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Nov 2007

Volume 25, Issue 6, pp. 1743-2664

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Extreme ultraviolet lithography: A review

Banqiu Wu and Ajay Kumar

J. Vac. Sci. Technol. B 25, 1743 (2007); http://dx.doi.org/10.1116/1.2794048 (19 pages) | Cited 57 times

Online Publication Date: 11 October 2007

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Extreme ultraviolet lithography (EUVL) was thoroughly reviewed over a broad range of topics, including history, tools, source, metrology, condenser and projection optics, resists, and masks. Since 1988, many studies on EUVL have been conducted in North America, Europe, and Japan, through state sponsored programs and industrial consortiums. To date, no “show stopper” has been identified, but challenges are present in almost all aspects of EUVL technology. Commercial alpha lithography step-and-scan tools are installed with full-field capability; however, EUVL power at intermediate focus (IF) has not yet met volume manufacturing requirements. Compared with the target of 180 W IF power, current tools can supply only approximately 55–62 W. EUV IF power has been improved gradually from xenon- to tin-discharge-produced plasma or laser-produced plasma. EUVL resist has improved significantly in the last few years, with 25 nm 1:1 line/space resolution being produced with approximately 2.7 nm (3σ) line edge roughness. Actual adoption of EUVL will depend on the extension of current optical lithography, such as 193 nm immersion lithography, combined with double patterning techniques. Mask fabrication and application technologies may be the most substantial challenges. Creating a defect-free EUVL mask is currently an obstacle to its application, although a combination of removable pellicle and thermophoretic protection may overcome nonpellicle challenge. Cost of ownership is a critical consideration for EUVL; nevertheless, it has been predicted that EUVL may be in pilot production at 32 nm and in large-scale production at 22 nm with the capability to extend to the next technology node.
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85.40.Hp Lithography, masks and pattern transfer
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Effect of process parameters on via formation in Si using deep reactive ion etching

I. U. Abhulimen, S. Polamreddy, S. Burkett, L. Cai, and L. Schaper

J. Vac. Sci. Technol. B 25, 1762 (2007); http://dx.doi.org/10.1116/1.2787869 (9 pages) | Cited 7 times

Online Publication Date: 12 October 2007

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The effect of process parameters on blind via formation for vertical interconnects using an STS deep reactive ion etch tool is reported. A modified Bosch process is used to create vias (20 and 25 μm in diameter) with varying depths and sidewall angles on 125 mm diameter silicon wafers using a photoresist mask. The effect of changing the flow rates of SF6 and C4F8 gases, the automatic pressure control angle, and coil and platen powers on via profile and sidewall morphology is studied. The effect of chamber cleaning and conditioning on controlling the diameter growth at the top surface of the via is also reported. The various via profiles are examined using an environmental scanning electron microscope and by observing via cross sections. Each parameter plays a critical role in obtaining a specified via profile. A sloped via sidewall is required for our application of fabricating vertical interconnects. After etching, vias are insulated by depositing 2 μm of silicon dioxide by plasma enhanced chemical vapor deposition at 250 °C. A barrier film of TaN is reactively sputtered after insulation deposition followed by a Cu sputtered seed film allowing electroplated Cu to fill the via. The sloped via sidewall is required due to the weak step coverage obtained by sputter deposition.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Hp Lithography, masks and pattern transfer
85.40.Sz Deposition technology

Fabrication of a Fresnel zone plate through electron beam lithographic process and its application to measuring of critical dimension scanning electron microscope performance

J. Kim, K. Jalhadi, S.-Y. Lee, and D. C. Joy

J. Vac. Sci. Technol. B 25, 1771 (2007); http://dx.doi.org/10.1116/1.2787874 (5 pages) | Cited 2 times

Online Publication Date: 12 October 2007

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It is important to be able to quantify the imaging performance of critical dimension scanning electron microscopes for such purposes as verifying the specification, and tracking and optimizing its performance during use. Imaging performance can be defined by parameters such as resolution, signal to noise ratio, drift, and instability under standard operation conditions. To perform tests to obtain such parameters, it is necessary to have both suitable test samples and appropriate software for image analysis. A Fresnel zone plate, as a reproducible and well characterized sample, is fabricated using direct-write electron beam lithography. A package of two-dimensional Fourier transform and analysis software, designed as a plug-in for the shareware IMAGE-JAVA program, has been developed for resolution analysis and is freely available online.
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85.40.Hp Lithography, masks and pattern transfer

Defects in HgTe grown by molecular beam epitaxy on (211)B-oriented CdZnTe substrates

E. Selvig, C. R. Tonheim, K. O. Kongshaug, T. Skauli, T. Lorentzen, and R. Haakenaasen

J. Vac. Sci. Technol. B 25, 1776 (2007); http://dx.doi.org/10.1116/1.2787876 (9 pages) | Cited 9 times

Online Publication Date: 12 October 2007

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The authors present a systematic study showing the evolution of the defect morphology and crystalline quality in molecular beam epitaxially grown HgTe epilayers with substrate temperature. The authors have characterized the layers using optical microscopy, atomic force microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and high-resolution x-ray diffraction. Four types of defects (microvoids, circular voids, hillocks, and high-temperature voids) have been characterized on epilayers grown in the substrate temperature range of 183.3–201.3 °C. The authors find that there is a minimum in the area covered by defects at a temperature just below the onset of Te precipitation, and they define this temperature as the optimal growth temperature. Above the optimal growth temperature the authors observe the appearance of high-temperature voids. By determining the onset of Te precipitation in HgTe, and performing thermodynamic calculations, the authors can also successfully predict the onset of Te precipitation in CdHgTe, which again is related to the optimal growth temperature in CdHgTe. Furthermore, the authors have found that the shape and density of the microvoids are particularly sensitive to the substrate temperature, and that these properties can be used to determine the deviation from the optimal growth temperature. From the shape and density of microvoids in one growth of HgTe, the authors can therefore determine the temperature correction needed to reach the optimal growth temperature for CdHgTe. The authors also suggest a mechanism for the formation of the microvoids based on the assumption of impurities on the substrate combined with a preferential Te diffusion in the [math11] direction across the steps.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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.
66.30.Lw Diffusion of other defects

Enhanced field emission from carbon nanotubes with a thin layer of low work function barium strontium oxide surface coating

Feng Jin, Yan Liu, Christopher M. Day, and Scott A. Little

J. Vac. Sci. Technol. B 25, 1785 (2007); http://dx.doi.org/10.1116/1.2790914 (4 pages)

Online Publication Date: 12 October 2007

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The authors report a field emitter structure based on barium strontium oxide coated carbon nanotubes (CNTs). This emitter consists of a thin tungsten ribbon with CNTs on the surface, and a thin layer of low work function barium strontium oxide coating on the CNTs. CNTs were grown on the surface of the tungsten ribbon by plasma enhanced chemical vapor deposition, and the oxide coatings were prepared using magnetron sputtering. This oxide coated CNT emitter was designed to combine the benefits of the high field enhancement factor from CNTs and the low work function from the emissive oxide coating. The field emission properties of the emitters were characterized. A field enhancement factor of 478 and a work function of 1.9 eV were obtained for the oxide coated CNTs. As a result of the reduction of surface work function, the field emission from the oxide coated CNTs increased by a factor of 2–3 compared to the uncoated CNTs. At 4.4 V/μm, the field emission current of 23.6 μA was obtained from an emitting surface of 0.012 cm2.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.Db Field emitters and arrays, cold electron emitters

Development of chemical-mechanical polished high-resolution zone plates

Stefan Rehbein, Peter Guttmann, Stephan Werner, and Gerd Schneider

J. Vac. Sci. Technol. B 25, 1789 (2007); http://dx.doi.org/10.1116/1.2790917 (5 pages) | Cited 1 time

Online Publication Date: 12 October 2007

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State-of-the-art zone plates for soft and hard x rays are commonly fabricated in nickel or gold by electroplating. The most critical fabrication step is the controlled filling of the plating mold, which directly affects the performance of the diffractive optics. One problem is that the electroplating rate depends on the actual zone width resulting in an inhomogeneous height profile across the optics. Another problem is the measurement of the actual zone height during the electroplating process to fill exactly the plating mold. In practice, underplating the mold results in a low diffraction efficiency of the zone plate. Overplating yields in unemployable optics. In this article, the authors apply a chemical-mechanical polishing (CMP) process to overcome the described problems. In the new processing step, the zone plate is planarized after overplating. The authors demonstrate for the first time that nickel zone plates with an outermost zone width down to 25 nm can be polished by applying a CMP process. This new step leads to a much better reproducibility in zone plate fabrication and their performance. In addition, to overcome the technical limit of the current aspect ratios of zone plates the authors propose to superimpose polished zone plate layers on top of each other. The authors assume that the introduced CMP process paves the way toward the development of future volume zone plates with ultrahigh aspect ratios for soft and hard x-ray applications.
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42.79.Ci Filters, zone plates, and polarizers
42.86.+b Optical workshop techniques
81.65.Ps Polishing, grinding, surface finishing
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution

Electrical properties and deep traps in ZnO films grown by molecular beam epitaxy

A. Y. Polyakov, N. B. Smirnov, A. I. Belogorokhov, A. V. Govorkov, E. A. Kozhukhova, A. V. Osinsky, J. Q. Xie, B. Hertog, and S. J. Pearton

J. Vac. Sci. Technol. B 25, 1794 (2007); http://dx.doi.org/10.1116/1.2790918 (5 pages) | Cited 3 times

Online Publication Date: 12 October 2007

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Capacitance-voltage (C-V), capacitance-frequency (C-f), admittance spectroscopy, deep trap spectra, and far infrared reflectance measurements were performed on undoped and N-doped ZnO films deposited on sapphire by molecular beam epitaxy. The results show existence of a heavily doped n+ layer near the interface with the substrate. The presence of these layers explains the large difference between the electron concentrations measured in the films by Hall effect and C-V profiling or calculated from the plasma minimum frequency in reflectance. C-V data obtained at low temperatures show a prominent persistent photocapacitance in the films. Admittance spectra were dominated by electron traps with ionization level EC−0.3 eV commonly observed in ZnO crystals grown by all techniques.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
73.61.Ga II-VI semiconductors
71.55.Gs II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects

Proposed single layer composite film used as high transmission phase shifting masks for the 32, 45, and 65 nm technology nodes

Fu-Der Lai and Jian Long Huang

J. Vac. Sci. Technol. B 25, 1799 (2007); http://dx.doi.org/10.1116/1.2790920 (5 pages)

Online Publication Date: 12 October 2007

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The optical constants of composite films are linearly dependent on their mole fraction. The (Al2O3)x–(TiO2)1−x composite films prepared by using rf unbalanced magnetron sputtering are completely oxidized using an O2/Ar flow rate ratio of 2.0. By tuning the Al2O3 mole fraction of (Al2O3)x–(TiO2)1−x composite films, the optical constants can be made to meet the optical requirements for a high transmittance attenuated phase shifting mask (HT-AttPSM) blank. It can be seen that the Al2O3 mole fraction in (Al2O3)x–(TiO2)1−x composite films which would best meet the optical requirements of a HT-AttPSM blank in ArF (immersion) lithography is calculated to be between 78% and 86%. In order to obtain a HT-AttPSM blank with an optimized transmittance of 20%, one Al2O3–TiO2 composite film is fabricated. All the films meet the requirements of the adhesion test and surface roughness for HT-AttPSM applications. Therefore, a single layer composite film of Al2O3–TiO2 could be applied to HT-AttPSM blanks, which can be utilized to design fine patterns with dimensions as small as 65, 45, and 32 nm.
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81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.66.Sq Composite materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Critical parameter determination of sonic flow controller diamond microtubes and micronozzles

S. S. Mammana, F. T. Degasperi, M. C. Salvadori, D. C. Sparapani, M. F. Laino, R. C. Rangel, F. S. Teixeira, and M. Cattani

J. Vac. Sci. Technol. B 25, 1804 (2007); http://dx.doi.org/10.1116/1.2790924 (4 pages)

Online Publication Date: 12 October 2007

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In this article, the authors measure throughput of sonic diamond microtubes and micronozzles that can work as passive gas flow controllers and flow meters under choking conditions. The behavior of the outlet pressure through the microdevices using an experimental setup with constant volume and constant temperature was determined in order to obtain the critical throughput, the critical mass flow rate, and the discharge coefficients of the diamond sonic microdevices.
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47.85.L- Flow control
81.05.U- Carbon/carbon-based materials
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.80.-v Instrumentation and measurement methods in fluid dynamics

On-wafer monitoring of charge accumulation and sidewall conductivity in high-aspect-ratio contact holes during SiO2 etching process

Butsurin Jinnai, Toshiyuki Orita, Mamoru Konishi, Jun Hashimoto, Yoshinari Ichihashi, Akito Nishitani, Shingo Kadomura, Hiroto Ohtake, and Seiji Samukawa

J. Vac. Sci. Technol. B 25, 1808 (2007); http://dx.doi.org/10.1116/1.2794050 (6 pages) | Cited 4 times

Online Publication Date: 12 October 2007

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The authors investigated charge accumulation in high-aspect-ratio contact-hole structures by using the new on-wafer monitoring device they fabricated on a Si substrate of 8 in. in diameter by using a conventional production process for semiconductor devices. The device has high-aspect-ratio contact-hole structures that are comparable with the practical interconnect structures of recent dynamic random access memory devices. In this article they discuss charge accumulation and the electric conductivity of fluorocarbon polymer deposited on the sidewall in high-aspect-ratio contact holes during plasma etching processes. They also monitored the charge accumulation during pulse-time-modulated (TM) plasma etching of high-aspect-ratio SiO2 contact-hole structures and found that the charge accumulation potential between the top and bottom of the contact-hole structures increased with the aspect ratio of the contact holes. Even in high-aspect-ratio contact holes the charge accumulated during TM plasma exposure was less than that accumulated during the conventional continuous-wave plasma exposure. The electrical conductivity of the fluorocarbon polymer deposited on the sidewall was increased by ion bombardment and was lower in high-aspect-ratio contact holes than in low-aspect-ratio contact holes. The new on-wafer monitoring device is a very effective tool for investigating local charge accumulation during the etching of device structures.
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52.77.Bn Etching and cleaning
84.30.Sk Pulse and digital circuits

Influence of RuO2 nanoparticles on electron emission from carbon nanotubes

Huarong Liu, Tsuneyuki Noguchi, and Shigeki Kato

J. Vac. Sci. Technol. B 25, 1814 (2007); http://dx.doi.org/10.1116/1.2794053 (5 pages) | Cited 4 times

Online Publication Date: 12 October 2007

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The authors studied the influence of RuO2 nanoparticles attached to multiwalled carbon nanotube (MWCNT) emitters on field emission. The threshold field, corresponding to 10 mA/cm2, was reduced 30% to ∼ 0.90 V/μm after attaching the particles. However, the particles deteriorated the stability of field emitters to some extent, especially in the high emission-current-density region of several A/cm2. The maximum emission-current density was limited to a lower current region compared with field emitters without RuO2. This can be explained reasonably by considering the vaporization of RuO2 particles that frequently causes significant self-ion-sputtering during strong emission because of the large contact resistance between the particles and MWCNTs. This explanation was experimentally proved by measuring the reduction of field-enhancement factor with the elapsed-emission time. This reduction is quicker for emitters with RuO2 than for emitters without RuO2. Experimental data also show that the standard deviation of Fowler-Nordheim plots for field emitters can be used to judge their stability and lifetime—a value of ∼ 5×10−3 suggests stable performance for our emitters.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Yield improvement of 0.13 μm Cu/low-k dual-damascene interconnection by organic cleaning process

Nam-Hoon Kim, Sang-Yong Kim, Hyun-Ki Lee, Kang-Yeon Lee, Chang-Il Kim, and Eui-Goo Chang

J. Vac. Sci. Technol. B 25, 1819 (2007); http://dx.doi.org/10.1116/1.2794049 (4 pages) | Cited 1 time

Online Publication Date: 15 October 2007

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Cu/low-k dielectrics are required to reduce resistance-capacitance (RC) delay and parasitic capacitance at the back-end-of-line (BEOL) interconnection. Integration of Cu/low-k dielectrics (black diamond) for BEOL interconnection in 0.13 μm technology has gained wide acceptance in the microelectronics industry in recent years. In this article, the authors discuss the process-integration issues of 0.13 μm Cu/low-k dual-damascene integration for static random access memory (SRAM) device yield. The same scheme of 0.13 μm Cu/fluorinated silicate glass–based device was used for the full process of making a low-k based device. Black diamond was used as a low-k material with a dielectric constant of 2.95. To reduce the damage of low-k and improve the yield of a low-k based device, H2O ashing, organic cleaning, and reduced down pressure in chemical-mechanical planarization were selected for the study. Specifically, the cleaning process after the ashing process was very effective for the removal of organic residues from via, trench, and surface contaminants. There was an increase of 40.79% in SRAM device yield compared to the low-k based device without the organic cleaning chemical process. As a result, the authors successfully integrated a 0.13 μm Cu/low-k dual-damascene interconnection with excellent yield performance after the improving process of organic cleaning.
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85.40.Ls Metallization, contacts, interconnects; device isolation

Growth of ZnSe nanowires by pulsed-laser deposition

Tinwei Zhang, Yiqun Shen, Wei Hu, Jian Sun, Jiada Wu, Zhifeng Ying, and Ning Xu

J. Vac. Sci. Technol. B 25, 1823 (2007); http://dx.doi.org/10.1116/1.2794052 (4 pages) | Cited 8 times

Online Publication Date: 15 October 2007

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Stoichiometric ZnSe nanowires have been grown by pulsed-laser deposition on GaAs (100) substrates coated with gold layers. The gold layer plays a key role as catalyst in the deposition of ZnSe nanowires. The thickness of the gold film greatly affected the density of the ZnSe nanowires synthesized on the substrate. No ZnSe nanowires were synthesized on the bare GaAs (100) substrate. The microstructures and the chemical compositions of the as-synthesized nanowires were investigated by scanning electron microscopy, x-ray diffraction, and Raman spectroscopy. The results reveal that the as-grown thin films consist of ZnSe nanowires with diameters ranging from 20 to 40 nm, and the nanowires appear to be randomly oriented on the Au-coated substrate. The as-grown nanowires were also observed to be elongated along different crystallographic directions.
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81.15.Fg Pulsed laser ablation deposition
68.65.La Quantum wires (patterned in quantum wells)
61.66.Bi Elemental solids
61.66.Dk Alloys
78.30.Fs III-V and II-VI semiconductors

Fabrication of periodic microstructures on flexible polyimide membranes

D. J. Shelton, J. S. Tharp, G. Zummo, W. R. Folks, and G. D. Boreman

J. Vac. Sci. Technol. B 25, 1827 (2007); http://dx.doi.org/10.1116/1.2794054 (5 pages) | Cited 6 times

Online Publication Date: 15 October 2007

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Periodic metallic microstructures were fabricated on polyimide membranes. Techniques were developed to maintain flatness of the membrane during processing while still allowing for flexibility in the final structure. For proper functionality of the structures, it was necessary to first fabricate a continuous metallic film and a continuous dielectric layer on top of the flexible substrate, which underlaid the periodic microstructure. Flexibility of the overall structure was maintained by using a polymer as the dielectric layer, which was constrained to have high optical transmission over the infrared wavelength range of 6–14 μm. Three candidate polymers were evaluated, and their measured optical properties are presented. Benzocyclobutene was found to be the best choice for this application. The final structure fully populated a 10 cm (4 in.) diameter flexible membrane with microstructures of excellent uniformity.
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42.86.+b Optical workshop techniques
42.70.Jk Polymers and organics
78.30.Jw Organic compounds, polymers
61.72.-y Defects and impurities in crystals; microstructure

Evolution of surface morphology of GaN thin films during photoelectrochemical etching

J. H. Leach, Ü. Özgür, and H. Morkoç

J. Vac. Sci. Technol. B 25, 1832 (2007); http://dx.doi.org/10.1116/1.2794055 (4 pages) | Cited 1 time

Online Publication Date: 15 October 2007

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The evolution of the surface morphology of unintentionally doped and Si-doped GaN samples subjected to photoelectrochemical (PEC) etching in the carrier-limited regime in aqueous KOH is reported. It was found that a nanoporous structure precedes whisker formation in samples in which high densities of whiskers ultimately form. Increasing the light intensity accelerated the rate of change of the surface morphology, but increasing the molarity of the KOH had no effect on the etching. The surface morphology in this regime tends to only depend on parameters of the starting layers, as well as how much etching in total has occurred. The identification of variations in surface morphology at different times during PEC etching of GaN may have utility in that assorted nanopatterning of the GaN surface can be intentionally achieved in a controllable, large-scale, and inexpensive manner.
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68.55.-a Thin film structure and morphology
68.47.Fg Semiconductor surfaces
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
82.45.-h Electrochemistry and electrophoresis
81.65.Cf Surface cleaning, etching, patterning
61.72.uj III-V and II-VI semiconductors

C-doped semi-insulating GaN HFETs on sapphire substrates with a high breakdown voltage and low specific on-resistance

Y. C. Choi, J. Shi, M. Pophristic, M. G. Spencer, and L. F. Eastman

J. Vac. Sci. Technol. B 25, 1836 (2007); http://dx.doi.org/10.1116/1.2794058 (6 pages) | Cited 5 times

Online Publication Date: 15 October 2007

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High breakdown voltage (BV) AlGaN/GaN heterojunction field effect transistors (HFETs) with a low specific on-resistance (ARDS(on)) were successfully fabricated using intentionally C-doped semi-insulating GaN buffers with a high resistivity on sapphire substrates. With the improvement of not only the resistivity of a C-doped GaN buffer but also the layout design near the gate feeding region, the fabricated devices exhibited a high BV of ∼ 1600 V and low ARDS(on) of 3.9 mΩ cm2. This result even reaches the 4H-SiC theoretical limit and the best ever reported for the high-power GaN-based HFETs realized on sapphire substrates to the best of our knowledge.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Large-scale growth of single-walled carbon nanotubes using cold-wall chemical vapor deposition

K. Y. Shin, C. T. Lee, J. S. Kao, C. C. Kei, C. M. Chang, C. N. Hsiao, J. H. Liang, K. C. Leou, and C. H. Tsai

J. Vac. Sci. Technol. B 25, 1842 (2007); http://dx.doi.org/10.1116/1.2796186 (5 pages)

Online Publication Date: 15 October 2007

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Carbon nanotubes have been considered as an alternative material for next generation nanoelectronic devices, such as the carbon nanotube field-effect transistor (CNT-FET) or nanosensor. Large-scale growth of single-walled carbon nanotubes (SWNTs) is particularly essential to the fabrication of the CNT-FET on a full wafer. In this study, SWNTs grown at designated positions on broken pieces in a conventional thermal furnace chemical vapor deposition (CVD) system and on a 4-in. full size silicon wafer in a cold-wall thermal CVD were compared. The distinct characteristics of SWNTs grown by the two systems are explained by the differences in the temperature distribution and the gas flow pattern, and their interplay with the catalysis and the feedstock gas decomposition. The adoption of cold-wall CVD process provides a simple method, but an essential step, toward commercial applications of SWNT-based devices.
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81.07.De Nanotubes
81.05.U- Carbon/carbon-based materials
81.16.Be Chemical synthesis methods
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Formation of single crystal sulfur supersaturated silicon based junctions by pulsed laser melting

Malek Tabbal, Taegon Kim, Jeffrey M. Warrender, Michael J. Aziz, B. L. Cardozo, and R. S. Goldman

J. Vac. Sci. Technol. B 25, 1847 (2007); http://dx.doi.org/10.1116/1.2796184 (6 pages) | Cited 7 times

Online Publication Date: 18 October 2007

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The authors demonstrate the formation of pn and nn+ junctions based on silicon supersaturated with sulfur (up to 0.46 at. %) using a combination of ion implantation and pulsed laser melting. Silicon wafers were implanted at 200 keV math to doses ranging from 1×1015 to 1×1016 ions/cm2 and subsequently melted and resolidified by using a homogenized excimer laser pulse. Above a threshold laser fluence of ∼ 1.4 J/cm2, the process produces a single crystal supersaturated alloy, free of extended defects, with a sharp junction between the laser melted layer and the underlying substrate, located near the maximum penetration of the melt front. Hall effect measurements indicate that the laser melted layers are n doped with a free carrier density up to 8×1018/cm3 that decreases by one-third upon postirradiation furnace annealing at 550 °C. Dark current-voltage measurements performed on these structures show good rectifying behavior. The photovoltaic characteristics of the junctions were enhanced by postirradiation annealing at 550–800 °C. These effects are attributed to the evolution of a population of point defects that survive the laser treatment. The influence of ion implantation dose, laser fluence, and annealing temperature on the properties of the junctions is also presented and discussed.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.66.-f Structure of specific crystalline solids
81.15.Fg Pulsed laser ablation deposition
61.72.up Other materials
81.40.Gh Other heat and thermomechanical treatments

Effects and mechanisms of nitrogen incorporation into hafnium oxide by plasma immersion implantation

Hei Wong, Banani Sen, B. L. Yang, A. P. Huang, and P. K. Chu

J. Vac. Sci. Technol. B 25, 1853 (2007); http://dx.doi.org/10.1116/1.2799969 (6 pages) | Cited 2 times

Online Publication Date: 22 October 2007

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The physics and effects of nitrogen incorporation into HfO2 films were studied in detail. The authors found that only a trace amount ( ∼ 5%) of nitrogen can be introduced into the HfO2 films using plasma immersion ion-implantation technique, regardless of implantation dose. They proposed that the nitrogen incorporation is due to the filling of O vacancies (VO) and replacement of VO O neighbors in the bulk with nitrogen atoms. At the interface, the nitrogen atoms exist in the form of Hf–N and Si–N bonding, which significantly improve the interface properties of the HfO2/Si structure. Temperature-dependent capacitance-voltage characteristics measurements indicate that both interface and oxide trap densities were greatly reduced with the incorporation of trace amount of nitrogen atoms.
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52.77.Dq Plasma-based ion implantation and deposition
61.72.up Other materials
77.55.-g Dielectric thin films

Characterization of ruthenium thin films as capping layer for extreme ultraviolet lithography mask blanks

Pei-yang Yan, Eberhard Spiller, and Paul Mirkarimi

J. Vac. Sci. Technol. B 25, 1859 (2007); http://dx.doi.org/10.1116/1.2799963 (8 pages) | Cited 4 times

Online Publication Date: 24 October 2007

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In extreme ultraviolet lithography (EUVL), the multilayer (ML) damage-free mask patterning processes and damage-free usage cycle are the keys in obtaining a successful, functional EUVL mask. A robust ML capping layer design will enable a long mask lifetime. In this article detailed investigation on the viability of ruthenium (Ru) thin films as capping layer for EUVL ML mask blanks is presented. The study is focused on Ru capping layer design for high reflectivity and its properties relevant to EUVL mask applications, such as microstructure, stress, optical properties at EUV wavelength, and chemical durability. The authors found that Ru thin films with a crystalline structure present a very high compressive stress which is insensitive to the primary ion deposition source energy. The Ru/Si interdiffusion layer, however, presents a much lower stress than the of Ru-only film. Amorphization of the Ru film is via atomic composition modification, which the authors believe could be one of the keys in reducing Ru film stress. The ruthenium cap, under a piranha chemical clean, was found to be more durable than Si capped ML blanks, indicating the advantages of using Ru as the EUVL ML mask blank capping layer.
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68.60.Bs Mechanical and acoustical properties
78.66.Bz Metals and metallic alloys
78.40.Kc Metals, semimetals, and alloys
85.40.Hp Lithography, masks and pattern transfer

