ silicon wafer. They successfully fabricated 200 nm period CAT gratings with support mesh periods of 25 and 40 μm in a 9 mm2 area of 4-μm-thick silicon membranes on ⟨110⟩ SOI wafers.
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42.79.Dj Gratings
42.86.+b Optical workshop techniques
81.65.Cf Surface cleaning, etching, patterning
back to top Metamaterials

Engineering surface plasmon grating couplers through computer simulation

Daniel P. Ceperley and Andrew R. Neureuther

J. Vac. Sci. Technol. B 26, 2183 (2008); http://dx.doi.org/10.1116/1.3021378 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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Surface plasmon grating couplers are optimized by separately characterizing the collection efficiency, rescattering, and transmission effects of isolated grating elements with finite difference time domain methods and then using signal flow graph methods to assess the performance of arrays of N identical elements. Small bars, ridges, and trenches on silver at a wavelength of 700 nm are shown to have different coupling patterns and efficiencies from near zero to the physical width of the element. The overall efficiency requires a suitable trade-off of coupling and surface wave transmission and an example structure exhibiting an equivalent 100% capture length over ten wavelengths is shown.
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42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings

Light transmission through a metallic/dielectric nano-optic lens

Hyungduk Ko, Hyun Chul Kim, and Mosong Cheng

J. Vac. Sci. Technol. B 26, 2188 (2008); http://dx.doi.org/10.1116/1.2990791 (4 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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The authors analyze transmission of a normally incident plane wave through a Ag/dielectric layered concentric ring structure using finite-difference time-domain (FDTD) analysis. The authors study the dependency of the transmission efficiency on the refractive index in slit. The numerical analysis indicates that the focusing beyond diffraction limit is found even at the extended focal length comparable to the distance of 7λ from exit plane using a circularly polarized coherent plane wave, λ = 405 nm. Especially, compared to Ag-only structure, the Ag/LiNbO3 structure exhibits over 2.85 orders of larger transmission power. Therefore, this Ag/dielectric layered lens has the potential for significantly the high resolution imaging and optical data storage.
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42.79.Bh Lenses, prisms and mirrors

Photomask image enhancement using grating-generated surface waves

Neal V. Lafferty, Anatoly Bourov, Andrew Estroff, and Bruce W. Smith

J. Vac. Sci. Technol. B 26, 2192 (2008); http://dx.doi.org/10.1116/1.3002560 (5 pages)

Online Publication Date: 1 December 2008

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In recent years, the anomalous transmission of subwavelength apertures has become an emergent subject within the physical sciences. While the gain mechanism of these structures is still uncertain, the effect has been observed in several studies. Similar transmission enhancements may be realized for near-wavelength sized photomask structures by including buried grooves in a dual write mask design. Several configurations of one-dimensional transmitting apertures and buried grooves have been investigated under TM illumination using the finite element method. Periodic subwavelength apertures with identical sized nontransmitting assist grooves were used to validate the model against reference data in the near-IR. The method was also used to investigate similar structures featuring a larger than wavelength transmitting aperture. Although transmission through the slot was increased by 1.67×, the primary lithographic benefit was an increase in the magnitude of the primary imaging orders relative to the zeroth diffracted order. A similar approach was extended to structures scaled to 248 nm to show application as a potential lithographic assist feature. A 5.7× transmission increase was observed using aluminum on fused silica configuration using 30 nm slots on a 192 nm pitch.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.30.Va Image forming and processing

Optical focusing of plasmonic Fresnel zone plate-based metallic structure covered with a dielectric layer

Hyun Chul Kim, Hyungduk Ko, and Mosong Cheng

J. Vac. Sci. Technol. B 26, 2197 (2008); http://dx.doi.org/10.1116/1.3021380 (7 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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By modulating the zone width of a plasmonic Fresnel zone plate, consisting of metallic nanostructures covered with a dielectric layer, the authors demonstrated numerically that a focused beam can be achieved with higher intensity and smaller spot size than the diffraction-limited conventional Fresnel zone plate. Rigorous electromagnetic simulation predicts a full width at half maximum of 162 nm (equivalent to an effective numerical aperture of 1.30) at 0.5 μm focal length, using 405 nm wavelength illumination. This sub-diffraction-limit focusing has potential in applications such as maskless nanolithography, high resolution scanning optical microscopy, optical data storage, and optical antenna. This focusing capability is related to extraordinary optical transmission, which is explained by the complex propagation constant in the zones afforded by higher refractive index dielectric layer and surface plasmons.
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78.66.Bz Metals and metallic alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
back to top EUV Lithography

Extreme ultraviolet lithography: Status and prospects

Jos Benschop, Vadim Banine, Sjoerd Lok, and Erik Loopstra

J. Vac. Sci. Technol. B 26, 2204 (2008); http://dx.doi.org/10.1116/1.3010737 (4 pages) | Cited 11 times

Online Publication Date: 1 December 2008

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Extreme ultraviolet lithography (EUVL) using 13.5 nm wavelength light is the leading candidate to succeed 193 nm immersion lithography, enabling semiconductor chips with features smaller than 22 nm. Several major programs worldwide have developed this technology in recent years [ D. A. Tichenor et al., OSA Proceedings on Soft X-Ray Projection Lithography, edited by A. M. Hawryluk and R. H. Stuten (1993), Vol. 18, p. 79; H. Kinachita, OSA Proceedings on Soft X-Ray Projection Lithography, edited by A. M. Hawryluk and R. H Stulen (1993), Vol. 18, p. 74; J. P. H. Benschop, W. M. Kaiser, and D. C. Ockwell, Proc. SPIE 3676, 246 (1999) ] and in 2006, ASML shipped the first EUV Alpha Demo tools (NA = 0.25 full-field scanners) to IMEC in Belgium [ A. M. Goethals et al., Proc. SPIE 6517, 651709 (2007) ] and CNSE in Albany [ O. Wood et al., Proc. SPIE 6517, 6517–041 (2007) ], USA. Currently the development of preproduction tools with targeted shipment of 2009 is well under way. This paper discusses the most critical items for EUVL development, namely, EUV imaging and EUV sources. Furthermore, it elaborates on the necessary development of masks and resists and, for example, quantifies how resist diffusion length can impact imaging capabilities. Results obtained and lessons learned with the Alpha Demo tools are discussed, as well as potential solutions to some of the remaining challenges. Additionally, this paper explains how EUV can realize high productivity (>100 wafers/h) and high resolutions (<22 nm) to continue the cost-effective shrink of semiconductors for several generations.
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85.40.Hp Lithography, masks and pattern transfer

Effects of mask absorber structures on the extreme ultraviolet lithography

Hwan-Seok Seo, Dong-Gun Lee, Hoon Kim, Sungmin Huh, Byung-Sup Ahn, Hakseung Han, Dongwan Kim, Seong-Sue Kim, Han-Ku Cho, and Eric M. Gullikson

J. Vac. Sci. Technol. B 26, 2208 (2008); http://dx.doi.org/10.1116/1.3002488 (7 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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In this paper, the authors present the results of an investigation of the dependence of mask absorber thickness on the extreme ultraviolet lithography (EUVL) and suggest a new mask structure to minimize shadowing effects. For this purpose, several patterned masks with various TaN absorber thicknesses are fabricated using in-house Ru-capped EUVL mask blanks. According to the simulation using practical refractive indices, which are obtained at EUV wavelengths, the absorber thickness can be reduced to that of out-of-phase (ΔΦ = 180°) ranges without loss of image contrast and normalized image log slope. Thickness to meet out-of-phase in real mask can be obtained by comparing field spectrum intensity ratio using the EUV coherent scattering microscopy (CSM). 52.4 nm in thickness is close to ΔΦ = 180° for TaN absorber since it shows the highest 1st/0th order intensity ratio as well as the best resolution in the microfield exposure tool (MET) test. When we apply 40-nm-thick TaN instead of 80-nm-thick TaN, the amounts of H-V bias reduction in wafer scale correspond to 80% (2.46–0.48 nm) by CSM and 70% (2.23–0.65 nm) by MET test results. Considering the fact that H-V bias in the MET is similar with that of simulation using the resist model, the degree of H-V bias in the alpha demo tool (ADT) is supposed to be much higher than that of MET due to its higher incident angle (θ = 6°). Our final goal is to develop a thin absorber EUVL mask which has a low H-V bias, high EUV printability and DUV contrast, and sufficient optical density at the border. To achieve this, blind layer treatment and integration with anti-reflective coating layer are in progress.
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85.40.Hp Lithography, masks and pattern transfer

Experimental validation of full-field extreme ultraviolet lithography flare and shadowing corrections

A. M. Myers, G. F. Lorusso, I. Kim, A. M. Goethals, R. Jonckheere, J. Hermans, B. Baudemprez, and K. Ronse

J. Vac. Sci. Technol. B 26, 2215 (2008); http://dx.doi.org/10.1116/1.3013297 (5 pages) | Cited 10 times

Online Publication Date: 1 December 2008

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Extreme ultraviolet lithography (EUVL) is the leading candidate for 22 nm half-pitch device manufacturing. IMEC has a fully integrated 300 mm EUVL process line incorporating an Alpha Demo Tool (ADT) from ASML, aimed to understand issues related to the introduction of EUV technology in high-volume manufacturing. This study experimentally investigates flare and shadowing correction strategies. Experimental characterization of the flare of the ADT is reported, as well as experimental rules for flare variation correction. With respect to shadowing, shadowing corrections are experimentally estimated. Comparisons of experimental data and rigorous simulation are also presented, and a computationally efficient methodology to generate a full-chip flare map is proposed.
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85.40.Hp Lithography, masks and pattern transfer

Actinic extreme ultraviolet mask inspection beyond 0.25 numerical aperture

K. A. Goldberg, P. Naulleau, I. Mochi, E. H. Anderson, S. B. Rekawa, C. D. Kemp, R. F. Gunion, H.-S. Han, and S. Huh

J. Vac. Sci. Technol. B 26, 2220 (2008); http://dx.doi.org/10.1116/1.3002490 (5 pages) | Cited 9 times

Online Publication Date: 1 December 2008

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The SEMATECH Berkeley actinic inspection tool (AIT) is an extreme ultraviolet (EUV)-wavelength mask inspection microscope designed for direct aerial image measurements and precommercial EUV mask research. Operating on a synchrotron bending magnet beamline, the AIT uses an off-axis Fresnel zoneplate lens to project a high-magnification EUV image directly onto a charge coupled device camera. The authors present the results of recent system upgrades that have improved the imaging resolution, illumination uniformity, and partial coherence. Benchmarking tests show image contrast above 75% for 100 nm mask features and significant improvements and across the full range of measured sizes. The zoneplate lens has been replaced by an array of user-selectable zoneplates with higher magnification and numerical aperture (NA) values up to 0.0875, emulating the spatial resolution of a 0.35 NA 4× EUV stepper. Illumination uniformity is above 90% for mask areas 2 μm wide and smaller. An angle-scanning mirror reduces the high coherence of the synchrotron beamline light source giving measured σ values of approximately 0.125 at 0.0875 NA.
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85.40.Hp Lithography, masks and pattern transfer

The effects of oxygen plasma on the chemical composition and morphology of the Ru capping layer of the extreme ultraviolet mask blanks

Leonid Belau, Jeong Y. Park, Ted Liang, and Gabor A. Somorjai

J. Vac. Sci. Technol. B 26, 2225 (2008); http://dx.doi.org/10.1116/1.3021368 (5 pages) | Cited 8 times

Online Publication Date: 1 December 2008

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Contamination removal from extreme ultraviolet (EUV) mask surfaces is one of the most important aspects to improve reliability for the next generation of EUV lithography. The authors report chemical and morphological changes of the ruthenium (Ru) mask surface after oxygen plasma treatment using surface sensitive analytical methods: x-ray photoelectron spectroscopy (XPS), atomic force microscopy, and transmission electron microscopy (TEM). Chemical analysis of the EUV masks shows an increase in the subsurface oxygen concentration, Ru oxidation, and surface roughness. XPS spectra at various photoelectron takeoff angles suggest that the EUV mask surface was covered with chemisorbed oxygen after oxygen plasma treatment. It is proposed that the Kirkendall effect is the most plausible mechanism that explains the Ru surface oxidation. The etching rate of the Ru capping layer by oxygen plasma was estimated to be 1.5±0.2 Å/min, based on TEM cross sectional analysis.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.37.Og High-resolution transmission electron microscopy (HRTEM)
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.35.Fx Diffusion; interface formation
81.65.Cf Surface cleaning, etching, patterning

Protection and reduction of surface oxidation of Mo/Si multilayers for extreme ultraviolet lithography projection optics by control of hydrocarbon gas atmosphere

