bluuebunny/crossref_metadata_2025 huggingface dataset:
Emerging technology for i
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u processing: Patterning alternatives
Authors: Ehrlich D. J. , Black J. G. , Rothschild M. , Pang S. W.
Published: July 2002

I n situ processing methods would permit fabrication of semiconductor devices by simplified methods and without exposure of surfaces to air, liquids, or a processing atmosphere shared with human operators. The principal alternative patterning methods which would replace current lithography in such schemes are reviewed briefly.
A low-current liquid metal ion source
Authors: Bell A. E. , Rao K. , Schwind G. A. , Swanson L. W.
Published: July 2002

Liquid metal ion sources (LMIS’s) of gallium operating at 300 K and at currents down to 1 nA have been investigated. The mechanism of operation of the LMIS at low currents is believed to be that of the usual Taylor cone mode. Values of the full width at half-maximum of the energy spread, in the very low current range, 3 nA–1 μA, at 300 K did not decline below 4.5 eV as the emission current was reduced. Angular intensity measurements were also obtained in the emission current range.
Angular distribution and energy spread measurements of Ga clusters emitted from an isotopically pure liquid metal ion source
Authors: Rao S. , Bell A. E. , Schwind G. A. , Swanson L. W.
Published: July 2002

By using an isotopically pure liquid metal ion source (LMIS) of gallium on a tungsten needle it has proven possible to determine the full width at half-maximum (FWHM) energy spread of Ga clusters up to Ga+4 as a function of both emission current and emission angle. A surprising result was that the FWHM of the dominant Ga+ peak remained constant with emission angle, while that of the cluster ions declined markedly. This parallels the behavior of the current associated with each Ga cluster species—the decline of each cluster ion species with angle is much faster than for either of the two monomeric species, Ga+ or Ga++, indicating a common mechanism for the formation of the latter two species. It is tempting to attribute the rapid falloff with emission angle of the cluster ions amounts and FWHM to a droplet origin for these species. Droplet emission is know to be strongly concentrated in the axial region of the LMIS.
Etching of GaAs for patterning by irradiation with an electron beam and Cl2 molecules
Authors: Akita K. , Taneya M. , Sugimoto Y. , Hidaka H. , Katayama Y.
Published: July 2002

Etching of GaAs for patterning by an electron beam (EB) and Cl2 molecules is described. When a GaAs substrate is exposed to a 10 keV EB and Cl2 molecules, etching of GaAs is observed only in the EB-scanned area. Etch rates are obtained as a function of substrate temperature. Morphologies of the etched surface are rather smooth and the photoluminescence intensity indicates that this etching process introduces much less damage to the sample than some processes using ions.
Nanoelectronics: Fanciful physics or real devices?
Authors: Randall J. N. , Reed M. A. , Frazier G. A.
Published: July 2002

Remarkable advances in microfabrication technology have allowed physicists to probe into the size regime where quantum mechanical effects begin to dominate transport. When 1D conducting wires made from two-dimensional electron gases (2DEGs) approach the same size as the deBroglie wavelength of electrons, electronic transport is determined by transmission through a small number of ‘‘waveguide modes’’ of the 1D channel. Low temperature experiments in this size regime show significant wavefunction interference effects. A number of devices based upon these physical phenomena have been proposed. Quantum localization has also been explored in perpendicular electronic transport through heteroepitaxial structures, the simplest case being one-dimensional resonant tunneling structures that exhibit strong quantum interference up to room temperature. Three-terminal devices that directly modulate this interference have been demonstrated. Ultimate scaling limitations of heterojunction tunneling devices will only be confronted in the limit of three-dimensional confinement, i.e., ‘‘quantum dots.’’ The implementation of these discrete electronic state structures in a quantum IC architecture will be discussed.
Correlation of alkali metal-induced work function changes on semiconductor and metal surfaces
Authors: Heskett D. , Wong T. Maeda , Smith A. J. , Graham W. R. , DiNardo N. J. , Plummer E. W.
Published: July 2002

The Cs/GaAs(110) system has been characterized using the techniques of angle-resolved ultraviolet photoemission spectroscopy and medium energy ion scattering spectroscopy. In agreement with previous studies, the adsorption of Cs on the GaAs(110) surface at room temperature is found to cause a decrease in the work function by ∼3.6 eV. In contrast to analogous measurements on metal surfaces, no minimum is observed in the work function change (Δφ) vs Cs coverage (Θ) up to saturation. Using medium energy ion scattering, the absolute saturation coverage of Cs/GaAs(110) at room temperature has been determined to be (4.0±0.1)×1014 atoms⋅cm−2 which corresponds to the density of metallic Cs. Based upon photoemission measurements, the lack of Fermi-level emission indicates that the interface is nonmetallic at this concentration. The implications of these results are discussed in comparison with alkali metal adsorption on metal surfaces.
A lateral-surface-superlattice structure on GaAs/AlGaAs for far-infrared and magnetocapacitance measurements
Authors: Ismail K. , Antoniadis D. A. , Smith Henry I. , Liu C. T. , Nakamura K. , Tsui D. C.
Published: July 2002