Zero-dimensional analysis for discharge characteristics

Wontaek Park

J. Vac. Sci. Technol. B 25, 1867 (2007); http://dx.doi.org/10.1116/1.2798726 (3 pages)

Online Publication Date: 26 October 2007

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A volume-averaged, zero-dimensional numerical simulator for ac discharge of plasma display panel (PDP) is developed. The vacuum-ultraviolet photons such as 147 and 173 nm are treated as particles that cannot be stored. The surface charge on the dielectric layer is introduced in this study. Solving particle continuity and electron energy balance equations simultaneously, the characteristics of ac-discharge phenomena, such as the temporal evolution of surface charge, electric field, and particle densities, are analyzed. This numerical simulation result shows that the increment of the percentage of xenon atoms in a neon-xenon mixture of PDP improves the luminous efficiency of the ac-discharge gas by raising the intensity of 173 nm vacuum-ultraviolet photons from xenon excimers.
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52.80.-s Electric discharges
52.75.-d Plasma devices
85.60.Pg Display systems

Highly selective zero-bias plasma etching of GaN over AlGaN

Michael L. Schuette and Wu Lu

J. Vac. Sci. Technol. B 25, 1870 (2007); http://dx.doi.org/10.1116/1.2796183 (5 pages) | Cited 1 time

Online Publication Date: 6 November 2007

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Highly selective, low-damage etching of GaN over AlGaN is realized by zero-bias, nitrogen-rich N2/Cl2/O2 inductively coupled plasma, affording sub-10‐nm/min etch rates and rms roughness of 3 Å, favorable for gate recessing of GaN-based high electron mobility transistors (HEMTs). Selectivity is tuned by varying the O2 fraction, source power, and pressure. No AlGaN etching is detectable even after 30 min, so the etching selectivity is considered to be infinite. The authors demonstrate linear recessing of a n+‐GaN/Al0.3Ga0.7N/GaN device structure, which stops abruptly upon clearing the 10‐nm-thick cap. SiO2 masking used in this study is compatible with HEMT processes, where a masking dielectric is used for passivation, gate footprint definition, and mechanical gate support. Current-voltage measurements on recessed Schottky diodes show a 40x decrease in reverse leakage current and a three-fold increase in forward saturation current, when compared to non-recessed diodes, as well as lack of sensitivity to etch duration. Diodes on this device structure also showed breakdown voltages greater than −200 V, compared to −90 V for nonrecessed diodes.
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85.30.Tv Field effect devices
85.30.Kk Junction diodes

Structural and optical characterization of WO3 nanorods/films prepared by oblique angle deposition

W. Smith, Z.-Y. Zhang, and Y.-P. Zhao

J. Vac. Sci. Technol. B 25, 1875 (2007); http://dx.doi.org/10.1116/1.2799968 (7 pages) | Cited 11 times

Online Publication Date: 6 November 2007

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The structural and optical properties of WO3 nanorods prepared by oblique angle depositions were studied and compared with WO3 thin films. The x-ray diffraction analysis revealed that both the thin films and nanorods annealed at temperatures of 400 and 500 °C had an orthorhombic structure, while only the thin films showed a monoclinic phase when annealed at 300 °C. The band gap energies of the thin films and nanorods all decreased with increasing annealing temperature. The polarized optical absorbance spectra of the as-deposited nanorod samples initially showed anisotropy, but after annealing at temperatures above 400 °C, they became isotropic. This is believed to result from the changes in morphology, crystal structure, and orientation of the nanorod arrays after annealing.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.66.Nk Insulators
61.46.Hk Nanocrystals
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
71.20.Ps Other inorganic compounds

Ion energy control at substrates during plasma etching of patterned structures

R. Silapunt, A. E. Wendt, and K. H. R. Kirmse

J. Vac. Sci. Technol. B 25, 1882 (2007); http://dx.doi.org/10.1116/1.2803723 (6 pages) | Cited 8 times

Online Publication Date: 6 November 2007

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In fluorocarbon-based plasma etching of dielectrics, deposition of fluorocarbon on the substrate contributes to a complex surface chemical structure that strongly affects etch rate and etch selectivity. Results reported herein demonstrate that the energy distribution of bombarding ions (IED) has a significant effect on this polymer layer, subsequently affecting etch rate and selectivity in submicron patterned structures. Specifically, we have narrowed the IED while keeping other process conditions unchanged by tailoring the shape of the rf voltage wave form used for substrate bias. Significant improvements in etch selectivity for organosilicate glass (OSG) over silicon carbide in a C4F8/N2/Ar plasma have been obtained by using a narrow IED compared to the broad IED resulting from the typical sinusoidal bias wave form. Trenches etched in OSG with the tailored bias voltage wave form show good feature profiles and high selectivity at feature bottoms. Slight differences in feature profiles between tailored and sinusoidal wave forms, as well as variations in etch selectivity with feature depth, are consistent with an enhancement in polymerization at the substrate in the case of the tailored bias voltage wave form.
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52.77.-j Plasma applications
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

Thermal model for a superstrate cooling apparatus for an integrated in-line manufacturing process for thin film photovoltaic devices

R. A. Enzenroth, K. L. Barth, W. S. Sampath, and V. Manivannan

J. Vac. Sci. Technol. B 25, 1888 (2007); http://dx.doi.org/10.1116/1.2803724 (4 pages) | Cited 1 time

Online Publication Date: 6 November 2007

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An efficient apparatus to cool glass substrates in vacuum has been developed. The regions near the substrate are maintained at a higher pressure than the surrounding vacuum environment. Heat is transferred from the substrate by thermal conduction through the gas phase to a closely spaced water cooled plate. This article presents a model to predict the heat transfer rate as a function of the Knudsen number and the substrate to cooled plate distance.
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84.60.Jt Photoelectric conversion

Structure and magnetic property of c-axis oriented L10-FePt nanoparticles on TiN/a-Si underlayers

Yoshiko Tsuji, Suguru Noda, and Yukio Yamaguchi

J. Vac. Sci. Technol. B 25, 1892 (2007); http://dx.doi.org/10.1116/1.2803726 (4 pages) | Cited 1 time

Online Publication Date: 6 November 2007

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L10-FePt is a promising material for high-density perpendicular magnetic recording media. The authors previously reported that c-axis oriented L10-FePt nanoparticle monolayers can be formed on (200)-oriented polycrystalline template TiN underlayers on SiO2 by using a conventional sputtering method. In this study, TiN nanostructures, such as the degree of (200) orientation, were improved by first depositing a buffer layer, such as amorphous Si onto SiO2, and the grain size could be controlled by adjusting either the deposition temperature or TiN thickness. When FePt nanoparticles were formed on a template TiN underlayer with a buffer layer of amorphous Si, both their degree of c-axis orientation and their magnetic properties were improved; FePt nanoparticles with nominal thickness of 1.4 nm had coercivity of 12.9 kOe in the out-of-plane direction at 300 K.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Ss Magnetic recording materials
81.15.Cd Deposition by sputtering

Influence of different surface-passivation dielectrics on high-temperature strain relaxation of AlGaN in AlGaN/GaN heterostructures

D. J. Chen, Y. Q. Tao, C. Chen, Z. L. Xie, Z. Y. Zhai, X. S. Wu, P. Han, R. Zhang, and Y. D. Zheng

J. Vac. Sci. Technol. B 25, 1896 (2007); http://dx.doi.org/10.1116/1.2803728 (3 pages)

Online Publication Date: 6 November 2007

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The influence of AlN, Si3N4 and SiO2 surface-passivation dielectrics on high-temperature strain relaxation of AlGaN in AlGaN/GaN heterostructures was investigated in the range from room temperature to 600 °C by means of x-ray diffraction. The Si3N4 and SiO2 films produce an additional biaxial tensile stress to the underlying AlGaN barrier layer, whereas the AlN film produces an additional biaxial compressive stress. The authors found that the process of long-time heating and cooling results in a nonreversible lattice relaxation in the AlGaN layer. The passivation dielectrics used in this work can mitigate this high-temperature strain relaxation. The AlN dielectric manifested a better effect than the Si3N4 and SiO2 dielectrics.
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68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Gh Other heat and thermomechanical treatments
81.65.Rv Passivation
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
77.55.-g Dielectric thin films

Effects of surface plasmon resonant scattering on the power conversion efficiency of organic thin-film solar cells

Y. C. Chang, F. Y. Chou, P. H. Yeh, H. W. Chen, S.-H. Chang, Y. C. Lan, T. F. Guo, T. C. Tsai, and C. T. Lee

J. Vac. Sci. Technol. B 25, 1899 (2007); http://dx.doi.org/10.1116/1.2806959 (4 pages) | Cited 6 times

Online Publication Date: 20 November 2007

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The power conversion efficiencies of organic solar cells fabricated with Ag and Ti nanoparticle arrays using nanosphere lithography are studied. The Ag nanoparticle array exhibits a broad absorption spectrum peaked at 420 nm, which spectrally overlaps with the absorption band of the organic absorbing layer centered at 520 nm, while no peak presented for the Ti nanoparticle array. Power conversion efficiencies by the solar cells with Ag and Ti nanoparticle arrays are 2.42% and 1.68%, respectively. This efficiency improvement is proposed to originate from the strong surface plasmon resonant scattering of visible light by Ag nanoparticle arrays.
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84.60.Jt Photoelectric conversion
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.16.Nd Micro- and nanolithography
78.40.Me Organic compounds and polymers
78.66.Qn Polymers; organic compounds
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Optimized plasma-deposited fluorocarbon coating for dry release and passivation of thin SU-8 cantilevers

Stephan Keller, Daniel Haefliger, and Anja Boisen

J. Vac. Sci. Technol. B 25, 1903 (2007); http://dx.doi.org/10.1116/1.2806960 (6 pages) | Cited 11 times

Online Publication Date: 20 November 2007

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Plasma-deposited fluorocarbon coatings are introduced as a convenient method for the dry release of polymer structures. In this method, the passivation process in a deep reactive ion etch reactor was used to deposit hydrophobic fluorocarbon films. Standard photolithography with the negative epoxy-based photoresist SU-8 was used to fabricate polymer structures such as cantilevers and membranes on top of the nonadhesive release layer. The authors identify the plasma density as the main parameter determining the surface properties of the deposited fluorocarbon films. They show that by modifying the pressure during fluorocarbon deposition, the surface free energy of the coating can be tuned to allow for uniform wetting during spin coating of arbitrary thin SU-8 films. Further, they define an optimal pressure regime for the release of thin polymer structures at high yield. They demonstrate the successful release of SU-8 cantilevers and membranes with thicknesses down to 2.3 and 1.7 μm respectively, which is a considerable improvement to what has been achieved by dry release of all-polymer structures to date. Furthermore, chemical reaction of the SU-8 with the fluorocarbon coating during processing leads to a considerable increase of the surface free energy on one side of the released cantilevers. This process-integrated back side passivation is interesting for the use of the devices in biosensing applications.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
52.77.Dq Plasma-based ion implantation and deposition
81.65.Rv Passivation
68.35.Md Surface thermodynamics, surface energies
82.30.-b Specific chemical reactions; reaction mechanisms
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Structural characteristics of single-crystal nanowires grown by self-catalytic chemical vapor deposition method

Maoqi He and S. Noor Mohammad

J. Vac. Sci. Technol. B 25, 1909 (2007); http://dx.doi.org/10.1116/1.2804613 (7 pages) | Cited 7 times

Online Publication Date: 29 November 2007

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Physical characteristics of III-V nitride nanowires grown by the self-catalytic chemical vapor deposition method have been studied. The nanowire shape (uniform or tapered) and nanowire branching are found to depend on a number of parameters that influence the nanowire growth. Among them, the Gibbs-Thompson effect and the diffusivity of adatoms through liquid droplet dictate the length-to-diameter relationship of nanowires. The Raman scattering spectrum shows that the nanowires exist primarily in the hexagonal phase. Local modes, electronic transitions of dopant atoms, and impurity atoms contribute to unexpected peaks in this spectrum.
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68.65.La Quantum wires (patterned in quantum wells)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.67.Lt Quantum wires
78.30.Fs III-V and II-VI semiconductors
66.30.Pa Diffusion in nanoscale solids

Atomic diffusion and electronic structure in Al0.52In0.48P/GaAs heterostructures

P. E. Smith, M. Lueck, S. A. Ringel, and L. J. Brillson

J. Vac. Sci. Technol. B 25, 1916 (2007); http://dx.doi.org/10.1116/1.2811705 (6 pages)

Online Publication Date: 29 November 2007

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In order to investigate the relationship between atomic diffusion and electronic structure in the epitaxial AlInP/GaAs system, the authors have performed cross-sectional cathodoluminescence spectroscopy and secondary ion mass spectrometry measurements of a SiOx-capped, lattice-matched Al0.52In0.48P/GaAs double heterostructure. The authors measure atomic diffusion of over 100 nm resulting from annealings ranging from 650 to 850 °C. An ∼ 40 meV increase in the emission energy of AlInP is observed after the highest temperature annealings. This increase is consistent with an increase in the Ga concentration of the ternary layer at the expense of In, and as a result of diffusion from neighboring GaAs layers. Additionally, the authors observe a broad, AlInP-localized feature at ∼ 1.98 eV. The intensity of this emission relative to the AlInP band-edge emission depends sensitively on the annealing temperature and, therefore, the amount of cross diffusion, and corresponds well energetically to literature reports of P vacancies. These results clarify cross diffusion and defect emission in AlInP/GaAs, and demonstrate that these effects can have a significant impact on the electronic structure of lattice-matched III-V heterostructures.
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68.35.Fx Diffusion; interface formation
73.20.At Surface states, band structure, electron density of states
78.60.Hk Cathodoluminescence, ionoluminescence
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Atomic layer deposited HfO2/HfSixOyNz stacked gate dielectrics for metal-oxide-semiconductor structures

Seokhoon Kim, Sanghyun Woo, Hyungchul Kim, Wooho Jeong, Taeyong Park, Honggyu Kim, Sung Bae Kim, and Hyeongtag Jeon

J. Vac. Sci. Technol. B 25, 1922 (2007); http://dx.doi.org/10.1116/1.2811707 (6 pages) | Cited 1 time

Online Publication Date: 29 November 2007

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HfSixOyNz layers were grown on Si substrates prior to HfO2 growth in order to investigate the growth of an interfacial layer between HfO2 and Si substrate and the chemical composition changes at the interfacial region. The effects of the HfSixOyNz buffer layers were also investigated. The HfSixOyNz and HfO2 films were grown by remote plasma atomic layer deposition using N2/O2 plasma and O2 plasma, respectively. The HfSixOyNz films were grown using a TDEAH precursor and N2/O2 mixed plasma. The Hf-N and N-O bonds of the HfSixOyNz layers were easily broken by annealing at 800 °C in N2 ambient because their bonds were relatively weak. The peak intensities of the Si-O-N, Hf-O-Si, and Si-O bonds at the interfacial region increased after annealing. The excess N atoms due to the breaking of the Hf-N and N-O bonds can form bonds with Si atoms in the interfacial region and cause the growth of SiOxNy or SiNx. The excess Hf and O atoms can grow HfSixOy or SiO2 due to interactions with Si atoms. The formation of the HfSixOyNz layer can suppress the growth of Hf silicate or an interfacial layer. The formation of a thick HfSixOyNz layer enhanced the thermal stability of the interfacial layer of the HfO2 film as it had a larger amount of effective fixed oxide charges than a thin HfSixOyNz layer.
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77.55.-g Dielectric thin films
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.)
52.77.Dq Plasma-based ion implantation and deposition
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Mechanisms of porous dielectric film modification induced by reducing and oxidizing ash plasmas

N. Posseme, T. Chevolleau, T. David, M. Darnon, O. Louveau, and O. Joubert

J. Vac. Sci. Technol. B 25, 1928 (2007); http://dx.doi.org/10.1116/1.2804615 (13 pages) | Cited 26 times

Online Publication Date: 4 December 2007

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This work focuses on the impact of oxidizing and reducing ash chemistries on the modifications of two porous SiOCH films with varied porosities (8% [low porosity (lp)-SiOCH] and 45% [high porosity (hp)-SiOCH]). The ash processes have been performed on SiOCH blanket wafers in either reactive ion etching (RIE) or downstream (DS) reactors. The modifications of the remaining film after plasma exposures have been investigated using different analysis techniques such as x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy (FTIR), x-ray reflectometry, mercury probe capacitance measurement (C‐V), and spectroscopic ellipsometry (SE). FTIR analyses show that the lp-SiOCH film is not significantly altered by any of the ash processes investigated (DS‐H2/He, RIE‐O2, and RIE‐NH3), except by downstream oxidizing plasmas (DS‐O2 or DS‐N2/O2) which induce some carbon depletion and moisture uptake, resulting in a slight increase of the k value. The porosity amplifies the sensitivity of the material to plasma treatments. Indeed, hp-SiOCH is fully modified (moisture uptake and carbon depletion) under oxidizing downstream plasma exposures (DS‐O2 and DS‐N2/O2), while it is partially altered with the formation of a denser and modified layer (40–60 nm thick), which is carbon depleted, hydrophilic, and composed of SiOxNyHz with RIE‐NH3 and DS‐N2/H2 plasmas and SiOxHy with RIE‐O2 plasma. In all the cases, the k value increase is mainly attributed to the moisture uptake rather than methyl group consumption. hp-SiOCH material is not altered using reducing DS chemistries (H2/He and H2/Ar). The porous SiOCH film degradation is presented and discussed with respect to chemistry, plasma parameters, and plasma mode in terms of film modification mechanism.
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77.55.-g Dielectric thin films
52.77.Bn Etching and cleaning
82.30.-b Specific chemical reactions; reaction mechanisms
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
78.66.Nk Insulators
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Graphoepitaxial cylindrical block copolymer nanodomains evaluated as bit patterned media template

Shuaigang Xiao and XiaoMin Yang

J. Vac. Sci. Technol. B 25, 1953 (2007); http://dx.doi.org/10.1116/1.2801860 (5 pages) | Cited 6 times

Online Publication Date: 6 December 2007

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To utilize self-assembled block copolymer structures to fabricate the template of bit patterned media, two basic issues of block copolymer nanodomains need to be considered: (a) size uniformity and (b) position accuracy. The manipulation of domain position was achieved here by graphoepitaxy of cylindrical block copolymer domains in a topographic trench pattern. Trench surface may be neutralized to guarantee the perpendicular orientation of cylindrical domains on the trench bottom surface and domain alignment along the trench sidewall. The size distributions of cylindrical domains on both flat surface and topographically patterned surface have been analyzed and the correlation between the size distribution and the local-range order is addressed. The distributions of the domain size and domain position-related parameters, such as the dot spacing along the axis (parallel to the trench edge) and across the axis, have been investigated as a function of the number of domain rows in the trench. Qualitatively, line edge roughness or linewidth roughness of trenches attributes to the larger variation of spacing across the axis. Finally, a surface trench without neutralization pretreatment was found to enable the graphoepitaxy of block copolymer domains with an areal density >1 Tdot/in.2.
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68.47.Mn Polymer surfaces
61.41.+e Polymers, elastomers, and plastics

Imaging layers for the directed assembly of block copolymer films: Dependence of the physical and chemical properties of patterned polymer brushes on brush molecular weight

K. O. Stuen, I. In, E. Han, J. A. Streifer, R. J. Hamers, P. F. Nealey, and P. Gopalan

J. Vac. Sci. Technol. B 25, 1958 (2007); http://dx.doi.org/10.1116/1.2799970 (5 pages) | Cited 7 times

Online Publication Date: 6 December 2007

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The directed assembly of polystyrene-block-poly(methyl methacrylate) films using chemically nanopatterned polymer brush surfaces with various molecular weights was investigated. The brushes (3–10 nm in thickness) were made from polystyrene that was end grafted to silicon wafers and patterned to have 40–60 nm period stripes consisting of unmodified polymer and polymer that was subjected to brief oxygen plasma. The best assembly of block copolymer films was achieved using brushes with molecular weights of 3 kg/mol or less. The brushes were analyzed by goniometry, infrared reflection-absorption spectroscopy, x-ray photoelectron spectroscopy, and ellipsometry. The brush thickness increased nonlinearly with molecular weight and the high molecular weight brushes reconstructed under solvent and thermal annealing. The lower molecular weight brushes form the best imaging layers due to their optimum thickness that provides uniform surface coverage and prevents reconstruction of the film surface. The thin brushes ensure contact between the block copolymer and the hydrophilic groups in the modified regions of the brush during annealing, maximizing the effective interfacial energy contrast and the driving force for perfect directed assembly.
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68.60.-p Physical properties of thin films, nonelectronic
78.66.Qn Polymers; organic compounds
78.30.Jw Organic compounds, polymers
79.60.Fr Polymers; organic compounds
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Pattern transfer using poly(styrene-block-methyl methacrylate) copolymer films and reactive ion etching

Chi-Chun Liu, Paul F. Nealey, Yuk-Hong Ting, and Amy E. Wendt

J. Vac. Sci. Technol. B 25, 1963 (2007); http://dx.doi.org/10.1116/1.2801884 (6 pages) | Cited 14 times

Online Publication Date: 6 December 2007

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Self-assembly block copolymers have drawn a lot of attention for its great potential on critical dimension (CD) control and line-edge roughness (LER) reduction, which become more and more crucial as the CD of transistors is only tens of nanometers nowadays. In this study, lamellar-forming poly(styrene-b-methyl methacrylate) copolymer which fabricates line patterns was chosen for its ability to provide higher aspect ratio and vertical sidewall profile in template stage, thus more suitable for the following etching process to substrate. A dry plasma etching process using pure oxygen and pure argon plasma as example chemical etching gas and physical etching gas, respectively, was studied. Etching selectivity and lateral etch rate, which are responsible for the final template height and CD loss, had been characterized on a capacitive reactive ion etching tool. The templates formed by the proposed process had high aspect ratios, excellent pattern fidelity, and low LER values. The PS lateral etch rate was small enough to provide a wide process window for retaining the CD of the pattern during the template forming process. Subsequent silicon etching using the PS template made by dry etching process yielded a steep and smooth sidewall profile.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Dn Self-assembly
81.65.Cf Surface cleaning, etching, patterning

Exploring the manufacturability of using block copolymers as resist materials in conjunction with advanced lithographic tools

Gordon S. W. Craig and Paul F. Nealey

J. Vac. Sci. Technol. B 25, 1969 (2007); http://dx.doi.org/10.1116/1.2801888 (7 pages) | Cited 3 times

Online Publication Date: 6 December 2007

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The authors discuss studies of the capabilities and advantages of using self-assembling block copolymers in the lithographic process. Directing the assembly of these materials on lithographically defined chemically nanopatterned surfaces offers the potential to improve the dimensional control of features at the nanoscale while retaining essential attributes of the lithographic process, such as registration, patterning of regular fabric architectures, and a high degree of pattern perfection.
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85.40.Hp Lithography, masks and pattern transfer

Submicron aligned wafer bonding via capillary forces

Michael R. Tupek and Kevin T. Turner

J. Vac. Sci. Technol. B 25, 1976 (2007); http://dx.doi.org/10.1116/1.2787866 (6 pages) | Cited 2 times

Online Publication Date: 6 December 2007

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Submicron wafer-to-wafer alignment is critical in wafer bonding for the fabrication of three-dimensional integrated circuits. In this work, the authors examine the sources of misalignment in traditional alignment methods and then examine the capabilities of an alternative alignment approach that uses capillary forces. A multiscale model was developed to investigate the potential of capillary assisted alignment. The model consists of a local model of a confined liquid droplet and a finite element model that predicts wafer-level distortions and misalignment. Using the model, the effect of pattern error and wafer nonflatness on misalignment in bonding was examined for both the traditional and capillary assisted methods. The results indicate that capillary assisted alignment has several distinct advantages over traditional methods that result primarily from the ability to align the wafers at many locations across the wafer.
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85.40.Ls Metallization, contacts, interconnects; device isolation

Creation of sub-20-nm contact using diblock copolymer on a 300 mm wafer for complementary metal oxide semiconductor applications

Wai-kin Li and Sam Yang

J. Vac. Sci. Technol. B 25, 1982 (2007); http://dx.doi.org/10.1116/1.2787732 (3 pages) | Cited 3 times

Online Publication Date: 6 December 2007

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The authors have demonstrated a method to form 20 nm contact features of uniform size over a large area by integrating a self-assembling diblock copolymer with optical lithography. The diblock copolymer contacts are formed in topographical placers which are patterned with using optical lithography. A diblock copolymer pattern can only be formed in a placer and not in the narrower trenches that connect to the placer. This concept can be applied to form local interconnects using a single mask dual damascene process, where vias are self-aligned to the line. Some design rule restrictions must be applied to certain structures to enable patterning with diblock copolymer. They also observed that diblock copolymer contact formation was strongly influenced by the shape of the placer and the size of the cylindrical contact hole could be varied by the molecular weight of the block copolymer.
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85.40.Hp Lithography, masks and pattern transfer

Nanostructures using self-assembled multilayers as molecular rulers and etch resists

C. Srinivasan, J. N. Hohman, M. E. Anderson, P. S. Weiss, and M. W. Horn

J. Vac. Sci. Technol. B 25, 1985 (2007); http://dx.doi.org/10.1116/1.2811712 (4 pages) | Cited 1 time

Online Publication Date: 6 December 2007

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Self-assembled multilayers, composed of alternating layers of α,ω-mercaptoalkanoic acids and Cu2+ ions (“molecular rulers”), are used as organic sidewall spacers and etch resists for the fabrication of registered microstructures with precisely tailored nanometer-scale spacings. The method outlined here eases the stringency of the lithographic processing for patterning second-generation features. Additionally, a new method to lift off the self-assembled multilayered films for the generation of the tailored nanogaps is demonstrated. The advantages of these techniques are discussed.
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68.65.Ac Multilayers
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.16.Dn Self-assembly

Rapid partial melt crystallization of silicon for monolithic three-dimensional integration

D. J. Witte, D. S. Pickard, F. Crnogorac, P. Pianetta, and R. F. W. Pease

J. Vac. Sci. Technol. B 25, 1989 (2007); http://dx.doi.org/10.1116/1.2798732 (4 pages) | Cited 1 time

Online Publication Date: 6 December 2007

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Controlling the crystallization process of semiconductor materials is essential for many applications, including monolithic three-dimensional integration of devices. In particular, crystallization must be done while keeping to the thermal budget of underlying device layers. Using a 532 nm laser pulse of 10 ms duration, we demonstrate partial melting of silicon, which yields crystallites several microns in size upon cooling. A ⟨100⟩ preferential orientation was observed in these crystallites, which may be a consequence of partial melting. By observing the melt evolution, we show that a partial melt can form on the millisecond time scale and does not require thermal equilibrium to exist. By reducing the laser pulse duration further, such a process could be compatible with the thermal constraints of three-dimensional integration.
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81.05.Cy Elemental semiconductors
81.20.-n Methods of materials synthesis and materials processing
64.70.D- Solid-liquid transitions
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
82.60.Hc Chemical equilibria and equilibrium constants
42.62.-b Laser applications

Surface energy induced patterning of organic and inorganic materials on heterogeneous Si surfaces

L. Tao, A. Crouch, F. Yoon, B. K. Lee, J. S. Guthi, J. Kim, J. Gao, and W. Hu

J. Vac. Sci. Technol. B 25, 1993 (2007); http://dx.doi.org/10.1116/1.2804577 (5 pages) | Cited 4 times

Online Publication Date: 6 December 2007

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A surface energy induced patterning (SEIP) method is developed to transfer resist patterns defined by lithography into various functional materials. A Si template is first chemically patterned using conventional lithography and selective attachment of trichlorosilane to achieve spatially different surface energies. Organic materials as well as inorganic films are deposited onto the chemically patterned template, followed by a thermal annealing process. The heterogeneous surface energies on the template induce material microfluidic reflow from the less to the more thermodynamically favorable areas. Using this method, patterned microstructures were achieved with SU-8, diblock copolymer, and aluminum film. In addition, the SEIP template was successfully used for atomic layer chemical vapor deposition to selectively pattern 200 nm–2 μm wide HfO2 structures.
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81.16.Nd Micro- and nanolithography
81.40.Gh Other heat and thermomechanical treatments
85.40.Hp Lithography, masks and pattern transfer
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
47.85.Np Fluidics
back to top Electron Beam Lithography

