bluuebunny/crossref_metadata_2025 huggingface dataset:
Photocontrolled double-barrier resonant-tunneling diode
Authors: Li H. S. , Chen Y. W. , Wang K. L. , Pan D. S. , Chen L. P. , Liu J. M.
Published: July 2002

A photocontrolled InGaAs/AlAs double-barrier resonant-tunneling diode, for the first time, has been demonstrated. The photoinduced valley current in the resonant-tunneling diode was optically controlled by varying the incident optical power level. With the incident optical power intense enough, the photogenerated valley current became dominant over the peak current. As a consequence, the negative differential resistance of the device was nullified. A photogeneration process, based on photogenerating carriers in the depletion region adjacent to the double barriers, is described and characterized. The device under illumination was modeled as a resonant-tunneling diode in series integration with a photodetector. The quantum efficiency for the photogeneration was measured and found comparable with theoretical prediction. The demonstrated photocontrolled double-barrier resonant-tunneling diode can be useful in a variety of applications.
Double quantum well charge transport in pseudomorphic Al0.3Ga0.7As/In0.15Ga0.85As/GaAs modulation doped heterostructures
Authors: Young A. P. , Fernandez J. M. , Chen Jianhui , Wieder H. H.
Published: July 2002

The influence of the spacer thickness upon the apparent mobility and the efficiency of electron transfer between two closely spaced quantum wells has been measured. By decreasing the distance of the δ-doped layer from the InGaAs channel below 100 Å, the efficiency of charge transfer into the InGaAs channel is increased. A dramatic drop is observed in the apparent mobility of the structure with the GaAs embedment when that distance is 50 Å. This indicates that the experimentally measured electron transport properties must be considered in terms of the parameters of two interacting channels, and are dominated by the properties of the embedded GaAs.
Efficient liquid nitrogen supply system for the cooling shroud in a molecular beam epitaxy system
Authors: Cook J. W. , Schetzina J. F.
Published: July 2002

The molecular beam epitaxy (MBE) process is generally surrounded by liquid nitrogen (LN2) cooled surfaces for optimum control of the environment in which the thin-film deposition takes place. The design and operation of a LN2 supply system for feeding the cryogenicly cooled surfaces in a MBE system is described here. The supply system is based on modification of a standard 50-ℓ LN2 storage dewar. The reservoir gravity feeds liquid through a vacuum-insulated line into the fill port of the MBE system. A solenoid-operated vent valve activated by a temperature controller regulates the level of LN2 in the MBE system. The LN2 supply system is efficient and costs much less than other alternatives.
Reflection high-energy electron diffraction study of the GaSb surface during molecular beam epitaxy
Authors: Yano Mitsuaki , Yamamoto Kazuhiko , Utatsu Takashige , Inoue Masataka
Published: July 2002

Surface stoichiometry of GaSb during molecular beam epitaxy is studied by using the reflection high-energy electron diffraction technique. This study has shown a desorption energy of 1.47 eV for excessively absorbed Sb atoms on the Sb-stabilized surface. It is also shown that the Ga-stabilized surface easily dissociates Ga atoms from the Sb sublayer to aggregate fine droplets. The activation energy is found to be 1.76 eV for the Ga droplet formation.
Molecular beam epitaxy of MnAs thin films on GaAs
Authors: Tanaka M. , Harbison J. P. , Sands T. , Cheeks T. L. , Keramidas V. G. , Rothberg G. M.
Published: July 2002

We have successfully grown single-crystalline ferromagnetic MnAs thin films on (001) GaAs substrates by molecular beam epitaxy. By reflection high energy electron diffraction and x-ray measurements, the growth direction of the MnAs thin films was found to be [100] on (001) GaAs, and the epitaxial relationship was [0001] MnAs //[10] GaAs and [110] MnAs // [110] GaAs. Magnetization measurements at room temperature have revealed that the epitaxial MnAs thin films have strong magnetic anisotropy, and that the easy magnetization direction is in-plane, along the [110] axis of the MnAs thin films which is parallel to the [110] axis of the GaAs substrate, with almost perfect square hysteresis loops, relatively high remanent magnetization, and low coercive field.
Structural refinement and measurement of biomolecules using novel software algorithms and methodologies
Authors: Williams P. M. , Davies M. C. , Jackson D. E. , Roberts C. J. , Tendler S. J. B.
Published: July 2002

The success of scanning probe microscopy in the imaging of biomolecules has led to the need for specially tailored image processing and data analysis routines. To permit the correlation of topographs with x-ray crystallographic and electron microscopy data, automated feature discrimination and measurement algorithms have been developed. Incorporation of statistical techniques, such as cluster analysis, have allowed surface features to be characterized into single molecules and aggregates where the number of molecules forming the clusters can be calculated. The application of these routines to topographic data of proteins collected in our laboratory has permitted accurate comparisons with information from complementary biophysical techniques to be made. We believe that such developments are critical for the continued success of probe techniques in the imaging of biomolecules.
Nitrogen profiles of high dose, high temperature plasma source ion implantation treated austenitic stainless steel
Authors: Franklyn C. B. , Nothnagel G.
Published: July 2002

