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

Issue 2 • Date Mar 2008

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Displaying Results 1 - 25 of 82
  • Issue Cover

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

    Page(s): toc1
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  • Fabrication and characterization of InGaAsP/InP double shallow-ridge rectangular ring laser photonic integration circuits by cascade reactive ion etching/inductively coupled plasma etching

    Page(s): L23 - L27
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    The authors report the fabrication and characterization of InGaAsP/InP rectangular ring laser photonic integration circuits based on active vertical-coupler structure by cascade reactive ion etching/inductively coupled plasma etching technology. This novel etching scheme can efficiently balance the photolithography, masking, and semiconductor etching requirements when several etching depths are demanded. For the 920 μm circumference of ring lasers with coupler length (Lc) of 300 μm, the smallest total threshold current (Ic+Id) of 75 mA is achieved. Varying threshold situation and its sensitivity to the coupling parameters predict that the performance of such devices is not dominated by the nonideal fabrication loss, even though total internal-reflection mirrors are formed by etching twice. Such successful fabrication indicates that this can be widely employed to fabricate the other photonic integrated circuit components where multilevel deep etching is required. View full abstract»

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  • Fabrication of nanopores with subnanometer precision on poly(methyl methacrylate) nanofibers by in situ electron beam irradiation

    Page(s): L28 - L31
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    Nanopores with subnanometer precision were fabricated and fine-tuned in freestanding poly(methyl methacrylate) (PMMA) nanofibers by in situ electron beam irradiation. The nanopores were formed and expanded by focused electron beam irradiation, which was attributed to the sputtering and decomposition of PMMA. Meanwhile, the fabricated nanopores could also be shrunk and closed by low electron intensity irradiation, which may have been caused by surface tension induced mass flow due to the glass transition of PMMA. This work provides a new method to fabricate precise nanopores. It also provides important evidence about the theory of direct nanofabrication by electron beam irradiation. View full abstract»

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  • Characterization of semiconducting polymers for thin film transistors

    Page(s): 445 - 457
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    A review of characterization methods used to study semiconducting polymers in thin film transistors is presented. The basic operation of polymeric thin film transistors (TFTs) is described. Methods for microstructural characterization of thin films of semiconducting polymers such as x-ray scattering are discussed. Examples of how these methods have been applied to study structural ordering in semicrystalline polymers such as poly(3-hexylthiophene) are presented. The electronic structure of these materials is important for understanding the operation of TFTs and has been studied using ultraviolet photoelectronic spectroscopy, optical spectroscopy, and electrochemical methods. Instabilities of the operation of TFTs have been examined using time-dependent current-voltage measurements, charge modulated spectroscopies, and scanning probe methods. These methods have revealed the nature of charge carriers and trap states in semiconducting polymers. View full abstract»

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  • Nanoimprint lithography: An old story in modern times? A review

    Page(s): 458 - 480
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    Nanoimprint lithography (NIL) is a high throughput, high-resolution parallel patterning method in which a surface pattern of a stamp is replicated into a material by mechanical contact and three dimensional material displacement. This can be done by shaping a liquid followed by a curing process for hardening, by variation of the thermomechanical properties of a film by heating and cooling, or by any other kind of shaping process using the difference in hardness of a mold and a moldable material. The local thickness contrast of the resulting thin molded film can be used as a means to pattern an underlying substrate on wafer level by standard pattern transfer methods, but also directly in applications where a bulk modified functional layer is needed. Therefore it is mainly aimed toward fields in which electron beam and high-end photolithography are costly and do not provide sufficient resolution at reasonable throughput. The aim of this review is to play between two poles: the need to establish standard processes and tools for research and industry, and the issues that make NIL a scientific endeavor. It is not the author’s intention to duplicate the content of the reviews already published, but to look on the NIL process as a whole. The author will also address some issues, which are not covered by the other reviews, e.g., the origin of NIL and the misconceptions, which sometimes dominate the debate about problems of NIL, and guide the reader to issues, which are often forgotten or overlooked. View full abstract»

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  • Fabrication process for cantilevers with integrated tunnel junctions

