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Nov 2006

Volume 24, Issue 6, pp. L27-3262

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Acid generation efficiency in a model system of chemically amplified extreme ultraviolet resist

Takahiro Kozawa, Seiichi Tagawa, Hiroaki Oizumi, and Iwao Nishiyama

J. Vac. Sci. Technol. B 24, L27 (2006); http://dx.doi.org/10.1116/1.2393297 (4 pages) | Cited 65 times

Online Publication Date: 27 November 2006

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A highly sensitive extreme ultraviolet (EUV) resist is strongly needed to reduce the development costs of high power EUV sources. Although highly sensitive chemically amplified resists based on acid-catalyzed reactions have been used in mass production lines, the chain length of acid catalytic reactions must be suppressed within several nanometers to meet the resolution requirement below the 32 nm technology node. Under such circumstances, the initial acid yield produced by EUV exposure is critical to the formation of ultrafine patterns. Using an acid sensitive dye, the authors evaluated the number of acid molecules generated by an EUV photon. The observed acid yield was well explained by the ionization model for acid generation originally proposed for chemically amplified electron beam resists.
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81.16.Nd Micro- and nanolithography
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On the use of alloying elements for Cu interconnect applications

K. Barmak, C. Cabral, K. P. Rodbell, and J. M. E. Harper

J. Vac. Sci. Technol. B 24, 2485 (2006); http://dx.doi.org/10.1116/1.2357744 (14 pages) | Cited 23 times

Online Publication Date: 27 October 2006

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To address the future use of alloying elements for Cu interconnect applications in integrated circuits, first, available bulk experimental data such as residual resistivity per at. % solute and binary phase diagrams are used to arrive at a set of 24 potential elements. Next, experimental results in thin films and lines allow the authors to arrive at a smaller set that includes ten elements, namely, Pd, Au, Al, Ag, Nb, Cr, B, Ti, In, and Mn, with higher priority and six, namely, Zn, V, C, Mg, P, and Sn with lower priority for further studies. These additional studies are needed before a strong case for or against alloying additions to Cu can be made. The available thin film and line data are summarized in a series of tables that should prove useful for the readers. In particular, the thin film data allow the authors to obtain an effective average residual resistivity (EARR) per at. % solute that combines the effects of impurity scattering, second phase precipitates, and grain size refinement resulting from solute additions.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration
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Micromechanical resonators and filters for microelectromechanical system applications

Mehrnaz Motiee, Raafat R. Mansour, and Amir Khajepour

J. Vac. Sci. Technol. B 24, 2499 (2006); http://dx.doi.org/10.1116/1.2356865 (10 pages) | Cited 1 time

Online Publication Date: 30 October 2006

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Microelectromechanical system (MEMS) based mechanical resonators and filters have shown promising characteristics in achieving high Q values and good stability. In this article, new designs for integrated circuit–compatible microelectromechanical intermediate frequency (IF) filters are introduced. These filters have been fabricated and tested, and experimental results are included in this work. One of the novel filters is composed of two-cantilever beam resonators coupled by a soft flexural-mode beam. Different configurations of these filters and their (RF) simulation and experimental responses are presented. One of the advantages of these filters is that the coupling elements can be added from more than one side in order to have elliptical responses. The authors also introduce a novel V-shape coupling element that is used to mechanically couple two clamped-clamped MEMS resonators laterally. The stiffness of the proposed V-shape coupling element is adjustable via changing the length of the V sidelines and/or the V conjunction angle to flatten the filter passband. A two-pole bandpass filter operating in the IF range is constructed using these coupling elements. A lumped modeling approach is presented for a fast and accurate filter design and optimization. Using finite element analysis, the validity and accuracy of the lumped model are investigated. The fabricated filters have center frequencies varying from 700 kHz to 1.7 MHz, with quality factors of 300–1500 when tested at ambient pressure. The experimental results are presented and compared with lumped and finite element simulation results.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
84.30.Vn Filters
84.30.Bv Circuit theory

Microscopic approach to an equation for the heat flow between wafer and E-chuck

Michael Klick and Mathias Bernt

J. Vac. Sci. Technol. B 24, 2509 (2006); http://dx.doi.org/10.1116/1.2357745 (9 pages) | Cited 1 time

Online Publication Date: 30 October 2006

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Wafer cooling and heating by means of a gas at the wafer backside is a key technology in semiconductor manufacturing. A detailed understanding of the physical mechanisms is needed to yield the best process results. Besides the commonly used Smoluchowski interface condition, a microscopical approach is deduced describing the whole pressure range. Different thermal gas species and surface properties, as well as the velocity and angular distribution of the atoms, are basic features of the model. The angular distribution of the desorbed atoms is shown to have a significant influence on the wafer temperature. The heat transfer properties between the gas and two different surfaces are described by one value, the effective accommodation coefficient. The final wafer temperature is simulated as a function of the input power, the backside pressure, and the gas species. Helium has the best cooling properties of the inert gases, followed by neon. The influence of a pollution of the wafer surface on the uniformity of the wafer temperature has been determined. The surface roughness has no significant influence on the cooling abilities of an electrostatic chuck.
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85.30.De Semiconductor-device characterization, design, and modeling
44.00.00 Heat transfer

Metal-insulator-metal capacitors using atomic-layer-deposited Al2O3/HfO2/Al2O3 sandwiched dielectrics for wireless communications

Shi-Jin Ding, Yu-Jian Huang, Yanbo Li, D. W. Zhang, C. Zhu, and M.-F. Li

J. Vac. Sci. Technol. B 24, 2518 (2006); http://dx.doi.org/10.1116/1.2357746 (5 pages) | Cited 2 times

Online Publication Date: 30 October 2006

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High density metal-insulator-metal (MIM) capacitors are required for radio frequency and analog/mixed-signal integration circuit applications. In this article, high permittivity Al2O3/HfO2/Al2O3 (AHA) dielectrics have been evaluated in comparison with HfO2 using atomic layer deposition technique for MIM capacitor applications. The results indicate that the AHA dielectrics exhibit electrical performance superior to the HfO2 dielectric while retaining similar capacitance density. With respect to 2 nm individual Al2O3 barriers, the MIM capacitor can offer a capacitance density of 2.6 fF/μm2, voltage coefficients of capacitance of 71 ppm/V2 and 9 ppm/V, a leakage current as low as 3×10−9 A/cm2 at 1 MV/cm and 125 °C, an operating voltage of around 3 V for a ten-year lifetime at 125 °C in terms of 50% failure.
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84.32.Tt Capacitors
77.22.Ch Permittivity (dielectric function)
73.40.Rw Metal-insulator-metal structures

Area selective atomic layer deposition of titanium dioxide: Effect of precursor chemistry

Ashwini Sinha, Dennis W. Hess, and Clifford L. Henderson

J. Vac. Sci. Technol. B 24, 2523 (2006); http://dx.doi.org/10.1116/1.2359728 (10 pages) | Cited 15 times

Online Publication Date: 30 October 2006

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Area selective atomic layer deposition (ALD) of titanium dioxide using polymer films as masking layers has been investigated. A number of factors which must be considered while designing a successful area selective ALD process have been determined and are briefly discussed. Reactivity of the polymer with the ALD precursor species, diffusion of ALD precursors through the polymer mask, and remnant precursor content in the masking film during ALD cycling are key factors. This article investigates the effect of different precursor chemistries in view of the above mentioned factors. Titanium tetrachloride and titanium isopropoxide have been used as two different metal precursors in conjunction with poly(methyl methacrylate) films as photodefinable masking layers. Processing problems arising from factors such as diffusion of precursors through the masking layer can be solved through careful choice of ALD precursors.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
82.50.-m Photochemistry

Focused ion beam fabrication of two dimensional photonic crystals in silicon-on-insulator

K. Balasubramanian, P. J. Heard, and M. J. Cryan

J. Vac. Sci. Technol. B 24, 2533 (2006); http://dx.doi.org/10.1116/1.2359729 (5 pages) | Cited 5 times

Online Publication Date: 30 October 2006

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This article presents results for the optical characterization of two-dimensional photonic crystals (PhCs) in silicon-on-insulator fabricated using focused ion beam (FIB) etching. A detailed description of fabrication techniques is given and the use of gas assisted etching for large area etches is outlined. The optical characterization shows PhC band edges at the expected wavelengths but with reduced depth. Three dimensional finite difference time domain modeling is used to investigate this discrepancy and this suggests that reduced sidewall verticality is not critical in this strong vertical guiding regime. Other possible explanations for reduced band edge depth are discussed including gallium implantation and FIB induced optical damage.
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42.70.Qs Photonic bandgap materials
81.65.Cf Surface cleaning, etching, patterning
61.72.up Other materials

Development of a regeneration-type neural interface: A microtube guide for axon growth of neuronal cells fabricated using focused-ion-beam chemical vapor deposition

Takayuki Hoshino, Akinori Ozasa, Reo Kometani, Takafumi Suzuki, Shinji Matsui, and Kunihiko Mabuchi

J. Vac. Sci. Technol. B 24, 2538 (2006); http://dx.doi.org/10.1116/1.2359730 (6 pages) | Cited 4 times

Online Publication Date: 31 October 2006

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The authors’ goal is to develop a neural interface system that enables connection of the human nervous system with external devices and allows transmission of information in both directions. One way to connect interface to neurons is a regenerative electrode, where the electrode is placed between the two cut ends of a nerve. The cut nerve fiber can regenerate through channels in a metallic electrode on a two-dimensional (2D) plane of the regenerative electrode. As this type of electrode enables both the recording of signals from a single nerve fiber and the stimulation of a single nerve fiber, attempts have been made to develop it using traditional 2D microfabrication techniques. However, it is difficult to process such electrodes with these 2D microfabrication techniques, particularly the high-density integrated structure of the electrical wiring. The authors previously designed a neural interface system—a type of regenerative electrode consisting of an electrode segment and many carbon microtubes for guiding the regenerating axons of the neuronal cells—that can be made through three-dimensional processing. In the current study, the authors have fabricated a prototype of the guiding segment of the electrode (which was previously reported) and evaluated the biocompatibility of diamondlike carbon (DLC) made by focused-ion-beam chemical vapor deposition (FIB-CVD) and carbon microtubes in vitro. The microtubes were fabricated using FIB-CVD. DLC was deposited with a scanning 30 keV Ga+ ion beam in an atmosphere containing phenanthrene (C14H10). The scanning patterns were determined by a computer-aided-design system before the fabrication. The beam was scanned over a Au-coated glass capillary or polycarbonate membrane to deposit DLC and form the carbon microtubes. For observation of the axon growth through the microtubes, the authors fabricated bifurcated carbon microtubes with an inner diameter of 3–6 μm on the glass capillary and straight microtubes on the polycarbonate membrane. The fabricated microtubes were immersed in a culture medium containing nerve growth factor and PC12 cells were cultured inside the capillary and on the membrane to evaluate whether they could extend axons through the microtubes. Here, the authors show that cultured rat phaeochromocytomas adhered to and survived for days on a DLC surface while preserving their morphology provided that the adhesion molecule poly-D-lysine was used as an organic substance to anchor the cells to the DLC surface. As a result, cells spread and neurites projected on the DLC area, suggesting that the DLC had little cytotoxic effect.
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87.85.J- Biomaterials
87.16.D- Membranes, bilayers, and vesicles
87.85.Wc Neural engineering
87.17.-d Cell processes

Generalized model of the metal/n-GaN Schottky interface and improved performance by electrochemical Pt deposition

Oleg Cojocari and Hans L. Hartnagel

J. Vac. Sci. Technol. B 24, 2544 (2006); http://dx.doi.org/10.1116/1.2359731 (9 pages) | Cited 2 times

Online Publication Date: 31 October 2006

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A modified model of the Schottky interface is proposed, which includes a near-surface layer (NSL) in the depletion region of the semiconductor. An important effect of the NSL is the ability to make the value of the Schottky barrier strongly voltage dependent, in agreement with experimental behavior. The proposed model can therefore qualitatively explain the observed peculiarities of Schottky contacts to the GaN and related materials. Pt/n-GaN Schottky contacts were fabricated by both electrochemical deposition and e-beam evaporation techniques. The use of electrochemistry resulted in significantly better performance of Schottky contacts. A comparative study of evaporated and electroplated contacts justifies the NSL model.
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73.30.+y Surface double layers, Schottky barriers, and work functions
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Chemical lithography

Peng Yao, Garrett J. Schneider, Janusz Murakowski, and Dennis W. Prather

J. Vac. Sci. Technol. B 24, 2553 (2006); http://dx.doi.org/10.1116/1.2359732 (7 pages)

Online Publication Date: 31 October 2006

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In this article, the authors present and demonstrate a novel, versatile lithography method with high resolution that they call chemical lithography (ChemLith). The concept is based on the fact that most of the commonly used photoresists change their solubility upon an acid-catalyzed chemical reaction. In photolithography, photoacid generator is mixed in the resist formula and the acid is generated by photon-initiated reactions. Using photons sets the fundamental limit on the feature size for photolithography. To overcome this limit, they propose to physically introduce the catalyzing acid (proton source) to the desired position on the resist surface. This concept can be implemented in two different ways, using a template in a manner similar to nanoimprint lithography or using an atomic force microscope tip similar to nanoprobe based nanolithography. They have achieved nanoscale feature size in both cases, which confirms the potential of ChemLith as an advanced lithography technique.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Direct correlation of negative magnetoresistance with concentrations of localized holes in Be delta-doped GaAs structures

J. P. Noh, S. Iwasaki, D. W. Jung, A. Z. M. Touhidul Islam, and N. Otsuka

J. Vac. Sci. Technol. B 24, 2560 (2006); http://dx.doi.org/10.1116/1.2359733 (6 pages)

Online Publication Date: 31 October 2006

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The origin of negative magnetoresistance of GaAs structures with a pair of Be and Si delta-doped layers is investigated with samples in which Be and Si doping concentrations are selectively varied. Magnitudes of negative magnetoresistance are directly correlated to concentrations of localized holes in these samples, suggesting that the negative magnetoresistance results from scattering of carriers by spins associated with these localized holes. The temperature dependence of magnetoresistance curves of the samples which exhibit large negative magnetoresistance is described by the Brillouin function with the Landé g factor and total angular momentum J whose values are expected for a localized hole in GaAs.
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75.47.Pq Other materials
72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Ey III-V and II-VI semiconductors
61.72.S- Impurities in crystals

Direct-write electron-beam lithography of an IR antenna-coupled microbolometer onto the surface of a hemispherical lens

C. T. Middlebrook, G. Zummo, and G. D. Boreman

J. Vac. Sci. Technol. B 24, 2566 (2006); http://dx.doi.org/10.1116/1.2360978 (4 pages) | Cited 3 times

Online Publication Date: 31 October 2006

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This article describes a method for performing direct-write lithography of an IR antenna-coupled microbolometer onto the surface of a hemispherical lens. Antennas on a dielectric half-space receive power more efficiently from the substrate side than from the air side. The use of a hemispherical lens facilitates reception through the substrate as well as elimination of trapped surface waves that would normally occur in the substrate. Using direct-write lithography onto the surface of the hemispherical lens eliminates the potential of an air gap between the antenna and lens. Additionally, the accuracy of alignment between the antenna and the center of the lens is controlled at the lithographic step. As a result, there is increased responsivity is observed in the antenna-coupled microbolometer when illuminated from the substrate-side compared to air-side illumination.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Effect of the addition of argon to reactive nitrogen gas on field emission properties of amorphous carbon nitride films

Junjie Li, Hidenori Mimura, Yoichiro Neo, Changzhi Gu, Haijun Li, and Shuxia Chen

J. Vac. Sci. Technol. B 24, 2570 (2006); http://dx.doi.org/10.1116/1.2360980 (5 pages) | Cited 2 times

Online Publication Date: 31 October 2006

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Amorphous carbon nitride films (a‐CNx) were deposited as the electron field emitters by rf magnetron sputtering method at room temperature. The effect of adding Ar to reactive nitrogen gas on the field emission of a‐CNx films is investigated. The addition of Ar increases the proportion and size of sp2-bonded clusters in the films and an overfull Ar addition decreases the N content in the film, measured by photoluminescence, x-ray photoelectron spectroscopy, and Raman spectra. Field emission testing results show that the Ar addition effectively improves the field emission ability of a‐CNx films. Related to the change of chemical bonding structure and components in the films, the authors found that the enhanced field emission of the films was attributable to the increased proportion of sp2-bonded clusters, including sp2 C–N and sp2 C–C bondings, and the decreased N content in the film. As a conduction part of the amorphous network in the films, these rich as-formed sp2-bonded clusters not only enable the tunneling in the film to make electron emission easier but also lead to degrading the electron emission barriers and raising the Fermi level to enhance electron emission.
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79.70.+q Field emission, ionization, evaporation, and desorption
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Ht Disordered structures
78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Field electron emission characteristics of diamond films with different grain morphologies

X. Lu, Q. Yang, W. Chen, C. Xiao, and A. Hirose

J. Vac. Sci. Technol. B 24, 2575 (2006); http://dx.doi.org/10.1116/1.2362742 (6 pages) | Cited 6 times

Online Publication Date: 31 October 2006

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Diamond films with different grain morphologies were prepared in order to compare their field electron emission properties. For the diamond films with well-oriented grains, the field electron emission properties are enhanced when the grain shape changes from flat to flattened pyramid and then to pyramid due to the increase in the field enhancement factors. Compared with the well-oriented diamond films, the diamond film with randomly oriented grains exhibits larger emission current due to the increase in the effective emission area. For the diamond film with cauliflowerlike grains, the nanotip structures improve the electron emission properties significantly through an increase in both the field enhancement factor and the effective emission area.
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79.70.+q Field emission, ionization, evaporation, and desorption
68.55.-a Thin film structure and morphology

InAs/AlSb high-electron-mobility transistors by molecular-beam epitaxy for low-power applications

M. D. Lange, R. S. Tsai, W. R. Deal, P. S. Nam, L. J. Lee, R. S. Sandhu, R. Hsing, B. D. Poust, J. L. Kraus, A. L. Gutierrez-Aitken, B. R. Bennett, J. B. Boos, A. M. Noori, S. L. Hayashi, and M. S. Goorsky

J. Vac. Sci. Technol. B 24, 2581 (2006); http://dx.doi.org/10.1116/1.2362758 (5 pages) | Cited 3 times

Online Publication Date: 31 October 2006

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InAs/AlSb high-electron-mobility transistor technology has transitioned from research to development stages in recent years. Development efforts at Northrop Grumman Space Technology, in collaboration with the Naval Research Laboratory and the University of California, Los Angeles, have focused on X-band and W-band low-noise amplifier monolithic millimeter-wave integrated circuits fabricated for applications requiring ultralow-power dissipation. The materials for the circuits discussed in this article were grown at Northrop Grumman Space Technology on 3-in.-diameter semi-insulating GaAs substrates by molecular-beam epitaxy. Atomic-force microscopy of the as-grown surface on each wafer showed that the rms roughness for all of the wafers ranged between 0.5 and 3.5 nm, and this range of roughness was fully compatible with the fabrication process. The high electron mobility that InAs can provide was achieved reproducibly in these materials. It was maintained almost always above 25 000 cm2 V−1 s−1, and in several cases even exceeded 30 000 cm2 V−1 s−1. The associated electron sheet concentration ranged between 1.2×1012 and 1.8×1012 cm−2. These combined mobilities and sheet concentrations gave corresponding sheet resistances in the range of 170±40 Ω/sq, with nonuniformity below 6% over these 3-in.-diameter wafers. These materials characteristics enabled successful fabrication of several recently published X-band and W-band low-noise amplifier circuits, and figures of merit for the circuits that were made specifically from these materials are referenced in this article.
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85.30.Tv Field effect devices
85.40.Sz Deposition technology
84.40.Lj Microwave integrated electronics
84.30.Le Amplifiers

Epitaxial growth and strain relaxation of MgO thin films on Si grown by molecular beam epitaxy

F. Niu, A. L. Meier, and B. W. Wessels

J. Vac. Sci. Technol. B 24, 2586 (2006); http://dx.doi.org/10.1116/1.2362759 (6 pages) | Cited 6 times

Online Publication Date: 31 October 2006

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High quality epitaxial MgO thin films have been grown on Si (001) wafers by molecular beam epitaxy using SrTiO3 (STO) as a buffer layer. The STO buffer layer reduces both the large lattice mismatch of 23% and the large thermal mismatch of 520% between MgO and Si. X-ray diffraction (XRD) measurements indicate that the MgO film grown on the STO buffered Si is epitaxial with MgO (002)‖Si (004) and MgO [110]‖Si [002]. The full width at half maximum (FWHM) of MgO (002) rocking curve width Δω is 0.30° (out-of-plane), and the FWHM of MgO (202) ϕ angle scan width Δϕ is 0.34° (in-plane) for a 155 nm thick film. Strain relaxation and growth mechanisms of the MgO film on Si were studied by in situ reflection high-energy electron diffraction (RHEED) analysis in combination with XRD and atomic force microscopy. The results indicate that the MgO first forms a pseudomorphic wetting layer and subsequently undergoes a Stranski-Krastanov transition to form three-dimensional coherent islands to relieve misfit strain. A decrease in the width of the RHEED spots with increasing MgO thickness is observed that is attributed to reduction of coherency strain. A smooth surface redevelops once MgO growth continues, which is attributed to island coalescence.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Controlled electroplating for high-aspect-ratio zone-plate fabrication

A. Holmberg, M. Lindblom, and H. M. Hertz

J. Vac. Sci. Technol. B 24, 2592 (2006); http://dx.doi.org/10.1116/1.2362761 (5 pages) | Cited 7 times

Online Publication Date: 31 October 2006

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The authors report a method for monitoring, control, and end-point detection of electroplating in nanostructures. The method is demonstrated on nickel plating into polymer molds, which is an important process in the fabrication of soft x-ray zone-plate diffractive optics. The lack of reproducibility presently limits the achievable nickel aspect ratio and, thus, reduces the zone-plate diffraction efficiency. The reported method provides reproducible plating via real-time control of the plating rate. It combines in situ light transmission measurements with current measurements to determine the thickness of the growing layer. The accuracy of the thickness prediction was better than ±4% (1σ) for 100–300 nm nickel layers. Furthermore, a slight change in the light transmission signal indicates when a gratinglike zone-plate structure is slightly overplated and the plating should be stopped. This end-point detection provides the optimal filling of high-aspect-ratio molds for improved diffraction efficiency.
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81.16.-c Methods of micro- and nanofabrication and processing
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution
42.79.Ci Filters, zone plates, and polarizers
42.86.+b Optical workshop techniques
41.50.+h X-ray beams and x-ray optics

Mobility and charge density tuning in double δ-doped pseudomorphic high-electron-mobility transistors grown by metal organic chemical vapor deposition

Chong-Yi Lee, Hung-Pin Shiao, Kuan-Chu Kuo, Hsin-Yen Wu, and Wen-Hsiang Lin

J. Vac. Sci. Technol. B 24, 2597 (2006); http://dx.doi.org/10.1116/1.2362783 (4 pages) | Cited 1 time

Online Publication Date: 1 November 2006

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In this article, the authors present mobility and charge density tuning for metal organic chemical vapor deposition (MOCVD)-grown double δ-doped pseudomorphic high-electron-mobility transistors (PHEMTs). Good epitaxial wafers were obtained by MOCVD as indicated by uniform and abrupt interfaces seen in measurements taken using a transmission electron microscope and two pronounced Si-δ-doped peaks in the secondary ion mass spectrometry analysis. The 1-μm-gate-length PHEMT device exhibited good dc performance with a threshold voltage of −1.34 V, a maximum drain current of 570 mA/mm, and a maximum transconductance of 279 mS/mm. From the dependences of mobility and charge density between the δ-doping level and spacer layer thickness, most PHEMT design requirements in the ranges between 5750 and 7500 cm2/V s (for mobility) and 2.4×1012 and 3.6×1012 cm−2 (for charge density) can be satisfied.
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85.30.Tv Field effect devices
61.72.uj III-V and II-VI semiconductors

