bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy band of manipulated atomic structures on an insulator substrate
Authors: Yamada Toshishige , Yamamoto Yoshihisa , Harrison Walter A.
Published: July 2002

Stimulated by recent progress in atom manipulation technology, the electronic properties of periodic structures artificially created with atoms on a substrate surface are studied, where constituent atoms are isolated from substrate atoms and interact with one another through neighboring-atom interactions. By reducing the lattice constant from infinity, the neighboring-atom interaction is gradually turned on, and discrete atomic states broaden to form energy bands. Band structures of a simple one-dimensional atomic chain, a two-dimensional square array, and two parallel atomic chains formed by Si are calculated as a function of lattice constant using the tight-binding theory with universal parameters. For practical lattice constants, these Si structures are all metallic due to the existence of the π band, within which the Fermi energy lies; however, at very low spacings, possible for carbon, the double chain can become insulating. For group-II elements such as Mg, the π band and the conduction band are empty while the valence band is fully occupied. The band-gap variation with lattice constant is reflected in the electronic properties directly: e.g., a Mg atomic chain is insulating for lattice constants greater than or less than 4.2 Å, at which the band gap disappears and the chain becomes metallic.
Passivate SiNx halftone phase shifting mask for deep ultraviolet exposure
Authors: Ito S. , Iwamatsu T. , Sato H. , Asano M. , Kawano K. , Miyashita F.
Published: July 2002

Halftone phase shift masks with a single-layer SiNx absorption film whose stoichiometric ratio x was controlled were developed at 365 and 248 nm, respectively. Because this stoichiometric ratio x was smaller than 1.33 (Si3N4), the SiNx halftone films were unstable, especially during 248 nm exposure, causing a transmittance error. In this article, we show how to get stable SiNx film for 248 nm exposure.
Characterization of resist profiles using water enhanced focused ion beam micromachining
Authors: Stark T. J. , Griffis D. P. , Russell P. E.
Published: July 2002

The use of water enhanced focused ion beam micromachining has been investigated as a technique to aid in the characterization of resist profiles. The increase in removal rate and the decrease in redeposition associated with the water enhancement allows clean cross sections (no redeposition of substrate material) to be formed at precise locations allowing accurate resist sidewall characterization and eliminates the need for wafer cleaving. The experimental conditions (water flux and beam exposure parameters) were optimized to produce cross sections with minimum artifacts. It was found that water pressure of approximately 80 mTorr, line step distances corresponding to half the beam diameter and dwell time roughly twice that required to clear the resist resulted in nearly vertical cross section faces with minimum edge artifacts.
SiO2 to Si selectivity mechanisms in high density fluorocarbon plasma etching
Authors: Kirmse K. H. R. , Wendt A. E. , Disch S. B. , Wu J. Z. , Abraham I. C. , Meyer J. A. , Breun R. A. , Woods R. Claude
Published: July 2002

This study examines the influence of plasma chemistry on SiO2 to Si etch selectivity in high density C2H2F4(1,1,1,2-tetrafluoroethane)/O 2 and CHF3/H2 discharges. Etch rate measurements of Si and SiO2 have been combined with chemical characterizations of the discharge using optical diagnostics and an in-line quadrupole mass spectrometer. The gas phase concentrations of CF2 and F as well as the mass spectrum of ions incident at the substrate have been measured for conditions producing SiO2/Si selectivities from 1 to over 30. For low density sources with high neutral to ion fluxes, the conventional theory is that selectivity is governed by the relative content of fluorine versus carbon in the fluorine and fluorocarbon radicals incident on the substrate. However, for the high density plasma discharges studied, the conventional theory may apply only when the contributions of both neutral radicals and fluorocarbon ions, CF+x, are considered. For the case of oxygen addition to C2H2F4 discharges, reactions between the fluorocarbon surface film and oxygen in the gas phase may also be important in controlling selectivity.
Effects of etch-induced damage on the electrical characteristics of in-plane gated quantum wire transistors
Authors: Ko K. K. , Berg E. W. , Pang S. W.
Published: July 2002

In-plane gated (IPG) quantum wire transistors were fabricated using dry etching in a Cl2/Ar plasma generated with an electron cyclotron resonance source. The electrical characteristics of the IPG transistors were correlated with the geometrical dimensions as well as the dry etching and passivation conditions. In-plane gates with the width of the channel (Wc) and the width of the gate isolation (Wg) ranging from 100 to 850 nm were studied. Good field-effect transistor characteristics with transconductances up to 371 mS/mm were obtained on these devices. At a gate-source voltage (VGS) of 2 V, the saturated drain-source current (IDSAT) increased from 68 to 153 μA as Wc increased from 440 to 800 nm. No current was measured on IPG transistors with Wc ≤−130 nm. The quasi-one-dimensional channel can be completely pinched off with VGS ≤−1 V. It was found that the gate leakage current decreased with a wider Wg and a deeper depth for the gate isolation. The leakage current at VGS=2 V decreased significantly from 250 to <0.1 pA when the etch depth increased from 320 to 440 nm. The gate leakage current and IDS were also found to increase with rf power used for etching due to additional defects generated at higher ion energy. These defects, however, can be passivated with low energy chlorine species, and reduction of the gate leakage current from 40 to 4.4 nA was observed after a 1 min Cl2 plasma passivation.
Study on improving InxGa1−xAs/InyGa1−yP heterointerfaces in gas-source molecular beam expitaxy
Authors: Yan C. H. , Tu C. W.
Published: July 2002