Masahito Niibe, Keigo Koida, and Yukinobu Kakutani

J. Vac. Sci. Technol. B 26, 2230 (2008); http://dx.doi.org/10.1116/1.2998703 (6 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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To protect the surface oxidation of Mo/Si multilayer films by extreme ultraviolet (EUV) irradiation under a vacuum atmosphere with residual water, two experiments were carried out. One consisted of examining the oxidation protection effect for isopropyl alcohol (IPA) and n-decane gases. The reflectivity change of the Ru-capped multilayer film by EUV irradiation was investigated under a vacuum atmosphere with residual water vapor at a pressure of 1.3×10−5 Pa, and, in addition, each hydrocarbon (HC) gas was introduced by changing its pressure. A protective effect against oxidation was observed in both gases when introduced at a pressure in the order of 10−6 Pa. For IPA, no remarkable decrease in the reflectivity was observed even when the introductory pressure was raised to the order of 10−4 Pa. However, for n-decane, the reflectivity decreased remarkably when pressure in the order of 10−5 Pa was introduced. The other experiment consisted of examining the reduction effect of the oxidized surface by EUV irradiation when introducing HC gas. Ru- and Si-capped multilayers were once oxidized by EUV irradiation under a water vapor atmosphere. However, for the Ru-capped multilayer, the reflectivity was recovered when EUV was irradiated in the presence of ethanol gas at a pressure of 3.8×10−5 Pa. The oxide layer of the Ru cap was reduced at this time.
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81.65.Mq Oxidation

Decomposition of catechol and carbonaceous residues on TiO2(110): A model system for cleaning of extreme ultraviolet lithography optics

Peter Jacobson, Shao-Chun Li, Chuandao Wang, and Ulrike Diebold

J. Vac. Sci. Technol. B 26, 2236 (2008); http://dx.doi.org/10.1116/1.3002566 (5 pages) | Cited 6 times

Online Publication Date: 1 December 2008

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High energy photons used to expose photoresists in extreme ultraviolet lithography (92 eV, 13.5 nm) photoexcite electrons from Mo/Si multilayer mirror surfaces. Photoemitted electrons participate in the formation of carbonaceous residues on the mirror surface significantly affecting the mirror reflectivity. We explore mitigation strategies utilizing TiO2(110) as a model for the capping layer. Two carbon containing surfaces are examined; an ordered catechol monolayer and a carbonaceous layer. Excimer laser sources (XeF and KrF) coupled with oxidizing gas backgrounds (NO and O2) are shown to be effective for the photocatalytic removal of carbon. Utilizing x-ray photoemission spectroscopy and scanning tunneling microscopy carbon removal is shown to proceed through oxidation of the overlayer.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.50.-m Photochemistry
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Interaction of benzene with TiO2 surfaces: Relevance to contamination of extreme ultraviolet lithography mirror capping layers

Shimon Zalkind, Boris V. Yakshinskiy, and Theodore E. Madey

J. Vac. Sci. Technol. B 26, 2241 (2008); http://dx.doi.org/10.1116/1.2978392 (6 pages) | Cited 8 times

Online Publication Date: 1 December 2008

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The authors focus on thermal and nonthermal (radiation-induced) surface processes that affect the reflectivity of TiO2-capped multilayer mirrors used in extreme ultraviolet (EUV) lithography. Low energy electron beams mimic excitations initiated by EUV radiation. Where appropriate, comparison is made with electron bombardment in the vapor of methyl methacrylate (C5H8O2). Benzene adsorbs and desorbs reversibly on TiO2, and the steady state coverage Θ is found to be proportional to the logarithm of the benzene pressure p. This behavior is described by the Tempkin adsorption isotherm, which has the form Θ = const+log p. This isotherm is a consequence of a linear dependence of benzene adsorption energy on Θ. In addition, measurements of cross sections σ (cm2) for electron-stimulated dissociation of benzene on clean and C-covered TiO2 in the range of 10–100 eV reveal surprisingly large values (e.g., ∼ 3.5×10−17 cm2 at 10 eV primary energy). Thus, low energy secondary electrons excited by EUV lithography photons are expected to contribute substantially to carbon accumulation on clean TiO2 cap layers.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.43.Nr Desorption kinetics
back to top Line Edge Roughness/Resists

Stability of HSQ nanolines defined by e-beam lithography for Si nanowire field effect transistors

Suresh Regonda, Mukti Aryal, and Wenchuang (Walter) Hu

J. Vac. Sci. Technol. B 26, 2247 (2008); http://dx.doi.org/10.1116/1.3002561 (5 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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Multiple instability states, e.g., grouped collapse, single collapse, wavy, and grouped wavy states, have been observed in hydrogen silses quioxane (HSQ) nanolines defined by electron beam lithography (EBL). Experimental data show that the critical aspect ratio of the HSQ lines dramatically increase when the line pitch reduced to sub-100-nm, which is opposite to theoretical models for capillary forces and swelling strain. Such contradiction can be well explained only if Young’s modulus is considered as a significantly varying factor. Further, experimental data show a dramatic decrease in swelling strain and increase in oxygen contents in HSQ with increasing EBL dose, indicating that it is the change in Young’s modulus rather than the capillary force or swelling strain that dominates the instability behaviors at the nanoscale. Stable high aspect ratio HSQ nanolines over metal pads were used to make working Si nanowire transistors on Si on insulator substrates. 12–14 nm HSQ lines with aspect ratios of 11–14 have been obtained. Fabricated field effect transistors using back-gate configuration has shown expected performance towards biosensing applications.
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85.40.Hp Lithography, masks and pattern transfer
85.35.-p Nanoelectronic devices
85.30.Tv Field effect devices
81.16.Nd Micro- and nanolithography

Novel negative-tone molecular resist based on polyphenol derivative for extreme ultraviolet lithography

Hiroaki Oizumi, Takafumi Kumise, and Toshiro Itani

J. Vac. Sci. Technol. B 26, 2252 (2008); http://dx.doi.org/10.1116/1.2976599 (5 pages) | Cited 7 times

Online Publication Date: 1 December 2008

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This study investigated the extreme ultraviolet (EUV) lithographic performance of negative-tone molecular resists based on 2,7-bis[bis(2,3,5-trimethyl-4-hydroxyphenyl)methyl]naphthalene (MGR002) and their negative-tone imaging mechanism. EUV imaging experiments were performed using the high-numerical-aperture (NA = 0.3), small-field EUV exposure tool (HINA). Patterning results showed the resolution of one resist to be 29 nm at an EUV exposure dose of 18 mJ/cm2 and the obtainable aspect ratio to be as high as 2. Analyses by matrix-assisted laser desorption/ionization mass spectroscopy, Fourier transform infrared spectroscopy, and UV-visible absorption spectroscopy of EUV-exposed resists revealed that one reason for the good performance is that the negative-tone imaging mechanism involves both cross-linking and a change in polarity.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Latent image formation in chemically amplified extreme ultraviolet resists with low activation energy for deprotection reaction

Takahiro Kozawa, Seiichi Tagawa, Julius Joseph Santillan, and Toshiro Itani

J. Vac. Sci. Technol. B 26, 2257 (2008); http://dx.doi.org/10.1116/1.2990787 (4 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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The trade-off relationships between resolution, sensitivity, and line edge roughness have become a serious problem in device manufacturing as the minimum feature size is reduced. To solve this problem, the improvement of pattern formation efficiency is necessary. The efficiency of pattern formation is mainly determined by the efficiencies of incident radiation absorption, acid generation, and deprotection. The deprotection efficiency is the number of times an acid can induce catalytic reactions during the diffusion of a unit distance. The highest expected deprotection efficiency is achieved by a diffusion-controlled reaction. In this study, the authors investigated the feasibility of low-Ea resists for 22 nm fabrication. It was found that their efficiency is inadequate for 22 nm fine patterning even when a diffusion-controlled rate is assumed. For 22 nm fabrication with 5–10 mJ cm−2 exposure dose, increases in acid generation efficiency and polymer absorption are essential.
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81.16.Nd Micro- and nanolithography
82.20.Pm Rate constants, reaction cross sections, and activation energies
81.16.Rf Micro- and nanoscale pattern formation
81.16.Be Chemical synthesis methods

Dissolution characteristics of chemically amplified extreme ultraviolet resist

Toshiro Itani, Koji Kaneyama, Takahiro Kozawa, and Seiichi Tagawa

J. Vac. Sci. Technol. B 26, 2261 (2008); http://dx.doi.org/10.1116/1.2987959 (4 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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The dissolution characteristics of the resist film into alkaline developer have been investigated in order to understand inherent extreme ultraviolet (EUV) resist characteristics and improve resist performance. The combined increase in dissolution “slope” and dissolution contrast (Rmax/Rmin) was confirmed to improve the resolution capability of an EUV resist. Also, a higher Rmin value, which means easy and smooth dissolution of the resist into the alkaline developer, will mean a lower line-width roughness (LWR). However, more evidence and further detailed investigation are necessary to prove this relationship between this dissolution characteristic and LWR. It was also found that the slope of dissolution rate curve for the poly(hydroxystyrene) resist increases as protecting ratios is increased. However, it was found that higher protection ratios increase the amount of released resist outgassing upon EUV exposure. The dissolution rate analysis of presently available high performance EUV resist Selete standard resist 2 (SSR2) was also performed. Based on these results, a high slope and dissolution contrast value of the SSR2 correlated with its improved resolution capability at the 26 nm hp L/S.
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64.75.Bc Solubility

Improvement in linewidth roughness by postprocessing

Manish Chandhok, Kent Frasure, E. Steve Putna, Todd R. Younkin, Willy Rachmady, Uday Shah, and Wang Yueh

J. Vac. Sci. Technol. B 26, 2265 (2008); http://dx.doi.org/10.1116/1.3013860 (6 pages) | Cited 10 times

Online Publication Date: 1 December 2008

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In order to meet the linewidth roughness (LWR) requirements for the 16 nm node, postprocessing methods need to be investigated to reduce the LWR after the lithography step. We present the results of five different techniques applied to a single extreme ultraviolet photoresist. The results show that rinse has the most promise in achieving the nearly two time LWR improvement needed. However, other techniques such as etch/trim, hardbake, vapor smoothing, and ozonation give at least 10%–20% LWR reduction and could be further optimized. Some of the physical based techniques which melt the photoresist reduce the midspatial frequency (50–10 nm period) roughness, whereas chemical based techniques reduce the low order spatial frequencies ( ∼ 500–50 nm period). Hence, a combination of techniques may be the ultimate solution.
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85.40.Hp Lithography, masks and pattern transfer

Epoxy silsesquioxane resists for UV nanoimprint lithography

J. De Girolamo, M. Chouiki, J.-H. Tortai, C. Sourd, S. Derrough, M. Zelsmann, and J. Boussey

J. Vac. Sci. Technol. B 26, 2271 (2008); http://dx.doi.org/10.1116/1.2998709 (5 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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Photopolymerizable epoxy polyhedral oligomeric silsesquioxane monomers with variable aliphatic spacer have been prepared and cured under UV radiation. Due to their organic/inorganic composition, these materials are promising candidates for microelectronic applications which requires high thermal and mechanical stabilities as well as a low dielectric constant, for example, for the fabrication of electrical interconnects. The authors pointed out by ellipsometric measurements that the use of a sensitizer in addition to the photoinitiator enhances the kinetic of the cationic polymerization of epoxy groups. The polymerization performed either in an EVG770® nanoimprint lithography stepper or under normal atmospheric conditions has been investigated by infrared spectroscopy, delivering information concerning polymerization mechanisms and allowing the optimization of the resin composition. Thermogravimetric analyses have shown that an annealing step is necessary after the UV curing of the resin to eliminate inert residues of the photoinitiator dissociation and thus improving the thermal resistance of the polymer. Finally they have demonstrated that the obtained polymers form interpenetrated networks and that their mechanical properties are retained up to a temperature of 375 °C.
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81.16.Nd Micro- and nanolithography
82.35.Lr Physical properties of polymers
77.22.Ch Permittivity (dielectric function)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Gh Other heat and thermomechanical treatments
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Understanding the effects of photoacid distribution homogeneity and diffusivity on critical dimension control and line edge roughness in chemically amplified resists

Cheng-Tsung Lee, Richard A. Lawson, and Clifford L. Henderson

J. Vac. Sci. Technol. B 26, 2276 (2008); http://dx.doi.org/10.1116/1.2976601 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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Resist critical dimension (CD) control and line edge roughness (LER) reduction has been one of the most challenging issues for sub-100 nm feature patterning in integrated circuit manufacturing. Among those factors dominating CD and LER, photoacid distribution homogeneity and diffusivity are major elements which are correlated to resist material design and have a direct impact on the lithography performance. In this work, a mesoscale stochastic model has been applied to investigate the joint effect of photoacid distribution homogeneity and diffusivity on resist lithography performance. Simulation results suggest that the high photoacid generator (PAG) loading and low photoacid diffusivity provided by polymer bound-PAG resist systems can provide superior lithography performance as compared to traditional blended-PAG resists, which is in good agreement with our previous experimental characterization of polymer bound-PAG resists. The results also suggest that resist image blur is proportional to the square root of the product of photoacid concentration generated at the line edge and the photoacid diffusion coefficient. LER was observed to be proportional to the product of the standard deviation of the extent of deprotection along the nominal line edge and the reciprocal of the gradient of the deprotection profile along the resist line edge.
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85.40.Hp Lithography, masks and pattern transfer

Contributions of resist polymers to innate material roughness

Theodore H. Fedynyshyn, David K. Astolfi, Russell B. Goodman, Susan Cann, and Jeanette Roberts