Influence of the development process on ultimate resolution electron beam lithography, using ultrathin hydrogen silsesquioxane resist layers

Anda E. Grigorescu, Marco C. van der Krogt, Cees W. Hagen, and Pieter Kruit

J. Vac. Sci. Technol. B 25, 1998 (2007); http://dx.doi.org/10.1116/1.2794316 (6 pages) | Cited 9 times

Online Publication Date: 6 December 2007

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The influence of the development process on the ultimate resolution of electron beam lithography using ultrathin HSQ layers was studied. Different developers, of different types and strengths, were used to develop lines exposed at a variety of doses. Optimum exposures could be found for lines of widths between 7 and 12 nm, at a pitch of 20 nm. Lines smaller than 5 nm could not be fabricated using any of these developers. Changing the development time had no influence on this result. Width versus dose curves are presented for all three developers and a 60 s development time. A scaling is presented to enable an easy calculation of the exposure latitude for each linewidth. Using 100 keV electron beam lithography, we achieved 6 nm isolated features in a 10 nm thick HSQ layer on a silicon substrate. We also showed that dense structures (5 nm wide at a pitch of 20 nm) could be obtained using a 1:5 developer solution of Microposit 351:H2O.
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81.16.Nd Micro- and nanolithography

Nanofabrication of high aspect ratio 24 nm x-ray zone plates for x-ray imaging applications

Yan Feng, Michael Feser, Alan Lyon, Steve Rishton, Xianghui Zeng, Sharon Chen, Simone Sassolini, and Wenbing Yun

J. Vac. Sci. Technol. B 25, 2004 (2007); http://dx.doi.org/10.1116/1.2789447 (4 pages) | Cited 22 times

Online Publication Date: 6 December 2007

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Building high-performance zone plate is a critical step for achieving nanometer resolution in advanced x-ray imaging and microscopy. Zone plates with smaller outmost zone width and higher aspect ratio are increasingly in demand, simply because the resolution and efficiency of an x-ray microscope are ultimately determined by these two features. In this paper, we will present detailed discussion of achieving high aspect ratio and high resolution x-ray zone plate through electron beam lithography, trilevel resist process and gold plating, fabrication problems, and limitations. We will also present the technique to double the aspect ratio of the zone plate and measure the results of x-ray diffraction efficiency of single and aspect ratio doubled zone plates.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
07.85.Tt X-ray microscopes
81.16.Nd Micro- and nanolithography
61.05.cp X-ray diffraction
81.15.Pq Electrodeposition, electroplating

Accurate control of remaining resist depth for nanoscale three-dimensional structures in electron-beam grayscale lithography

S.-Y. Lee and K. Anbumony

J. Vac. Sci. Technol. B 25, 2008 (2007); http://dx.doi.org/10.1116/1.2781521 (5 pages) | Cited 4 times

Online Publication Date: 6 December 2007

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In electron-beam (e-beam) grayscale lithography, a three-dimensional (3D) structure is transferred onto the resist or substrate. In either case, accurate control of the remaining resist depth and, accordingly, profile is critical for successful fabrication of the structure. Usually, the remaining resist depth control is guided by the empirically derived dose (or exposure)-depth relationship using a two-dimensional model. However, such an approach may require multiple calibrations and also lead to significant dimensional errors for nanoscale structures due to the depth-dependent variation of exposure and the nonlinearity between exposure and developing rate. In this study, a resist developing model is incorporated into e-beam dose control schemes in order to take the exposure variation and nonlinearity into account. Through computer simulation, it has been demonstrated that significant improvement in dimensional accuracy may be achieved by including the 3D resist developing model in the e-beam dose control for fabricating nanoscale 3D structures.
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81.16.Nd Micro- and nanolithography

Optimal temperature for development of poly(methylmethacrylate)

Bryan Cord, Jodie Lutkenhaus, and Karl K. Berggren

J. Vac. Sci. Technol. B 25, 2013 (2007); http://dx.doi.org/10.1116/1.2799978 (4 pages) | Cited 18 times

Online Publication Date: 6 December 2007

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The authors have investigated a range of poly(methylmethacrylate) (PMMA) development temperatures as low as −70 °C and characterized their effect on the resolution of PMMA as an electron resist. The results show that cooling, in addition to reducing the sensitivity of the commonly used positive-tone mode of PMMA, also increases the sensitivity of its less commonly used negative-tone mode. They have shown that the resolution-enhancing properties of cold development peak at approximately −15 °C as a result of these competing sensitivity changes. At lower temperatures, the high doses required to expose the resist produce significant cross-linking of the polymer, altering its solubility properties and sharply degrading the contrast. If the correct development temperature is used, however, sub-10 nm features are readily achievable in PMMA-based scanning electron-beam lithography.
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85.40.Hp Lithography, masks and pattern transfer

Imaging with surface sensitive backscattered electrons

T. Luo and A. Khursheed

J. Vac. Sci. Technol. B 25, 2017 (2007); http://dx.doi.org/10.1116/1.2781523 (3 pages) | Cited 2 times

Online Publication Date: 6 December 2007

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This article presents simulation and experimental results of an angle-filtered backscattered electron (BSE) technique in the scanning electron microscope (SEM). Simulation results predict that for an incident primary beam energy of 5 keV, BSEs with low emission angles (90°–91°) contain scattering information coming mostly from within 2 nm below the specimen surface. A buried layer track is tested with a 10 keV primary beam inside a normal SEM. The BSE image at low emission angles (between 90° and 91°) provides only surface contamination details while the buried layer is not present. This result indicates that the low emission angle BSEs can be used for surface sensitive imaging.
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81.65.-b Surface treatments
79.20.Kz Other electron-impact emission phenomena

Novel magnetic microstigmator for electron beam astigmatism correction in the electron beam microcolumn system

Rong Rong, Ho Seob Kim, Seong Soon Park, Nam Woo Hwang, Kyoung Wan Park, Sang Won Jin, and Chong H. Ahn

J. Vac. Sci. Technol. B 25, 2020 (2007); http://dx.doi.org/10.1116/1.2804427 (5 pages)

Online Publication Date: 6 December 2007

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A novel magnetic microstigmator was developed for the astigmatism correction in the electron beam microcolumn system. The magnetic microstigmator consists of eight magnetic poles coupled with micromachined solenoid-type coils that are divided into four pairs. The proposed magnetic microstigmator was fabricated using microelectromechamical system technology and was assembled in an electron beam microcolumn for testing. The preliminary experimental results show that the developed magnetic microstigmator can effectively correct the astigmatism of the electron beam in the electron beam microcolumn with a driving current of 300 mA and low power.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
41.85.Gy Chromatic and geometrical aberrations
85.70.-w Magnetic devices

Using high-contrast salty development of hydrogen silsesquioxane for sub-10‐nm half-pitch lithography

Joel K. W. Yang and Karl K. Berggren

J. Vac. Sci. Technol. B 25, 2025 (2007); http://dx.doi.org/10.1116/1.2801881 (5 pages) | Cited 48 times

Online Publication Date: 6 December 2007

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When used as a negative-tone electron-beam resist, hydrogen silsesquioxane (HSQ) is typically developed in an aqueous alkali solution such as tetramethyl ammonium hydroxide. This development process results in low contrast. In this work, the authors instead used a mixture of salt and alkali to significantly increase the contrast of HSQ. Contrast values as high as 10 in a 115‐nm-thick resist were achieved by developing HSQ in an aqueous mixture of NaOH alkali and NaCl salt. Remarkably, this salty developer resulted in contrast enhancement without significant decrease in resist sensitivity. The improved contrast of HSQ enabled the fabrication of 7 nm half-pitch nested-“L” structures in a 35‐nm-thick resist with minimal loss in thickness using a 30 kV electron-beam acceleration voltage. They noticed a strong dependence of contrast enhancement on the concentration and type of cations and anions in the aqueous developer solution.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

Sub-30‐nm hybrid lithography (electron beam∕deep ultraviolet) and etch process for fully depleted metal oxide semiconductor transistors

S. Pauliac-Vaujour, P. Brianceau, S. Landis, J. Chiaroni, and O. Faynot

J. Vac. Sci. Technol. B 25, 2030 (2007); http://dx.doi.org/10.1116/1.2798731 (4 pages) | Cited 4 times

Online Publication Date: 6 December 2007

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Fully depleted silicon on insulator (FDSOI) devices with high-k dielectrics and metal gate are promising candidates for sub-45‐nm complementary metal oxide semiconductor technologies. At present, the gate length reduction becomes more and more difficult due to resist thickness diminution induced by critical dimension downscaling. In order to suppress resist thickness limitations, we have added a carbon layer with a SiO2 capping onto the conventional dielectric hard mask (SiO2 or Si3N4). In this study, FDSOI transistors with hafnium dielectric (HfO2), titanium nitride (TiN) metal gate were patterned by combining high resolution hybrid lithography (electron beam∕deep ultraviolet) and amorphous carbon hard mask. Full three-dimensional (3D) characterizations were carried out by using 3D atomic force microscope (CD-AFM from Veeco) to determine the best process window. Finally, after carbon hard mask trimming, sub-30‐nm gate length transistors were achieved and successfully electrically tested.
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85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices

Enhanced stitching for the fabrication of photonic structures by electron beam lithography

M. Gnan, D. S. Macintyre, M. Sorel, R. M. De La Rue, and S. Thoms

J. Vac. Sci. Technol. B 25, 2034 (2007); http://dx.doi.org/10.1116/1.2800325 (4 pages) | Cited 3 times

Online Publication Date: 6 December 2007

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Large-area electron beam lithography tools pattern substrates as a series of writing fields that are stitched together. Pattern defects, termed stitching errors, can arise at field boundaries and these can have detrimental effects on device performance. These problems are exaggerated by substrate tilt. In this article, the authors demonstrate the application of a substrate tilt correction procedure to minimize stitching errors in the fabrication of photonic structures by electron beam lithography. The authors show that the magnitude of stitching errors is dependent on the position within the field boundary and is influenced by substrate tilt. Application of tilt correction procedures is shown to reduce stitching errors and give rise to a corresponding reduction in propagation losses in photonic wire waveguides. The authors show that the results of measured propagation losses arising from stitching errors are in good agreement with numerical results.
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42.82.Et Waveguides, couplers, and arrays
42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer

Evaluation of hybrid lithography and mix and match scenarios for electron beam direct write applications

C. Hohle, C. Arndt, K.-H. Choi, J. Kretz, T. Lutz, F. Thrum, and K. Keil

J. Vac. Sci. Technol. B 25, 2038 (2007); http://dx.doi.org/10.1116/1.2779043 (3 pages) | Cited 2 times

Online Publication Date: 6 December 2007

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An overview about process window evaluation and characteristic features of photoresists for e-beam/optical hybrid lithography as well as mix and match applications and implementation into new integration concepts is given. For that, several commercially available deep ultraviolet (DUV) (248 nm), ArF (193 nm), and e-beam resist samples from various suppliers were exposed at Qimonda’s dynamic random access memory pilot line environment using both e-beam and optical exposure. Due to the diverse, sometimes contradictory requirements and properties of the different material platforms (e.g., resolution, sensitivity, vacuum stability, etch resistance, etc.), a unique material for true hybrid lithography is difficult to find. At least the tested DUV resist is limited applicable for e-beam exposures putting up with low e-beam sensitivity.
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85.40.Hp Lithography, masks and pattern transfer

Patterning issues in superconducting nanowire single photon detector fabrication

C. Constancias, R. Espiau de Lamaëstre, O. Louveau, P. Cavalier, and J.-C. Villégier

J. Vac. Sci. Technol. B 25, 2041 (2007); http://dx.doi.org/10.1116/1.2806965 (4 pages) | Cited 2 times

Online Publication Date: 6 December 2007

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Superconducting single photon detectors (SSPD) made of superconducting NbN ultrathin film were successfully synthesized down to 70 nm nanowire width. Their fabrication process is detailed, with emphasis on electron beam lithography. A high-resolution electron beam lithography tool was operated at 100 kV in combination with a negative tone resist NEB22A2, in order to achieve the required resolution and fabrication yield. The sensitivity of ultrathin NbN films to various resist stripping treatments is evidenced by electrical transport measurements, and circumvented by deposition of adequate protecting layers. SSPDs made of a 4.4 nm thick NbN film were electrically characterized, and show a critical current density above 3×106 A cm−2 and a critical temperature above 11 K.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
74.78.Na Mesoscopic and nanoscale systems
81.16.Rf Micro- and nanoscale pattern formation
74.25.F- Transport properties
74.25.Sv Critical currents
74.10.+v Occurrence, potential candidates

Influence of temperature on HSQ electron-beam lithography

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

J. Vac. Sci. Technol. B 25, 2045 (2007); http://dx.doi.org/10.1116/1.2794324 (4 pages) | Cited 21 times

Online Publication Date: 6 December 2007

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The authors present a study of the influence of temperature on hydrogen silsesquioxane (HSQ) e-beam lithography during drying, developing, and postdevelopment baking. In accordance with the observation that tempering at relatively low temperatures can already lead to noticeable cross-linking, comparable to the effect of e-beam exposure, the authors find that decreasing the prebake temperature below 90 °C and drying the HSQ resist at room temperature in vacuum yields better resolution compared with resist that was dried in a furnace or on a hotplate at 90 °C or above. Developing the exposed resist not at room temperature (23 °C) but at 60 °C results in significant contrast enhancement. Further solidification of the developed resist is obtained by baking the material above 300 °C. Correlations between these findings and IR data are presented.
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85.40.Hp Lithography, masks and pattern transfer

Extracting the Boersch effect contribution from experimental energy spread measurements for Schottky electron emitters

M. S. Bronsgeest, J. E. Barth, G. A. Schwind, L. W. Swanson, and P. Kruit

J. Vac. Sci. Technol. B 25, 2049 (2007); http://dx.doi.org/10.1116/1.2794067 (6 pages) | Cited 6 times

Online Publication Date: 6 December 2007

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Energy spread is critical to the performance of probe forming systems working at high resolution. The energy spread in the probe is the convolution of the intrinsic spread upon emission and the broadening due to Coulomb interactions in the beam. In order to optimize the design, the two need to be distinguished. The Boersch effect in a Schottky electron gun is difficult to calculate because of the low initial velocity at emission and the strong potential gradient. This article presents a method to extract it from experimental data. Extracting the Boersch effect by deconvoluting the experimental spectrum with the intrinsic distribution is difficult because of noise in the data. Instead, the Boersch effect was determined by fitting convolutions to the measured spectra. A bell shaped function with two free parameters was selected to describe the Boersch contribution. By fitting the convolution of the intrinsic energy distribution and this bell with its free parameters as fitting parameters, the Boersch contribution of experimental spectra could be adequately determined.
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07.77.Ka Charged-particle beam sources and detectors
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Multilayer phase-only diffraction gratings: Fabrication and application to extreme ultraviolet optics

Farhad Salmassi, Eric M. Gullikson, Erik H. Anderson, and Patrick P. Naulleau

J. Vac. Sci. Technol. B 25, 2055 (2007); http://dx.doi.org/10.1116/1.2798725 (4 pages)

Online Publication Date: 6 December 2007

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The use of phase-only diffractive devices has long played an important role in advanced optical systems in varying fields. Such devices include gratings, diffractive and holographic optical elements, diffractive lenses, and phase-shift masks for advanced lithography. Extending such devices to the increasingly important regime of extreme ultraviolet (EUV) wavelengths, however, is not trivial. Here, the authors present an effective fabrication and etch process enabling high-resolution patterning of Mo/Si multilayers for use in EUV phase devices, providing another method for fabrication of high numerical aperture diffractive devices or high-resolution EUV phase shift masks.
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42.79.Dj Gratings
42.79.Bh Lenses, prisms and mirrors
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.40.Eq Holographic optical elements; holographic gratings

Process characterization of inductively coupled plasma etched silicon nanopillars by micro-Raman

G. M. Laws, A. Handugan, T. Eschrich, P. Boland, C. Sinclair, S. Myhajlenko, and C. D. Poweleit

J. Vac. Sci. Technol. B 25, 2059 (2007); http://dx.doi.org/10.1116/1.2781514 (5 pages) | Cited 3 times

Online Publication Date: 6 December 2007

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The authors report on the top-down fabrication of silicon nanopillar arrays using electron beam lithography and enhanced plasma etch protocols for producing smoothed sidewalls. They have used cold development (2–4 °C) to minimize line edge roughness in the patterned features. Standard reactive ion etch and inductively coupled plasma etch techniques have been used to fabricate nanopillar arrays, 60–100 nm in diameter, with aspect ratios up to 20:1. They describe the use of a cyclic plasma oxidation and etch procedure to reduce sidewall roughness of silicon etched by the Bosch® process. The optimization of the smoothing process is demonstrated to produce near roughness free sidewalls. Raman spectroscopy has been used to characterize both the attributes of the nanopillars (including black silicon) and the effects of plasma processing. Preliminary results indicate that the Raman technique can distinguish the quality of the nanopillars (from processing perspective) based on intensity, spectral shifts, and changes in the linewidth. These changes are attributed to an increase in local heating of smoothed nanopillars caused by a modulation in optical absorption.
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81.05.Cy Elemental semiconductors
68.47.Fg Semiconductor surfaces
81.16.Nd Micro- and nanolithography
81.65.Mq Oxidation
81.65.Cf Surface cleaning, etching, patterning
78.30.Am Elemental semiconductors and insulators

Improving electron beam resist sensitivity by preexposure to deep ultraviolet radiation

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

J. Vac. Sci. Technol. B 25, 2064 (2007); http://dx.doi.org/10.1116/1.2794070 (4 pages)

Online Publication Date: 6 December 2007

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Electron beam lithography, when combined with optical lithography, is a promising approach to obtain good throughput. A bottleneck for this is resist sensitivity and the concomitant shot-noise limit for resolution. It is possible to obtain increased sensitivity without reducing resolution by preexposing electron beam resist to deep ultraviolet radiation before electron beam patterning. Results show that up to a 30% reduction in required dosage is obtained with this method; the associated trade off in dissolution of unexposed areas and critical dimension sensitivity is minimal. Resolution is also maintained and sub-50 nm lines with good aspect ratio have been demonstrated.
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85.40.Hp Lithography, masks and pattern transfer

Fabrication of spiral-phase diffractive elements using scanning-electron-beam lithography

Hsin-Yu Tsai, Henry I. Smith, and Rajesh Menon

J. Vac. Sci. Technol. B 25, 2068 (2007); http://dx.doi.org/10.1116/1.2806961 (4 pages) | Cited 3 times

Online Publication Date: 6 December 2007

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The authors report on the fabrication of binary spiral zone plates and investigate an approach using gray scale scanning-electron-beam lithography to fabricate spiral-phase plates. The optical performance of the spiral zone plates is characterized via photoresist exposures and compared to theory.
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42.79.Ci Filters, zone plates, and polarizers
42.40.Eq Holographic optical elements; holographic gratings
42.82.Cr Fabrication techniques; lithography, pattern transfer

Real-time spatial-phase locking for vector-scan electron beam lithography

Yugu Yang and J. T. Hastings

J. Vac. Sci. Technol. B 25, 2072 (2007); http://dx.doi.org/10.1116/1.2781518 (5 pages) | Cited 2 times

Online Publication Date: 6 December 2007

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Spatial-phase locked electron beam lithography (SPLEBL) provides feedback control of electron beam position by monitoring the signal from a fiducial grid on the substrate. Continuous, or “real-time,” spatial-phase locking has been investigated for raster-scan Gaussian beam and for shaped-beam systems. Discontinuous feedback, or “look-then-write,” techniques have been implemented for vector-scan systems. However, it would be advantageous to provide real-time spatial-phase locking for vector-scan systems because of their wide adoption for research, prototyping, and specialty device production. Here, the authors present a phase locking algorithm, performance simulations, and initial experimental results for real-time, vector-scan SPLEBL. The authors demonstrate that real-time, vector-scan SPLEBL can provide subnanometer precision phase locking for different feature filling strategies, exposure parameters, and pattern geometries using reasonable data lengths and practical grid signal-to-noise ratios.
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84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors

Metal-semiconductor-metal electron detectors

Rafael Aldana and R. Fabian Pease

J. Vac. Sci. Technol. B 25, 2077 (2007); http://dx.doi.org/10.1116/1.2798745 (4 pages) | Cited 1 time

Online Publication Date: 6 December 2007

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Metal-semiconductor-metal (MSM) junctions are a standard photon detector for high-speed applications due to fast response time (subpicosecond) and long device lifetime, high gain (QE>100%), small device area, and reduced capacitance per area. Here, the authors characterize how such devices perform as electron detectors, performing preliminary gain and frequency response experiments on MSM illuminated by an electron beam. Experiments were performed on both a Hitachi scanning electron microscope SEM 2500, and in a custom-made vacuum system used as a testbed for analog to digital conversion. The experiments demonstrated a gain of 300× at 5 kV acceleration voltage and frequency response up to 0.85 GHz, which complied with the specifications required by the analog to digital converter. Using other semiconductor materials (GaAs) as well as e-beam lithography to define smaller fingers will lead to faster response times.
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29.40.Wk Solid-state detectors

Nanometer-scale gaps in hydrogen silsesquioxane resist for T-gate fabrication

Niu Jin, Sookyung Choi, Liang Wang, Guang Chen, DongHyun Kim, Vipan Kumar, and Ilesanmi Adesida

J. Vac. Sci. Technol. B 25, 2081 (2007); http://dx.doi.org/10.1116/1.2798734 (4 pages)

Online Publication Date: 6 December 2007

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The authors present a novel T-gate fabrication process which takes advantage of the unique high-resolution property of the low-k dielectric material, hydrogen silsesquioxane (HSQ), as a negative tone electron beam resist. By optimizing layout design and process parameters, the authors demonstrate ∼ 30 nm gap between two HSQ rectangular geometries, which is then used to define the T-gate footprint and support the T gate. An InGaAs/InAlAs/InP high electron mobility transistor with 80 nm gate length was fabricated using this HSQ-based resist technique. Excellent dc and rf performances are presented.
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85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices

Effects of developer temperature on electron-beam-exposed hydrogen silsesquioxane resist for ultradense silicon nanowire fabrication

Sookyung Choi, Niu Jin, Vipan Kumar, Ilesanmi Adesida, and Mark Shannon

J. Vac. Sci. Technol. B 25, 2085 (2007); http://dx.doi.org/10.1116/1.2794315 (4 pages) | Cited 11 times

Online Publication Date: 6 December 2007

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The effects of developer temperature on hydrogen silsesquioxane (HSQ) resist for the fabrication of ultradense silicon nanowires are reported. At higher developer temperatures, the contrast of HSQ significantly increased and sharply defined gratings were obtained. In addition, higher developer temperature provided larger processing windows for various grating periodicities. Pattern transfer with HSQ masks using both dry and wet etching processes to fabricate silicon nanowires on silicon-on-insulator substrates is demonstrated. 27-nm-period silicon nanowire arrays obtained using the high temperature development along with the two etching processes are presented and discussed.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.Bc Nanocrystalline materials
81.65.Cf Surface cleaning, etching, patterning
back to top EUV Lithography

Extreme ultraviolet lithography: From research to manufacturing

Bruno La Fontaine, Yunfei Deng, Ryoung-han Kim, Harry J. Levinson, Uzodinma Okoroanyanwu, Richard Sandberg, Tom Wallow, and Obert Wood

J. Vac. Sci. Technol. B 25, 2089 (2007); http://dx.doi.org/10.1116/1.2794061 (5 pages) | Cited 6 times

Online Publication Date: 7 December 2007

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The authors explore the critical issues remaining for the introduction of extreme ultraviolet lithography (EUVL) in semiconductor manufacturing. Among all technical issues, source power appears to be the most significant challenge that the technology is facing at this time. The lack of sufficiently high-power sources integrated in the first generation of full-field commercial scanners has profound implications on the remaining issues, and therefore on the risk associated with the insertion of EUVL technology. At the core of the problem is the cost of ownership of EUVL, which depends most heavily on source power. Moreover, the lifetime of the scanner mirrors and of the masks can only be tested properly with high-power sources on these first scanners. Without the ability to perform these tests, the technology might suffer unrecoverable delays. Fortunately, there has been good progress in the development of laser-produced plasma sources, which appear to be the most capable candidates for high-power scalability at this time. Furthermore, a booming new technology, fiber lasers, provides prospects of highly efficient and cost-effective EUV sources for high-volume manufacturing. Finally, significant progress has been made in the development of EUV resists to support the 32 nm half-pitch node.
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85.40.Hp Lithography, masks and pattern transfer

Nanoscale patterning in high resolution HSQ photoresist by interferometric lithography with tabletop extreme ultraviolet lasers

P. W. Wachulak, M. G. Capeluto, M. C. Marconi, D. Patel, C. S. Menoni, and J. J. Rocca

J. Vac. Sci. Technol. B 25, 2094 (2007); http://dx.doi.org/10.1116/1.2801870 (4 pages) | Cited 5 times

Online Publication Date: 7 December 2007

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Arrays of nanodots and nanoholes were patterned with a highly coherent tabletop 46.9 nm laser on high resolution hydrogen silsesquioxane photoresist using multiple exposure interferometric lithography. The authors observed for λ = 46.9 nm radiation a penetration depth in excess of 150 nm. This laser-based extreme ultraviolet interferometric setup allows printing of 0.5×0.5 mm2 areas with different nanoscale patterns using a compact tabletop system and exposure times of tens of seconds.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Growth and printability of multilayer phase defects on extreme ultraviolet mask blanks

Ted Liang, Erdem Ultanir, Guojing Zhang, Seh-Jin Park, Erik Anderson, Eric Gullikson, Patrick Naulleau, Farhad Salmassi, Paul Mirkarimi, Eberhard Spiller, and Sherry Baker

J. Vac. Sci. Technol. B 25, 2098 (2007); http://dx.doi.org/10.1116/1.2779044 (6 pages) | Cited 9 times

Online Publication Date: 7 December 2007

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The ability to fabricate defect-free reflective Mo–Si multilayer (ML) blanks is a well-recognized challenge in enabling extreme ultraviolet (EUV) lithography for semiconductor manufacturing. Both the specification and reduction of defects necessitate the understanding of their printability and how they are generated and grow during ML deposition. A ML phase defect can be depicted by its topographical profile on the surface as either a bump or pit, which is then characterized by height or depth and width. These phase defects are complex in nature and their impact to resist printing. The authors developed an effective way to study phase defects with programmed defect mask (PDM) as “model” test vehicle. The defects are produced with tuned ML deposition process and placed in varying proximity to absorber patterns on the mask. This article describes the recent study of ML phase defect printability from exposures of a ML PDM on the EUV microexposure tool with annular, monopole, and dipole illuminations.
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85.40.Hp Lithography, masks and pattern transfer

Evaluation of surface roughness of Zerodur® substrates machined by Ar+ ion beam with energy of 3–10 keV