    Page(s): 481 - 486
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    The authors have developed a process for making submicron cantilevers, clamped beams, and more complicated electromechanical structures that carry integrated electrical leads. Such objects are useful as test structures for measuring the electrical properties of molecular sized objects, as high frequency electromechanical components for radio frequency and microwave applications, and as sensor components for studying fluctuations in small systems. Their process uses two realigned electron beam lithography steps, a thin-film angled deposition system, and differential removal of sacrificial aluminum layers to produce freely suspended submicron electromechanical components. The authors have produced cantilevers and beams on a variety of substrates (silica, silicon, and polyimide) and have produced insulating, conductive, and multilayer electromechanical structures. The process allows the use of essentially any material that can be deposited from a thermal or electron-beam deposition source. The authors have integrated mechanically adjustable gold-vacuum-gold contacts onto the cantilevers and have demonstrated vacuum tunneling. The behavior of these contacts indicates an exponential dependence on tunneling gap. The authors have demonstrated electrostatic control over the tunnel gap spacing as well. View full abstract»

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  • SiC via fabrication for wide-band-gap high electron mobility transistor/microwave monolithic integrated circuit devices

    Page(s): 487 - 494
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    A process for achieving high yield of SiC through wafer via holes without trenching or micromasking and with excellent electrical connection after subsequent metal plating across full wafers was developed for use in high electron mobility transistors (HEMTs) and microwave monolithic integrated circuits (MMICs) using an inductively coupled plasma etch. Consideration was given to the choice of wafer platen, hard mask, gas chemistry, surface treatments, and plasma parameters in order to achieve an acceptable etch rate while at the same time minimizing trenching and micromasking that can harm via yield. In addition, the issue of wafer thickness variation and etch nonuniformity leading to punch through of Au pads at the bottom of the vias was addressed by the addition of a metal layer to the front side of the wafer. The etch rate achieved for 25% of a 2 in. diameter wafer is approximately 3800 Å/min while demonstrating acceptable levels of trenching and micromasking with little or no Au punch through. The final process has been demonstrated to achieve ≫95% yield across a full 2 in. diameter, 100 μm thick wafer with a high density of vias. View full abstract»

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  • Optical and electrical properties of amorphous zinc tin oxide thin films examined for thin film transistor application

    Page(s): 495 - 501
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    Structural, electronic, and optical properties of amorphous and transparent zinc tin oxide films deposited on glass substrates by pulsed laser deposition (PLD) were examined for two chemical compositions of Zn:Sn=1:1 and 2:1 as a function of oxygen partial pressure (PO2) used for the film deposition and annealing temperature. Different from a previous report on sputter-deposited films [Chiang etal, Appl. Phys. Lett. 86, 013503 (2005)], the PLD-deposited films crystallized at a lower temperature ≪450 °C to give crystalline ZnO and SnO2 phases. The optical band gaps (Tauc gaps) were 2.80-2.85 eV and almost independent of oxygen PO2, which are smaller than those of the corresponding crystals (3.35-3.89 eV). Films deposited at low PO2 showed significant subgap absorptions, which were reduced by postthermal annealing. Hall mobility showed steep increases when carrier concentration exceeded threshold values and the threshold value depended on the film chemical composition. The films deposited at low PO2≪2 Pa had low carrier concentrations. It is thought that the low PO2 produced high-density oxygen deficiencies and generated electrons, but these electrons were trapped in localized states, which would be observed as the subgap absorptions. Similar effects were observed for 600 °C crystallized films and their resistivities were increased by formation of subgap states due to the reducing high-- - temperature condition. High carrier concentrations and large mobilities were obtained in an intermediate PO2 region for the as-deposited films. View full abstract»

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  • Improvement on cold carbon field-electron emitter for commercial x-ray tube

