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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 25 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 3 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 17 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 6 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 7 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 4 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 7 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 10 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 2 times

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 2 times

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 22 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 4 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 11 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 7 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 13 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 9 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
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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 6 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