Yuichi Kurashima, Ryou Uozumi, Iwao Miyamoto, Manabu Ando, and Atsushi Numata

J. Vac. Sci. Technol. B 25, 2104 (2007); http://dx.doi.org/10.1116/1.2800333 (6 pages) | Cited 5 times

Online Publication Date: 7 December 2007

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Ion beam figuring is suitable for the final correction of the surface figure error of aspherical substrates in an extreme ultraviolet lithography apparatus. In ion beam processing, however, the surfaces are considered to become rougher. This paper reports the investigation of the surface roughness of Zerodur® machined with an Ar+ ion beam having an energy of 3–10 keV. For an Ar+ ion beam with energies in the range of 3–10 keV, the mid-spatial frequency roughness of the surfaces machined to a depth of less than 50 nm was comparable to the surface roughness of an unprocessed one. The high-spatial frequency roughness of the unprocessed surface was 0.26 nm rms; whereas the high-spatial frequency roughness of the surface machined with energies of 3, 5, 7, and 10 keV was 0.46, 0.54, 0.63, and 0.65 nm rms, respectively. The HSFR of the machined surface increases with an increase in the energy of the ion beam.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
68.35.B- Structure of clean surfaces (and surface reconstruction)

Figuring and smoothing capabilities of elastic emission machining for low-thermal-expansion glass optics

M. Kanaoka, C. Liu, K. Nomura, M. Ando, H. Takino, Y. Fukuda, H. Mimura, K. Yamauchi, and Y. Mori

J. Vac. Sci. Technol. B 25, 2110 (2007); http://dx.doi.org/10.1116/1.2789440 (4 pages) | Cited 2 times

Online Publication Date: 7 December 2007

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The use of elastic emission machining (EEM) for fabricating optics from low-thermal-expansion glass for extreme ultraviolet (EUV) lithography is examined. EUV optics require figure accuracy and surface roughness of 0.1 nm root mean square (rms) or better. EEM using a rotating-sphere head is demonstrated to achieve this level of surface smoothness after a certain depth of removal dependent on the material being processed. In tests of continuous machining for 12 h, no increase in surface roughness is observed, demonstrating the high temporal stability of this noncontact processing method. EEM using a rotating-sphere head is thus confirmed to have sufficient figuring and smoothing capability for the fabrication of EUV optics.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.86.+b Optical workshop techniques
42.70.Ce Glasses, quartz
85.40.Hp Lithography, masks and pattern transfer

Estimation of diffusion lengths of acid and quencher in chemically amplified resist on the basis of extreme ultraviolet exposure results

Yuusuke Tanaka, Yukiko Kikuchi, DooHoon Goo, Hiroaki Oizumi, and Iwao Nishiyama

J. Vac. Sci. Technol. B 25, 2114 (2007); http://dx.doi.org/10.1116/1.2787867 (4 pages) | Cited 1 time

Online Publication Date: 7 December 2007

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Line- and space-type patterns with a half pitch (hp) of 32–65 nm were printed with the extreme ultraviolet microexposure tool at the Lawrence Berkeley National Laboratory using the positive-tone chemically amplified resist MET-1K, and the diffusion lengths of the acid and quencher in the resist were estimated by fitting the calculated shapes of resist patterns to the experimental results. Simulations of the resist process employed an acid/quencher mutual-diffusion model. It was found that not only acid diffusion but also quencher diffusion had a considerable effect on the fidelity of hp 32–45 nm patterns. When the diffusion lengths were assumed to be 40 nm for the acid and 30 nm for the quencher, the calculated shapes of resist patterns agreed well with the experimental results for both line- and space-type patterns. If quencher diffusion were not considered, the acid diffusion length would be underestimated, which would make it difficult to explain the shapes of various types of resist patterns using the same acid diffusion length. In order to fabricate various types of hp 32 nm patterns, the diffusion lengths of both the acid and the quencher should be less than 10 nm.
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85.40.Hp Lithography, masks and pattern transfer

In situ x-ray absorption near-edge structure analysis for extreme ultraviolet lithography projection optics contamination

Masahito Niibe, Yukinobu Kakutani, Keigo Koida, Shuichi Matsunari, Takashi Aoki, Shigeru Terashima, Hiromitsu Takase, Katsuhiko Murakami, and Yasuaki Fukuda

J. Vac. Sci. Technol. B 25, 2118 (2007); http://dx.doi.org/10.1116/1.2779047 (5 pages) | Cited 7 times

Online Publication Date: 7 December 2007

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A contamination evaluation system for extreme ultraviolet (EUV) lithography projection optics was developed in the NewSUBARU SR facility, in which in situ surface analysis and elemental concentration mapping were carried out with the use of the x-ray absorption near-edge structure (XANES) method. For concentration mapping, the linearity between the x-ray absorption intensity and contamination thickness was confirmed by examining standard samples. The problem of quantitativity, which was caused by the antagonistic reaction of carbon deposition and surface oxidation on the mirror surface, was successfully solved by taking the ratio of intensities of the upper and lower sides of the absorption edge. Very useful information for protecting the surface of EUV lithography optics was obtained when the in situ XANES analysis was applied to the experiment of EUV irradiation with the introduction of ethanol gas to the vacuum atmosphere.
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78.70.Dm X-ray absorption spectra
42.70.-a Optical materials

Bit-array patterns with density over 1 Tbit/in.2 fabricated by extreme ultraviolet interference lithography

Harun H. Solak and Yasin Ekinci

J. Vac. Sci. Technol. B 25, 2123 (2007); http://dx.doi.org/10.1116/1.2799974 (4 pages) | Cited 8 times

Online Publication Date: 7 December 2007

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The use of patterned magnetic media in future data storage devices requires the fabrication of two-dimensional periodic patterns with resolution well below 35 nm in terms of the pattern period. The authors have used extreme ultraviolet interference lithography based on transmission diffraction gratings to demonstrate arrays of structures in negative resists calixarene and hydrogen silsesquioxane. The produced patterns have density exceeding 1 Tbit/in.2. Analysis of structure size and position on one of the patterns indicates variations of subnanometer magnitude.
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85.40.Hp Lithography, masks and pattern transfer

Extreme ultraviolet lithography at IMEC: Shadowing compensation and flare mitigation strategy

G. F. Lorusso, A. M. Goethals, R. Jonckheere, J. Hermans, K. Ronse, A. M. Myers, I. Kim, A. Niroomand, F. Iwamoto, and D. Ritter

J. Vac. Sci. Technol. B 25, 2127 (2007); http://dx.doi.org/10.1116/1.2781516 (5 pages) | Cited 18 times

Online Publication Date: 7 December 2007

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The extreme ultraviolet lithography (EUVL) program at IMEC is aimed to tackle many unsolved critical issues of EUV lithography as the technology moves towards production, by focusing specifically on tool, resist, and mask projects. Here, the authors describe the structure of the IMEC EUVL program and the status of the EUV alpha demo tool. In particular, they discuss their proposed strategies for flare mitigation and shadowing effect correction. They demonstrate how it is possible to implement an effective rule-based flare mitigation strategy. In addition, they propose a relatively simple methodology to fully compensate for shadowing pattern placement error and critical dimension bias.
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85.40.Hp Lithography, masks and pattern transfer

Advanced resist testing using the SEMATECH Berkeley extreme ultraviolet microfield exposure tool

Patrick P. Naulleau, Christopher N. Anderson, Kim Dean, Paul Denham, Kenneth A. Goldberg, Brian Hoef, Dimitra Niakoula, Bruno La Fontaine, and Tom Wallow

J. Vac. Sci. Technol. B 25, 2132 (2007); http://dx.doi.org/10.1116/1.2781522 (4 pages)

Online Publication Date: 7 December 2007

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Recent upgrades made to the SEMATECH Berkeley microfield exposure tool are summarized and some of the latest resist characterization results are presented. Tool illumination uniformity covering the full 200×600 μm2 wafer-side field of view is demonstrated and intrawafer focus control of 1.8 nm is shown. Printing results demonstrate chemically amplified resist resolution of 28 nm dense and 22.7 nm semi-isolated. Moreover, contact printing results show that shot noise is not a dominant issue in current 35 nm contact printing performance.
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85.40.Hp Lithography, masks and pattern transfer

Effects of photoacid generator incorporation into the polymer main chain on 193 nm chemically amplified resist behavior and lithographic performance

Cheng-Tsung Lee, Clifford L. Henderson, Mingxing Wang, Kenneth E. Gonsalves, and Wang Yueh

J. Vac. Sci. Technol. B 25, 2136 (2007); http://dx.doi.org/10.1116/1.2801868 (4 pages) | Cited 5 times

Online Publication Date: 7 December 2007

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The need for chemically amplified resists (CARs) that can resolve sub-65‐nm node features with sufficient linewidth roughness (LWR) control and sensitivity to meet the requirements outlined in the International Technology Roadmap for Semiconductors has placed a significant and daunting challenge for the design of resist materials that can achieve these goals. In this article, the ability to improve the performance of CARs designed for 193 nm lithography via the direct bonding of a photoacid generator (PAG) anion into the resist polymer main chain has been investigated. The bound-PAG anion resist is shown to achieve higher sensitivity and resolution with smaller LWR than their blended-PAG resist analog. Binding of the PAG anion provides reduced photoacid diffusivity, higher maximum PAG loadings, and more homogeneous PAG distributions that help achieve these three critical resist requirements.
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85.40.Hp Lithography, masks and pattern transfer

Influence of solubility switching mechanism on resist performance in molecular glass resists

Richard A. Lawson, Cheng-Tsung Lee, Clifford L. Henderson, Robert Whetsell, Laren Tolbert, and Wang Yueh

J. Vac. Sci. Technol. B 25, 2140 (2007); http://dx.doi.org/10.1116/1.2801885 (5 pages) | Cited 9 times

Online Publication Date: 7 December 2007

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Five different molecular glass chemically amplified photoresists which utilized different solubility switching mechanisms and chemistries, based on a tris(4-hydroxyphenyl)ethane (THPE) core, were synthesized and their performance compared. Three different positive tone systems were designed based on acid catalyzed deprotection of a phenolic hydroxyl group protected with one of the following groups: tert-butoxycarbonyl (tBoc), tetrahydropyranyl, or ethoxyethyl. Two negative tone systems were designed; one using cationic epoxide polymerization of pendant epoxides and one using condensation of the unprotected THPE with a multifunctional cross-linking additive. The tBoc system and negative tone systems showed good performance under deep UV and large field e-beam patterning, but the epoxide system showed far superior performance for high resolution electron beam patterning. It was able to produce 50 nm 1:1 line/space patterns and 30 nm lines on 1:3 line/space patterns with high sensitivity, good contrast, and a very low line edge roughness (3σ) of 2.3 nm using 100 keV electron beam patterning.
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85.40.Hp Lithography, masks and pattern transfer

Progress in extreme ultraviolet interferometric and holographic lithography

A. Isoyan, Y.-C. Cheng, F. Jiang, J. Wallace, F. Cerrina, and S. Bollepalli

J. Vac. Sci. Technol. B 25, 2145 (2007); http://dx.doi.org/10.1116/1.2794069 (6 pages) | Cited 6 times

Online Publication Date: 7 December 2007

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The Center for Nanotechnology has developed an advanced beamline dedicated to nanopatterning using the radiation from a new undulator on the Aladdin storage ring at the Synchrotron Radiation Center of the University of Wisconsin-Madison. Computer generated holograms and transmission interferometric gratings were fabricated and tested on the new extreme ultraviolet (EUV) exposure system. The authors have developed an accurate model, based on Fresnel-Kirchhoff integral diffraction theory, to analyze performance of real EUV interferometric and holographic lithography systems.
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42.40.Jv Computer-generated holograms
42.40.Kw Holographic interferometry; other holographic techniques
42.40.Eq Holographic optical elements; holographic gratings
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography

Dual-domain scanning illuminator for the SEMATECH Berkeley microfield exposure tool

Christopher N. Anderson, Patrick P. Naulleau, Paul Denham, Drew Kemp, and Senajith Rekawa

J. Vac. Sci. Technol. B 25, 2151 (2007); http://dx.doi.org/10.1116/1.2804610 (4 pages) | Cited 1 time

Online Publication Date: 7 December 2007

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Illumination uniformity and reproducibility in extreme ultraviolet (EUV) microfield exposure tools are critical to many aspects of the EUV lithography development task. Here, the authors present a scanning-field-averaging illuminator delivering consistent, uniform illumination to synchrotron-based microfield exposure tools. The system is integrated into the existing Fourier-synthesis custom coherence illuminator at the SEMATECH Berkeley microfield exposure tool and its effectiveness is demonstrated lithographically. Following the upgrade, the authors report a 6.5% peak-to-valley intensity variation across the full 200×600 μm2 wafer-side field of view.
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85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.72.Bj Visible and ultraviolet sources

Analysis of Coulomb and Johnsen-Rahbek electrostatic chuck performance for extreme ultraviolet lithography

M. R. Sogard, A. R. Mikkelson, M. Nataraju, K. T. Turner, and R. L. Engelstad

J. Vac. Sci. Technol. B 25, 2155 (2007); http://dx.doi.org/10.1116/1.2798724 (7 pages) | Cited 3 times

Online Publication Date: 7 December 2007

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The successful implementation of extreme ultraviolet lithography (EUVL) requires the use of an electrostatic chuck to both support and flatten the mask during scanning exposure. The EUVL Mask and Chucking Standards, SEMI P37 and P40, specify the nonflatness of the mask frontside and backside, as well as the chucking surface, to be on the order of 50 nm peak-to-valley. Thus, characterizing and predicting the capability of the electrostatic chuck to reduce mask nonflatness to meet this specification are critical issues. Details describing the performance of the Coulomb electrostatic chuck have been presented in earlier publications. In this paper, the governing equation identifying the force-gap relationship for a Johnsen-Rahbek (J-R) chuck is described and compared to the Coulomb response. Using finite element techniques, numerical models of Coulomb and J-R electrostatic chucks have been constructed and evaluated for their clamping performance. The models include the effects of reticle and chuck nonflatness, surface friction, and the finite stiffness of the chuck. Modeling predictions are presented for the two types of chucks. The simulations indicate that using a reticle and chuck (Coulomb or J-R style) that meet the SEMI standards for flatness can result in a clamped reticle flatness of less than 100 nm. However, there may be a need to increase the chuck stiffness specified in SEMI P40. These results, which provide the first comprehensive comparison of Coulomb and J-R chucks, are currently being used to establish specifications for chuck geometry and to identify the range of flatness variations that can be accommodated with electrostatic chucking.
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85.40.Hp Lithography, masks and pattern transfer
back to top Ion Beam Lithography and X-ray Lithography

Production of noble gas ion beams in a focused ion beam machine using an electron beam ion trap

Falk Ullmann, Frank Grossmann, Vladimir P. Ovsyannikov, Jacques Gierak, Eric Bourhis, Jacques Ferré, Jean Pierre Jamet, Alexandra Mougin, and Günter Zschornack

J. Vac. Sci. Technol. B 25, 2162 (2007); http://dx.doi.org/10.1116/1.2799971 (6 pages) | Cited 2 times

Online Publication Date: 7 December 2007

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The aim of this article is to report on preliminary investigations in evaluating a new kind of focused ion beam (FIB) instrument realized by coupling an advanced FIB “nanowriter” with a compact electron beam ion trap. The authors demonstrate the possibility to produce noble gas ion beams (He, Ar, Xe, and Kr) in a FIB machine using an electron beam ion trap. Preliminary results obtained using highly charged ions as projectiles are presented.
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29.25.Ni Ion sources: positive and negative
07.77.Ka Charged-particle beam sources and detectors
41.75.Ak Positive-ion beams

Fabrication of zinc nanotip arrays by ion beam sputtering

Liang-Chiun Chao, Chung-Chi Liau, Jun-Wei Lee, and Fu-Chieh Tsai

J. Vac. Sci. Technol. B 25, 2168 (2007); http://dx.doi.org/10.1116/1.2798710 (3 pages) | Cited 4 times

Online Publication Date: 7 December 2007

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Zinc nanotip arrays were fabricated on polycrystalline zinc foils using capillaritron ion beam sputtering. The geometry and structure of the nanotip are found to be dependent on the ion species, beam energy, and exposure fluence. After 12 keV argon ion beam sputtering, zinc nanotips with end radii less than 5 nm and aspect ratios larger than 20 were obtained. Cone-shaped nanostructures with an aspect ratio of 3 and tip radius of 25 nm were found after oxygen ion beam sputtering. Energy dispersive x-ray spectroscopy and scanning electron microscopy analysis indicate that the high aspect ratio nanotip formation mechanism after argon ion beam sputtering is due to differential erosion and anisotropic hardness of zinc nanocrystal, while the formation mechanism of cone-shaped nanostructures after oxygen ion beam sputtering is due mainly to the formation of ZnO on the apex, acting as an etch stop. The field emission properties of zinc nanotips are presented.
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81.16.-c Methods of micro- and nanofabrication and processing
81.65.Cf Surface cleaning, etching, patterning
61.46.Hk Nanocrystals
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.82.Bg Metals and alloys
61.80.Jh Ion radiation effects

Fabrication of three-dimensional structures of resist by proton beam writing

Yusuke Furuta, Naoyuki Uchiya, Hiroyuki Nishikawa, Junji Haga, Takahiro Sato, Masakazu Oikawa, Yasuyuki Ishii, and Tomihiro Kamiya

J. Vac. Sci. Technol. B 25, 2171 (2007); http://dx.doi.org/10.1116/1.2806974 (4 pages) | Cited 2 times

Online Publication Date: 7 December 2007

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The fabrication of three-dimensional (3D) structures was demonstrated by proton beam writing (PBW) using a MeV light-ion microbeam system at Japan Atomic Energy Agency. The fabrication of the 3D structures was performed using PBW in a thick SU-8 layer with a thickness of up to 50 μm, which is a typical negative resist. The authors exposed the negative resist on a silicon substrate to focused MeV proton beams within 1 μm in diameter, using two different beam energies to obtain two different depths in the resist aiming at fabrication of 3D structures. The two different beam energies were obtained using a 75 μm Kapton film as a beam energy degrader to generate 1.6 MeV proton beam from 3.0 MeV, or using the accelerator voltage control in order to produce beam energy of 1.2 MeV. The 3D lines and space structures with the same shape were fabricated using the two different methods. An Arc de Triomphe shape was also manufactured to demonstrate the superior and unique features of the PBW as a versatile tool for deep micromachining for 3D structures with high aspect ratio.
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61.80.Jh Ion radiation effects

Focused ion beam iodine-enhanced etching of high aspect ratio holes in InP photonic crystals

V. Callegari, P. M. Nellen, J. Kaufmann, P. Strasser, F. Robin, and U. Sennhauser

J. Vac. Sci. Technol. B 25, 2175 (2007); http://dx.doi.org/10.1116/1.2804607 (5 pages) | Cited 9 times

Online Publication Date: 7 December 2007

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The authors investigate the focused ion beam (FIB) fabrication of photonic crystal (PhC) holes in InP combining physical sputtering using 30 keV gallium ions and iodine-enhanced etching at 150 °C with a protective platinum or tungsten layer. The authors show that it is equivalent to conventional dry-etching methods such as inductively coupled plasma reactive ion etching in terms of achievable aspect ratio (>10), surface roughness (12.6 nm rms), and stoichiometry. The protective layers can be selectively removed after fabrication. This new FIB fabrication method lifts the previous constraints of funnel-shaped holes and limited aspect ratios of physical sputtering and reduces the Ga implantation and amorphous layer. Thus, rapid prototyping (5 s fabrication time per hole) of planar PhCs or planar PhC elements, such as PhC Y splitters, becomes feasible.
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81.65.Cf Surface cleaning, etching, patterning
42.70.Qs Photonic bandgap materials
68.35.B- Structure of clean surfaces (and surface reconstruction)

Deposition of carbonaceous structures using focused Au and Si ion-beam-induced chemical vapor deposition methods

Ryo Okada, Takuma Yo, Junichi Yanagisawa, and Shinji Matsui

J. Vac. Sci. Technol. B 25, 2180 (2007); http://dx.doi.org/10.1116/1.2798712 (4 pages) | Cited 2 times

Online Publication Date: 7 December 2007

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Focused ion-beam-induced chemical vapor deposition (FIB-CVD) using Au or Si ions and phenanthrene as a precursor gas was performed to obtain carbon-related materials containing no Ga elements. It was confirmed that narrow wires were deposited on a substrate by 15 keV Au and 30 keV Si FIB irradiations under the phenanthrene gas atmosphere. The shape of the deposited materials was, however, strongly affected by the FIB scanning speed, which might be subject to the supply of the phenanthrene gas molecules on the surface during the time interval between each FIB scan. The height of the deposited materials using the 15 keV Au FIB was three to eight times higher than that using the 30 keV Si FIB, although the other FIB parameters were almost the same. This might be explained by the difference in the electronic energy loss of those ions in the deposited materials. From Auger electron spectroscopy, the composition of the deposited material using the Au FIB was found to be a carbon-related material with no Ga but Au atoms inside.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.80.Jh Ion radiation effects
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
79.20.Fv Electron impact: Auger emission
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Membrane folding by helium ion implantation for three-dimensional device fabrication

William J. Arora, Sybren Sijbrandij, Lewis Stern, John Notte, Henry I. Smith, and George Barbastathis

J. Vac. Sci. Technol. B 25, 2184 (2007); http://dx.doi.org/10.1116/1.2779049 (4 pages) | Cited 9 times

Online Publication Date: 7 December 2007

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The authors demonstrate that silicon nitride membranes can be folded out of plane into three-dimensional structures by helium ion implantation. The folds have a radius of 1 μm and can be directed both up or down by varying implant energy.
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61.80.Jh Ion radiation effects
66.30.-h Diffusion in solids
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Design studies for a high brightness, energetic neutral atom source for proximity lithography

Hong-jie Guo, Barry Craver, Jackson Reynolds, and John C. Wolfe

J. Vac. Sci. Technol. B 25, 2188 (2007); http://dx.doi.org/10.1116/1.2804604 (4 pages) | Cited 2 times

Online Publication Date: 7 December 2007

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Line-edge roughness due to mask and wafer charging in ion beam proximity lithography can be simply and completely eliminated by neutralizing the ions before they reach the mask. This dramatically increases the usable depth of field and enables high quality imaging below 20 nm. Neutralization is accomplished by charge transfer scattering in a high pressure cell, a process that preserves both the energy and direction of the parent ion with remarkable accuracy. In this article, the authors discuss the design of an energetic atom source and characterize an optimized helium ion injector based on a dc-multicusp ion source. The injector provides a crossover at a fixed position in the charge transfer cell over a design energy range from 30 to 50 keV. For 100 W discharge power, the full width at half maximum diameter and normalized brightness of the crossover are 95 μm and 100 A/m2 sr V, respectively.
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85.40.Hp Lithography, masks and pattern transfer

Mechanical nanostepping for atom beam lithography

B. Craver, A. Roy, H. Nounu, and J. C. Wolfe

J. Vac. Sci. Technol. B 25, 2192 (2007); http://dx.doi.org/10.1116/1.2804605 (4 pages) | Cited 4 times

Online Publication Date: 7 December 2007

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One solution to stencil mask density limitations in particle lithography is to print dense patterns using multiple offset exposures of a lower density mask. The goal of this article is to demonstrate the ability to make high accuracy stepped exposures in proximity lithography with energetic neutral atoms where magnetic or electrostatic deflection is impossible. The authors’ approach is to clamp the mask to the wafer, setting the proximity gap with a suitable spacer, and to mechanically incline the mask/wafer stack relative to the beam. This approach is remarkably insensitive to vibration and thermal drift; nanometer scale image offsets have been obtained with ±2 nm placement accuracy for experiments lasting over 1 h. The reported error may include significant contributions from shot noise, resist roughness, and metrology errors, not related to the stepping process itself. The authors also show that the standard deviation of Gaussian image blur is 4.4±1.4 nm, about three times smaller than the secondary electron range limitation in electron beam lithography. Thus, the technology has the potential to form high density, periodic patterns with ∼ 10 nm resolution.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Fabrication of a needle array using a Si gray mask for x-ray lithography

Harutaka Mekaru, Takayuki Takano, Koichi Awazu, Masaharu Takahashi, and Ryutaro Maeda

J. Vac. Sci. Technol. B 25, 2196 (2007); http://dx.doi.org/10.1116/1.2794314 (6 pages) | Cited 4 times

Online Publication Date: 7 December 2007

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The authors fabricated a gray mask for x-ray lithography using a silicon-on-insulator wafer by employing microelectronic mechanical system fabrication technologies. Generally, when a three-dimensional (3D) resist structure is fabricated using x-ray lithography, an x-ray mask is rotated or scanned to adjust the exposure time of x ray irradiating the resist. However, the authors maintain that 3D resist structure can be made not only by manipulating the x-ray exposure time but also it could be accomplished rather more effectively by making basic changes in the very structure of x-ray masks. Here they present a procedure for making such a mask. Moreover, the use of such a mask could simplify the x-ray lithography process and make it operator friendly. The structure proposed here is known as gray mask and comprises of Si x-ray absorber on SU-8 membrane. Such a structure, unlike stencil mask structure, allows the formation of pattern with isolated features. The x-ray gray mask was evaluated on a beam line BL-4 at TERAS Synchrotron Radiation Facility at the AIST. By using the x-ray gray mask, the authors fabricated cone shaped and gimlet shaped polymethylmethacrylate (PMMA) resist structures. The base diameter and the maximum height of the cone shaped structure were 32 and 75 μm; the base width and the maximum height of the gimlet were 34 and 76 μm. They also showed that cross-sectional shape of PMMA resist structures matched quite well with the simulation results.
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85.40.Hp Lithography, masks and pattern transfer
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
back to top Maskless Lithography

Challenges in 1 Teradot/in.2 dot patterning using electron beam lithography for bit-patterned media

XiaoMin Yang, Shuaigang Xiao, Wei Wu, Yuan Xu, Keith Mountfield, Robert Rottmayer, Kim Lee, David Kuo, and Dieter Weller

J. Vac. Sci. Technol. B 25, 2202 (2007); http://dx.doi.org/10.1116/1.2798711 (8 pages) | Cited 24 times

Online Publication Date: 7 December 2007

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Electron beam lithography presents a great opportunity for bit-patterned media (BPM) applications due to its resolution capability and placement accuracy. However, there are still many challenges associated with this application including tool availability, resist capability, process development, and associated metrology needs. This paper will briefly discuss these challenges and show the results of sub-25 nm pitch (1 Tdots/in.2) patterning from both a simulation and experimental perspective. The simulation results indicate that the energy contrast between the exposed and unexposed areas goes down quickly as the pitch size gets smaller and smaller, making it more difficult for image formation of high-resolution dot patterning. The strategy to overcome this issue is to optimize the development process, which aims at increasing the resist contrast and enlarging the process window. By using this approach, the authors have successfully demonstrated a pitch resolution down to 18 nm for a positive-tone resist ZEP520 and 12 nm for a negative-tone resist silsesquioxane, corresponding to the areal density of ∼ 2.0 and ∼ 4.5 Tdots/in.2, respectively. Using the ZEP520 resist process, a Cr dot array with a pitch of 21 nm ( ∼ 1.5 Tdots/in.2) for template fabrication is demonstrated. High-quality scanning electron microscopy and atomic force microscopy images were used as primary metrology for both the dot size uniformity and the placement accuracy analysis.
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85.40.Hp Lithography, masks and pattern transfer

In situ monitoring and control of material growth for high resolution electron beam induced deposition