Plasma source ion implantation over a period of 30 min, with actual ion implantation times of ∼15 s, has been studied. Estimates of steady-state heat diffusion indicate bulk average temperatures of <50 °C. Experimental profiles show nitrogen diffusion up to ≳1 μm, indicating surface temperatures of ∼500 °C. Resultant implantation and diffusion profiles are compared with conventional plasma nitrided samples.
Study of the I–V characteristics of planar-doped-barrier electron emitters
Authors: Jiang Wei-Nan. , Mishra Umesh K.
Published: July 2002

Unlike conventional planar-doped-barrier (PDB) diodes which have relative low built-in accelerating fields, tunneling of electrons through the energy band gap becomes an important, and at times dominant, current transport mechanism under the high accelerating field which is essential for high performance PDB electron emitters. Thermionic emission across the triangular barrier is also found to be important. A systematic study on the temperature dependent I–V characteristics of PDB diodes with high accelerating field has been carried out, and different carrier transport mechanisms across the PDB diodes will be discussed in this article.
Characterization of silicon field emission microtriodes
Authors: Liu D. , Marcus R. B.
Published: July 2002

The properties of single silicon field emission microtriodes have been examined. Gate and collector currents were measured in a vacuum of 2×10−8 Torr, and current–voltage, current–time, Fowler–Nordheim (I/V2 versus 1/V), and triode characteristics were determined. The data showed that the electron emission followed Fowler–Nordheim behavior. Single emitters had turn-on gate-to-cathode voltages (V) above 25 V (typically 50–90 V) and reproducible emission currents were measured in the range 5 pA–1 μA. Temporal fluctuations in emission current of 10%, 16%, and 40% were found for emission currents of 0.35, 50 nA, and 0.5 μA, respectively. The triode characteristics showed an Ig/Ic ratio of 0.25% and higher. Transconductances were found to be 3×10−8 Ω−1/tip. Electrostatic discharge and other device failure mechanisms have been observed and are described.
Optimal surface cleaning of GaAs (001) with atomic hydrogen
Authors: Petit E. J. , Houzay F.
Published: July 2002

Atomic hydrogen is commonly used to clean GaAs surfaces. The goals of this work are to optimize the cleaning process and to control surface reactions in order to avoid decomposition of GaAs. Chemically polished GaAs (001) surfaces have been cleaned by thermally generated atomic hydrogen and analyzed by surface sensitive techniques. We propose an optimal process involving two exposures. The first one at room temperature etches As oxides. The second one at 300 °C completes the reduction of Ga oxides. We demonstrate that the variations of the ionization energy, work function, and Fermi level are very sensitive to the completion of the cleaning reaction. These parameters can be used to monitor surface reactions on-line in order to avoid excessive desorption of As and GaAs decomposition.
Cleaning of silicon surfaces by hydrogen multipolar microwave plasma excited by distributed electron cyclotron resonance
Authors: Raynaud P. , Pomot C.
Published: July 2002

Hydrogen plasma produced by a microwave multipolar reactor has been used to clean a single crystal of silicon. The substrate is kept at room temperature and floating potential during the plasma treatment and then heated at 700 °C. The effect of atomic species created in the plasma on the silicon surface is studied by in situ analysis (spectroscopic ellipsometry, low energy electron diffraction, and Auger electron spectroscopy) and ex situ analysis (atomic force microscopy). Quasi-instantaneous removal of carbon is demonstrated, showing the high efficiency of hydrogen plasma to remove carbon of the silicon surface. This cleaning treatment allows the obtainability of silicon surfaces exempt of contaminants (carbon and oxygen) and roughness (very low perturbed thickness). The peaks values of the imaginary part of dielectric function of Si surface cleaned by hydrogen plasma exceed those previously reported (values of εi at 4.25 eV=48.25). This process seems to be compatible with very large scale integrated and ultra-large scale integration technology.
Process characterization and analysis of sealed vacuum microelectronic devices
Authors: Mei Q. , Zurn S. , Polla D. L.
Published: July 2002

Cold-cathode microdiodes with tungsten and heavily doped polycrystalline silicon emitters have been fabricated using silicon planar processing and solid-state surface micromachining techniques. This work has focused on building reliability into vacuum microelectronic devices and eliminating the need for external vacuum pumping as commonly used in these devices. The following technology advances have been incorporated into sealed microdiode devices: (1) recessed cavities with lateral chemical etch delivery channels, (2) electron beam-evaporated vacuum enclosures, (3) the use of atomic force microscopy to analyze the fine grain emitter surface structure, (4) the use of soft x-ray photoelectron spectroscopy to determine surface chemical composition of cathode and anode surfaces, and (5) the use of ultraviolet photoelectron spectroscopy to measure as-processed work function.
Modeling image formation: Application to mask optimization
Authors: Xiao Jiabei , Khan Mumit , Nachman Ramez , Wallace John , Chen Zheng , Cerrina Franco
Published: July 2002

From an image formation point of view, the design of x-ray masks has been optimized for realistic exposure systems using synchrotron radiation. The analysis has then been carried forward to study the effect of environmental factors such as vibrations. We conclude that the ideal x-ray mask is based on thin absorbers (0.3–0.4 μm) for Au and W, that the existence of a sidewall slope improves the exposure latitude, and that vibrations (amplitude less than 1/2 critical dimension) do not represent a source of concern. All in all, the x-ray lithography mask emerges with more relaxed specifications and with a simpler manufacturing process.
New approach of rim phase-shifting mask for high-density circuit layout
Authors: Dao G. , Tam N. , Hainsey R. , Qian Q. D. , Neff J. , Nasre-Esfahani B. , Deeter T. , Fujimoto H. , Troccolo P.
Published: July 2002