The As/P exchange behavior on a GaAs and an InxGa1−xAs surface exposed to a P2 flux and on an InyGa1−yP surface exposed to an As2 flux has been studied by reflection high-energy electron diffraction (RHEED) in a gas-source molecular beam epitaxy system. We found the exposure of InxGa1−xAs to a P2 flux results in a severe substitution of As atoms by P atoms at the normal growth temperature (520 °C), forming a strained transition layer and causing a rough surface within 10 s, which is indicated by a spotty RHEED pattern. The InyGa1−yP surfaces, however, remained relatively stable under an As2 flux. Two methods (a thin protective layer and low-temperature growth) for eliminating the As/P exchange have been developed, and both result in abrupt interfaces.
Simultaneous imaging of Si(111) 7×7 with atomic resolution in scanning tunneling microscopy, atomic force microscopy, and atomic force microscopy noncontact mode
Authors: Güthner Peter
Published: July 2002

The reconstructed Si (111) 7×7 surface was imaged in several operation modes of the combined ultrahigh vacuum atomic force microscope/scanning tunnel microscope. By imaging single atom defects on the sample surface a clear proof of the atomic resolution in noncontact mode of the force microscope was possible. By simultaneous measurements of several interaction parameters and by the investigation of force-distance curves, it was possible to explain the origin of the interaction.
Analysis of vacuum microelectronic components by the use of special finite elements
Authors: Kopka Peter , Ermert Helmut
Published: July 2002

For vacuum microelectronic devices special finite elements have been introduced which are able to describe field enhancements near cone emitters with a small radius of emitter curvature in an effective way. Compared to conventional methods, simulations using these elements can be carried out very precisely with less computer time and storage.
In1−xAlxP/InAlAs/InGaAs and InAlAs/InAs0.3P0.7 high-electron mobility transistor structures grown by solid source molecular beam epitaxy
Authors: Hoke W. E. , Lemonias P. J. , Weir D. G. , Hendriks H. T. , Chou L.-J. , Hsieh K. C.
Published: July 2002

InP-based high-electron mobility transistor (HEMT) structures have been grown containing strained In1−xAlxP Schottky layers with x=0.15–0.25. The band gaps of the strained layers in the HEMT structure were determined by photoreflectance spectroscopy. For x=0.15, Hall mobilities were comparable to those obtained in an analogous InAlAs/InGaAs structure. Lower mobilities were obtained with higher x value. Misfit dislocations were observed in plan view transmission electron microscopy for x=0.25 but not x=0.15. HEMT structures were also grown with InAsP channel layers containing moderate sheet densities. Photoluminescence measurements of the quantum well region indicated transitions to two electronic subbands. The InAs1−xPx composition was found to be weakly dependent on the phosphorus flux and uniform on 2 in. wafers.
Study of interface abruptness of molecular beam epitaxial GaAs/AlAs superlattices grown on GaAs (311) and (100) substrates
Authors: Hsu Y. , Wang W. I. , Kuan T. S.
Published: July 2002

Molecular beam epitaxial GaAs/AlAs superlattices were grown on GaAs (311)A, (311)B, and (100) substrates at 600 °C. High resolution x-ray diffraction and transmission electron microscopy were employed to characterize the interface abruptness and the crystallinity of the superlattices. The high resolution x-ray diffraction results show a similar crystalline quality in both the (100) and (311) superlattices. A detailed analysis by transmission electron microscopy further reveals that superior interface profiles are achieved in the (311) superlattice. The observed inferior interface profile in the (100) orientation is most likely attributable to the meandering of steps during crystal growth.
Influence of surface and interface states on the electrical properties of an Al0.2Ga0.8As/In0.18Ga0.82As δ -modulation-doped heterostructure
Authors: Young A. P. , Wieder H. H.
Published: July 2002

The influence of surface states on the properties of a Al0.2Ga0.8As/In0.18Ga0.82As modulation-doped heterostructure has been measured experimentally. By comparing gated and ungated structures, it is shown that the recess etch of a thin doped cap results in the drastic reduction of both the charge density and mobility in the two-dimensional electron gas, with the charge density and mobility at low temperatures dropping by a factor of 2.1 and 4.5, respectively. By illuminating the sample, there is a small change in the charge density and mobility which can be attributed to the activation of acceptor type deep levels in the AlGaAs. Furthermore, by applying a positive gate bias, most of the mobility is recovered in both the dark and illuminated cases. The charge control law at low temperatures for a gated Hall bar shows nonlinearities that are attributed to interface states and not due to parallel conduction, DX centers, or deep level states in the bulk of the AlGaAs. These results show that the change in the nature and occupation of the states at the surface and the Al0.2Ga0.8As/In0.18Ga0.82As interface can have a direct impact on the properties of a heterojunction 40 nm away.
Fabrication and testing of vertical metal edge emitters with well defined gate to emitter separation
Authors: Fleming J. G. , Ohlberg D. A. A. , Felter T. , Malinowski M.
Published: July 2002