J. Vac. Sci. Technol. B 26, 2281 (2008); http://dx.doi.org/10.1116/1.2993259 (9 pages) | Cited 7 times

Online Publication Date: 1 December 2008

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The authors have extended the atomic force microscopy-based technique to measure intrinsic material roughness after base development to evaluate a number of different polymer types in resist formulations. These polymers include environmentally stable chemical amplified photoresist type copolymers and terpolymers, methacrylate polymers, and fluoropolymers. The surface roughness of resists containing these polymers was measured along with the clearing dose with both extreme ultraviolet (EUV) and deep ultraviolet (DUV) exposures. Selected resists containing a representative sampling of different lithographic polymers were imaged with both EUV and DUV exposures. It has been suggested by many that there is a fundamental inverse relationship between resist sensitivity and LER that leads to a fundamental limit to resist performance. It was found that no simple relationship exists between intrinsic material roughness (IMR) and sensitivity and instead some other, more complex relationship between the material properties of the polymer and resist process that is determining both the IMR and sensitivity. It was also found that no simple relationship existed between resist sensitivity and LER. This suggests that resist performance is not innately limited by any fundamental law but is instead open to further improvements through the use of new materials or material combinations.
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68.35.bm Polymers, organics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.16.Nd Micro- and nanolithography

Optical characterization of a hydrogen silsesquioxane lithography process

A. Samarelli, D. S. Macintyre, M. J. Strain, R. M. De La Rue, M. Sorel, and S. Thoms

J. Vac. Sci. Technol. B 26, 2290 (2008); http://dx.doi.org/10.1116/1.2998694 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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In this article the authors report on a new optical linewidth metrology method which uses measured changes in the resonant wavelength of fabricated ring resonator structures to establish the linewidth of waveguides. The technique has a precision of better than 0.5 nm for 500 nm linewidths and can be used for process control although it cannot be used with arbitrary optical structures. To demonstrate the technique they fabricated ring resonator structures on silicon on insulator substrates several times over a period of 70 days, using electron beam lithography with hydrogen silsesquioxane (HSQ) negative tone resist followed by dry etching. They show that waveguide width variations of less than 0.5 nm can consistently be achieved when the HSQ is diluted immediately prior to use but highly irreproducible results are soon obtained if a single dilution is prepared and used for an extended period.
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81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers

Influence of base and photoacid generator on deprotection blur in extreme ultraviolet photoresists and some thoughts on shot noise

Christopher N. Anderson, Patrick P. Naulleau, Dimitra Niakoula, Elsayed Hassanein, Robert Brainard, Gregg Gallatin, and Kim Dean

J. Vac. Sci. Technol. B 26, 2295 (2008); http://dx.doi.org/10.1116/1.2968615 (5 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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A contact-hole deprotection blur metric has been used to monitor the deprotection blur of an experimental open platform resist (EH27) as the wt % of base and photoacid generator (PAG) were varied. A six times increase in base wt % is shown to reduce the size of successfully patterned 1:1 line-space features from 52 to 39 nm without changing deprotection blur. Corresponding isolated line edge roughness is reduced from 6.9 to 4.1 nm. A two times increase in PAG wt % is shown to improve 1:1 line-space patterning from 47 to 40 nm without changing deprotection blur or isolated line edge roughness. A discussion of improved patterning performance as related to shot noise and deprotection blur concludes with a speculation that the spatial distribution of PAG molecules has been playing some role, perhaps a dominant one, in determining the uniformity of photogenerated acids in the resists that have been studied.
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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

The effect of thin metal overlayers on the electron beam exposure of polymethyl methacrylate

C. B. Samantaray and J. T. Hastings

J. Vac. Sci. Technol. B 26, 2300 (2008); http://dx.doi.org/10.1116/1.3021397 (6 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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Here, the authors consider the effect of thin metal coatings on the contrast, clearing dose, and resolution of polymethyl methacrylate (PMMA) electron beam resist. They present processes suitable for deposition, exposure through, and removal of 5-nm-thick Al, Cr, and Cu layers. Contrast and clearing dose were determined by exposing large features and resolution was assessed using single pixel lines at beam energies from 2 to 30 keV. In all cases the presence of the metal layer increases the clearing dose. They obtained a minimum linewidth of 40 nm from the single pixel patterns. Both the experimental results and Monte Carlo simulations of the point spread function (PSF) support the feasibility of direct writing of sub-40-nm patterns despite of additional forward electron scattering. Applying thin metal coatings on resist provides an alternative to conductive polymers for charge reduction and an excellent foundation for fiducial grids used in spatial-phase locked electron beam lithography.
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85.40.Hp Lithography, masks and pattern transfer

The effects of molecular weight on the exposure characteristics of poly(methylmethacrylate) developed at low temperatures

M. Yan, S. Choi, K. R. V. Subramanian, and I. Adesida

J. Vac. Sci. Technol. B 26, 2306 (2008); http://dx.doi.org/10.1116/1.3002562 (5 pages) | Cited 7 times

Online Publication Date: 1 December 2008

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Poly(methylmethacrylate) (PMMA) with various molecular weights exposed using 50 keV electron beam have been investigated at subzero developer temperatures. Contrast curves for Methyl Isobutyl Ketone (MIBK):Isopropyl Alcohol (IPA) = 1:3 and MIBK:IPA = 1:7 developers were determined. The contrast curves for different molecular weight PMMA resists converge into a single curve at lower temperatures. At low temperatures, the line edge roughness and resolution improved. However, minimum line pitch shows no significant improvement while dose latitudes for a particular line pitch increased. It is shown that at low temperatures, linewidth resolution and periodicity are invariant for the different PMMA molecular weights (50 K to 2.2M) used in this work.
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61.41.+e Polymers, elastomers, and plastics
61.80.Fe Electron and positron radiation effects

Effect of microstructure on deprotection kinetics in photoresist

David S. Fryer, Vivek Singh, Srinivas B. Bollepalli, and Alex A. Granovsky

J. Vac. Sci. Technol. B 26, 2311 (2008); http://dx.doi.org/10.1116/1.2998700 (5 pages)

Online Publication Date: 1 December 2008

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This article describes the result of predictions based on a novel continuum model for the effect of microstructure on deprotection reaction kinetics during postexposure bake (PEB). The effect of neighboring blocking groups is incorporated in a continuum PEB model. Provided blocking groups with neighbors react at a slower rate than isolated blocking groups, an up to 8% improvement in latent image contrast is predicted. In addition, a first principles calculation of the equilibrium structure for poly(methyl methacrylate-co-t-butyl methyl methacrylate) copolymer with acid present is reported. Hybrid quantum mechanics/molecular mechanics (QC/MM) results indicate that a strong hydrogen bond forms between blocked and unblocked neighbor sites in the presence of acid. The QC/MM prediction provides evidence confirming the rate constant for deprotection reaction with a neighboring blocked site is reduced relative to isolated blocking groups. The new PEB model form is shown to improve the fit to kinetic Fourier transform infrared data over conventional deprotection kinetics for those resists that contain carboxyl group deprotection chemistry. The new model also explains the difference in reaction rate between resists with otherwise identical deprotection chemistry by altering only neighboring blocked site content. Finally, a 50% greater lithographic advantage in development rate contrast is demonstrated for microstructure with increased neighboring blocked sites.
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85.40.Hp Lithography, masks and pattern transfer
back to top Metrology, Alignment, and Inspection

Field-programmable gate array implementation of real-time spatial-phase locking for electron-beam lithography

Yugu Yang and J. T. Hastings

J. Vac. Sci. Technol. B 26, 2316 (2008); http://dx.doi.org/10.1116/1.2991976 (6 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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Spatial-phase locked electron-beam lithography provides feedback control of electron-beam position by monitoring the signal from a fiducial grid on the substrate. Formerly, a real-time spatial-phase-locking algorithm has been implemented on general purpose microprocessor to provide control for raster-scan system. However, it would be advantageous to provide real-time spatial-phase locking for both vector- and raster-scan systems with accelerated sampling and computational rate demanded by many modern electron-beam lithography tools. In addition, it is desirable for the phase-locking system to be easily parallelizable for multibeam/multicolumn systems. Implementation of vector- and raster-scan spatial-phase locking algorithms on a field-programmable gate array (FPGA) addresses both of these issues. Initial experimental results demonstrate that the FPGA implementation can provide real-time spatial-phase locking effectively at accelerated speed even when the algorithm is performed in the noise limited regime.
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84.30.Sk Pulse and digital circuits
42.60.Fc Modulation, tuning, and mode locking
42.82.Cr Fabrication techniques; lithography, pattern transfer

Abbe singular-value decomposition: Compact Abbe’s kernel generation for microlithography aerial image simulation using singular-value decomposition method

Charlie Chung Ping Chen, Ahmet Gurhanli, Tse-Yu Chiang, Jen-Jer Hong, and Lawrence S. Melvin

J. Vac. Sci. Technol. B 26, 2322 (2008); http://dx.doi.org/10.1116/1.3013310 (9 pages)

Online Publication Date: 1 December 2008

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Abbe’s method and Hopkin’s method are among the most popular microlithography aerial image simulation methods. In particular, Hopkin’s method is generally more popular for the high speed aerial image simulation domain, and it is used in model-based optical proximity correction. This is due to a general perception that Hopkin’s method can generate more compact sets of kernels compared with Abbe’s method, due to the application of a singular-value decomposition (SVD) process to Hopkin’s large transmission cross coefficient matrix. On the other hand, the primitive Abbe’s method is very simple, since it only needs to decompose the source field into independent point sources with a two-dimensional partitioning criteria. Albeit its simplicity, compared with Hopkin’s method, in general, Abbe’s method, generates a larger set of kernels. In this article the authors propose applying SVD to the original Abbe’s kernels, the essential kernels according to their singular values. Experimental results show that the algorithm, the Abbe-SVD method, accomplishes over 68 times of both runtime and memory saving over the traditional Hopkin’s SVD method for kernel generation.
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85.40.Hp Lithography, masks and pattern transfer

Aberration correction for electron beam inspection, metrology, and lithography

Eric Munro, John Rouse, Haoning Liu, and Liping Wang

J. Vac. Sci. Technol. B 26, 2331 (2008); http://dx.doi.org/10.1116/1.2991515 (6 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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This article investigates, with computer simulations, whether electron optical aberration correctors could be used to improve the performance of electron beam equipment for the semiconductor manufacturing industry. The simulations are performed using the differential algebraic method. Three types of aberration corrector are investigated: (1) a quadrupole-octopole corrector for critical dimension scanning electron microscopy for metrology and inspection (it is shown that this type of corrector, which corrects spherical and chromatic aberrations, can provide a smaller probe diameter with a larger numerical aperture, thereby improving resolving power and throughput), (2) a hexapole planator for projection electron beam lithography (it is demonstrated that field curvature, astigmatism, and spherical aberration can be corrected, thereby permitting a larger field size), and (3) a mirror corrector for reflective electron beam lithography (it is shown how field curvature and chromatic aberration in such systems can be corrected by using an electron mirror).
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41.85.Gy Chromatic and geometrical aberrations
41.75.Fr Electron and positron beams
85.40.Hp Lithography, masks and pattern transfer
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Study of machine to machine overlay error for sub-60-nm memory devices

Jangho Shin, Sihyeung Lee, Jeongho Yeo, Hochul Kim, Junghyeon Lee, and Woosung Han

J. Vac. Sci. Technol. B 26, 2337 (2008); http://dx.doi.org/10.1116/1.2998727 (4 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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According to the 2007 international technology roadmap for semiconductors, the overlay budget of 60 nm memory devices is 11.3 nm. To meet such a tight requirement, each overlay error budget should be controlled carefully. It turns out that scanner contributions due to machine to machine overlay (MMO) error are nearly half of the total overlay error budget. In a conventional way, overlay errors are corrected by ten linear terms: offset x and y, wafer rotation x and y, wafer magnification x and y, shot rotation x and y, and shot magnification x and y. Especially for the shot correction, average correction values are applied commonly for all shots. MMO cannot be compensated by only linear correction to meet such a tight specification any longer. In this article, a grid matching strategy through per-shot-correction (PSC) is investigated so that scanner contributions are minimized. In PSC, shot correction is implemented for each shot with different correction parameter values. By matching wafer grids from machine to machine, overlay budget is feasible for sub-60-nm memory devices.
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84.30.Sk Pulse and digital circuits

Nanometer-level alignment to a substrate-embedded coordinate system

Euclid E. Moon and Henry I. Smith

J. Vac. Sci. Technol. B 26, 2341 (2008); http://dx.doi.org/10.1116/1.3010734 (4 pages)

Online Publication Date: 1 December 2008

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The authors describe a method that uses infrared (IR) radiation to detect alignment on the nanometer level between grating marks on the front side of a template and a checkerboard-type mark on the back side of an IR-transparent, double-side-polished substrate. The mark can cover the entire substrate back side. No alignment marks are required on the front of the substrate. A back-side-specific mark is utilized with λ = 1065 nm illumination to detect alignment within σ = 0.4 nm.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors

Resist charging effect in photomask: Its impact on pattern placement error and critical dimension

Jin Choi, Dong Seok Nam, Byung Gook Kim, Sang-Gyun Woo, and Han Ku Cho

J. Vac. Sci. Technol. B 26, 2345 (2008); http://dx.doi.org/10.1116/1.2978406 (6 pages)

Online Publication Date: 1 December 2008

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By the development of the double exposure technique or the double patterning technique, the pattern placement error of a photomask is interesting because of its impact on the size and position of wafer pattern. Among various sources to induce the pattern placement error, we have focused on the charging effect of the FEP-171 resist and have shown that the resist charging effect generates the pattern position error of a clear pattern and the critical dimension variation of a dark pattern. Based on experiment and simulation, we present quantitatively the dependence of position error on pattern density, pattern shape, and writing order. Furthermore, we have discussed the model to describe the charging effect and its agreement with experiment and the correction method to remove the resist charging effect.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
81.16.Rf Micro- and nanoscale pattern formation