We have built four-probe Van der Pauw structures on GaAs/AlGaAs modulation-doped layers. On top of the 4×4 mm active area we fabricated a 200 nm period Ti/Au Schottky metal grid-gate using x-ray nanolithography, evaporation, and liftoff. Electrons traveling from one contact to the other suffer electron back diffraction at specific gate voltages resulting in transconductance oscillations. Magneto-capacitance measurements indicate two sets of quantum oscillations corresponding to the charge density under and in-between the Schottky metal lines. Far infrared cyclotron resonance measurements show a shift in the resonance peak as a function of gate bias.
Atomic diffusion and surface segregation of Si in δ-doped GaAs grown by gas source molecular beam epitaxy
Authors: Cunningham J. E. , Chiu T. H. , Tell B. , Jan W.
Published: July 2002

We report on results that compare the planar confinement, diffusion, and surface segregation of Si δ-doped in GaAs for growth by gas source molecular-beam epitaxy and conventional molecular-beam epitaxy. For gas source molecular-beam epitaxy growth, Si diffusion versus inverse anneal temperature shows a unique two component Arrhenius form in which activation energies for diffusion differ by the fundamental GaAs band gap energy, 1.5 eV. Capacitance–voltage profiles of as-grown δ-doped Be and Si layers in GaAs produce record full width at half-maximum, 1.9 and 2.4 nm, respectively, for the gas source molecular-beam epitaxy case.
Explanation of Bohm diffusion
Authors: Kaufman Harold R.
Published: July 2002

Bohm diffusion has been found to be approximately valid for many plasmas in strong magnetic fields. Assuming Bohm diffusion describes electron diffusion directly [H. R. Kaufman, AIAA J. 23, 78 (1985)], with an equal ion loss possible from the ambipolar field that is generated [F. F. Chen, Introduction to Plasma Physics (Plenum, New York, 1974), p. 169], an order-of-magnitude analysis can show why such electron diffusion should be expected.
Characterization of GaAs/AlxGa1−xAs selective reactive ion etching in SiCl4/SiF4 plasmas
Authors: Guggina W. H. , Ketterson A. A. , Andideh E. , Hughes J. , Adesida I. , Caracci S. , Kolodzey J.
Published: July 2002

Selective reactive ion etching of GaAs over AlxGa1−xAs using SiF4/SiCl4 gas mixtures is studied. Etch rates of GaAs and AlxGa1−xAs are measured versus pressure, etch gas ratio, and plasma self-bias voltage. A selectivity ratio of 500:1 has been obtained for GaAs over Al0.35Ga0.65As at a gas composition ratio of SiCl4/SiF4=0.25, a pressure of 60 mTorr, and a self-bias voltage of −60 V. The etch stop mechanism is studied using Auger electron spectroscopy. Auger surface scan spectra indicate a high concentration of fluorine at the surface of etched AlGaAs samples suggesting the formation of an AlF3 etch stop layer.1 It is also shown that the AlF3 layer is easily removed with a very short dip in HCl/H2O or NH4OH/H2O. Hall effect measurements at 300 and 77 K are made on etched GaAs/Al0.3Ga0.7As modulation doped heterostructures to determine the effect of low-power etching on two-dimensional electron gas (2-DEG) sheet concentrations and carrier mobility. Slight reduction in both 2-DEG sheet carrier concentration and mobility are observed after the RIE process. This may be an indication of ion-beam induced damage to the AlGaAs/GaAs heterostructure. Finally, the effects of extended etching on the dc and microwave device characteristics of short gate length GaAs/AlGaAs/InGaAs MODFETs are reported.
Reflective systems design study for soft x-ray projection lithography
Authors: Jewell Tanya E. , Rodgers J. Michael , Thompson Kevin P.
Published: July 2002

We have investigated several all-reflective designs which have potential application for soft x-ray projection lithography. The resolution goal for all designs was 0.1 μm or better. Different design aspects including usable field size, distortion, obscuration, number of mirrors, surface shape (spherical versus aspheric), and system packaging were explored. Trade-off studies were made between three types of systems: strip field scanning systems, and large field nonscanning systems with both curved and flat mask. Several candidate unobscured designs with 0.1 μm resolution are presented.
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u tip exchange mechanism for the Demuth-type scanning tunneling microscope
Authors: Yokoyama Kazuo , Hashizume T. , Tanaka H. , Sumita I. , Takao M. , Sakurai T.
Published: July 2002

The probing tip plays a most important role on the performance and resolution of the scanning tunneling microscope (STM). If damaged, the tip must be replaced, idealy without breaking the ultrahigh vacuum conditions of the STM. We have developed a new in situ tip-exchange device for the widely-used ‘‘Demuth-type’’ STM without compromising the performance and simplicity of the system. The device can be incorporated into any STM system with an in-situ sample exchange mode.
Detailed measurements and simplified modeling of wafer charging in different barrel reactor configurations
Authors: Namura Takashi , Uchida Hirofumi , Todokoro Yoshihiro , Inoue Morio
Published: July 2002

The detailed profiles of the wafer charging in different barrel reactor configurations have been obtained by using the electrically erasable–programmable read-only memory devices. Charging profile in a parallel electrode system depends strongly on the wafer orientation with respect to the rf electric field, while minor changes are observed by the use of floating Al etch tunnel and by the reduction of the wafer-to-wafer separation. On the other hand, no wafer charging is detected in a co-axial electrode system. A simplified equivalent circuit model, which represents the potential in 2-dimensional rf plasma–wafer system, has been proposed. The charging profile derived from the simplified model coincides with the experimental results. This model gives an analytical explanation of the gate charging.
Incorporation/desorption rate variation at heterointerfaces in III–V molecular-beam epitaxy
Authors: Evans K. R. , Stutz C. E. , Taylor E. N. , Ehret J. E.
Published: July 2002