    Page(s): 502 - 505
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    A high-temperature-resistant smooth carbon field-electron emitter (SCFE) was proposed for replacing an original high-temperature-resistant carbon field-electron emitter. We compared their electron emission, processes, post-treatment technologies, and life. A comparison shows that the new SCFE has qualities. The SCFE showed a smoother surface, with bulk tightness, improved electron emission properties, decreased emitter thickness, and the contact between electrodes is better than ever. The electron emission area has been concentrated on a thinner edge, and we obtained high precision for the tube’s electrode construction. Initial experiments indicated that those x-ray tubes with the SCFE maintained their properties from August 2006 up to the present. View full abstract»

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  • The effect of added salts on the optical properties of water for high index immersion lithography fluids

    Page(s): 506 - 513
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    In immersion lithography, a high index fluid is used to enable increases in the numerical aperture (NA) of the imaging system and decrease the minimum printable feature size. Water has been used in first generation immersion lithography at 193 nm to reach the 45 nm node. To reach the 38 and 32 nm nodes, fluids with a higher index than water are needed. Ionic additives have a higher index than water and can be added to water in high concentration to obtain a high index fluid. Generally, addition of a high index additive leads to a higher absorbance. The next generation immersion fluid should have both a high index and low absorbance. Therefore, both the index and absorbance of a series of ionic additives in water were characterized to identify an additive with a high index and low absorbance at 193 nm. This study revealed that the anion dictates the optical properties of the additive. Of the anions studied, the methylsulfonate anion has the desired characteristics and was dissolved in water at high concentration using heavy metal cations. A saturated solution of lanthanum methylsulfonate had the highest index and lowest absorbance identified, n193=1.58 and α193=0.3 cm-1. These high index methylsulfonate solutions were used to image line and space patterns at various NAs. Images of 32 nm half-pitch were generated at 1.5 NA with the lanthanum solution. The methylsulfonate anion can be paired with microelectronics friendly quaternary ammonium cations to develop an immersion fluid with the target properties. View full abstract»

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  • Multilayer soft mold for UV imprinting the 50 nm pitch dot array

    Page(s): 514 - 517
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    A novel concept of multilayer soft mold for ultraviolet nanoimprint lithography was introduced. It is composed of (tridecafluoro-1,1,2,2-tetrahydro-octyl)-trichlorosilane (FOTS)/SiO2/pattern polymer (perfluorinated acrylate mixture)/glass, where the FOTS is for releasing and SiO2 is for surface hardening and adhesion between the FOTS and pattern polymer. By using the multilayer soft mold, a dot array as small as 50 nm pitch was replicated from the Si master and imprinted on a Ru/Ta/Si substrate successfully. The x-ray photoelectron spectroscopy, contact angle measurement, and nanoindentation test revealed that the multilayer soft mold has good adhesion between layers, lower surface energy, and stiffer surface than the soft mold of pattern polymer/glass, respectively. View full abstract»

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  • Electrical biasing and time dependent evolution of defects in poly(triphenylamine)-butane vinyl organic semiconductor devices

    Page(s): 518 - 524
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    Field effect transistors based upon the organic semiconductor poly(triphenylamine)-butane vinyl have been characterized. The carrier mobility is observed to vary significantly with time immediately after manufacture of the devices but to become very stable after extended periods (≫1 month). The stabilized, carrier mobility is estimated to be ∼6×10-5 cm2 V-1 s-1 from saturation source-drain current measurements. Repeated measurements of source-drain currents as a function of gate electrode potential evidence the presence of positive charge trapping at defects in the semiconductor layer during the measurement leading to uncertainty in mobility and threshold voltage determination. Constant bias stressing at -2 MV cm-1 results in a decrease in the carrier mobility and an increasingly negative threshold voltage shift consistent with positive charge trapping. Following the removal of the stressing field, the mobility increases back to its prestress value and the threshold voltage shift decreases. From these data, a crude estimate of the trap depth is estimated to be 0.7–0.8 eV. An anomalous channel length dependence of the carrier mobility is determined from source-drain saturation current as a function of gate-source voltage measurements. View full abstract»