Self-assembled monolayer fiducial grids for spatial-phase-locked electron-beam lithography

C. B. Samantaray and J. T. Hastings

J. Vac. Sci. Technol. B 26, 2351 (2008); http://dx.doi.org/10.1116/1.2993261 (5 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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The authors characterize a new fiducial grid based on a self-assembled monolayer (SAM) that is well suited to low-energy ( ⩽ 10 keV) spatial-phase locked electron-beam lithography (SPLEBL). SAMs significantly alter the secondary electron yield of the metal films on which they are formed. In addition, SAMs are not expected to strongly scatter the primary beam, even at low energies, because they are less than 2-nm-thick and are composed of low atomic number elements. In this work the authors evaluate the signal-to-noise ratio (SNR) of SAM grids on gold and copper coated electron-beam resist. 400 nm period octadecanethiol fiducial grids were microcontact printed onto the gold and copper metal layers using polydimethylsiloxane stamps. Gold serves as a model system and provides excellent SNR; however, its strong forward scattering makes it impractical in many applications. Copper offers reduced forward scattering but exhibits inverted secondary electron contrast and greatly reduced SNRs. In all cases, SNR decreases with increasing beam energy as overall secondary electron yield decreases. These results suggest that SAM fiducial grids are promising for low-energy SPLEBL; however, further optimization of the interlayer and SAM composition is warranted.
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68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
68.55.J- Morphology of films
back to top Imaging/Microscopy

Development of the compact low-energy soft x-ray CT instrument for the soft material structural analysis

Motosuke Miyoshi, Takao Hamakubo, Tatsuhiko Kodama, Masatoshi Tsuchiya, Atsushi Koishikawa, and Nobutada Aoki

J. Vac. Sci. Technol. B 26, 2356 (2008); http://dx.doi.org/10.1116/1.2978397 (6 pages)

Online Publication Date: 1 December 2008

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Microtomography using the combination of microfocus x-ray source and the cone-beam technique is now becoming widely used in material science and in industry. Recently, the structural analysis of soft materials, such as polymer fibers and biological materials, is strongly required. A compact low-energy soft x-ray computed tomography (CT) instrument capable of soft material observation was developed, and the proof-of-concept system was constructed and evaluated. In this article, the authors describe an instrument that they developed for the x-ray CT of soft materials. A newly developed x-ray tube for generating the low-energy continuum soft x ray is also described. Tomographic observation examples of both biomaterials and industrial polymers are demonstrated.
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81.70.Tx Computed tomography

X-ray diffraction microscopy: Reconstruction with partial magnitude and spatial a priori information

Leili Baghaei Rad, Ian Downes, Bing Dai, Diling Zhu, Andreas Scherz, Jun Ye, Piero Pianetta, and R. Fabian W. Pease

J. Vac. Sci. Technol. B 26, 2362 (2008); http://dx.doi.org/10.1116/1.3002487 (5 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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The goal is to nondestructively reconstruct the structure of a fabricated integrated circuit using x-ray diffraction measurement. In particular, to detect any deviation from the specification of the circuit design. Determining phase is critical. However, additional information exists as the phase of the design specification is known. Further phase information is determined by oversampling and a better estimate of the correct phase is obtained through convex optimization. The authors illustrate this technique with a simulated one dimensional example and a simple two dimensional experimental sample.
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07.85.Tt X-ray microscopes
85.30.De Semiconductor-device characterization, design, and modeling

Scanning proximal probes for parallel imaging and lithography

K. Ivanova, Y. Sarov, Tzv. Ivanov, A. Frank, J. Zöllner, Ch. Bitterlich, U. Wenzel, B. E. Volland, S. Klett, I. W. Rangelow, P. Zawierucha, M. Zielony, T. Gotszalk, D. Dontzov, W. Schott, et al.

J. Vac. Sci. Technol. B 26, 2367 (2008); http://dx.doi.org/10.1116/1.2990789 (7 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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Scanning proximity probes are uniquely powerful tools for analysis, manipulation, and bottom-up synthesis. A massively parallel cantilever-probe platform is demonstrated. 128 self-sensing and self-actuated proximal probes are discussed. Readout based on piezoresistive sensors and bending control based on bimorph dc/ac actuations are described in detail.
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07.79.Lh Atomic force microscopes
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
85.40.Hp Lithography, masks and pattern transfer

Neutral atom and molecule focusing using a Fresnel zone plate

Thomas Reisinger and Bodil Holst

J. Vac. Sci. Technol. B 26, 2374 (2008); http://dx.doi.org/10.1116/1.2987955 (6 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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Focusing of neutral atoms and molecules has several potential applications. The very first microscopy images using helium as an imaging probe were published earlier this year. Another possible application is to study the diffusion of atoms and molecules through materials with high spatial resolution by stepping a porous or permeable sample across the focused beam. With this application in mind, the authors present the best resolution transmission images hitherto achieved with helium atoms (less than 2 μm) of a thin carbon film with 2 μm holes. Furthermore, they present the first experiment using a Fresnel zone plate to focus neutral molecules. They used a beam of deuterium (D2) which was focused down to 15.2±0.5 μm. D2 was chosen because it fits in mass to the geometry of our system, which is optimized for helium. However, the method can be extended to hydrogen (H2) or other molecules by using a suitably adapted zone plate. In both cases the focus was limited by chromatic aberrations, caused by the velocity spread of the beams. Finally, they present calculations exploring the resolution limits for focusing of molecular beams using Fresnel zone plates. The calculations show that Fresnel focusing down to 170 nm full width at half maximum is possible with presently available techniques.
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37.20.+j Atomic and molecular beam sources and techniques
07.77.Gx Atomic and molecular beam sources and detectors
back to top Nanoimprint

Quality assessment of antisticking layers for thermal nanoimprint

H.-C. Scheer, W. Häfner, A. Fidler, S. Möllenbeck, and N. Bogdanski

J. Vac. Sci. Technol. B 26, 2380 (2008); http://dx.doi.org/10.1116/1.3013342 (5 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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Layers from fluorinated trichlorosilanes are in widespread use for the prevention of sticking in nanoimprint. It is generally assumed that these layers are monolayers, bonded to the substrate, and internally cross-linked. The authors have investigated a gas phase deposition process for such layers in detail, varying the amount of antisticking agent and the deposition time in a vacuum process. The quality of the layers was determined from the layer thickness and the contact angle was measured. In accordance with some recent literature, claiming that formation of dense cross-linked monolayers from fluorocarbon-trichlorosilanes is not possible, the results indicate that the deposited layers are not monolayers. Instead the authors suggest that they are even thinner disordered but cross-linked layers. Obviously monolayer formation is not required for sticking prevention.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.08.-p Liquid-solid interfaces
81.16.Nd Micro- and nanolithography

Patterning of polyfluorene based polymer light emitting diodes by reversal imprint lithography

B. L. Cardozo and S. W. Pang

J. Vac. Sci. Technol. B 26, 2385 (2008); http://dx.doi.org/10.1116/1.2976602 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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The authors demonstrated the fabrication of patterned arrays of polymer light emitting diodes (PLEDs) with a polyfluorene based emissive layer using reversal imprint lithography. A stack of patterned metal and polymer films is transferred to a glass substrate in a single reversal imprint step. Two different techniques for coating the patterned Si mold are shown, one involving the spin coating of polymer layers directly onto the mold and one involving inking of the polymers onto the mold from a spin-coated PDMS inkpad. Using these techniques, PLED devices with a minimum feature sizes as small as 1 μm and luminescence starting at 3.5 V have been demonstrated.
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85.60.Jb Light-emitting devices
85.40.Hp Lithography, masks and pattern transfer
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.55.Kz Solid organic materials
81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography

Fabrication of the nanoimprint mold using inorganic electron beam resist with post exposure bake

Noriyuki Unno, Jun Taniguchi, Miyako Shizuno, and Kiyoshi Ishikawa

J. Vac. Sci. Technol. B 26, 2390 (2008); http://dx.doi.org/10.1116/1.3010735 (4 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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Nanoimprint lithography (NIL) is the preferred technique for next-generation nanometer-scale patterning because of its cost effectiveness and simplicity when compared to conventional technology. The replicated pattern depends on the mold pattern, hence efficient methods for fabricating the fine mold are critically required and have recently become intensive subjects of research. This study reports a new method for the fabrication of a fine mold: this method uses low-acceleration-voltage (4 kV) electron beam lithography with spin on glass (SOG), which is used as a positive-tone inorganic resist. Although our SOG process does not contain chemically amplified material, postexposure bake (PEB) was characteristically used in the authors’ process. The PEB process caused the annealing effect for the SOG and also suppressed the proximity effect. Consequently, a line-and-space pattern nanoimprint mold with a sub-50 nm spacing was fabricated at 4 kV using their process, and ultraviolet NIL was successfully carried out using the fabricated mold.
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85.40.Hp Lithography, masks and pattern transfer

Fluorinated diamondlike carbon templates for high resolution nanoimprint lithography

M. Schvartzman, A. Mathur, Y. Kang, C. Jahnes, J. Hone, and S. J. Wind

J. Vac. Sci. Technol. B 26, 2394 (2008); http://dx.doi.org/10.1116/1.3013281 (5 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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Nanoimprint templates were fabricated from diamondlike carbon (DLC) films grown on Si, using negative-tone e-beam lithography and oxygen plasma etching. An antiadhesion coating was provided through fluorocarbon-based plasma treatment, which was found to form a Teflon-like thin layer on the treated DLC surface. The fluorinated templates were used to imprint arrays of dots with diameters down to 10 nm in polymethyl-methacrylate. Application of the fluorocarbon plasma treatment was also demonstrated in the antiadhesion treatment of the nanoimprint resist and in elastomer molding.
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81.05.U- Carbon/carbon-based materials
81.16.Nd Micro- and nanolithography
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

Experimental and numerical analyses on recovery of polymer deformation after demolding in the hot embossing process

Hideki Takagi, Masaharu Takahashi, Ryutaro Maeda, Yuki Onishi, Yasuroh Iriye, Takuya Iwasaki, and Yoshihiko Hirai

J. Vac. Sci. Technol. B 26, 2399 (2008); http://dx.doi.org/10.1116/1.2987956 (5 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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In a hot embossing process, optimization of the demolding temperature is quite important to achieve high throughput because the cooling step before demolding takes a relatively long time in the process cycle. The authors experimentally examined the influence of demolding temperature on polymer deformation. Polymer deformation was also examined using a finite element simulation tool which assumed the polymer as a viscoelastic body represented by the generalized Maxwell model. In both experiments and numerical simulations, demolding at higher temperature resulted in smaller deformation. Numerical simulations revealed that recovery of polymer deformation occurred in the cooling step after demolding at temperatures higher than the glass transition temperature of polymer. In addition, numerical simulation enables detailed analysis of the impacts of various parameters on the recovery phenomena. This numerical simulation method is expected to be a powerful tool for optimization of the hot embossing process cycle.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations

Improving organic thin-film transistor performance by nanoimprint-induced chain ordering

Dehu Cui, Huifeng Li, Hyunsoo Park, and Xing Cheng

J. Vac. Sci. Technol. B 26, 2404 (2008); http://dx.doi.org/10.1116/1.3013301 (6 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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The chain configuration in conjugated polymer films has a significant impact on the electronic and optical properties of polymer semiconductors, which in turn dictate the device performances of polymer electronics. This article presents a new method to control chain orientation in polymer semiconductors by direct nanoimprint. Nanoimprint-induced chain orientation in conjugated polymer imparts strong optical birefringence in patterned microstructures. X-ray diffraction on patterned films exhibits higher level of chain ordering as nanoimprint temperature increases. Polarized absorption spectra show progressive redshift at higher nanoimprint temperature. The carrier mobility in thin-film transistors based on nanoimprinted grating equals to 12 times of that without patterning. Anisotropies of material properties and device performance are observed in all conjugated polymer structures and devices patterned by nanoimprint. It is expected that the unique ability to control chain orientation will enable nanoimprint to play an important role in tailoring the performance of polymer electronics and sensors.
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85.30.Tv Field effect devices
78.20.Fm Birefringence
72.20.Fr Low-field transport and mobility; piezoresistance
78.66.Qn Polymers; organic compounds
71.20.Rv Polymers and organic compounds
61.41.+e Polymers, elastomers, and plastics

Full field imprint masks using variable shape beam pattern generators

Kosta Selinidis, Ecron Thompson, Gerard Schmid, Nick Stacey, Joseph Perez, John Maltabes, S. V. Sreenivasan, Douglas J. Resnick, Akjko Fujii, Yuko Sakai, Shiho Sasaki, and Naoya Hayashi