Fabrication and characterization of high breakdown voltage AlGaN/GaN heterojunction field effect transistors on sapphire substrates

Y. C. Choi, M. Pophristic, B. Peres, M. G. Spencer, and L. F. Eastman

J. Vac. Sci. Technol. B 24, 2601 (2006); http://dx.doi.org/10.1116/1.2366542 (5 pages) | Cited 8 times

Online Publication Date: 1 November 2006

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High-quality C-doped GaN buffers with a very low doping concentration were grown on 2 in. c-plane sapphire substrates, and high-power AlGaN/GaN heterojunction field effect transistors (HFETs) on sapphire substrates for high-power switching applications were fabricated using a self-align process. The fabricated devices with gate-drain spacing (Lgd) of 16 μm exhibited a high breakdown voltage (BV) over 1100 V and low specific on resistance (ARDS(on)) of 4.2 mΩ cm2, with no additional photolithography process for a field plate design. This result approaches the SiC theoretical limit and is a record achievement for GaN-based HFETs on sapphire substrates, to the best of our knowledge. Based on the investigation of the influence of Lgd on device characteristics, it was shown that Lgd had a strong effect on ARDS(on) and BV while no noticeable change in maximum transconductance (gm,max) and maximum drain current (IDS,max) was observed when Lgd was varied. The ARDS(on) of a device [1.5 μm gate length (Lg)] with Lgd>7 μm was mainly determined by the gate-drain channel resistance. For a device (1.5 μm Lg)with Lgd<7 μm, on the other hand, the ARDS(on) should be optimized by considering other important resistance components. The measured BVs increased with Lgd, suggesting that the actual device breakdown was determined by the gate-drain breakdown. The trend of the BV-ARDS(on) performance showed a clearly linear relation, suggesting that the device performance is very predictable with the variation of Lgd. As a result, with improvements in the material quality of a GaN buffer on sapphire substrate, the off-state BV and ARDS(on) were all enhanced to the point that high-power AlGaN/GaN HFETs on sapphire substrates are now strong competitors for high-power switching applications.
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85.30.Tv Field effect devices
84.32.Dd Connectors, relays, and switches

Proposal of a new microreactor for vertical chemical operation

Yuichi Utsumi, Toshifumi Asano, Yoshiaki Ukita, Katsuhiro Matsui, Masahiro Takeo, and Seiji Negoro

J. Vac. Sci. Technol. B 24, 2606 (2006); http://dx.doi.org/10.1116/1.2366609 (6 pages) | Cited 6 times

Online Publication Date: 1 November 2006

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The authors proposed and fabricated a new microreactor stack which would be able to achieve a vertical fluid flow operation for the environment analysis, postgenome analysis, gene diagnosis, and screening of useful materials for medicine manufacture. This reactor is characterized as a simple structure with new aspects of the vertical fluid transportation using a proposed fluid filter with array of micro-through-bores. The deep x-ray lithography process using synchrotron radiation was used for the fabrication of the fluid filter. The feasibility of vertical liquid transportation was investigated using computational fluid dynamics analysis. It is indicated that the vertical liquid transportation is possible using the proposed fluid filter, and high efficiency mixing of liquid was also expected during transportation through the fluid filter. It was confirmed that the fluid flow velocity through the filter can be controlled by varying the load pressure around several kilopascals. A rapid enzyme reaction was successfully carried out and product concentration was observed using ultraviolet absorption spectroscopy. It was demonstrated that the proposed chemical reactor had a good vertical fluid flow operation performance for unit chemical operation.
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89.20.Bb Industrial and technological research and development
47.85.Np Fluidics

Vertical-via interconnection for infrared antennas

T. A. Mandviwala, B. A. Lail, and G. D. Boreman

J. Vac. Sci. Technol. B 24, 2612 (2006); http://dx.doi.org/10.1116/1.2366613 (4 pages) | Cited 1 time

Online Publication Date: 1 November 2006

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The authors present fabrication process details and test data for a vertical-via interconnection suitable for low-frequency signal extraction from infrared antenna-coupled sensors. Electrical readout of the signal from an antenna-coupled bolometer was accomplished using two 300 nm diameter Au via structures that extended 300 nm in the vertical direction. These vertical vias passed through two isolation layers of SiO2 and through a 1500×600 nm2 cutout in a ground plane. Electromagnetic isolation of the antenna from its associated electrical-readout bondpads at 28.3 THz in the infrared was demonstrated by mapping the two-dimensional spatial response of the antenna and comparing it to spatial response data from a similar structure without the intervening ground plane.
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84.40.Ba Antennas: theory, components and accessories
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.82.Cr Fabrication techniques; lithography, pattern transfer

Electron-beam lithography of Co/Pd multilayer with hydrogen silsesquioxane and amorphous Si intermediate layer

Jung-Sub Wi, Tae-Yon Lee, Kyung-Bae Jin, Dae Hoon Hong, Kyung Ho Shin, and Ki-Bum Kim

J. Vac. Sci. Technol. B 24, 2616 (2006); http://dx.doi.org/10.1116/1.2366615 (5 pages) | Cited 6 times

Online Publication Date: 1 November 2006

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We propose a patterning method to form nanostructures of a Co/Pd multilayer by using electron-beam lithography with an amorphous silicon (a-Si) layer and two-step etching process. On the Co/Pd multilayer, a-Si is sputter deposited and hydrogen silsesquioxane (HSQ), the electron-beam resist, is spin coated sequentially. We found that an a-Si intermediate layer between the Co/Pd underlayer and HSQ overlayer improves adhesion of HSQ on the metallic underlayer after electron-beam dosing and chemical development; it also increases etch selectivity between the Co/Pd multilayer and its overlayers. We demonstrate that a Co/Pd multilayer can be patterned successfully as a nanowire array using the suggested process.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.05.Bx Metals, semimetals, and alloys
81.65.Cf Surface cleaning, etching, patterning

Electrical properties of fluorine-doped silicon-oxycarbide dielectric barrier for copper interconnect

Chun-Chieh Huang, Jow-Lay Huang, Ying-Lang Wang, and Juin-Jie Chang

J. Vac. Sci. Technol. B 24, 2621 (2006); http://dx.doi.org/10.1116/1.2366541 (6 pages)

Online Publication Date: 2 November 2006

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A fluorine-doped amorphous silicon-oxycarbide (SiCOF) dielectric barrier deposited by chemical vapor deposition system is used to replace nitrogen doped silicon carbide (SiCN) and silicon oxycarbide (SiCO) in the 45 nm Cu-interconnect structure due to its low leakage current and dielectric constant. In this article, the low leakage current and dielectric constant of SiCOF mechanism are reported for the first time. The low leakage current of the SiCOF films is due to less trapped sites of electron transportation via Pool-Frenkel model than SiCO. The dangling and weak bonds such as Si–H and –CHx are eliminated by fluorine to form Si–F, and less charge will be trapped in the SiCOF film. A dielectric polarization model is proposed to explain the low dielectric constant of SiCOF. The elimination of molecule dipole is attributed to the incorporated fluorine atoms, which destroy the Si–O–Si tetrahedral network structures. A carrier injection model combined with the polarization is proposed to explain the flatband voltage (Vfb) shift of the C-V curves. The polarization is further verified by using thermal oxide under carbide films to reject the carrier injection from the silicon. At a high electrical field of 2 MV/cm, undoped SiCO has an obvious C-V hysteresis loop, but SiCOF does not. Both at low 1 MV/cm and high 2 MV/cm electric fields SiCOF had a lower C-V hysteresis loop and flatband voltage shift than undoped SiCO. The root causes of this phenomena are the unsaturated bonds in the film and the interface trap sites of SiCO(SiCOF)/silicon elimination. SiCOF is therefore a good candidate as a dielectric barrier for processes with a back end line requirement under 45 nm.
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77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.20.Ht High-field and nonlinear effects
85.40.Ls Metallization, contacts, interconnects; device isolation

Magnetization losses in submicrometer CoFeB dots etched in a high ion density Cl2-based plasma

C. G. C. H. M. Fabrie, J. T. Kohlhepp, H. J. M. Swagten, B. Koopmans, M. S. P. Andriesse, and E. van der Drift

J. Vac. Sci. Technol. B 24, 2627 (2006); http://dx.doi.org/10.1116/1.2366547 (4 pages) | Cited 1 time

Online Publication Date: 2 November 2006

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Faceting of the etch masks and chlorinated etch residues can reduce the magnetization of patterning magnetic materials substantially, and therefore, constitutes a considerable concern. To get more insight into the magnetization losses, CoFeB dots were etched in a high ion density Cl2-based plasma with a width ranging from 0.3 to 6.4 μm. The magnetic properties of the CoFeB dots were measured by magnetometry. Submicrometer CoFeB dots showed significant magnetization reductions despite H2O rinsing. Scanning electron microscopy (SEM) studies revealed that etching in a Cl2-based plasma caused faceting of the masks, leading to sloped sidewalls. SEM pictures were used to determine the geometric volume, which was compared to the effective magnetic volume resulting from the magnetometry measurements. The SEM data are in good agreement with the magnetometry data, and a chloride penetration depth of only a few nanometers could be derived, indicating that the postetch rinsing is sufficient to prevent considerable corrosion of the CoFeB dots.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
75.50.Bb Fe and its alloys
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Actinic extreme ultraviolet lithography mask blank defect inspection by photoemission electron microscopy

Jingquan Lin, Ulrich Neuhaeusler, Jawad Slieh, Armin Brechling, Ulf Kleineberg, Ulrich Heinzmann, Andreas Oelsner, Dima Valdaitsev, Gerd Schoenhense, Nils Weber, Matthias Escher, and Michael Merkel

J. Vac. Sci. Technol. B 24, 2631 (2006); http://dx.doi.org/10.1116/1.2366607 (5 pages) | Cited 5 times

Online Publication Date: 2 November 2006

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A new method for the actinic inspection of defects inside and on top of extreme ultraviolet (EUV) lithography multilayer-coated mask blanks is presented. The experimental technique is based on photoemission electron microscopy supported by the generation of a standing wave field inside and above the multilayer mask blank when illuminated near the resonance Bragg wavelength at around 13.5 nm. Experimental results on programed defect samples based on electron beam lithographic structures or silica balls overcoated with an EUV multilayer show that buried defects with a lateral size down to 50 nm are detectable. Furthermore, phase structures as shallow as 6 nm in height on a programed phase grating sample have been detected by this technique. The contrast of the phase defect structures has shown to be strongly dependent on and controlled by the phase of the standing wave field at the mask blank surface, and thus can be optimized by tuning the inspection wavelength.
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85.40.Hp Lithography, masks and pattern transfer

Efficient fabrication and characterization of cobalt nanoparticles embedded in metal∕oxide∕semiconductor structures for the application of nonvolatile memory

Jung Yup Yang, Kap Soo Yoon, Won Joon Choi, Young Ho Do, Ju Hyung Kim, Chae Ok Kim, and Jin Pyo Hong

J. Vac. Sci. Technol. B 24, 2636 (2006); http://dx.doi.org/10.1116/1.2366612 (4 pages) | Cited 1 time

Online Publication Date: 2 November 2006

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Metal-oxide-semiconductor (MOS) capacitors with Co nanoparticles (Co NPs) were successfully fabricated by utilizing an external laser irradiation method for the application of nonvolatile memory. Experimental images of cross-sectional transmission electron microscopy showed that the Co NPs of 5 nm in diameter were clearly embedded in SiO2 layer. Capacitance-voltage measurements of Pt/SiO2/Co NPs∕SiO2 on p-type Si (100) substrate certainly exhibited typical MOS behavior with a flatband voltage shift of 1.1 V. In addition, the charge retention characteristics of MOS capacitors with the Co NP were investigated using capacitance-time measurements. The present results indicate that their unique laser process gives rise to a possible promise for the efficient formation or insertion of metal NPs inside the MOS structures.
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85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits
84.32.Tt Capacitors

Study of diffusion barriers for Au metal on liquid phase oxidized GaAs

Po-Wen Sze, Jian-Jiun Huang, Dei-Wei Chou, and Yeong-Her Wang

J. Vac. Sci. Technol. B 24, 2640 (2006); http://dx.doi.org/10.1116/1.2366545 (5 pages)

Online Publication Date: 3 November 2006

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TiW, TiN, Pd, and Mo as the diffusion barriers (DBs) in Au/DB/GaAs native oxide multilayer structures are investigated. The GaAs native oxides are prepared by liquid phase oxidation, and the results indicate that TiW and Mo films can effectively block Au diffusion at temperatures of up to 550 °C for 30 min. However, TiN and Pd films can effectively block Au diffusion only at 450 °C for 30 min. The failure of TiN and Pd appears related to the embedded oxygen in the barrier layers which cause the interdiffusion between Au and the barrier films. In comparison, TiW and Mo show better blocking properties that prevent Au from diffusing into oxide films. They also act as a diffusion barrier even at temperatures above 550 °C.
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68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
61.72.Cc Kinetics of defect formation and annealing
77.55.-g Dielectric thin films
85.40.Ls Metallization, contacts, interconnects; device isolation

Effects of various plasma pretreatments on 193 nm photoresist and linewidth roughness after etching

Myeong-Cheol Kim, Denis Shamiryan, Youngjae Jung, Werner Boullart, Chang-Jin Kang, and Han-Ku Cho

J. Vac. Sci. Technol. B 24, 2645 (2006); http://dx.doi.org/10.1116/1.2366616 (8 pages) | Cited 18 times

Online Publication Date: 3 November 2006

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Among the pretreatment methods which are performed just after the lithographic process to minimize the roughness increase of 193 nm photoresist during the subsequent etching processes, an in situ plasma pretreatment is the most cost effective. A HBr plasma pretreatment has proven quite effective and a few papers have described the mechanism. In an effort to understand further, the authors evaluated four plasma pretreatments using HBr, Ar, H2, or Cl2 gases and compared their results. Fourier transform infrared (FTIR) spectroscopy was performed for the investigation of the chemical changes effected by the plasma pretreatments. Cross-section scanning electron microscope (SEM) images were used to measure the photoresist film thickness, while top-down SEM images and an off-line program were used to determine linewidth roughness (LWR) changes for 70 and 80 nm line features. They found two different types of roughness. The first type is a low-frequency roughness, which repeats about every 400 nm and increases the LWR value substantially. The second type is a high-frequency roughness, which appears about every 100 nm and causes a moderate increase in the LWR value. From the top-down SEM images, they recognize that the low-frequency roughness is caused by collapse of the 193 nm photoresist during the following bottom antireflective coating and hard-mask etching processes. The no plasma and the Ar plasma pretreated samples show this low-frequency roughness and produce the worst LWR values of about 11 nm at the 70 nm linewidth features after ashing processes. The HBr and the H2 plasma pretreated samples, which mainly show the high-frequency roughness, result in the best LWR values of about 6 nm at the 70 nm linewidth features after ashing processes. The FTIR analysis shows that both the HBr and H2 plasma pretreatments reduce the CO content substantially, down to about 20%–40% of the original CO content of the 193 nm photoresist as-coated film. On the other hand, the Ar plasma pretreated photoresist film still has about 60% of the CO content of the pristine 193 nm photoresist. The authors conclude that the low-frequency roughness has a critical relationship with the CO content in the 193 nm photoresist. They also find that the elements being incorporated into the 193 nm photoresist during the plasma pretreatment are important for their impact on the LWR. Especially, the Cl2 plasma pretreatment, which eliminates about the same amount of the original CO content in the photoresist as both the HBr and H2 plasma pretreatments, deteriorates the LWR notably just after the pretreatment and produces the most severe deformation after etching processes. Of the plasma pretreatments evaluated in this work, the HBr plasma pretreatment is the best in view of both the LWR and the application. The H2 plasma pretreatment, which shows the same lowest LWR value as the HBr plasma pretreatment, reduces the photoresist thickness substantially. However, even the HBr plasma pretreatment has one critical disadvantage because it generates the high-frequency type of roughness, which is not found in the case of the inert Ar plasma pretreatment. The H and Br radicals react with the 193 nm photoresist during the HBr pretreatment and appear to cause some side reactions and generate the high-frequency type of roughness during subsequent plasma processes. To minimize both the low- and high-frequency deformations simultaneously, we propose an inert gas plasma pretreatment process of which process parameters such as pressure and power are optimized to reduce the CO content of the 193 nm photoresist less than 40% of the original CO content as coated.
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85.40.Hp Lithography, masks and pattern transfer

Mobility study of a new naphthalenetetracarboxylic diimide derivative

D. Yang, R. P. Shrestha, Y. X. Li, L. Yan, and E. A. Irene

J. Vac. Sci. Technol. B 24, 2653 (2006); http://dx.doi.org/10.1116/1.2366611 (6 pages) | Cited 3 times

Online Publication Date: 6 November 2006

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New naphthalenetetracarboxylic diimide derivative based thin film organic transistors (OTFTs) have been fabricated on a variety of dielectrics: SiO2, polyethylene, and polyvinylidene fluoride trifluoroethylene. Resulting inverted gate OTFTs were found to be p channel with Au contacts. In situ annealing studies revealed densification and significant mobility improvement. The mobility of as-deposited films was around 10−4 cm2 V−1 s−1 for the best material and this could be improved by two orders of magnitude by a judicious annealing regimen and using a low static dielectric constant material for the gate dielectric.
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85.30.Tv Field effect devices
85.40.Ls Metallization, contacts, interconnects; device isolation

Immersion lithography for laser mask writing

Derek W. Bassett and Roger T. Bonnecaze

J. Vac. Sci. Technol. B 24, 2659 (2006); http://dx.doi.org/10.1116/1.2366614 (9 pages)

Online Publication Date: 9 November 2006

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The viability of fluid management in immersion lithography for laser mask writing is demonstrated. The so-called “drag-a-drop” method is proposed, where a droplet of fluid is held between the moving lens and the mask due to surface tension forces without the need of a fluid circulation system. Theoretical calculations and experimental measurements show that a stable droplet can be held onto a 6 mm diameter lens, typical in size for laser mask writing, translating at velocities up to 600 mm/s. Experiments also show that the stability of the droplet is greatly enhanced by the addition of a hydrophobic topcoat on the surface of the mask. Receding edge instabilities with the deposition of droplets similar to those seen in 193 nm immersion lithography and a new advancing edge instability with complete drop breakup were seen at sufficiently high velocities. A stability map is presented that predicts the onset of these two instabilities as a function of the dimensionless capillary number, a ratio of the viscous forces to surface tensions forces, and Weber number, a ratio of inertial forces to surface tension forces. Moving the lens and attached droplet off and on the edge of the mask during the scanning process can be done repeatedly with no fluid loss. The constancy of the index of refraction of the droplet is an important consideration for immersion lithography. The index can change due to changes in temperature and composition. Calculations and experiment with 193 nm immersion indicate that maintaining a constant index of refraction in laser mask writing with the drag-a-drop system is feasible. The application of immersion lithography appears to be a viable means of increasing the resolution of laser mask writing.
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85.40.Hp Lithography, masks and pattern transfer

Suppression of surface segregation of silicon dopants during molecular beam epitaxy of (411)A In0.75Ga0.25As/In0.52Al0.48As pseudomorphic high electron mobility transistor structures

H. Sagisaka, T. Kitada, S. Shimomura, S. Hiyamizu, I. Watanabe, T. Matsui, and T. Mimura

J. Vac. Sci. Technol. B 24, 2668 (2006); http://dx.doi.org/10.1116/1.2382944 (4 pages) | Cited 1 time

Online Publication Date: 9 November 2006

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The authors achieved considerable suppression of surface segregation of Si dopants in In0.75Ga0.25As/In0.52Al0.48As high electron mobility transistor (HEMT) structures grown on (411)A InP substrates by molecular beam epitaxy (MBE). The (411)A HEMT structures were conventionally grown at a high substrate temperature (Ts) of 540 °C in order to form the extremely flat (411)A heterointerfaces. This results in considerable surface segregation of Si dopants. Surface segregation of Si dopants was suppressed by lowering growth temperature of the top InAlAs barrier layer (TB) down to 450 °C with keeping Ts of 540 °C for other parts. Sheet carrier concentration (Ns) of two-dimensional electron gas (2DEG) was measured as a function of thickness (Lb) of the top InAlAs barrier for TB = 450 and 540 °C samples. Observed Ns of the TB = 540 °C sample vanished when Lb approached to 7 nm, while 2DEG with of Ns ∼ 2×1012 cm−2 remained for the TB = 450 °C sample. Surface segregation of Si-sheet-doped (411)A InAlAs layers grown at TB was also characterized by secondary ion mass spectrometry measurements. Si segregation length (λSi:1/e decay length of Si concentration) observed for TB = 450 °C sample was 2.3 nm, which is 56% smaller than that for TB = 540 °C (λSi = 5.2 nm).
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68.35.Dv Composition, segregation; defects and impurities
85.40.Ry Impurity doping, diffusion and ion implantation technology
85.40.Sz Deposition technology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
85.30.Tv Field effect devices
72.20.-i Conductivity phenomena in semiconductors and insulators
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.uj III-V and II-VI semiconductors

Anisotropic high aspect ratio etch for perfluorcyclobutyl polymers with stress relief technique

Nazli Rahmanian, Seunghyun Kim, and Gregory P. Nordin

J. Vac. Sci. Technol. B 24, 2672 (2006); http://dx.doi.org/10.1116/1.2382945 (6 pages) | Cited 1 time

Online Publication Date: 9 November 2006

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The authors have developed an anisotropic, high aspect ratio (18:1) etch for perfluorocyclobutyl (PFCB) polymers with trenches as narrow as 800 nm using a CO/O2 etch chemistry in an inductively coupled plasma reactive ion etcher. Anisotropy is achieved by carbon sidewall passivation. The motivation for this etch development is to use the air trenches as very compact waveguide splitters [ S. Kim et al., Opt. Eng. 45, 054602 (2006) ]. The authors report a new trench widening mechanism due to tensile stress of the PFCB films and a method of avoiding this widening through the use of additional stress relief trenches on both sides of the desired trench.
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52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
81.65.Rv Passivation
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
84.40.Az Waveguides, transmission lines, striplines

Plasma oxidation of polyhedral oligomeric silsesquioxane polymers

D. Eon, V. Raballand, G. Cartry, C. Cardinaud, N. Vourdas, P. Argitis, and E. Gogolides

J. Vac. Sci. Technol. B 24, 2678 (2006); http://dx.doi.org/10.1116/1.2382947 (11 pages) | Cited 6 times

Online Publication Date: 9 November 2006

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Copolymers containing polyhedral oligomeric silsesquioxane (POSS™) units have been developed to be used as photoresist components in a bilayer resist scheme for 193 nm lithography. This article reports on the behavior of these new POSS based materials under oxygen plasmas. The authors demonstrate using in situ ellipsometry and in situ x-ray photoelectron spectroscopy that during the first seconds in the plasma a silicon oxide layer is formed on the top surface of the POSS materials. This superficial layer prevents etching and material consumption. An ion-enhanced oxidation model is proposed to describe and explain the experimental data and further investigate POSS etching mechanisms in oxygen plasma. The model shows that the oxide formation rate is reduced exponentially with the oxide thickness. It also predicts that thickness loss has its main roots in the layer densification that occurs when the oxide is formed and shows that the oxide formation is ion enhanced and thus favored at −100 V compared to 0 V bias.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.Mq Oxidation
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
79.60.Fr Polymers; organic compounds
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Effects of SiO2/Si3N4 hard masks on etching properties of metal gates