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

    Page(s): 525 - 533
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    A systematic study of the evolution of the defect morphology and crystalline quality in molecular beam epitaxially grown CdxHg1-xTe epilayers with growth temperature is presented. The layers were characterized with optical microscopy, atomic force microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and high-resolution x-ray diffraction. Four types of defects (microvoids, hillocks, high-temperature voids, and needles) were characterized on epilayers grown in the growth temperature range 188.9-209.9 °C. There is a minimum in the area covered by defects at a temperature just below the onset of Te precipitation, which is defined as the optimal growth temperature. Microvoids with various shapes, and at various stages of growth, were observed side-by-side in many of the CdxHg1-xTe layers, along with hillocks and needles. The defect density of microvoids changes by several orders of magnitude in the studied temperature range. A mechanism for the formation of microvoids and needles is suggested. High-temperature voids associated with Te precipitates appear above the optimal growth temperature. The onset of Te precipitation is well described by a thermodynamic model. View full abstract»

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  • Optimization of resolution-enhancement technology and dual-layer bottom-antireflective coatings in hypernumerical aperture lithography

    Page(s): 534 - 540
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    Resolution-enhancement technique (RET) and dual-layer bottom-antireflective coatings (DL-BARC) must be adopted in hypernumerical aperture (NA≫1) lithography for a 45 nm half-pitch device. However, interactions of RET, polarization effect, and the resist process significantly impact on lithography performance. An in-house program and PROLITH 9.0 were employed to perform comprehensive optimization of RET and DL-BARC structures in order to improve pattern fidelity with a reasonable process window (PW). High-fidelity resist patterns are obtained when we employed optimum DL-BARC structures in conjunction with optimum RET. An alternating phase-shift mask and a conventional illumination is one kind of optimum combination of RET. An attenuated phase-shift mask and a cross-dipole illumination is the other one. Line-width changes are controlled within 4 nm. Sidewall angles are greater than 88°. View full abstract»

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  • Silicon laterally resonant microcantilevers for absolute pressure measurement with integrated actuation and readout

    Page(s): 541 - 550
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    This work is focused on the design, fabrication, and characterization of silicon laterally resonant microcantilevers for measuring absolute pressure. The authors have demonstrated the integration of resonance electrostatic actuation and capacitive readout with a microstructure based on a couple of electrodes and an external amplifier. The microcantilevers have been fabricated with a standard silicon on insulator micromachining process. The characterization method is based on measuring the current at the third harmonic of the excitation frequency flowing through the time-varying cantilever-based capacitor. The variation in resonance response of microcantilevers has been investigated as a function of pressure (10-2-105 Pa), both in terms of resonance frequency and quality factor. Theoretical models and experimental data show very good agreement. The microstructure behavior demonstrates the feasibility of an absolute pressure sensor working over a six-decade range with integrated electrical actuation and readout. View full abstract»

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  • Effects of Mo seeding on the formation of Si nanodots during low-energy ion bombardment

    Page(s): 551 - 558
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    Effects of seed atoms on the formation of nanodots on silicon surfaces during normal incidence Ar+ ion bombardment at room temperature are studied with real-time grazing-incidence small-angle x-ray scattering (GISAXS), real-time wafer curvature stress measurements and ex situ atomic force microscopy. Although Si surfaces remain smooth during bombardment at room temperature, when a small amount of Mo atoms is supplied to the surface during ion bombardment, the development of correlated structures (“dots”) is observed. Stress measurements show that initially a compressive stress develops during bombardment, likely due to amorphization of the surface and insertion of argon. However, seeding causes a larger tensile stress to develop with further bombardment, possibly due to the formation of higher density regions around the Mo seed atoms on the surface. Detailed fits of the GISAXS evolution during nanostructure growth show that the instability is larger than predicted by the Bradley-Harper theory of curvature-dependent sputter yield. These results suggest that the tensile stress is playing a dominant role in driving the nanodot formation. View full abstract»

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  • Electrical properties of conductive and resistive ZnSe layers