J. Vac. Sci. Technol. B 26, 2410 (2008); http://dx.doi.org/10.1116/1.2976573 (6 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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Imprint lithography has been included on the ITRS lithography roadmap at the 32, 22, and 16 nm nodes. Step and flash imprint lithography (S-FIL®) is a unique method that has been designed from the beginning to enable precise overlay for creating multilevel devices. A photocurable low viscosity monomer is dispensed dropwise to meet the pattern density requirements of the device, thus enabling imprint patterning with a uniform residual layer across a field and across entire wafers. Further, S-FIL provides sub-100-nm feature resolution without the significant expense of multielement, high quality projection optics, or advanced illumination sources. However, since the technology is 1X, it is critical to address the infrastructure associated with the fabrication of templates. For device manufacturing, one of the major technical challenges remains the fabrication of full field 1X templates with commercially viable write times. Recent progress in the writing of sub-40-nm patterns using commercial variable shape e-beam tools and nonchemically amplified resists has demonstrated a very promising route to realizing these objectives, and in doing so, has considerably strengthened imprint lithography as a competitive manufacturing technology for the sub-32-nm node. Here the authors report the first imprinting results from sub-40-nm full field patterns, using Samsung’s current flash memory production device design. The fabrication of the template is discussed and the resulting critical dimension control and uniformity are reported. A second experiment has also demonstrated feasibility for resolving several types of features at half pitches of 32 nm.
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85.40.Hp Lithography, masks and pattern transfer
84.30.Sk Pulse and digital circuits

Contact angles in a thermal imprint process

Nicolas Bogdanski, Saskia Möllenbeck, and Hella-Christin Scheer

J. Vac. Sci. Technol. B 26, 2416 (2008); http://dx.doi.org/10.1116/1.2987967 (5 pages)

Online Publication Date: 1 December 2008

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In a thermal imprint process, contact angles may evolve in two situations, between the stamp and the polymer, when a cavity remains unfilled, or, in cases where the polymer locally dewets the substrate, between the substrate and the polymer. For two polymers of different polarity, such contact angles are determined experimentally and compared to values calculated from surface energy data. In doing so, the specific temperature dependence of surface energies of a thermoplastic polymer as well as the typical course of an imprint process, where cooling times often exceed the imprint times, are considered. The differences between experimental and theoretical values are critically discussed. The results indicate that the respective adhesive layers govern the surface status of the substrate and the stamp as well.
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68.08.-p Liquid-solid interfaces
68.03.Cd Surface tension and related phenomena
68.35.Md Surface thermodynamics, surface energies
82.35.Gh Polymers on surfaces; adhesion

Metal transfer assisted nanolithography on rigid and flexible substrates

Myung-Gyu Kang and L. Jay Guo

J. Vac. Sci. Technol. B 26, 2421 (2008); http://dx.doi.org/10.1116/1.2993172 (5 pages) | Cited 9 times

Online Publication Date: 1 December 2008

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A nanolithography technique based on metal transfer printing is demonstrated. The transferred metal conveniently acts as an etch mask for pattern transfer to a substrate. This lithography technique can be used on flexible plastic substrate as well as on rigid substrate due to the low pressure and temperature used in the metal transfer process. Dense nanosize metal particle arrays with different shapes such as square, diamond, and nanobar were created with high yield over large area, and localized surface plasmon spectra of those particle arrays were measured. Pattern linewidth was reduced to 50 nm in metal grating by depositing metals on the poly(dimethysiloxane) grating sidewall using a shadow evaporation process.
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81.16.Nd Micro- and nanolithography
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Easy duplication of stamps using UV-cured fluoro-silsesquioxane for nanoimprint lithography

Carlos Pina-Hernandez, Peng-Fei Fu, and L. Jay Guo

J. Vac. Sci. Technol. B 26, 2426 (2008); http://dx.doi.org/10.1116/1.2987966 (4 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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A simple procedure for duplicating original nanoimprint masters was developed by using a new fluorinated photocurable silsesquioxane (SSQ) resin cast on either hard or flexible substrates. With an appropriate viscosity, this resin can be spin coated on the substrate, and the original SiO2 masters easily replicated in this resin by using a low pressure nanoimprinting process. The resin has a sufficient modulus in its cured state, which makes it suitable for nanoimprinting other polymeric materials. Due to the high thermal stability and UV transparency of SSQ materials, such a stamp can be used for both UV and thermal nanoimprinting. Furthermore, the fluoroalkyl groups contained in the silsesquioxane resin provide the low surface energy necessary for easy demolding after nanoimprinting. These features combined make the material an excellent candidate to fabricate a multitude of duplicates from an original nanoimprint lithography master for mass fabrication.
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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

Comparison of monomer and polymer resists in thermal nanoimprint lithography

M. Zelsmann, K. Perez Toralla, J. De Girolamo, D. Boutry, and C. Gourgon

J. Vac. Sci. Technol. B 26, 2430 (2008); http://dx.doi.org/10.1116/1.3013863 (4 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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In this article, the authors compare a polymer resist to a thermally curable monomer resist in a full 8 in. wafer thermal nanoimprint lithography process. Using exactly the same imprinting conditions, the authors compare the printing quality and investigate the resist distribution through large area gratings (6×6 mm2) with various densities. It is shown that a liquid monomer solution greatly enhance the printing uniformity because of a much wider resist redistribution and flow during the process. Redistribution of the monomer resist is observed over an entire grating, while it is observed only over a few periods of a grating for the polymer in the same conditions. Furthermore, a low molecular weight resist allows reducing the imprinting force as well as the total cycle time.
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81.16.Nd Micro- and nanolithography
back to top Process Simulation

Exploration of etch step interactions in the dual patterning process for process modeling

Lawrence S. Melvin, Brian S. Ward, Hua Song, Sang Uhk Rhie, Kevin D. Lucas, Vincent Wiaux, Staf Verhaegen, and Mireille Maenhoudt

J. Vac. Sci. Technol. B 26, 2434 (2008); http://dx.doi.org/10.1116/1.3021377 (7 pages)

Online Publication Date: 1 December 2008

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Double patterning is a manufacturing process targeted for the 22 nm half pitch manufacturing node that harbors strong potential for reaching high volume manufacturing. The double patterning process requires twice as many manufacturing steps for a device layer as are required for a traditional single reticle device layer. However, the double patterning process does have a direct interaction between the individually processed layers at the final etch processing step. Current optical proximity correction process modeling capabilities can be designed to account for the interactions between these two processes. However, it is unclear at this time whether or not real process differences are present due to an interaction between the two patterns in double patterning. It is also not certain if proximity effects play a role in the process. This study will use currently available data from the IMEC double patterning process to determine if there is a significant interaction between the photoresist and hardmask patterns during substrate etch, and if there is a significant interaction, a discussion of how a process model could be constructed to capture this effect.
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81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
81.16.Rf Micro- and nanoscale pattern formation

Pattern specific optical models

Edita Tejnil, Konstantinos Adam, Michael C. Lam, and Gabriel Berger

J. Vac. Sci. Technol. B 26, 2441 (2008); http://dx.doi.org/10.1116/1.2991518 (6 pages)

Online Publication Date: 1 December 2008

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Computational efficiency of the models used in optical proximity correction (OPC) continues to be important in photolithography employing resolution enhancement. Improved hardware and model efficiency can mitigate the increase in run time resulting from the rise in modeling complexity necessary to meet advanced semiconductor process requirements. The current approach for fast image calculations in OPC utilizes the Hopkins formulation of the imaging equations combined with the sum-of-coherent-systems (SOCS) approximation. In this paper, approaches to identify the SOCS terms, which can be neglected in an OPC model applied to a given layout, are explored. One approach is quantified in terms of computational efficiency and model accuracy. The pattern-specific computational efficiency improvement ranges from 7% to 55% for six different patterning conditions used in 193 nm immersion lithography at the 45 nm semiconductor technology node.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Rf Micro- and nanoscale pattern formation
42.30.Sy Pattern recognition
back to top Beam Induced Processing

Catalyst patterning for carbon nanotube growth on elevating posts by self-aligned double-layer electron beam lithography

M. Häffner, A. Heeren, A. Haug, E. Schuster, A. Sagar, M. Fleischer, H. Peisert, M. Burghard, T. Chassé, and D. P. Kern

J. Vac. Sci. Technol. B 26, 2447 (2008); http://dx.doi.org/10.1116/1.2991516 (4 pages)

Online Publication Date: 1 December 2008

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For gas-flow aligned growth of carbon nanotubes (CNTs), it is important to minimize interaction of the growing CNTs with the substrate. The authors present a method to fabricate thin catalyst films on top of protruding hydrogen silsesquioxane (HSQ) patterns. Self-alignment of the catalyst film with the HSQ pattern is achieved by exposing two layers of resist, polymethyl methacrylate (PMMA) on top of HSQ, simultaneously. By selecting appropriate development parameters for PMMA and HSQ, a common exposure dose can be applied. After a standard lift-off process HSQ is developed and CNTs are grown on the protruding HSQ patterns resulting in gas-flow aligned CNTs that can be further processed, e.g., for the fabrication of CNT based transistors.
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81.07.De Nanotubes
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

Direct patterning of plasma enhanced chemical vapor deposition silicon dioxide by electron beam lithography

Devin K. Brown

J. Vac. Sci. Technol. B 26, 2451 (2008); http://dx.doi.org/10.1116/1.2998704 (4 pages)

Online Publication Date: 1 December 2008

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Hydrogen silsesquioxane (HSQ) is a popular high resolution negative tone resist for electron beam lithography. This work investigates whether a HSQ-like film can be mimicked via plasma enhanced chemical vapor deposition (PECVD) rather than spin coating. It is shown that PECVD oxide acts as mainly a negative tone resist.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
68.55.aj Insulators

Preferential orientation effects in partial melt laser crystallization of silicon

D. J. Witte, M. P. A. Masbou, F. Crnogorac, R. F. W. Pease, and D. S. Pickard

J. Vac. Sci. Technol. B 26, 2455 (2008); http://dx.doi.org/10.1116/1.2998702 (5 pages)

Online Publication Date: 1 December 2008

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The ability to produce a known crystalline orientation in semiconductor materials is essential for many applications, including monolithic three-dimensional integration of devices. In particular, crystallization must be done without exceeding the thermal budget of surrounding or underlying devices. Using a 532 nm laser pulse of 2 ms duration on a 185 nm thick amorphous silicon film, the authors demonstrate that partial melting of silicon can yield crystallites several microns in size with a strong ⟨001⟩ preferential orientation. They investigate the effects of laser pulse duration, film thickness, and heat flow rate on the degree of texturing. By using a thinner silicon film and reducing the laser pulse duration further, such a process could be compatible with the thermal constraints of three-dimensional integration.
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68.55.ag Semiconductors
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition

Electron-beam-induced deposition of platinum at low landing energies

A. Botman, D. A. M. de Winter, and J. J. L. Mulders

J. Vac. Sci. Technol. B 26, 2460 (2008); http://dx.doi.org/10.1116/1.2976576 (4 pages) | Cited 6 times

Online Publication Date: 1 December 2008

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Electron-beam-induced deposition of platinum from methylcyclopentadienyl-platinum-trimethyl was performed with a focused electron beam at low landing energies, down to 10 eV. The deposition growth rate is maximal at 140 eV, with the process being over ten times more efficient than at 20 kV. No significant dependence of composition with landing energy was found in the deposits performed at energies between 40 and 1000 eV. This study provides further evidence for the dissociation process being primarily driven by the sub-20-eV secondary electrons.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.40.Sz Deposition technology

Investigation of morphological changes in platinum-containing nanostructures created by electron-beam-induced deposition

A. Botman, M. Hesselberth, and J. J. L. Mulders

J. Vac. Sci. Technol. B 26, 2464 (2008); http://dx.doi.org/10.1116/1.2990790 (4 pages) | Cited 7 times

Online Publication Date: 1 December 2008

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Focused electron-beam-induced deposition (EBID) allows the rapid fabrication of three-dimensional nanodevices and metallic wiring of nanostructures, and is a promising technique for many applications in nanoresearch. The authors present two topics on platinum-containing nanostructures created by EBID. First, they report on a TEM study of the microstructure of nanodeposits created from Pt(PF3)4. They have performed imaging and electron energy loss spectroscopy with a transmission electron microscope (TEM). The deposited material, composed mainly of platinum, phosphor, oxygen, and trace amounts of fluorine, is amorphous. Platinum is evenly distributed in the nanostructure, while phosphorus is observed to cluster. The size and amount of phosphorus clusters depend on the thickness of the structure. Second, they document an aging process in structures created from MeCpPtMe3, which have a resistivity which increases with the time they are exposed to air, from 2×105 to 1.8×108 μΩ cm over 55 days. They demonstrate that covering the structures with an EBID-deposited insulating protective layer of TEOS can prevent this oxidation. In doing so, they achieved the lowest reported resistivity for EBID from this platinum precursor, of 1.5×103 μΩ cm.
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61.46.-w Structure of nanoscale materials
81.16.-c Methods of micro- and nanofabrication and processing
81.40.Gh Other heat and thermomechanical treatments
79.20.Uv Electron energy loss spectroscopy
81.65.-b Surface treatments
73.63.Bd Nanocrystalline materials