W. F. van Dorp, C. W. Hagen, P. A. Crozier, and P. Kruit

J. Vac. Sci. Technol. B 25, 2210 (2007); http://dx.doi.org/10.1116/1.2804603 (5 pages) | Cited 5 times

Online Publication Date: 7 December 2007

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During electron beam induced deposition on electron transparent membranes, the transmitted annular dark field (ADF) signal can be monitored. A method was developed to use the ADF signal to obtain insight into the growth process and to control the mass of individual nanometer-sized deposits. Arbitrary two-dimensional patterns can be defined. The smallest sampling time of the ADF signal monitoring is presently about 40 ms. For arrays of dots that were deposited, the growth of each individual dot was monitored. It is observed that the growth is different for each dot, although the average deposit growth rate is linear with the dwell time. Apart from monitoring the ADF signal during the growth, the amount of deposited mass can be controlled for individual deposits by terminating the growth process when the ADF signal exceeds a threshold value. The dynamic ADF feedback control was applied to reduce variations in deposit mass. This attempt did not succeed, but the method was successfully applied to prevent the occurrence of a proximity effect. When the electron beam irradiates the side of an already existing structure, the amount of deposited material is higher than if the electron beam irradiates an area that is under normal incidence. With the dynamic ADF feedback control, this effect can be compensated in situ and the amount of deposited material that is probed by the beam is constant regardless of the local growth rate. The mass deposition resolution of the feedback system is estimated by assuming a volume and a density of the deposits. It is estimated that the ultimate mass resolution is a single molecule.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.80.Fe Electron and positron radiation effects
82.45.Mp Thin layers, films, monolayers, membranes

Redeposition characteristics of focused ion beam milling for nanofabrication

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

J. Vac. Sci. Technol. B 25, 2215 (2007); http://dx.doi.org/10.1116/1.2806973 (4 pages) | Cited 8 times

Online Publication Date: 7 December 2007

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In this article, a new method is presented to measure the focused ion beam induced sputter distribution, obtained with 30 keV Ga+ ions. Small holes with diameters ranging from 400 to 1750 nm have been created in a lamella with a thickness of approximately 300 nm. Short ion beam pulses sputter small amounts of material from the bottom of the hole that redeposit at the opposite side. Assuming axial spatial symmetry, imaging the hole before and after redeposition yields a quantitative cross section of the sputter distribution. It has been found that at low ion currents (<6 pA) and low ion dose (<10+8) the method produces reliable, reproducible results for 30 keV Ga+ ions on silicon. The method is compared with SRIM simulations in Si and with previously published results. The simulated and measured results are in good agreement. At the higher dose∕current regime, small Ga droplets are formed, probably as a result of sputtered Ga dopants in Si. As a result of this, the method becomes less accurate and the simulation is no longer valid due to the fact that the substrate milling has to include the many Ga dopants to a certain depth.
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81.16.Rf Micro- and nanoscale pattern formation
61.80.Jh Ion radiation effects

Resolution in focused electron- and ion-beam induced processing

Ivo Utke, Vinzenz Friedli, Martin Purrucker, and Johann Michler

J. Vac. Sci. Technol. B 25, 2219 (2007); http://dx.doi.org/10.1116/1.2789441 (5 pages) | Cited 17 times

Online Publication Date: 7 December 2007

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The key physical processes governing resolution of gas-assisted focused electron-beam and ion-beam induced deposition and etching are analyzed via an adsorption rate model. The authors quantify how the balance of molecule depletion and replenishment determines the resolution inside the locally irradiated area. Scaling laws are derived relating the resolution of the deposits to molecule dissociation, surface diffusion, adsorption, and desorption. Supporting results from deposition experiments with a copper metalorganic precursor gas on a silicon substrate are presented and discussed.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.65.Cf Surface cleaning, etching, patterning
68.43.Mn Adsorption kinetics
68.35.Fx Diffusion; interface formation
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Fabrication of 22 nm half-pitch silicon lines by single-exposure self-aligned spatial-frequency doubling

Alex K. Raub, Dong Li, Andrew Frauenglass, and S. R. J. Brueck

J. Vac. Sci. Technol. B 25, 2224 (2007); http://dx.doi.org/10.1116/1.2801889 (4 pages) | Cited 5 times

Online Publication Date: 7 December 2007

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The relentless progression of semiconductor technology to smaller feature sizes will likely soon outstrip the theoretical linear system limits of today’s optical lithography tools (a half-pitch of λ/4n or 34 nm with a 193 nm wavelength source and water immersion). We demonstrate a self-aligned process involving only a single lithographic exposure followed by spatial-frequency doubling that results a half-scaling of the original pattern and have achieved a 22 nm half-pitch pattern with 193 nm water immersion. A lithographic pitch of 89 nm was realized with a 193 nm ArF-excimer laser source and de-ionized-water immersion interferometric lithography. A self-aligned spatial-frequency doubling technique, taking advantage of the well-known anisotropic etching of silicon by KOH, was used to affect the frequency doubling. A protective layer (metal) was deposited parallel to the (110) direction of a (100) silicon wafer and the sample was immersed in an appropriate KOH solution, resulting in a series of 44.5 nm opening width V-grooves terminated in 57° (111) faces etched into the silicon through the mask openings. The metal mask was removed to expose the previously protected high-etch rate (100) surface of the sample for a second wet KOH etch. This results in a pattern at twice the original spatial frequency. A frequency-doubled pitch of 44.5 nm was achieved. An alternate, manufacturing friendly, processing scheme related to standard gate sidewall passivation is proposed.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors

Focused electron beam induced deposition of nickel

A. Perentes, G. Sinicco, G. Boero, B. Dwir, and P. Hoffmann

J. Vac. Sci. Technol. B 25, 2228 (2007); http://dx.doi.org/10.1116/1.2794071 (5 pages) | Cited 11 times

Online Publication Date: 7 December 2007

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Focused electron beam induced depositions of nickel-containing materials obtained by using bis(methylcyclopentadienyl)nickel(II) Ni(C5H4CH3)2 and tetrakis(trifluorophosphine)nickel(0) Ni(PF3)4 as precursors, were compared in terms of chemical composition and electrical resistivity. Ni(PF3)4 decomposed into higher Ni content materials than that obtained with Ni(C5H4CH3)2 (typically 40 and 10 at. %, respectively). Attempts of increasing the Ni content by injecting controlled flows of molecular oxygen or hydrogen simultaneously to the precursor vapors resulted in all cases in the increase of incorporated oxygen only. The lowest electrical resistivities of 150 nm wide lines obtained from Ni(C5H4CH3)2 and Ni(PF3)4 were 1 and 1×10−3 Ω cm, respectively. The electrical resistivity of the latter lines showed an e(−T) dependence with temperature, typical of magnetic heterogeneous alloys and granular alloys containing insulating particles. Transmission electron microscopy investigations of a freestanding rod obtained from Ni(PF3)4 showed a nanocrystalline structure of nickel grains surrounded by a partially amorphous cladding.
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81.05.Bx Metals, semimetals, and alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.46.Hk Nanocrystals

Oxygen assisted focused electron beam induced deposition of Si-containing materials: Growth dynamics

A. Perentes and P. Hoffmann

J. Vac. Sci. Technol. B 25, 2233 (2007); http://dx.doi.org/10.1116/1.2798746 (6 pages) | Cited 8 times

Online Publication Date: 7 December 2007

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The growth dynamics of oxygen assisted focused electron beam induced deposition of Si-containing materials (from SiOxCy to SiO2) were investigated as a function of relevant process parameters. The results obtained from organosilanes of different families (alkoxy, alkyl, and isocyanatosilanes) are compared. Residual water molecules in the SEM chamber were found to be responsible for side reactions leading to carbon etching and oxygen incorporation in focused electron beam induced deposition (FEBID) materials and ruled the deposition process during conventional FEBID. Depending on the precursor reactivity to oxygen, the material growth rate either increased or decreased with increasing additional O2 until it remained constant from 1 SCCM. Accounting for the FEBID material density, oxygen always increased the deposition efficiency in terms of Si atoms deposited per second. Less carbon residues in the deposits were obtained at large replenishment times (above 50 μs) and low dwell times (below 15 μs), which hint to relatively slow process steps in the complex deposition mechanism in our deposition equipment. O2 assisted FEBID showed to be insensitive to electron density variations, and secondary electrons were demonstrated to have sufficient energy to initiate the oxidation reaction and achieve 90% of the deposition process.
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81.07.Bc Nanocrystalline materials
81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation
61.46.-w Structure of nanoscale materials

High brightness 100-electron-beam source for high-resolution applications

Yanxia Zhang and P. Kruit

J. Vac. Sci. Technol. B 25, 2239 (2007); http://dx.doi.org/10.1116/1.2794073 (6 pages) | Cited 3 times

Online Publication Date: 7 December 2007

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The design of a 100-beam source for high-resolution applications is presented, comprising a Schottky emitter, an aperture lens array, an accelerator lens, and a conjugate blanker array. The beamlets emerge at 30 kV, compatible with most scanning electron microscope-type systems commercially available. The aberrations due to the aperture lens array and the accelerator lens are carefully minimized. For a Schottky source with a brightness of 1.5×108 A/m2 sr V, the multibeam source is designed to allow a transmission of more than 1000 nA current to the reduction optics with uniform spot sizes.
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42.79.Ag Apertures, collimators
42.79.Bh Lenses, prisms and mirrors

Cathode ray tube type electron gun as a source for multibeam electron lithography

A. J. van den Brom, A. H. V. van Veen, W. M. Weeda, G. Z. M. Berglund, M. Wieland, and P. Kruit

J. Vac. Sci. Technol. B 25, 2245 (2007); http://dx.doi.org/10.1116/1.2801869 (5 pages) | Cited 4 times

Online Publication Date: 7 December 2007

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The authors have investigated the potential of using a dispenser cathode in space charge limited regime for employment in an electron beam lithography electron source. The space charge limitation guarantees stable and uniform emission even if there are small work function variations or bumps and depressions on the surface. Employment of a dispenser cathode in the space charge limited regime enables high beam currents and splitting of the electron beam into many sub-beams for parallel multibeam electron lithography. In the reported experiment, the electron beam is split into 194 sub-beams. The reduced brightness, defined as current divided by normalized emittance, was measured at different cathode temperatures and extraction potentials for a cathode ray tube type electron source equipped with an I-type dispenser cathode. In the central 25 sub-beams, reduced brightness values of up to 106 A m−2 sr−1 V−1 were observed. Such a high reduced brightness in combination with a high total emission current (up to 20 mA) indicates potential application in electron beam lithography systems. In accord with theory, the experimentally observed reduced brightness is directly proportional to the emission current density. It was found, however, that the brightness drops if the emission current density is increased beyond the level where the emitter leaves the space charge limited regime. Within the space charge regime, increasing reduced brightness as a function of increasing current density is found to be caused by a decreasing virtual source size, while the angular current density remains nearly invariant.
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85.40.Hp Lithography, masks and pattern transfer
84.47.+w Vacuum tubes
29.25.Bx Electron sources

Annealing of electron beam induced deposits of platinum from Pt(PF3)4

Matthew H. Ervin, Daniel Chang, Barbara Nichols, Alma Wickenden, John Barry, and John Melngailis

J. Vac. Sci. Technol. B 25, 2250 (2007); http://dx.doi.org/10.1116/1.2806978 (5 pages) | Cited 8 times

Online Publication Date: 7 December 2007

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Electron beam induced deposition (EBID) is of interest as a damage-free and resist-less means of incorporating nonconventional materials such as polymer fibers, nanowires, and carbon nanotubes into integrated circuits. A novel inorganic platinum precursor—Pt(PF3)4—is investigated in this work, as it has previously been demonstrated to deposit Pt with resistivities close to bulk Pt when deposited using high dose rates. In this work, the effects of 100 and 200 °C anneals on these Pt deposits are examined. Annealing these deposits is observed to shrink the deposits and decrease their P content. As a result, the measured Pt resistivities decreased with annealing by factors of 1.6–9.9.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
81.40.Gh Other heat and thermomechanical treatments

Electrospun DNA nanofibers

Leon M. Bellan, Elizabeth A. Strychalski, and Harold G. Craighead

J. Vac. Sci. Technol. B 25, 2255 (2007); http://dx.doi.org/10.1116/1.2801886 (3 pages) | Cited 2 times

Online Publication Date: 7 December 2007

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The authors have electrospun fluorescently labeled DNA molecules into nanofibers with diameters of approximately 27 nm. They were able to image the nanofibers via fluorescence microscopy, scanning electron microscopy, and atomic force microscopy. Fibers were deposited over prepatterned features such as electrodes and trenches, allowing future measurement and manipulation of the DNA nanofibers. As an example of such a measurement, they have used an atomic force microscope to measure the Young’s modulus of a single DNA nanofiber.
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87.14.G- Nucleic acids
87.15.B- Structure of biomolecules

Multiple beam sub-80‐nm lithography with miniature electron beam column arrays

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

J. Vac. Sci. Technol. B 25, 2258 (2007); http://dx.doi.org/10.1116/1.2811710 (8 pages) | Cited 2 times

Online Publication Date: 7 December 2007

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Miniature electron beam columns have the potential for high resolution, high throughput maskless lithography applications because they can be scaled in number to form high density column arrays with low fabrication costs. This is achieved using manufacturing techniques that leverage rf packaging technologies and standard bulk micromachining and integrated circuit fabrication processes to produce reliable components with repeatable performance characteristics. A 1×4 electrostatic column array designed to target the 45 nm node has been built using monolithically fabricated lenses and packages. The lenses, which consist of stacks of patterned silicon and insulator, are mounted to a ceramic package. Internal to the package are traces which carry all interconnects to drive the column. Each column in the array is individually correctable. The monolithic lens design simplifies the pick-and-place assembly of high density column arrays and enables precise column-to-column registration. The design also facilitates scaling up of the column density to achieve higher throughput, and simulations presented previously suggest that the design can be extended to meet the 22 nm resolution requirement. This article presents the first results from simultaneous multiple beam lithography using miniature column arrays. Independent patterns were exposed synchronously at 1 keV using two columns in a 1×4 monolithic column array, resulting in 75 nm features written into ZEP-520A resist. Other experiments suggest reliable high voltage lens performance and good beam current and position stability. These preliminary results from arrays of limited numbers of columns demonstrate progress toward the development of full-scale direct write lithography systems driven by miniature column arrays.
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85.40.Hp Lithography, masks and pattern transfer

CsBr/GaN heterojunction photoelectron source

Juan R. Maldonado, Zhi Liu, Yun Sun, Scott Schuetter, Piero Pianetta, and R. F. W. Pease

J. Vac. Sci. Technol. B 25, 2266 (2007); http://dx.doi.org/10.1116/1.2779042 (5 pages) | Cited 2 times

Online Publication Date: 7 December 2007

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Experimental results on a new CsBr/GaN heterojunction photocathode structure are presented. The results indicate a fourfold improvement in photoyield relative to CsBr/Cr photocathodes. A model is presented based on intraband states in CsBr and electron injection from the GaN (with 1% addition of indium) substrate to explain the observed photoyield enhancement. The photocathode lifetime at high current density (>40 A/cm2) is limited by laser heating of the small illuminated area. Calculations are presented for sapphire and diamond substrates, indicating a factor of 20 reduction in temperature for the latter. The results are encouraging for the realization of a high photoyield photocathode operating at high current density with long lifetime.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.60.Ha Photomultipliers; phototubes and photocathodes
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Subwavelength proximity nanolithography using a plasmonic lens

Sungkyu Seo, Hyun Chul Kim, Hyungduk Ko, and Mosong Cheng

J. Vac. Sci. Technol. B 25, 2271 (2007); http://dx.doi.org/10.1116/1.2804517 (6 pages) | Cited 13 times

Online Publication Date: 7 December 2007

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This article presents a novel device, the plasmonic lens (PL), consisting of equally spaced ring apertures in a metal film deposited on a fused silica substrate. It was fabricated by electron-beam lithography (EBL) and reactive-ion etching (RIE). When illuminated by a collimated laser, a cylindrical surface plasmon (SP) is excited in the PL, scattered by the structure, and propagates. As a result, the PL focuses a subwavelength spot in the midfield, i.e., the focal length is several microns. The authors experiment demonstrated that 90–300 nm spots (up to λ/4) with pitches of 400–500 nm, focal length of 1.7 μm, were printed by a PL using 405 nm laser. The authors three-dimensional electromagnetic simulation predicted a full width at half maximum (FWHM) of 210 nm, equivalent to an aberration-free lens having an unity numerical aperture (NA = 1). The experimental result agreed well with the simulation. A theoretical model is also presented. Given its small footprint and subwavelength resolution, the PL holds great promise in direct-writing and scanning microscopy.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
42.82.Cr Fabrication techniques; lithography, pattern transfer

Monolithic multichannel secondary electron detector for distributed axis electron beam lithography and inspection

D. S. Pickard, C. Kenney, S. Tanimoto, T. Crane, T. Groves, and R. F. W. Pease

J. Vac. Sci. Technol. B 25, 2277 (2007); http://dx.doi.org/10.1116/1.2804611 (7 pages) | Cited 3 times

Online Publication Date: 7 December 2007

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The attractiveness of electron beam systems would be greatly enhanced if the throughput could be improved. One approach, described previously by the authors employs a uniform axial magnetic field to focus thousands of electron beams simultaneously [ D. S. Pickard et al., J. Vac. Sci. Technol. B 21, 2709 (2003); T. R. Groves and R. A. Kendall, ibid., 16, 3168 (1998) ]. The beamlets never combine to form a common crossover, thereby avoiding the throughput limitations due to space charge blurring. With this approach, one challenge was to fashion a detection scheme that maintains a tight beamlet packing density (250 μm pitch) while minimizing cross-talk between adjacent secondary electron signals, either by crossing trajectories or within the detector. A pin-diode-based detector was investigated as a potential component of the multielement detection scheme for the authors’ system. The detector features a two-dimensional array of elements on high resistivity float-zone silicon. The detector attributes that were attractive to their application include modest internal amplification (>5000 at 25 kV), fast response time (measured at <10 ns), ability to be made compact and with dense packed electrodes (<250 μm), low electrode capacitance (<1 pF), and ability for (complementary metal-oxide semiconductor) circuitry to be integrated directly onto the detector array so that low noise amplification of each signal can be performed. This detector requires a retarding field for the primary beam, which accelerates the secondary electrons to energies sufficient to excite a large number of internal secondaries.
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81.16.Nd Micro- and nanolithography
85.30.Kk Junction diodes
29.40.Wk Solid-state detectors

Atomic-force lithography with interferometric tip-to-substrate position metrology

Euclid E. Moon, Jan Kupec, Mark K. Mondol, Henry I. Smith, and Karl K. Berggren

J. Vac. Sci. Technol. B 25, 2284 (2007); http://dx.doi.org/10.1116/1.2787794 (4 pages) | Cited 1 time

Online Publication Date: 7 December 2007

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Inadequacies in lateral tip stability and registration presently limit lithographic applications of scanning probes. The authors describe a tool they constructed to write sub-10-nm features with 1 nm pattern registration. The tool utilizes an interferometric metrology technique called interferometric-spatial-phase imaging (ISPI) to continuously measure tip position relative to a substrate. Direct tip-to-substrate position measurement permits correction for the multitude of error sources encountered in the long mechanical path between a tip and a substrate. Experimental results indicate that the lateral tip position is stabilized by ISPI to 3σ = 0.3 nm, and pattern placement accuracy in a two-dimensional (2D) grid array is 3σ = 0.2 nm. According to ISPI measurements, 2D closed figures written in a polymer are overlaid to <1 nm. Analysis of patterns written by the tip while under ISPI control provides an error bound that is in good agreement with the ISPI measurements.
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07.79.Lh Atomic force microscopes
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
68.37.Ps Atomic force microscopy (AFM)
81.16.Ta Atom manipulation
81.16.Nd Micro- and nanolithography
back to top Modeling Simulation and CAD

Electron beam and optical proximity effect reduction for nanolithography: New results

Martin Peckerar, David Sander, Ankur Srivastava, Adakou Foli, and Uzi Vishkin

J. Vac. Sci. Technol. B 25, 2288 (2007); http://dx.doi.org/10.1116/1.2806967 (7 pages) | Cited 3 times

Online Publication Date: 10 December 2007

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Proximity effect correction by dose modulation is widely practiced in electron-beam lithography. Optical proximity control is also possible using a combination of shape adjustment and phase control. Assigning “the right” dose (or fill factor and phase for optics) is a well known mathematical inverse problem. Linear programming, by definition, is the appropriate method for determining dose. In the past, the technique was too slow for full-scale implementation in mask making. Here, the authors discuss how recent developments in computer speed and architecture have improved the prospects for full-scale implementation. In addition, the authors discuss some numerical techniques, analogous to gridding and relaxation, that make linear programming more attractive in mask making.
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85.40.Hp Lithography, masks and pattern transfer

Image contrast slope and line edge roughness of chemically amplified resists for postoptical lithography

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

J. Vac. Sci. Technol. B 25, 2295 (2007); http://dx.doi.org/10.1116/1.2794326 (6 pages) | Cited 24 times

Online Publication Date: 10 December 2007

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The reduction of line edge roughness (LER) or linewidth roughness is the most challenging issue associated with the development of resist processes for the next generation lithography. The extent of LER has been reported to correlate with the image contrast slope. Although the postoptical lithography such as electron beam and extreme ultraviolet lithographies can create high contrast images, low-energy electrons degrade image contrasts in these lithographies. The precise prediction of image contrasts requires the incorporation of the effects of low-energy electrons into process simulators. For the reduction of LER, better understanding of LER formation is needed. In this work, the authors proposed a simulation method for the calculation of latent images for postoptical lithographies on the basis of the sensitization mechanisms of chemically amplified resists.
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85.40.Hp Lithography, masks and pattern transfer

Study of the assist features effect on the through focus behavior in isoline with an innovative method

Jianliang Li, Qiliang Yan, and Lawrence S. Melvin

J. Vac. Sci. Technol. B 25, 2301 (2007); http://dx.doi.org/10.1116/1.2789448 (6 pages) | Cited 1 time

Online Publication Date: 10 December 2007

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Driven by the ever shrinking feature size in the chip design and the complexity of the heuristic subresolution assist feature (SRAF) placement rules, more wafer data for calibration and more effort on the part of design engineers are necessary for each process node. The main purpose of placing assist features around the main feature is to improve the through focus robustness on the target edge of the main feature. Therefore, it is desirable to study the effect of assist feature placement on the main feature in terms of the focus sensitivity with a quick and accurate method. In this paper, an innovative way of calculating the signal dependence on the locations of the SRAF placed in the isoline pattern is proposed. The results indicated that the optimal location for the assist feature placement to increase the depth of focus is about 380 nm from the isoline center and is independent of the isoline structure for an annular illumination system. The results are verified by using independent tools and measured before and after optical proximity correction. Consistency of the optimal assist feature location is observed, and a qualitative explanation of the observations is presented.
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85.40.Hp Lithography, masks and pattern transfer
85.30.De Semiconductor-device characterization, design, and modeling

Pattern matching, simulation, and metrology of complex layouts fabricated by electron beam lithography

N. Tsikrikas, D. Drygiannakis, G. P. Patsis, I. Raptis, A. Gerardino, S. Stavroulakis, and E. Voyiatzis

J. Vac. Sci. Technol. B 25, 2307 (2007); http://dx.doi.org/10.1116/1.2798714 (5 pages) | Cited 1 time

Online Publication Date: 10 December 2007

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Validation of design rules taking into account fine details such as line-edge roughness, and full chip layout simulation for design inconsistencies, before actual fabrication, are among the main objectives of current software assisted metrology tools. Line-edge roughness quantification should accompany critical dimension (CD) measurements since it could be a large fraction of the total CD budget. A detailed simulation and metrology approach of line-edge roughness quantification versus the length scales in a layout are presented in this work using a combination of electron beam simulation for the exposure part, and stochastic simulations for the modeling of resist film, postexposure bake, and resist dissolution. The method is applied also on a test layout with critical dimension of 200 nm and the resulted simulation and scanning electron microscopy images are compared with the aid of a pattern matching algorithm which enables the identification of the desired layout for metrology on a complex layout containing many printed features.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Bh Computer-aided design of microcircuits; layout and modeling
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
back to top Nanoimprint and Soft Lithography

Visualization of mold filling stages in thermal nanoimprint by using pressure gradients

Helmut Schift, Sandro Bellini, Morten Bo Mikkelsen, and Jens Gobrecht

J. Vac. Sci. Technol. B 25, 2312 (2007); http://dx.doi.org/10.1116/1.2806972 (5 pages) | Cited 4 times

Online Publication Date: 10 December 2007

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A method for the visualization of mold filling during a thermoplastic imprint at a microscopic level was developed, which is based on superposition of images of a series of different states of imprint. The animated movie sequence gives an insight into the complex flow of polymer and shows how voids are forming and vanishing during the imprint process. It can therefore be used as a tool for optimization of processes and improvement of stamp design.
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61.41.+e Polymers, elastomers, and plastics
81.16.-c Methods of micro- and nanofabrication and processing

Ultrastiff stage for imprint lithography

Y. Jeon, M. Feldman, and L. Jiang

J. Vac. Sci. Technol. B 25, 2317 (2007); http://dx.doi.org/10.1116/1.2798722 (4 pages)

Online Publication Date: 10 December 2007

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The high-resolution capabilities of imprinting and step and flash make these techniques strong contenders for the next generation lithography. Unfortunately, alignment remains an area of concern for imprinting because it must be completed before the template is moved into contact with the wafer. The large forces on the template during the process, even for step and flash, place additional demands on the stiffness as well as the reproducibility of the template stage. A prototype flexure stage has been developed to meet these demands. A compressive load, slightly below the Euler limit, is used to produce relatively free motion in the vertical direction while maintaining extremely high horizontal stiffness. In addition, the horizontal stage position is viewed by an optical system based on a microscope objective with a central stop. With it, the horizontal position of a diffraction grating fixed to the stage has been measured to a few nanometers, over a vertical range of several hundred microns. Consequently, not only does the high transverse stiffness of the stage minimize unwanted horizontal motions but also any that occur are measured over the entire required range of motion.
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81.16.Nd Micro- and nanolithography

Chemical nanoimprint lithography for step-and-repeat Si patterning

Hideo Namatsu, Masatoshi Oda, Atsushi Yokoo, Makoto Fukuda, Koichi Irisa, Shigeyuki Tsurumi, and Kazuhiko Komatsu

J. Vac. Sci. Technol. B 25, 2321 (2007); http://dx.doi.org/10.1116/1.2806970 (4 pages) | Cited 1 time

Online Publication Date: 10 December 2007

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Chemical nanoimprint lithography is proposed as a new nanoimprint category. The authors investigate chemical nanoimprint utilizing an electrochemical reaction based on the anodic oxidation that occurs as a result of moisture that is present between a mold and a substrate. For stable nanoimprint patterning, the authors have developed a silicon carbide mold with low resistance. The mold also has excellent surface flatness and mechanical strength. In addition, the authors have developed the prototype of chemical nanoimprinter equipped with a step-and-repeat system. The imprinter also has a temperature-humidity controller and a mold-pressure adjustment system, in addition to a voltage supply source.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.65.Mq Oxidation
81.16.Pr Micro- and nano-oxidation
81.40.Jj Elasticity and anelasticity, stress-strain relations

Optimizing nanoimprint and transfer-bonding techniques for three-dimensional polymer microstructures

Hyunsoo Park, Huifeng Li, and Xing Cheng

J. Vac. Sci. Technol. B 25, 2325 (2007); http://dx.doi.org/10.1116/1.2804518 (4 pages) | Cited 2 times

Online Publication Date: 10 December 2007

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Successful fabrication of three-dimensional multilayer microstructures in thermoplastic polymers using optimized layer-transfer and transfer-bonding techniques are reported in this work. For successful multilayer fabrication, it is very important to control the adhesion between two polymer layers and between mold and polymer. The authors discuss two techniques, bonding with a thin adhesive layer and direct thermal bonding near glass transition temperature, to achieve good bonding between two polymer layers while maintaining the structural integrity of the bottom polymer layers. Bonding with an adhesive layer achieves near 100% yield and heterogeneous materials can be bonded by this method. Direct thermal bonding is a generic approach that is suitable for all thermoplastic polymers. It opens up the possibilities of creating 3D multilayer structures in functional polymers for advanced applications. The capability and flexibility of the techniques developed here are expected to have deep impact on the applications of soft materials such as polymers in micro- and nanofabricated devices and systems.
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61.41.+e Polymers, elastomers, and plastics
81.16.Nd Micro- and nanolithography
68.65.Ac Multilayers