The rim phase-shifting mask (PSM) approach has been demonstrated by various researchers to provide significant improvement in performance for deep submicron optical lithography, particularly for the contact layer. The main advantage of the rim PSM approach is its relative ease of application to logic devices. The rim PSM approach, however, requires a significant allocation of reticle space due to mask biasing issues as well as the addition of rim shifters around features. A more important concern is the secondary peak intensity produced by the rim shifters when two or more features are placed in close proximity, as is commonly seen in any dense circuit layout. In this article, a new approach is proposed to make tightly packed rim contacts. Based on the basic principle of phase-shifting, one rim feature is inverted relative to the other to eliminate the secondary peak intensity between two adjacent rim features; we dub this technique ‘‘iRim’’ for ‘‘inverted Rim.’’ Various reticle fabrication methods are available. For the iRim technique to function properly in the case where a phase error exists, it is found that the rim and iRim features need to be structurally identical. In this case, both contacts will possess the same phase error and the resulting focus shift will therefore be in the same direction, eliminating any loss in depth of focus. The iRim configuration is also proposed to be a metrology device for precise phase determination.
Stress-induced pattern-placement errors in thin membrane masks
Authors: Liddle J. Alexander , Volkert C. A.
Published: July 2002

A simple analytical model for determining stress-induced pattern-placement errors in a variety of thin membrane masks is described. The predicted distortions for proximity x-ray, projection ion-beam, and projection electron-beam (SCALPELTM) masks, currently proposed for use with the various technologies, are compared to the maximum allowable errors for successful lithography at sub-0.25 μm design rules. This comparison indicates that these errors may have a significant impact on mask cost and cost of ownership for x-ray and ion-beam lithography.
Pattern distortions in stencil masks
Authors: Randall John N.
Published: July 2002

Stencil marks are required for some forms of projection and proximity printing with charged particles. There are several technological problems associated with the use of stencil masks such as forbidden geometries and gross pattern deformations caused by mask openings which are large even in one dimension. In this article, we will deal with the issue of mask deformation due to thermal effects and pattern-dependent redistribution of stress. We will also discuss approaches to minimizing these pattern distortions.
An industrial plasma process for avoiding charge effect
Authors: Romand Philippe , Weill André , Panabière Jean-Pierre , Prola Alain
Published: July 2002

Insulating materials such as photoresists retain charges during electron or ion exposure. The ultimate performances of techniques such as scanning electron microscopy (SEM), trilayer e-beam lithography, or plasma etching can be strongly affected by this phenomenon: observations of highly resolved resist patterns and the subsequent dimensional measurements by SEM are limited by significant charge effects; resist charge during trilayer electron-beam exposure can produce considerable pattern placement errors; surface charging is also reported to damage etching profiles and to produce microloading effects during plasma etching. Techniques such as metal deposition, use of intrinsically conducting polymers, or Ar+ or H+ high energy implantation are mentioned among others for reducing the electrical resistance of the photoresist patterns. However, due to several major drawbacks (metallic contamination, nonavailability of materials, and global cost of the process), none of these methods has been accepted today at a manufacturing level. This article reports on a new process for increasing the electrical conductance of novolak based photoresist patterns and consequently for avoiding these charge effects.

It consists in subjecting the photoresist to a nonchemically reactive plasma. The process appears to be cost-effective, robust, and presents a wide latitude. The dependence of the electrical conductivity on the various experimental parameters is described. X-ray photon analyses previously conducted at Centre National d’Etude des Télécommunications (CNET) have shown that argon plasma etching, under specific conditions, can create the graphitization of the surface of the photoresist, leading to a net decrease in the electrical resistivity. The results of the various physicochemical analyses reported here indicate that the composition of the materials obtained after plasma treatment is very close to that obtained by high energy ion implantation. It is shown that the argon plasma treatment yields a sufficiently high conductivity level to avoid the charge effects occurring in the three techniques mentioned above. Considering the gain in throughput (30–60 wafers per hour) and in capital cost, compared to the high energy ion implantation process, the argon plasma treatment can be considered as a real industrial process.
Highly accurate critical dimension measurement for sub-0.5-μm devices
Authors: Yamashita Hiroshi , Nakajima Ken , Nozue Hiroshi
Published: July 2002

In the measurement of patterned resists, deviation of the critical dimension (CD) is frequently observed. We have found that contamination on the resist on a Si wafer can degrade the static repeatability more than the charging phenomenon at low accelerating voltage (Vacc), that is, near 1 kV. We investigate the dependence of contamination rate (Rc) and the normalized yield of secondary electrons (δ′) on Vacc and emission current (Ie) in order to clarify the influence of the contamination and charging effects. Experimental results indicate that we can minimize the Rc by optimizing Vacc and Ie. The Rc change cannot be attributed only to the contamination and charging effects, however. It seems, instead, that two competitive reactions (deposition and etching) occur simultaneously during the measurement at low voltage. The etching effect can be interpreted as a dissociation reaction at the resist surface. To reduce the CD deviation and improve the accuracy of the CD measurement, the accelerating voltage and current density must be optimized. Doing so improves the static repeatability from 0.008 to 0.003 μm (3σ).
Profile simulation of electron cyclotron resonance planarization of an interlevel dielectric
Authors: Labun A. H.
Published: July 2002