Ion track lithography and graphitic nanowires in diamondlike carbon

J. Krauser, A.-K. Nix, H.-G. Gehrke, H. Hofsäss, C. Trautmann, A. Weidinger, F. Wünsch, and J. Bruns

J. Vac. Sci. Technol. B 26, 2468 (2008); http://dx.doi.org/10.1116/1.3010738 (5 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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Ion track lithography is well established and is based on heavy ions of several hundred MeV energy passing through a polymer film and thereby changing the material properties along the trajectory of each ion. By selective chemical track etching, small channels (down to 20–30 nm diameter) are formed which can be filled with another material or can serve as mask for further etching steps. Another application uses unetched ion tracks directly for nanostructuring. The authors’ investigations showed that graphitic nanowires are formed along ion tracks in insulating diamondlike carbon films. The diameter of these conducing filaments is in the order of 8 nm. In the present article the authors describe a combination of these two possibilities to create several nanodevices such as cold field emission devices, quantum-based electronics, or interconnections in very-large-scale integrated circuits. Since the lithographic structure and the conducting filament are produced by the same ion track, the two parts of the device are self-aligned and need no further adjustment. Furthermore, it should be mentioned that the structure is created by a single ion and therefore is automatically very small in diameter and does not require special beam focusing.
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81.16.Nd Micro- and nanolithography
85.35.-p Nanoelectronic devices
85.40.Ls Metallization, contacts, interconnects; device isolation
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer
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)

Optical properties of sputtered fluorinated ethylene propylene and its application to surface-plasmon resonance sensor fabrication

P. D. Keathley and J. T. Hastings

J. Vac. Sci. Technol. B 26, 2473 (2008); http://dx.doi.org/10.1116/1.3013368 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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The optical properties of sputtered fluorinated ethylene propylene (FEP) thin films (100–400 nm) were analyzed using spectroscopic ellipsometry. Glass (similar to BK7) and silicon substrates were used, and deposition rates on glass were found to be on average 37% higher than on silicon. Refractive indices of the deposited films at 630 nm ranged from 1.379 to 1.392 on glass and from 1.381 to 1.417 on Si, which roughly corresponds to a 4.3% increase when compared to the bulk material value of 1.335. By using the optical properties of the deposited FEP films, it was shown through modeling that they present a possible alternative when fabricating dual-mode surface-plasmon resonance sensors that can differentiate bulk and surface refractive index changes.
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78.66.Qn Polymers; organic compounds
42.79.Pw Imaging detectors and sensors
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
78.68.+m Optical properties of surfaces
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Relief and trench formation on chalcogenide thin films using electron beams

G. B. Hoffman, W.-C. Liu, W. Zhou, R. Sooryakumar, P. Boolchand, and R. M. Reano

J. Vac. Sci. Technol. B 26, 2478 (2008); http://dx.doi.org/10.1116/1.3002564 (6 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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Electron beam irradiation of amorphous GeSe4 thin films reveals formation of reliefs and trenches as a function of electron beam dose. Mounds as high as 115 nm are observed at low electron beam dose and trenches as deep as 180 nm at high dose. The geometry of trench and mound formation is examined as a function of electron beam dose, film thickness, conductive overlayer thickness, exposure count, and beam step size. Thicker films are found to more likely form trenches than thinner ones. Physical mechanisms for trench and mound formation are proposed. Both types of deformations provide a route toward the direct write of optical waveguides, gratings, and waveguide-cavity coupled structures onto thin films of chalcogenide glass.
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68.55.-a Thin film structure and morphology
61.80.Fe Electron and positron radiation effects
61.43.Fs Glasses
back to top Diblock Copolymers

Impact of trench width roughness on the graphoepitaxial assembly of block copolymers

Adam M. Welander, Paul F. Nealey, Heidi Cao, and Robert Bristol

J. Vac. Sci. Technol. B 26, 2484 (2008); http://dx.doi.org/10.1116/1.2987963 (5 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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In this paper, the authors investigated constraints on the quality of topographic features needed for graphoepitaxial assembly of cylinder forming poly(styrene-b-methyl methacrylate) (PS-b-PMMA) thin films, showing the impact of trench width roughness (TWR) on feature size uniformity and defect formation. Topographically patterned substrates were prepared using chemically amplified photoresist and reactive ion etching in conjunction with commercially available lithographic tools and masks. A dose/focus array was utilized to systematically produce trenches with widths between 40 and 400 nm with roughness of 5–35 nm on top of which block copolymers were assembled. Scanning electron microscopy images were taken and analyzed using IMAGEJ software for the metrology of the trenches and ordered block copolymer domains after the removal of the PMMA cylinders. Analysis showed little or no change in domain size variation of the block copolymer with respect to the TWR of lithographically defined features. The impact of TWR on defect formation is qualitatively investigated by classifying all images as having few, some, or many defects. From this analysis, the commensurability between the natural length scale of the block copolymer (l0) and the trench width (W) had a significant effect on defectivity, whereas TWR did not play a dominant role.
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85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
68.08.Bc Wetting
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.35.bm Polymers, organics

Si-containing block copolymers for self-assembled nanolithography

C. A. Ross, Y. S. Jung, V. P. Chuang, F. Ilievski, J. K. W. Yang, I. Bita, E. L. Thomas, Henry I. Smith, K. K. Berggren, G. J. Vancso, and J. Y. Cheng

J. Vac. Sci. Technol. B 26, 2489 (2008); http://dx.doi.org/10.1116/1.2981079 (6 pages) | Cited 9 times

Online Publication Date: 1 December 2008

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Block copolymers can self-assemble to generate patterns with nanoscale periodicity, which may be useful in lithographic applications. Block copolymers in which one block is organic and the other contains Si are appealing for self-assembled lithography because of the high etch contrast between the blocks, the high etch resistance of the Si-containing block, and the high Flory–Huggins interaction parameter, which is expected to minimize line edge roughness. The locations and long range order of the microdomains can be controlled using shallow topographical features. Pattern generation from poly(styrene)-poly(ferrocenyldimethylsilane) and poly(styrene)-poly(dimethylsiloxane) block copolymers, and the subsequent pattern transfer into metal, oxide, and polymer films, is described.
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81.16.Nd Micro- and nanolithography
81.16.Dn Self-assembly
61.41.+e Polymers, elastomers, and plastics
81.16.Rf Micro- and nanoscale pattern formation
68.55.am Polymers and organics

Directed assembly of asymmetric ternary block copolymer-homopolymer blends using symmetric block copolymer into checkerboard trimming chemical pattern

Huiman Kang, Gordon S. W. Craig, and Paul F. Nealey

J. Vac. Sci. Technol. B 26, 2495 (2008); http://dx.doi.org/10.1116/1.3013336 (5 pages) | Cited 6 times

Online Publication Date: 1 December 2008

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Here, the authors studied the directed assembly of the asymmetric ternary blends, composed of polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) and the corresponding PS and PMMA homopolymers, on a checkerboard chemical pattern which was fabricated by e-beam lithography, controlling the periodicity (LS), length (D), and spacing of the exposed lines or dashed lines in the chemical pattern. The checkerboard chemical pattern, which cannot be generated with typical self-assembled block copolymer morphologies, consists of either offset, parallel, dashed lines, or alternating lines and dashed lines, and is used in the fabrication of dynamic random access memory. The degree of perfection and domain uniformity of the assembled block copolymer thin films on the complex pattern were a function of the commensurability of the volume fraction of PS in the blend (ϕS) with the fraction of area on the pattern wet by PS (FS), as well as the volume fraction of homopolymer in the blend (ϕH). The best assembly occurred ϕS and FS were commensurate, and ϕH was optimized for the given blend and pattern.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.55.J- Morphology of films
85.40.Hp Lithography, masks and pattern transfer
84.30.Sk Pulse and digital circuits

The replication of three dimensional structures using UV curable nanoimprint lithography

K. Mohamed, M. M. Alkaisi, and R. J. Blaikie

J. Vac. Sci. Technol. B 26, 2500 (2008); http://dx.doi.org/10.1116/1.3021375 (4 pages)

Online Publication Date: 1 December 2008

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The study investigates the use of ultraviolet nanoimprint lithography (UV-NIL) for patterning three dimensional (3D) structures. Generating the 3D structures is a challenging task especially on an insulating substrate such as quartz. These transparent molds are essential for the UV-NIL process. The 3D profiles were created on the negative tone photoresist, Microresist ma-N2403 using a Raith150 electron beam lithography (EBL) tool in a single step variable dose controlled exposure. The developed 3D resist profiles subsequently were utilized as the 3D masking layer. The 3D patterns were transferred into the quartz mold substrates by a single-step reactive ion etching (RIE). The replication of the 3D mold structure by using the UV-NIL technique requires a two-step imprint process. The master mold profile was replicated onto a Microresist Ormocomp US-S4 resist on the first imprint to become the soft mold. The cured Ormocomp soft mold, subsequently was used as a mold for replicating the 3D pattern structures on the Microresist mr-UVCur06 resist in the second imprint step to create a positive replica of the original mold. A test pattern of a 3D pyramid-shaped array with multilevel features was successfully been replicated using this technique. The replicated 3D pattern on the resist could be utilised as the final 3D masking layer for the pattern transfer onto final substrate using RIE.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
81.16.Rf Micro- and nanoscale pattern formation

In situ characterization of block copolymer ordering on chemically nanopatterned surfaces by time-resolved small angle x-ray scattering

K. O. Stuen, C. Liu, A. M. Welander, G. Liu, J. J. de Pablo, P. F. Nealey, D. K. Satapathy, K. Nygård, O. Bunk, H. H. Solak, and J. F. van der Veen

J. Vac. Sci. Technol. B 26, 2504 (2008); http://dx.doi.org/10.1116/1.2991977 (5 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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The assembly of lamella-forming block copolymer blend thin films on chemically nanopatterned striped surfaces was monitored in real time with small angle x-ray scattering (SAXS) in transmission mode. The strongest diffraction from the assembled grating structure was detected after 4.5 min of annealing as the temperature was ramped from 100 to 240 °C at a rate of about 20 °C/min. Real-space images were also obtained from samples annealed for specific times using top-down scanning electron microscopy (SEM) and this identified structures formed during annealing that are unique to the block copolymer blends. The data are compared to previously reported SEM and molecular simulation studies with pure block copolymers. Because it can be used in real time and probes the entire film thickness, transmission SAXS proved to be a useful tool for better understanding the block copolymer annealing process.
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82.35.Gh Polymers on surfaces; adhesion
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.16.Rf Micro- and nanoscale pattern formation
81.40.Gh Other heat and thermomechanical treatments
68.55.am Polymers and organics
78.70.Ck X-ray scattering
back to top Directed Self Assembly

Carbon nanotube–based magnetic actuation of origami membranes

Hyun Jin In, Hyungwoo Lee, Anthony J. Nichol, Sang-Gook Kim, and George Barbastathis

J. Vac. Sci. Technol. B 26, 2509 (2008); http://dx.doi.org/10.1116/1.3002559 (4 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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Multiwalled carbon nanotubes (CNTs) with nickel and cobalt catalyst tips have been grown on foldable titanium nitride membranes. Once magnetized to saturation under an external magnetic field, these ferromagnetic tips, which reside atop each CNT, can be used to actuate the entire membrane on which the nanotubes are grown. Magnetic modeling is performed to analyze the magnetic properties of the teardrop-shaped CNT tips, and initial experimental results show that magnetic torques and forces arising from the CNT tips are sufficient to rotate the membrane up to 180° and keep it latched without springing back.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
81.16.Hc Catalytic methods
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
85.35.Kt Nanotube devices
85.70.-w Magnetic devices

Assisted convective-capillary force assembly of gold colloids in a microfluidic cell: Plasmonic properties of deterministic nanostructures

T. Pinedo Rivera, O. Lecarme, J. Hartmann, E. Rossitto, K. Berton, and D. Peyrade

J. Vac. Sci. Technol. B 26, 2513 (2008); http://dx.doi.org/10.1116/1.3021396 (7 pages) | Cited 6 times

Online Publication Date: 1 December 2008

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A new colloidal assembly technique in a microfluidic cell is proposed in this work. This technique is based on classic capillary force assembly (CFA) assisted by air-suction flow and temperature control during the assembly process. Their influence on the assembly macroscopic (triple contact-line speed, receding contact angle) and microscopic (colloidal motion at the triple contact line) parameters is examined. It is shown that the extent and the performance of the assembly process are significantly enhanced by this approach. Finally, the plasmonic properties of deterministic linear (2–5 colloid long) and tripod gold nanostructures created with this technique are investigated.
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81.16.Dn Self-assembly
82.70.Dd Colloids
78.66.Bz Metals and metallic alloys

Pulsed laser techniques for nanographoepitaxy

F. Crnogorac, D. J. Witte, and R. F. W. Pease

J. Vac. Sci. Technol. B 26, 2520 (2008); http://dx.doi.org/10.1116/1.3013373 (4 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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Graphoepitaxy is a technique that has been demonstrated as a means for fashioning regions of single crystal semiconductors on amorphous substrates. In that earlier work the heating period was long (1 s or more) and the substrate needed to be held close to the melting point of the semiconductor. With a view to achieving three-dimensional integrated circuits, the authors have investigated the possibility using graphoepitaxy to yield device quality single crystal islands of silicon on an amorphous substrate without excessive heating of the underlying layers by using transient (<1 ms) heating. A stationary laser pulse of 532 nm wavelength, 100 μs duration, and 22 μm diameter impinged on a 50 nm thick amorphous silicon film deposited on 12 nm thick SiO2 inverted pyramid template. We demonstrated successful graphoepitaxial orientation of crystallized silicon but only under conditions that gave excessive heating (>400 °C) of lower layers, thus indicating that this technique is impractical for three-dimensional integrated circuits.
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81.16.Nd Micro- and nanolithography
68.55.ag Semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.Mk Laser-assisted deposition
61.72.Cc Kinetics of defect formation and annealing
81.15.Fg Pulsed laser ablation deposition