Vertical metal edge emitter arrays with well defined gate to emitter separations have been fabricated. The emitter to gate spacing is determined by the thickness of a deposited layer which can also serve as a current limiting resistor. Current limiting resistors can also be formed by a self-aligned etch of the underlying substrate. Parts with 300 nm emitter to gate spacing created using a chemical mechanical polishing based process begin to emit at as low as 60 V. While those created using a reactive ion etching process with 200 nm emitter to gate spacing begin to emit at 40 V. Emission stability is good and dc current densities of up to 3 A/cm2 from 100 emitter arrays on a close packed 5 μm pitch have been demonstrated.
New approach to manufacturing field emitter arrays with sub-half-micron gate apertures
Authors: Lee Chun Gyoo , Ahn Ho Young , Park Byung Gook , Lee Jong Duk
Published: July 2002

As an attempt to develop a field emitter array with sub-half-micron gate openings for low voltage operation, a new fabrication method has been proposed and demonstrated. The key element of the new process is forming the gate insulator by local oxidation of silicon (LOCOS), resulting in the reduction of the gate hole size due to the lateral encroachment of oxide, ultimately compared with the nitride disc size formed by a conventional contact printer. Feasibility of scaling down the gate hole size of a field emitter to sub-half-micron has been proved successfully, and the field emitter with a 450 nm diam gate opening has been fabricated and characterized. For a 2500-tip array with 450 nm diam gate openings, the anode current of 115 μA(∼50 nA/tip) was measured at the gate voltage of 41 V, while the gate current was less than 0.3% of the anode current. Considering the cathode current level required for flat panel display applications and the measured emission characteristics, the fabricated emitter array is expected to operate at a column drive voltage of about 16 V peak-to-peak.
Novel high-density plasma tool for large area flat panel display etching
Authors: Heinrich F. , Bänziger U. , Jentzsch A. , Neumann G. , Huth C.
Published: July 2002

A novel dry etch tool—large area source supported ion etching (LASSIE)—has been developed appropriate for the processing of substrate sizes of presently up to 600×400 mm2. The plasma is produced through an array of four inductively coupled plasma sources driven by one common 13.56 MHz generator. A second rf generator serves for substrate biasing. Plasma diagnostic data suggest that LASSIE has strong capabilities for future large area etch applications avoiding several drawbacks of conventional reactive ion etching (RIE) in parallel-plate reactors. In particular considerably higher etch rates are to be expected since the plasma densities are roughly one order of magnitude higher than in conventional RIE. In addition the processing will be more flexible and better controlled due to the decoupling of plasma densities and ion bombardment energies. A scale-up with respect to the processing of wafer sizes larger than presently envisaged is easily achieved by the LASSIE concept.
Implications of excess strain in As compound/P compound III–V multilayer superlattices grown by metal-organic vapor-phase epitaxy
Authors: Clawson A. R. , Hanson C. M.
Published: July 2002

The As/P exchange behavior at interfaces of As compound/P compound heterojunction superlattices has been assessed by observing changes in average lattice spacing when very thin but different thickness As compound layers are inserted into InP, or P compound layers inserted into GaAs. Compositional changes are inferred from strain behavior measured by x-ray diffraction. Implications of the data are: (1) As rapidly displaces P and P slowly displaces As; (2) As atoms displace P atoms and reconstruct as a discrete single layer above 600 °C and as a double layer below 600 °C when InP surfaces are exposed to AsH3; and (3) interfaces and layers of different P compounds on GaAs show the same temperature-dependent inclusion of As.
Friction on the atomic scale: An ultrahigh vacuum atomic force microscopy study on ionic crystals
Authors: Lüthi R. , Meyer E. , Bammerlin M. , Howald L. , Haefke H. , Lehmann T. , Loppacher C. , Güntherodt H.-J. , Gyalog T. , Thomas H.
Published: July 2002

We performed atomic force microscopy in ultrahigh vacuum on the ionic crystal of KBr(001). The morphology and the tribological properties of this cleavage face are characterized and discussed. The local friction coefficient was extracted by means of the two-dimensional histogram technique. For loads below 3 nN a linear behavior was found between normal and lateral forces yielding a friction coefficient of less than 0.04. In this load regime, wearless friction is observed. For higher loads, the friction coefficient increases to a value of about 0.7–1.2. The corresponding topography images reveal the typical onset of wear. On the atomic scale a periodicity of 4.7 Å was found which corresponds to the distance of equally charged ions on the KBr(001) surface. On this scale, the lateral force map exhibits the typical stick-slip phenomenon which is discussed in terms of a novel theoretical approach.
Reliability analysis of 4 in. field-emission display
Authors: Kim J. M. , Hong J. P. , Kim J. W. , Choi J. H. , Park N. S. , Kang J. H. , Jang J. E. , Ryu Y. S. , Yang H. C. , Gorfinkel B. I. , Roussina E. V.
Published: July 2002

4 in. field-emission display (FED) devices have been constructed and analyzed utilizing Spindt-type cathodes, uniquely developed low-voltage phosphors and spacers. The cathode was especially fabricated without using a resistive layer. The reliability and the feasibility of the FED device have been tested both in a vacuum chamber and in a fully sealed condition. The electrical aging effect on microtip emission properties were carried out, which resulted in significant enhancement in electrical characteristics of the FED device. The fully sealed FED device was analyzed as a function of lifetime. Additionally, the characteristics of the phosphor and the spacer used in our FED device are discussed.
Monitoring of subquartermicron line and space pattern by ellipsometry
Authors: Arimoto Hiroshi
Published: July 2002