Fabrication of terahertz holograms

E. D. Walsby, J. Alton, C. H. Worrall, H. E. Beere, D. A. Ritchie, J. Leach, M. Padgett, and D. R. S. Cumming

J. Vac. Sci. Technol. B 25, 2329 (2007); http://dx.doi.org/10.1116/1.2799976 (4 pages)

Online Publication Date: 10 December 2007

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The authors demonstrate the fabrication of polypropylene eight-level holograms with arbitrary patterns for use in terahertz beam forming and imaging applications. They make a binary master in silicon using multistage deep reactive ion etching. The pattern is then transferred into polypropylene using an imprint technique to make the final hologram. Patterns are tested using a 2 THz quantum cascade laser. The results show that the desired image is formed with the inclusion of a zero order mode. The process is low cost and with high fidelity. The demonstration of holograms in low loss material opens a new field of opportunity for those working on terahertz applications.
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42.40.My Applications
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Jk Polymers and organics
42.55.Px Semiconductor lasers; laser diodes

UV-nanoimprint with the assistance of gas condensation at atmospheric environmental pressure

Hiroshi Hiroshima and Masanori Komuro

J. Vac. Sci. Technol. B 25, 2333 (2007); http://dx.doi.org/10.1116/1.2800334 (4 pages) | Cited 16 times

Online Publication Date: 10 December 2007

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Nanoimprint should be carried out in an ordinary environment from the standpoint of cost-performance. However, bubble defects arise when the process is done in air and the problem can become worse with large patterns and thin resin films. UV-nanoimprint using resin droplets reduces air capture by expelling air during resin spreading and, in some cases, achieves bubble free UV-nanoimprint by air dissolution in resin. When the authors simulated the smooth spreading of a large resin droplet in wafer warping, resin spreading occurred on mold plateaus but hardly reached into mold recesses where a significant amount of air was sealed and the air in a mold recess was not completely dissolved in resin within 10 min under an imprint pressure of 0.5 MPa. In contrast, a captured gas of concentrated pentafluoropropane (CHF2CH2CF3, 1,1,1,3,3-pentafluoropropane, HFC-245fa, CAS No. 460-3-1) whose vapor pressure is 0.15 MPa at room temperature was completely condensed and dissolved within 2 s, leaving no trace of bubble defects in UV-nanoimprint. UV-nanoimprint with the assistance of gas condensation at atmospheric pressure thus handles spin coat resin film and dramatically improves throughput by quickly eliminating bubble defects. The authors confirmed that the process is applicable to thin resin film whose resulting residual layer is 25 nm thick.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Fabrication of 3D-photonic crystals via UV-nanoimprint lithography

Thomas Glinsner, Paul Lindner, Michael Mühlberger, Iris Bergmair, Rainer Schöftner, Kurt Hingerl, Holger Schmid, and Ernst-Bernhard Kley

J. Vac. Sci. Technol. B 25, 2337 (2007); http://dx.doi.org/10.1116/1.2798733 (4 pages)

Online Publication Date: 10 December 2007

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Optical lithography will reach its limits due to the diffraction effects encountered and the necessity for using complex resolution enhancement techniques like optical proximity correction, phase shift masks, and off-axis illumination [ L. W. Liebmann et al., in Advanced Semiconductor Lithography (2001), Vol. 45] . The restrictions on wavelength, in combination with high process and equipment costs, make low-cost, simple imprinting techniques competitive with next-generation lithography methods. There are several nanoimprint lithography (NIL) techniques which can be categorized depending on the process parameters and the imprinting method—either step and repeat or full wafer single-step imprinting. A variety of potential applications has been demonstrated using NIL (e.g., surface acoustic wave devices, vias and contact layers with dual damascene imprinting process, Bragg structures, patterned media) [ M. D. Stewart et al., Proc. SPIE 5751, 210 (2005) ; P. Dorsey et al., in Discrete Track Recording (DTR) Media Fabricated using Nanoimprint Lithography, NNT 1–3 December (2004) ]. In this work UV-NIL has been selected for the fabrication process of 3D-photonic crystals.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Qs Photonic bandgap materials
81.65.Cf Surface cleaning, etching, patterning

Time dependent analysis of the resist deformation in thermal nanoimprint

Yoshihiko Hirai, Yuki Onishi, Toshiaki Tanabe, Masayoshi Nishihata, Takuya Iwasaki, Hiroaki Kawata, and Yasuroh Iriye

J. Vac. Sci. Technol. B 25, 2341 (2007); http://dx.doi.org/10.1116/1.2804429 (5 pages) | Cited 5 times

Online Publication Date: 10 December 2007

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Time evolution of the resist deformation process in the thermal nanoimprint lithography (NIL) has been investigated by both experiment and simulation study. For the numerical simulation, the authors newly developed a simulator using generalized Maxwell model as the viscoelastic constitutive model in conventional finite element method, which handles the complete NIL operations including resist pressing, cooling, and demolding processes. The dependency on the linewidth of the filling rate was investigated by both experiments and simulation and they sufficiently agreed with each other. It is confirmed that narrow pattern (high aspect ratio pattern) was difficult to be filled in a short period under the same imprinting pressure.
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81.16.Nd Micro- and nanolithography
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Nanoimprint lithography processes on 200 mm Si wafer for optical application: Residual thickness etching anisotropy

N. Chaix, C. Gourgon, C. Perret, S. Landis, and T. Leveder

J. Vac. Sci. Technol. B 25, 2346 (2007); http://dx.doi.org/10.1116/1.2801878 (6 pages) | Cited 5 times

Online Publication Date: 10 December 2007

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It is well known that one limitation of thermal nanoimprint lithography is the difficulty to imprint simultaneously nano- and microstructures because of the resulting different residual layer thicknesses, which induce a very poor control of the pattern sizes during the etching steps. Line gratings with densities varying from 1 to 15 have been imprinted on 8 in. wafers. The residual thickness varies from 38 to 158 nm. Different plasma chemistries have been studied for the etching of the residual layer. The patterns have been characterized after the imprint and the etching steps by scatterometry. The results show that some chemistries are very promising for the control of the patterns during the etching step. A O2/C12/Ar process has been particularly studied, and it has been demonstrated that it presents a very high anisotropy, which allows the use of long etching times in order to remove the residual layer in gratings with various densities with no variation of the critical dimension.
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85.40.Hp Lithography, masks and pattern transfer

Stretching and selective immobilization of DNA in SU-8 micro- and nanochannels

B. Yang, V. R. Dukkipati, D. Li, B. L. Cardozo, and S. W. Pang

J. Vac. Sci. Technol. B 25, 2352 (2007); http://dx.doi.org/10.1116/1.2806975 (5 pages) | Cited 2 times

Online Publication Date: 10 December 2007

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Nanoimprint lithography is used to fabricate 200 nm–10 μm wide SU-8 channels reversal imprinted onto Si substrates. The immobilization and stretching of double stranded λ-DNA molecules within the micro- and nanochannels are demonstrated and controlled by varying the hydrophobicity of SU-8 using oxygen plasma exposure. Site-directed immobilization of DNA is achieved by the integration of 10 μm wide SU-8 patterns with 6 μm gaps into 100 μm wide and 1 μm deep Si channels.
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07.10.Cm Micromechanical devices and systems
81.16.Nd Micro- and nanolithography
47.85.Np Fluidics

Fabrication of three dimensional structures for an UV curable nanoimprint lithography mold using variable dose control with critical-energy electron beam exposure

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

J. Vac. Sci. Technol. B 25, 2357 (2007); http://dx.doi.org/10.1116/1.2794317 (4 pages) | Cited 4 times

Online Publication Date: 10 December 2007

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In three dimensional (3D) printing the most challenging aspect is in the mold making process. The authors have developed a process for making 3D structures in a simple two-step process. The 3D profiles are created on a negative tone photoresist using electron beam lithography with variable dose and critical-energy electron beam exposure. Resist contrast profiles have been obtained with a negative tone photoresist from Microresist (ma-N2403) and subsequently have been utilized as the 3D masking layer. The 3D patterns have been transferred into a quartz mold by single-step reactive ion etching (RIE) with suitable resist-to-substrate selectivity. The precision of the fabricated structures is important, especially for micro-optic devices. Surface roughness below 2 nm has been achieved when the RIE process pressure is lower than 6 mTorr. The differences between intended and final dimensions are also analyzed. By employing this technique, complex structures for 3D quartz molds can be fabricated with simplified steps.
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85.40.Hp Lithography, masks and pattern transfer

Sub-100-nm three-dimensional nanoimprint lithography

Noriyuki Unno, Jun Taniguchi, and Yoshiaki Ishii

J. Vac. Sci. Technol. B 25, 2361 (2007); http://dx.doi.org/10.1116/1.2811715 (4 pages) | Cited 5 times

Online Publication Date: 10 December 2007

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In the next generation, there is going to be a strong need for three-dimensional nanoscale patterning technology for various optical devices and dual damascene process. A breakthrough in this field has been made by nanoimprint lithography (NIL) because of its lower cost and process simplicity. In this current study, the characteristics of proximity effect caused by forward scattering of electrons with spin on glass, which is used as a positive-tone inorganic resist, was examined using low-acceleration-voltage (<5 kV) electron-beam lithography. As a result, a sub-100-nm three-dimensional nanoimprint mold was fabricated by control-of-acceleration-voltage electron-beam lithography. And by using ultraviolet NIL, a replicated pattern was obtained that approximately corresponded to the fabricated mold.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography

Surface characterization of imprinted resist above glass transition temperature

T. Lévéder, S. Landis, L. Davoust, S. Soulan, J.-H. Tortai, and N. Chaix

J. Vac. Sci. Technol. B 25, 2365 (2007); http://dx.doi.org/10.1116/1.2799975 (5 pages) | Cited 2 times

Online Publication Date: 10 December 2007

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Nanoimprint lithography is a high resolution and low cost patterning technique. Many difficulties have been overcome from the process point of view. This article is dedicated to the resist pattern characterization when they are annealed above the glass transition temperature of the material. This approach may be directly transposed to imprint process optimization when the demolding scheme is performed above the glass transition temperature. Simple model describing shape evolution with temperature is proposed and correlation with demolding process is presented. The results showed that a stamp release well above glass transition temperature is possible and may slightly impact the initial imprinted shape. Furthermore, this work may be transposed to determine temperature evolution of polymer dynamic viscosity.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

Micro-nano mixture patterning by thermal-UV novel nanoimprint

Keisuke Okuda, Naoyuki Niimi, Hiroaki Kawata, and Yoshihiko Hirai

J. Vac. Sci. Technol. B 25, 2370 (2007); http://dx.doi.org/10.1116/1.2801859 (3 pages) | Cited 4 times

Online Publication Date: 10 December 2007

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Hybrid patterning by thermal and UV nanoimprint lithography (NIL) is demonstrated to fabricate micro and nano mixed structures. The SU-8 resist is thermally imprinted using a quartz mold, which has fine nanostructures and micro Cr mask patterns. After the thermal nanoimprint, UV light is exposed to the resist through the mold. Then, the mold is released and the resist is developed to fabricate microstructures. Using this process, nanodots having 200 nm feature sizes are successfully demonstrated on the microgratings with 40 μm width and 20 μm height. Also, fabrication of nanocorn array on the bottom of the deep microwell is demonstrated using Ni mold replicated from the resist master structure fabricated by the hybrid NIL.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Dj Gratings
85.40.Hp Lithography, masks and pattern transfer

Benchmarking of 50 nm features in thermal nanoimprint

C. Gourgon, N. Chaix, H. Schift, M. Tormen, S. Landis, C. M. Sotomayor Torres, A. Kristensen, R. H. Pedersen, M. B. Christiansen, I. Fernandez-Cuesta, D. Mendels, L. Montelius, and T. Haatainen

J. Vac. Sci. Technol. B 25, 2373 (2007); http://dx.doi.org/10.1116/1.2794064 (6 pages) | Cited 4 times

Online Publication Date: 10 December 2007

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The objective of this benchmarking is to establish a comparison of several tools and processes used in thermal NIL with Si stamps at the nanoscale among the authors’ laboratories. The Si stamps have large arrays of 50 nm dense lines and were imprinted in all these laboratories in a ∼ 100 nm thick mr-18010E film. Other materials, such as mr-17010E, were also tested. Good patterns were obtained and some limitations were identified. Reducing the pressure to 15 bars enables the printing of 50 nm structures without pulling them off. At higher pressures, some bending effects resulting in pattern deformation were observed. It was proven that a pressure of 1.5 bars is sufficient to imprint perfect 50 nm lines. The influence of the antiadhesive layer and mold design has been characterized by the demonstration of pulled off lines in some cases. Moreover, it has been shown that the scatterometry method is particularly useful for the characterization of 50 nm lines and that the residual layer thickness corresponds to the theoretical estimate as long as the lines are well defined. One process was demonstrated which combines high reproducibility with high throughput, achieving a cycle time of 2 min.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

Coarse-grain simulation of viscous flow and stamp deformation in nanoimprint

V. Sirotkin, A. Svintsov, S. Zaitsev, and H. Schift

J. Vac. Sci. Technol. B 25, 2379 (2007); http://dx.doi.org/10.1116/1.2812534 (5 pages) | Cited 2 times

Online Publication Date: 10 December 2007

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A refined coarse-grain software for the simulation of thermal nanoimprint lithography is described. This software takes into account the stamp bending during squeeze flow and is able to provide results well suited for the quantitative prediction of the residual resist thickness with an accuracy better than 10%.
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81.16.Nd Micro- and nanolithography

Photopolymerization kinetic study of UV nanoimprint lithography dedicated resists

P. Voisin, M. Zelsmann, H. Ridaoui, M. Chouiki, C. Gourgon, J. Boussey, and K. Zahouily

J. Vac. Sci. Technol. B 25, 2384 (2007); http://dx.doi.org/10.1116/1.2804519 (4 pages) | Cited 2 times

Online Publication Date: 10 December 2007

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This article reports on the properties of ultraviolet nanoimprint lithography dedicated imprinting materials. Studied solutions are composed of a diacrylate-based monomer and a variable amount (1%, 2%, and 4% in weight) of three different photoinitiators from Ciba Specialty Chemicals (Irgacure 819, Irgacure OXE02, and Irgacure 379). Photopolymerization kinetic studies were conducted on these solutions. Quantity and type of photoinitiator could be optimized in order to obtain a polymerization rate higher than 95% with an exposure dose as low as 20 mJ/cm2. The etch resistance of this home-developed imprinting resist was characterized under standard plasma etching conditions. We observed that the polymerization rate has a large influence on the plasma etch resistance, and we show that the etch rates of our best material is comparable to the one measured for 193 nm photolithography resists and makes it a very good candidate as a masking layer for direct pattern transfer.
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82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer

Bilayer metal wire-grid polarizer fabricated by roll-to-roll nanoimprint lithography on flexible plastic substrate

Se Hyun Ahn, Jin-Sung Kim, and L. Jay Guo

J. Vac. Sci. Technol. B 25, 2388 (2007); http://dx.doi.org/10.1116/1.2798747 (4 pages) | Cited 25 times

Online Publication Date: 10 December 2007

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The bilayer metal wire-grid polarizer has several advantages over single-layer wire-grid polarizer and conventional polarizer since it provides higher polarization efficiency and can be easily fabricated. In this work, the authors demonstrate the fabrication of bilayer metal wire-grid polarizer on flexible plastic substrate by a continuous roll-to-roll nanoimprint lithography (R2RNIL) process and evaluate its performance. To fabricate wire-grid polarizer, subwavelength grating structure in epoxysilicone material is first created on a flexible PET substrate by UV R2RNIL followed by aluminum deposition. In initial measurement, extinction ratio exceeding 1000 has been achieved.
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81.16.Nd Micro- and nanolithography
42.79.Ci Filters, zone plates, and polarizers
42.86.+b Optical workshop techniques

Impact of glass temperature for thermal nanoimprint

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

J. Vac. Sci. Technol. B 25, 2392 (2007); http://dx.doi.org/10.1116/1.2811718 (4 pages) | Cited 7 times

Online Publication Date: 10 December 2007

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To address the importance of the parameter glass transition temperature Tg for the choice of an adequate process temperature in a thermal nanoimprint process, three polymers with different values of Tg were investigated with respect to their imprint behaviors (poly)vinyl-chloride, (poly)styrene, and (poly)methyl-methacrylate. In order to evaluate the imprint results obtained at different temperatures, the volume of the polymer squeezed into the cavities was observed, and the temperature margins for the appearance of typical pattern size dependent failure types were derived. It turned out that despite the comparable molecular weight of these materials, the imprint temperature has to be chosen at different levels above Tg. Thus, Tg is not sufficient to characterize imprint polymers, and, in addition to the molecular weight, the viscosity at a definite temperature should be known. Tg alone can only indicate a lower limit for the process temperature.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

Characterizing nanoimprint profile shape and polymer flow behavior using visible light angular scatterometry

Rayan M. Al-Assaad, Suresh Regonda, Li Tao, Stella W. Pang, and Wenchuang (Walter) Hu

J. Vac. Sci. Technol. B 25, 2396 (2007); http://dx.doi.org/10.1116/1.2800327 (6 pages) | Cited 3 times

Online Publication Date: 10 December 2007

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The profile shape and the flow behavior of polymer nanoscale gratings made by a thermal nanoimprint process are precisely examined using visible light angular scatterometry. Nanoimprinted poly(methyl methacrylate) (PMMA) lines with 60–800 nm width, 100–200 nm height, and varied residual thicknesses of 70–400 nm have been investigated using this optical approach, and insightful observations are made regarding residual stress buildup during thermal nanoimprint. In addition, a nonlinear profile model has been developed for scatterometry to monitor the “melting” behavior of PMMA gratings under annealing around its glass transition temperature. The polymer nanostructures were found to relax primarily at high stress regions.
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81.16.Nd Micro- and nanolithography
81.07.-b Nanoscale materials and structures: fabrication and characterization
85.40.Hp Lithography, masks and pattern transfer
61.41.+e Polymers, elastomers, and plastics
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
78.40.Me Organic compounds and polymers

Nonresidual layer imprinting and new replication capabilities demonstrated for fast thermal curable polydimethysiloxanes

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

J. Vac. Sci. Technol. B 25, 2402 (2007); http://dx.doi.org/10.1116/1.2800326 (5 pages)

Online Publication Date: 10 December 2007

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Additional capabilities of a thermal curable polydimethylsiloxane based nanoimprinting resist that allows a fast replication (a few seconds) of 70 nm line width structures at low temperatures and low pressures (20 psi) are reported here. Challenging features such as nanopillars and high aspect ratio structures were accurately replicated. Moreover, a composite stamp was fabricated and successfully used to replicate structures from a DVD master. Additionally, it was found that a substrate with surface treatment by fluorinated silane is appropriate to imprint nanogratings with no residual layer. The residual layer can be eliminated on both a hard and a flexible substrate. The stamping of structures without residual layers can be used to create size controlled polymer nanofibers.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.Ps Polishing, grinding, surface finishing
61.41.+e Polymers, elastomers, and plastics

Simple fabrication of UV nanoimprint templates using critical energy electron beam lithography

Jaebum Joo, Kimin Jun, and Joseph M. Jacobson

J. Vac. Sci. Technol. B 25, 2407 (2007); http://dx.doi.org/10.1116/1.2806976 (5 pages)

Online Publication Date: 10 December 2007

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Ultraviolet nanoimprint lithography (UV-NIL) is a promising nanoscale patterning method, but the template fabrication processes are expensive and time consuming because a chrome layer is necessary both as a charge dissipation layer to minimize pattern distortion during electron beam patterning and as a physical mask during subtractive quartz etching. In this paper, the authors propose a simple UV-NIL template fabrication scheme based on the direct electron beam patterning of hydrogen silsesquioxane (HSQ) on quartz substrates using critical energy electron beam lithography (CE-EBL). By operating at the critical energy (E2) where the charge balance between incoming and outgoing electrons leaves the surface neutral, charge induced pattern distortion typically seen on quartz is practically eliminated. This template fabrication process eliminates conventional deposition and etching of charge dissipation layers. Quartz with sub-100-nm HSQ structures was used as a UV-NIL template, and SU-8 polymer structures were successfully replicated by a UV nanoimprint process. This simple template fabrication approach may lead to the development of new biological devices, nanoelectronics, and optoelectronics.
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81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
81.16.Rf Micro- and nanoscale pattern formation

Creating micro- and nanostructures on tubular and spherical surfaces

O. Lima, L. Tan, A. Goel, M. Negahban, and Z. Li

J. Vac. Sci. Technol. B 25, 2412 (2007); http://dx.doi.org/10.1116/1.2804428 (7 pages) | Cited 5 times

Online Publication Date: 10 December 2007

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The authors developed a new technique to create micro- and nanometer scale structures on curved free-standing objects by combining embossing/imprinting lithography approaches with mechanical loadings on elastic films. Embossing/imprinting generates small structures and mechanical loading determines shape or geometry of the final object. As a result, a portion of the tubes with a radius between 0.5 and 3.5 mm and a portion of the spheres with a radius between 2.4 and 7.0 mm were fabricated with grating line features (period of 700 nm) and microlens array features (lens radius of 2.5 μm) atop, respectively. It was found that both static analyses and finite element models can give good estimates on the radii of those curved objects, based on the dimension of the two layers, loading format, as well as mechanic strains. Thus, good control over shape and dimension of the free-standing structure can be achieved.
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81.16.Nd Micro- and nanolithography
81.07.-b Nanoscale materials and structures: fabrication and characterization

Solid-state electrochemical nanoimprinting of copper

Peter L. Schultz, Keng H. Hsu, Nicholas X. Fang, and Placid M. Ferreira

J. Vac. Sci. Technol. B 25, 2419 (2007); http://dx.doi.org/10.1116/1.2799977 (6 pages) | Cited 4 times

Online Publication Date: 10 December 2007

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For the first time, the authors report highly selective dry etching of copper with a resolution of 80 nm using solid-state electrochemical nanoimprint technology. By exploiting the high mobility of copper ions in solid electrolytes such as copper sulfide, they are able to obtain etching rates up to 5 Å/s without the use of contaminating liquids and excessive mechanical forces. Given the dearth of dry etch processes for metals in general and the fact that nanopatterning of metals is typically achieved indirectly using multistep processes, such a direct patterning technique offers potential application in a number of process steps in metallic interconnects and other nanoscale device fabrication.
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81.05.Bx Metals, semimetals, and alloys
81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
82.45.Aa Electrochemical synthesis
85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation

Economic approximate models for backscattered electrons

Leili Baghaei Rad, Ian Downes, Jun Ye, David Adler, and R. Fabian W. Pease

J. Vac. Sci. Technol. B 25, 2425 (2007); http://dx.doi.org/10.1116/1.2794068 (5 pages)

Online Publication Date: 10 December 2007

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The Monte Carlo method is widely used to simulate the signal from a scanning electron microscope. Although the results closely match the actual signal, the method is inherently slow due to the repeated calculation of random trajectories. The authors re-examine the alternative approach of using an approximate model to describe the signal. The authors develop a progressive approximate model which describes the spatial probability distribution of an electron along its entire path. The model also includes information about the angular and energy distribution of the electron. The model is compared to the Monte Carlo method by determining the yield of backscattered electrons as the beam is scanned across a step feature. For this simple feature the model-based approach computes the signal approximately two orders of magnitude faster.
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79.20.Kz Other electron-impact emission phenomena
02.50.Ng Distribution theory and Monte Carlo studies

Improved release strategy for UV nanoimprint lithography

Sophie Garidel, Marc Zelsmann, Nicolas Chaix, Pauline Voisin, Jumana Boussey, Arnaud Beaurain, and Bernard Pelissier

J. Vac. Sci. Technol. B 25, 2430 (2007); http://dx.doi.org/10.1116/1.2806969 (5 pages) | Cited 12 times

Online Publication Date: 10 December 2007

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The adhesion between the fused silica mold and the resist remains a key issue in ultraviolet nanoimprint lithography (UV-NIL), especially in step and repeat processes. In this paper, we present results on antisticking layers (ASLs) of tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (F13-TCS) deposited in vapor phase and of a commercial product, Optool DSX™, from Daikin Chemical, deposited in liquid phase. The antisticking properties and structural morphologies of the formed self-assembled monolayer are investigated using contact angle, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy (XPS) measurements. Obtained surface energies are as low as 10 mN/m for both types of ASL. The stability of these formed layers during the UV-NIL process remains the main important issue. It was tested on an EVG® step and repeat UV-NIL equipment using acrylate-based resists. After only 50 prints, we observed a high increase in the surface energy of the mold, which indicates a drastic degradation of the antisticking (ASL). XPS measurements show that fluorine is removed from the mold surface. This surface modification is attributed to free radicals created during the UV cure of the resist that easily cleaved fluorocarbon chains. This can be confirmed by the fact that the polar component of the surface energy was increased by a larger factor than the dispersive one. To overcome this problem, the acrylate-based resist was modified by the adjunction of a fluorine surfactant. To go further in the mold/resist interaction, we developed an original setup that directly measures the adhesion force. Almost no degradation of the organic ASL was observed in terms of surface energy and fluorine density after more than 50 prints when using a sufficiently high amount of surfactant in the resist.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.35.Md Surface thermodynamics, surface energies
68.08.-p Liquid-solid interfaces

Viscosity measurement of nanoimprint lithography resists with a rheological nanoindenter

A. A. Svintsov, O. V. Trofimov, and S. I. Zaitsev

J. Vac. Sci. Technol. B 25, 2435 (2007); http://dx.doi.org/10.1116/1.2794321 (4 pages) | Cited 3 times

Online Publication Date: 10 December 2007

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Considering Navier-Stokes equation, penetration of a tip in viscous film was considered allowing acquisition of viscosity from experimental data. Viscosity of thin (<500 nm) films as a function of temperature in the range of 25–200 °C was measured with the rheological indenter for thermoplastic polymers and (as a function of annealing temperature and annealing time) for thermocurable polymers with submicron spatial resolution. The approach could be used in design, tailoring, and optimization of soft materials for different applications.
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81.16.Nd Micro- and nanolithography
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.60.Bs Mechanical and acoustical properties
back to top Optical Lithography

Phase control in multiexposure spatial frequency multiplication

Yong Zhao, Chih-Hao Chang, Ralf K. Heilmann, and Mark L. Schattenburg

J. Vac. Sci. Technol. B 25, 2439 (2007); http://dx.doi.org/10.1116/1.2794318 (5 pages) | Cited 4 times

Online Publication Date: 10 December 2007

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Multiexposure spatial frequency multiplication is a technique that allows the spatial frequency of grating patterns to be increased by integer factors 2,3,4,… by applying a nonlinear development process between patterning steps. One of the main technical issues with this technique is how to accurately place subsequent patterns on a substrate with respect to previously established patterns, which is referred to as phase control of the overlay. The authors report a technique that achieves accurate phase control over large areas during spatial frequency multiplication by utilizing a surrounding alignment grating. Three key factors—the angle, period, and phase of the alignment grating—have been accurately measured and utilized to position subsequent patterns with respect to previous patterns. Some factors that can dramatically diminish the accuracy of phase control, such as particle-induced substrate distortion and nonlinear distortion of the alignment grating, have also been considered and minimized in order to improve the accuracy of phase control. For spatial frequency doubling with a 574 nm principal pitch, the authors achieved overlay phase errors with a mean of −1.0 nm±2.8 nm(1σ) between level 1 and level 2 grating patterns over a 25×32.5 mm2 area.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
42.79.Dj Gratings

