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Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

Issue 6 • Date Nov 2007

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Displaying Results 1 - 25 of 181
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Extreme ultraviolet lithography: A review

    Page(s): 1743 - 1761
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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 capab- - ility to extend to the next technology node. View full abstract»

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  • Effect of process parameters on via formation in Si using deep reactive ion etching

    Page(s): 1762 - 1770
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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. View full abstract»

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

    Page(s): 1771 - 1775
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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. View full abstract»

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

    Page(s): 1776 - 1784
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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 [111] direction across the steps. View full abstract»

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

    Page(s): 1785 - 1788
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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 Vm, the field emission current of 23.6 μA was obtained from an emitting surface of 0.012 cm2. View full abstract»

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  • Development of chemical-mechanical polished high-resolution zone plates

    Page(s): 1789 - 1793
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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. View full abstract»

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

    Page(s): 1794 - 1798
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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. View full abstract»

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

    Page(s): 1799 - 1803
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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 Al2O3TiO2 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 Al2O3TiO2 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. View full abstract»

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  • Critical parameter determination of sonic flow controller diamond microtubes and micronozzles

    Page(s): 1804 - 1807
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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. View full abstract»

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

    Page(s): 1808 - 1813
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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. View full abstract»

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  • Influence of RuO2 nanoparticles on electron emission from carbon nanotubes

    Page(s): 1814 - 1818
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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 Vm 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. View full abstract»

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

    Page(s): 1819 - 1822
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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. View full abstract»

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  • Growth of ZnSe nanowires by pulsed-laser deposition

    Page(s): 1823 - 1826
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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. View full abstract»

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  • Fabrication of periodic microstructures on flexible polyimide membranes

    Page(s): 1827 - 1831
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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. View full abstract»

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  • Evolution of surface morphology of GaN thin films during photoelectrochemical etching

    Page(s): 1832 - 1835
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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. View full abstract»

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

    Page(s): 1836 - 1841
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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. View full abstract»

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

    Page(s): 1842 - 1846
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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. View full abstract»

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

    Page(s): 1847 - 1852
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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 32S+ 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. View full abstract»

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

    Page(s): 1853 - 1858
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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. View full abstract»

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

    Page(s): 1859 - 1866
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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. View full abstract»

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  • Zero-dimensional analysis for discharge characteristics

    Page(s): 1867 - 1869
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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. View full abstract»

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  • Highly selective zero-bias plasma etching of GaN over AlGaN

    Page(s): 1870 - 1874
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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. View full abstract»

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

    Page(s): 1875 - 1881
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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. View full abstract»

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Aims & Scope

The Journal of Vacuum Science and Technology B is devoted to reports of original research, review articles, and Critical Review articles.

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Gary E. McGuire
International Technology Center