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

Issue 2 • Date Mar 2006

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Displaying Results 1 - 25 of 109
  • Issue Cover

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

    Page(s): toc1
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  • Mo/Al/Mo/Au Ohmic contact scheme for AlxGa1-xN/GaN high electron mobility transistors annealed at 500 °C

    Page(s): L16 - L18
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    Low-resistance Ohmic contacts on Al0.3Ga0.7N/GaN high electron mobility transistors (HEMTs) were formed with a Mo/Al/Mo/Au metallization scheme which was annealed at a relatively low temperature of 500 °C. A contact resistance of 0.11±0.05 Ω mm and a specific contact resistivity of 2.63×10-7 Ω cm2 were achieved. This represents the best low-temperature-annealed Ohmic contacts on GaN-based HEMTs achieved to date. View full abstract»

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  • Innovative approach for replicating micropatterns in a conducting polymer

    Page(s): L19 - L22
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    An intermediate layer lithography (ILL) method is developed in this work to replicate micropatterns in a conducting polymer. In the ILL, an intermediate layer of a nonconducting polymer material is introduced between a silicon substrate and a conducting polymer layer. Subsequently, the conducting polymer film is patterned through a mold insertion. We illustrate this method by patterning polypyrrole. The ILL is simple, free of aggressive chemistry, and straightforward to use. In particular, unlike existing lithographic methods, it is suited at creating well-resolved micropatterns of a conducting polymer without degrading material properties of the conducting polymer. In this sense, we believe that the ILL is a promising approach to create conducting polymer patterns. View full abstract»

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  • Electrical conductivity of high aspect ratio trenches in chemical-vapor deposition W technology

    Page(s): 523 - 533
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    This article discusses the resistivity scaling challenges associated with the use of high aspect ratio trenches as W interconnects for the sub-130-nm semiconductor technology node. In this work, chemical-vapor deposition of W is employed to manufacture conductive trenches in a deposition sequence that includes a TiN barrier, a nucleation W, and a bulk W film. Composition, microstructure, resistivity, grain size, and surface roughness for these films are determined in the low thickness range. The results are used to examine the contribution of the electron-surface scattering and grain-boundary scattering to the overall increase in the electrical resistivity observed at film thickness comparable to the electron mean free path. Calculated and measured values for the film resistivity are matched by using a variable coefficient of elastic electron scattering at the grain boundaries. In first approximation, grain-boundary electron scattering is found to be the dominant mechanism and is almost entirely responsible for the resistivity increase in the thickness range studied. By using resistivity data obtained for each film and Kirchhoff’s rule for laminate structures, a simple physical model is used to predict the variation of the trench resistance as a function of geometrical factors such as film thickness and core (seam) size. The agreement between the calculated and measured trench resistances is surprisingly good in view of the several simplification assumptions that are made and that no fitting parameters are used. The proposed model predicts reasonably well the sensitivity of the trench resistance with respect to the TiN film thickness. However, the impact of the nucleation W layer is overestimated, which suggests possible unaccounted interactions, related to structural or morphological changes in the bulk W. It is concluded that the trench conductivity is already significantly size limited for critical dimensions in the sub-130-nm range. The control of the fi- - lm bulk resistivity and grain-boundary engineering of the conducting materials is therefore identified as the most important pathway for achieving desired electrical properties in conducting trenches filled by standard chemical-vapor deposition W technology. View full abstract»

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  • Formation of body-centered-cubic tantalum via sputtering on low-κ dielectrics at low temperatures