Surface composition is known to influence cation and anion incorporation rates during III–V molecular-beam epitaxy (MBE). [See, for example, Van Hove and Cohen, Appl. Phys. Lett. 47, 726 (1985).] Thus, incorporation rates are expected to vary at heterointerfaces. The details of how incorporation rates vary in time during heterointerface formation are of interest because they completely determine resulting compositional profiles and/or layer thicknesses. In this study desorption mass spectrometry is used to determine the time dependence of incorporation rates during MBE growth of III–V heterostructures, with an emphasis on the heterointerface formation process. Under many conditions incorporation rates are found to vary in a nonsteplike manner, resulting in nonsteplike compositional profiles. Three different heterointerfaces are investigated: AlGaAs on GaAs, GaInAs on GaAs, and GaAsSb on GaAs. At growth temperatures for which significant Ga desorption occurs, AlGaAs on GaAs interfaces are found to be enriched in Al content relative to adjacent AlGaAs. In addition, transients are observed in the Ga desorption rate which suggest the occurrence of an Al–Ga displacement reaction. When Sb desorption is significant, GaAsSb on GaAs interfaces are found to be enriched in Sb content relative to adjacent GaAsSb. And when In desorption is significant, GaInAs on GaAs interfaces are found to be enriched in In content relative to adjacent GaInAs. The latter result is verified by x-ray and photoluminescence measurements on separately grown, narrow, single GaInAs/GaAs quantum wells. Compositional grading for each system investigated is found to occur over a distance of about two to four monolayers. These results are shown to be consistent with a model which assumes simple first order desorption behavior and which incorporates strain-dependent activation energies for desorption.
An elastic cross section model for use with Monte Carlo simulations of low energy electron scattering from high atomic number targets
Authors: Browning R. , Eimori T. , Traut E. P. , Chui B. , Pease R. F. W.
Published: July 2002

The form of the screened Rutherford elastic scattering cross section has been modified to approximate the Mott scattering cross section for low energy electrons interacting with high atomic number targets, both for the total and the differential elastic cross section. A modified form of the total scattering cross section has been found that fits the Mott scattering cross section derived using a partial wave expansion. The fit is from atomic number 6–92 over the energy range 1–100 keV. The differential elastic cross section has been modeled using a screened Rutherford distribution plus an isotropic distribution. The ratio of forward to backscattering found from the Mott cross section was used as a fitting criteria. The screened Rutherford distribution is fitted to the forward scattering half-angle of the Mott distribution and the size of the isotopic distribution is then adjusted to give the correct forward to backscattering ratio. This differential form has been used in a Monte Carlo simulation of the backscattering from Au. Both the total and the differential cross sections are straightforward to implement in a Monte Carlo simulation of electron/target scattering.
Characterization of scanning probe microscope tips for linewidth measurement
Authors: Griffith J. E. , Grigg D. A. , Vasile M. J. , Russell P. E. , Fitzgerald E. A.
Published: July 2002

For accurate linewidth measurement in scanning probe metrology the shape and size of the probe tip must be known. Since the probe can be degraded during a scan, quick in situ characterization is desirable. A technique is described employing an array of known structures that allows tip characterization with the probe microscope itself. This technique can be used to measure either the shape of a probe tip or the flexing caused by attractive forces near a sidewall. The results suggest that the sharpest probes may experience significant bending in the vicinity of a wall.
Electron cyclotron resonance plasma etching using downstream magnetic confinement
Authors: Choquette Kent D. , Wetzel Robert C. , Freund Robert S. , Kopf Rose F.
Published: July 2002

We demonstrate that electron cyclotron resonance plasma etching with a magnetically confined plasma in the region of the sample produces an enhanced etch rate, an anisotropic etch profile, and low self-bias voltage. Results are presented for GaAs etch rates, etch profiles, and macroscopic etch uniformity using a SiCl4 plasma, comparing the effects of a confining magnetic field and a diverging magnetic field in the reactor. The etch rates and saturated ion current density to the sample are found to be correlated. An anisotropic near vertical etch profile with smooth-etched surfaces is obtained with a negative self-bias voltage of typically 5–25 V for electrically floating samples in a magnetically confined plasma. When the magnetic field lines are perpendicular to the sample surface, the measured macroscopic etch uniformity is ±6% across a 5 cm diam wafer.
High quality In0.48Ga0.52P grown by gas source molecular beam epitaxy
Authors: Kuo J. M. , Fitzgerald E. A.
Published: July 2002

We report the growth of high quality In0.48Ga0.52P lattice matched to GaAs substrates by gas source molecular beam epitaxy. A full width at half-maximum (FWHM) of the (004) double crystal x-ray diffraction peak as small as 19 arc sec was measured from a 1.8 μm thick epilayer. Such line width is the narrowest reported thus far for any growth technique. Room temperature cathodoluminescence shows a band gap of ∼1.92 eV and the narrowest measured FWHM is 29 meV. Electron mobilities as high as 3200 and 25 700 cm2/V s have been obtained from Hall measurements at 300 and 77 K, respectively, which are comparable with the highest values ever reported.
Anisotropic and damageless etching of single-crystalline silicon using chlorine trifluoride molecular beam
Authors: Saito Yoji , Hirabaru Masahiro , Yoshida Akira
Published: July 2002