Directed self-assembly of individual vertically aligned carbon nanotubes

Amit Goyal, Sheng Liu, Zafar Iqbal, Linus A. Fetter, and Reginald C. Farrow

J. Vac. Sci. Technol. B 26, 2524 (2008); http://dx.doi.org/10.1116/1.2990788 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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The deposition of high-aspect-ratio particles such as carbon nanotubes may be done in sub-100-nm windows in insulating thin films over metal using electrophoresis. Surface charge on the insulator causes the windows to become nanoscopic electrostatic lenses. Under certain conditions only one nanotube will be deposited at the base of a window. Finite element analysis shows that the number of deposited nanotubes is controlled by the electric field and the geometry of the windows and nanotubes. This discovery enables the process integration of carbon-based electronics with more traditional technologies such as complementary metal oxide semiconductor using the current generation of lithography and process technology. Devices such as vertical field effect transistors and interconnected nanoprobe arrays may now be fabricated in the metal levels to facilitate three-dimensional polylithic circuit architectures.
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81.16.Dn Self-assembly
68.55.aj Insulators
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution
85.35.Kt Nanotube devices
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
back to top New Nanopatterning Techniques

Three-dimensional alignment with 10 nm order accuracy in electron-beam lithography on rotated sample for three-dimensional nanofabrication

Kenji Yamazaki and Hiroshi Yamaguchi

J. Vac. Sci. Technol. B 26, 2529 (2008); http://dx.doi.org/10.1116/1.2976600 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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Three-dimensional (3D) alignment with 10 nm order accuracy in 3D electron-beam (EB) lithography has been achieved by means of highly accurate rotation control and mark location using the transmission electron signal. Accurately aligned EB writing from various directions on micron order resists blocks on a small substrate provides great structural flexibility in the creation of 3D nanostructures. As a demonstration of the accuracy, a 3D hydrogen silsesquioxane nanostructure was made by 3D EB writing and two-step development using different developers. Moreover, a 3D poly(methyl methacrylate) nanostructure was made by repeated 3D EB writing and development to demonstrate 3D nanofabrication with great structural flexibility.
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81.16.Nd Micro- and nanolithography

Microscale self-assembly using molten alloys with different melting points

Christopher J. Morris and Madan Dubey

J. Vac. Sci. Technol. B 26, 2534 (2008); http://dx.doi.org/10.1116/1.2978395 (5 pages)

Online Publication Date: 1 December 2008

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The authors demonstrate a system for self-assembling 280 μm sized parts onto a separate template using two molten alloys having differing melting points. The use of two alloys decoupled the formation of mechanical and electrical connections and improved the resulting electrical contact resistance by over two orders of magnitude.
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85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Cg Contact resistance, contact potential

Chip-based microfabricated electrospinning nozzles

Leon M. Bellan, Chris Alpha, Tom Corso, Jack Henion, and Harold G. Craighead

J. Vac. Sci. Technol. B 26, 2539 (2008); http://dx.doi.org/10.1116/1.2976579 (4 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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The authors have used microfabricated nozzles with inner diameters as small as 5 μm to produce electrospinning jets. A chip containing an array of individually addressable nozzles was incorporated with a commercial automated fluid delivery system and a floating high voltage supply. Using this system, the authors were able to produce polymeric nanofibers with various geometries, including beads-on-a-string, straight continuous fiber, and fibers that had broken in flight. The authors have shown that the use of this small electrospinning nozzle produces a smaller, more uniform spot compared to other source geometries.
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47.85.Np Fluidics
47.60.Kz Flows and jets through nozzles
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.20.-n Methods of materials synthesis and materials processing
back to top Cell/Pattern Interactions

High-aspect-ratio plasma-induced nanotextured poly(dimethylsiloxane) surfaces with enhanced protein adsorption capacity

M. E. Vlachopoulou, P. S. Petrou, S. E. Kakabakos, A. Tserepi, and E. Gogolides

J. Vac. Sci. Technol. B 26, 2543 (2008); http://dx.doi.org/10.1116/1.3010723 (6 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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The use of SF6 plasma-nanotextured poly(dimethylsiloxane) (PDMS) substrates of columnarlike surface topography as templates for protein adsorption is presented. Fresh and aged plasma-nanostructured surfaces are investigated, since ageing affects surface wettability, a critical parameter in protein adsorption. It is found that protein adsorption on such substrates increases with plasma treatment duration and surface ageing. An enhancement (up to ten times) in adsorption of biotinylated bovine serum albumin is observed on aged nanostructured PDMS substrates compared to untreated ones. Good spot homogeneity is obtained on surfaces treated for up to 6 min. The use of optimized plasma-nanostructured surfaces as substrates for protein microarrays of intense and uniform spots is demonstrated.
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87.80.-y Biophysical techniques (research methods)
87.14.E- Proteins
87.15.-v Biomolecules: structure and physical properties
52.77.-j Plasma applications
81.65.-b Surface treatments
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging

Fabrication of elastomer pillar arrays with modulated stiffness for cellular force measurements

S. Ghassemi, N. Biais, K. Maniura, S. J. Wind, M. P. Sheetz, and J. Hone

J. Vac. Sci. Technol. B 26, 2549 (2008); http://dx.doi.org/10.1116/1.3013424 (5 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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The mechanical properties of a cell’s environment can alter behavior such as migration and spreading, and control the differentiation path of stem cells. Here the authors describe a technique for fabricating substrates whose rigidity can be controlled locally without altering the contact area for cell spreading. The substrates consist of elastomeric pillar arrays in which the top surface is uniform but the pillar height is changed across a sharp step. Preliminary results demonstrate the effects on cell migration and morphology at the step boundary.
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87.80.Ek Mechanical and micromechanical techniques
87.18.-h Biological complexity
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
87.17.Rt Cell adhesion and cell mechanics

Optimizing substrate disorder for bone tissue engineering of mesenchymal stem cells

Nikolaj Gadegaard, Matthew J. Dalby, Mathis O. Riehle, and Chris D. W. Wilkinson

J. Vac. Sci. Technol. B 26, 2554 (2008); http://dx.doi.org/10.1116/1.2978407 (4 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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A key tenet of bone tissue engineering is the development of scaffold materials that can stimulate stem cell differentiation in the absence of chemical treatment to become osteoblasts without compromising material properties. Recently, the authors have shown that two types of slightly disordered arrays of nanopits stimulate human mesenchymal stem cells (MSCs) to produce bone mineral in vitro, in the absence of osteogenic supplements. In this article, they aim at optimizing the topographic parameters to stimulate MSCs to form bone cells. They have developed a high-speed electron beam technique to pattern 1 cm2 areas with 109 dots. In three steps, they (1) systematically changed the degree of disorder from ±30 to 150 nm from a perfect square arrangement with a 300 nm pitch, (2) changed the pit diameter from 50 to 193 nm, and (3) explored the importance of pits versus pillars. They found that arrays of pillars 35 nm tall with a diameter of 193 nm and a disorder of ±30 nm provided the optimal conditions for stimulating MSCs to form bone cells.
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87.18.-h Biological complexity

Nanomodified surfaces and guidance of nerve cell processes

Fredrik Johansson, Waldemar Hällström, Per Gustavsson, Lars Wallman, Christelle Prinz, Lars Montelius, and Martin Kanje

J. Vac. Sci. Technol. B 26, 2558 (2008); http://dx.doi.org/10.1116/1.2998698 (4 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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Axonal growth and guidance were studied on different micro- and nanostructured surfaces. Nanoimprinted grooves in a polymer, epitaxial III/V nanowires, porous silicon patterns, and chemically altered surfaces were all shown to induce axonal guidance. Neurons were also found to be able to attach and grow on gallium phosphide nanowires without compromising cell survival. The results are important for the construction of a new generation of neuroelectrical interfaces, including high spatial resolution electrodes. The advantages of the different nanostructured surfaces are discussed.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Rf Micro- and nanoscale pattern formation
68.65.La Quantum wires (patterned in quantum wells)
back to top Nanopattering and Energy

Imprinted large-scale high density polymer nanopillars for organic solar cells

Mukti Aryal, Fatih Buyukserin, Kamil Mielczarek, Xiao-Mei Zhao, Jinming Gao, Anvar Zakhidov, and Wenchuang (Walter) Hu

J. Vac. Sci. Technol. B 26, 2562 (2008); http://dx.doi.org/10.1116/1.2981076 (5 pages) | Cited 27 times

Online Publication Date: 1 December 2008

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Nanoimprint with a large-scale nanoporous Si mold is developed to fabricate high density periodic nanopillars ( ∼ 1010/cm2) in various functional polymers. A anodic alumina membrane is first obtained using electrochemical anodization. The membrane is used as a mask for a two-step plasma etching process to obtain a Si mold of 50–80 nm wide and 100–900 nm deep pores. The mold is used in nanoimprint lithography to fabricate ordered and high density polymer nanopillars and nanopores in SU-8, hydrogen silsesquixane, polymethylmethacrylate, poly(3-hexylthiophane) (P3HT), and phenyl-C61-butyric acid methyl ester (PCBM). Then, the imprinted P3HT nanopillars were used to make bulk heterojunction solar cells by depositing PCBM on top of the pillars. Imprinting provides a way to precisely control the interdigitized heterojunction morphology, leading to improved solar cell performance.
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81.16.Nd Micro- and nanolithography
84.60.Jt Photoelectric conversion
82.45.Cc Anodic films
81.65.Cf Surface cleaning, etching, patterning
back to top Nanobio Devices

Direct write electron beam patterning of DNA complex thin films

R. A. Jones, W. X. Li, H. Spaeth, and A. J. Steckl

J. Vac. Sci. Technol. B 26, 2567 (2008); http://dx.doi.org/10.1116/1.2993258 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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The authors report on the first use of direct write electron beam lithography (DW-EBL) patterning of DNA-based materials. Water insoluble and organic solvent soluble DNA:CTMA complexes were formed by reaction of DNA polymers with cationic surfactants and other molecular species. Thin films with thicknesses ranging from 85 to 300 nm were prepared by spin coating. DW-EBL was conducted using a Raith 150 system. The resulting exposed areas demonstrated either positive or negative resist properties depending on development solution. The characteristics of the DNA:CTMA material as a patternable electron sensitive resist medium are presented for different exposure conditions (10–30 kV), development conditions, structure sizes (100 nm to 20 μm), and structure complexities. Contrast values of ∼ 2 have been obtained in both positive and negative resist modes. Both simple (20 μm diameter circle and square) and complex (Fresnel lens) patterns with nanometer scale features (<100 nm) in DNA films are possible using this method.
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81.16.Rf Micro- and nanoscale pattern formation
85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography
85.65.+h Molecular electronic devices

Hybridization sensing by electrical enhancement with nanoparticles in nanogap

Chun-Chi Chen, Fu-Hsiang Ko, Edward Yi Chang, Feng-Chih Chang, and Shiao-Wei Kuo

J. Vac. Sci. Technol. B 26, 2572 (2008); http://dx.doi.org/10.1116/1.3002489 (6 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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In this work, the monolayer of gold nanoparticles within 72 nm gap has been proposed to function as a DNA sensor. The authors suggest that the nanoparticles in the nanogap could act as hopping sites which amplify the conductance of hybridized DNA strands. The conductance amplification between single strand and hybridized DNAs through gold nanoparticles is observed. Various concentrations of capture and target DNA are discussed for optimal hybridization sensing purpose. With the help of 1 nM capture DNAs, this sensor is able to analyze target DNA sequences at very low concentration of 1 fM. Furthermore, by means of adjusting the denature temperature to 60 °C, even single mismatch hybridization could be discriminated.
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87.85.Rs Nanotechnologies-applications
87.85.jc Electrical, thermal, and mechanical properties of biological matter

Control of DNA motion in microchannels integrated with dual electrodes

B. L. Cardozo and S. W. Pang

J. Vac. Sci. Technol. B 26, 2578 (2008); http://dx.doi.org/10.1116/1.2991859 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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The authors have fabricated a microfluidic system for the control of DNA motion consisting of 400 or 900 nm wide Si channels covered by a bonded glass layer containing integrated dual electrodes. By applying an ac potential to an electrode pair on both sides of the channels, precise lateral positioning of DNA has been demonstrated for the first time. By modifying the amplitude or frequency of the ac potential applied to the electrode pairs, they control DNA motion within the channel, causing it to increase speed, decrease speed, reverse directions, or halt. The precise control of DNA average position within channels is expected to be an important step in the development of microfluidic single molecule analysis systems.
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87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
87.80.Ek Mechanical and micromechanical techniques
87.14.-g Biomolecules: types
back to top Nanoelectronics

Hybrid high resolution lithography (e-beam/deep ultraviolet) and etch process for the fabrication of stacked nanowire metal oxide semiconductor field effect transistors