Wan Sik Hwang, Byung-Jin Cho, Daniel S. H. Chan, Vladimir Bliznetsov, and Won Jong Yoo

J. Vac. Sci. Technol. B 24, 2689 (2006); http://dx.doi.org/10.1116/1.2382950 (6 pages) | Cited 3 times

Online Publication Date: 9 November 2006

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Reduced etching rates of advanced metal gates (TaN, TiN, and HfN) using SiO2/Si3N4 hard masks are observed in Cl2 plasma. Si and O released from hard masks react with metal surfaces newly exposed to the plasma during the etching, thereby forming metal oxides. The metal oxides formed on the etched surface retard the etch rates. The suppression of etch rates with hard mask is more obvious for TiN than for TaN and HfN, because Ti oxides are readily formed on the etched TiN surface due to their low Gibbs free energies of formation. The surface of TiN degrades with etching time with SiO2 mask, because etching rates of Si oxides and Ti oxides are different in the (TiO2)1−x(SiO2)x residues remaining on the etched surface. In contrast, a conventional poly-Si electrode does not show the mask effects on etch rates and surface roughness.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
65.40.G- Other thermodynamical quantities
82.60.Cx Enthalpies of combustion, reaction, and formation
68.35.B- Structure of clean surfaces (and surface reconstruction)

Time of flight secondary ion mass spectroscopy investigation of ultralow-k dielectric modifications in hydrogen and deuterium plasmas

P. Lazzeri, G. J. Stueber, G. S. Oehrlein, R. McGowan, E. Busch, S. Pederzoli, M. Bersani, and M. Anderle

J. Vac. Sci. Technol. B 24, 2695 (2006); http://dx.doi.org/10.1116/1.2382949 (7 pages) | Cited 9 times

Online Publication Date: 10 November 2006

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Photoresist stripping processes based on hydrogen reductive chemistry have emerged as attractive replacements of the conventional treatments performed using O2 plasma. H2 discharges and plasma processes based on gas mixtures containing H2 provide, in fact, adequate stripping rates while reducing the chemical modifications of the porous ultralow-k (ULK) dielectric materials employed in interconnect technology. In this work the authors investigate the chemical modification of a number of organosilicate low-k dielectrics interacting with remote H2 plasma. The materials include both spin-on and plasma-enhanced chemical vapor deposited dielectrics with k, porosity, and chemical composition spanning on a broad range of values. The mechanisms of plasma∕dielectric reaction and the depth of interaction are evaluated by means of time of flight secondary ion mass spectrometry. In order to study the nature of the plasma∕dielectric interactions and the chemical modifications introduced in the ULK materials, deuterium (D2) is used to substitute for H2 in the discharge. Although the plasma-generated radicals interact strongly with the materials, negligible stoichiometry modifications are observed during exposure of silica-rich ULK materials. On the other hand, the dielectrics with higher carbon content undergo major compositional changes. The chemical damage introduced by H2-based discharges depends strongly on the formulation of the organosilicate material. The substrate temperature is also seen to affect the influx of plasma species. This acts on the extent of material modifications. Nevertheless, the nature of plasma∕dielectric interactions does not vary for processes performed in the temperature range of 200–300 °C.
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82.33.Ln Reactions in sol gels, aerogels, porous media
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.77.-j Plasma applications
52.80.-s Electric discharges
77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
61.43.Gt Powders, porous materials
82.80.Rt Time of flight mass spectrometry

Thin-film transistors with amorphous indium gallium oxide channel layers

H. Q. Chiang, D. Hong, C. M. Hung, R. E. Presley, John F. Wager, C.-H Park, D. A. Keszler, and G. S. Herman

J. Vac. Sci. Technol. B 24, 2702 (2006); http://dx.doi.org/10.1116/1.2366569 (4 pages) | Cited 28 times

Online Publication Date: 13 November 2006

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Indium gallium oxide-based thin-film transistors (TFTs) are formed using rf magnetron sputtering of the channel layer. These TFTs exhibit qualitatively ideal characteristics, including excellent drain current saturation. Various deposition parameters, annealing treatments, and stoichiometries are explored. Varying the oxygen partial pressure is found to have a significant effect on device performance. Decreasing the oxygen partial pressure increases the incremental channel mobility μinc while decreasing (becomes more negative) the turn-on voltage Von. Increasing indium concentration of the channel material increases μinc, while decreasing Von. The maximum value of μinc, ∼ 27 cm2 V−1 s−1, is obtained by annealing at 600 °C, with corresponding Von and drain current on-to-off ratio values of approximately −14 V and >106, respectively. Additionally, TFTs subjected to a 200 °C postdeposition annealing exhibit μinc and Von of ∼ 19 cm2 V−1 s−1 and 2 V, respectively.
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85.30.Tv Field effect devices
81.40.Gh Other heat and thermomechanical treatments
81.15.Cd Deposition by sputtering

Demonstration of spatially programmable chemical vapor deposition: Model-based uniformity∕nonuniformity control

Ramaswamy Sreenivasan, Raymond A. Adomaitis, and Gary W. Rubloff

J. Vac. Sci. Technol. B 24, 2706 (2006); http://dx.doi.org/10.1116/1.2359735 (10 pages) | Cited 1 time

Online Publication Date: 16 November 2006

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A new chemical vapor deposition (CVD) reactor design was developed to intentionally induce spatially nonuniform film thickness deposition patterns on a single wafer. A segmented showerhead design allows individual regions of a wafer to be exposed to different precursor concentrations simultaneously during a run resulting in different thickness profiles on the wafer and a thickness gradient at the boundaries between segment regions. Different recipes were cycled through each of the segments in a sequence of deposition experiments to develop a model relating precursor concentration to film thickness in each segment region. As a demonstration of spatial programmability, the system was reprogramed using this model to produce uniform thickness amongst the segments; intersegment uniformity approaching 0.60% (thickness standard deviation) was demonstrated. Potential applications of this reactor design to combinatorial CVD are discussed.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth

Quantifying release in step-and-flash imprint lithography

Edwin P. Chan and Alfred J. Crosby

J. Vac. Sci. Technol. B 24, 2716 (2006); http://dx.doi.org/10.1116/1.2366586 (7 pages) | Cited 6 times

Online Publication Date: 21 November 2006

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Step-and-flash imprint lithography (S-FIL) is a leading candidate as the next-generation lithographic technique for replicating sub-10-nm features. The success of this technique is largely connected to the proper control of the interface formation and separation during the imprinting process. In particular, the release process of the imprinted layer from the master template is not straightforward. During release, the path of interface separation must follow precisely the complex topography of geometric features on the sub-100-nm length scale. While the issue of release is currently being addressed, more work is required to understand the underlying mechanisms in controlling release to increase the robustness of this technique in order to make it industrially viable. In this article, the authors describe a metrology for quantifying release in S-FIL. They show that the surface property and the elastic modulus of the template material control the release characteristics. They demonstrate that substituting the rigid template with a soft, elastomeric template can drastically lower the separation force necessary for release.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
68.35.Gy Mechanical properties; surface strains
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
82.35.-x Polymers: properties; reactions; polymerization

Low-resistance Ohmic contacts developed on undoped AlGaN/GaN-based high electron mobility transistors with AlN interlayer

Yunju Sun and L. F. Eastman

J. Vac. Sci. Technol. B 24, 2723 (2006); http://dx.doi.org/10.1116/1.2395964 (3 pages) | Cited 3 times

Online Publication Date: 21 November 2006

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A low-resistance Ohmic contact on undoped GaN/AlGaN/AlN (10 Å)/GaN high electron mobility transistors is first demonstrated using a Ta/Ti/Al/Mo/Au metallization scheme. A contact resistance of 0.16±0.03 Ω mm is achieved by rapid thermal annealing of the evaporated contact at 700 °C for 1 min followed by 800 °C for 30 s in a N2 ambient. Excellent edge acuity is also demonstrated for this annealed Ta/Ti/Al/Mo/Au Ohmic contact.
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73.40.Ns Metal-nonmetal contacts
85.30.Tv Field effect devices
85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Cg Contact resistance, contact potential
61.72.Cc Kinetics of defect formation and annealing

Electron cyclotron plasma etching damage investigated by InGaAs/GaAs quantum well photoluminescence

S. N. M. Mestanza and N. C. Frateschi

J. Vac. Sci. Technol. B 24, 2726 (2006); http://dx.doi.org/10.1116/1.2366543 (5 pages)

Online Publication Date: 22 November 2006

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Photoluminescence (PL) was used to study the damage of (100) GaAs surfaces exposed to BCl3/Ar plasma generated by an electron cyclotron resonance system. With PL measurement of strained InGaAs/GaAs quantum wells within the etched top GaAs layer, our analysis shows that this technique assesses damages to the structure not detected by atomic force microscopy and photoreflectance. A transport model is used to show a 100 times reduction in the Debye length for a 100 nm layer underneath the etching surface.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
78.67.De Quantum wells
78.55.Cr III-V semiconductors

Characterization and optimization of a P-channel poly(o-methoxyaniline) based thin film transistor

Roshan P. Shrestha, Dongxing Yang, Yuxiang Li, Li Yan, and Eugene A. Irene

J. Vac. Sci. Technol. B 24, 2731 (2006); http://dx.doi.org/10.1116/1.2382946 (6 pages)

Online Publication Date: 22 November 2006

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Poly(o-methoxyaniline) based thin film organic transistors (OTFT’s) have been fabricated on a variety of dielectrics: SiO2, polyethylene, and polyvinylidene fluoride trifluoroethylene. Resulting inverted gate OTFT’s were found to be P channel with Au contacts. The mobility was measured to be around 10−3 cm2 V−1 s−1 for as-deposited thin film OTFT structures but could be improved by an order of magnitude by doping, annealing, and decreasing the static dielectric constant of the gate dielectric.
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85.30.Tv Field effect devices

Effects of Zn content on structural and transparent conducting properties of indium-zinc oxide films grown by rf magnetron sputtering

Jae-Soung Park, Ju-Il Song, Young-Woo Heo, Joon-Hyung Lee, Jeong-Joo Kim, W. T. Lim, L. Stafford, D. P. Norton, and S. J. Pearton

J. Vac. Sci. Technol. B 24, 2737 (2006); http://dx.doi.org/10.1116/1.2393246 (4 pages) | Cited 11 times

Online Publication Date: 22 November 2006

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Indium-zinc oxide (IZO) films were grown on glass substrates by rf magnetron sputtering using targets of 50 mol % In2O3–50 mol % In2O3(ZnO)3 and In2ZnkOk+3 (k = 3, 4, 5, and 7) at room temperature and 300 °C. The difference in Zn content between the films and the sputter targets varied with the growth temperature. The structural, electrical, and optical properties of the IZO films were investigated as a function of Zn content. The crystal structure of IZO films grown at room temperature changed from amorphous to crystalline at a Zn content (Zn/(Zn+In)) of 68 at. %. IZO films grown at 300 °C using a target of 50% In2O3–50% In2O3(ZnO)3 had a Zn content of 40 at. % and its x-ray diffraction peaks were matched with those of ITO. As the Zn content in IZO thin films grown at 300 °C increased from 40 to 74 at. %, the conductivity and optical band gap energy decreased.
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68.55.-a Thin film structure and morphology
73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
81.05.Hd Other semiconductors
81.15.Cd Deposition by sputtering
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Deviations from ideal nucleation-limited relaxation in high-Ge content compositionally graded SiGe/Si

David M. Isaacson, Carl L. Dohrman, and Eugene A. Fitzgerald

J. Vac. Sci. Technol. B 24, 2741 (2006); http://dx.doi.org/10.1116/1.2366584 (7 pages) | Cited 4 times

Online Publication Date: 27 November 2006

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The authors report the sudden rise in threading dislocation density in Ge-rich relaxed graded SiGe layers grown at higher growth temperatures (T>550 °C). They attribute this rise in threading dislocation density in relaxed Ge to dislocation nucleation. This observation is contrary to conventional graded buffers in Si-rich material, where higher growth temperatures result in reduced threading dislocation densities (TDDs). Additionally, a coupling effect between the effective strain during graded buffer growth and the growth rate was observed, as evidenced by increased TDD values at reduced growth rates. They conclude that reduced growth rates allow more time for the surface to evolve (i.e., roughen) during growth, thereby trapping mobile dislocations and necessitating the nucleation of additional dislocations to continue relaxing the structure.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.37.Lp Transmission electron microscopy (TEM)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Mechanisms of isotropic and selective etching between SiGe and Si

V. Caubet, C. Beylier, S. Borel, and O. Renault

J. Vac. Sci. Technol. B 24, 2748 (2006); http://dx.doi.org/10.1116/1.2393244 (7 pages)

Online Publication Date: 27 November 2006

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The impact of SiGe isotropic etching selectively to Si on structures such as silicon on nothing or gate all around has been evaluated through the electrical performances of devices that were subjected to different etching processes. New prospects and evolutions in microelectronics can be foreseen, thanks to the development of the opposite process, i.e., the isotropic etching of Si selectively to SiGe. This process is based on the passivation of the SiGe layer during etching in a chemical dry etching tool. Scanning electron microscopy and x-ray photoelectron spectroscopy studies allowed the analysis of the influence of each parameter (gas mixture, pressure, and microwave power) and the proposal of etching and passivation mechanisms. This led to the definition of a highly selective Si:SiGe process.
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81.65.Cf Surface cleaning, etching, patterning
81.65.Rv Passivation
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.05.Cy Elemental semiconductors
81.05.Hd Other semiconductors

Custom design of optical-grade thin films of silicon oxide by direct-write electron-beam-induced deposition

Heinz D. Wanzenboeck, Markus Fischer, Robert Svagera, Johann Wernisch, and Emmerich Bertagnolli

J. Vac. Sci. Technol. B 24, 2755 (2006); http://dx.doi.org/10.1116/1.2393245 (6 pages) | Cited 8 times

Online Publication Date: 27 November 2006

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This work describes a rapid fabrication approach of thin silicon oxide films on confined areas by electron-beam-induced deposition. This maskless direct-write process utilizes a localized chemical vapor deposition (CVD) on specific areas utilizing a focused electron beam. The deposition from siloxane vapor in the presence of oxygen is initiated by the energy of an electron beam of 1 nm diameter. By scanning the beam, thin films with arbitrary geometries and three-dimensional structures were deposited. In contrast to blanket deposition with conventional methods such as thermal CVD or plasma-enhanced CVD, the lateral confined layers can be fabricated at room temperature. With a maskless process, the final structure is fabricated within a single process step. The process was optimized towards a high deposition rate and high material purity. The influence of process parameters on the deposition efficiency is discussed. A characterization of the chemical composition and of the surface roughness was performed with auger electron spectroscopy, energy-dispersive x-ray, and atomic force microscopy, respectively. The optical properties were investigated by transmission measurement at 248 nm. The correlation to processing conditions and the growth mechanism induced by the electron beam is discussed. This work illustrates the flexibility of this maskless method and the potential to control material properties via the process parameters. The fabrication of exemplary structures such as three-dimensional silicon oxide pillars and transparent films illustrates the application potential of this versatile direct-write method.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.66.-w Optical properties of specific thin films
42.70.-a Optical materials

Coulomb blur in a multi-electron-beam system

Yasunari Sohda, Osamu Kamimura, and Hiroya Ohta

J. Vac. Sci. Technol. B 24, 2761 (2006); http://dx.doi.org/10.1116/1.2382948 (4 pages)

Online Publication Date: 28 November 2006

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Coulomb blur in a multi-electron-beam system with a single column was investigated by simulations and experiments in 1024 two-dimensional electron beams with double lens-doublet optics. Monte Carlo simulation showed three main points. First, in spite of a high current density, Coulomb blur and energy broadening were the same as those in the case of a shaped beam covering a multi-electron-beam area. The Coulomb blur for a 50 keV electron beam at 1 μA total beam current was simulated as 20 nm, which was less than half of that in the case of a single beam. Second, the Coulomb blur is slightly nonuniform depending on the distance from the beam center. Third, the decrease in the Coulomb blur by beam blanking is similar to that by beam absence at the objective plane. In addition, Coulomb blurs of the axial beam were estimated by experiments at various currents. The results show that the experimental blurs were in good agreement with the simulated blurs. In conclusion, the authors clarified that multiplying the number of beams is effective for decreasing Coulomb blur at the same total current.
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41.75.Fr Electron and positron beams
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Interconnecting single nano-objects on surfaces for transport experiments

A. Della Torre, P. P. Pompa, L. L. del Mercato, R. Cingolani, R. Rinaldi, S. Shiv Shankar, and M. Sastry

J. Vac. Sci. Technol. B 24, 2765 (2006); http://dx.doi.org/10.1116/1.2366606 (4 pages)

Online Publication Date: 30 November 2006

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The authors report a highly controlled approach, based on electron-beam lithography, to interconnect individual nano-objects for transport experiments. The process is based on a three-step procedure, consisting of fabrication of four alignment markers, localization of the nano-object after its immobilization onto functionalized surfaces, and interconnection of the single nanostructure by patterning two nanoelectrodes on its sides. The approach is highly reproducible and widely applicable and allows an alignment accuracy of 15–20 nm. Here they demonstrate the reliability of such technique by using a thin triangular gold nanoprism as the active element and show the I-V characteristics of the single nanostructure.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
81.05.Bx Metals, semimetals, and alloys

Fabrication of nanoelectromechanical resonators using a cryogenic etching technique

N. Nelson-Fitzpatrick, K. Westra, P. Li, S. McColman, N. Wilding, and S. Evoy

J. Vac. Sci. Technol. B 24, 2769 (2006); http://dx.doi.org/10.1116/1.2366608 (3 pages) | Cited 1 time

Online Publication Date: 30 November 2006

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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Reverse transfer of nanostencil patterns using intermediate sacrificial layer and lift-off process

Chan Woo Park, Oscar Vazquez Mena, Marc A. F. van den Boogaart, and Jürgen Brugger

J. Vac. Sci. Technol. B 24, 2772 (2006); http://dx.doi.org/10.1116/1.2366610 (4 pages)

Online Publication Date: 30 November 2006

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We propose a new process by which patterns produced by nanostencil lithography can be reversed, so that the final pattern on the substrate has the same contrast (filled or empty) as that of the stencil. In this process, the stencil pattern is first formed on an intermediate sacrificial layer, and then transferred onto the underlying substrate in a reverse manner. Using this process, we can form various pattern structures that cannot be produced by the normal stencil process, such as an array of pores or multiple parallel bridges. Because a bridge in the stencil is transferred also as a bridge on the substrate, we can not only avoid the widening of a narrow bridge pattern by the stress-induced bending of the membrane, but also reduce the width of the bridge even further using the pattern blurring. Using SiO2 as an intermediate layer, we have fabricated various reversed Cr patterns on Si, including an array of 800 nm circular pores and a 100-nm-wide and 150-nm-long nanobridge.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
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Enabling in situ atomic scale surface imaging for vertical molecular beam epitaxy machines

Dong Jun Kim, Deokjoon Cha, Gregory J. Salamo, and Haeyeon Yang

J. Vac. Sci. Technol. B 24, 2776 (2006); http://dx.doi.org/10.1116/1.2395963 (3 pages) | Cited 2 times

Online Publication Date: 30 November 2006

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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.Ta Quantum dots
81.07.Vb Quantum wires
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back to top Optical Lithography

Immersion patterning down to 27 nm half pitch

T. M. Bloomstein, T. H. Fedynyshyn, I. Pottebaum, M. F. Marchant, S. J. Deneault, and M. Rothschild

J. Vac. Sci. Technol. B 24, 2789 (2006); http://dx.doi.org/10.1116/1.2366678 (9 pages) | Cited 4 times

Online Publication Date: 30 November 2006

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Liquid immersion interference lithography at 157 nm has been used to print gratings of 27 nm half pitch with a fluorine-doped fused silica prism having index of 1.66. In order to achieve these dimensions, new immersion fluids have been designed and synthesized. These are partially fluorinated organosiloxanes with indexes up to 1.5. Their absorbance is on the order of 0.4/μm (base 10), enabling the use of liquid films with micron-size thickness. To utilize these semiabsorptive fluids, an immersion interference printer has been designed, built, and implemented for handling micron-scale liquid layers.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Rf Micro- and nanoscale pattern formation
68.15.+e Liquid thin films

Effect of resist surface characteristics on film-pulling velocity in immersion lithography

S. Schuetter, T. Shedd, G. Nellis, A. Romano, R. Dammel, M. Padmanaban, F. Houlihan, A. Krawicz, G. Lin, D. Rahman, S. Chakrapani, M. Neisser, and C. Van Peski

J. Vac. Sci. Technol. B 24, 2798 (2006); http://dx.doi.org/10.1116/1.2387160 (5 pages)

Online Publication Date: 30 November 2006

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In an immersion lithography system, liquid loss may occur at the receding contact line associated with the free surface of the liquid that is confined between the stationary lens apparatus and the moving wafer (or substrate). This deposited liquid may lead to defects in the printed features. The critical velocity for liquid loss is a function of the substrate surface properties, the geometry of the immersion lens, and the properties of the immersion liquid. This article investigates the effect of both the fluid properties of the immersion liquid and surface characteristics of the substrate on liquid loss velocity. Specifically, glycerine-water mixtures of varying viscosities were tested to determine the effect on critical velocity. In this article the authors experimentally investigate the impact of the partition coefficient or log P, which is a measure of the relative hydrophobicity of different surfaces. The correlation is used to approximately isolate the effect of the static, receding contact angle from log P on the critical velocity for liquid loss and an additional correction term for the correlation is proposed based on correlating these results.
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66.20.-d Viscosity of liquids; diffusive momentum transport
81.16.Nd Micro- and nanolithography
68.03.Cd Surface tension and related phenomena

Impact of stray light depending on image quality: An approximation using total integrated scatter

Young-Chang Kim, Peter De Bisschop, Geert Vandenberghe, Luc Van Den Hove, Hanku Cho, and Jootae Moon

J. Vac. Sci. Technol. B 24, 2803 (2006); http://dx.doi.org/10.1116/1.2357965 (5 pages)

Online Publication Date: 30 November 2006

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Stray light (or flare) in optical microlithography causes critical dimension (CD) variation depending on local mask transmission. This CD change can be approximately estimated using image quality and total integrated scatter (TIS) which is defined as the integral of stray-light characteristic function, power spectral density. This TIS approximation is experimentally verified for various features on ArF lithographic processes and is particularly useful for determination of tool specification for a given application.
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81.16.Nd Micro- and nanolithography

Phase shift mask interferometric birefringence monitor

Gregory R. McIntyre and Andrew Neureuther

J. Vac. Sci. Technol. B 24, 2808 (2006); http://dx.doi.org/10.1116/1.2395951 (7 pages) | Cited 1 time

Online Publication Date: 30 November 2006

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A new type of birefringence monitor based on phase shift masks is proposed and initially characterized for optical lithography using simulation of the electromagnetic artifacts and of the images that result. Birefringence is important in steppers at 193 nm due to its inherent existence in crystal structures. The technique developed in this article employs a set of crossed polarizers with one located in a pinhole within an opaque layer in the back side of the photomask and the other just above the image plane. The small amount of rotation due to birefringence in the projection optics will create a fairly small transmission in the presence of birefringence. The detection of the small amount of birefringence is greatly enhanced by providing a circularly polarized reference wave from a subresolution chromeless grating with which the birefringent component interferometrically interacts with. Simulation studies show a theoretical sensitivity of this technique of 1.3% of the clear field intensity per nanometer of birefringence, where the signal is dependent on fast axis orientation. Implementation of other variations of birefringence monitors is discussed using as a key enabler a chromeless grating of subresolution pitch in place of a rotating wave plate.
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07.60.Ly Interferometers
42.79.Ci Filters, zone plates, and polarizers
42.79.Dj Gratings