The planarization of SiO2 interlevel dielectric layers by electron cyclotron resonance reactors has been modeled as the outcome of simultaneous sputter etching and plasma-enhanced chemical vapor deposition. This combination of etching and deposition has been simulated by the repeated sequential execution of two third-party topography evolution codes, one for each process. The simulations reproduced observed profiles and gap-filling properties for etch/deposition ratios from 0.45 to 0.30 and also illustrated the origin of cracks in certain nonideal gaps. The influence of the width and separation of the metal lines over which deposition was simulated was also reproduced.
Electron beam technology: The other end of the spectrum
Authors: Bakish R.
Published: July 2002

A brief review of high power electron guns capable of energies in terms of kilo- and mega-watts is presented. Their use in industrial areas where they have and continue to make contributions will be presented. Melting and refining in the metallurgical industry, looking at its different segments, will be considered first together with a brief reference to their place in single crystal growing and zone refining. This will be followed by a review of their contributions to welding, heat treating and micro-machining. Their role as evaporation tools: in the electronics industry (thin films), for the production of a variety of barriers, for the production of overlay coatings and for production of fiber-reinforced materials and other materials with advanced properties will be discussed.
Lithographic performance of a negative resist under scattering with angular limitation for projection electron lithography exposure at 100 keV
Authors: Tarascon R. G. , Bolan K. , Blakey M. , Camarda R. M. , Farrow R. C. , Fetter L. A. , Huggins H. A. , Kraus J. S. , Liddle J. A. , Mixon D. A. , Novembre A. E. , Watson G. P. , Berger S. D.
Published: July 2002

Scattering with angular limitation for projection electron lithography (SCALPEL)TM [S. D. Berger and J. M. Gibson, Appl. Phys. Lett. 57, 153 (1990)] has been used to evaluate the lithographic performance of a negative-acting silicon containing chloromethylstyrene resist at 100 keV [A. E. Novembre, M. J. Jurek, A. Kornblit, and E. Reichmanis, Polym. Eng. Sci. 29, 920 (1989)]. This article presents the preliminary evaluation of the resist in a small field of view SCALPEL machine using masks with a membrane area of 1 mm2. A resolution of 0.15 μm was obtained at 61 μC/cm2. Furthermore, the good electron-beam sensitivity of this well-characterized negative resist has allowed us to optimize the alignment, astigmatism, and focus of the experimental tool.
Spatial frequency filtering using multiple-pass printing
Authors: Ye Jun , Berglund C. N. , Pease R. F. W.
Published: July 2002

Previous work has shown that dimensional errors [critical dimension (CD) and registration] on photomasks have ‘‘nonwhite’’ spatial frequency spectra with strong peaks caused by the pattern generators [J. Ye et al. (unpublished)], and that the errors’ impact on integrated circuit performance and yield depends on their spatial frequencies [C. N. Berglund et al., J. Vac. Sci. Technol. B 10, 2633 (1992)]. In this article, we study in the spatial frequency domain the effect on these errors of multiple-pass printing with offsets between passes, and find it equivalent to a band-stop filter with the stopping band locations determined by the relative offset and dose between the passes. Therefore, we can systematically design multiple-pass printing strategies that are tuned to minimize mask dimensional errors at those spatial frequencies that are particularly undesirable either due to their large magnitude or due to the fact that they have a particularly bad impact on chip performance and yield. While good designs reduce the error, bad designs may increase the error by converting errors between CD and registration through higher order effects. A good design needs to consider together the relative offset and dose, the spot and address size, and the process parameters.
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t electron beam proximity correction on tungsten x-ray masks
Authors: Gesley M. A. , McCord M. A.
Published: July 2002

100 kV electron beam exposures of tungsten x-ray masks have been made using ghost proximity correction. 0.15 μm lithography is possible on masks having a 0.3 μm thick tungsten absorber. 0.25 μm features are resolved on masks with a 0.6 μm tungsten film thickness. The linewidth control (±5%) and dose latitude (2.5 nm edge shift per 1% dose change) are as good or better than those obtained by dose modulation, and contrast is sufficiently high to permit dry etch pattern transfer into the tungsten absorber. The process latitude makes 100 kV ghost exposures suitable for patterning 1 Gbit dynamic random access memories on 1m x-ray masks.
Applicability test for synchrotron radiation x-ray lithography in 64-Mb dynamic random access memory fabrication processes
Authors: Fujii Kiyoshi , Yoshihara Takuya , Tanaka Yuusuke , Suzuki Katsumi , Nakajima Takashi , Miyatake Tsutomu , Orita Eisaku , Ito Kazuhiro
Published: July 2002