At room temperature, anisotropic etching of both (100) and (111) oriented single-crystalline silicon substrates is successfully achieved, using a thermally excited ClF3 molecular beam. The morphology of the etched surface is better than that using Cl2. The etching rate is more than 50 Å/min, and the ratio of etching rate of vertical direction to that of horizontal direction is more than eight. Process-induced damage in the metal–oxide semiconductor device was not observed from the capacitance–voltage characteristic measurements.
Ultraviolet laser-induced interaction of Cl2 with GaAs(110)
Authors: Haase G. , Liberman V. , Osgood R. M.
Published: July 2002

We have studied the ultraviolet laser-induced interaction of molecular chlorine with a well-defined GaAs(110) surface under ultrahigh vacuum conditions. Without illumination, chlorine was found to adsorb both molecularly and dissociatively at 85 K. Illumination of a molecular chlorine-covered surface at 85 K with 193, 248, and 351 nm radiation led to the desorption of Cl atoms and to the formation of AsCl3. We suggest that the surface reaction, that is responsible for the AsCl3 formation, is initiated by molecular chlorine dissociation. While direct absorption by an individual Cl2 molecule may be the cause for the chlorine dissociation at 351 nm, we propose an intermolecular charge–transfer absorption within the condensed Cl2 overlayer for the cases of 248 and 193 nm. Support for this mechanism comes from the dependence of time-of-flight distributions and AsCl3 coverage measurements on the molecular chlorine surface coverage, on the laser wavelengths and on the use of different substrates.
Effect of friction on atomic force microscopy of ion implanted highly oriented pyrolytic graphite
Authors: Annis B. K. , Pedraza D. F.
Published: July 2002

An atomic force microscope investigation of the surface of highly oriented pyrolytic graphite (HOPG) after implantation with 165 keV C+ ions established the presence of a dendritic ridge structure. Examples were found for which the image contrast of the ridge structure reversed when scanned in the backward direction. This result is demonstrated to be due to variations in the surface friction. The surface of the ridge structure was found to be characterized by a coefficient of friction that was approximately one-half that on the remainder of the surface. Smaller attractive forces between the scanning tip and the surface were also observed on the ridges as well. In favorable cases, it is apparent that consideration of mechanical effects in atomic force microscopy can provide qualitative surface information in addition to the topographical images. A comparison is made with unimplanted HOPG, and some instrumental methods for enhancing or reducing the effect of friction are discussed.
Study of gate oxide breakdown caused by charge buildup during dry etching
Authors: Nojiri Kazuo , Tsunokuni Kazuyuki
Published: July 2002

Charge buildup and its effect on gate oxide breakdown have been studied for several types of etchers. In a barrel asher, the charging polarity during plasma treatment depends on the direction of the Si wafer with respect to electric fields. In a magnetron reactive ion etching and an electron cyclotron resonance (ECR) etcher, gate electrodes are positively charged. In the ECR etcher, the charge buildup depends on the frequency of the radio-frequency generator connected to the wafer stage. The gate oxide breakdown during plasma treatment strongly depends on the charging polarity. A simple model is presented to successfully explain the phenomena with respect to gate oxide breakdown by charge buildup, and it is shown that gate oxide breakdown can be predicted by measuring the ΔVFB of the metal/silicon nitride/silicon dioxide/silicon capacitor and the time dependent dielectric breakdown characteristics of the gate oxide.
Phase-shifting lithography: Maskmaking and its application
Authors: Watanabe Hisashi , Todokoro Yoshihiro
Published: July 2002

The use of phase-shifting masks (PSMs) allows substantial improvement in resolution and depth-of-focus of optical systems. Before the advantages of PSMs can be realized in a production process, several problems of mask technology must be solved. In order to advance PSMs from a development tool to a production tool for very large scale integration (VLSI) devices, the technologies concerning mask fabrication, mask inspection, and mask repair have been investigated. A silicone-based resist has been developed for simplifying the mask fabrication processes. The printability and detectability of shifter defects have been investigated in order to specify the requirements of systems of PSM manufacture and inspection. The developed silicone-based resist has been applied for mask defect repair. These technologies can bring PSMs closer to being a practical production tool for VLSI. To verify the effectiveness of PSMs for device manufacturing, PSMs have been successfully applied to gate definition of a high-speed GaAs field effect transistor, contact hole fabrication, and storage node (cell capacitor) fabrication of a dynamic random access memory device.
Multiwavelength distributed Bragg reflector laser array fabricated using near field holographic printing with an electron-beam generated phase grating mask
Authors: Tennant D. M. , Koch T. L. , Verdiell J-M. , Feder K. , Gnall R. P. , Koren U. , Young M. G. , Miller B. I. , Newkirk M. A. , Tell B.
Published: July 2002

We describe near optimum near field holography grating masks patterned by e-beam lithography and a distributed Bragg reflector (DBR) multiwavelength laser array fabricated using near field printing with this mask. Grating pitches in the array ranged from 242.861 to 243.750 nm in 0.127 nm steps. Data on the pitch precision and pitch adjustment is presented. Use of a conventional UV source rather than laser illumination both greatly simplified the printing process and eliminated coherent artifacts from the printed gratings. Chemically etched InP test gratings are shown to be extremely ‘‘clean’’ in appearance and low in edge roughness. DBR laser arrays designed with 100 GHz frequency separation were processed using the mask described. The measured frequency separation was 99 GHz which could be further adjusted with a tuning section of the four-section laser design. Characterization of a similar grating mask containing 16 wavelengths with similar pitch increments is also described.
Particle–particle interaction effects in image projection lithography systems
Authors: Berger S. D. , Eaglesham D. J. , Farrow R. C. , Freeman R. R. , Kraus J. S. , Liddle J. A.
Published: July 2002