    Page(s): 559 - 565
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    The authors have investigated the electrical properties for one typical set of Al-doped ZnSe layers: one is conductive (type I) and the other is resistive (type II). The two types of ZnSe:Al layers are grown on different substrates by molecular-beam epitaxy under the same conditions: type I is on a 15° tilted (001) GaAs substrate and type II is on an exact (001) substrate. In capacitance-voltage curves, it is found that the measured capacitance in type II is 20 times smaller than that of type I. Moreover, it is estimated that the net-doping density of type II (∼1015 cm-3) is two orders of magnitude lower than that of type I (∼1017 cm-3). Frequency-dependence measurements of capacitance indicate that type II suffers from deep levels more seriously than type I. In photoluminescence spectra, it is shown that strong deep-level emission peaks exist at the energies of 2.03 and 2.24 eV, but their emission features are almost the same in types I and II. In photocapacitance spectra, it is found that electron-trap centers exist in the midgap region, located at 1.1, 1.2, and 1.3 eV below the conduction-band minimum, and the photocapacitance generated in the midgap of type II is seven times larger than that of type I. Moreover, it is estimated that the total density of the three trap centers in type II (∼1017 cm-3) is similar to the net-doping density of type I. Consequently, it is suggested that the midgap trap centers contribute to the carrier compensation in ZnSe:Al layers and induce the different electrical properties in types I and II. View full abstract»

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  • Field emission from as grown and nitrogen incorporated tetrahedral amorphous carbon/silicon heterojunctions grown using a pulsed filtered cathodic vacuum arc technique

    Page(s): 566 - 575
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    This article reports the field emission measurements on as grown tetrahedral amorphous carbon (ta-C) and nitrogen incorporated tetrahedral amorphous carbon (ta-C: N) films grown using a pulsed filtered cathodic vacuum arc technique. The effect of varying thickness on field emission in the as grown ta-C films and the effect of varying nitrogen content in ta-C: N films have also been studied. The values of threshold field of emission (Eturn on) increase with decrease of thickness in the as grown ta-C films. Nitrogen incorporation up to 5.2 at. % in ta-C films decreases the value of Eturn on from 9.9 to 5.1 Vm and thereafter it starts increasing again. To understand the mechanism of electron emission, a realistic energy band diagram of ta-C:N/n++Si heterojunction has been proposed from the experimentally measured valence and conduction band offsets, using in situ x-ray photoelectron spectroscopy and optical spectroscopy data already published in DRM 9 (2000) 1148. The data are explained using the Fowler and Nordheim theory. The field emission results obtained reveal that there exists a barrier to emission and the main barrier is at the front surface and this is related to the conduction band offset of the ta-C:N/n++Si heterojunction. View full abstract»

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  • Comparison of deep silicon etching using SF6/C4F8 and SF6/C4F6 plasmas in the Bosch process

    Page(s): 576 - 581
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    Silicon was etched with the Bosch process using C4F8 and C4F6 plasmas in the deposition step to show a feasibility of the use of UFC plasmas in the Bosch process. The use of C4F8 and C4F6 plasmas resulted in different characteristics of fluorocarbon films and radicals, affecting the etch profiles. It was shown that the use of a C4F6 plasma in the deposition step of the Bosch process produced thicker and more strongly bonded fluorocarbon films, compared to a C4F8 plasma. It was because more CF2 radicals and lower F/C ratio fluorocarbon films were generated in C4F6 plasmas than those in C4F8 plasmas, confirmed by OES and XPS measurements. By changing only the duration of the deposition step under the same process conditions, highly anisotropic deep etching of silicon was successfully achieved using both SF6/C4F8 and SF6/C4F6 plasmas in the etching and/deposition steps of the Bosch process. View full abstract»

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  • High-aspect-ratio nanopillar structures fabricated by nanoimprinting with elongation phenomenon

    Page(s): 582 - 584
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    The authors found that fine pillar structures (nanopillars) with a high aspect ratio were formed by nanoimprinting with elongation phenomenon. Polymer nanopillars with higher aspect ratios than that of corresponding holes on the mold were obtained without any etching processes after nanoimprinting. The finest nanopillars were 95 nm in diameter and 4.1 μm high made of polystyrene. Elongated nanopillars of poly(methylmethacrylate) and polystyrene were confirmed. Elongation of nanopillars depended on process conditions such as the diameter of holes on the mold, the unmolding temperature, and the molecular weight of the polymer resin. View full abstract»

