bluuebunny/crossref_metadata_2025 huggingface dataset:
Quasiperiodic nanostructures in focused ion beam deposited tungsten at high angles of incidence
Authors: Xu Xin , Melngailis John
Published: July 2002

As reported in our previous work, at high (near glancing) angles of incidence of the ion beam, a quasiperiodic, comb-blade-like metal structure can form in focused ion beam induced deposition, most typically in tungsten but also in gold, platinum, or copper depositions. This kind of discontinuity tends to increase the resistance if a metal link needs to be made across a rather deep and near-vertical wall. On the other hand, if controlled, it may find some useful applications in nanofabrication. We investigated this phenomenon by using ‘‘milling-and-deposition’’ on single crystal silicon and examining the correlation between the ‘‘period’’ and various experimental parameters. We found that there is no correlation between the period and step size of beam scanning. The average period depends on the beam incidence angle (relative to the surface normal), and especially on the ion beam energy. The average period is 55, 75, and 105 nm for the Ga+ energy at 10, 20, and 25 keV, respectively, when the beam incidence angle during deposition is around 75°. The thickness of the ‘‘comb blades’’ is about 75±25 nm. The period becomes larger as the beam energy and beam incidence angle increases.
Metal ion deposition from ionized mangetron sputtering discharge
Authors: Rossnagel S. M. , Hopwood J.
Published: July 2002

A technique has been developed for highly efficient postionization of sputtered metal atoms from a magnetron cathode. The process is based on conventional magnetron sputtering with the addition of a high density, inductively coupled rf (RFI) plasma in the region between the sputtering cathode and the sample. Metal atoms sputtered from the cathode due to inert gas ion bombardment transit the rf plasma and can be ionized. The metal ions can then be accelerated to the sample by means of a low voltage dc bias, such that the metal ions arrive at the sample at normal incidence and at a specified energy. The ionization fraction, measured with a gridded mass-sensitive energy analyzer is low at 5 mTorr and can reach 85% at 30 mTorr. Optical emission measurements show scaling of the relative ionization to higher discharge powers. The addition of large fluxes of metal atoms tends to cool the Ar RFI plasma, although this effect depends on the chamber pressure and probably the pressure response of the electron temperature. The technique has been scaled to 300 mm cathodes and 200 mm wafers and demonstrated with Cu, AlCu, and Ti/TiN. Deposition rates are equal to or in some cases larger than conventional magnetron sputtering. A primary application of this technique is lining and filling semiconductor trenches and vias on a manufacturing scale.
Study of surface stoichiometry and luminescence efficiency of near-surface quantum wells treated by hydrogen ions and atomic hydrogen
Authors: Chang Ying-Lan , Widdra Wolf , Yi Sang I. , Merz James , Weinberg W. H. , Hu Evelyn
Published: July 2002

A near-surface quantum well (QW) structure has been used as an effective probe of surface states before and after different hydrogen treatments. By correlating the surface composition with the luminescence efficiency of the near-surface QW, we find that the surface passivation is dominated by the defect density of the interface between the AlGaAs surface barrier and the overlying oxide. A complete recovery or further enhancement of luminescence can be readily achieved by treatments using hydrogen ions. However, atomic hydrogen at low exposures is not capable of modifying that interface, and is not effective in passivation. These results corroborate a passivation mechanism which involves removal of As from the interface between the AlGaAs surface barrier and the overlying oxide, and the reduction of interface state density.
Study of magnetic characteristics of tips for magnetic force microscopy
Authors: Sueoka K. , Sai F. , Parker K. , Arnoldussen T.
Published: July 2002

The magnetic characteristics of magnetic force microscopy (MFM) tips were studied by using several methods with a Lorentz transmission electron microscope a magnetoresistive head, and a thin-film inductive head. The results obtained indicate that high-resolution observation with little disturbance of the sample’s magnetic state can be achieved by using a CoPtCr-coated MFM tip.
Formation of ohmic contacts to n-GaAs using (NH4)2S surface passivation
Authors: Fischer V. , Kim T.-J. , Holloway P. H. , Ristolainen E. , Schoenfeld D.
Published: July 2002

Ohmic contacts between Au and sulfur-passivated n-GaAs have been formed without annealing after deposition of the metal. The GaAs samples doped with either 2×1016 or 3×1018 cm−3 Si were passivated with (NH4)2S in an aqueous solution, then the passivating sulfur was thermally desorbed in a vacuum. Desorption was followed immediately by in situ thermal evaporation of Au with the substrate at room temperature. Ohmic I-V behavior was measured ex situ. C-V measurements on a sample with a native oxide surface barrier layer showed the surface carrier concentration on the higher doped sample increased from 3×1018 to 7×1018 cm−3 after S desorption. Secondary ion mass spectroscopy data showed that S had diffused into the GaAs surface region. Thus S passivation prevented interfacial oxide formation during the exposure to air after the sample was passivated and before the vacuum chamber was pumped to a low pressure. Sulfur apparently diffused into the surface region during flash desorption in vacuum and increased the surface n-doping concentration which led to ohmic contacts without post-annealing of the Au films.
SiO2-induced silicon emitter emission instability
Authors: Bintz W. J. , McGruer N. E.
Published: July 2002