This article reports on the ellipsometric monitoring of 0.3- and 5-μm pitch line/space patterns fabricated by electron-beam (EB) lithography (HL700F). The effects of exposure dosage on pattern formations and the subsequent ellipsometric measurements were investigated. The results suggest that ellipsometry can be practical for monitoring pattern widths and cross-sectional shapes. Regression analysis was applied to predict the linewidths by using ellipsometric parameters. A good agreement between the predicted and actual values was achieved. Remaining errors of 3.7 and 2.8 nm are considered to be due to actual fluctuations in pattern widths or errors in CD-SEM measurements. Exposure doses which would provide a good index to ensure that patterns are well formed, and that the remaining resist is thick enough were also predicted. Regression analysis results were used to evaluate the widths of monitoring patterns fabricated regularly by a variable shaped EB machine (HL600) over the course of six months.
Scanning acoustic tunneling microscopy and spectroscopy: A probing tool for acoustic surface oscillations
Authors: Hesjedal T. , Chilla E. , Fröhlich H.-J.
Published: July 2002

A method is presented for the universal probing of surface acoustic waves (SAWs). For measuring high frequency SAWs by scanning tunneling microscopy (STM) a stroboscopic snapshot technique was employed, named scanning acoustic tunneling microscopy. The amplitude and the phase of a state of oscillation within a SAW field are a superposition of the surface topography and the oscillation trajectory. Measuring with atomic resolution the observed contrast can be understood by a spherical tunneling model. A STM based system is proposed that reaches submicron resolution for the quantitative evaluation of elastic constants. With this system the velocity dispersion is obtained from the detection of laser generated SAW pulses by a broadband STM. Scanning acoustic tunneling spectroscopy using different acoustic modes opens a door for quantitative studies of nanoscale structures.
Investigation on a novel vacuum microelectronic pressure sensor with stepped field emission array
Authors: Xia S. H. , Liu J. , Cui D. F. , Han J. H. , Chen S. F. , Wang L.
Published: July 2002

This article investigates a novel vacuum microelectronic pressure sensor in which the cathode emission array is distributed over a stepped cathode base instead of over a conventional flat cathode base. Our computer simulation results indicate that using the stepped field emission array gives the potential of increasing the sensor’s sensitivity and expanding its measurement range. Computer simulations are presented, and some experimental results are briefly reported.
Gallium desorption behavior at AlGaAs/GaAs heterointerfaces during high-temperature molecular beam epitaxy
Authors: Mahalingam K. , Dorsey D. L. , Evans K. R. , Venkat Rama
Published: July 2002

A Monte Carlo simulation study is performed to investigate the Ga desorption behavior during AlGaAs-on-GaAs heterointerface formation by molecular beam epitaxy. The transients in the Ga desorption rate upon opening the Al shutter are shown to be associated with the concurrent reduction in the V/III flux ratio. Monte Carlo simulations employing a constant V/III flux ratio yield a “steplike” variation in the Ga desorption rate with the resulting interfaces closer in abruptness to the ideal AlGaAs-on-GaAs interface. Further details on the stoichiometry of the interface and its relationship with predicted Ga desorption profiles is presented.
Study on surface and interface structures of nanocrystalline silicon by scanning tunneling microscopy
Authors: Gao Juning , Yang Haiqiang , Liu Ning , Shi Dongxia , Jiang Yueshan , Xue Zengquan , Pang Shijin , He Yuliang
Published: July 2002

The scanning tunneling microscope has been employed to study the morphology, atomic surface structures, and grain interface of hydrogenated nanocrystalline silicon (nc-Si:H)before and after hydrofluoric acid (HF) etching. It was found: (1) The nc-Si:H films were composed of many different sizes of grains and these grains were composed of many finer grains. (2) There were line structures on the surface of the fine grains and loop structures at the grain boundaries without HF treatment. After etching, two more structures were observed: loop structures on the surface of fine grains and spider bonding structures besides the interface of fine grains. (3) The loop structures found at the grain boundaries was larger and more irregular than those on the grain surfaces. Line structures were similar to crystal silicon, but the distance between lines was enlarged. Considering the experimental results, a discussion was made about the formation mechanism of these atomic structures.
Formation of nanocrystals in a-Si thin films induced by pulsed laser ultraviolet irradiation
Authors: Chvoj Z. , Cháb V. , Borusı́k O.
Published: July 2002

We extend the theoretical model of recrystallization of a-Si films induced by pulsed laser irradiation and determine c-Si cluster distribution in the solid phase and we discuss the possibility of nanocluster formation in the a-Si thin layer. Our theory is based on the description of nucleation and growth of the crystalline phase in molten Si during fast heating and cooling processes. We are able to describe nonequilibrium solidification, including the distribution of nanocrystals as a function of laser pulse energy. Calculations of temperature distribution during recrystallization processes and the kinetics of crystalline phase formation show that nucleation of c-Si in l-Si must be taken into account in simulations of recrystallization of a-Si induced by high energy density pulsed laser irradiation (>200 mJ/cm2). The presence of nanoclusters in the Si layer is possible if recrystallization starts from the strong supercooled l-Si, e.g., if a-Si is melted immediately.
Error budget of step height and pitch measurement using a scanning tunneling microscope with a three-dimensional interferometer
Authors: Fujii Toru , Yamaguchi Masataka , Suzuki Masatoshi , Yamada Hirofumi , Nakayama Kan
Published: July 2002