Generation of isofocal target patterns using process modeling during optical proximity correction

Lawrence S. Melvin, Ebo Croffie, and Abani Biswas

J. Vac. Sci. Technol. B 24, 2815 (2006); http://dx.doi.org/10.1116/1.2397069 (5 pages)

Online Publication Date: 30 November 2006

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Isofocal patterns produce the most ideal manufacturing conditions on a reticle, however, most semiconductor designs contain few isofocal features. A new way of looking at defocus conditions based on the change in intensity with respect to nominal focus [ L. S. Melvin III et al., J. Vac. Sci. Technol. B 23, 2631 (2005) ]—referred to as IΔ—can be used to resize the target pattern to isofocal dimensions. The pattern is quantitatively analyzed using IΔ to find modified pattern shapes that give isofocal target patterns for optical proximity correction and/or resolution enhancement techniques. The target pattern is then made isofocal by resizing the pattern to the modified shape prior to the use of optical proximity correction and/or resolution enhancement techniques. Results of this concept demonstrate excellent improvement in the feature robustness of different features at various defocus conditions. The proposed isofocal targeting method can be applied to layers where trade-offs between pattern shape and final pattern fidelity may be manipulated to improve process depth of focus.
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85.40.Hp Lithography, masks and pattern transfer
back to top EUV Lithography

Novel absorber stack for minimizing shadow effect in extreme ultraviolet mask

Tae Geun Kim, Byung Hun Kim, In-Yong Kang, Yong-Chae Chung, Jinho Ahn, Seung Yoon Lee, In-Sung Park, Chung Yong Kim, and Nae-Eung Lee

J. Vac. Sci. Technol. B 24, 2820 (2006); http://dx.doi.org/10.1116/1.2393295 (4 pages) | Cited 1 time

Online Publication Date: 30 November 2006

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Finding an optimized absorber stack is becoming a more critical issue in the fabrication of extreme ultraviolet (EUV) mask since it is directly related to the performance of lithography such as pattern fidelity and productivity. Optical simulation, deposition, and measurement have been conducted to establish an optimized absorber stack including antireflection coating (ARC), absorber layer, and capping (or buffer) layer, which satisfies major requirements for EUV mask applications. TaN and the other absorber candidates do not show acceptable reflectivity value (lower than 5%) in deep ultraviolet (DUV) wavelength region (199 or 257 nm) for pattern inspection. DUV reflectivity can be lowered by applying C and Al2O3 layers as top ARCs for 199 and 257 nm wavelengths, respectively, while keeping the EUV reflectivity at 13.5 nm less than 1%. ARC-covered TaN absorber stacks result in a reduction of printed CD variation owing to the mitigation of the shadow effect. However, long-term stability and fabricability of these stacks should be examined further.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
42.79.Wc Optical coatings

Actinic inspection of extreme ultraviolet programed multilayer defects and cross-comparison measurements

Kenneth A. Goldberg, Anton Barty, Yanwei Liu, Patrick Kearney, Yoshihiro Tezuka, Tsuneo Terasawa, John S. Taylor, Hak-Seung Han, and Obert R. Wood

J. Vac. Sci. Technol. B 24, 2824 (2006); http://dx.doi.org/10.1116/1.2375085 (5 pages) | Cited 17 times

Online Publication Date: 30 November 2006

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The production of defect-free mask blanks remains a key challenge for extreme ultraviolet (EUV) lithography. Integral to this effort is the development and characterization of mask inspection tools that are sensitive enough to detect critical defects with high confidence. Using a single programed-defect mask with a range of buried bump-type defects, the authors report a comparison of measurements made in four different mask inspection tools: one commercial tool using 488 nm wavelength illumination, one prototype tool that uses 266 nm illumination, and two noncommercial EUV “actinic” inspection tools. The EUV tools include a dark field imaging microscope and a scanning microscope. Their measurements show improving sensitivity with the shorter wavelength non-EUV tool, down to 33 nm spherical-equivalent-volume diameter, for defects of this type. Measurements conditions were unique to each tool, with the EUV tools operating at a much slower inspection rate. Several defects observed with EUV inspection were below the detection threshold of the non-EUV tools.
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85.40.Hp Lithography, masks and pattern transfer

Distortion of chucked extreme ultraviolet reticles from entrapped particles

V. Ramaswamy, R. L. Engelstad, K. T. Turner, A. R. Mikkelson, and S. Veeraraghavan

J. Vac. Sci. Technol. B 24, 2829 (2006); http://dx.doi.org/10.1116/1.2375078 (5 pages) | Cited 5 times

Online Publication Date: 30 November 2006

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Successful imaging of patterns with critical dimensions less than 45 nm with extreme ultraviolet lithography (EUVL) requires stringent controls on all sources of image placement (IP) errors. Among the potential sources of IP error is the mechanical distortion of the patterned mask when mounted in the exposure tool. An EUVL reticle can exhibit both in-plane distortion and out-of-plane distortion due to the presence of debris lodged between the mask and the electrostatic chuck. Even particles with a compressed height as small as 100 nm have the potential to consume a significant portion of the IP error budget. To alleviate this problem, a thorough understanding of the response of the reticle∕particle∕chuck system during electrostatic chucking is essential. This article describes experimental indentation testing to characterize relevant nanoscale material properties and the subsequent use of the data in finite element models that simulate the system response under typical chucking conditions.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
81.70.Bt Mechanical testing, impact tests, static and dynamic loads

Electrostatic chucking for extreme ultraviolet lithography: Simulations and experiments

M. Nataraju, J. Sohn, S. Veeraraghavan, A. R. Mikkelson, K. T. Turner, R. L. Engelstad, C. K. Van Peski, and K. J. Orvek

J. Vac. Sci. Technol. B 24, 2834 (2006); http://dx.doi.org/10.1116/1.2388967 (6 pages) | Cited 2 times

Online Publication Date: 30 November 2006

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The purpose of this research is to assess the effectiveness of electrostatic chucks in reducing low-spatial frequency mask (or reticle) flatness variations and to validate finite element (FE) models of the chuck-mask interaction. The flatness of a sample extreme ultraviolet lithography reticle and an electrostatic pin chuck were measured using a Zygo interferometer. The measured flatness data were entered into the FE models, and electrostatic chucking was simulated by applying an area-weighted average pressure on the reticle. The shape of the mask when clamped by the electrostatic chuck was then predicted using the FE model. To validate these predictions, experiments were conducted in which the previously measured reticle was electrostatically clamped using the pin chuck. These experiments were conducted in a vacuum chamber to minimize the effects of humidity. Interferometric plots of the chucked reticle surface were obtained and compared with the FE predictions. It was found that the measured and predicted shapes were in good agreement. Results from the experiments and simulations will be used to establish specifications for the chuck design and to identify the range of flatness variations that can be accommodated with electrostatic chucking.
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85.40.Hp Lithography, masks and pattern transfer
back to top Synchrotron Lithography

Three-dimensional patterning using fine step motion in synchrotron radiation lithography

M. Fukuda, K. Deguchi, M. Suzuki, and Y. Utsumi

J. Vac. Sci. Technol. B 24, 2840 (2006); http://dx.doi.org/10.1116/1.2366620 (4 pages)

Online Publication Date: 30 November 2006

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A simple method of fabricating blazed diffraction gratings using synchrotron radiation lithography was developed that employs an ordinary binary mask with a line-and-space pattern, a step-and-expose procedure that provides a linear cumulative-dose distribution, and a thick resist with a linear sensitivity curve. This method enables the fabrication of blazed gratings with a grating pitch of 1 μm and a blaze angle of 15°–40°. The angle and pitch can be changed by changing the dose from step to step and/or by using mask spaces of different widths.
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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
42.79.Dj Gratings

Properties of zone plates used for lithography

R. Zheng, L. Jiang, and M. Feldman

J. Vac. Sci. Technol. B 24, 2844 (2006); http://dx.doi.org/10.1116/1.2393293 (4 pages) | Cited 1 time

Online Publication Date: 30 November 2006

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The applications of zone plates to lithography are well known: to pattern, to measure, and to align between levels. Recent work has shown that zone plates with low numerical apertures and as few as two zones can produce focused spots that are nearly diffraction limited and that have minimal side lobes. With x-ray lithography such zone plates can be used to pattern vias down to at least 30 nm in diameter. In addition, the small size of these zone plates permits them to be arranged in densely packed arrays, attractive for direct write and metrology applications. In spite of the importance of their potential applications, the imaging properties of these zone plates are generally unrecognized, and sometimes quite surprising. This work models zone plates with seven or fewer zones, as a function of their phase shifts and transmissions. X-ray wavelengths are emphasized, but the simulation results are supported by experimental work on zone plate geometries scaled up in size to the visible region.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
81.16.Nd Micro- and nanolithography
42.79.Ci Filters, zone plates, and polarizers

Pulse reverse plating for uniform nickel height in zone plates

M. Lindblom, H. M. Hertz, and A. Holmberg

J. Vac. Sci. Technol. B 24, 2848 (2006); http://dx.doi.org/10.1116/1.2395953 (4 pages) | Cited 6 times

Online Publication Date: 30 November 2006

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Nickel soft x-ray zone plates are fabricated by through-mask electroplating. The authors report on how a uniform nickel thickness can be obtained over the entire zone plate using pulse and pulse reverse plating. If the plating is carried out at a constant current the nickel thickness has been observed to decrease with radius. This results in lower outer zones and reduced diffraction efficiency in the outer parts of the zone plates. Here they show that the height profile can be controlled by adjusting the current density of the pulses. A high current density is found to primarily affect the edges while a low current density was observed to affect the central parts of the structures. This is true for both cathodic and anodic currents, which means that local plating and dissolution rates can be adjusted to obtain a uniform mass distribution.
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42.79.Ci Filters, zone plates, and polarizers
42.86.+b Optical workshop techniques
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution
back to top Maskless Lithography

Spatial light modulator for maskless optical projection lithography

G. P. Watson, V. Aksyuk, M. E. Simon, D. M. Tennant, R. A. Cirelli, W. M. Mansfield, F. Pardo, D. O. Lopez, C. A. Bolle, A. R. Papazian, N. Basavanhally, J. Lee, R. Fullowan, F. Klemens, J. Miner, et al.

J. Vac. Sci. Technol. B 24, 2852 (2006); http://dx.doi.org/10.1116/1.2387156 (5 pages) | Cited 5 times

Online Publication Date: 30 November 2006

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Spatial light modulators (SLMs) designed to replace photomasks for optical lithography have been designed, fabricated, and tested. These microelectromechanical devices are fabricated with alternating polycrystalline Si and sacrificial SiO2 layers that are patterned by a 193 nm wavelength scanner to dimensions as small as 150 nm. Aerial image simulations were used to define the mechanical requirements of the devices. Piston motion of electrically actuated devices was measured with an optical profilometer. The measurements were fit to a simple equation to within 1 nm precision, which is adequate for defining 50 nm features lithographically. Transient response measurements show that one version of the SLM responds to actuation as quickly as 20 μs, fast enough for current 193 nm wavelength excimer laser sources.
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42.79.Hp Optical processors, correlators, and modulators
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.82.Bq Design and performance testing of integrated-optical systems
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer

Integrated multi-electron-beam blanker array for sub-10‐nm electron beam induced deposition

Yanxia Zhang, C. T. H Heerkens, M. J. van Bruggen, and P. Kruit

J. Vac. Sci. Technol. B 24, 2857 (2006); http://dx.doi.org/10.1116/1.2366677 (4 pages) | Cited 2 times

Online Publication Date: 30 November 2006

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An integrated multi-electron-beam blanker array is proposed for the multi-electron-beam source reported by van Bruggen et al. [J. Vac. Sci. Technol. B 23, 2833 (2005)] , which aims at the throughput improvement of sub-10‐nm electron beam induced deposition. The integrated blanker array consists of a current limiting aperture array, a blanker array, and a microaperture-lens array. The integrated blanker array generates 100 individually controlled beamlets, projecting the virtual source image in the principle plane of the field lens. The electrostatic cross-talk, charging, and contamination are reduced by the grounded current limiting aperture plate above the blankers. The blanker array and microaperture-lens array are fabricated on a first wafer, while the current limiting aperture array is fabricated on a second, 100 μm thick wafer. The wafers will be bonded with an alignment accuracy of approximately 200 nm. The first test chips, where the blankers are grouped and controlled by external circuitries, are under fabrication and key processes are tested.
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07.77.Ka Charged-particle beam sources and detectors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
41.75.Fr Electron and positron beams
41.85.Ne Electrostatic lenses, septa
back to top Masks

Electrostatic chuck fringe field simulation and its impact on electron beam extreme ultraviolet mask patterning

Junru Ruan and John Hartley

J. Vac. Sci. Technol. B 24, 2861 (2006); http://dx.doi.org/10.1116/1.2393291 (5 pages)

Online Publication Date: 30 November 2006

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The use of electrostatic chucks in electron beam extreme ultraviolet (EUV) mask patterning has been proposed for distortion control. The high voltages used in electrostatic chucking have the potential to establish fringe field near the edge of the critical area between the mask and the bottom lens plane of the electron optics. This electrostatic field may deflect the trajectories of imaging electrons, and images near the edge of the patterned mask would be degraded. The authors developed three-dimensional (3D) models for the electrostatic chucks and EUV masks and obtained the fringe field information using first order finite element method in Munro’s electron beam software (MEBSSW Ltd., 14 Cornwall Gardens, London SW7 4AN, England). Using electron ray tracing in the field enabled them to compute the deflection and blur introduced on an otherwise perfect point image. To understand how fringe fields influence the image condition of electron optic system when writing on the edge of EUV mask critical area, they need to combine two-dimensional (2D) modeling of electron optic system and 3D modeling of the fringe field. Aberration coefficients for the electron optics are obtained in the 2D models and are used for setting up the initial ray conditions for a large number of electrons as they enter the space between the final lens and the writing plane. These rays are then traced in the fringe field, and the final positions of the electrons recorded and statistically counted. The current density profiles for the images are then plotted as the histogram of electron counts versus position coordinates on the image plane. Comparing the current density profiles of the image with and without fringe field, they are able to determine the displacement and CD uniformity error introduced by the fringe field effect.
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81.16.Nd Micro- and nanolithography
02.70.Dh Finite-element and Galerkin methods

Predicting electron projection lithography mask membrane image placement errors

M. J. Boruszewski, R. L. Engelstad, H. Sakaue, H. Arimoto, and H. Eguchi

J. Vac. Sci. Technol. B 24, 2866 (2006); http://dx.doi.org/10.1116/1.2366655 (5 pages)

Online Publication Date: 30 November 2006

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Electron projection lithography (EPL) has been identified as a viable candidate of the next-generation lithography technologies for moderate-volume production of systems-on-a-chip for the sub-65 nm nodes. EPL is especially suited for the fabrication of contact structures. The development of a low-distortion mask is essential for meeting the stringent requirements at these lower nodes. This research focuses on quantifying in-plane distortions (IPDs) due to mask fabrication and the effects of different mounting schemes in the e-beam writer and exposure tools for a 200 mm EPL stencil mask. In order to quantify the IPD of the freestanding membranes, three-dimensional finite element (FE) models have been developed and benchmarked with experimentally measured data. Metrology measurements in both the membrane-side up and membrane-side down configurations can be used to correct for image placement errors (due to the fabrication and chucking of the mask) by compensating for IPD during the exposure process. To correct for higher order distortions associated with pattern specific errors, FE models were generated to simulate the entire process flow, including chucking. As a sample test case, a stencil pattern was replicated uniformly over the membrane arrays. The actual mask was fabricated and metrology measurements were taken. Selected membranes were experimentally measured to compare with FE results and the data correlated well in both direction and magnitude. Results illustrate that FE modeling and simulation can be used to predict mask distortions due to fabrication. Such techniques can be instrumental in meeting the stringent error budget required at the lower lithographic nodes.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
back to top Charged Particle Sources, Optics and Systems

Helium ion microscope: A new tool for nanoscale microscopy and metrology

B. W. Ward, John A. Notte, and N. P. Economou

J. Vac. Sci. Technol. B 24, 2871 (2006); http://dx.doi.org/10.1116/1.2357967 (4 pages) | Cited 43 times

Online Publication Date: 30 November 2006

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ALIS Corporation has developed a new helium ion microscope which has many advantages over both traditional scanning electron microscopes (SEMs) and focused ion beams (FIBs). This new technology is expected to produce an ultimate focused spot size of 0.25 nm. This high resolution is attributed to the high source brightness (B>4×109 A/cm2 sr), low energy spread (ΔE/E ∼ 2×10−5), and small diffraction effects (λ ∼ 80 fm). The interaction of helium ions with matter offers several valuable contrast mechanisms and a surface interaction volume which is much smaller than a SEM or conventional FIB.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Real-time determination of electron-beam probe shape using an in situ fiducial grid

J. T. Hastings

J. Vac. Sci. Technol. B 24, 2875 (2006); http://dx.doi.org/10.1116/1.2357964 (6 pages) | Cited 1 time

Online Publication Date: 30 November 2006

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Electron-beam probe shape is typically determined by imaging a known or quasirandom target; however, neither standard targets nor two-dimensional image acquisition and processing are suitable for real-time probe characterization during lithographic exposures. Here a new technique for continuously monitoring probe shape is proposed and evaluated. Fourier analysis of the signal generated by an in situ fiducial grid allows estimation of the x and y widths and rotation of a Gaussian beam. The grid itself is rotated with respect to the beam deflection axes to allow real-time estimation of two-dimensional probe shape from a one-dimensional line scan across the grid. Monte Carlo simulations of beam parameter variances versus signal-to-noise ratio reveal regions of operation where the algorithm’s precision is limited by either noise or grid geometry. Experiments using a 1 μm period grid to estimate probe shape as a function of defocus demonstrate the effectiveness of the new approach.
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85.40.Hp Lithography, masks and pattern transfer
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
02.70.Uu Applications of Monte Carlo methods

Orientation dependence of linewidth variation in sub-50-nm Gaussian e-beam lithography and its correction

M. Lu, D. M. Tennant, and C. J. Jacobsen

J. Vac. Sci. Technol. B 24, 2881 (2006); http://dx.doi.org/10.1116/1.2393292 (5 pages) | Cited 2 times

Online Publication Date: 30 November 2006

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The width of tilted line patterns, such as are needed when drawing circular structures, is found to vary with the oblique angle when it falls into the sub-50-nm scale in Gaussian e-beam lithography. The authors’ analysis shows that this orientation dependence of linewidth variation originates from the nonuniformity of discrete primitive filling in Cartesian coordinates. Two correction schemes based on pattern segmentation are proposed. Test exposures of high resolution zone plate patterns show that both two schemes work well; a double-insert scheme is superior in terms of dose distribution uniformity.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
85.40.Hp Lithography, masks and pattern transfer
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.79.Ci Filters, zone plates, and polarizers

Photoelectron emission studies in CsBr at 257 nm

Juan R. Maldonado, Zhi Liu, Yun Sun, Piero A. Pianetta, and Fabian W. Pease

J. Vac. Sci. Technol. B 24, 2886 (2006); http://dx.doi.org/10.1116/1.2363410 (6 pages) | Cited 4 times

Online Publication Date: 30 November 2006

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CsBr/Cr photocathodes were found [ J. R. Maldonado et al., J. Vac. Sci. Technol. B 22, 3025 (2004) ; J. R. Maldonado et al., Proc. SPIE 5520, 46 (2003) ] to meet the requirements of a multielectron beam lithography system operating with a light energy of 4.8 eV (257 nm). The fact that photoemission was observed with a light energy below the reported 7.3 eV band gap for CsBr was not understood. This article presents experimental results on the presence of intra-band-gap absorption sites (IBASs) in CsBr thin film photoelectron emitters, and presents a model based on IBAS to explain the observed photoelectron emission behavior at energies below band gap. A fluorescence band centered at 330 nm with a full width at half maximum of about 0.34 eV was observed in CsBr/Cr samples under 257 nm laser illumination, which can be attributed to IBAS and agrees well with previously obtained synchrotron photoelectron spectra [ J. R. Maldonado et al., J. Vac. Sci. Technol. B 22, 3025 (2004) ] from the valence band of CsBr films.
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79.60.Dp Adsorbed layers and thin films
71.20.Ps Other inorganic compounds
78.60.-b Other luminescence and radiative recombination
85.60.Ha Photomultipliers; phototubes and photocathodes

Arrayed miniature electron beam columns for mask making

J. P. Spallas, C. S. Silver, and L. P. Muray

J. Vac. Sci. Technol. B 24, 2892 (2006); http://dx.doi.org/10.1116/1.2395955 (5 pages) | Cited 5 times

Online Publication Date: 30 November 2006

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A significant problem facing integrated circuit mass-production lithography at future technology generations is the throughput of mask writers. Novelx has developed the technologies to build a distributed multiaxial parallel beam system consisting of a monolithic array of individually correctable electron beam columns. These technologies can be scaled to manufacture a system with a sufficient number of columns to write a single mask at the 32 nm node with a write time of an order of magnitude faster than what is forecasted at the back end of the 45 nm node. The key to these technologies is a new type of miniature electron beam column fabricated and assembled using manufacturable processes. Both single and 1×4 multicolumn systems have been assembled and tested, and have demonstrated 90 nm lithography. The columns in these systems operate at low voltage and are all electrostatic. The lenses are monolithically fabricated bonded stacks of micromachined silicon and glass. The monolithic lenses are assembled onto a single package. The multicolumn lens stacks consist of four independent and electrically isolated lenses. The silicon and package are scalable for continued miniaturization, and can be fabricated in larger monolithic arrays of individually correctable beams. The authors show that the 1×4 column system currently in operation can be scaled to a 4×4 column system and that a mask writer using the 4×4 column system is capable of writing a single mask at the 32 nm dynamic random access memory 1/2 pitch node in 10 h.
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85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer

Comparison of parameters for Schottky and cold field emission sources

G. A. Schwind, G. Magera, and L. W. Swanson

J. Vac. Sci. Technol. B 24, 2897 (2006); http://dx.doi.org/10.1116/1.2366675 (5 pages) | Cited 6 times

Online Publication Date: 30 November 2006

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Total energy distribution (TED) measurements were carried out for point electron sources operating in the cold field (T = 300 K) and Schottky (T = 1800 K) emission regimes. The full width at half maximum (FWHM) values of the TED’s for both emission regimes were found to increase significantly above the respective theoretical values as the emitter radius (a) was decreased and as the angular current density (I′) was increased. This increase in the FWHM arises from the stochastic electron-electron interactions in the beam commonly known as the Boersch [Z. Phys. 139, 115 (1954)] effect. A method was devised to extract the magnitude of the Boersch effect from the experimental TED’s. The TED’s were investigated as a function of I′ and a. In addition, the reduced brightness for both emitters was calculated from the virtual source size and I′ values as a function of the FWHM values.
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73.30.+y Surface double layers, Schottky barriers, and work functions
79.70.+q Field emission, ionization, evaporation, and desorption
back to top Ion Beam Lithography Technology

High brightness inductively coupled plasma source for high current focused ion beam applications