Study of process contributions to total overlay error budget for sub-60-nm memory devices

Jangho Shin, Hyunjae Kang, SungWon Choi, Seoukhoon Woo, Hochul Kim, SukJoo Lee, Junghyeon Lee, and Chang-Jin Kang

J. Vac. Sci. Technol. B 25, 2444 (2007); http://dx.doi.org/10.1116/1.2787772 (3 pages) | Cited 5 times

Online Publication Date: 10 December 2007

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According to the 2006 International Technology Roadmap for Semiconductors, the overlay budget of 60 nm memory devices is 11 nm. To meet such a tight requirement, the total overlay error budget should be controlled carefully. There are many ways to analyze overlay budget; here, however, a simple but accurate methodology is introduced. In this study, total overlay error budget consists of four major contribution categories: scanner, process, metrology, and mask contributions. Scanner contributions are evaluated by measuring machine-to-machine overlay errors in the conventional way. Process contributions are estimated by inverse reactive-ion etch (RIE) lag and chemical mechanical polishing (CMP) erosion. Metrology contributions are evaluated by overlay metrology tools. Finally, mask contributions represent mask-to-mask misregistration. By applying this methodology to 60 nm memory devices, it turns out that process contributions are more than 30% of the total overlay error budget for a contact layer. In this article, the optimum process window is investigated so that process effects can be minimized.
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85.30.De Semiconductor-device characterization, design, and modeling
84.30.Sk Pulse and digital circuits

Deep ultraviolet photolithography capability of ZEP520A electron beam resist for mix and match lithography

Devin K. Brown

J. Vac. Sci. Technol. B 25, 2447 (2007); http://dx.doi.org/10.1116/1.2794072 (4 pages)

Online Publication Date: 10 December 2007

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ZEP520A is a positive high resolution electron beam resist enabling nanometer scale features; however, electron beam lithography (EBL) is a characteristically slow process. It is demonstrated that ZEP520A can be exposed by deep ultraviolet (DUV) photolithography and is useful for mix and match lithography schemes. Submicron resolution was achieved, an optical pattern was successfully aligned to an EBL pattern, and 1 cm2 was exposed in 11 min with DUV compared to 27 h with EBL.
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85.40.Hp Lithography, masks and pattern transfer

Photolithography using an optical microscope

Ron Gonski and John Melngailis

J. Vac. Sci. Technol. B 25, 2451 (2007); http://dx.doi.org/10.1116/1.2779046 (2 pages)

Online Publication Date: 10 December 2007

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The authors propose and demonstrate how to use an ordinary optical microscope as a flexible optical lithography tool. Until the advent of digital cameras, most high power optical microscopes had a vertical cone shaped fixture with a Polaroid film holder to record optical micrographs on the film. For conversion to lithography, the Polaroid film holder is simply removed and a vu-graph transparency, which serves as a mask, is substituted in the plane of the film. The transparency has the desired pattern printed on it by a laser printer or a copier. Ideally, the transparency has to be backlighted by a converging light source such that (ignoring diffraction) a pinhole anywhere in the transparency illuminates the entire lens at the base of the cone shaped fixture. The authors used a 11.4 cm diameter, 12.7 cm focal length Fresnel lens and a fiber light to generate the appropriately converging mask illumination. With the highest magnification, 100× lens the image on the mask was demagnified approximately by 700× on the sample. With this lens, the authors could expose lines of slightly less than 1 μm width.
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85.40.Hp Lithography, masks and pattern transfer
07.60.Pb Conventional optical microscopes

Experimental demonstration of dark field illumination using contact hole features

Michael M. Crouse, Emil Schmitt-Weaver, Steven G. Hansen, and Robert Routh

J. Vac. Sci. Technol. B 25, 2453 (2007); http://dx.doi.org/10.1116/1.2800323 (8 pages) | Cited 2 times

Online Publication Date: 10 December 2007

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The use of off-axis illumination in present lithography processes has enabled patterning to push below k1<0.40. This continual drive toward printing smaller feature sizes at the 193 nm wavelength has led to the investigation and successful implementation of a number of new resolution enhancement technique (RET) approaches. In this work, the application of dark field imaging as a RET for low-k1 contact hole features was examined using both simulation and experiment on a standard lithography tool set. Here dark field imaging is defined as imaging where a portion of the illumination source is placed outside of the projection optics. This approach is similar to standard off-axis illumination approaches using the familiar two-beam imaging but at greater incident angle where the zeroth diffraction order is not captured and image modulation is created by higher diffraction orders. This approach creates a number of “unexpected” effects and the authors show these for contact hole patterns using ASML Twinscan lithography tools operationally modified to operate in dark field mode. They demonstrate the following new dark field effects for contact holes: reduced and negative mask error enhancement factor, inverted develop critical dimension as a function of pitch, and image tone reversal at phase edges. Additionally, experimentally relevant items such as stray light and dark field exposure energy requirements are discussed.
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85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.30.Va Image forming and processing

Double patterning overlay budget for 45 nm technology node single and double mask approach

Pierluigi Rigolli, Catia Turco, Umberto Iessi, Gianfranco Capetti, Paolo Canestrari, and Aldo Fradilli

J. Vac. Sci. Technol. B 25, 2461 (2007); http://dx.doi.org/10.1116/1.2805246 (5 pages) | Cited 3 times

Online Publication Date: 10 December 2007

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Double patterning (double exposure and double etch) is definitely a viable solution for overcoming the physical resolution limit of k1 = 0.25 of imaging systems. This article presents the overlay budget for a double patterning technique using a 45 nm technology node flash memory device with k1 ∼ 0.20 and 193 nm dry lithography. Adopting double exposure, the final pattern is composed of two lithography patterns within the resolution capability of the exposure tool and then combined with the double etching processes. The photoetch photoetch approach creates the overlay between the two exposures which is the most critical issue to be addressed. This article presents the adopted scanner setup, mask requirements, and efficient overlay metrology setup in order to achieve the overlay roadmap of 6 nm for the 45 nm technology node.
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85.40.Hp Lithography, masks and pattern transfer

Application of contrast enhancement layer to 193 nm lithography

Ryoung-han Kim and Harry J. Levinson

J. Vac. Sci. Technol. B 25, 2466 (2007); http://dx.doi.org/10.1116/1.2798705 (5 pages) | Cited 2 times

Online Publication Date: 10 December 2007

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The feasibility of contrast enhancement layer (CEL) for extending the practical limit of 193 nm lithography was studied using an analytical model, exposed latent image inside the resist, and finite difference time-domain analysis. All studies showed that the CEL is applicable to 193 nm regime and beneficial for obtaining a contrast enhancement effect which appeared to be nonlinear and more effective on the images of low incident contrast. However, because of its nonlinear behavior, material parameters should be carefully chosen and optimized to obtain a large contrast improvement. In addition, thick topcoat induced aberration was also taken into account to evaluate the feasibility of the CEL. As a conclusion, it is shown that the CEL is promising for the use of future technologies.
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85.40.Hp Lithography, masks and pattern transfer

Lithography, plasmonics, and subwavelength aperture exposure technology

Yves Ngu, Marty Peckerar, Mario Dagenais, John Barry, and Birendra (Raj) Dutt

J. Vac. Sci. Technol. B 25, 2471 (2007); http://dx.doi.org/10.1116/1.2812524 (5 pages) | Cited 3 times

Online Publication Date: 10 December 2007

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This article presents the first experimental evidence that plasmonic excitation in metal films perforated with regular arrays of subwavelength apertures can produce high resolution far-field radiation patterns of sufficient intensity to expose photoresist when propagated through the optical system of a conventional stepper. The pattern fill factor (i.e., the total clear aperture area divided by the total mask area) is more than an order of magnitude smaller than the ratio of the mask clear area divided by the total mask area of a conventional mask. This could lead to a significant increase in mask making throughput. Contact window arrays were exposed with critical dimensions down to 260 nm using 248 nm incident radiation. While the exposure times are longer (somewhat less than three times more energy is required on the mask), the image pattern appears to be a cooperative effect of scattering from multiple apertures. If the array is defective, meaning that it contains a small number of unopened apertures, the pattern still prints as a coherent, cleared feature.
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78.66.Bz Metals and metallic alloys
81.16.Nd Micro- and nanolithography
73.22.Lp Collective excitations

Laser interferometric nanolithography using a new positive chemical amplified resist

R. Luttge, H. A. G. M. van Wolferen, and L. Abelmann

J. Vac. Sci. Technol. B 25, 2476 (2007); http://dx.doi.org/10.1116/1.2800328 (5 pages) | Cited 7 times

Online Publication Date: 10 December 2007

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The authors report on the progress of laser interference lithography at 266 nm laser wavelength with a chemical amplified resist containing a polyvinyl derivate dissolved in propylene glycol monoethyl ether ester. A continuous-wave deep-UV source combined with a Lloyd mirror is a simple and useful tool for the fabrication of nanoscale periodic structures generally called nanoarrays. Aiming for a robust pattern transfer technique to fabricate nanoarrays into magnetic materials, the authors investigated the utility of a chemical amplification positive tone resist, despite the relatively high theoretical resolution limit of 133 nm (λ/2) pattern period for the laser source used. Taking advantage of this new type of resist, the authors demonstrated for the first time the fabrication of an 18 Gbit/in.2 dot pattern on a platinum thin film.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
85.40.Hp Lithography, masks and pattern transfer
back to top Photoresist Technology

Acid distribution in chemically amplified extreme ultraviolet resist

Takahiro Kozawa, Seiichi Tagawa, Heidi B. Cao, Hai Deng, and Michael J. Leeson

J. Vac. Sci. Technol. B 25, 2481 (2007); http://dx.doi.org/10.1116/1.2794063 (5 pages) | Cited 33 times

Online Publication Date: 11 December 2007

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Acid generators are sensitized by secondary electrons in chemically amplified resists for ionizing radiation. As acid generators react with low-energy electrons (as low as thermal energy), this sensitization mechanism generates a significant blur and an inhomogeneous acid distribution at the image boundary, which results in line edge roughness (LER) formation. The evaluation of resolution blur intrinsic to the reaction mechanisms is important in the optimization of resist processes for extreme ultraviolet (EUV) lithography, especially from the viewpoint of LER. In this study, the authors simulated acid generation induced by EUV photons in poly(4-hydroxystyrene) with 10 wt % triphenylsulfonium triflate and clarified the extent of resolution blur in latent acid images and theoretical acid generation efficiency. The average distance between the EUV absorption point and the acid generation point (resolution blur) is 6.3 nm. The theoretical acid generation efficiency through the ionization path is 2.6 per EUV photon in the model system. Considering the deprotonation efficiency of polymer radical cations and the contribution of electronic excited states, the acid generation efficiency including the excitation path is 2.0–2.8 in typical resist materials with 10 wt % acid generator loading.
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85.40.Hp Lithography, masks and pattern transfer

Dissolution characteristics and reaction kinetics of molecular resists for extreme-ultraviolet lithography

Minoru Toriumi, Julius Santillan, Toshiro Itani, Takahiro Kozawa, and Seiichi Tagawa

J. Vac. Sci. Technol. B 25, 2486 (2007); http://dx.doi.org/10.1116/1.2787850 (4 pages) | Cited 6 times

Online Publication Date: 11 December 2007

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Molecular resist of polyphenol was evaluated as an extreme-ultraviolet resist compared with a polymer resist of p(tert-butoxycarbonyl-hydroxystyrene). The molecular resist shows higher sensitivity than the polymer resist. The dissolution behavior was studied by quartz crystal microbalance method. The molecular resist shows thinner swelling layer than the polymer resist. The deprotection mechanism was approximated by simple reaction equations, and Fourier-transform infrared spectra were interpreted to give the products of a quantum yield and a deprotection rate constant as 6.2×10−8 and 6.0×10−8 cm3/molecules s for molecular and polymer resists. Both deprotection efficiencies are almost same. The higher sensitivity of the molecular resist is due to the dissolution behavior not the reaction mechanism.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
78.30.Jw Organic compounds, polymers
64.75.-g Phase equilibria

Are extreme ultraviolet resists ready for the 32 nm node?

Karen Petrillo, Yayi Wei, R. Brainard, G. Denbeaux, Dario Goldfarb, C.-S. Koay, J. Mackey, Warren Montgomery, W. Pierson, T. Wallow, and Obert Wood

J. Vac. Sci. Technol. B 25, 2490 (2007); http://dx.doi.org/10.1116/1.2787815 (6 pages) | Cited 5 times

Online Publication Date: 11 December 2007

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The International Technology Roadmap for Semiconductors (ITRS) insertion point of extreme ultraviolet (EUV) lithography is the 32 nm half-pitch node, and significant worldwide effort is being focused toward this goal. Potential road blocks have been identified and are being addressed. Readiness of EUV photoresists is one of the risk areas. According to the ITRS (www.itrs.net), a production-worthy EUV resist at 32 nm half-pitch has to have a photospeed of ∼ 5 mJ/cm2 and line edge roughness (3σ) of 1.4 nm. Toward this goal, the joint INVENT activity (AMD, CNSE, IBM, Micron, and Qimonda) at Albany has evaluated a broad range of EUV photoresists on various EUV exposure tools worldwide, including EUV MET at Lawrence Berkeley National Laboratory, EUV MET at SEMATECH Albany, and EUV interferometer at the Paul Scherrer Institute, Switzerland. This article will give a survey of the results, assessing the strengths and weaknesses of current materials.
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85.40.Hp Lithography, masks and pattern transfer

Measurements of acid generation by extreme ultraviolet irradiation in lithographic films

Martin Glodde, Dario L. Goldfarb, David R. Medeiros, Gregory M. Wallraff, and Gregory P. Denbeaux

J. Vac. Sci. Technol. B 25, 2496 (2007); http://dx.doi.org/10.1116/1.2779045 (8 pages) | Cited 8 times

Online Publication Date: 11 December 2007

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Extreme ultraviolet (EUV) lithography requires photoresist materials that incorporate highly efficient photoacid generators (PAGs) due to the low intensity of the currently available EUV light sources. It is therefore necessary to understand the parameters that control acid generation mechanisms in photoresists under EUV irradiation, such as photoacid generator and base quencher structure, polymer matrix effects, and the interaction of ionizing radiation with the resist components. In this study, a known acid detection technique based on a dye indicator (coumarin 6) has been optimized for the quantification of the amount of photoacid produced by irradiation of lithographic resist films. Incorporation of acid-base indicators to solid polymer matrices has already been employed in previous studies; however, the environmental stability of the reactive species and the influence of the polymer resin have not been considered to date. Here, the authors present a comprehensive evaluation of PAGs that were exposed to 13.5 nm radiation and compared to 248 nm exposures. For some specific cases studied, it was possible to correlate the acid generation efficiency to the PAG structure and polymer matrix effects. Moreover, it is found that environmental effects such as humidity have a significant impact on acid strength, acid detection, and acid generation efficiency. The acid generation efficiency experiments were complemented with dose to clear exposures for selected resist systems. The results obtained indicate that the use of acid detection methods implemented for the design of EUV resist compositions with optimized photospeed requires careful attention to the complex role of the reactivity of all formulation components and photoreaction products in the presence of ionizing radiation.
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85.40.Hp Lithography, masks and pattern transfer

Geometry impact on ultrahigh resolution pattern collapse

A. Jouve, J. Simon, L. Gonon, and J. H. Tortai

J. Vac. Sci. Technol. B 25, 2504 (2007); http://dx.doi.org/10.1116/1.2801866 (4 pages) | Cited 3 times

Online Publication Date: 11 December 2007

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Pattern collapse is one critical issue that lithography must overcome to address future high resolution nodes (32 and 22 nm). Published pattern collapse models showed that lines collapse when the capillary pressure exerted by the liquid overcomes the mechanical strength of the material. To simplify equations, those models consider that the maximum capillary pressure is exerted only on one side of the pattern, when the rinse liquid fills the space on one side of the pattern while no liquid remains on the other side. The collapsing behavior of 60 nm dense lines printed with extreme ultraviolet interferometric lithography (EUV-IL) and electron beam lithography (EBL) has been studied. These experiments confirm that this phenomenon can be correctly modeled with an asymmetric rinse liquid filling configuration. Then the influence of the pattern shape of sub-60‐nm dense lines on collapse behavior is checked. The authors demonstrate that reentering slope deteriorates the pattern holding, whereas top rounding improves it. Finally, they observe that exposure defaults due to the tool properties such as stitching (EBL) or exposure dose heterogeneity (EUV-IL) considerably influence pattern collapse and should be considered for a better prediction.
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68.03.Kn Dynamics (capillary waves)

Pixelated chemically amplified resists: Investigation of material structure on the spatial distribution of photoacids and line edge roughness

Young-Hye La, Insik-In , Sang-Min Park, Robert P. Meagley, Melvina Leolukman, Padma Gopalan, and Paul F. Nealey

J. Vac. Sci. Technol. B 25, 2508 (2007); http://dx.doi.org/10.1116/1.2800330 (6 pages) | Cited 4 times

Online Publication Date: 11 December 2007

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Preorganized pixel-forming photoresists were prepared to investigate the effect of well-defined material structures and the spatial distribution of photoacid on line edge roughness of chemically amplified photoresists. Asymmetric poly(styrene)-block-poly(t-butylacrylate) (PS-b-PtBA) diblock copolymers, which formed PS cylinders or spheres within a PtBA matrix, were used as photoresists by adding catalytic amounts of photoacid generators (PAGs). PAGs resided only in the PtBA matrix domain, resulting in the PAG chemistry occurring only in the matrix domain. The pixelated photoresists showed a significant solubility switch after UV or x-ray exposure and postexposure bake, such that the polymer in the exposed regions dissolved in aqueous base solution. Granular structures that were matched with the domain spacing and structure of the block copolymer photoresists were observed on the edge of the patterned features. This model system demonstrated that line edge roughness is directly correlated to the structure of pixelated photoresist materials.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
61.41.+e Polymers, elastomers, and plastics

Direct measurement of the spatial extent of the in situ developed latent image by neutron reflectivity

Vivek M. Prabhu, Bryan D. Vogt, Shuhui Kang, Ashwin Rao, Eric K. Lin, and Sushil K. Satija

J. Vac. Sci. Technol. B 25, 2514 (2007); http://dx.doi.org/10.1116/1.2800329 (7 pages) | Cited 3 times

Online Publication Date: 11 December 2007

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The spatial distribution of polymer photoresist and deuterium labeled base developer highlights a fraction of the line edge that swells but does not dissolve. This residual swelling fraction remains swollen during both the in situ aqueous hydroxide dissolution (development) and water rinse steps uncovering that the final lithographic feature is resolved by a collapse mechanism during the drying step. These new insights into the mechanism of lithographic feature formation were enabled by contrast variant neutron reflectivity methods with nanometer resolution.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
back to top Metrology

High throughput defect detection with multiple parallel electron beams

H. M. P. van Himbergen, M. D. Nijkerk, P. W. H. de Jager, T. C. Hosman, and P. Kruit

J. Vac. Sci. Technol. B 25, 2521 (2007); http://dx.doi.org/10.1116/1.2789449 (5 pages) | Cited 2 times

Online Publication Date: 11 December 2007

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A new concept for high throughput defect detection with multiple parallel electron beams is described. As many as 30 000 beams can be placed on a footprint of a in.2, each beam having its own microcolumn and detection system without cross-talk. Based on the International Technology Roadmap for Semiconductors requirements, some high level properties of the implementation of this concept were derived. A projection lens was designed that can both focus the primary beam into a small spot and simultaneously collect 75% of the secondary electrons. Conceptual design studies were performed for three crucial components of the detector chain: the scintillator, the light optics, and the detection array. The throughput of this concept is expected to be at least a factor of 300 higher than standard electron beam based defect detection systems.
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81.70.-q Methods of materials testing and analysis
41.85.-p Beam optics

Photoresist cross-sectioning with negligible damage using a dual-beam FIB-SEM: A high throughput method for profile imaging

James S. Clarke, Michael B. Schmidt, and Ndubuisi G. Orji

J. Vac. Sci. Technol. B 25, 2526 (2007); http://dx.doi.org/10.1116/1.2804516 (5 pages)

Online Publication Date: 11 December 2007

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Imaging of photoresist cross sections in a focused ion beam (FIB)–scanning electron microscope (SEM) is demonstrated with negligible damage. An in situ chromium sputtering technique is used to deposit metal on the site of interest, replacing the conventional and more damaging metal deposition by high energy ion decomposition of metal-organic precursors. Here, a high current ion beam is rastered over a small chromium target suspended over the wafer surface resulting in a less damaging metal deposition step. The subsequent resist critical dimensions measured via FIB-SEM are calibrated against profile measurements taken by critical dimension atomic force microscopy, implemented here as a reference measurement system (RMS) without the influence of beam exposure. The use of a nondamaging RMS allows an accurate measurement of resist damage during imaging. As a practical demonstration of this sputtering method, a 50 nm 1:1 line/space array in extreme ultraviolet photoresist is analyzed through focus and exposure.
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81.16.Nd Micro- and nanolithography
81.15.Cd Deposition by sputtering
81.15.Jj Ion and electron beam-assisted deposition; ion plating
back to top Nanodevices

Hybrid semiconductor/nanoelectronic circuits: Freeing advanced lithography from the alignment accuracy burden

Konstantin K. Likharev

J. Vac. Sci. Technol. B 25, 2531 (2007); http://dx.doi.org/10.1116/1.2794060 (6 pages)

Online Publication Date: 11 December 2007

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This is a brief review of the recent work on devices and architectures for hybrid semiconductor/nanoelectronic circuits using an area-distributed “CMOL” interface between its subsystems. Such circuits may provide unprecedented performance in several applications including memories, digital logic circuits, and bioinspired mixed-signal networks, while requiring nanoscale resolution for fabrication of just one simple pattern (a grid of parallel, similar lines) without layer alignment. Detailed calculations have shown that switching to the hybrid circuit technology may allow an extension of the Moore’s law by 10 to 15 years.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Photolithographic synthesis of high-density DNA probe arrays: Challenges and opportunities

Adam R. Pawloski, Glenn McGall, Robert G. Kuimelis, Dale Barone, Andrea Cuppoletti, Paul Ciccolella, Eric Spence, Farhana Afroz, Paul Bury, Christy Chen, Chuan Chen, Dexter Pao, Mary Le, Becky McGee, Elizabeth Harkins, et al.

J. Vac. Sci. Technol. B 25, 2537 (2007); http://dx.doi.org/10.1116/1.2794325 (10 pages) | Cited 6 times

Online Publication Date: 11 December 2007

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The continual need for increased manufacturing capacity in the production of GeneChip™ DNA probe arrays, and the expanding use of these arrays into new areas of application such as molecular medicine, has stimulated the development of new chemistries and production methods with higher efficiency and resolution. For current production methods based on contact photolithography, modifications in substrate materials and photoactivated synthesis reagents have provided significant improvements in array performance and information content ( ≥ 4×106 sequences/cm2). An alternative next-generation manufacturing process is also in development, which utilizes photoacid generating polymer films, and automated projection lithography systems. This process has the ability to fabricate arrays with 1 micron feature pitch and smaller, providing an unprecedented sequence density of 108/cm2 and greater.
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87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.15.-v Biomolecules: structure and physical properties

Helium ion microscope invasiveness and imaging study for semiconductor applications

Richard H. Livengood, Yuval Greenzweig, Ted Liang, and Michael Grumski

J. Vac. Sci. Technol. B 25, 2547 (2007); http://dx.doi.org/10.1116/1.2794319 (6 pages) | Cited 6 times

Online Publication Date: 11 December 2007

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The helium ion gas field ion source is a novel charged particle source technology with potentially greater capabilities than electron beam based tools for imaging and nanomachining [ Ward et al., J. Vac. Sci. Technol. B (to be published); Morgan et al., Microscopy Today 14, 24 (2006); V. N. Tondare, J. Vac. Sci. Technol. A 23, 1498 (2005) ]. Potential strengths of He ions over electrons (scanning electron microscopy) are improved thin film surface sensitivity, material contrast, IBIC voltage contrast, Rutherford backscattering material contrast, and the ability to utilize in situ electron charge neutralization on floating substrates which have enhanced charging properties (e.g., masks, photoresist). In this article, the authors will discuss and illustrate examples highlighting several of these attributes. Helium ions, unlike electrons, induce collision events in the material lattice. A critical area to understand is the operating conditions and sample types for which the advantages of helium ion imaging can be realized. Dose, beam current, acceleration voltage, and material interaction are all key areas for modeling and empirical analysis to determine potential invasiveness. The focus of the study presented in this article relates to analyzing the potential lattice damage induced in silicon substrate for ion doses ranging from 1×1014 to 5×1015 ions/cm2. This range represents relatively light dose (fast scan) to intermediate dose (slow scan) imaging applications. Findings for doses in this range (as typically used in image applications) show little to no damage to the silicon lattice. This finding also agrees with SRIM [ Ziegler et al., The Stopping and Ranges of Ions in Solids (Pergamon, New York, 1985), Vol. 1 ] Monte Carlo simulations, which predict that helium ion induced defect densities to be 4×1017 to 4×1018 dis/cm3. However, it is clear that with higher doses, defect densities will increase to a level that may be invasive to device structures (e.g., metal oxide semiconductor field effect transistor channels or gate oxides).
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68.37.Vj Field emission and field-ion microscopy
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
61.80.Jh Ion radiation effects
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Dry etch release processes for micromachining applications

Tongtong Zhu, Petros Argyrakis, Enrico Mastropaolo, Kin Kiong Lee, and Rebecca Cheung

J. Vac. Sci. Technol. B 25, 2553 (2007); http://dx.doi.org/10.1116/1.2794074 (5 pages) | Cited 4 times

Online Publication Date: 11 December 2007

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The authors report on the comparative study of two dry etch processes for polysilicon sacrificial layer release using vapor phase xenon difluoride (XeF2) continuous etching and inductively coupled plasma (ICP) etching with sulfur hexafluoride (SF6) gas. Test structures of 0.5 μm thick polysilicon have been patterned and etch channels varying in widths from 1 to 500 μm have been fabricated successfully for the purpose of comparison. The influence of etch pressure, aperture opening size, and ICP etch power on the undercut etching rate as well as selectivity between mask and substrate have been studied. It has been possible to achieve an undercut etch rate of up to 11.6 μm/min under a pressure of 3 Torr in XeF2 etch gas, while for SF6 plasma, an undercut etch rate of 2.56 μm/min at 65 mTorr is obtained. Moreover, the optimized process has been employed for the fabrication of silicon carbide (SiC) resonators.
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52.77.Bn Etching and cleaning
81.16.Rf Micro- and nanoscale pattern formation
85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning

Mechanical properties of suspended graphene sheets

I. W. Frank, D. M. Tanenbaum, A. M. van der Zande, and P. L. McEuen

J. Vac. Sci. Technol. B 25, 2558 (2007); http://dx.doi.org/10.1116/1.2789446 (4 pages) | Cited 79 times

Online Publication Date: 11 December 2007

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Using an atomic force microscope, we measured effective spring constants of stacks of graphene sheets (less than 5) suspended over photolithographically defined trenches in silicon dioxide. Measurements were made on layered graphene sheets of thicknesses between 2 and 8 nm, with measured spring constants scaling as expected with the dimensions of the suspended section, ranging from 1 to 5 N/m. When our data are fitted to a model for doubly clamped beams under tension, we extract a Young’s modulus of 0.5 TPa, compared to 1 TPa for bulk graphite along the basal plane, and tensions on the order of 10−7 N.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
68.60.Bs Mechanical and acoustical properties
62.25.-g Mechanical properties of nanoscale systems