Scanning tunneling microscopy (STM) is well known for its high lateral resolution and nondestructive surface profiling capability but its potential as a profiler for dimensional measurement has rarely been exploited because of its unreliable vertical accuracy. In NANO III, a STM was presented that was capable of 250 μm line scanning secured by a parallel spring mechanism in the X direction; it employed an interferometric monitoring STM tip, allowing feedback controlled motion in the Z direction. For this device, errors of step height and pitch measurements on a surface topography standard are estimated. The uncertainty of the 3 μm pitch and 100 nm step height measurements using the STM is 1.05 and 0.41 nm, respectively. The uncertainties are induced by thermal expansion, the motion of the scanners, the nonlinearity of the interferometer, and geometrical error. In the 100 nm, step height measurement, the sum of the standard deviation of the measured data and the total error is still in the subnanometer range.
Fabrication of probe tips for reflection scanning near-field optical microscopes: Chemical etching and heating-pulling methods
Authors: Xiao Mufei , Nieto Jesús , Machorro Roberto , Siqueiros Jesús , Escamilla Hector
Published: July 2002

Work is described on the fabrication of uncoated probe tips for reflection scanning near-field optical microscopes. A chemical etching process with a rotator, and a simple device to make the tips by a heating-pulling method without a heating laser are introduced. Both techniques allow some manipulation of the tips. Merits and demerits of these two methods are discussed. Finally, it is suggested that observation of the far field scattering pattern of the tips can be used to check the usefulness of the tips.
Highly preferred (111) texture aluminum-copper films formed with argon plasma treatment of the titanium underlayer and their electromigration endurance as interconnects
Authors: Kamoshida Kazuyoshi , Ito Yasuyuki
Published: July 2002

A new fabrication technology for producing hypertextured aluminum-copper (Al–Cu) films has been developed. The key feature of this technology is the argon (Ar) plasma treatment of the titanium (Ti) underlayer. The full width at half-maximum values of the Al (111) rocking curve decrease with increasing Ti etched thickness. That is, the texture of the Al–Cu film improves with increasing Ti etched thickness. The Ti surface treated with Ar plasma has a high surface energy because the Al island wetting angle is small. We think this means the Ar-plasma-treated Ti surface structure is amorphouslike and rough. Consequently, highly preferred (111) texture Al–Cu films were obtained with argon plasma treatment of the Ti underlayer. The electromigration (EM) lifetime of these films is one order of magnitude higher than that of films obtained without the plasma treatment. The longer EM lifetime of the hypertextured Al lines is considered to be due to the small grain-boundary diffusivities for the bamboo microstructure. The argon plasma treatment of the titanium underlayer, combined with Al–Cu deposition, makes it possible to form highly EM-resistant multilevel interconnections without any of the drawbacks of the conventional method.
Magnetic force microscope images of magnetic domains in magnetic garnet
Authors: Tian F. , Wang C. , Shang G. Y. , Wang N. X. , Bai C. L.
Published: July 2002

Magnetic domains in (YGdBi)3(GaFe)5O12 magnetic garnet have been studied using magnetic force microscopy (MFM). MFM results have demonstrated that the undisturbed magnetic domain structure in the garnet could be obtained with a soft magnetic tip. It is further observed that the stray field emanating from a hard tip could magnetize the low-coercivity garnet and alter the widths of the domain region. In addition, when an external magnetic field is applied to the garnet, a sequence of variations of the magnetic domain configuration in the garnet is clearly identified. The discussions on the effect of magnetic tip of MFM on magnetic domains and the external field on magnetic tips will also be presented.
Imaging, polymerization, and reconstruction of polystyrene films with a scanning tunneling microscope
Authors: Hua Z. Y. , Xu W.
Published: July 2002

Polystyrene microparticles can be investigated by using a scanning tunneling microscope. The observed images show the hydrogen atoms on the phenyl groups and the extended polymer chains without entanglement. After a sustained tip scanning, some of the polystyrene surfaces develop a highly ordered structure. Furthermore, the polymerization of styrene monomers can be initiated by the tip field, to form nanometer-scale polystyrene films on graphite substrates, in air at room temperature. The yield was verified by time-of-flight secondary ion-mass spectroscopy.
Nanostructuring by reactive accelerated cluster erosion
Authors: Gruber A. , Gspann J. , von Blanckenhagen P.
Published: July 2002

Accelerated ionized cluster beams are used for surface nanostructuring of bulk diamond, chemically vapor deposited (CVD) diamond films, single-crystalline silicon, or glass, among others. Beams of CO2 clusters with about 1000 molecules per unit charge are accelerated to up to 120 keV kinetic energy for mask projective surface bombardment. Patterning is achieved via physical as well as chemical surface erosion. Very smooth eroded surfaces result for bulk natural diamond, silicon, and glass. Polycrystalline, strongly faceted CVD diamond films are effectively planarized. Submicrometer structures with adjustable wall inclinations can be generated. Atomic force microscopy of isolated impact structures reveals hillocks instead of craters. The collective motion of the impacted surface material is considered crucial for the cluster impact induced nanomodifications.
Fabrication and characterization of volcano-shaped field emitters surrounded by planar gates
Authors: Lee Chun Gyoo , Park Byung Gook , Lee Jong Duk
Published: July 2002