N. S. Smith, W. P. Skoczylas, S. M. Kellogg, D. E. Kinion, P. P. Tesch, O. Sutherland, A. Aanesland, and R. W. Boswell

J. Vac. Sci. Technol. B 24, 2902 (2006); http://dx.doi.org/10.1116/1.2366617 (5 pages) | Cited 13 times

Online Publication Date: 30 November 2006

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A high brightness plasma ion source has been developed to address focused ion beam (FIB) applications not satisfied by the liquid metal ion source (LMIS) based FIB. The plasma FIB described here is capable of satisfying applications requiring high mill rates (>100 μm3/s) with non-gallium ions and has demonstrated imaging capabilities with sub- 100-nm resolution. The virtual source size, angular intensity, mass spectra, and energy spread of the source have been determined with argon and xenon. This magnetically enhanced, inductively coupled plasma source has exhibited a reduced brightness (βr) of 5.4×103 A m−2 sr−1 V−1, with a full width half maximum axial energy spread (ΔE) of 10 eV when operated with argon. With xenon, βr = 9.1×103 A m−2 sr−1 V−1 and ΔE = 7 eV. With these source parameters, an optical column with sufficient demagnification is capable of forming a sub-25-nm spot size at 30 keV and 1 pA. The angular intensity of this source is nominally three orders of magnitude greater than a LMIS making the source more amenable to creating high current focused beams, in the regime where spherical aberration dominates the LMIS-FIB. The source has been operated on a two lens ion column and has demonstrated a current density that exceeds that of the LMIS-FIB for current greater than 50 nA. Source lifetime and current stability are excellent with inert and reactive gases. Additionally, it should be possible to improve both the brightness and energy spread of this source, such that the (βr/ΔE2) figure-of-merit could be within an order of magnitude of a LMIS.
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52.50.Dg Plasma sources
29.25.Ni Ion sources: positive and negative
07.77.Ka Charged-particle beam sources and detectors
41.85.Gy Chromatic and geometrical aberrations

Using laser-cooled atoms as a focused ion beam source

J. L. Hanssen, E. A. Dakin, J. J. McClelland, and M. Jacka

J. Vac. Sci. Technol. B 24, 2907 (2006); http://dx.doi.org/10.1116/1.2363406 (4 pages) | Cited 5 times

Online Publication Date: 30 November 2006

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The authors describe a new method for creating a high quality focused ion beam using laser-cooled neutral atoms in a magneto-optical trap as an ion source. They show that this new technique can provide spot resolutions and brightness values that are better than the state of the art in focused ion beams. The source can be used with a range of different ionic species and can be combined with laser cooling techniques to exert unprecedented control over the ion emission, for example, producing single ions “on demand.” The beam quality is a result of a high brightness and a narrow energy distribution, both of which stem from the cold temperature ( ≈ 100 μK) of the atoms. The ions are produced by subjecting the cold neutral atoms to a photoionization laser, after which they become a compact source of nearly monoenergetic ions. With the application of a potential gradient, the ions form a beam that can be focused via standard ion optical techniques. They discuss estimations based on the initial size of the ion cloud and the energy distribution and show that the resulting beam has a low emittance.
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61.80.Jh Ion radiation effects
07.77.Ka Charged-particle beam sources and detectors

Mechanical characteristics and applications of diamondlike-carbon cantilevers fabricated by focused-ion-beam chemical vapor deposition

Jun-ya Igaki, Ken-ichiro Nakamatsu, Reo Kometani, Kazuhiro Kanda, Yuichi Haruyama, Takashi Kaito, and Shinji Matsui

J. Vac. Sci. Technol. B 24, 2911 (2006); http://dx.doi.org/10.1116/1.2357960 (4 pages) | Cited 15 times

Online Publication Date: 30 November 2006

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Diamondlike-carbon (DLC) cantilevers were fabricated with a commercially available focused-ion-beam chemical-vapor-deposition (FIB-CVD) system using a beam of 30 keV Ga+ ions, and the mechanical characteristics of the cantilevers were measured. Vibration frequency of the cantilevers was passively measured using scanning electron microscopy. Resonant frequency of DLC cantilevers fabricated at 0.1–0.5 pA beam current was found to be constant. The equivalent spring constant of the cantilevers was identified by squeezing the tip of a Si3N4 cantilever and a DLC cantilever together. Using the measured displacement, the spring constant of the DLC cantilever was calculated as (1.1±0.2)×10−2 N/m. Furthermore, Young’s modulus and the density of the DLC cantilevers were measured to be 187±32 GPa and (3.8±0.7)×103 kg/m3, respectively. The DLC cantilevers were used as mass sensors in an ultrasensitive sensing application. A small amount of DLC was deposited on the tip of a DLC cantilever as a mass adhesion by FIB-CVD at 0.5 pA beam current. As a result, the authors were able to measure a small amount of mass shift in the femtogram range using a DLC cantilever.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.25.-g Mechanical properties of nanoscale systems
62.20.D- Elasticity
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
06.30.Dr Mass and density

Estimation of scattered particle exposure in ion beam aperture array lithography

V. Parekh, A. Ruiz, P. Ruchhoeft, H. Nounu, D. Litvinov, and J. C. Wolfe

J. Vac. Sci. Technol. B 24, 2915 (2006); http://dx.doi.org/10.1116/1.2366619 (5 pages) | Cited 4 times

Online Publication Date: 30 November 2006

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In ion beam proximity lithography, ions that are incident on the nominally opaque regions of a stencil mask can scatter into the open windows and escape, exposing a wide area of the substrate. Since these ions can lose much of their initial energy in the mask, the scattered particle exposure is concentrated near the resist surface. The resulting loss of contrast can be mitigated to some extent by using aperture array lithography (AAL) where a mask of reduced density minimizes the number of windows from which a scattered ion can escape. Even so, the problem worsens as the pitch of an array, printed by multiple, offset exposures of the AAL mask, shrinks below about 250 nm. The only solution is to increase the mask thickness, hence the window aspect ratio, to reduce the escape angles of the scattered particles. In this article, the authors characterize an effective background dose η in the first 75 nm of poly(methylmethacrylate) resist for 30 keV He+ ion exposures of 0.6 μm thick masks with 45, 80, and 110 nm circular windows on 150, 300, and 400 nm pitches, respectively. They project that η would be (6.8±0.8)%(σ) of the primary ion dose for the printing of dense arrays, with period equal to twice the window diameter, over this range of feature sizes.
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85.40.Hp Lithography, masks and pattern transfer
back to top Electron Beam Lithography Technology

Electron beam lithography for magnetic recording heads: Characterization and optimization of critical components

XiaoMin Yang, Jianyun Zhou, Shuaigang Xiao, and Keith Mountfield

J. Vac. Sci. Technol. B 24, 2920 (2006); http://dx.doi.org/10.1116/1.2357966 (6 pages)

Online Publication Date: 30 November 2006

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Electron beam lithography has been implemented with a chemically amplified negative tone NEB-31 resist to fabricate the write top pole and read sensors for magnetic recording. To better understand the proximity effect and optimize these two critical components in electron beam patterning, Monte Carlo simulation with SELID software has been employed to characterize the energy distribution of the write top pole structure and simulate the resist profile in the break point (BP) region. To obtain a sharp BP angle and a pole area that has a uniform and narrow pole width, the authors have optimized the computer-aided design and the yoke/pole dose ratios based on their simulation results. The authors have also experimentally verified these results with NEB-31 resist. In addition, the electron backscattering effect from the relevant metallic underlayers, such as NiFe and Ta of varying thickness on the top pole critical dimension as a function of BP angle was simulated and analyzed. Experiments were conducted to verify the simulation results, and both are in good agreement.
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85.40.Hp Lithography, masks and pattern transfer
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Two-dimensional Bragg grating lasers defined by electron-beam lithography

Guy A. DeRose, Lin Zhu, John M. Choi, Joyce K. S. Poon, Amnon Yariv, and Axel Scherer

J. Vac. Sci. Technol. B 24, 2926 (2006); http://dx.doi.org/10.1116/1.2375080 (5 pages) | Cited 2 times

Online Publication Date: 30 November 2006

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Two-dimensional Bragg grating (2DBG) lasers with two quarter-wave slip line defects have been designed and fabricated by electron-beam lithography and reactive ion etching. Unlike conventional two-dimensional photonic crystal defect lasers, which use a large refractive index perturbation to confine light in a plane, the 2DBG structures described here selectively control the longitudinal and transverse wave vector components using a weak index perturbation. Two line defects perpendicular to each other are introduced in the 2DBG to define the optical resonance condition in the longitudinal and transverse directions. In this article, we describe the lithography process used to pattern these devices. The 2DBG lasers were defined using polymethylmethacrylate resist exposed in a Leica Microsystems EBPG 5000+ electron-beam writer at 100 kV. A proximity correction code was used to obtain a uniform pattern distribution over a large area, and a dosage matrix was used to optimize the laser design parameters. Measurements of electrically pumped 2DBG lasers showed modal selection in both the longitudinal and transverse directions due to proper design of the grating and defects, making them promising candidates for single-mode, high power, high efficiency, large-area lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.40.Hp Lithography, masks and pattern transfer

Predicted effect of shot noise on contact hole dimension in e-beam lithography

P. Kruit, S. Steenbrink, and M. Wieland

J. Vac. Sci. Technol. B 24, 2931 (2006); http://dx.doi.org/10.1116/1.2387153 (5 pages) | Cited 5 times

Online Publication Date: 30 November 2006

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The requirements on dimensional control of contact holes scale with the technology node and are reaching values of only a few nanometers. The allowed 3σ variation of the diameter is typically 10%. In traditional optical lithography, cross section variations occur mainly on a global scale as a result of slowly varying image or process parameters. For electron beam lithography and extreme ultraviolet (EUV) lithography, local variations need more attention. The authors have developed a model for the critical dimension (CD) variations resulting from shot noise and checked the results with Monte Carlo simulations. The model predicts that the necessary number of particles to write a contact is independent of the contact diameter, when both the requirements, the resolution, and resist’s acid diffusion length scale with the size of the contacts. The minimum number of particles required under ideal circumstances is about 500 per contact, but under more realistic circumstances, e.g., for electron beam lithography at low voltages, a typical number of electrons per contact is 3900. This means that contact holes at the “32 nm node” (45 nm diameter at 90 nm pitch with 3σ of 4.5 nm) require a dose of about 30 μC/cm2 and at the “22 nm node” about 60 μC/cm2. If the molecular size of the resist molecules contributes to a size variance, or if high energy electrons or EUV photons are used, the required dose may be substantially higher.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
02.70.Uu Applications of Monte Carlo methods

Process optimization and proximity effect correction for gray scale e-beam lithography

Raghunath Murali, Devin K. Brown, Kevin P. Martin, and James D. Meindl

J. Vac. Sci. Technol. B 24, 2936 (2006); http://dx.doi.org/10.1116/1.2357962 (4 pages) | Cited 6 times

Online Publication Date: 30 November 2006

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Three-dimensional microstructures find applications in diffractive optical elements, photonic elements, etc., and can be efficiently fabricated by e-beam lithography. Good process control and efficient proximity effect correction are important for achieving the desired structures. With polymethylmethacrylate as the resist, a process optimization of different develop conditions is carried out to identify a process that is most conductive to gray scale features. A novel proximity effect correction scheme called effective dose-depth (EDD) method is proposed. Using the EDD method for grating design and the optimized process, blazed gratings have been fabricated with excellent uniformity and low surface roughness.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Dj Gratings
68.35.B- Structure of clean surfaces (and surface reconstruction)

Electron-beam patterning and process optimization for magnetic sensor fabrication

Shuaigang Xiao and XiaoMin Yang

J. Vac. Sci. Technol. B 24, 2940 (2006); http://dx.doi.org/10.1116/1.2366699 (5 pages) | Cited 1 time

Online Publication Date: 30 November 2006

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Electron-beam lithography has been widely applied to define critical features in magnetic recording thin-film heads. To be a viable resist candidate for read sensor fabrication, e-beam resists need to be optimized in three major aspects—resolution, etching resistance, and strippability. Here the authors investigated four typical resists for their applicability in the production of sub-50 nm read sensors and extendibility into sub-30 nm regime, including a negative-tone chemically amplified resist (CAR), a negative-tone non-CAR, a positive-tone CAR, and a positive-tone non-CAR. Pattern design for positive-/negative-tone resists, resist resolution capability, sloped resist pole profile, underlayer preparation for Si-containing imaging layer, hybrid lithography for low-sensitivity non-CARs, and process issues in ion-beam etching of sensor stacks are discussed in detail. Finally, 20 nm giant magnetoresistive sensor fabrication was demonstrated.
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85.40.Hp Lithography, masks and pattern transfer
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.75.Ss Magnetic field sensors using spin polarized transport
81.65.Cf Surface cleaning, etching, patterning
81.16.Rf Micro- and nanoscale pattern formation

Sub- 100-nm lithography with miniature electron beam columns

L. P. Muray, C. S. Silver, and J. P. Spallas

J. Vac. Sci. Technol. B 24, 2945 (2006); http://dx.doi.org/10.1116/1.2375088 (6 pages) | Cited 9 times

Online Publication Date: 30 November 2006

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Miniature low-voltage electron beam columns are well suited for low cost imaging and high throughput direct-write lithography applications. Previous generations of miniature columns have demonstrated high-resolution imaging and proof-of-concept lithography. However, those columns suffered from difficult fabrication techniques and costly assembly, making them impractical for broad application. A new type of miniature electron beam column has been developed with the goal of manufacturability using bonded stacks of batch fabricated silicon lenses and glass insulators. Bulk micromachining and integrated chip fabrication techniques facilitate the fabrication of columns with precise aperture-to-aperture alignment and high aperture circularity. The lens stacks are bonded to a multilayer ceramic package with embedded interconnects. This approach enables a small package that can include buried internal and external passive and active devices, ground planes, and controlled impedance-matched lines. The package is fully scalable for continued miniaturization, and can be easily designed to accommodate 1×4 or larger modules of individually correctable columns for arrayed operation. This article presents the first lithography results with these miniature columns over a beam energy range of 0.5–2 keV. Patterns were written into ∼ 45 nm ZEP-520A resist using a raster-scan writing strategy. A nominal dose of 7 μC/cm2 yielded 90 nm isolated and 180 nm line-space patterns. High-resolution images resolved <35 nm features.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation

Silicon photodiodes for low-voltage electron detection in scanning electron microscopy and electron beam lithography

C. S. Silver, J. P. Spallas, and L. P. Muray

J. Vac. Sci. Technol. B 24, 2951 (2006); http://dx.doi.org/10.1116/1.2363405 (5 pages) | Cited 6 times

Online Publication Date: 30 November 2006

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Silicon photodiode (SPD) detectors can be used for secondary electron detection in miniature electron beam columns, where small apertures, tight lens spacings, and short working distances make traditional detectors impractical. Monte Carlo simulations presented in this article suggest that in these configurations, SPDs have an advantage over traditional secondary electron detectors due to their potentially higher collection efficiency. Responsivity results presented here for SPDs with 40 and 60 Å passivation layers show measurable responsivity for electron energies down to 80 eV. High contrast images obtained using a SPD mounted with the Novelx miniature electron beam column and biased with a floating voltage to accelerate low-energy electrons demonstrate the effectiveness of SPDs for secondary electron detection. Based on these simulations and results, it is believed that SPDs present a reliable, inexpensive solution for secondary electron detection in miniature electron beam columns, as well as a robust mechanism for system calibration in column arrays for lithography.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.De Semiconductor-device characterization, design, and modeling
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
85.40.Hp Lithography, masks and pattern transfer

Technique to automatically measure electron-beam diameter and astigmatism: BEAMETR

S. Babin, M. Gaevski, D. Joy, M. Machin, and A. Martynov

J. Vac. Sci. Technol. B 24, 2956 (2006); http://dx.doi.org/10.1116/1.2387158 (4 pages) | Cited 8 times

Online Publication Date: 30 November 2006

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Accuracy and resolution of scanning electron microscopy and an electron-beam lithography system directly depend on beam diameter; it should be monitored and tuned frequently. A technique is described to determine beam size using an automatic procedure. In the developed method, a specially designed and fabricated test pattern is scanned using an e-beam. A spectrum of the signal is analyzed; beam diameter is automatically determined using a software program. Results of design, fabrication, and analysis of the beam calibration test pattern are presented.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
06.20.fb Standards and calibration
81.16.Nd Micro- and nanolithography
back to top Nanoimprint Lithography

Replication of diffractive-optical arrays via photocurable nanoimprint lithography

Matthias D. Galus, Euclid Moon, Henry I. Smith, and Rajesh Menon

J. Vac. Sci. Technol. B 24, 2960 (2006); http://dx.doi.org/10.1116/1.2363401 (4 pages) | Cited 2 times

Online Publication Date: 30 November 2006

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Photocurable nanoimprint lithography was used to replicate an array of Fresnel zone plates onto a SiO2 substrate. This array was transferred into the substrate and used for zone-plate-array lithography (ZPAL). The experimentally determined point-spread function showed good agreement with simulation. The authors also demonstrate the use of ZPAL as a tool for patterning and replicating diffractive optics.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays
42.79.Ci Filters, zone plates, and polarizers
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
42.30.Lr Modulation and optical transfer functions

Nanowire fin field effect transistors via UV-based nanoimprint lithography

A. Fuchs, M. Bender, U. Plachetka, L. Kock, T. Wahlbrink, H. D. B. Gottlob, J. K. Efavi, M. Moeller, M. Schmidt, T. Mollenhauer, C. Moormann, M. C. Lemme, and H. Kurz

J. Vac. Sci. Technol. B 24, 2964 (2006); http://dx.doi.org/10.1116/1.2395956 (4 pages) | Cited 2 times

Online Publication Date: 30 November 2006

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A triple step alignment process for UV nanoimprint lithography (UV-NIL) for the fabrication of nanoscale fin field effect transistors (FinFETs) is presented. An alignment accuracy is demonstrated between two functional layers of less than 20 nm (3σ). The electrical characterization of the FinFETs fabricated by a full NIL process demonstrates the potential of UV-NIL for future nanoelectronic devices.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Hybrid mold reversal imprint for three-dimensional and selective patterning

C. Peng and S. W. Pang

J. Vac. Sci. Technol. B 24, 2968 (2006); http://dx.doi.org/10.1116/1.2366676 (5 pages) | Cited 5 times

Online Publication Date: 30 November 2006

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Three-dimensional (3D) nanostructures are needed in many applications including sensors, actuators, and microanalysis systems. In this work, a novel technology combining UV lithography, hybrid mold, and reversal imprint for fabricating 3D structures is developed. A hybrid mold made from quartz is used. The mold has structures patterned by lithography and dry etching. The quartz mold also has selected patterns formed by 50 nm thick Cr. A layer of UV definable SU-8 polymer is spin coated onto the hybrid mold and patterned by optical lithography. The mold with the patterned SU-8 layer and no residue is then transferred to a substrate with topography by reversal imprint with temperatures as low as 50 °C and pressures of nominally 2 MPa. Depending on the dimensions of patterns on the mold compared to the ones on the substrate and the imprint pressure, patterns can be selectively transferred to substrates through reversal imprint. This technology greatly simplifies the fabrication process and provides more flexibility in building complex 3D structures.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning

Evidence for internal stresses induced by nanoimprint lithography

Hyun Wook Ro, Yifu Ding, Hae-Jeong Lee, Daniel R. Hines, Ronald L. Jones, Eric K. Lin, Alamgir Karim, Wen-li Wu, and Christopher L. Soles

J. Vac. Sci. Technol. B 24, 2973 (2006); http://dx.doi.org/10.1116/1.2387157 (6 pages) | Cited 7 times

Online Publication Date: 30 November 2006

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The thermal embossing form of nanoimprint lithography is used to pattern arrays of nanostructures into three different polymer films. The shape of the imprinted patterns is characterized with nanometer precision using both x-ray scattering and reflectivity techniques. The time dependent response of the pattern shape at temperatures near the glass transition temperature reveals large levels of residual stress induced by the imprinting process. During the imprint, large shear fields are generated as the viscous polymer flows into the mold. If these shear distortions do not have time to relax during the imprinting, internal stresses are frozen into the final pattern. At elevated temperatures in the freestanding structures (once the mold has been separated from the imprint), there is an accelerated reduction in pattern height in the reverse direction from which the material originally flowed into the mold. Factors that influence this residual stress include the relative molecular mass or viscosity of the resist and the amount of time the pattern is annealed at high temperature in the presence of the mold.
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68.60.Bs Mechanical and acoustical properties
62.20.-x Mechanical properties of solids
81.16.Nd Micro- and nanolithography
78.70.Ck X-ray scattering
81.40.Gh Other heat and thermomechanical treatments

Direct die-to-database electron beam inspection of fused silica imprint templates

D. J. Resnick, L. J. Myron, E. Thompson, T. Hasebe, T. Tokumoto, C. Yan, M. Yamamoto, H. Wakamori, M. Inoue, Eric Ainley, Kevin J. Nordquist, and William J. Dauksher

J. Vac. Sci. Technol. B 24, 2979 (2006); http://dx.doi.org/10.1116/1.2357963 (5 pages) | Cited 1 time

Online Publication Date: 30 November 2006

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Imprint lithography has been included on the ITRS Lithography Roadmap at the 32 and 22 nm nodes. Step and flash imprint lithography (S-FIL™) is a unique method for printing sub-100-nm geometries. Relative to other imprinting processes S-FIL has the advantage that the template is transparent, thereby facilitating conventional overlay techniques. 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. With respect to inspection, although defects as small as 70 nm have been detected using optical techniques, it is clear that it will be necessary to take advantage of the resolution capabilities of electron beam inspection techniques. This article reports the first systematic study of die-to-database electron beam inspection of patterns that were imprinted using an Imprio 250 system. The die-to-database inspection of the wafers was performed on an NGR2100 inspection system. Metal 1 and logic patterns with dimensions as small as 70 nm were inspected. Using a pixel address of 3 nm and a defect threshold of 20 nm, problem areas in the design of the pattern layout were clearly identified. Ultimately, the most desirable solution is to directly inspect the fused silica template. This article also reports the results on the first experiments of direct inspection fused silica substrates at data rates of 200 MHz.
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85.40.Hp Lithography, masks and pattern transfer

Multiple level nanochannels fabricated using reversal UV nanoimprint

B. Yang and S. W. Pang

J. Vac. Sci. Technol. B 24, 2984 (2006); http://dx.doi.org/10.1116/1.2393247 (4 pages) | Cited 4 times

Online Publication Date: 30 November 2006

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There is a wide range of applications for three-dimensional (3D) nanochannels in biomedical systems and fluidic control. In this article, a simple and versatile technique to create 3D nanochannels with width from 200 nm to 2 μm is demonstrated using sequentially stacked reversal UV nanoimprint of SU-8. Its advantages include controllable channel profile, low pressure and temperature for imprints, and flexibility in designing 3D channels by stacking. In a typical reversal UV imprint, SU-8 is spin coated on a glass mold and then transferred onto Si substrates by an UV imprint process at low temperature of 55 °C, low pressure of 2 MPa, and UV exposure of 1–4 s. While reversal UV imprinting top SU-8 layer onto bottom SU-8 layer, the UV exposure and imprint sequence of the top SU-8 layer and its effect on channel profile control are investigated. It has been found that initially UV-cured top SU-8 layer is preferred for good channel profile control because UV-cured SU-8 layer is prevented from flowing down into bottom SU-8 layer.
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81.16.Nd Micro- and nanolithography
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
87.85.J- Biomaterials
87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Atomic force microscopy local anodic oxidation of thin Si3N4 layers for robust prototyping of nanostructures