Using commercially available software (Discrete Coulomb Interactions Software from Munro’s Electron Beam Software Ltd.) we have investigated image broadening as a result of stochastic interactions for projection systems. We have derived empirically, design constraints applicable to ion and electron projection systems and used them to analyze system designs suggested in the literature. We conclude that for many of the suggested designs stochastic interactions will prevent useful throughputs from being achieved. Finally, we discuss system design approaches which are necessary for a successful high-throughput, high-resolution image projection lithography system.
Giant variation in Schottky barrier height observed in the Co/Si system
Authors: Sullivan J. P. , Tung R. T. , Eaglesham D. J. , Schrey F. , Graham W. R.
Published: July 2002

In the literature, the Schottky barrier height (SBH) of Co/Si-related interfaces consistently has been found to lie close to 0.65 eV on n-type Si. This apparent insensitivity of the SBH to the phase of the silicide and crystallographic orientation of the substrate had previously been thought to support Fermi-level pinning mechanisms. We have, however, through careful control of molecular-beam epitaxy processing, grown single crystal type B CoSi2/Si(111) layers which exhibit a giant variation in SBH. CoSi2/Si(111) interfaces prepared by room temperature and high temperature processing exhibit n-type SBHs close to 0.7 eV and p-type SBHs close to 0.45 eV, in good agreement with the SBHs of other Co/Si-related interfaces. However, CoSi2/Si(111) interfaces prepared by special layered growth techniques (here labeled as ‘‘X’’ interfaces) exhibit n-type SBHs less than 0.3 eV and p-type SBHs over 0.7 eV—a difference of over 400 meV from the room temperature and high temperature interfaces. Other CoSi2/Si(111) interfaces prepared by different processing conditions also often exhibit low n-type SBHs and elevated p-type SBHs, but over a somewhat smaller range. Plan-view and high-resolution transmission electron microscopy clearly indicated the existence of structural defects or inhomogeneity in the low n-type SBH samples.
Spatial-phase-locked electron-beam lithography: Initial test results
Authors: Ferrera Juan , Wong Vincent V. , Rishton S. , Boegli V. , Anderson E. H. , Kern D. P. , Smith Henry I.
Published: July 2002

Earlier spatial-phase-locked e-beam lithography (SPLEBL) was proposed as a means of eliminating the well-known problem of feature placement precision in scanning electron-beam lithography. In SPLEBL, a grid with long-range spatial-phase coherence is created on a substrate (or on top of its resist coating) and this grid is used to feedback information on beam location to the control system. In initial tests a standard deviation (σ) of 0.3 nm for phase-locking precision in one dimension was demonstrated, which represents the finest field stitching ever obtained with any lithographic method. In two dimensions (2D), σx, σy=0.6, 0.4 nm was obtained. Moiré spatial-phase locking was also demonstrated in 2D. Two strategies for the global-fiducial grid appear feasible: plating base modulation and a thin film of holographically exposed photoresist on thin-film Al above the e-beam resist. Either would permit spatial-phase locking without exposure of resist.
Imaging of uncoated tobacco mosaic virus by scanning tunneling microscopy
Authors: Guckenberger Reinhard , Arce Fernando Terán , Hillebrand Anton , Hartmann Thomas
Published: July 2002

Uncoated tobacco mosaic virus (TMV) can reliably be imaged in humid air (relative humidity above 30%) at relatively high voltages (typically 7 to 10 V) and at very low currents (typically 0.1 to 0.5 pA). Imaging works best with tips that show a small dependence of working distance on tunneling voltage. With such tips, a thickness of the virus of 10 nm and more is measured. When using tips of unsuitable characteristics, heights much smaller than 10 nm and even negative values are found. From these observations, a voltage drop over the TMV on the order of volts can be deduced, which depends on tunneling current and humidity.
Deflection microwave and millimeter-wave amplifiers
Authors: Tang Cha-Mei , Lau Y. Y. , Swyden T. A.
Published: July 2002

A new class of microwave and millimeter-wave amplifiers, called deflectron amplifiers, which are based on the deflection of low voltage electron beams in a microstructure were analyzed. This concept may be applied in two ways: as microelectronic amplifiers or as bunched beam cathodes to power conventional amplifier configurations such as klystrodes and traveling wave tubes. Estimates for gain and efficiency are obtained from a circuit analysis. Particle codes are used to test the viability of the concept. Frequencies of operation are projected up to a few tens of GHz for microelectronic amplifiers and up to ∼80 GHz for power amplifiers.
Metal ion implantation: Conventional versus immersion
Authors: Brown I. G. , Anders A. , Anders S. , Dickinson M. R. , MacGill R. A.
Published: July 2002