To evaluate the applicability of synchrotron radiation x-ray lithography (SRXL) in ultra-large-scale integration manufacturing processes, we simulate a part of a dynamic random access memory process using SRXL. Four levels of x-ray masks (field, gate, bit contact, and bit line), including fiducial patterns for coordinate/overlay measurement, alignment marks, and 0.4-μm-rule memory cells were fabricated using an i-line stepper. The maximum overlay error between the different level masks was 60–100 nm. In SRXL processes alignment errors of the x-ray stepper were 60–100 nm (3σ), and the overlay errors over a 20-mm-exposure field were 130–160 nm (‖mean‖+3σ) in most of alignment levels. Critical dimension control of 27–47 nm was obtained for gate length and contact hole diameter.
Process technology for InGaAs/InAlAs modulation doped field effect transistors on InP substrates
Authors: Fink T. , Raynor B. , Haupt M. , Köhler K. , Braunstein J. , Grün N. , Hornung J.
Published: July 2002

We present a process for fabricating lattice-matched InGaAs/InAlAs modulation doped field effect transistors (MODFETs) on InP wafers including molecular beam epitaxial growth of a high electron mobility transistor structure consisting of In0.53Ga0.47As and In0.52Al0.48As layers, and electron-beam lithography for gate definition. For selective gate recessing we investigated both wet and dry etch processes. Viable procedures have been found with a citric acid: H2O2:H2O wet etching solution and with an HBr/Ar gas mixture for reactive ion etching (RIE). The selectivities obtained for InGaAs with respect to InAlAs were 14:1 for the wet etchant and 6.7:1 for RIE. Another crucial process step is the MODFET isolation. Earlier work by other groups has shown that implant isolation is difficult on InGaAs [S. J. Pearton et al., Mater. Res. Soc. Symp. Proc. 144, 433 (1989)]. Therefore, we studied both oxygen ion implantation as well as wet-chemical mesa etching for device isolation on the same wafer. Although the isolation sheet resistance achieved with ion implantation is inferior to that obtained in a mesa process, we found similar MODFET performance for both approaches. For devices with a 0.3-μm gate length and 1.3-μm source–drain distance, a transconductance of more than 600 mS/mm and threshold voltages of −1.3 and −0.6 V for wet and dry recessed transistors, respectively, were obtained. Wafer mapping measurements showed that the MODFET data are uniform over an entire 2-in. wafer and also from wafer-to-wafer within a batch.
Nanostructures or submicrostructures from gas/solid reactions as probed by atomic force microscopy
Authors: Kaupp Gerd
Published: July 2002

Uniform nanostructures are formed by chemical reaction of gases with the surface regions of crystals. Their size and shape are determined and depicted by atomic force microscopy (AFM). Both depend on the crystal face and this proves that the bulk crystal structure is governing the long-range molecular transports in the range of up to 200 nm. Craters and volcanoes (eggs’ pallets), volcanoes, or valleys and heights are formed without intervening liquid phases upon reaction of a-cinnamic acid 1 and trans-stilbene 3 with gaseous bromine or (benzyl-) thiohydantoin 5 with gaseous methylamine. If chlorine is reacted briefly with a-cinnamic acid a nanoliquid is formed on the surface and this leads to nanostructuring with the AFM tip at low force via transport of liquid and recrystallization effects. Thus holes with flat bottoms are generated which increase steadily upon continuous AFM scanning. In the case of stilbene and bromine, the initial nanostructures undergo a thermal phase transformation which produces uniform flattened plugs of 250 nm height. The chemical generation of nanostructures is very efficient.
Resists and processes for 1 kV electron beam microcolumn lithography
Authors: Lo C. W. , Rooks M. J. , Lo W. K. , Isaacson M. , Craighead H. G.
Published: July 2002

Low-voltage electron beam lithography has been considered for some time for high-resolution lithography because of reduced proximity effects, increased resist sensitivities, and reduced substrate damage. An accelerating voltage of 1 kV is being considered for the operation of microcolumns that are being developed for use in an innovative, high-speed, high-resolution electron beam lithography system. The development of resists and processes for use at 1 kV then becomes one of the essential components in this developing technology. Since 1 keV electrons have a penetration depth of ∼60 nm in organic polymers, the resists used for electron beam exposures must be correspondingly thin. This makes the development of processes for pattern transfer a challenge. Here, we report on three resist and processing schemes for use at 1 kV which can be used to produce 50–100 nm wide structures. Structures as small as 50 nm wide with 3 to 1 aspect ratios, and trenches 300 nm deep and less than 100 nm wide have been successfully transferred into Si substrates. Despite the use of very thin resists, the transferred patterns do not suffer from noticeable defects.
Electron gun with field-emission array cathodes for vacuum microwave devices
Authors: Golenitsky I. I. , Sazonov V. P. , Chubun N. N. , Rumyantsev S. A.
Published: July 2002

Based on computer simulation, the possibility is studied for the creation of electron guns with multielectrode field-emission array cathodes (MFEAC) for vacuum microwave devices. In comparison with the known Spindt field-emission cathode of the diode type, MFEACs provide low levels of electrons transverse velocities on cathode. Two additional electrodes separated with thin dielectric films are employed in MFEAC: One of the electrodes (focusing) is electrically connected to a emitter, and the second one (accelerating) is connected to an extracting electrode. All the electrodes in MFEAC jointly make up electrostatic lens, which focuses microbeams coming from point emitters. The technique is presented for computer simulation of microbeam formation processes in MFEACs cell and in electron gun with MFEAC; the optimum sizes of the MFEAC cell are specified, providing the suppression of electron’s transverse velocities. The results are described for the simulation of electron gun for a miniature multiple-beam klystron with 100 W output average power in the short-wave section of cm-wavelength range.
Structural and optical behavior of strained InAs quantum boxes grown on planar and patterned GaAs (100) substrates by molecular-beam epitaxy
Authors: Xie Qianghua , Konkar A. , Kalburge A. , Ramachandran T. R. , Chen P. , Cartland R. , Madhukar A. , Lin H. T. , Rich D. H.
Published: July 2002