Irene Fernandez-Cuesta, Xavier Borrisé, and Francesc Pérez-Murano

J. Vac. Sci. Technol. B 24, 2988 (2006); http://dx.doi.org/10.1116/1.2375082 (5 pages) | Cited 2 times

Online Publication Date: 30 November 2006

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Local anodic oxidation by atomic force microscopy (AFM) of thin silicon nitride layers deposited on silicon wafers allows the definition of stamps for nanoimprint lithography. The study of the mechanism and kinetics of the AFM induced oxidation shows that the patterns on silicon nitride can be generated faster and at lower voltages than directly on silicon surfaces. Stamp fabrication is completed by chemical wet etching of the samples after the AFM patterning, resulting in a robust process because of the excellent properties of silicon nitride as a mask for selective wet etching. As a demonstrator, a stamp for nanoimprint lithography is fabricated that will be used for the realization of biosensors based on interdigitated nanoelectrodes.
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81.16.Pr Micro- and nano-oxidation
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

Deposition and patterning of diamondlike carbon as antiwear nanoimprint templates

S. Ramachandran, L. Tao, T. H. Lee, S. Sant, L. J. Overzet, M. J. Goeckner, M. J. Kim, G. S. Lee, and W. Hu

J. Vac. Sci. Technol. B 24, 2993 (2006); http://dx.doi.org/10.1116/1.2363409 (5 pages) | Cited 12 times

Online Publication Date: 30 November 2006

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In this work, antiwear nanoimprint templates were made by depositing and patterning diamondlike carbon (DLC) films on Si and quartz. A capacitively coupled plasma enhanced chemical vapor deposition (PECVD) system was configured to deposit 100 nm–1 μm thick DLC films on Si and quartz substrates. These films were characterized with Raman spectroscopy, electron energy loss spectroscopy, atomic force microscopy, nanoindentation, contact angle measurements, and optical transmission measurements. The rf power and pressure of the PECVD process were varied to obtain uniform coating of DLC films with smooth surface ( ∼ 0.2 nm rms), low surface energy ( ∼ 40 mJ/m2), and high hardness ( ∼ 22 GPa). The resulting films’ wear resistance is more than three times better than quartz. The DLC films were patterned by nanoimprint lithography using polymethylmethacrylate (PMMA) followed by CF4 plasma etch. Thermal nanoimprint tests with DLC templates were performed in PMMA. Atomic force microscopy measurements indicated excellent pattern-transfer fidelity and template-polymer separation.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
78.35.+c Brillouin and Rayleigh scattering; other light scattering
79.20.Uv Electron energy loss spectroscopy
68.60.Bs Mechanical and acoustical properties

Thermal imprint with negligibly low residual layer

Nicolas Bogdanski, Matthias Wissen, Saskia Möllenbeck, and Hella-Christin Scheer

J. Vac. Sci. Technol. B 24, 2998 (2006); http://dx.doi.org/10.1116/1.2388964 (4 pages) | Cited 15 times

Online Publication Date: 30 November 2006

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Thermal imprint into polymer layers that are thin compared to the pattern height allows for imprints with extremely low and uniform residual layers where lift-off works without previous dry etching. The authors report about possible restrictions of this method such as unintended self-assembling and recovery of polymer underneath the imprinted structures. Both can be attributed to structure size properties and temperature influence and hinder a subsequent successful lift-off. Taking the example of two different temperatures and two different initial layer thicknesses the authors investigate their impact on the resulting structure shape and potential defects. In addition, to qualitatively estimate the residual layer thickness the authors apply lift-off and discuss the results with focus on the usability of this approach as a lithography technique.
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81.16.Nd Micro- and nanolithography
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Dn Self-assembly

Submicron three-dimensional structures fabricated by reverse contact UV nanoimprint lithography

N. Kehagias, Vincent Reboud, G. Chansin, M. Zelsmann, C. Jeppesen, F. Reuther, C. Schuster, M. Kubenz, G. Gruetzner, and C. M. Sotomayor Torres

J. Vac. Sci. Technol. B 24, 3002 (2006); http://dx.doi.org/10.1116/1.2388962 (4 pages) | Cited 4 times

Online Publication Date: 30 November 2006

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The fabrication of a three-dimensional multilayered nanostructure is demonstrated with a newly developed nanofabrication technique, namely, reverse contact ultraviolet nanoimprint lithography. This technique is a combination of reverse nanoimprint lithography and contact ultraviolet lithography. In this process, a UV cross-linkable polymer and a thermoplastic polymer are spin coated onto a patterned hybrid metal-quartz stamp. These thin polymer films are then transferred from the stamp to the substrate by contact at a suitable temperature and pressure. The whole assembly is then exposed to UV light. After separation of the stamp and the substrate, the unexposed polymer areas are rinsed away with acetone leaving behind the negative features of the original stamp with no residual layer.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Influence of light polarization on UV stabilization of prepatterned resists

M. Wissen, N. Bogdanski, S. Moellenbeck, P. Helm, and H.-C. Scheer

J. Vac. Sci. Technol. B 24, 3006 (2006); http://dx.doi.org/10.1116/1.2395961 (5 pages)

Online Publication Date: 30 November 2006

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Details of a mix and match process of thermal nanoimprint lithography and UV lithography have been investigated, where the smaller patterns were defined by imprint, whereas the larger patterns were prepared by UV lithography within the same layer of negative tone resist. Stabilization of the prepatterned resist after imprint by UV curing within the open windows of a mask is different from stabilization under flood exposure. In addition to reflection at the substrate, which leads to a height dependent, vertically modulated exposure dose pattern, the pattern edges, due to diffraction effects, result in an additional lateral modulation of the exposure dose. Distinct local intensity minima and maxima develop within the resist. The intensity differences are particularly strong in the case of pattern widths in the wavelength dimension. Furthermore the direction of light polarization affects the exposure dose pattern. In the case of pattern widths well above the wavelength mainly an underexposure along the edges of the prepatterned layer remains, independent of the polarization direction. The authors found that, under exposure conditions best suited for UV lithography, the stabilization of a prepatterned layer remains incomplete. Full stabilization requires overexposure on the cost of resolution of the UV lithography and edge steepness of the lithographically defined patterns.
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85.40.Hp Lithography, masks and pattern transfer

Influence of mold depth on capillary bridges in nanoimprint lithography

N. Chaix, S. Landis, D. Hermelin, T. Leveder, C. Perret, V. Delaye, and C. Gourgon

J. Vac. Sci. Technol. B 24, 3011 (2006); http://dx.doi.org/10.1116/1.2393249 (5 pages) | Cited 3 times

Online Publication Date: 30 November 2006

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Nanoimprint lithography (NIL) processes are often plagued by different kinds of defects. The so-called capillary bridge is related to capillary forces between the stamp surface and the polymer during the pressing process. These defects affect both the printed and unprinted areas of the polymer film. Implementation of NIL as an industrial process requires that these defects be understood and minimized. As such, establishing a relationship between capillary bridge growing and pressing conditions, specifically the mold to polymer distance, is a key step. Two NIL stamps with various feature depths (12–224 nm) were studied in this work to establish a link between bridge formation and mold filling. Printing processes were performed using small forces to guarantee contact between the mold and resist without totally filling stamp cavities. The resulting capillary bridges were characterized as a function of cavity depth and printing temperature. Results indicate that the number of defects is strongly influenced by the cavity size for depths <80 nm as well as printing temperature.
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81.16.Nd Micro- and nanolithography
81.10.Fq Growth from melts; zone melting and refining
85.40.Hp Lithography, masks and pattern transfer
47.55.nb Capillary and thermocapillary flows

Layer thickness-induced lens distortions during thermal nanoimprint

H.-C. Scheer, N. Bogdanski, S. Möllenbeck, M. Wissen, M. Nishilata, and Y. Hirai

J. Vac. Sci. Technol. B 24, 3016 (2006); http://dx.doi.org/10.1116/1.2388966 (5 pages) | Cited 1 time

Online Publication Date: 30 November 2006

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Arrays of convex spherical lenses with heights in the micrometer range and diameters of 100 and 200 μm, respectively, were imprinted into thin layers of polystyrene by thermal imprint. The masters were prepared by gray tone lithography and dry etching. They feature three distinct lens heights, so that during imprint into medium layer thickness three different situations prevail: imprint into thick layers, imprint into thin/adequate layers, and imprint into highly thinned layers. Only during imprint in such highly thinned layers slight recovery was detected combined with stretching-induced polymer layer breakup. For all other cases the replication quality was good and did not show recovery effects. This is in contrast to the imprint of flat stamps into layer thickness of similar sizes. Differences detected in height of the replicated lenses compared to the master are due to thermal expansion in the thermal nanoimprint lithography process. Negligible residual layers were obtained at only slightly changed curvature radius.
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42.79.Bh Lenses, prisms and mirrors
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer
back to top Resist Science and Technology

Epoxy-containing ArF resists with narrow molecular weight distribution

Masamitsu Shirai, Makoto Manabe, Shou Tsuji, and Toshiro Itani

J. Vac. Sci. Technol. B 24, 3021 (2006); http://dx.doi.org/10.1116/1.2357971 (4 pages) | Cited 5 times

Online Publication Date: 30 November 2006

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Terpolymers consisting of γ-butyrolactone-2-yl methacrylate, 2-methyl-2-adamantyl methacrylate, and 1-methyl-1-(6-methyl-7-oxabicyclo[4,1,0]hept-3-yl)ethyl methacrylate were prepared by the reversible addition-fragmentation chain transfer polymerization technique. The molecular weight distribution of the polymers was 1.29–1.39. Although the polymers have epoxy units and cross-linking of the polymer occurred during prebake treatment, they worked as a highly sensitive positive-tone resist. The cross-linking efficiency of the resist was dependent on the type of amines used as a quencher. The line edge roughness values were dependent on the prebake temperature.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
82.35.-x Polymers: properties; reactions; polymerization
61.41.+e Polymers, elastomers, and plastics
85.40.Hp Lithography, masks and pattern transfer

Pattern noise in electron beam resists: PMMA, KRS-XE, TOK, HSQ

Marshal A. Miller, Wojtek J. Poppe, Andrew R. Neureuther, Alex Liddle, and Bruce Harteneck

J. Vac. Sci. Technol. B 24, 3025 (2006); http://dx.doi.org/10.1116/1.2393248 (6 pages)

Online Publication Date: 30 November 2006

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The variation in the printing of nominally identical contacts with electron-beam exposure is used to quantitatively determine the statistical variation in chemically amplified resists (KRS-XE with and without top coat, TOK) and non-chemically-amplified resists (PMMA and HSQ). Uniform 17×23 arrays of 24 and 32 nm contacts were exposed at fixed doses with a 100 keV electron beam. By looking at data observed from top view scanning electron microscopy images, a normal distribution was fitted to the fraction of contacts that printed versus dose to determine the standard deviation of the distribution relative to the dose at which 50% of the contacts printed. The top coat on KRS-XE increased contact uniformity and reduced the required dose. Quantitative analysis shows that PMMA contained as much noise as the chemically amplified resist systems, KRS-XE and TOK. Except HSQ, this normalized standard deviation ranged from 0.16 to 0.21 which is indicative that the contact hole printing process may be dominated by less than 40 events. HSQ exhibited lower standard deviation values, corresponding to over 1000 effective events.
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85.40.Hp Lithography, masks and pattern transfer

Contribution of photoacid generator to material roughness

Theodore H. Fedynyshyn, Indira Pottebaum, David K. Astolfi, Alberto Cabral, Jeanette Roberts, and Robert Meagley

J. Vac. Sci. Technol. B 24, 3031 (2006); http://dx.doi.org/10.1116/1.2395954 (9 pages) | Cited 8 times

Online Publication Date: 30 November 2006

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The authors have developed an atomic-force-microscopy-based technique to measure intrinsic material roughness after base development. This method involves performing an interrupted development of the resist film and measuring the resulting film roughness after a certain fixed film loss. Employing this technique, the authors previously established that the photoacid generator (PAG) is a major material contributor of film roughness and that PAG segregation in the resist is likely responsible for nanoscale dissolution inhomogeneities. The additional roughness imparted on a test polymer by incorporation of a series of iodonium, sulfonium, diazo, and imido PAGs was measured. The roughness was then correlated to the inhibition properties of the various PAGs. This was accomplished both through a NMR technique that measures interaction of the PAG with the polymer and by evaluating the dissolution inhibition properties of the PAG through a percolation model. Several PAGs that result in significantly lower material roughness and thus the potential for significantly reduced linewidth roughness in resist imaging have been identified.
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68.55.-a Thin film structure and morphology
61.41.+e Polymers, elastomers, and plastics
64.75.-g Phase equilibria
76.60.-k Nuclear magnetic resonance and relaxation

Three-dimensional resist development simulation with discrete models

T. Schnattinger, E. Bär, and A. Erdmann

J. Vac. Sci. Technol. B 24, 3040 (2006); http://dx.doi.org/10.1116/1.2397071 (4 pages) | Cited 2 times

Online Publication Date: 30 November 2006

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Control and minimization of line-edge roughness (LER) is a crucial problem for further advancements in lithography. To simulate LER, a switch from continuous to discrete, molecular level resist models is required. This article presents a new algorithm for the discrete resist structure generation with nonoverlapping polymer distributions and a novel development simulation approach. The presented concept allows simultaneously the simulation of macroscopic profile dimensions as well as of microscopic roughness properties of the resist. Required microscopic dissolution times of the polymers are derived from the corresponding simulated local macroscopic development rates. By retaining all other resist parameters unchanged in the simulation, the isolated influence of varying the assumed polymer size, branching geometry, and dissolution time variations on LER is examined with this new method. Small, strongly tangled polymers lead to considerably lower LER values than bigger or less bended polymers. Compared to the investigated polymer size and geometry, the examined range of variances in the dissolution times has only a weak influence on LER.
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85.40.Hp Lithography, masks and pattern transfer

Exposure dose effects on the reaction-diffusion process in model extreme ultraviolet photoresists

Kristopher A. Lavery, Bryan D. Vogt, Vivek M. Prabhu, Eric K. Lin, Wen-Li Wu, Sushil K. Satija, and Kwang-Woo Choi

J. Vac. Sci. Technol. B 24, 3044 (2006); http://dx.doi.org/10.1116/1.2375086 (4 pages) | Cited 6 times

Online Publication Date: 30 November 2006

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The effect of exposure dose on the latent image deprotection profile in a model extreme ultraviolet (EUV) photoresist polymer, poly(hydroxystyrene-co-d9-tert-butyl acrylate), is measured with neutron reflectometry. As the photoacid concentration is increased by exposure dose, the spatial extent of propagation increases but eventually becomes self-limited by the products of the reaction. A long-range deprotection path occurs with diffusion length between 10 and 100 Å, while an additional subnanometer short-range deprotection length scale proceeds monotonically with dose. These measurements show that the photoacid diffusion length into unexposed regions of a photoresist is limited even in the absence of base quencher additives. These fundamental data can be used to highlight materials effects on photoresist processing and to improve quantitative models for EUV photoresists needed at the sub-32‐nm half pitch lithography.
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85.40.Hp Lithography, masks and pattern transfer

Scanning x-ray microscopy investigations into the electron-beam exposure mechanism of hydrogen silsesquioxane resists

Deirdre L. Olynick, J. Alexander Liddle, Alexei V. Tivanski, Mary K. Gilles, Tolek Tyliszczak, Farhad Salmassi, Kathy Liang, and Stephen R. Leone

J. Vac. Sci. Technol. B 24, 3048 (2006); http://dx.doi.org/10.1116/1.2395957 (7 pages) | Cited 7 times

Online Publication Date: 30 November 2006

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Electron-beam exposed hydrogen silsesquioxane cross-linking chemistry is investigated by scanning transmission x-ray microscopy (STXM) and atomic force microscopy (AFM). Using STXM, a maximum in the chemical contrast is obtained by measuring the x-ray absorption at 535.4 eV, corresponding to the 1s K-edge transition in oxygen. An area-dependent and dose-dependent chemical conversion is observed for feature sizes between 150 nm and 10 μm and doses between 0.4 and 40 mC/cm2. The activated (cross-linked) regions extend beyond the exposure zones, especially for higher dosed exposures. With AFM, thickness changes in the latent images (e-beam exposed but undeveloped) are observed, which also display a dependence on exposed area. Potential mechanisms, involving chemical diffusion outside the exposure zone, are discussed.
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61.80.Fe Electron and positron radiation effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
66.30.Ny Chemical interdiffusion; diffusion barriers
78.70.Dm X-ray absorption spectra
85.40.Hp Lithography, masks and pattern transfer

Analysis of acid yield generated in chemically amplified electron beam resist

Takahiro Kozawa, Takumi Shigaki, Kazumasa Okamoto, Akinori Saeki, Seiichi Tagawa, Toshiyuki Kai, and Tsutomu Shimokawa

J. Vac. Sci. Technol. B 24, 3055 (2006); http://dx.doi.org/10.1116/1.2366656 (6 pages) | Cited 51 times

Online Publication Date: 30 November 2006

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Acid-related matters are a critical issue in a chemically amplified resist, in which photo- or radiation (ionizing radiation)-generated acids drive pattern formation reactions in exposed areas. The photosensitization of resist materials has been formulated by Dill et al. [ IEEE Trans. Electron. Dev. 22, 445 (1975) ]. The applicability of the formulation by Dill et al. to acid generation in chemically amplified photoresists has been proven by many researchers. The acid yields in photoresists are predicted well by the formulation of Dill et al. However, the formulation of Dill et al. cannot be applied to chemically amplified resists for ionizing radiation such as electron beams and extreme ultraviolet rays because polymer ionization significantly contributes to acid generation in these resists. In this study, the authors formulated acid generation in a chemically amplified resist for ionizing radiation. By the analysis of the dependence of acid yield on acid generator concentration, the details of acid generation paths were clarified.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Effect of cold development on improvement in electron-beam nanopatterning resolution and line roughness

L. E. Ocola and A. Stein

J. Vac. Sci. Technol. B 24, 3061 (2006); http://dx.doi.org/10.1116/1.2366698 (5 pages) | Cited 37 times

Online Publication Date: 30 November 2006

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This article presents the results about the effect of cold development on the improvement in patterning resolution and line edge roughness for electron-beam lithography resists. Cold development shows improved resolution and contrast for resists that are exposed by polymer chain scission. It does not work for chemically amplified resists. A discussion on why this works for resists like ZEP 520 and PMMA and not for positive chemically amplified resists (such as UV113) is presented. Results for 13 nm structures obtained after metal liftoff using a 30 kV e-beam tool using ZEP 520 resist are shown. These results have impact in the photomask industry and other manufacturers that require squeezing out as much resolution out of their existing tools and materials. It is found that, even with the improvement by cold development, there is a “shot noise” of 2% uncertainty limit that is not surpassed for resists exposed at 100 kV. This explains why high throughput and high resolution electron-beam nanolithography is not possible.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Correlation between proton dynamics and line edge roughness in chemically amplified resist for post-optical lithography

Akinori Saeki, Takahiro Kozawa, Seiichi Tagawa, and Heidi B. Cao

J. Vac. Sci. Technol. B 24, 3066 (2006); http://dx.doi.org/10.1116/1.2393250 (7 pages) | Cited 10 times

Online Publication Date: 30 November 2006

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In chemically amplified (CA) resists for electron beam (EB) and extreme ultraviolet (EUV) lithographies, acids (a pair of proton and counteranion) generated upon exposure are utilized for resist pattern formation. As protons and counteranions are separately generated during the exposure, they initially have different spatial distributions. In this work, the authors investigated the effects of proton dynamics during the recombination between protons and counteranions and subsequent acid diffusion during postexposure bake on the line edge roughness (LER) formation of the latent image. The proton dynamics and acid diffusion were simulated by a Monte Carlo technique based on diffusion under Coulomb potential induced by many-body charged species. Based on the results shown here, the correlation between the linewidth and LER as a function of exposure dose and the concentration of base additives are discussed in terms of proton and acid trajectories. The obtained aspects not only provide detailed insight into the nature of reaction mechanism in CA-EB (EUV) resist but also would be of help in the development of resists and the optimization of process conditions.
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85.40.Hp Lithography, masks and pattern transfer

Time-dependent exposure dose of hydrogen silsesquioxane when used as a negative electron-beam resist

Nathaniel Clark, Amy Vanderslice, Robert Grove, and Robert R. Krchnavek

J. Vac. Sci. Technol. B 24, 3073 (2006); http://dx.doi.org/10.1116/1.2366697 (4 pages) | Cited 8 times

Online Publication Date: 30 November 2006

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Hydrogen silsesquioxane (HSQ) is used as a high-resolution, negative-tone, inorganic electron-beam resist for use in nanoimprint lithography. Previous studies show that 1 week long exposure delay in air decreases sensitivity and enhances the contrast of HSQ [ F. C. M. J. M. van Delft, J. Vac. Sci. Technol. B 20, 2932 (2002) ]. In this work, the authors report that the electron-beam dose required for high-resolution (sub-50-nm) HSQ patterning is shown to be very sensitive to the time the sample has been at room temperature. For example, a sample written with nanoscale features at constant e-beam dose will increase in size approximately 66% per hour of time at room temperature. The minimum feature size for a given dose depends on the ambient conditions the sample was stored in (air, nitrogen, vacuum). Samples stored in vacuum are not exempt from the feature broadening. Long e-beam writing times for large-area patterning of nanoscale features will likely suffer from this time dependence unless the exposure dose is varied during the e-beam writing. The experiments relating the various ambient conditions and the minimum feature size under dose control are presented.
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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
back to top Metrology, Inspection and Alignment

Transmission electron microscopy: A linewidth measurement technique for lithography

John B. Warren and Aaron Stein

J. Vac. Sci. Technol. B 24, 3077 (2006); http://dx.doi.org/10.1116/1.2387159 (6 pages) | Cited 1 time

Online Publication Date: 4 December 2006

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The authors describe preparation methods for patterning high resolution e-beam resists on electron beam transparent samples that facilitate the direct comparison of linewidth measurements from transmission and scanning electron microscopy imaging of the same feature. A goniometer-equipped JEOL 1200EX transmission electron microscope (TEM) with a resolution of 0.45 nm (120 keV) and a JEOL SEM 6500F scanning electron microscope (SEM) with a resolution that varies from 1.5 nm (15 keV) to 5.0 nm (1 keV) are used to acquire digital images suitable for linewidth measurements. This comparison emphasizes the differences between TEM images based on mass-absorption contrast and surface topology sensitive SEM images when making linewidth measurements.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
81.16.Nd Micro- and nanolithography

Nanometer-precision pattern registration for scanning-probe lithographies using interferometric-spatial-phase imaging

Euclid E. Moon and Henry I. Smith

J. Vac. Sci. Technol. B 24, 3083 (2006); http://dx.doi.org/10.1116/1.2393294 (5 pages) | Cited 4 times

Online Publication Date: 4 December 2006

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The authors propose a solution to drift and disturbances between a scanning-probe tip and a substrate that commonly distort scanned images and undermine effective lithographic patterning. An interferometric position detection method is employed to continuously suppress drift and control the tip-scanning trajectory with nanometer precision, relative to the substrate. An associated interferometric method is used to control tip height during approach to the substrate. Patterns with arbitrary geometries are written by means of a tap-imprint method, using probes with sub-0.7-nm tip diameters.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
07.79.-v Scanning probe microscopes and components
07.60.Ly Interferometers