    Page(s): 534 - 538
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    Sputtered Ta films (60 nm) were deposited at room temperature onto selected substrates, including silicon, SiO2, porous methyl silsesquioxane (porous MSQ), parylene-N (Pa-N) caulked porous MSQ, benzocyclobutene (BCB), and SiLK layers. It was observed that the Ta structure after deposition mainly depends on the underlayer surface chemistry. β-Ta with a resistivity of ∼130–160 μΩ cm and an average grain size of ∼20 nm was observed after sputter depositing 60-nm-thick Ta films onto the oxygen-rich materials of native oxide of Si, SiO2, and porous MSQ. α-Ta with a much lower resistivity (∼35 μΩ cm) and an average grain size of ∼16 nm was observed after sputter deposition of Ta onto a substrate with a 4-nm-thick hydrocarbon Pa-N film on porous MSQ. α-Ta was also formed when sputter depositing on the hydrocarbon BCB and SiLK low-κ dielectrics. The lattice constants of the α-Ta films were slightly larger (3.310–3.351 Å) than those of the bulk Ta (3.305 Å). View full abstract»

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  • Nanofabrication module integrated with optical aligner

    Page(s): 539 - 542
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    In this article, we describe a simple module that can be integrated with a commercial optical aligner for nanoimprint lithography or optical lithography. The module provides a convenient low-cost technique to transform an optical aligner for microfabrication into a nanofabrication machine. This combination enables the creation of nanoscale features and alignment of multiple-layer lithographic patterns with submicron accuracy within one instrument. Imprinting of 30 nm half-pitch lines has been demonstrated by the module, as well as submicron alignment. The module has also been used to fabricate micro- and nanoscale patterns simultaneously by the combination of optical and imprint lithography. View full abstract»

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  • Hot-wire chemical-vapor-deposited nanometer range a-SiC:H diffusion barrier films for ultralarge-scale-integrated application

    Page(s): 543 - 546
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    Hydrogenated amorphous silicon-carbon alloy thin films (a-SiC:H) deposited from C2H2 and SiH4 by the hot-wire chemical-vapor deposition (HWCVD) technique on low-k hydrogen silsesquioxane (HSQ) layers show effective barrier properties against Cu diffusion. These a-SiC:H films with different thicknesses were deposited on HSQ films and the leakage current in a metal-insulator-semiconductor device structure such as Cu/a-SiC:H/HSQ/Si/Al was determined. It was observed that HWCVD a-SiC:H acts as a very efficient diffusion barrier layer on HSQ with an effective dielectric constant of the combined stack much lower than that of SiO2. Secondary-ion-mass spectroscopy analysis indicates that an a-SiC:H film of less than 10 nm would provide the desired barrier effect. View full abstract»

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  • Depth resolution studies in SiGe delta-doped multilayers using ultralow-energy O2+ secondary-ion-mass spectrometry

    Page(s): 547 - 553
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    Improvements in depth resolution using low primary ion energy secondary-ion-mass spectrometry have been demonstrated. This comprehensive study is done using a wide range of impact angles at ultralow energies. In this work, using Ge delta-doped Si samples, we confirm that depth resolution can be improved by lowering the primary ion impact energy at ultralow energy. By varying the angle of incidence from 0° to 70°, we noted that a better depth resolution is achievable not only at normal incidence but over a wider range of impact angles as the probe energy is reduced. The best depth resolution was observed using Ep∼250 eV and θ∼0°–40° with full width at half maximum (FWHM) ∼1.5 nm and λd≪1 nm throughout the depth profiled (120 nm). Using Ep∼500 eV, we observed a good depth resolution of FWHM ∼2.2 nm and λd∼1.2 nm throughout the depth evaluated at θ∼0°–30°. Using Ep∼1 keV, a good depth resolution of FWHM ∼3.5 nm and λd∼1.8 nm was observed at θ∼0°–20°. The dynamic range was also evaluated, the best being achieved at θ∼50° for Ep∼250 eV, θ∼40° for Ep∼500 eV, and at θ∼30° for Ep∼1 keV. Contributions from roughening and atomic mixing to the depth resolution of δ layers are discussed using the mixing-roughness-information depth model. View full abstract»

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  • High-resolution three-dimensional reconstruction: A combined scanning electron microscope and focused ion-beam approach

