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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 67 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 8 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) | Cited 1 time

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 10 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 3 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 5 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 2 times

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 13 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 9 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 7 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 8 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 2 times

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 32 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 7 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 18 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 2 times

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 10 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 24 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 5 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 25 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 56 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 6 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 4 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 22 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 7 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 4 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