Integrated aerial image sensor: Design, modeling, and assembly

Jing Xue, Kurt Moen, and Costas J. Spanos

J. Vac. Sci. Technol. B 24, 3088 (2006); http://dx.doi.org/10.1116/1.2393296 (6 pages) | Cited 1 time

Online Publication Date: 4 December 2006

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The subject of this article is a novel integrated aerial image sensor (IAIS) system suitable for integration within the surface of an autonomous test wafer. The IAIS could be used as a lithography processing monitor, affording a “wafer’s eye view” of the process, and therefore facilitating advanced process control and diagnostics without integrating (and dedicating) the sensor to the processing equipment. The main IAIS challenge is to retrieve nanometer-scale aerial image detail, while utilizing micrometer-scale photodetector pixels. To address this problem, the authors propose a design of an on-wafer aperture mask that, when combined with an appropriate periodic aerial image, will produce a low spatial frequency interference pattern. They demonstrate a design example aimed at the 65 nm technology node through TEMPEST simulation. Also they detail the IAIS modeling techniques based on Abbe’s formulation [ Archiv f. Mikroskopische Anat 9, 413 (1873) ]. The performance of the IAIS under different lithography settings can be predicted accordingly. The intent is to create a library that captures the aerial image to detector image correspondence in order to facilitate rapid analysis. They also examine several approaches towards the integration of charge-coupled device chips with a near field aperture mask. Capillary force assisted alignment assembly techniques appear quite promising and are being discussed in detail.
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42.79.Pw Imaging detectors and sensors
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
85.30.De Semiconductor-device characterization, design, and modeling
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

From nanoscale displacement sensing and estimation to nanoscale alignment

Jun Gao, Carl Picciotto, Wei Wu, and William M. Tong

J. Vac. Sci. Technol. B 24, 3094 (2006); http://dx.doi.org/10.1116/1.2375089 (7 pages)

Online Publication Date: 4 December 2006

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In this article, the authors present theoretical background and practical procedures for linking displacement sensing and estimation to nanoscale alignment. The authors discuss the application of nanoscale displacement sensing and estimation (nDSE)-based overlay metrology tool. The authors propose a new look at what constitutes displacement and alignment. From there, the authors develop several frameworks to bridge these two concepts based on a set of new pseudodisplacement concepts and on the careful selection of references. Direct displacement-measurement-based alignment (DDMA) is the first method the authors have used to generate reliable alignment results. The authors achieved sub-100-nm (down to 21 nm) alignment accuracy. Indirect displacement-measurement-based alignment (IDMA) is the most accurate method in theory. IDMA truly utilizes nDSE to achieve precision coplacement between different layers and processes. IDMA and DDMA, along with a group of other nDSE-based algorithms/procedures, are vibration tolerant, making them ideal as overlay alignment tools for nanoimprint lithography.
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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)

Study of overlay metrology in atomic force microscope lithography (overlaying lithography with atomic force microscope)

Xiaona Li, Li Han, and Wenqi Gu

J. Vac. Sci. Technol. B 24, 3101 (2006); http://dx.doi.org/10.1116/1.2375087 (4 pages)

Online Publication Date: 4 December 2006

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Atomic force microscope (AFM) has been considered as a useful lithographic tool of the future nanofabrication. In this article, overlay metrology in AFM lithography was investigated. A method of overlay metrology with cross marks was designed and applied to write two-layer patterns. The alignment arithmetic was developed on the basis of mark-registration method of electron beam lithography. A set of vernier was designed to measure the overlay precision. Further analysis about the overlay errors was presented. Experimental results indicated that the overlay metrology can obtain overlay precision less than 30 nm and a higher precision will be realized by improving the system.
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07.79.Lh Atomic force microscopes
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Ta Atom manipulation
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

Impact of registration error of reticle on total overlay error budget

Doo-Youl Lee, Yong-Jin Chun, Je-Bum Yoon, Sang-Hee Lee, Suk-Joo Lee, Han-Ku Cho, and Joo-Tae Moon

J. Vac. Sci. Technol. B 24, 3105 (2006); http://dx.doi.org/10.1116/1.2395959 (5 pages) | Cited 2 times

Online Publication Date: 4 December 2006

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As the overlay specification decreases drastically, it is necessary to consider how the total overlay is influenced by each contributing factor. In particular, it is expected that the contribution on overlay error budget can be quantitatively analyzed in terms of the correlation among registration errors of the reticle. The reticle contribution of about 25% is assessed by the breakdown of the sources of overlay metrology uncertainty through the double exposure technique (DET) process. A positive correlation of around 0.7 mitigates the reticle contribution by 180%, compared to the uncorrelated case. In both DET and double patterning technique (DPT) processes, it is needed to positively correlate the registration errors among many reticles in order to decrease the reticle contribution. To maintain the gain of 180% due to positive correlation, the correlation coefficient requisite has to be increased it is difficult to achieve highly positive correlation among more than three reticles. From an integration point of view, three reticles used in DET and DPT generate three combinations of reticle sets. When the positive correlation between two reticle sets is determined to be 0.78, the other reticle set will statistically have a smaller correlation coefficient, 0.61<0.78. With an overlay specification of 12% of design rule and a reticle contribution of 25%, the specification for registration error was expected to be 7.7 nm (4×) at the 45 nm node and 5.5 nm (4×) at the 32 nm node in the uncorrelated case between two reticles. The positive correlation of around 0.7–0.78 helps to reduce the reticle specification by around 200% even in the DPT process.
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85.40.Hp Lithography, masks and pattern transfer

Pattern reconstruction of scanning electron microscope images using long-range content complexity analysis of the edge ridge signal

Hanying Feng, Jun Ye, and R. Fabian Pease

J. Vac. Sci. Technol. B 24, 3110 (2006); http://dx.doi.org/10.1116/1.2363408 (5 pages)

Online Publication Date: 4 December 2006

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Based on the observation that human visual system connects broken edge segments according to long-range pattern contents, the authors here describe a general methodology for pattern reconstruction from scanning electron microscope (SEM) based on intuitive conjectures of human intelligence. In particular, we formulate the problem of pattern reconstruction as a problem of minimizing an objective function, which includes the information of pattern complexity and template matching. This approach of objective function minimization is also consistent with the famous “Occam’s razor” principle. They then describe a potential objective function formulation, introduce implementations with acceptable computation complexity, and demonstrate reconstruction results on edge ridge signals extracted from real SEM images. This methodology can greatly improve the robustness of SEM image processing and has the potential to be applied to many other fields, such as computer vision and robust human voice detection as well as inspection of nanoscale structures in the SEM.
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42.30.Wb Image reconstruction; tomography
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
back to top Modeling and Simulation

True three-dimensional proximity effect correction in electron-beam lithography

Kasi Anbumony and S.-Y. Lee

J. Vac. Sci. Technol. B 24, 3115 (2006); http://dx.doi.org/10.1116/1.2388960 (6 pages) | Cited 4 times

Online Publication Date: 4 December 2006

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Proximity effect in e-beam lithography is mainly due to the “nonideal” distribution of exposure (energy deposited in the resist). The proximity effect correction schemes developed so far employ a two-dimensional (2D) model, i.e., exposure variation along the resist depth dimension is not considered. The exposure distribution estimated by the 2D model can be significantly different from the actual exposure distribution, especially for the nanoscale patterns. In this article, a three-dimensional (3D) correction method which uses a 3D point spread function in controlling e-beam dose distribution within each circuit feature in order to achieve a certain desired 3D remaining resist profile after development is described. The dose to be given to each region of a feature is determined based on the estimated remaining resist profile (with the emphasis on the sidewall shape) through iterations. Simulation results demonstrating the potential improvements by the 3D correction are provided.
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85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer

Modeling of linewidth measurement in scanning electron microscopes using advanced Monte Carlo software

S. Babin, S. Borisov, A. Ivanchikov, and I. Ruzavin

J. Vac. Sci. Technol. B 24, 3121 (2006); http://dx.doi.org/10.1116/1.2366701 (4 pages) | Cited 7 times

Online Publication Date: 4 December 2006

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Accurate measurement of linewidth is a critical problem in sub-100 nm semiconductor manufacturing, where required accuracy is below 1 nm. Critical dimension scanning electron microscopes (CD-SEMs) are usually used for such measurements. A cross correlation of CD-SEMs, while demonstrating a good relative trend, is often subjected to a significant absolute linewidth error. There is no proven algorithm for absolute edge detection in CD-SEMs. In this article, the authors demonstrate that edge detection depends greatly on parameters of SEM settings, such as beam diameter, and pattern properties, such as the wall angle of a pattern. When both the signal and pattern are known, an offset for a specific SEM algorithm can be found. An algorithm for automatic edge detection in CD-SEMs can be tuned for beam parameters and the type of pattern. A SEM signal was simulated using the advanced Monte Carlo software CHARIOT. Input data for the modeling were three dimensional microstructures and e-beam parameters. A known pattern was then compared to a simulated signal. Such a comparison allowed to define the edge position and calibrate a SEM so that any system- and pattern-dependent errors could be removed.
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68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
back to top Nanofabrication

Reversing the hydrogen silsesquioxane image by silicon nitride and silicon oxide chemical mechanical polishing

F. C. M. J. M. van Delft, F. J. H. van der Kruis, P. P. J. van Eerd, H. A. van Esch, and H. W. J. J. van de Laar

J. Vac. Sci. Technol. B 24, 3125 (2006); http://dx.doi.org/10.1116/1.2357969 (3 pages)

Online Publication Date: 4 December 2006

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Patterns, e-beam written in hydrogen silsesquioxane (HSQ), have been reversed in tone by chemical mechanical polishing of silicon nitride deposited on top of these HSQ patterns. First, high-resolution patterns have been written in an 80 nm thick HSQ layer on a 6 in. silicon wafer. After development, 200 nm thick plasma enhanced chemical vapor deposited silicon nitride has been deposited at 300 °C on top of these patterns. Next, the silicon nitride has been Syton polished down to 50 nm thickness. Finally, the HSQ has been removed wet chemically from in between the nitride features using buffered oxide etch (7:1). Features of 50 nm wide have been resolved, but even smaller isolated spaces are feasible. The same method has been tested with silicon oxide obtained from boron doped tetraethyl orthosilicate. Although the wet-chemical removal of HSQ is less selective in this case, still 50 nm wide features have been resolved in silicon oxide this way.
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81.65.Ps Polishing, grinding, surface finishing
81.65.Cf Surface cleaning, etching, patterning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Hp Lithography, masks and pattern transfer

Thin membrane self-alignment using nanomagnets for three-dimensional nanomanufacturing

Anthony J. Nichol, William J. Arora, and George Barbastathis

J. Vac. Sci. Technol. B 24, 3128 (2006); http://dx.doi.org/10.1116/1.2375084 (5 pages) | Cited 7 times

Online Publication Date: 4 December 2006

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In this article the authors present the use of nanomagnets as fine alignment features for structures assembled by folding nanopatterned membranes. The membranes are patterned with arrays of nanomagnets that passively align to other arrays. They analyze the scaling of the force between magnets and calculate the required structural compliance for the magnetic forces to actuate the membranes. A model of the alignment system that captures the magnetic forces and the membrane dynamics has been developed. They show that an external magnetic field provides magnetic saturation of the nanomagnets and aligns the membranes rotationally. The magnetic dipole approximation used in the model was confirmed experimentally by patterning cobalt and iron nanomagnets on silicon nitride cantilevers and actuating in an external magnetic field. Self-alignment between the two arrays of cobalt nanomagnets was achieved confirming the magnetic alignment principle.
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81.16.Rf Micro- and nanoscale pattern formation

Microelectrical noise detector for rapid, specific, and sensitive identification of bacteria

Sungkyu Seo, Hyun Chul Kim, Mosong Cheng, Xinchang Ruan, and Wei Ruan

J. Vac. Sci. Technol. B 24, 3133 (2006); http://dx.doi.org/10.1116/1.2395960 (6 pages) | Cited 2 times

Online Publication Date: 4 December 2006

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Recently, sensing of phase-triggered ion cascades (SEPTIC), a nanotechnology for rapid detection of live, pathogenic bacteria on the scale of minutes with unparalleled specificity, has drawn a lot of attention. SEPTIC utilizes a nanowell device, consisting of two metal electrodes with a gap between 5 and 200 nm, to probe the ion effluxes from specific bacteria when they are infected by phages. Whether the effluxes occur can be identified by evaluating the power spectral density of the voltage noise in the nanowell. This article presents further development of SEPTIC, using E. coli, E. coli phage T7, and a control bacteria as analytes. A microwell, identical to a nanowell except that the gap is 4 μm, proved capable of probing the ion efflux as well. When ion efflux occurred, abnormal pulses that were much higher than the noise level and lasted for 0.1–0.3 s were observed in the voltage noise output from the microwell. These durations agree with the average duration of ion efflux. While in negative tests, observed abnormal pulses were much shorter than 0.1 s. Also, positives showed 1/f noise while negatives showed white noise in 1–10 Hz. No false positives or negatives were observed. Given the size of microwell and the simplified detection electronics, the cost of SEPTIC is significantly reduced and the robustness is well improved, indicating very promising applications in clinical diagnosis and biodefense.
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87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.17.-d Cell processes
05.40.Ca Noise
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Robust shadow-mask evaporation via lithographically controlled undercut

B. Cord, C. Dames, K. K. Berggren, and J. Aumentado

J. Vac. Sci. Technol. B 24, 3139 (2006); http://dx.doi.org/10.1116/1.2375090 (5 pages) | Cited 7 times

Online Publication Date: 4 December 2006

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Suspended shadow-mask evaporation is a simple, robust technique for fabricating Josephson-junction structures using scanning electron-beam lithography. The basic process entails the fabrication of an undercut structure in a resist bilayer to form a suspended “bridge,” followed by two angle evaporations of superconducting material with a brief oxidation step in between. The result is two overlapping wires separated by a thin layer of oxide. Josephson junctions with sub-50-nm diameters are of particular interest in quantum computing research. Unfortunately, standard shadow-mask fabrication techniques are highly variable at linewidths below 100 nm, due to the difficulty of simultaneously fabricating a narrow line and a large undercut region. While most previous processes used poly(methylmethacrylate) (PMMA) for the top (imaging)layer and either lower-molecular-weight PMMA or a PMMA/methacrylic acid copolymer for the bottom (support) layer, the authors’ process uses a PMMA/poly(methylglutarimide) (PMGI) bilayer. The advantage of using PMGI as the support layer is that it develops in aqueous base solutions, while PMMA is insensitive to aqueous solutions and only develops in certain organic solvents. This allows the two layers to be developed independently, ensuring that the imaging layer is not biased during the development of the support layer and allowing the process to achieve the full resolution of the PMMA imaging layer, which can be extremely high. Additionally, the extent of the undercut in the support layer can be precisely controlled by defining it lithographically, rather than simply varying the PMGI development time as in previous processes. Although PMGI is sold as a “liftoff resist” and widely assumed to be electron insensitive, their experiments have shown that this is not the case. Instead, when dilute developer and low electron doses are used, PMGI behaves very much like a conventional photoresist. By exploiting this behavior, as well as its high electron sensitivity with respect to PMMA, the authors were able to define undercuts by defining low-dose regions adjacent to their features, exposing the underlying PMGI separately. In this manner, it is possible to create well-controlled undercut regions as large as 600 nm. Extensive modeling of both the exposure and development processes was used to verify their results. By using a Monte Carlo simulation of electron scattering to simulate the electron exposure and mass-transfer relationships to simulate the process of developing the undercut region, the authors were able to produce a model that closely matches experimental results. With the process fully characterized, it is possible to produce nearly any linewidth/undercut combination, limited only by PMMA resolution and the mechanical stability of large overhang structures. This robustness, combined with the high resolution of the PMMA imaging layer, will allow the reliable fabrication of many interesting devices and circuits based on nanoscale Josephson junctions.
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85.25.Cp Josephson devices
81.65.Mq Oxidation

Direct wiring of carbon nanotubes for integration in nanoelectromechanical systems

S. Bauerdick, A. Linden, C. Stampfer, T. Helbling, and C. Hierold

J. Vac. Sci. Technol. B 24, 3144 (2006); http://dx.doi.org/10.1116/1.2388965 (4 pages) | Cited 12 times

Online Publication Date: 4 December 2006

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The authors present the use of electron beam induced deposition (EBID) for direct wiring of carbon nanotubes (CNTs). Since this technique is a maskless, direct patterning method, EBID is applicable to suspended nanotubes potentially integrated in predefined nanoelectromechanical systems (NEMS). The authors developed a process including CNT adsorption from solution on prepatterned planar samples, evaluation and localization of CNTs by scanning force microscopy, preparation of GDSII layouts, and contacting CNTs by EBID of tungsten. EBID was performed in an integrated e-beam lithography and nanoengineering workstation using tungsten hexacarbonyl as precursor. With well controlled exposure conditions, a resistivity on the order of 10−2 Ω cm has been achieved. Moreover, electrical measurements on CNTs contacted by EBID tungsten leads clearly show transistorlike behavior. First tests on EBID metal lead integration on alumina NEMS structures were carried out. Thus EBID can enable a top metallization of CNTs on suspended NEMS structures, which should enhance also the mechanical stability between the lead and the CNT.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation
84.32.Hh Inductors and coils; wiring
back to top Charged Particle Deposition and Etching

Micromachined piezoresistive proximal probe with integrated bimorph actuator for aligned single ion implantation

A. Persaud, K. Ivanova, Y. Sarov, Tzv. Ivanov, B. E. Volland, I. W. Rangelow, N. Nikolov, T. Schenkel, V. Djakov, D. W. K. Jenkins, J. Meijer, and T. Vogel

J. Vac. Sci. Technol. B 24, 3148 (2006); http://dx.doi.org/10.1116/1.2375079 (4 pages) | Cited 2 times

Online Publication Date: 4 December 2006

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The authors report a microfabrication procedure of self-actuated piezoresistive scanning probes (SAPSPs). They are designed for a SAPSP instrument that is integrated with an ion beam for aligned single ion implantation in ultrahigh vacuum. The novelty of the design is an integrated hollow pyramid, instead of a previously mechanically hand mounted pyramid [ J. Vac. Sci. Technol. B 23, 2798 (2005) ]. The pyramid has dual purpose. First it collimates the ion beam and suppresses secondary particles from the back side of the cantilever, so that secondary particles from the target material can be used for single ion detection. Second the pyramid also provides an atomic force microscope tip for the scanning probe. A crucial step in the fabrication is the back side opening via etching for the hollow pyramid. The fabrication procedure will be discussed in detail.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.79.Lh Atomic force microscopes
07.10.Cm Micromechanical devices and systems
81.16.Ta Atom manipulation
81.65.Cf Surface cleaning, etching, patterning
61.80.Jh Ion radiation effects

Characterization of hydrogen silsesquioxane as a Cl2/BCl3 inductively coupled plasma etch mask for air-clad InP-based quantum well waveguide fabrication

D. Park, T. H. Stievater, W. S. Rabinovich, N. Green, S. Kanakaraju, and L. C. Calhoun

J. Vac. Sci. Technol. B 24, 3152 (2006); http://dx.doi.org/10.1116/1.2395952 (5 pages) | Cited 6 times

Online Publication Date: 4 December 2006

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Air-clad InGaAsP/InGaAs quantum well waveguides have been fabricated by inductively coupled plasma (ICP) etching using hydrogen silsesquioxane (HSQ) as an etch mask. First, HSQ has been studied for its contrast and resolution in electron beam lithography by varying e-beam exposure conditions and developer concentrations. Second, its etch resistance has been investigated in a chlorine-based ICP along with UVN30, a commercially available negative tone e-beam resist. Then, the optimum conditions for the exposure and development of HSQ for a chlorine-based ICP etching of InP-based material have been explored in terms of etch resistance. InGaAsP/InGaAs quantum well material was patterned with HSQ by electron beam lithography. The waveguide was formed by the Cl2/BCl3 ICP etching of InGaAsP/InGaAs quantum well material and subsequent HCl-based wet etching of InAlAs sacrificial layer. The optical properties of the released waveguides were investigated and the initial optical measurements show low waveguide loss.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
81.65.Cf Surface cleaning, etching, patterning
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.60.-q Optoelectronic devices

Enhancing etch resistance of hydrogen silsesquioxane via postdevelop electron curing

Joel K. W. Yang, Vikas Anant, and Karl K. Berggren

J. Vac. Sci. Technol. B 24, 3157 (2006); http://dx.doi.org/10.1116/1.2395949 (5 pages) | Cited 7 times

Online Publication Date: 4 December 2006

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In this work, the authors enhanced the etch resistance of the negative-tone electron resist, hydrogen silsesquioxane (HSQ) to CF4 reactive ion etching (RIE) by curing HSQ after development. They fabricated superconducting nanowires that were 15 nm wide by pattern transfer into a 6-nm-thick layer of NbN using cured HSQ as the etch mask. HSQ was cured using a postdevelop electron-beam exposure step prior to RIE in CF4 chemistry. This curing step was shown not to impact the resolution of the HSQ structures while increasing their etch resistance. The results of the authors demonstrate that the etch resistance of HSQ can be tuned after development, which is a desirable resist property of HSQ in addition to its high resolution and low line-edge roughness.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
52.77.Bn Etching and cleaning
81.07.-b Nanoscale materials and structures: fabrication and characterization
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Etching of Pyrex glass substrates by inductively coupled plasma reactive ion etching for micro/nanofluidic devices

Hyun Chul Jung, Wu Lu, Shengnian Wang, L. James Lee, and Xin Hu

J. Vac. Sci. Technol. B 24, 3162 (2006); http://dx.doi.org/10.1116/1.2388959 (3 pages) | Cited 11 times

Online Publication Date: 4 December 2006

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The inductively coupled plasma (ICP) reactive ion etching of Pyrex glass was carried out using SF6/Ar plasmas. The etch rate and surface and sidewall smoothnesses were investigated systematically through their dependence on bias voltage, ICP power, pressure, flow rate, and cathode temperature. Near vertical sidewalls and smooth etched surfaces were obtained by optimized etching parameters. The maximum etch rate, 0.65 μm/min, was achieved at a pressure of 5 mTorr, a bias of 720 V, and an ICP power of 2500 W. Microfluidic devices with various sizes on Pyrex glass have been designed and fabricated. Two types of electrokinetic flow patterns, which are extensional and rotational flows under different biases, have been successfully demonstrated with five cross microfluidic devices.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Kf Glasses (including metallic glasses)
52.77.Bn Etching and cleaning
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Electron beam induced deposition of low resistivity platinum from Pt(PF3)4

John D. Barry, Matthew Ervin, Jay Molstad, Alma Wickenden, Todd Brintlinger, Patrik Hoffman, and John Meingailis

J. Vac. Sci. Technol. B 24, 3165 (2006); http://dx.doi.org/10.1116/1.2395962 (4 pages) | Cited 17 times

Online Publication Date: 4 December 2006

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The authors have deposited Pt from Pt(PF3)4 using a focused 10 keV electron beam (scanning electron microscopy) in an FEI 620 dual beam system and measured the resistivity and composition of the deposits. To measure resistivity, lines of Pt were deposited across four gold fingers and the cross-sectional area of the lines was measured by focused ion beam sectioning. The resistivity varies between about 30 and 650 μΩ cm and is orders of magnitude lower than the resistivity achieved by e-beam-induced deposition using the usual organometallic precursor, (methylcyclopentadienyl) trimethyl platinum. In general, the higher the beam current the lower the resistivity. They have used wavelength dispersive x-ray analysis to measure the composition of rectangles deposited with various beam currents. Typical at.% values of (Pt:P:F) are 81:17:2 and 58:32:10. Minimum linewidth that they have deposited is 80 nm, and with a stationary beam of 2.8 nA they have deposited a pillar of 135 nm in diameter. They have also deposited Pt structures on freestanding carbon nanotubes and have used the deposits to contact nanofibers. Electron-beam-induced deposition of a “good” metal is particularly useful in geometries where standard lithography is awkward, such as making contacts to fibers or nanotubes randomly dispersed on a surface or freestanding.
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81.05.Bx Metals, semimetals, and alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.61.At Metal and metallic alloys
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Mechanical property evaluation of Au-coated nanospring fabricated by combination of focused-ion-beam chemical vapor deposition and sputter coating