    Page(s): 554 - 561
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    The ability to obtain three-dimensional information has always been important to gain insight and understanding into material systems. Three-dimensional reconstruction often reveals information about the morphology and composition of a system that can otherwise be obscured or misinterpreted by two-dimensional images. In this article, we describe tomographic measurements with 10 nm scale resolution, combining focused ion-beam processing with field-emission scanning electron microscopy to obtain a series of high-resolution two-dimensional cross-sectional images. The images were then concatenated in a computer and interpolated into three-dimensional space to assess and visualize the structure of the material. The results of this research demonstrate the use of tomographic reconstruction of SiSi/Ge and θ Al2Cu samples to reproduce the three-dimensional morphology with sub-10 nm resolution. View full abstract»

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  • Microelectronically fabricated LiCoO2/SiO2/polycrystalline-silicon power cells planarized by chemical mechanical polishing

    Page(s): 562 - 569
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    Monolithic integration of different electronic circuit elements onto a single chip is beneficial for the purpose of reducing overall system cost as well as improving performance and reliability. Integrating a power unit onto a silicon chip requires the implementation of a thin-film solid-state battery that is compatible with existing silicon integrated circuit technology in terms of manufacturing methods, materials, and performance. One of the materials in the battery industry, studied by us, is silicon dioxide (SiO2). The high level of process control for thin SiO2 layers which is a result of microelectronic advances, its insulating properties, and its past reported permeability to light ions have motivated us to exploit SiO2 as a solid-state electrolyte in our integrated thin-film battery. This SiO2 electrolyte layer is thermally grown from an amorphous silicon (a-Si) thin layer deposited on doped polycrystalline silicon (polysilicon) which serves as the anode against a thin-film-sputtered LiCoO2 cathode. We have fabricated and characterized ultrathin solid-state thin-film power cells consisting of LiCoO2, SiO2, and polysilicon. Cells containing an ultrathin SiO2 lithium-free electrolyte with a thickness range of 7–40 nm and active-area sizes of 5×5, 2×2, 1×1, and 0.5×0.5 mm2 were created using established microelectronics processing and expertise. Ultrathin cells require smooth surfaces (nanometer-scale roughness) as opposed to higher roughness encountered in bulk batteries and microbatteries. To ensure a very thin and flat electrolyte, this work demonstrates the implementation of a planarization step by using chemical mechanical polishing (CMP) in the fabrication of the integrated solid-state thin-film lithium-ion battery. Polishing the polysilicon layer reduced its 1×1 μm2 root-mean-square roughness from 8.06 to 0.53 nm and led to smoother interfaces and to higher quality of the SiO2 grown on top of it. The cells were charged and discharged using conventional microelectronic electrical testing equipment and exhibited improved performance when prepared with the additional CMP planarization step. Up to 40% of the charge was retrieved from the planarized cells compared to a maximum of 14.5% retrieved from the nonplanarized cells. The open circuit voltage (VOC) of the LiCoO2/SiO2/polysilicon cell was estimated by comparing the initial charge voltage values obtained with different electrolyte thicknesses and was found to be 2.19±0.02 V. The results presented in this work show the importance of interfacial quality in the process of moving to integrated power on a chip. View full abstract»

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  • Impact of supercritical CO2 drying on roughness of hydrogen silsesquioxane e-beam resist

    Page(s): 570 - 574
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    Surface roughness (SR) and, especially, the closely related line-edge roughness (LER) of nanostructures are important issues in advanced lithography. In this study, the origin of surface roughness in the negative tone electron resist hydrogen silsesquioxane is shown to be associated with polymer aggregate extraction not only during resist development but also during resist drying. In addition, the impact of exposure dose and resist development time on SR is clarified. Possibilities to reduce SR and LER of nanostructures by optimizing resist rinsing and drying are evaluated. A process of supercritical CO2 resist drying that delivers remarkable reduction of roughness is presented. View full abstract»

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  • ZrO2 gate dielectrics produced by ultraviolet ozone oxidation for GaN and AlGaN/GaN transistors