Vacuum-arc-produced metal plasma can be used as the ion feedstock material in an ion source for doing conventional metal ion implantation, or as the immersing plasma for doing plasma immersion ion implantation. The basic plasma production method is the same in both cases; it is simple and efficient and can be used with a wide range of metals. Vacuum arc ion sources of different kinds have been developed by the authors and others and their suitability as a metal ion implantation tool has been well established. Metal plasma immersion surface processing is an emerging tool whose characteristics and applications are the subject of present research. There are a number of differences between the two techniques, both in the procedures used and in the modified surfaces created. For example, the condensibility of metal plasma results in thin film formation and subsequent energetic implantation is thus done through the deposited layer; in the usual scenario, this recoil implantation and the intermixing it produces is a feature of metal plasma immersion but not of conventional energetic ion implantation. Metal plasma immersion is more suited (but not limited) to higher doses (≳1017 cm−2) and lower energies (Ei<tens of keV) than the usual ranges of conventional metal ion implantation. These and other differences provide these vacuum-arc-based surface modification tools with a versatility that enhances the overall technological attractiveness of both.
Bright-field analysis of field-emission cones using high-resolution transmission electron microscopy and the effect of structural properties on current stability
Authors: Goodhue W. D. , Nitishin P. M , Harris C. T. , Bozler C. O. , Rathman D. D. , Johnson G. D. , Hollis M. A.
Published: July 2002

High-resolution transmission electron microscopy has been used to analyze 150 nm diameter by 150 nm high polycrystalline molybdenum field-emission cones. The analysis shows that the cones comprise 5 to 10 nm thick grains with tips having gross radii of curvature of about 5 nm and protrusions having radii of curvature of about 1 nm. Such small protrusions may explain why analysis of experimental emission data indicates that the effective emission area of such tips is only 0.1 to 0.5 nm.2 Furthermore, the fact that the structure is composed of small grains indicates that there is a substantial number of molybdenum atoms at grain boundaries and that many configurations of grains and boundaries are possible with minimal free energy. A qualitative model is proposed which links the structural properties to current stabilization and hydrogen passivation effects.
Deep etch x-ray lithography at the advanced light source: First results
Authors: Malek Chantal Khan , Jackson Keith , Brennen Reid A. , Hecht Michael H. , Bonivert William D. , Hruby Jill
Published: July 2002

Deep etch x-ray lithography permits the manufacture of very accurate high-aspect-ratio microstructures, which can be used as master templates for subsequent replication by electroforming and/or molding processes. This allows for mass production of three-dimensional microstructures in a variety of materials. In this article we report on the first results using x rays from the Advanced Light Source (ALS) at the Lawrence Berkeley Laboratory, as well as on the processing and technology developed to produce high-aspect-ratio microstructures. The first masks used were simple stencil masks chemically or laser etched in thick metal sheets. For resist, we used commercial acrylic cast sheets. Microstructures 840 μm thick were fabricated by deep x-ray lithography and used as templates for copper electroforming. A technology for the high contrast masks required to work at these short wavelengths is being developed and a deep etch x-ray lithography facility is under construction at the ALS.
Deposition of Au on a sulfur covered Mo(100) surface: Adsorbate–adsorbate interaction and growth*
Authors: Dunphy J. C. , Chapelier C. , Ogletree D. F. , Salmeron M. B.
Published: July 2002

Gold was deposited on a clean and on a sulfided Mo(001) surface to study the initial stages of growth and the influence of chemisorbed layers. On the clean surface, Au forms a c(2×2) structure at low coverages. At coverages above half of a monolayer more complicated structures are revealed by low energy electron diffraction and scanning tunneling microscopy. On the sulfided surface, Au was found to bind directly to the metal by displacing the S to a higher coverage structure. At sulfur saturation Au forms three-dimensional clusters separated by areas covered by sulfur in the highest coverage structure.
Long-term and thermal stability of hydrogen ion-passivated AlGaAs/GaAs near-surface quantum wells
Authors: Chang Ying-Lan , Yi Sang I. , Shi Song , Hu Evelyn , Weinberg W. H. , Merz James
Published: July 2002

Al0.3Ga0.7As/GaAs quantum well samples, irradiated by (100 eV) hydrogen ions at low exposure, have shown improved luminescence for times greater than two years, when stored at room temperature in atmosphere. In situ temperature programmed desorption (TPD) was used to investigate the desorption of AsH3 from an oxidized AlGaAs surface treated by hydrogen ions. Surface modification determined by TPD and Auger electron spectroscopy measurements was correlated with ex situ photoluminescence measurements to further determine the reasons underlying the long-term room temperature durability of this treatment, as well as the stability of the hydrogen ion passivation at elevated temperatures. Results indicate the importance of the native oxide of the substrate, present during the hydrogenation process, and which may serve as an over-passivation layer. However, the thermal stability study also indicates that this over-passivation layer is not thick enough to prevent the degradation of the underlying substrate at elevated temperatures.
Development of a multitask and multiinstrument sample transfer system
Authors: Thevuthasan S. , Baer D. R. , Englehard M. H. , Liang Y. , Worthington J. N. , Howard T. R. , Munn J. R. , Rounds K. S.
Published: July 2002

A multiinstrument, multitask UHV sample transfer system being developed for integration with a wide range of synthesis and analysis instruments is described. The specimen transfer capability allows a sample to be synthesized, processed, and characterized by several surface science techniques without exposing the sample to air. Although several types of transfer systems now exist, no existing system has the range of operation desired for a user facility which will be equipped with a wide range of vacuum and controlled atmosphere-based techniques. Three different kinds of sample platens, which can be used in ambient, high-temperature, and surface chemistry experiments, have been designed and tested. The temperature range of the specimen can be as high as 2000 K during heating and as low as 150 K during cooling.
Hydrogen bonding arrangements at Si–SiO2 interfaces
Authors: Jing Z. , Lucovsky G. , Whitten J. L.
Published: July 2002