Surface gate and contact alignment for buried, atomically precise scanning tunneling microscopy–patterned devices

Martin Fuechsle, Frank J. Rueß, Thilo C. G. Reusch, Mladen Mitic, and Michelle Y. Simmons

J. Vac. Sci. Technol. B 25, 2562 (2007); http://dx.doi.org/10.1116/1.2781512 (6 pages) | Cited 5 times

Online Publication Date: 11 December 2007

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The authors have developed a complete electron beam lithography (EBL)-based alignment scheme for making multiterminal Ohmic contacts and gates to buried, planar, phosphorus-doped nanostructures in silicon lithographically patterned by scanning tunneling microscopy (STM). By prepatterning a silicon substrate with EBL-defined, wet-etched registration markers, they are able to align macroscopic contacts to buried, conducting STM-patterned structures with an alignment accuracy of ∼ 100 nm. A key aspect of this alignment process is that, by combining a circular marker pattern with step engineering, they are able to reproducibly create atomically flat, step-free plateaus with a diameter of ∼ 300 nm so that the active region of the device can be patterned on a single atomic Si(100) plane at a precisely known position. To demonstrate the applicability of this registration strategy, they show low temperature magnetoresistance data from a 50 nm wide phosphorus-doped silicon nanowire that has been STM-patterned onto a single atomically flat terrace.
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85.40.Hp Lithography, masks and pattern transfer
85.30.-z Semiconductor devices
85.35.-p Nanoelectronic devices

Novel coexisted sol-gel derived poly-Si-oxide-nitride-oxide-silicon type memory

Hsin-Chiang You, Chi-Chang Wu, Fu-Hsiang Ko, Tan-Fu Lei, and Wen-Luh Yang

J. Vac. Sci. Technol. B 25, 2568 (2007); http://dx.doi.org/10.1116/1.2794327 (4 pages) | Cited 1 time

Online Publication Date: 11 December 2007

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The authors use a very simple sol-gel spin coating method at 900 °C and 1 min rapid thermal annealing to fabricate three different poly-Si-oxide-nitride-oxide-silicon-type flash memories. The memory windows estimated from the curve of drain current versus applied gate voltage are 3, 3.3, and 4 V for (i) HfO2 thin film, (ii) hafnium silicate nanocrystal, and (iii) coexisted hafnium silicate and zirconium silicate nanocrystal memory, respectively. Together with the measurement from gate disturbance and drain disturbance on these fabricated devices, the coexisted nanocrystal devices exhibit better reliability than both the thin film type memory and single nanocrystal type memory.
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84.30.Sk Pulse and digital circuits
85.35.-p Nanoelectronic devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Adaptive wiring for 20 nm scale epitaxial silicon Ohmic contacts to silicon nanowires

M. J. Rooks, G. M. Cohen, J. O. Chu, P. M. Solomon, J. A. Ott, R. J. Miller, R. Viswanathan, and W. Haensch

J. Vac. Sci. Technol. B 25, 2572 (2007); http://dx.doi.org/10.1116/1.2798738 (5 pages)

Online Publication Date: 11 December 2007

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Contacts to silicon nanowires are formed by etching holes through a dielectric stack of silicon dioxide and silicon nitride. P-type, in situ doped epitaxial silicon is grown through the holes, then polished flat and silicided or capped by metal to form the device electrodes. This novel contact method has been used in two ways, either in conjunction with adaptive wiring patterned with electron-beam lithography or in a random-connection process with a fixed wiring pattern printed with photolithography. By using the former process, the authors report the fabrication of closely spaced contacts to silicon nanowires. Electron-beam lithography allows the authors to adapt the wiring pattern to each individual target device, and is used to define 20 nm scale contacts. In the latter process, the authors use a technique wherein a large array of contact lines is printed without alignment to individual nanowires. In this case, nanowires are connected by chance, relying on relatively long contact lines with relatively large spacing (down to 200 nm). The authors compare the advantages of the two wiring techniques.
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81.07.Lk Nanocontacts
81.07.Vb Quantum wires
81.65.Cf Surface cleaning, etching, patterning
81.65.Ps Polishing, grinding, surface finishing
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

Hybrid carbon nanotube-silicon complementary metal oxide semiconductor circuits

I. Meric, V. Caruso, R. Caldwell, J. Hone, K. L. Shepard, and S. J. Wind

J. Vac. Sci. Technol. B 25, 2577 (2007); http://dx.doi.org/10.1116/1.2800322 (4 pages)

Online Publication Date: 11 December 2007

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A hybrid technology is presented that combines carbon nanotube field-effect transistors (CNFET) with conventional, silicon-based complementary metal oxide semiconductor (CMOS) technology. The fabrication involves the chemical vapor deposition growth and optical characterization of carbon nanotubes, which are then transferred with lithographic precision onto a commercially fabricated CMOS substrate. In this manner, CNFET devices are fabricated on top of the interconnection network of the CMOS chip, providing a three-dimensional integration of active devices, “sandwiching” wiring, and passives. As a demonstration of this approach, a simple hybrid CNFET/CMOS inverter is fabricated and tested.
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85.30.Tv Field effect devices
85.40.Sz Deposition technology
85.40.Ls Metallization, contacts, interconnects; device isolation

Hydrogen plasma-enhanced atomic layer deposition of copper thin films

Liqi Wu and Eric Eisenbraun

J. Vac. Sci. Technol. B 25, 2581 (2007); http://dx.doi.org/10.1116/1.2779050 (5 pages) | Cited 10 times

Online Publication Date: 11 December 2007

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The growth of plasma-enhanced atomic layer deposition (PEALD) grown copper films appropriate for nanoscale electronics applications is reported. Self-limiting PEALD copper growth behavior, employing copper(II) acetylacetonate and atomic hydrogen as reactants, was observed. Deposition of continuous layers as thin as 10 nm was achieved on TaN, Ru, and SiO2 substrates in a temperature range between 85 and 135 °C. A copper purity greater than 95 at. %, as measured by Auger electron spectroscopy, was observed. For a 30 nm thick film, PEALD copper resistivity was 5.3 μΩ cm on TaN and 8.8 μΩ cm on Ru. Conformal depositions have been achieved over high aspect ratio ( ∼ 5:1) structures.
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81.05.Bx Metals, semimetals, and alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
52.77.Dq Plasma-based ion implantation and deposition
68.55.A- Nucleation and growth
73.61.At Metal and metallic alloys
79.20.Fv Electron impact: Auger emission

Emission characteristics of Au60Be40 and Au62Si23Be15 liquid metal ion sources

G. A. Schwind and L. W. Swanson

J. Vac. Sci. Technol. B 25, 2586 (2007); http://dx.doi.org/10.1116/1.2781520 (7 pages)

Online Publication Date: 11 December 2007

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The angular current densities, relative abundance, and total energy distributions (TEDs) of the various ion species from the binary Au60Be40 and ternary Au62Si23Be15 liquid metal ion sources (LMISs) have been measured. The results support a postionization mechanism for the formation of the various monoatomic M+2 species, while the M+ species are formed by a combination of field evaporation, field ionization, and charge exchange mechanisms. All ion species show an increase in the full width at half maximum of the TEDs with total emission current, mass, and charge. The dominant monoatomic species at 5 μA total emission current are Au+ (64%), Au+2 (15%), Be+2 (10%), and Be+ (3.2%) for the binary LMIS and Au+ (63%), Au+2 (13%), Si+2 (3.2%), Be+2 (2.1%), and Be+ (0.71%) for the ternary LMIS. The predicted beam sizes for Au+2 and Be+2 for the binary LMIS at a beam current of 5 pA in a typical focusing column are 15 and 8 nm, respectively.
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79.70.+q Field emission, ionization, evaporation, and desorption
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Fabrication of ultrahigh aspect ratio freestanding gratings on silicon-on-insulator wafers

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

J. Vac. Sci. Technol. B 25, 2593 (2007); http://dx.doi.org/10.1116/1.2779048 (5 pages) | Cited 12 times

Online Publication Date: 11 December 2007

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The authors report a silicon-on-insulator (SOI) process for the fabrication of ultrahigh aspect ratio freestanding gratings for high efficiency x-ray and extreme ultraviolet spectroscopy. This new grating design will lead to blazed transmission gratings via total external reflection on the grating sidewalls for x rays incident at graze angles below their critical angle (about 1°–2°). This critical-angle transmission (CAT) grating combines the alignment and figure insensitivity of transmission gratings with high broadband diffraction efficiency, which traditionally has been the domain of blazed reflection gratings. The required straight and ultrahigh aspect ratio freestanding structures are achieved by anisotropic etching of ⟨110⟩ SOI wafers in potassium hydroxide (KOH) solution. To overcome structural weakness, chromium is patterned as a reactive ion etch mask to form a support mesh. The grating with period of 574 nm is written by scanning-beam interference lithography (SBIL) which is based on the interference of phase-locked laser beams. Freestanding structures are accomplished by etching the handle and device layers in tetramethylammonium hydroxide and KOH solution, respectively, followed by hydrofluoric acid etching of the buried oxide. To prevent collapse of the high aspect ratio structures caused by water surface tension during drying, the authors use a supercritical point dryer after dehydration of the sample in pure ethanol. The authors have successfully fabricated 574 nm period freestanding gratings with support mesh periods of 70, 90, and 120 μm in a 10 μm thick membrane on ⟨110⟩ SOI wafers. The size of a single die is 10×12 mm2 divided into four 3×3.25 mm2 windows. The aspect ratio of a single grating bar achieved is about 150, as required for the CAT grating configuration.
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42.79.Dj Gratings

Soft x-ray imaging of spin dynamics at high spatial and temporal resolution

Brooke L. Mesler, Peter Fischer, Weilun Chao, Erik H. Anderson, and Dong-Hyun Kim

J. Vac. Sci. Technol. B 25, 2598 (2007); http://dx.doi.org/10.1116/1.2806977 (5 pages) | Cited 7 times

Online Publication Date: 11 December 2007

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Soft x-ray microscopy provides element specific magnetic imaging with a spatial resolution down to 15 nm. At XM-1, the full-field soft x-ray microscope at the Advanced Light Source in Berkeley, a stroboscopic pump and probe setup has been developed to study fast magnetization dynamics in ferromagnetic elements with a time resolution of 70 ps, which is set by the width of the x-ray pulses from the synchrotron. Results obtained from a 2 μm×4 μm×45 nm rectangular permalloy sample exhibiting a seven domain Landau pattern reveal dynamics up to several nanoseconds after the exciting magnetic field pulse. Domain wall motion, a gyrotropic vortex motion, and a coupling between vortices in the rectangular geometry are observed.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
75.50.Bb Fe and its alloys

Ultrathin magnetic multilayer films for low-field microwave notch filters

Bijoy K. Kuanr, Alka V. Kuanr, T. Fal, R. E. Camley, and Z. Celinski

J. Vac. Sci. Technol. B 25, 2603 (2007); http://dx.doi.org/10.1116/1.2801887 (4 pages)

Online Publication Date: 11 December 2007

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Microwave filters that use thin films of ferromagnetic metals are now being established as a valuable option compared to yttrium iron garnet based filters due to their higher frequency response. In these filters the signal propagation is inhibited over a wide frequency band, depending on the applied dc magnetic field. However, the continuous application of an applied field to achieve an operating frequency in the higher gigahertz range increases the power consumption of the device. The main contribution of this article is to provide techniques which significantly boost the operating frequency of notch filters in zero or very low applied magnetic fields. To do this, the authors fabricated high quality epitaxial Fe films which are interlayer exchange coupled through nonmagnetic Si layer of different thicknesses. The films were used in flip-chip geometry on top of a Cu-coplanar waveguide to create band-stop filters. In contrast to filters based on Fe alone, the multilayer filters can operate above 25 GHz with a very small applied magnetic field. The observed upshift in frequency is attributed to the induced interlayer exchange coupling energy mediated through the nonmagnetic Si layer between the two Fe layers. These frequency shifts are in good agreement with theoretical calculations of the ferromagnetic resonance modes taking into account anisotropy, exchange, and Zeeman energies.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
84.40.Az Waveguides, transmission lines, striplines

Study of fluorine bombardment on the electrical properties of AlGaN/GaN heterostructures

Anirban Basu, Vipan Kumar, and Ilesanmi Adesida

J. Vac. Sci. Technol. B 25, 2607 (2007); http://dx.doi.org/10.1116/1.2789444 (4 pages) | Cited 1 time

Online Publication Date: 11 December 2007

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The effects of fluorine ion bombardment on the channel transport properties of AlGaN/GaN heterostructures have been investigated. Ion bombardment of the heterostructure was carried out within a CF4 plasma in a reactive ion etching system at various self-bias voltages. Hall mobility and sheet electron concentration for the two-dimensional electron gas showed strong dependence on bombardment duration and postbombardment annealing. A systematic study of the behavior of implanted fluorine ions in the annealed heterostructure reveals diffusion followed by accumulation of the ions at the heterointerface. Implications of such behavior on the performance of high electron mobility transistors are briefly discussed.
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81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
61.72.uj III-V and II-VI semiconductors

Prospects for nanowire sculptured-thin-film devices

Sean M. Pursel and Mark W. Horn

J. Vac. Sci. Technol. B 25, 2611 (2007); http://dx.doi.org/10.1116/1.2787749 (5 pages) | Cited 9 times

Online Publication Date: 11 December 2007

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In this paper, we introduce a modified serial bideposition (SBD) method, asymmetric SBD, for depositing sculptured thin films (STFs) which may allow added control of the surface area, void accessibility, and optical properties of STFs. Results on using TiO2 STFs with spectral-hole filters as vapor/liquid sensors are presented. In addition, solar cell, microcavity, biological sensing, and bioabsorption devices utilizing STFs are discussed.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
42.79.Ci Filters, zone plates, and polarizers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
84.60.Jt Photoelectric conversion
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth

First-principles calculation of electronic structure and magnetic properties of copper adsorbed polar-ZnO surface

Yoon-Suk Kim and Yong-Chae Chung

J. Vac. Sci. Technol. B 25, 2616 (2007); http://dx.doi.org/10.1116/1.2806962 (3 pages)

Online Publication Date: 11 December 2007

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The electronic structure and magnetic properties of a Cu adsorbed polar-ZnO surface system were investigated using the ab initio projector-augmented-wave method. It is found that the H3 site is the most stable adsorption site of Cu adsorbed polar-ZnO surfaces with stable ferromagnetism. The Zn-terminated ZnO:Cu surface system (H3 site adsorption) is predicted to have a half-metallic property and stable ferromagnetism of 0.72 μB magnetic moments.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
82.53.St Femtochemistry of adsorbed molecules
71.15.-m Methods of electronic structure calculations
71.20.Nr Semiconductor compounds
75.30.Cr Saturation moments and magnetic susceptibilities

Nickel nanowires for planer microwave circuit applications and characterization

Ryan L. Marson, Bijoy K. Kuanr, Sanjay R. Mishra, R. E. Camley, and Z. Celinski

J. Vac. Sci. Technol. B 25, 2619 (2007); http://dx.doi.org/10.1116/1.2801964 (5 pages) | Cited 5 times

Online Publication Date: 11 December 2007

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The dynamic properties of uniform one-dimensional arrays of high aspect ratio nickel nanowires have been studied by ferromagnetic resonance (FMR) technique at 24 GHz. The fundamental magnetic parameters such as spontaneous magnetization, gyromagnetic ratio (γ), and magnetic anisotropies of the nanowires are derived from the angular variation of resonance field Hr(θH) positions. The effective fields of the nanowire system were observed to decrease with increasing length of the nanowires. Further, the use of nanowires as a tunable stop-band notch filter in a coplanar waveguide geometry has been assessed. The stop-band frequency (fr) is observed to be tunable up to 14 GHz with an applied field (H) of up to 4 kOe. The kink in the fr(H) data gives the measure of the effective field (Heff) of the nanowire system. The theoretical fitting of fr(H) data to resonance relation yields values of Heff and γ which are a little higher than the conventional FMR results.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
84.40.Az Waveguides, transmission lines, striplines

In situ visualization of local electric field in an ultrasharp tungsten emitter under a low voltage scanning transmission electron microscope

Jun-Ichi Fujita, Yuta Ikeda, Satoshi Okada, Kodai Higashi, Shotaro Nakasawa, Masahiko Ishida, and Shinji Matsui

J. Vac. Sci. Technol. B 25, 2624 (2007); http://dx.doi.org/10.1116/1.2800332 (4 pages) | Cited 4 times

Online Publication Date: 11 December 2007

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Field emissions from a multiwalled carbon nanotube embedded in a conventional electropolished tungsten probe soften the tip of the tungsten by Joule heating, and the Coulomb attraction to the nanotube finery pulled from the tungsten tip resulted in an ultrasharp apex of the tungsten probe having a curvature of 5 nm radius. We also found that scanning transmission electron microscopy (STEM), when operated at low accelerating voltage, can visualize a local electric field at the probe apex. This local electric field, induced around the probe apex, deflected the primary electron beam of the STEM, producing a dark circular shadow surrounding the probe apex in the STEM image. The authors analyzed the distribution of this local field using a simple Rutherford scattering model.
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79.70.+q Field emission, ionization, evaporation, and desorption
back to top Photonics

Fabrication and tuning of nanoscale metallic ring and split-ring arrays

A. K. Sheridan, A. W. Clark, A. Glidle, J. M. Cooper, and D. R. S. Cumming

J. Vac. Sci. Technol. B 25, 2628 (2007); http://dx.doi.org/10.1116/1.2794328 (4 pages) | Cited 6 times

Online Publication Date: 11 December 2007

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Metallic structures with dimensions smaller than the wavelength of light demonstrate optical properties which depend strongly on the nanoparticle size, shape, and interparticle spacing. The optical properties are caused by the excitation of localized surface plasmon resonances that lead to strong enhancement and confinement of the optical field and can be exploited for many applications including surface-enhanced Raman spectroscopy, near-field scanning optical microscopy, and negative refractive index materials. In order to fully exploit the properties of these structures, both a highly reproducible and flexible fabrication technique and an in-depth understanding of the optical properties are needed. In this article, the authors demonstrate the fabrication of arrays of gold rings and split rings on glass using electron beam lithography. Electron beam lithography allows not only precise control of the size, shape, and spacing of the arrays but also the scope to design novel shapes at will. We characterize these arrays using polarization dependent spectroscopy. The structures can support multiple plasmon resonances, demonstrating that excellent uniformity across the array is achieved. These resonances are further characterized using a finite difference time domain method to model the electric field distribution around the ring structures.
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81.16.Nd Micro- and nanolithography
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.68.+m Optical properties of surfaces
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.86.+b Optical workshop techniques

Fabrication of two dimensional GaN nanophotonic crystals (31)

Bifeng Rong, Huub W. M. Salemink, Erik M. Roeling, Rob van der Heijden, Fouad Karouta, and Emile van der Drift

J. Vac. Sci. Technol. B 25, 2632 (2007); http://dx.doi.org/10.1116/1.2794066 (5 pages) | Cited 4 times

Online Publication Date: 11 December 2007

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The authors have investigated chlorine based inductively coupled plasma etching of GaN by using different gas mixtures of Ar, Cl2, and N2. The etch mechanism and N2 role have been studied. We found that both ion energy and ion current density are important. The N2 plays a multiple role in etching GaN, chemical reaction, and ion bombardment. A reliable process to fabricate GaN nanophotonic crystals has been developed. Plasma conditions have been optimized toward a balance of ion current density, ion energy, and chemical species density. As a result, flat bottom, anisotropic photonic crystal with a = 215 nm d = 129 nm has been fabricated at an etch rate of 320 nm/min and an etch depth of 650 nm. For comparison, an etch rate of 530 nm/min has been obtained in etching trench lines down to 1.61 μm deep with a width of 500 nm. The developed process has been used to fabricate GaN photonic crystal (PC) waveguides for 1.55 μm wavelength. Transmission measurements reveal the ΓM stop band in hole type PC and illustrate the feasibility of the fabrication process.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.-c Methods of micro- and nanofabrication and processing
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

Semitransparent Cu electrode on a flexible substrate and its application in organic light emitting diodes

Myung-Gyu Kang and L. Jay Guo

J. Vac. Sci. Technol. B 25, 2637 (2007); http://dx.doi.org/10.1116/1.2801873 (5 pages) | Cited 13 times

Online Publication Date: 11 December 2007

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A semitransparent nanomesh Cu electrode on a polyethylene terephthalate (PET) substrate using metal transfer from a polydimethylsiloxane (PDMS) stamp and nanoimprint lithography is reported. A nanoscale dense mesh pattern is replicated by using a high modulus PDMS stamp. It is found that a uniform pressure of 30 psi and a temperature of 100 °C are needed for the transfer of the Cu mesh structure from the PDMS stamp onto the PET substrate. A fabricated semitransparent Cu electrode exhibits high transmittance in the visible range and good electrical conductivity. The authors show that the transmittance is increased by reducing the linewidth of the mesh pattern and an average transmittance of 75% is achieved. An organic light emitting diode on a flexible substrate is fabricated to demonstrate the potential use of a semitransparent Cu electrode as a transparent conducting electrode.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.05.Bx Metals, semimetals, and alloys
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
85.60.Jb Light-emitting devices

Photoluminescence enhancement in metallic nanocomposite printable polymer

V. Reboud, N. Kehagias, M. Striccoli, T. Placido, A. Panniello, M. L. Curri, M. Zelsmann, F. Reuther, G. Gruetzner, and C. M. Sotomayor Torres

J. Vac. Sci. Technol. B 25, 2642 (2007); http://dx.doi.org/10.1116/1.2789445 (3 pages) | Cited 5 times

Online Publication Date: 11 December 2007

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A 1.7-fold enhancement in the spontaneous emission intensity of dye chromophore loaded in a printable polymer is achieved by coupling the dye emission to surface plasmons of metallic nanoparticles. The nanocomposite material, embossed into arrays of wires by nanoimprint lithography process, shows good imprint properties. The results prove the potential of the prepared luminescent functional materials for micro- and nanofabrication and suggest the use of nanocomposite materials in prospective nanoplasmonic applications.
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78.55.Kz Solid organic materials
73.22.Lp Collective excitations
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.07.Bc Nanocrystalline materials
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

Fabrication of high aspect ratio Si nanogratings with smooth sidewalls for a deep UV-blocking particle filter

Pran Mukherjee, Myung-Gyu Kang, Thomas H. Zurbuchen, L. Jay Guo, and Fred A. Herrero

J. Vac. Sci. Technol. B 25, 2645 (2007); http://dx.doi.org/10.1116/1.2804612 (4 pages) | Cited 4 times

Online Publication Date: 11 December 2007

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To measure space plasmas and neutral particles one must filter out high-energy ultraviolet photons that would increase background count or damage sensors. To enable sensitive neutral particle measurements, a photon-to-particle rejection rate of 1014 is desired, far exceeding the requirements of prior filters. The authors propose a high-aspect ratio Si grating with densely packed, sub-100 nm slits. In this article, the authors report the development of a new technique for fabricating sturdy, self-supported transmission gratings in silicon using nanoimprint lithography and deep reactive ion etching, resulting in grating slits with scalloping under 7 nm and high (8.5:1) aspect ratios.
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42.79.Dj Gratings
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Ci Filters, zone plates, and polarizers

V-groove plasmonic waveguides fabricated by nanoimprint lithography

Irene Fernandez-Cuesta, Rasmus Bundgaard Nielsen, Alexandra Boltasseva, Xavier Borrisé, Francesc Pérez-Murano, and Anders Kristensen

J. Vac. Sci. Technol. B 25, 2649 (2007); http://dx.doi.org/10.1116/1.2779041 (5 pages) | Cited 7 times

Online Publication Date: 11 December 2007

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Propagation of channel plasmon-polariton modes in the bottom of a metal V groove has been recently demonstrated. It provides a unique way of manipulating light at nanometer length scale. In this work, we present a method based on nanoimprint lithography that allows parallel fabrication of integrated optical devices composed of metal V grooves. This method represents an improvement with respect to previous works, where the V grooves were fabricated by direct milling of the metal, in terms of robustness and throughput.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
81.16.Nd Micro- and nanolithography
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

58 nm half-pitch plastic wire-grid polarizer by nanoimprint lithography

Lei Chen, Jian Jim Wang, Frank Walters, Xuegong Deng, Mike Buonanno, Stephen Tai, and Xiaoming Liu

J. Vac. Sci. Technol. B 25, 2654 (2007); http://dx.doi.org/10.1116/1.2801967 (4 pages)

Online Publication Date: 11 December 2007

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Plastic nanowire-grid polarizers based on small period, 58 and 75 nm half-pitch, Al gratings are fabricated and studied. Al gratings are made by coating Al on the polymer grating sidewalls at oblique angles. The nanopolymer gratings on plastic film over large area are made by nanoimprint lithography. By optimizing the grating period, grating linewidth, Al coating depth, and thickness, excellent maximum transmittance (Tmax) (80%–90%) and extinction ratio ( ∼ 30 dB) are achieved.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Dj Gratings
42.82.Cr Fabrication techniques; lithography, pattern transfer

Optimization of hydrogen silsesquioxane for photonic applications

C. W. Holzwarth, T. Barwicz, and Henry I. Smith

J. Vac. Sci. Technol. B 25, 2658 (2007); http://dx.doi.org/10.1116/1.2787832 (4 pages) | Cited 8 times

Online Publication Date: 11 December 2007

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Increasingly complex electronic-photonic integrated circuits, based on strong confinement of photons, has increased the importance of low-refractive-index overcladding materials. In addition to providing high optical transparency and sufficient thickness for adequate optical insulation, overcladding materials must also fill in high-aspect-ratio gaps, withstand high temperatures, and provide acceptable thermal conductivity. Previously, all of these qualities were simultaneously achievable only through tetraethylorthosilicate (TEOS)-based deposition of SiO2. Here, the authors demonstrate how hydrogen silsesquioxane (HSQ) can be used as a lower-cost alternative to TEOS, with superior gap-filling and self-planarization properties. HSQ is a spin-on dielectric designed for low-k applications. The standard curing process for HSQ results in a low-k porous film that is not adequate for photonic applications. It shows very low thermal conductivity, optical absorption due to Si–H bonds, and high intrinsic tensile stress, which limits the achievable layer thickness. By optimizing the HSQ curing process, they eliminate these shortcomings while maintaining HSQ’s excellent gap-filling and self-planarization properties. They demonstrate that HSQ layers can be made almost arbitrary thick, with no detectable Si–H bonds while easily filling sub-100‐nm gaps. They demonstrate Si3N4 optical microring resonators with quality factor of 240 000, consistent with the best published values using TEOS as an overcladding.
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42.70.Qs Photonic bandgap materials
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.79.Wc Optical coatings
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Jw Organic compounds, polymers

Membrane stacking: A new approach for three-dimensional nanostructure fabrication

Amil A. Patel and Henry I. Smith

J. Vac. Sci. Technol. B 25, 2662 (2007); http://dx.doi.org/10.1116/1.2799979 (3 pages) | Cited 3 times

Online Publication Date: 11 December 2007

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Future applications of nanotechnology, including integrated photonics, will require new three-dimensional (3D) fabrication techniques beyond those employed by the semiconductor industry. The authors investigate membrane stacking as a potential avenue for fabricating photonic crystals and other 3D structures with high yield. They fabricated membranes in silicon nitride with freestanding photonic structures and investigated the technology for stacking them.
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82.45.Mp Thin layers, films, monolayers, membranes
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
42.70.Qs Photonic bandgap materials
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