    Page(s): 575 - 581
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    We investigated the suitability of ZrO2 as a high-k dielectric for GaN material systems. Thin Zr films (4 nm) were deposited by electron-beam evaporation at room temperature on n-type GaN and Al0.22Ga0.78N (29 nm)/GaN high electron mobility transistor (HEMT) structures. The Zr-coated samples were subsequently oxidized at temperatures in the range of 200–400 °C in an ozone environment. Atomic force microscopy studies after oxidation show that the ZrO2 forms a conformal layer on the underlying GaN template. Cross-section transmission electron microscopy studies showed little intermixing of the ZrO2 with the AlGaN/GaN. The relative dielectric constant of the ZrO2 was determined to be 23. In comparison with HEMTs with bare gates (no dielectric between the gate metal and AlGaN), the HEMTs with ZrO2 showed two to three order of magnitude reduction in gate leakage current. Optimization of the HEMT process on sapphire substrates with ZrO2 under the gates yielded devices with powers of 3.8 W/mm and 58% power-added efficiency at 4 GHz. View full abstract»

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  • Pattern formation by erosion sputtering on GaSb: Transition from dot to ripple formation and influence of impurities

    Page(s): 582 - 586
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    The transition from dot to ripple formation during erosion sputtering was studied as a function of the angle of incidence of the bombarding ions. For GaSb as target material we found that dot structures are obtained for angles smaller than ≈10° with respect to the surface normal. We also observed an influence of impurities on the pattern formation. Small amounts of impurities serve as nucleation centers for the formation of differently shaped nanostructures. In addition, larger fragments of GaSb on the surface influence the pattern formation qualitatively; the fragment is sputtered and the sputtered material redeposited in the vicinity assists the generation of ordered dot structures. With the use of low-energy electron diffraction, we looked at the crystallographic surface properties of the dots. Dots produced with a small fluence (3×1017 cm-2) could be recrystallized by moderate annealing. Higher fluences, however, cause an irreversible amorphization. View full abstract»

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  • Real-time reflectometry-controlled focused-electron-beam-induced deposition of transparent materials

    Page(s): 587 - 591
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    An optical in situ technique is presented for monitoring the optical thickness of transparent materials during focused-electron-beam (FEB)-induced deposition. Three precursors were used: formic acid [HCOOH], tetramethyl orthosilicate [Si(OCH3)4], and titanium nitrate [Ti(NO3)4]. Two of them led to optically interesting materials for ultraviolet or visible applications. By cofocusing a laser (514 nm) with the scanning FEB in the plane of the sample, we continuously monitored the intensity of the reflected light during deposit growth. Periodic intensity variations due to interference effects as function of deposit thickness were observed and interpreted. Complex-refractive indices at the 514 nm wavelength of the materials deposited from HCOOH, Si(OCH3)4, and Ti(NO3)4 were calculated from the periodic signal and were, respectively, 1.51+i0.055, 1.56+i0.14, and 2.19+i0.013. View full abstract»

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  • Self-organized Cu nanowires on glass and Si substrates from sputter etching Cu/substrate interfaces

    Page(s): 592 - 598
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    We have fabricated self-organized ∼30-nm-wide Cu lines on glass and Si(100) substrates by Ar beam etching the Cu/substrate interfaces. We deposited thin Cu layers on the substrates and etched the deposited layer by a neutralized Ar ion beam at a grazing angle of incidence. At the stage when almost all Cu is removed by etching, we have observed Cu lines on the substrate. The lines orientation is entirely controllable through the experiment geometry and the lines are basically similar on glass and Si substrates. By atomistic Monte Carlo simulations, we have demonstrated that the Cu lines result from the self-organized morphologies that develop on Cu surfaces during sputter etching. To better understand ways to control the process we have investigated, by simulations, the line width as a function of the removed depth, surface diffusivity, and Ar beam flux. We have concluded that the sputter etch technique offers a unique opportunity to fabricate controlled arrays of Cu lines on substrates. View full abstract»

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  • Use of SiO2 nanoparticles as etch mask to generate Si nanorods by reactive ion etch