Micron-sized volcano field emitters have been developed and demonstrated using a new fabrication process. The key element of the process is the formation of the volcano-shaped thin-film emitter by sputtering technique, which results in very thin emission sites due to the shadowing effect of the masking oxide disk. For the emitter array with 1.5-μm-diam gate apertures, an anode current of 0.1 μA per emitter was obtained at the gate voltage of about 88 V. The emission performance is comparable to that of the cone-like field emitter with the same gate hole size. Since the field conversion factor of an off-axis rim must be much smaller than that of the apex of a cone emitter with the same effective emission radius, the comparable operating voltage between two types implies the formation of the rim emitters with extremely thin emission sites by the new process.
Electron optical system for the x-ray mask writer EB-X2
Authors: Saito Kenichi , Morita Hirofumi , Kato Junichi , Shimazu Nobuo
Published: July 2002

An electron optical system that yields a beam voltage of 100 kV and a beam edge resolution of 20 nm was developed for a variably shaped electron beam writing system, the EB-X2. In order to improve the beam edge resolution, the objective lens and main deflector were designed on the basis of the uniform field concept, and the optimum beam half-angle was determined by beam profile calculations. The optimized design provides a beam edge resolution of 20 nm for a 650-μm-square deflection field and a beam current of 250 nA. Given the high acceleration voltage, it is possible that the electron optical column could be too high to fit into a clean room. To shorten the height of the electron optical column, the lens configuration was carefully examined. The results show that the height of the column is a minimum when the first shaping aperture is placed in the principal plane of the illumination lens. This finding enabled us to reduce the height of the column to 880 mm. The electron optical column was constructed and the beam edge resolution was measured. The measured values agree well with the calculated ones, which confirms that the constructed column has the performance expected of the EB-X2 electron optical system.
Stochastic Coulomb interactions in ion projection lithography systems with aberration-broadened crossover
Authors: Kruit P. , Barth J. E. , Lammer G. , Chalupka A. , Vonach H. , Löschner H. , Stengl G.
Published: July 2002

The allowable current in ion beam projection lithography is limited by stochastic Coulomb interactions. Theories for the dependence of these interactions on the parameters of the system, i.e., length, beam energy, print size, crossover diameter, etc. are thus important to guide the design of future machines. All existing theories on blur from stochastic Coulomb interaction assume a homogeneous current distribution in the crossover, where a large part of the blur is produced. However, in actual lithography machines, the crossover may be substantially broadened by the spherical aberration of the ion lenses, thus giving a very inhomogeneous current distribution in the crossover. In most analytical theories, the stochastic blur is independent of the radius of the homogeneously field crossover rc for very small crossovers, and relates to rc as (1/rc)1/2 or (1/rc)1/3 for larger ones. If aberration broadening could do the same, the effect of broadening the crossover from rc=1.5 to 50 μm would decrease the blur by a factor as much as 6, without the negative effect of increasing the curvature-of-field blur. We find physical arguments that such a large factor is impossible. Monte Carlo simulations first of all show that the blur reduction is larger near the edges of the image field than in the center, near the optical axis. For the simulated model system, the reduction on axis can be increased to a factor 2 at very large aberration coefficients.
Fabrication of high-temperature superconductor Josephson junctions by focused ion beam milling
Authors: Chen C.-H. , Trajanovic Z. , Dong Z. W. , Lobb C. J. , Venkatesan T. , Edinger K. , Orloff J. , Melngailis J.
Published: July 2002

We have fabricated high-critical-temperature Josephson junctions using a focused ion beam (FIB) milling to define the gap, in a-axis oriented YBa2Cu3O7 (YBCO) films. A good quality normal metal/YBCO interface is obtained by in situ Au deposition. The effect of FIB milling has been studied with different milling conditions and the resulting devices exhibit different I–V characteristics, i.e., flux flow or superconductor/normal/superconductor Josephson junction behavior. The junctions exhibit Shapiro steps in their I–V characteristics under microwave irradiation. The critical current and normal resistance product (IcRn) of the order of 1 mV has been obtained. We also show that there is a voltage modulation in the superconducting quantum interference devices as a function of an applied magnetic flux up to 80 K.
Algorithm for shifter placement with flexible order prioritizing
Authors: Haruki Tamae , Tomita Junji , Asai Satoru , Hanyu Isamu
Published: July 2002

Alternating phase shifting masks have been investigated as a method for forming the devices of 0.18 μm or less. To design these mask patterns, the phase difference between adjacent apertures should be 180°. However, it is theoretically impossible to accomplish this without phase conflicts. Therefore, design modifications at each conflicting portion is necessary after the shifter placement. On the basis of our investigations, modifying the design layout can be facilitated by reflecting the designers’ various demands in the shifter layout that is designed by the automated computer-aided design (CAD). We formulated an evaluation function by taking the priorities for designers’ demands into account and developed a model of the design layout and a resolution method implemented by a genetic algorithm. Then, a shifter placement CAD was made available on the layout editor. We confirmed that the various demands of designer are satisfied and that the computational performance is satisfactory for practical use.
Viability of conventional KrF imaging for 150 nm lithography
Authors: Azuma T. , Matsunaga K. , Kawamura D. , Mimotogi S. , Onishi Y.
Published: July 2002