S. Pauliac-Vaujour, C. Comboroure, C. Vizioz, S. Barnola, P. Brianceau, V. Maffini Alvaro, C. Dupré, and T. Ernst

J. Vac. Sci. Technol. B 26, 2583 (2008); http://dx.doi.org/10.1116/1.3021392 (4 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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This article highlights some aspects associated with the fabrication of stacked nanowire metal oxide semiconductor field effect transistors (MOSFETs) and more precisely the active area conception. These novel architectures, with gate-all-around or independent gates (ΦFET), are promising solutions to improve electrostatic control with high on-current (Ion) and to reduce power consumption for sub-32-nm transistors. Their fabrication is highly complex regarding lithography and etching. For this study, stacked nanowires were achieved by using hybrid lithography (e-beam/deep ultraviolet) combined with anisotropic and isotropic etchings of a Si/SiGe multilayer to form suspended silicon nanowires. Therefore, we needed high aspect ratio resist features in order to perform the anisotropic etch of the Si/SiGe multilayer (thickness: 250 nm). For this purpose, we compared two ways to pattern the sub-32-nm silicon stacked nanowires. On one hand, a resist trimming was performed on thick large critical dimension patterns before etching. On the other hand, an amorphous carbon hard mask combined with a thin oxide capping layer was added on our structure to suppress resist thickness limitations and extend high resolution lithography capabilities. The best results so far were obtained using the first of these two techniques, which yielded 25 nm stacked nanowire MOSFETs.
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85.30.Tv Field effect devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.65.Cf Surface cleaning, etching, patterning

Silicon single-electron transistor with oxide tunnel barriers fabricated using chemical mechanical polishing

Vishwanath Joshi, Alexei O. Orlov, and Gregory L. Snider

J. Vac. Sci. Technol. B 26, 2587 (2008); http://dx.doi.org/10.1116/1.2978877 (5 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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This article describes the fabrication process for a silicon single-electron transistor (Si-SET) with tunnel barriers made of thermal silicon dioxide. The fabrication method uses electron-beam lithography, dry etching, and chemical mechanical polishing to make devices with well-defined geometry and good yield. The method introduces chemical mechanical polishing as a key processing technique in the production of nanometer scale features required for the device. The fabricated SETs show charging energies in excess of 20 meV and operating temperatures above liquid nitrogen. All the process steps are fully compatible with the current complementary metal oxide semiconductor (CMOS) technology and combined with the higher operating temperature of the SETs, the fabrication method paves the way for designing of hybrid CMOS-SET architectures. Si-SET can also be a key enabling device for the manufacturable implementation of quantum-dot cellular automata.
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85.35.Gv Single electron devices
85.40.Hp Lithography, masks and pattern transfer
81.65.Ps Polishing, grinding, surface finishing
81.65.Cf Surface cleaning, etching, patterning

Prospects of free electron analog to digital technology

Rafael Aldana and R. Fabian Pease

J. Vac. Sci. Technol. B 26, 2592 (2008); http://dx.doi.org/10.1116/1.2991988 (4 pages)

Online Publication Date: 1 December 2008

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Free electron analog to digital conversion is accomplished by deflecting an electron beam bunch transversally by the voltage to be sampled and then quantizing the deflected angle in an array of electron detectors. Miniaturization of the whole system, especially the deflection plates, leads to an improved performance. A system restricted by the fundamental limit of diffraction could achieve a sampling rate of 1 THz with 8 bit resolution; the source requirements would be a brightness of 2×1013 A cm−2/sr at 5 kV and a source jitter of 1 fs. A more practical system using a negative electron affinity photocathode electron source with a brightness of 1×107 A cm−2/sr at 5 kV will allow the system to sample 4 bits at 750 GHz or 6 bits at 450 GHz.
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84.30.-r Electronic circuits

Single atom doping for quantum device development in diamond and silicon

C. D. Weis, A. Schuh, A. Batra, A. Persaud, I. W. Rangelow, J. Bokor, C. C. Lo, S. Cabrini, E. Sideras-Haddad, G. D. Fuchs, R. Hanson, D. D. Awschalom, and T. Schenkel

J. Vac. Sci. Technol. B 26, 2596 (2008); http://dx.doi.org/10.1116/1.2968614 (5 pages) | Cited 14 times

Online Publication Date: 1 December 2008

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The ability to inject dopant atoms with high spatial resolution, flexibility in dopant species, and high single ion detection fidelity opens opportunities for the study of dopant fluctuation effects and the development of devices in which function is based on the manipulation of quantum states in single atoms, such as proposed quantum computers. The authors describe a single atom injector, in which the imaging and alignment capabilities of a scanning force microscope (SFM) are integrated with ion beams from a series of ion sources and with sensitive detection of current transients induced by incident ions. Ion beams are collimated by a small hole in the SFM tip and current changes induced by single ion impacts in transistor channels enable reliable detection of single ion hits. They discuss resolution limiting factors in ion placement and processing and paths to single atom (and color center) array formation for systematic testing of quantum computer architectures in silicon and diamond.
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85.40.Ry Impurity doping, diffusion and ion implantation technology
85.35.Ds Quantum interference devices
07.79.Lh Atomic force microscopes

ZnO nanostructures grown on zinc nanocones by thermal oxidation

Liang-Chiun Chao, Chung-Chi Liau, Syuan-Jhih Lin, and Jun-Wei Lee

J. Vac. Sci. Technol. B 26, 2601 (2008); http://dx.doi.org/10.1116/1.2968616 (3 pages)

Online Publication Date: 1 December 2008

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ZnO nanostructures were grown on metallic zinc nanocones by thermal oxidation. The metallic nanocones are prepared by argon ion beam sputtering utilizing a capillaritron ion source. The aspect ratios of zinc nanocones are found to be dependent on ion beam energy and substrate temperatures. By maintaining the substrate temperature to be less than 60 °C, the aspect ratio of zinc nanocones increases from 1.2 to 2.7 as ion beam energy increases from 6 to 12 keV. Zn nanocones with aspect ratio larger than 25 are obtained by utilizing a 12 keV ion beam and allowing the substrate to increase to ∼ 180 °C by in situ ion beam heating. Thermal oxidation of zinc nanocones results ZnO nanowires and nanoblades grown outwardly from the shank. This provides a convenient route for the fabrication of ZnO nanowires for field emission flat panel display and dye-sensitized solar cell applications.
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81.16.Pr Micro- and nano-oxidation
85.45.Fd Field emission displays (FEDs)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
84.60.Jt Photoelectric conversion
back to top Patterned Media/Data Storage

Toward 1 Tdot/in.2 nanoimprint lithography for magnetic bit-patterned media: Opportunities and challenges

XiaoMin Yang, Yuan Xu, Carl Seiler, Lei Wan, and Shuaigang Xiao

J. Vac. Sci. Technol. B 26, 2604 (2008); http://dx.doi.org/10.1116/1.2978487 (7 pages) | Cited 14 times

Online Publication Date: 1 December 2008

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Nanoimprint lithography presents unique opportunities for patterned media applications due to its advantages of sub-10 nm resolution capability, patterning of a whole disk in a single imprint step with reasonably high throughput, and the relatively low capital cost in comparison to other next generation lithography technologies. However, there are several critical issues that still remain very challenging. This article will briefly discuss these challenges in general and then focus on imprint lithography work including the fabrication of templates and demonstrate the imprinted results. In this work two types of polarities of high-density templates (pillar tone and hole tone) have been fabricated on fused silica substrates for the UV imprint process. The difficulties and limitations in each of the template fabrication processes will be discussed. The authors have successfully demonstrated template fabrication followed by imprinted results with a pitch of 24 nm (1.1 Tdots/in.2) for both tones of templates. Initial imprinted results of dense dot patterns with a pitch as small as 18 nm (2.0 Tdots/in.2) have been achieved. High-resolution scanning electron microscopy images are used as the primary metrology for both the dot size uniformity and the placement accuracy analysis. The difficulties and the limitations in template fabrication, the imprint process, and associated metrology will be discussed.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Potential of a rotary stage electron beam mastering system for fabricating patterned magnetic media

T. Miyazaki, K. Hayashi, K. Kobayashi, Y. Kuba, H. Ohyi, T. Obara, O. Mizuta, N. Murayama, N. Tanaka, Y. Kawamura, and H. Uemoto

J. Vac. Sci. Technol. B 26, 2611 (2008); http://dx.doi.org/10.1116/1.3013277 (8 pages) | Cited 6 times

Online Publication Date: 1 December 2008

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To fabricate master templates of high-density patterned magnetic media, the authors developed a high-resolution and high-throughput rotary stage electron beam mastering system. They accomplished the fabrication of discrete track media groove patterns with 45 nm track pitch, and also a dense bit array with both track and bit pitch of 35 nm for bit patterned media under the conditions of a bit rate of 1.22 MHz/bit at 50 kV acceleration voltage. The high resolution and high throughput are derived from using a continuous stage movement flyback lithography (CSFL) function. CSFL is enabled by differentiated capabilities, such as an electron optical column that achieves a large beam current at a small beam diameter, and a friction-driven slider stage that provides a highly accurate positioning capability and a dynamic focus correction feature and r-theta stage driving. The CSFL capability, working in conjunction with a blankingless beam shift lithography (BLSL), is very effective for fabricating various kinds of servo pattern elements, such as grooves and dots, grooves and right-angled grooves, grooves and half-pitch-shift dot arrays, and various pit length patterns, to construct effective servo patterns.
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81.16.Rf Micro- and nanoscale pattern formation
85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
back to top Nanomachine, Nanomanipulation, and NEMS

Electrothermal actuation studies on silicon carbide resonators

Enrico Mastropaolo and Rebecca Cheung

J. Vac. Sci. Technol. B 26, 2619 (2008); http://dx.doi.org/10.1116/1.3013862 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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The electromechanical behavior of SiC clamped-clamped beam (bridge) resonators with u-shaped aluminium (Al) electrodes on top has been studied as a function of electrode length, width, and spacing. Negative and positive deflections have been observed, indicating a complex interplay exhibited by the combined single material and bimorph characteristics of the resonator structures. It has been found that, both experimentally and theoretically, devices with electrodes applied on the root of the beam have similar or higher displacement amplitudes compared to devices with electrodes covering the half or the entire beam. Moreover, the displacement and vibration amplitudes can be maximized by increasing the electrode width and/or decreasing the spacing.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Novel SU-8 optical waveguide microgripper for simultaneous micromanipulation and optical detection

Roberto R. Panepucci and Jose A. Martinez

J. Vac. Sci. Technol. B 26, 2624 (2008); http://dx.doi.org/10.1116/1.2993171 (4 pages)

Online Publication Date: 1 December 2008

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A novel microgripper device structure with optical waveguides as arms is presented. The devices shown here have waveguide dimensions of 50×30 μm2. The device fabrication, using SU-8 polymer, is described. Its capability to perform micromanipulation while simultaneously carrying out optical detection is demonstrated.
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42.82.Et Waveguides, couplers, and arrays
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.79.Gn Optical waveguides and couplers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Resistivity change of the diamondlike carbon, deposited by focused-ion-beam chemical vapor deposition, induced by the annealing treatment

Reo Kometani, Toshinari Ichihashi, Kazuhiro Kanda, Tsuneo Suzuki, Koichi Niihara, Sunao Ishihara, Takashi Kaito, and Shinji Matsui

J. Vac. Sci. Technol. B 26, 2628 (2008); http://dx.doi.org/10.1116/1.2978400 (4 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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Diamondlike carbon (DLC) deposited by focused-ion-beam chemical vapor deposition (FIB-CVD) has the interesting material characteristics because DLC deposited by FIB-CVD using the gallium (Ga) FIB contained Ga. The DLC wires were subjected to annealing, and it was found that their resistivity and the Ga content of DLC decreased. To understand the reason for the decrease in resistivity, changes in the fine structure and composition of DLC due to annealing were examined by transmission electron microscope electron energy loss spectroscopy and Rutherford backscattering spectroscopy/elastic recoil detection analysis, respectively. The results revealed that the graphite content of DLC increased due to hydrogen (H) elimination induced by annealing. Thus, it was concluded that the resistivity of the annealed DLC wires decreased due to the increase in the graphite content of DLC.
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73.63.-b Electronic transport in nanoscale materials and structures
61.46.-w Structure of nanoscale materials
81.05.U- Carbon/carbon-based materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Gh Other heat and thermomechanical treatments

Nanofabrication of super-high-aspect-ratio structures in hydrogen silsesquioxane from direct-write e-beam lithography and hot development

L. E. Ocola and V. R. Tirumala

J. Vac. Sci. Technol. B 26, 2632 (2008); http://dx.doi.org/10.1116/1.3021395 (4 pages) | Cited 7 times

Online Publication Date: 1 December 2008

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Super-high-aspect-ratio structures (>10) in hydrogen silsesquioxane resist using direct write electron beam lithography at 100 kV and hot development and rinse are reported. Posts of 100 nm in width and 1.2 μm tall have been successfully fabricated without the need of supercritical drying. Hot rinse solution with isopropyl alcohol has been used to reduce surface tension effects during drying. Dose absorption effects have been observed and modeled using known Monte Carlo models. These results indicate that for e-beam exposures of thick negative resists (>1 μm), the bottom of the structures will have less cross-link density and therefore will be less stiff than the top. These results will have impact in the design of high-aspect-ratio structures that can be used in microelectromechanical system devices and high-aspect-ratio Fresnel zone plates.
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81.16.Nd Micro- and nanolithography
68.03.Cd Surface tension and related phenomena
42.79.Ci Filters, zone plates, and polarizers
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.16.Rf Micro- and nanoscale pattern formation
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