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  • Indium-doped ZnO nanospirals synthesized by thermal evaporation

    Page(s): 585 - 588
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    Indium-doped ZnO nanospirals were synthesized by one-step thermal evaporation. Transmission electron micrographs show that the nanospirals are structurally uniform and free of defects. The helical nanostructures, which are constructed by rolling nanobelts grown along the <1010> direction with the ±(0001) polar planes as the dominate surfaces, are energetically favored in terms of the electrostatic polar charge model. The typical radius of curvature of the nanospirals is several micrometers. The In-doped nanospirals are expected to have interesting optoelectronic and mechanical properties and could be potential building blocks in nanoscale optoelectronic and electromechanical systems. View full abstract»

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  • Route to production of suspended perforated membranes

    Page(s): 589 - 592
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    The authors report a flexible approach to fabrication of suspended perforated membranes. Interferometric lithography is used to pattern photoresist to create an etch mask on a silicon substrate. Reactive ion etching results in the formation of a matrix of silicon pillars. The interstices of the pillar matrix are then filled with the membrane material. Subsequent removal of the silicon matrix and underlying substrate yields a suspended membrane with perforations where the pillar matrix protruded prior to removal. The method combines interferometric lithography and conventional lithography to provide both periodic and nonperiodic patterns in a seamless process flow. The use of a matrix of sacrificial pillars enables the formation of higher aspect ratio holes than standard liftoff or etched film approaches. Perforated membranes of a siloxane based silica, photocurable polymer, and evaporated Cr are presented, demonstrating the wide process latitude of this approach. Such suspended membranes have application in photonic, metamaterials, DNA translocation, and biological and chemical sensors. View full abstract»

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  • Fabrication of suspended dielectric mirror structures via xenon difluoride etching of an amorphous germanium sacrificial layer

    Page(s): 593 - 597
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    The authors present a simplified fabrication method for the creation of free-standing dielectric mirrors for use in monolithic wavelength tunable surface-normal photonic devices, including vertical-cavity surface emitting lasers. This process utilizes a nonplasma dry etching process, based on the noble gas halide, xenon difluoride (XeF2), to remove an inorganic sacrificial film comprised of low-temperature deposited amorphous germanium -Ge). By utilizing nonplasma dry etching of an inorganic film, this procedure circumvents the need for critical point drying and avoids the limitations imposed by polymer-based sacrificial layers. In this procedure the authors observe remarkably rapid lateral etching, with rates in excess of 150 μm/min for electron-beam evaporated α-Ge films. The viability of this novel surface micromachining process is demonstrated by presenting the static and dynamic mechanical characteristics of electrostatically actuated suspended dielectric Bragg reflectors. View full abstract»

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  • Simulation study on stress and deformation of polymeric patterns during the demolding process in thermal imprint lithography

    Page(s): 598 - 605
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    Thermal imprint lithography or hot embossing is a processing technique using molding to produce surface patterns in polymer resist at micro- and nanoscales. While fast molding is important to improve the yield of the process, the process step that determines the success of imprinting high aspect ratio structures is demolding, a process to separate the mold insert from the patterned resist after conformal molding. In this paper the authors studied the stress and deformation behavior in polymer resist during the cooling and demolding process of thermal imprint lithography via finite element method. A simple model structure of the Si stamp/poly(methyl methacrylate) (PMMA) resist/Si substrate was used for the simulation, assuming that PMMA is viscoelastic. As demolding proceeds, Von Mises stress in the PMMA layer is highly localized in two locations, one at the transition corner zone between the residual layer and the replicated PMMA pattern and the other close to the contact region with the moving stamp edge, creating two maximums. The presence of the second maximum stress indicates that a structural failure may occur not only when demolding starts, but also immediately before demolding ends. The second maximum stress becomes significant as the angular offset from the ideal normal demolding to the substrate surface increases or for the structures located far away from the symmetric centerline. In addition, the authors will discuss the influence of other parameters, including demolding rate and stamp geometries. 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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Meet Our Editors

Gary E. McGuire
International Technology Center