Ken-ichiro Nakamatsu, Kazuhiro Kanda, Yuichi Haruyama, Toshinari Ichihashi, Takashi Kaito, and Shinji Matsui

J. Vac. Sci. Technol. B 24, 3169 (2006); http://dx.doi.org/10.1116/1.2397068 (4 pages) | Cited 3 times

Online Publication Date: 4 December 2006

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Au-coated nanosprings were fabricated by a combination of focused-ion-beam chemical vapor deposition (FIB-CVD) and sputter coating. A Au thin layer was successfully coated onto nanosprings fabricated by FIB-CVD. To confirm the mechanical motion, the authors performed an optical microscopy observation in which the Au sputter-coated nanosprings were able to expand and contract mechanically, as flexibly as macroscale springs. The measured spring constants of the Au-coated nanosprings ranged from 0.27 to 16 N/m, depending on the coil-section diameter. In addition, through the quantitative measurement of the mechanical characteristic of the nanosprings, the authors estimated that Au-coated nanosprings had a sufficient mechanical strength, which is useful for application in nanoelectromechanical system with three dimensions.
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81.07.Bc Nanocrystalline materials
62.25.-g Mechanical properties of nanoscale systems
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
back to top Directed Assembly

Precise positioning of single-walled carbon nanotubes by ac dielectrophoresis

Sarbajit Banerjee, Brian E. White, Limin Huang, Blake J. Rego, Stephen O’Brien, and Irving P. Herman

J. Vac. Sci. Technol. B 24, 3173 (2006); http://dx.doi.org/10.1116/1.2387155 (6 pages) | Cited 20 times

Online Publication Date: 4 December 2006

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The precise placement of single-walled carbon nanotubes (SWCNTs) in device architectures by ac dielectrophoresis involves the optimization of the electrode geometry, applied voltage and frequency, load resistance, and type of nanotube sample used. The authors have developed a toolkit to controllably integrate SWCNTs in device structures by the use of floating potential metal posts and appropriate electrode geometries, as designed using electric field simulations, and used it to fabricate structures such as crossed nanotube junctions.
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85.35.Kt Nanotube devices

Control of an electrospinning jet using electric focusing and jet-steering fields

Leon M. Bellan and H. G. Craighead

J. Vac. Sci. Technol. B 24, 3179 (2006); http://dx.doi.org/10.1116/1.2363403 (5 pages) | Cited 23 times

Online Publication Date: 4 December 2006

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Electrospinning can be used to deposit a wide variety of nanoscale polymeric fibers that have electrical, optical, or biological properties of interest. While there have been many studies of material properties, the typical deposited nanofibers are in the form of a randomly oriented mat. The authors are interested in forming functional devices utilizing the properties of the individual nanofibers. To this end they have used electric fields to both confine and steer an electrospun polymer jet for controlled deposition of functional materials. They have used an electrode between the electrospinning tip and grounded sample to suppress the chaotic whipping mode, thereby focusing the characteristic spot size of the deposited fibers to a smaller diameter. The same electrode setup was then modified to produce a time-varying steering field. Using this system, they have deposited isolated electrospun polymer fibers in a controlled fashion. They have also demonstrated that it is possible to terminate electrospun fibers using the modulated electric field.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.15.Pq Electrodeposition, electroplating
81.07.-b Nanoscale materials and structures: fabrication and characterization

Contactless capturing of particles in liquid using pulsed alternating dielectrophoresis

Cheng-Ping Luo, Andreas Heeren, Wolfgang Henschel, Monika Fleischer, and Dieter P. Kern

J. Vac. Sci. Technol. B 24, 3184 (2006); http://dx.doi.org/10.1116/1.2366630 (4 pages) | Cited 1 time

Online Publication Date: 4 December 2006

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Dielectrophoresis is an effective method for manipulation of particles in a medium, which can be achieved by applying electrical potentials to appropriately arranged electrodes. In the case of positive dielectrophoresis, the particles will move to regions of strong electric field and be captured at the edge or the surface of the electrodes, usually. The drawback thereby is that the particles may attach to the electrodes, leading to unwanted side effects. Negative dielectrophoresis moves them away from high field regions. In this article, the authors present a new method for contactless capturing of particles by using pulsed alternating dielectrophoresis. A signal sequence consisting of two pulsed ac voltages of different frequencies is applied to the electrodes. Each of them generates either positive or negative dielectrophoresis, respectively. With appropriate settings of dwell times and amplitudes, the particles are attracted toward the electrodes without attaching to them. Furthermore, the average distance from the electrodes can be tuned. Their experiments show that latex beads could be kept at a distance of up to about 20 μm from the electrodes.
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82.45.-h Electrochemistry and electrophoresis

Highly porous silicon membrane fabrication using polymer self-assembly

C. T. Black, K. W. Guarini, G. Breyta, M. C. Colburn, R. Ruiz, R. L. Sandstrom, E. M. Sikorski, and Y. Zhang

J. Vac. Sci. Technol. B 24, 3188 (2006); http://dx.doi.org/10.1116/1.2366700 (4 pages) | Cited 19 times

Online Publication Date: 4 December 2006

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A combination of diblock copolymer self-assembly and state-of-the-art semiconductor device fabrication methods is used to create highly uniform suspended porous silicon membranes. Integration of these two processing techniques is key to realizing manufacturable high quality devices. Three different methods are shown for adjusting membrane pore dimensions between 10 and 35 nm, allowing device optimization for specific applications.
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81.16.Dn Self-assembly
61.43.Gt Powders, porous materials

Nanoscale floating-gate characteristics of colloidal Au nanoparticles electrostatically assembled on Si nanowires

H.-S. Jeon, C.-W. Cho, C.-H. Lim, B. Park, H. Ju, S. Kim, and S.-B. Lee

J. Vac. Sci. Technol. B 24, 3192 (2006); http://dx.doi.org/10.1116/1.2375083 (4 pages) | Cited 5 times

Online Publication Date: 4 December 2006

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Nanoscale floating-gate characteristics of colloidal Au nanoparticles electrostatically assembled on Si nanowires have been investigated. Colloidal Au nanoparticles with ∼ 5 nm diameters were selectively deposited onto the lithographically defined n-type Si nanowire surface by 2 min electrophoresis between the channel and the side gates. The device transfer characteristics measured at room temperature showed hysteresis, with the depletion mode cutoff voltage applied by the side gates shifted by as much as 1.5 V, with the source-drain bias at 1.4 V. The results demonstrate that the electrostatic assembly of colloidal Au nanoparticles is a useful method for the fabrication of Si nanowire based nanoscale floating-gate nonvolatile memory structures.
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84.30.Sk Pulse and digital circuits
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.Tv Field effect devices

Gold nanoparticle wires made using RNA-based self-assembly

D. R. S. Cumming, A. D. Bates, B. P. Callen, J. M. Cooper, R. Cosstick, C. Geary, A. Glidle, L. Jaeger, J. L. Pearson, M. Proupín-Pérez, and C. Xu

J. Vac. Sci. Technol. B 24, 3196 (2006); http://dx.doi.org/10.1116/1.2363404 (4 pages)

Online Publication Date: 4 December 2006

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Self-assembly or bottom-up techniques based on molecular recognition are attracting a great deal of interest for nanofabrication. One such technology is based on the use of self-assembling tecto-RNA that has been shown to be able to make structures with nanoscale features (<10 nm) over large areas of the order of several microns. The technique is extremely flexible in that different RNA designs can be used to create dramatically different patterns, and the technology has the potential to scale up so that it might be used to pattern whole chips, or even wafers. In a step towards using molecular recognition techniques to build devices such as electronic circuits or sensors it is necessary to be able to add device structures or link functional units together. The authors show that the tecto-RNA method can be extended to attach gold nanoparticles using DNA linkers. The self-assembling properties of the RNA can in turn be used to link together the gold nanoparticles to form wires and clusters in a Mg2+-ion controlled, as opposed to electrostatically aggregated, process. Using this method they have fabricated a gold nanoparticle wire between two nanoelectrodes and evaluated the electrical properties of the resultant device.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Dn Self-assembly

Ultrafast patterning of nanoparticles by electrostatic lithography

Jaebum Joo, SangJun Moon, and Joseph M. Jacobson

J. Vac. Sci. Technol. B 24, 3205 (2006); http://dx.doi.org/10.1116/1.2363407 (4 pages) | Cited 6 times

Online Publication Date: 4 December 2006

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Electron beam lithography is one of the best tools for patterning nanostructures, but its usage is limited due to slow processing. To enhance the patterning speed, the authors used a low dose electron beam to generate a “latent” charge pattern image and then create a real pattern by attaching positively charged particles by electrospray. Hard baked 2.3 μm thick polymethylmethacrylate substrates were irradiated with a 2 keV electron beam with a dose of 50 nC/cm2. Positively charged silver nanoparticles were generated by an electrospray technique in which a nanoparticle solution mixed with hexane was sprayed through a 15 μm diameter capillary tip with an applied potential of 4.5 kV. Charged nanoparticles were deposited to the charge patterned sites by electrostatic attraction with a resolution of 0.7 μm. This patterning approach, which we call “electrostatic lithography,” represents a speed increase of ∼ 20 times over standard fast electron beam resists that require typical doses of 1 μC/cm2. This approach may lead to a general capability for ultrafast patterning of nanomaterial building blocks including nanoparticles and nanotubes without requiring additional etching or other processing steps.
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81.16.Rf Micro- and nanoscale pattern formation
81.15.Rs Spray coating techniques
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.80.Fe Electron and positron radiation effects
back to top Nanoelectronic and Nanomagnetic Devices

Approach to variable frequency measurements of carbon nanotube transistors

Islamshah Amlani, Jonathan Lewis, Ruth Zhang, Kevin Nordquist, Steve Rockwell, and Dan Woodward

J. Vac. Sci. Technol. B 24, 3209 (2006); http://dx.doi.org/10.1116/1.2397070 (4 pages) | Cited 3 times

Online Publication Date: 4 December 2006

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An approach to variable frequency characterization of high impedance devices such as a carbon nanotube field-effect transistor is presented. A top-gated nanotube transistor is configured as a common source amplifier, and frequency response function of the device is measured. Evidence of signal amplification is observed in time domain as well as frequency domain up to a unity gain frequency of approximately 600 kHz. The observed roll-off in frequency is solely due to the measurement setup.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices

1‐ to 2‐nm-wide nanogaps fabricated with single-walled carbon nanotube shadow masks

E. P. De Poortere, H. L. Stormer, L. M. Huang, S. J. Wind, S. O’Brien, M. Huang, and J. Hone

J. Vac. Sci. Technol. B 24, 3213 (2006); http://dx.doi.org/10.1116/1.2375081 (4 pages) | Cited 4 times

Online Publication Date: 4 December 2006

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The authors present a method for producing nanometer-scale gaps, based on metal evaporation through a suspended single-walled carbon nanotube acting as a shadow mask. 83% of the nanogap devices display current-voltage dependencies characteristic of direct electron tunneling. Fits to the current-voltage data yield gap widths in the 0.8–2.3 nm range for these devices, dimensions that are well suited for single-molecule transport measurements.
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85.35.Kt Nanotube devices
85.40.Hp Lithography, masks and pattern transfer

Fabrication and characterization of novel cross point structures for molecular electronic integrated circuits

Wei Chen, Xueqing Liu, Zhongkui Tan, Konstantin K. Likharev, James E. Lukens, and Andreas Mayr

J. Vac. Sci. Technol. B 24, 3217 (2006); http://dx.doi.org/10.1116/1.2366618 (4 pages) | Cited 5 times

Online Publication Date: 4 December 2006

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Molecular electronic devices have the potential to dramatically increase the density and performance of integrated circuits. In order to realize this potential, reliable and scalable fabrication of nanoscale molecular electronic devices is essential. The authors have developed a new type of cross point structure in which the molecules are self-assembled between two metallic electrodes separated by an aluminum oxide layer. The gap between the electrodes is only a few nanometers wide and is defined by the aluminum oxide layer thickness, so it can be adjusted to match the length of the molecules with high (subnanometer) precision. This fabrication method applies to the study of transport properties of single molecules and at the same time is compatible with processes used in electronic industry, so that it may be used in the future to integrate molecular devices with silicon-based integrated circuits. Since the molecular self-assembly is the last step of the process, damage to molecules can be minimized. The authors have achieved a relatively high yield of high-quality support structures even at this early stage of technology development. Preliminary experimental data for electron transport through self-assembled oligo-phenylene-ethynylene-based molecules are compatible with the general theory of sequential single-electron tunneling.
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85.65.+h Molecular electronic devices
85.35.-p Nanoelectronic devices

Threshold voltage adjustment on spherical, single-crystal silicon substrates by focused ion beam implantation

V. Zomorrodian, B. Craver, G. Radhakrishnan, M. Patel, E. J. Charlson, P. Ruchhoeft, and J. C. Wolfe

J. Vac. Sci. Technol. B 24, 3221 (2006); http://dx.doi.org/10.1116/1.2387152 (6 pages)

Online Publication Date: 4 December 2006

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The development of spherical, rather than planar, imaging arrays would enable compact wide field-of-view cameras by reducing the size and complexity of the optical components. One approach is to fabricate the sensors and readout integrated circuits directly on a spherical shell machined from a single-crystal silicon substrate. Several significant advances in processing these substrates have already been reported. This article addresses one of the fundamental electronic issues: a threshold voltage correction procedure that accounts for the dependence of oxide thickness, fixed oxide charge, and interface trapped charge on crystallographic orientation and the variation of implant depth and projected dose on substrate geometry. Substrates with 15 mm radius of curvature and 25 mm diameter were machined from a B-doped (3 Ω cm) (100) silicon ingot. The threshold voltage of as-formed capacitors varied from −0.4 V in the center to −2.0 V at a radius of 10 mm. A 110 keV B+ focused ion implantation system was used to adjust threshold voltage point by point with 1 mm resolution. The authors demonstrate, for the first time, the ability to correct threshold voltage to within 0.12 V over an 83° field of view.
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42.79.Pw Imaging detectors and sensors
42.82.-m Integrated optics
61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology
84.32.Tt Capacitors
85.60.-q Optoelectronic devices

Chemically responsive molecular transistors fabricated by self-aligned lithography and chemical self-assembly

J. Tang, Y. Wang, C. Nuckolls, and S. J. Wind

J. Vac. Sci. Technol. B 24, 3227 (2006); http://dx.doi.org/10.1116/1.2357968 (3 pages) | Cited 9 times

Online Publication Date: 4 December 2006

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The authors present the fabrication and characterization of molecular transistors comprising at most a small number of molecules, which display a distinct chemical function. The fabrication involves a self-aligned technique capable of patterning metal electrodes with interelectrode separations of ∼ 2 nm with very high yield. The electrodes are bridged by molecules with a metal-ion core which can be inserted by in situ designed chemical reaction. The presence or absence of the ion modulates the electrical conductance of the device.
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85.65.+h Molecular electronic devices
85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Super-self-aligned back-gate∕double-gate planar transistors: Novel fabrication approach

Hao Lin, Haitao Liu, Arvind Kumar, Uygar Avci, Jay S. Van Delden, and Sandip Tiwari

J. Vac. Sci. Technol. B 24, 3230 (2006); http://dx.doi.org/10.1116/1.2397067 (4 pages)

Online Publication Date: 4 December 2006

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This work presents a reproducible, super-self-aligned approach for fabricating back-gate∕double-gate transistors with a thin silicon channel and thick doped source∕drain polysilicon access regions. Such a device structure can lead to ultimate electrostatic control of the channel without sacrificing source∕drain series resistance in a deeply scaled field effect transistor. The approach consists of a unique combination of silicon complementary-metal-oxide-semiconductor front-end processing techniques, along with wafer bonding, sidewall spacer formation (in oxide and nitride), solid-state junction diffusion, and multistage chemical mechanical polishing for wafer-level planarization. The authors further demonstrate the formation of a reliable contact at the source∕drain junction interface between doped polysilicon and the undoped silicon channel. In the design, through oxidation, the authors are able to introduce strain in the structure, as well as buried interconnects in a plane below the device. Both n-channel and p-channel devices have shown high drive currents, strong back-gate coupling, and high effective carrier mobility.
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85.30.Tv Field effect devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.40.Ls Metallization, contacts, interconnects; device isolation

Directly patterning ferroelectric films by nanoimprint lithography with low temperature and low pressure

K. C. Hsieh, H. L. Chen, C. H. Lin, and C. Y. Lee

J. Vac. Sci. Technol. B 24, 3234 (2006); http://dx.doi.org/10.1116/1.2395958 (5 pages) | Cited 4 times

Online Publication Date: 4 December 2006

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In this article, the authors demonstrate an imprint method for patterning ferroelectric films. In contrast to conventional nanoimprint lithography, the patterned mold is directly imprinted in a ferroelectric film or a metal/ferroelectric film bilayer structure. In general, direct imprint in a ferroelectric or metal film needs ultrahigh pressure or temperature to form patterns. In this article, the authors improve the direct imprint processes by using a sharp mold and an underlying soft gel film for the reduction of the imprint pressure and temperature. The imprint pressure can be reduced to be compatible with the conventional nanoimprint instrument. The authors also successfully use the metal/ferroelectric bilayer structure to overcome the pattern flattened problem in a gel film. The cover metal layer can also be the upper conductive layer in the ferroelectric application. For direct contact of the metal film with mold, no surfactant should be coated on the surface of mold. It also indicates that no mold-rework processes are necessary for this direct imprint ferroelectric film method.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
back to top MEMS, NEMS, and Nanophotonics

Characterization and operation of a mechanically actuated silicon microgripper

Marius M. Blideran, Monika Fleischer, Wolfgang Henschel, Dieter P. Kern, Jochen Sterr, Klaus Schock, Stephan Kleindiek, Matthias G. Langer, Karsten Löffler, and Francois Grauvogel

J. Vac. Sci. Technol. B 24, 3239 (2006); http://dx.doi.org/10.1116/1.2357961 (5 pages) | Cited 2 times

Online Publication Date: 4 December 2006

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Since the manipulation of biological objects is usually performed in a life-sustaining environment, electrical fields or thermal gradients through the liquid may cause perturbations. The authors present a microgripper fabricated in silicon by a combination of bulk and surface micromachining processes that exhibits several advantages compared to previous reports. In order to avoid any possible perturbation caused by electrical fields, their microgripper is mechanically actuated. The complete system including the microgripper, a piezoactuator, and a nanomanipulator is described in detail together with manipulation of micrometer sized glass spheres.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
06.60.Sx Positioning and alignment; manipulating, remote handling
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
87.80.Fe Micromanipulation of biological structures
87.85.Va Micromachining

Accurate resonant frequency spacing of microring filters without postfabrication trimming

C. W. Holzwarth, T. Barwicz, M. A. Popović, P. T. Rakich, E. P. Ippen, F. X. Kärtner, and Henry I. Smith

J. Vac. Sci. Technol. B 24, 3244 (2006); http://dx.doi.org/10.1116/1.2363402 (4 pages) | Cited 10 times

Online Publication Date: 4 December 2006

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Optical microring resonators are compact building blocks for many microphotonic systems, as they enable narrow-band filtering. Of particular interest are integrated banks of microphotonic filters, with accurately spaced operational frequencies, for simultaneously processing multiple channels of information. Accurate spectral spacing has not yet been reported as it requires subnanometer control of the average dimensions of the optical resonators used to build high-performance microphotonic filters. Here, the authors present a technique enabling the relative dimensional control needed to achieve accurate spectral spacing, without postfabrication trimming. The authors fabricated eight-channel second-order microring-resonator filter banks with accurate spectral spacing using scanning-electron-beam lithography. The microrings are made of silicon-rich silicon nitride, and the subnanometer relative dimensional control is achieved through carefully calibrated adjustments of the electron-beam dose. When combining the dose alternations with small changes in microring radii, the authors demonstrate filter banks with accurate channel spacings ranging from 90 to 180 GHz. We show that we can accurately control a 2.7 nm change in average width of the ring waveguide to 0.11 nm, despite a 6 nm step size in the scanning-electron-beam lithography system.
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42.79.Ci Filters, zone plates, and polarizers
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer

Reproduction of the Morpho blue by nanocasting lithography

Akira Saito, Yusuke Miyamura, Masaki Nakajima, Yoko Ishikawa, Kenji Sogo, Yuji Kuwahara, and Yoshihiko Hirai

J. Vac. Sci. Technol. B 24, 3248 (2006); http://dx.doi.org/10.1116/1.2395950 (4 pages) | Cited 5 times

Online Publication Date: 4 December 2006

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The Morpho butterfly’s blue, which is a specific color produced by nanostructures, is expected to serve to various industrial applications such as posters, displays, cosmetics, etc. The natural Morpho blue has recently been emulated successfully by an artificial stepped nanostructure, but the fabrication of the nanostructure is too expensive using conventional lithography method. To solve the problem, nanocasting lithography (NCL) is newly applied using UV curable polymer to replicate the stepped nanostructure and improve heat resistance for the following deposition process. After fabrication of the stepped polymer structure by NCL, TiO2 and SiO2 layers are deposited using the vacuum electron beam deposition and the Morpho blue structure is efficiently reproduced at low cost. The reflective characteristic of the reproduced structure is almost same as the natural Morpho blue.
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81.16.Nd Micro- and nanolithography
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Wafer-scale fabrication of polymer distributed feedback lasers

M. B. Christiansen, M. Schøler, S. Balslev, R. B. Nielsen, D. H. Petersen, and A. Kristensen

J. Vac. Sci. Technol. B 24, 3252 (2006); http://dx.doi.org/10.1116/1.2387154 (6 pages) | Cited 3 times

Online Publication Date: 4 December 2006

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The authors demonstrate wafer-scale, parallel process fabrication of distributed feedback (DFB) polymer dye lasers by two different nanoimprint techniques: By thermal nanoimprint lithography (TNIL) in polymethyl methacrylate and by combined nanoimprint and photolithography (CNP) in SU-8. In both techniques, a thin film of polymer, doped with rhodamine-6G laser dye, is spin coated onto a Borofloat glass buffer substrate and shaped into a planar waveguide slab with first order DFB surface corrugations forming the laser resonator. When optically pumped at 532 nm, lasing is obtained in the wavelength range between 576 and 607 nm, determined by the grating period. The results, where 13 laser devices are defined across a 10 cm diameter wafer substrate, demonstrate the feasibility of NIL and CNP for parallel wafer-scale fabrication of advanced nanostructured active optical polymer components, with a yield above 95%.
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42.55.Mv Dye lasers
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
back to top Nanobiology and Nanomedicine

Progress towards tubes with regular nanopatterned inner surfaces

K. Seunarine, M. Tormen, N. Gadegaard, M. Riehle, C. D. W. Wilkinson, L. Businaro, and F. Romanato

J. Vac. Sci. Technol. B 24, 3258 (2006); http://dx.doi.org/10.1116/1.2357970 (5 pages) | Cited 2 times

Online Publication Date: 4 December 2006

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The repair of vascular tubing is an important task in tissue engineering. The behavior of cells is strongly influenced by the topology of the surfaces, on both a micrometric and a nanometric scale, in their vicinity. Thus the authors wish to make tubes that are patterned on the inner surface. One way to do this is to use the good depth of focus capabilities of x-ray exposure to print an array of dots, 200 nm diameter and 400 nm pitch, onto a curved surface coated in resist. A die made from this structure allows nanoembossing into a biodegradable polymer. A closed vessel can then be made by adding a lid, that also has a similar nanopatterned surface. Details of the accuracy of transfer are given. It is concluded that x-ray printing is a suitable approach for the formation of internally patterned tubing.
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87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.85.Lf Tissue engineering
87.17.-d Cell processes
81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
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