    Page(s): 599 - 603
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    Silicon nanorods 20 nm in diameter are fabricated by reactive ion etch (RIE) to study anisotropy and damage profile in decananometer scale. RIE of gas mixture of SF6/O2 and SF6/CHF3 is tuned to achieve high anisotropy. The gas specie of SF6/O2 can reach 90% anisotropy, 84° taper angle, and 10:1 selectivity when SiO2 is used as the etching mask. The gas species of SF6/CHF3 can reach 95% anisotropy, 87° taper angle, and 10:1 selectivity with Cr as the mask. The fabrication technique of nanorods uses a monolayer of silicon dioxide nanoparticle as the etching mask. The nanorods uniformly cover up the entire 2 in. wafers with high density of 2×1011 cm-2. Surface damageafter the etching process of nanostructures is monitored using the microwave-reflectance photoconductance decay with KOH removal-and-probe technique. Highly damaged silicon is found within a depth of 30 nm and the lightly damaged part extends more than 100 nm. View full abstract»

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  • Three primary color luminescence from natively and thermally oxidized nanocrystalline silicon

    Page(s): 604 - 607
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    Three primary color luminescence from nanocrystalline silicon (nc-Si) prepared by hydrofluoric (HF) acid solution and subsequent oxidation treatments were studied using photoluminescence and Fourier transform infrared spectroscopy measurements. HF-treated nc-Si exhibited stable and strong red luminescence in the air. When the HF-treated nc-Si surface was oxidized by native and/or thermal treatment, the luminescence color varied continuously from red to blue. The reason is the enlargement of the effective band gap energy because of a reduced particle size caused by surface oxidation. The blue and green luminescence of thermally oxidized nc-Si could be distinctly seen in the air with the naked eye. These results suggest that the HF and post-thermal oxidation treatments can realize good stability and higher brightness in the air for three primary color luminescence from nc-Si. View full abstract»

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  • Dopant diffusion modeling for heteroepitaxial SiGe/Si devices

    Page(s): 608 - 612
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    A comprehensive model to predict dopant diffusion (Sb, As, B, and P) in epitaxially strained silicon germanium (SiGe) CMOS transistors is presented. The effect of germanium is primarily comprehended as a change in point defect populations (self-interstitials and vacancies). Our analysis validates this approximation for most dopants (Sb, As, Ge, and P). With germanium concentration, the vacancy population increases much more than the interstitial concentration. Consequently, the fractional interstitial mediated diffusion decreases with increasing germanium. For boron an additional change in pair formation/migration energy is required to explain the observed experimental data. The model is used to explore heteroepitaxially grown SiGe/Si device design options. View full abstract»

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  • Mechanism of solid-liquid-solid on the silicon oxide nanowire growth

    Page(s): 613 - 617
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    The solid-liquid-solid growth mechanism of synthesizing SiOx nanowires is expressed in detail through analyzing the structure and composition of the catalysts and the nanowires. The silicon source for growing nanowires was directly provided from the silicon wafer. A thin catalyst layer of platinum (∼5 nm) was first deposited on the silicon wafer by sputtering. The platinum film collapsed into dots with diameter about hundreds of nanometers during the thermal process. These dots transformed into crystalline platinum silicide (Pt3Si) and served as nucleation seeds for the silicon oxide nanowire growth. Due to the high process temperature (∼1100 °C) and long duration time (∼5 h), the silicon wafer transformed into amorphous silicon oxides and melted into the Pt3Si catalyst dots until supersaturated to form SiOx nanowires. Such nanowires are amorphous and have an average diameter of about 40–60 nm and length of several hundreds of micrometers. View full abstract»

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  • Statistical variation analysis of sub-5-nm-sized electron-beam-induced deposits

    Page(s): 618 - 622
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    We report on the statistical analysis of the variations in the size and position of sub-5 nm tungsten-containing dots in regular arrays deposited by electron-beam-induced deposition. Full widths at half maximum of the dots are 4.2 and 2.0 nm in average. It can be observed in the recorded annular dark-field images that there is a variation in intensity for these dots. We have analyzed these variations and it is found that the relative standard deviation for the mass per dot is 0.092 for the 4.2 nm dots and 0.26 for the 2.0 nm dots. Comparing this to a relative standard deviation in the estimated number of precursor molecules that are pinned down per dot of 0.041 for the 4.2 nm dots and 0.11 for the 2.0 nm dots, it appears that the dot-to-dot variation in mass for both dot sizes compares reasonably well with the values expected from Poisson statistics on the number of molecules per dot. It can be concluded that at these dimensions, the statistics on the number of pinned precursor molecules dominates the control of feature sizes. View full abstract»