Strained, coherent InAs islands were grown on GaAs (100) planar substrates by molecular-beam epitaxy (MBE). These coherent islands were buried under GaAs cap layers grown by MBE and migration enhanced epitaxy at low temperature (∼ 400 °C), the latter case exhibiting an order of magnitude stronger photoluminescence (PL). The PL and PL excitation spectra reveal the discrete nature of the density of states of three-dimensionally confined electronic states in the islands. The possibility of placing InAs on a regular array of prepatterned square mesas, size-reduced via buffer layer growth to a ≤150 nm mesa top, was explored. The InAs on mesas with sub-100 nm lateral dimensions is found to have an enhanced critical thickness for two-dimensional to three-dimensional island morphology transition, going from ∼1.8 monolayers (ML) for growth on planar substrate to ≥5 ML for 70 nm mesas. Spectrally and spatially resolved cathodoluminescence studies show these InAs volumes to be optically active.
Carbon-doped InAlAs/InGaAs heterojunction bipolar transistors in solid-source molecular-beam epitaxy using carbon tetrabromide
Authors: Hwang Wen-Yen , Miller D. L.
Published: July 2002

Carbon tetrabromide was used to dope (In,Ga)As layers lattice-matched to InP grown by solid-source molecular beam epitaxy. A hole concentration as high as 1×1020 cm−3 was achieved at a substrate temperature of 400 °C with an As4 source. A dc current gain of 50 was obtained for a carbon-doped N-p-n (In,Al)As/(In,Ga)As heterojunction bipolar transistor (HBT) lattice-matched to InP with the base doped at 1×1019 cm−3. The dc current gain of carbon-doped (In,Al)As/(In,Ga)As HBTs decreased rapidly when the doping concentrations exceeded about 1×1019 cm−3. This correlated with a reduction in photoluminescence intensity for (In,Ga)As doped with CBr4 in the same range, which suggests that the electron minority carrier properties of (In,Ga)As degrade above about 1×1019 cm−3 when using CBr4 doping.
Electron trapping in thin oxide on GaAs and InP at 77 K
Authors: Eftekhari G.
Published: July 2002

Electron trapping in thin anodized layers on GaAs and InP at 77 K was studied using the flat band voltage shift method. Compared with the trap characteristics at room temperature, the capture cross section and density were increased. The trap sites with very small capture cross section at room temperature were not detected at 77 K. A few trap sites were detected at 77 K which possibly act as shallow levels at room temperature. For both GaAs and InP diodes, trap characteristics were found to be a function of the processing conditions.
Low-energy electron interference with Spindt-type microtips
Authors: Py Christophe , Baptist Robert
Published: July 2002

A low-energy electron interferometer was constructed to estimate the potential of field-effect microtips for new applications of electron optics using the De Broglie wave aspect of electrons. Without any shaping or filtering of the beam, interferences with energies down to 140 eV were obtained. This is the first time to our knowledge that an interferometric effect has been observed with microtips fabricated by microelectronics means. We conclude that these sources could be used in compact devices based on the quantum properties of electrons.
Application of the focused ion beam technique to the direct fabrication of vertical-type field emitters
Authors: Ishikawa J. , Ohtake T. , Gotoh Y. , Tsuji H. , Fukayama N. , Inoue K. , Nagamachi S. , Yamakage Y. , Ueda M. , Maruno H. , Asari M.
Published: July 2002

The focused ion beam (FIB) technique has been applied to the direct fabrication of vertical-type field emitters for vacuum microelectronics. A gate and emitter can be formed directly by etching metal/insulator/semiconductor (MIS) structure with an FIB. A rotationally deflected FIB erodes the metal surface to produce a ring-shaped groove, and finally produces a small protrusion made of semiconductor (field emitter). The present process is simple, self-aligned, and a direct process which does not require the electrode material to have a specified chemical property. In the present study, sputter etched structures have been evaluated with a dynamical simulation, and compared with those fabricated under the similar condition. The calculated structure agreed with the fabricated structure, which means the present simulation gives a reasonable estimation of the FIB fabricated structures. Also, attempts have been made to optimize fabrication conditions and emitter materials.
Alignment scheme for through-the-lens alignment
Authors: Zipfel George , Stanton Stuart , White Donald , Vaidya Sheila , Cirelli Ray
Published: July 2002

A real-time through-the-lens alignment system that locks the mask and wafer together via a feedback system on a deep ultraviolet (DUV) camera is described. The mask can be moved to actively track wafer motions even when the resist is being exposed. In support of this, we have devised a novel, high sample rate alignment system. Bench top experiments have verified the basic principles behind the design, emphasizing the ‘‘active’’ alignment mode. A one-dimensional aligner will be installed on a stepper to test the concept with exposures on silicon wafers. The goal is to produce an alignment system that improves both overlay accuracy and throughput on DUV steppers.
Resist charging in electron beam lithography
Authors: Liu W. , Ingino J. , Pease R. F.
Published: July 2002