Viability of conventional KrF imaging featuring a numerical aperture of 0.6 for 150 nm lithography is investigated by applying a novel process to reduce resist thickness down to around 100 nm. Both simulation data of aerial image contrast and resist development are applied to understand a degradation model of clear process window predicted by the aerial image contrast calculations. Comparing simulation results of the process windows’ dependencies on the resist thickness, which are derived from combinations of aerial image contrast and resist development calculations, experimental results respecting the process windows’ dependencies on the resist thickness are then discussed to elucidate how the aerial image contrast could be degraded. It is found that the minimum requirements of the process windows of 150 nm equal lines and spaces for the early stage of 1 Gbit dynamic random access memory development could narrowly be guaranteed in the case of the thickness range of less than 300 nm, and also that a great advance in the process window would be obtained when using an unconventional imaging system with 2/3 annular aperture. Further improvement of the degraded resist profiles is demonstrated in order to obtain a more stable pattern fabrication process.
X-ray lithography for ⩽100 nm ground rules in complex patterns
Authors: Hector Scott , Pol Victor , Krasnoperova Azalia , Maldonado Juan , Flamholz Alex , Heald Dave , Stahlhammer Carl , Galburt Dan , Amodeo Ralph , Donohue Tom , Wind Shalom , Buchigniano James , Viswanathan Raman , Khan Mumit , Bollepalli Srinivas , Cerrina Franco
Published: July 2002

Complex patterns with 75–125 nm feature sizes exposed with x-ray lithography are shown. Lithographic results for 75–125 nm lines with varying pitch are compared to simulations of image formation and resist dissolution, showing good qualitative agreement. Exposure dose latitude, nested-to-isolated print bias, image shortening, linewidth change with gap, and linearity of printed linewidth versus mask linewidth are quantified for 11–22.5 μm gaps. Critical dimension control error budgets for resist linewidth uniformity are determined for logic patterns at 75 and 100 nm ground rules. Image shortening is quantified for 75–125 nm ground rule static random access memory-like patterns, indicating hammerheads added to line ends reduce shortening to acceptable levels for ⩾100 nm ground rules at ⩽17.5 μm gaps. With tight gap control and tight mask linewidth control, 100 nm ground rule complex patterns can be printed with good latitude using x-ray lithography.
Theoretical discussion of diffusion effects in negative chemically amplified resists based on contrast curve simulation
Authors: Patsis G. P. , Meneghini G. , Glezos N. , Argitis P.
Published: July 2002

Gel formation theory is discussed in the case of chemically amplified resists (CARs) and a specific epoxy-based resist is used in order to model the results. It is found that existing gel formation models may be classified in four classes and there are two important parameters (inhibitor activity and maximum number of available crosslinkable sites) which must be specially interpreted in order to account for chemical amplification and diffusion mechanisms in CARs. It is also proved that a Charlesby–Pinner representation of the gel-dose relationship reveals qualitative characteristics of the process and composition changes.
Quarter-micron chemically amplified reaction image determination using arrested development
Authors: Rhyner Steven J. , Taylor James W.
Published: July 2002

An experimental technique is described to determine the reaction image in the negative-tone, chemically amplified resist, Shipley SAL 605, for a specific set of exposure and thermal processing conditions. Isolated 0.25-μm line formation at varying arrested development times is used in this study to assign an “effective” dose to locations within the resist through bulk dissolution rate data. This method was validated under different development conditions resulting in calculated and experimental line width agreement with an average deviation of 27 nm, and sidewall angle within 4° for developer puddle times between 20 and 113 s. End-on development provides unique access to determine chemically amplified reaction processing effects by diminishing the role of development. A comparison between the arrested development and end-on developed cross-sections indicates a strong development effect contributing to the sidewall angle at various puddle times.
Protective film by magnetic plasma polymerization on a Y–Ba–Cu–O superconductor
Authors: Xinyu Jin , Yu Zhang , Rui Wang , Kangsheng Chen , Suzhen Liang
Published: July 2002

A new method of deposition of an organosilicon thin film by magnetic-controlling plasma polymerization has been successfully used to protect a YBa2Cu3O7−δ (YBCO) superconductor from corrosion. The organosilicon (hexamethyldisilane-HMDS) protective film obtained is homogeneous, compact, pinhole free, and highly crosslinked. The deposition rate of the polymer film increases rapidly first and then decreases, as radio frequency input power and HMDS monomer pressure increase, respectively. The deposition rate of a plasma polymer film with magnetic controlling is 20 times higher than that without magnetic controlling. The YBCO superconductor covered with an organosilicon film by magnetic-controlling plasma polymerization has been protected from corrosion in water over 48 h.
Semiconductor on glass photocathodes for high throughput maskless electron beam lithography
Authors: Baum A. W. , Schneider J. E. , Pease R. F. W. , McCord M. A. , Spicer W. E. , Costello K. A. , Aebi V. W.
Published: July 2002