An important issue in semiconductor device operation is the rate at which current or voltage stress creates defects that can eventually degrade device operation. Based on recent results on nitrided gate dielectrics, we have concluded that bonded-H at the Si–SiO2 interface plays a role in the formation of metastable defects that can be activated, and subsequently neutralized, by sequential trapping of injected holes and electrons. In this article, differences in defect behavior for Si–SiO2 interfaces that have been exposed to nitrogen (N-) atoms or N–H groups are discussed. Based on these results, a microscopic model for interfacial defects is proposed.
Investigation of modulation-doped GaAs/AlGaAs single quantum well by photoreflectance
Authors: Tyan S. L. , Lee M. L. , Wang Y. C. , Chou W. Y. , Hwang J. S.
Published: July 2002

The interband transitions, built-in electric field, and energy of the two-dimensional electron gas (2DEG) of the modulation-doped GaAs/AlGaAs single quantum well at different temperatures (100–300 K) have been studied by the modulation spectroscopy of photoreflectance (PR). The built-in electric field was evaluated using the observed Franz–Keldysh oscillations and found to be increasing from 20±1 to 75±3 kV/cm with an increase in temperature from 100 to 300 K. In addition to the allowed quantum transitions, the forbidden transition 12L in the quantum well was also observed. Moreover, the energy level of the 2DEG was determined from the PR spectra and was found to decrease with the increasing temperature. The energy of the 2DEG of the higher doping sample is greater than that of the lower one.
Reduced field emission of niobium and copper cathodes
Authors: Mahner E. , Müller G. , Piel H. , Pupeter N.
Published: July 2002

We have investigated the enhanced field emission of broad-area niobium and copper cathodes by means of an UHV field emission scanning microscope which allows the localization and characterization of individual electron emitting sites down to submicron size. For the first time, ex situ prepared samples of cm2 size stayed field emission free up to 150 MV/m for both high-purity Nb and OFHC copper. Only weak electron emission from a few sites with field enhancement factors of less than 30 was observed at 200 MV/m. This progress results from an advanced preparation technique based on ultrapure water rinsing inside a clean room which reduces any kind of surface contamination. Alternatively, the enhanced field emission from microscopic particles and other surface irregularities on Nb can be much suppressed by in situ UHV annealing at 1400 °C followed by a fast cool down. However, many new strong emitters appear on such surfaces after moderate heating at temperatures around 400 °C. These observations support the crucial role of the surface segregation of interstitial atoms for the enhanced field emission of Nb samples.
Interferometry with low-energy electrons
Authors: Morin Roger , Degiovanni Alain
Published: July 2002

The first experimental results combining an electrostatic electron biprism and a low-energy electron projection microscope are presented. In these experiments, a low-energy electron beam is split into two coherent beams which interfere afterwards. The interference pattern consists in many parallel fringes. The electron energy ranges from a few tens eV up to a few hundred eV.
Growth of very low deep impurity density (N
t<5×1011 cm−3) InxGa1−xP on GaAs by metalorganic chemical vapor deposition
Authors: Huang Z. C. , Yang Bing , Chen H. K. , Chen J. C.
Published: July 2002

InxGa1−xP layers lattice matched and lattice mismatched to GaAs substrates have been grown by metalorganic chemical vapor deposition (MOCVD). Deep level transient spectroscopy, double crystal x-ray diffraction, and current–voltage measurement were employed to characterize InxGa1−xP layers and InxGa1−xP/GaAs heterojunctions. We have observed a shallow electron trap located at EC−60 meV in InxGa1−xP layers with x<0.469, and a deep electron trap at EC−0.85 eV with x≳0.532. However, no deep levels were detected in InxGa1−xP (0.469<x<0.532) layers. The deep levels, if they exist, have a concentration of less than 5×1011 cm−3 which is the lowest deep level concentration reported so far in MOCVD grown InxGa1−xP materials. This is also the first observation in which lattice mismatches ranging from −0.125% to +0.224% (0.469<x <0.532) do not generate deep levels in MOCVD grown InxGa1−xP.
Atomistic modeling of imaging of ionic surfaces with a scanning force microscope
Authors: Shluger Alexander L. , Rohl Andrew L. , Wilson R. M. , Williams R. T.
Published: July 2002

We present a simple theoretical model of the scanning force microscopy experiment using an atomistic simulation technique. The scanning of the perfect (100) surfaces of NaCl and LiF, the Mg2+ impurity ion on the surface of LiF, and the monoatomic step edge on the surface of NaCl were modeled at different constant vertical forces exerted on the tip. The calculations were made using an atomistic treatment of the interaction between a crystalline sample and tip nanoasperity combined with a semiempirical treatment of the mesoscopic van der Waals attraction between tip and surface and the macroscopic parameter of cantilever deflection. Comparing these results with experimental data, we discuss the quality of our model and the different conditions of surface imaging with atomic resolution.
Fabrication of planar quantum magnetic disk structure using electron beam lithography, reactive ion etching, and chemical mechanical polishing
Authors: Krauss Peter R. , Chou Stephen Y.
Published: July 2002