Charging of the workpiece in electron beam lithography is well recognized as a source of pattern placement error. Despite considerable previous effort there is little quantitative understanding of the problem. A new technique was recently reported in which the surface potential of a resist film during and after exposure was measured directly. Here we describe results obtained using an improved version of the technique for charging of resists under a wide variety of conditions. Some results are as expected, e.g., thicker resists tended to charge more negatively than did thinner ones. Other results are surprising; for example, under certain conditions (7 keV, 0.4 μm polybutene sulfone) there was zero potential at the surface and at higher energies (10 keV) the surface charged positively (0.7 V). The detailed mechanism for positive charging under these conditions is still unclear.
Fabrication of dry etched mirrors for In0.20Ga0.80As/GaAs waveguides using an electron cyclotron resonance source
Authors: Ko K. K. , Kamath K. , Zia O. , Berg E. , Pang S. W. , Bhattacharya P.
Published: July 2002

High quality In0.20Ga0.80As/GaAs total internal reflecting mirrors have been demonstrated. The mirrors were fabricated by dry etching using a Cl2/Ar plasma generated with an electron cyclotron resonance source. The etched mirrors have smooth sidewalls and vertical profile. Mirror reflectivities up to 93% have been measured. The mirror reflectivity has been studied as a function of etch conditions including ion energy and ion flux. The effects of etch profile on reflectivity were also investigated. It was found that the reflectivity of the etched mirrors was not sensitive to either the ion energy or the ion flux used for the etching. As long as a vertical profile and smooth surface morphology are maintained, the reflectivity remains at ∼90% even when high radio-frequency power (200 W) and high microwave power (150 W) were used for etching. However, significant degradation of the mirror reflectivity to only 47% was found on mirrors with a slight undercut profile and rougher sidewalls. The results suggest that mirror reflectivity is much more sensitive to etch profile. Triangular ring lasers with etched mirrors were also fabricated, and threshold current as low as 3.7 mA has been demonstrated, showing the high quality of the etched mirrors.
Fabrication of sub-10 nm silicon tips: A new approach
Authors: Huq S. E. , Chen L. , Prewett P. D.
Published: July 2002

Nanometer scale silicon tips are becoming increasingly important for use as field emitters. Applications include high resolution field emission displays and ultrahigh-speed devices. Of crucial importance is the precise control of tip shape and size if field emitters are to be used as microelectronic elements. This article reports on the fabrication procedure of silicon based gridded field emitter tips, using a new fabrication route which eliminates the need for an oxidation sharpening step.
Nanolithography using a laser focused neutral atom beam
Authors: Natarajan Vasant , Behringer R. E. , Tennant D. M. , Timp G.
Published: July 2002

Drawing on techniques developed for laser cooling and trapping of neutral atoms, we demonstrate a novel lithographic tool where near-resonant laser light is used to directly control the position of neutral atoms during deposition. The power of this technique is demonstrated by focusing sodium atoms into narrow lines as they traverse a one-dimensional standing wave. We have studied the dependence of the linewidth and contrast on the light field parameters, such as detuning, intensity, and interaction length. The dependencies follow the predictions from a simple model and, under optimal conditions, we obtain high contrast lines with a resolution of 45 nm over an area of 0.2×6 mm2. Numerical simulations indicate that further improvement below 10 nm is likely in the near future.
Effect of thin film interference on process latitude in deep ultraviolet lithography
Authors: Azuma T. , Sato T. , Aochi H.
Published: July 2002

The effect of thin film interference on process latitude in deep UV lithography is investigated using a precise electrical linewidth measurement technique. The experimental results calculated by exposure–defocus plots show swing curve type dependencies of critical dimension variation, maximum depth-of-focus (DOF) range, and centered focus position. It is demonstrated that the maximum DOF ranges for equivalent incoupling points along the swing curve approximately follow a linear equation introduced in accordance with simulation results of aerial image contrast. It is also verified that a thinner resist with a resist thickness corresponding to an optimum incoupling point along the swing curve can provide a distinct advantage in maximum DOF range, in spite of a remarkably low aerial image contrast, especially in the case of critical patterns. Moreover, it is found that the centered focus positions of the critical patterns exhibit a trend to offset in the positive defocus direction with increasing resist thickness.
Asymmetric overhung resist profile fabricated by optical lithography
Authors: Jinbo Hideyuki , Ito Toshio , Yamashita Yoshio
Published: July 2002

We propose a new and simple fabrication technique for resist patterns of asymmetric overhung profiles. This technique uses an asymmetric blind phase edge line (AB PEL) mask and a negative photoresist which has a large absorption coefficient. The AB PEL mask has repeated chrome line patterns, called blind patterns, to reduce light intensity at large undercut overhangs of resist space. The bottom part of the resist film under the blind area is not sufficiently irradiated to become insoluble in the developer. An asymmetric overhung profile with 0.25 μm space width at the resist top is fabricated. This profile enables fabrication of asymmetric gate recesses for field-effect transistors in compound semiconductors.
Novel postexposure bake simulator: First results
Authors: Capodieci Luigi , Krasnoperova Azalia , Cerrina Franco , Lyons Chris , Spence Chris , Early Kathy
Published: July 2002