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  • Effects of n-type modulation-doping barriers and a linear graded-composition GaInAsP intermediate layer on the 1.3 μm AlGaInAs/AlGaInAs strain-compensated multiple-quantum-well laser diodes

    Page(s): 623 - 628
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    We report the fabrication, characterization, and comparison of four 1.3 μm AlGaInAs/AlGaInAs strain-compensated multiple-quantum-well (SC-MQW) laser structures: (1) sample A—with only an undoped SC-MQW active region, (2) sample B—with an undoped SC-MQW active region and a linear graded-composition (LGC) GaInAsP intermediate layer, (3) sample C—with an n-type modulation-doping (MD) SC-MQW active region, and (4) sample D—with an n-type MD-SC-MQW active region combined with a LGC GaInAsP intermediate layer. The inclusion of either n-type modulation-doped SC-MQW active region or LGC GaInAsP intermediate layer can improve the performance of a laser diode (LD). The LD sample D, which includes both an n-type MD-SC-MQW active region and a LGC GaInAsP intermediate layer, exhibits the best overall performance including a threshold current of 12.5 mA, a characteristic temperature of 85 K in 20–80 °C temperature range, a lasing wavelength shift of 0.38 nm/K, and a relaxation frequency response of 9.9 GHz. View full abstract»

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  • Modeling of field-assisted emission from the image states of a glass substrate

    Page(s): 629 - 633
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    A device has been reported recently in which electrons transit through the image states of a negative-electron-affinity glass substrate before being emitted to the vacuum. The external field required for this emission may be as low as 10 V/cm, which is up to three orders of magnitude lower than the fields encountered with other materials. In order to address what appears to be an essential aspect of this device, we present a modeling of field-assisted emission from the image states of a dielectric substrate. The analysis includes a characterization of the image states and considers direct tunneling and thermal excitation to higher energy levels as possible mechanisms for the emission. The model turns out to provide surface charge densities and emission currents that are in excellent agreement with experiments. For the working conditions of the device, the simulations show that the emission has a dominant thermally enhanced field emission component and that the image states play a significant role in pinning the Fermi level to values that are close to the vacuum level. View full abstract»

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  • Explicit expression on specifications of mask mean to target and mask uniformity

    Page(s): 634 - 638
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    An analytic expression on the relationship of the mask mean to target (MTT) and the mask uniformity specifications is suggested. The MTT and uniformity (M-U) curve defines the boundary of the specification region, and this curve is explicitly expressed as mask error enhancement factors (MEEFs), dose sensitivities, and critical dimension (CD) tolerances of cell and peripheral patterns. This curve shows linear relationships between mask M-U. The decrease of the mask uniformity allows the increase of the mask MTT margin. M-U specifications are suggested for 63, 73, and 90 nm design rules. In this experiment, the tolerance of the cell pattern is given as the product of the MEEF and the mask uniformity margin which is specified as 60% of the total CD variation at the given design rule, while that of the peripheral pattern is set to be 10% of the design rule. An isolated pattern is selected as a peripheral pattern because its pitch size is infinite. The mask MTT specification for 63 nm is ±2.3 nm at the mask uniformity of 2.23 nm. For 73 nm design rule, specifications of mask MTT are ±1.94 and ±1.48 nm at the mask uniformities of 2.32 and 3.31 nm at the process constants (k1’s) of 0.295 and 0.322, respectively. For 90 nm design rule, the mask MTT specifications are ±3.89 and ±4.13 nm at mask uniformities of 3.89 and 4.13 nm for k1’s of 0.364 and 0.396, respectively. 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.

Full Aims & Scope

Meet Our Editors

Editor
Gary E. McGuire
International Technology Center