A planar quantum magnetic disk (QMD) with a magnetic storage density of 65 Gbit/in.2, over two orders of magnitude greater than the state-of-the-art magnetic storage density, has been fabricated. The planar QMD structure consists of single-domain nickel (magnetic) nanopillars uniformly embedded in a SiO2 (nonmagnetic) disk. Electron beam lithography was used to define the QMD bit’s size and location, and reactive ion etching was used to form an SiO2 template. Nickel electroplating was used to selectively deposit nickel into the template openings, and chemical mechanical polishing was used to planarize the surface. The resulting QMD consists of ultrahigh density arrays of single-domain magnetic pillars with a 50 nm diameter and 100 nm period uniformly embedded in 200-nm-thick SiO2 and with a surface roughness of 0.5 nm root mean square. Each single-domain structure has a quantized magnetic moment and acts as a single bit to store one bit of binary information. Furthermore, a method for mass production of QMDs, the nanoimprint technique, is discussed.
Single electron and hole quantum dot transistors operating above 110 K
Authors: Leobandung Effendi , Guo Lingjie , Wang Yun , Chou Stephen Y.
Published: July 2002

Both single electron and hole quantum dot transistors in silicon-on-insulator were fabricated and characterized. The quantum dots were formed using electron-beam nanolithography and reactive ion etching. The single electron quantum dot transistors show the oscillation of the drain current as a function of the gate voltage at temperatures up to 170 K and drain biases up to 80 mV. The oscillation is due to electron tunneling through the discrete energy levels inside the quantum dot. The average energy level spacing is ∼60 meV. Data analysis shows that the discrete energy levels are caused by Coulomb interaction as well as quantum size effects. The single hole quantum dot transistors show similar oscillations up to 110 K and drain biases up to 50 mV. The average energy level spacing is ∼36 meV.
Wet silylation and oxygen plasma development of photoresists: A mature and versatile lithographic process for microelectronics and microfabrication
Authors: Gogolides Evangelos , Tzevelekis Dimitrios , Grigoropoulos Spyridon , Tegou Evangelia , Hatzakis Michael
Published: July 2002

A near-surface imaging process using wet silylation and oxygen plasma development is described. New characterization techniques of films spun on wafers are presented for: (a) quantitative Si concentration determination using proton nuclear magnetic resonance spectroscopy (H), and (b) glass transition and/or flow temperature determination (Tg) of the silylated photoresist using thermomechanical analysis. H-line, I-line, and deep ultraviolet lithography (at 248 nm) results are presented, while extension to 193 nm lithography is discussed. Very anisotropic and high aspect ratio pattern transfer to Si, with fluorine-only containing plasmas is demonstrated. Possible applications are discussed.
Instability and reliability of silicon field emission array
Authors: Li Q. , Xu J. F. , Song H. B. , Liu X. F. , Kang W. P.
Published: July 2002

The instability and reliability of silicon field emission cathode are investigated. The total instability is divided into four components which are extracted from the emitting current curve I(t). The appearance of the I(t) curve, the meaning and causes of the four components are described and discussed, respectively. Reliability is defined and a set of failure modes are reported. To make a normalized measurement of reliability, a computerized system is proposed.
Effects of electron-beam parameters on critical-dimension measurements
Authors: Mizuno Fumio , Satoh Osamu
Published: July 2002

One of the important requirements for critical-dimension scanning electron microscopes is to improve the reproducibility of measurement in response to the scaling of features on semiconductor devices. A reproducibility of 3 nm, about 1/100 of the minimum pattern size, will be required for the next generation subquarter-micron devices. It is clear that the sampling pitch, incident angle, and blurring of the electron beam produce measurement errors in the order of a few nm and the precise control of these parameters is necessary, but not sufficient for achieving a reproducibility of 3 nm.
Chemical dry etching mechanisms of GaAs surface by HCl and Cl2
Authors: Senga Takehito , Matsumi Yutaka , Kawasaki Masahiro
Published: July 2002

Dry etching mechanisms of thermal and photochemical reactions with Cl2 and HCl on GaAs(100) Ga-rich c(8×2) surfaces were investigated, using x-ray and ultraviolet photoelectron spectroscopy. At a substrate temperature of −100 °C, the etchant gases are chemisorbed on the GaAs surface. Cl2 deposition on GaAs produces about five times more Cl-containing species than HCl deposition. The GaAs surface is disrupted with Cl2 when the substrate temperature is increased to 250 °C after the saturated deposition of Cl2 at −100 °C. A similar etching procedure with HCl forms an ordered surface of GaAs with As atoms on the top layer. After desorption of the etchant gases, the photoirradiation effect at room temperature was investigated by pulsed laser irradiation with excimer (193 and 248 nm) and YAG (266, 355, and 532 nm) lasers at an intensity of 2–10 mJ/cm2. Only the 193 nm irradiation removes Cl-containing species from the surface. With cw laser irradiation at 488 nm (60 mW/cm2), photochemical reactions take place on the GaAs substrate on which Cl2 has been deposited.
Effect of silicon substrate microroughness on gate oxide quality
Authors: Hegde Rama I. , Chonko Mark A. , Tobin Philip J.
Published: July 2002

The process induced surface microroughness of both the silicon substrate and top surface of 15 nm gate oxide were investigated by atomic force microscopy. Varying degrees of surface microroughness on the Si and on the gate oxide were induced by timed wet silicon etch (750:1 HNO3:HF solution). The Rms roughness of the initial silicon substrate was <0.2 nm, while the value increased to 0.65 nm after extended etch. For short etch times, the initial Si surface roughness was reproduced at the gate oxide surface. The average electrical field strength required to maintain a fixed current density of 1.5×10−5 A/cm2 was found to increase with decrease of the gate oxide surface roughness.