We have designed and implemented a simulator that models the physics of the chemically amplified photoresist process postexposure bake (PEB) step, based on a general mathematical formulation. The photoacid loss due to kinetic reaction and the photoacid diffusion are simulated using experimentally determined model parameters. The PEB simulator, which can be used in conjunction with any lithographic image modeling software, has been integrated into the CXrL ToolSet, a comprehensive modeling system for x-ray lithography. The PEB simulator converts the deposited dose into an initial concentration of photoacid, and then computes its evolution and the corresponding evolution of the protected sites, for a given bake time and temperature. System dynamics are defined by coupled partial differential equations containing acid loss and diffusion terms. As the two phenomena take place at the same time during PEB, the numerical algorithm does not separate the terms in the calculation. An alternating direction implicit and explicit numerical differentiation technique for solving a multidimensional partial differential equation in x and z has been employed, resulting in a system which reduces computational complexity without loss of accuracy or speed. Linewidth can be extracted from the final profile of the protected sites, or, alternatively, the concentration of the protected sites can be converted into a dissolution rate and fed to other dissolution modeling tools to generate a developed resist profile. Process latitude simulations can be performed to study linewidth variation with respect to dose, gap or focus, bake temperature, and time. An initial evaluation has been performed by comparing simulation results with data from an x-ray lithography experimental study.
X-ray exposure system for induced chemistry and dry processes in microlithography
Authors: Vladimirsky Y. , Morris K. , Klopf J. M. , Vladimirsky O. , Saile V. , Scott J.
Published: July 2002

A new x-ray microlithography exposure system has been designed and built at the Center for Advanced Microstructures and Devices (CAMD) to meet the specific demands of synchrotron radiation assisted processing for microfabrication and high aspect ratio micromachining. The system consists of a broadband transmission (1.2–6.5 Å) beamline and a multichamber x-ray exposure station which can simultaneously provide x-ray exposure and activation, plasma, or reactive ion etching (RIE). The beamline is operational at the CAMD 1.3–1.5 GeV synchrotron storage ring. The x-ray exposure station includes filter and exposure chambers. A filter chamber is incorporated into the exposure system to optimize the radiation spectra for thick resist (in excess of 1 mm) exposures and to protect the Be window from reactive gases during exposure. Two assisting agents, x-ray irradiation and rf (13.53 MHz) induced plasma for RIE, can be used separately or in combination. Samples of ∼500-μm-thick PMMA resist have been exposed in neutral and reactive atmospheres and successfully developed. The preliminary results indicate that He gas acts as a ‘‘catalyst’’ for PMMA losses during exposure.
Emission property and current fluctuation of starlike thin-film field emitter array with self-feedback function
Authors: Kaneko Akira , Sumita Isao , Kimura Hideyoshi , Matsuura Jun , Kondo Yukihiro
Published: July 2002

An advanced thin-film field emitter array (FEA) with self-feedback function which suppresses the fluctuation of emission current was fabricated by self-aligned processing. Each starlike miniature field emitter in the FEA has a double layer of a resistive and an electron emitting layer. 200-μm-square FEAs of Mo or W emitters, both had a threshold voltage of about 50 V, emitted the current of 4 μA at a gate voltage of 90 V. The emission current of a 5-mm-sq FEA was 300 μA at 85 V. Insertion of the resistive layer with 2.4 MΩ worked to stabilize the current fluctuations, but insufficient for practical applications. However, it was found that the resistive value should be above 50 MΩ to suppress the emission current fluctuations less than 5%. It is confirmed that the electron emission in a 5-mm-sq FEA was stably continued during ∼1200 h.
Analytic expressions for emission characteristics as a function of experimental parameters in sharp field emitter devices
Authors: Jensen K. L. , Zaidman E. G.
Published: July 2002

An analytical treatment of elliptical field emitting structures which includes image charge effects off axis and the variation of field along the tip is given. The angular distribution of electron emission along the tip, the total emitted current, and the area factor are calculated as a function of emitter to anode distance, tip radius, tip height, and the anode-tip voltage difference. Errors arise if the planar Fowler–Nordheim (FN) equation is used to govern electron emission; we show how to correct this by a modification of the FN equation which includes changes in fields and image charge due to curvature. An analytic form of the area factor is given and compared to a calculation based on the exact transmission coefficient and various Wentzel–Kramers–Brillouin-based approximations to it. The analysis is extended beyond diode geometries with the inclusion of additional electrodes, allowing devices such as triodes to be modeled.
Characterization of field emitter structures by means of modeling electron trajectories in vacuum
Authors: Kopka Peter , Ermert Helmut
Published: July 2002

A typical vacuum microelectronic structure with a conical field emitter tip, gate and anode is simulated by computer. The electric field is calculated as a function of the applied voltage using the finite element method, and the emission current density on the surface of the emitter is evaluated applying Fowler–Nordheim theory. By solving Newton’s equations of motion, the electron trajectories are found. The solution of Poisson’s equation shows that the influence of space charge on the electric field is negligible. Field distributions and electron trajectories which permit a more precise understanding of the operation mode of the structure are presented. Based on these results, the current–voltage characteristics and some derived parameters (transconductance, low-signal-gain, corner frequency) are shown, including guidelines for the design.