Previous results obtained from negative electron affinity (NEA) photocathodes have shown high brightness (1×108 A/cm2sr at 3 kV), energy spreads as low as 50 meV at room temperature, uniform sensitivity to red and infrared light over cm2 areas, picosecond-scale switching, and low emission noise. These properties make possible a number of new electron beam tools, including a high-throughput multibeam maskless wafer exposure tool. Simulations show that up to 10 μA of current at 50 kV can be delivered to the wafer in such a system with a total spot diameter of 70 nm. The main obstacle to the use of NEA photocathodes in lithography instruments is the issue of cathode stability and lifetime. An ultrahigh system vacuum was built to activate and evaluate NEA photocathodes in a demountable system that includes areas with poorer vacuum. In this system a low quantum efficiency photocathode (<0.1%) was maintained at constant emission up to 190 nA with no discernible decay. A higher-efficiency cathode provided a brightness estimated at 2.2×107 A/cm2sr at 5 kV. Lifetime measurements on this cathode showed no measurable effect from resist exposure, and stable emission of 375 nA for 15 h, followed by a steady decay of ∼1.5%/h with no re-cesiation. Higher current results (3.75–1.3 μA) show a decay rate of ∼6%/h without re-cesiation. The use of cesium in a feedback loop was shown as an effective way to stabilize emission. Furthermore, the decay is limited to an area 2.6 mm in diameter, as the rest of the cathode is shielded by nonevaporable getter material. This result indicates that the source lifetime can be extended hundreds of times by simply moving the cathode to expose a fresh area. A moveable NEA photocathode in combination with a cesium source in a feedback loop promises to be a highly reliable, long-lifetime electron source.
Spherical aberration corrector using space charge
Authors: Chao L. C. , Orloff J. , Wang Li
Published: July 2002

We have investigated the use of space charge for the correction of spherical aberration in focused ion beam systems. A negative space charge cloud can be formed to reduce the spherical aberration of a lens for ions or for electrons, depending on the details of the space charge distribution. Spherical aberration is important in focused ion beam applications where large aperture angles are needed to obtain high beam currents used for milling or deposition, because it results in large tails on the current density distribution. A space charge distribution (cloud) can be produced with a small electron gun inside an electrostatic lens that can reduce this problem. We report on the properties of one such design.
Fabrication and transport study of finite lateral superlattices
Authors: Hannan M. , Grundbacher R. , Fay P. , Adesida I. , Giannetta R. W. , Wagner C. J. , Melloch M. R.
Published: July 2002

Transport measurements are reported for a two-dimensional electron gas subject to a finite lateral superlattice potential. Devices are fabricated in high mobility GaAs/AlGaAs heterostructures with modulation periods in the range of 2000–3000 Å and differing numbers of gates. Conductance plateaus are observed at gate voltages where the thermopower is stationary. These features indicate the possible formation of effective one-dimensional conductance channels through the potential landscape formed by the lateral gates. The plateau conductances are much less than the basic quantum unit (2e2/h).
Application of amorphous silicon subwavelength gratings in polarization switching vertical-cavity surface-emitting lasers
Authors: Chou Stephen Y. , Schablitsky Steven J. , Zhuang Lei
Published: July 2002

Amorphous silicon subwavelength gratings have been fabricated. Their use as quarter-wave plates in polarization switching vertical-cavity surface-emitting lasers with tunable oscillation frequency as high as several terahertz is proposed. The substantial increase in frequency comes from a reduction in the oscillator cavity length due to the small thickness of the grating (only about one-third of the wavelength thick). The frequency tuning is provided by fabricating the wave plate and a partial reflector monolithically on a movable microcantilever.
Inductively coupled plasma etching of (Ba,Sr)TiO3 thin films
Authors: Lee H. M. , Kim D. C. , Jo W. , Kim K. Y.
Published: July 2002

Etching behaviors of (Ba,Sr)TiO3 (BST) thin films were studied by an inductively coupled plasma (ICP). Using Cl2 gas with Ar gas, etch rate of the BST thin films and their selectivity for SiO2 hard masks were systematically investigated over a wide range of gas mixing ratio and ICP power. The films were etched at rates of 400 Å/min using 20% of Cl2 flow and 80% of Ar flow under ambient pressure below 10 mTorr and at a reactive ion etch power of 150 W and at an ICP power of 700 W. Chemical analysis by Auger electron spectroscopy showed that postetch residues had Ba- and Sr-rich phases which were not found on the surface of the SiO2 hard mask. It was found that the residues of the BST films can be removed with the addition of SF6 gas in the etchant gas mixture.
New plasma chemistries for dry etching of InGaAlP alloys: BI3 and BBr3
Authors: Hong J. , Cho H. , Maeda T. , Abernathy C. R. , Pearton S. J. , Shul R. J. , Hobson W. S.
Published: July 2002

Inductively coupled plasma etching of InGaP, AlInP and AlGaP in BI3 or BBr3 discharges was investigated as a function of source power, dc chuck bias and plasma composition. InGaP etches at the fastest rates (>6000 Å min−1) in both chemistries, followed by AlGaP. It is found that AlInP provides an excellent etch stop for the other two materials in both mixtures. The InGaP surface morphology improves with increasing BI3 or BBr3 content, and with increasing dc chuck bias. The etched features for this material are highly anisotropic. Etch selectivities for InGaP over SiO2 and SiNx of ⩾8 are obtained in both plasma chemistries, and there is no etch incubation time with either mixture, indicating that both can scavenge the native oxide on InGaP, AlGaP and AlInP.
Kinetics of Si growth by an electron-beam-irradiation technique using a Si2H6 source
Authors: Hirose F. , Sakamoto H.
Published: July 2002

Room-temperature selective Si growth is possible by irradiating an electron beam on a Si surface in a Si2H6 ambient. The growth has an apparent substrate temperature dependence, such that the selective growth of Si is allowed at substrate temperatures only below 330 °C. We have found by the H2 thermal desorption experiments that the Si surface during the growth is covered with higher Si hydrides such as: SiH2, SiH3, and Si2H6 molecules. This indicates that the selective Si growth is caused by the higher Si hydrides. The reaction schemes of the Si growth are discussed in this article.