An emission instability attributed to an oxide layer on a silicon emitter tip surface has been characterized. The instability leads to a current runaway which often results in device failure. When device failure does not occur, the instability is a one time event while the device remains in a vacuum environment. The magnitude of the instability increases with increasing oxide thickness and can be effectively eliminated by etching in buffered HF immediately before testing or device packaging.
Field emission from pyramidal cathodes covered in porous silicon
Authors: Wilshaw P. R. , Boswell E. C.
Published: July 2002

Square-based pyramidal emitters formed by wet etching of p-type silicon wafers have been anodized to give a thin surface layer of porous silicon. At the surface of such material are very small fibrils with widths ≤3 nm. Field emission measurements from pyramidal cathodes of plain and anodized silicon show a dramatic improvement, when the porous silicon is present. In this case, average peak emission currents of 25 μA have been obtained with the highest measured being 90 μA, improved uniformity between cathodes was produced and emission began at lower voltages. It was found that plain cathodes too blunt to emit did so when covered in porous silicon. The reasons why such silicon fibrils improve emission are discussed.
CoSi2 microstructures by means of a high current focused ion beam
Authors: Bischoff L. , Teichert J. , Hesse E. , Panknin D. , Skorupa W.
Published: July 2002

The Rossendorf focused ion beam IMSA-100 was constructed and used for writing implantation of cobalt to form CoSi2-submicron structures on silicon by ion beam synthesis. Two types of cobalt containing liquid alloy ion sources were developed with Co–Nd and Co–Ge alloys. The fabrication of CoSi2 structures by stoichiometric implantation of Co+ (E=30–35 keV, Iion=1.3 nA) and Co2+ ions (E=60 keV, Iion=0.6 nA) at doses between 0.3 and 5×1017 cm−2 and a subsequent two step annealing (600 °C, 60 min; 1000 °C, 30 min in N2) is demonstrated. The dose dependence as well as the influence of the substrate temperature between room temperature and 400 °C during ion implantation on the ion beam synthesis process were studied. The quality of the silicide submicron structures was investigated by scanning electron microscopy, energy dispersive x-ray analysis, and electrical measurements. While the room temperature implantation and subsequent annealing generate an inhomogeneous CoSi2 film, 400 °C substrate heating during implantation leads to a continuous film with a resistivity below 20 μΩ cm, comparable with broad beam implantation.
Investigation of porous silicon by scanning tunneling microscopy and atomic force microscopy
Authors: Yu Tao , Laiho R. , Heikkilä L.
Published: July 2002

The size and distribution of surface features of porous silicon layers have been investigated by scanning tunneling and atomic force microscopy. Pores and hillocks down to 1–2 nm size were observed, with their shape and distribution on the sample surface being influenced by crystallographic effects. The local density of electronic states show a strong increase above 2 eV, in agreement with recent theoretical predictions.
Field emission properties of ultrasmall Zr spots on W*
Authors: Fursey G. N. , Glazanov D. V.
Published: July 2002

The aims of the investigation were to obtain small and supersmall Zr/ZrO spots on W surface, estimating the limit emission capabilities of such systems, and to analyze their physical mechanisms, which determine their stability. Ultrasmall Zr spots with radii of ∼100 Å were obtained. For such spots field emission current densities of ∼109 A/cm2 were achieved in stationary regime. The numerical simulation of the emitter heating in the three-dimensional axial-symmetrical model showed good qualitative agreement with the experimental results for both localized and nonlocalized emission.
Field emission properties of self-shielded tungsten sources
Authors: Lo W. K. , Skvarla M. , Lo C. W. , Craighead H. G. , Isaacson M. S.
Published: July 2002

The electron emission properties of self-shield W tips were studied by field emission microscopy and spectroscopy. Self-shielded tips were formed by focused ion beam milling an annular depression on the apex of an electrochemically etched W〈111〉 tip. The resultant tip structure consists of a flat bottomed crater (the outer rim of which forms the shielding electrode) with a central protrusion (the emitter). In situ processing consisted of moderate thermal flashing and partial buildup. Significantly greater angular emission current densities were measured, as compared to both unshielded W〈111〉 built-up tips and standard W〈310〉 tips. Energy analysis of the emitted electrons showed no deviations from normal W〈111〉 emission. Self-shielding may offer a generally applicable method for increasing the brightness of field emission sources in a variety of electron optical instruments.
Heating and failure of niobium tip cathodes due to a high-density pulsed field electron emission currenta)
Authors: Shkuratov S. I. , Barengolts S. A. , Litvinov E. A.
Published: July 2002

This article presents the investigative results of pulsed threshold current densities of niobium tip cathodes at temperatures ranging from 4.2 to 300 K. It has been shown that the superconducting-to-normal phase state transition of the cathode has no effect on pulsed threshold current densities. Estimations have been made for the factors limiting the current from a superconducting emitter. The experiments have shown that the cooling of the cathode from 300 to 4.2 K changes the dynamics of cathode heating considerably and leads to a steady increase in the threshold current densities with the delay time range of 10−9–10−6 s. Numerical analysis of thermal processes in the emitter has shown that the above effects are not due to the difference between the electron and the phonon temperatures (the electron–phonon relaxation time does not exceed 10−9 s), but to the more intense heat transfer processes and the reduction of Joule heating, with the cooling of the cathode. It has been shown that the space charge of emitted electrons produces a considerable effect on the temperature and current density distribution in the tip apex. Investigations have shown that the mechanism of the tip cathode failure depends on the delay time range. The simple relationship for estimation of average pulsed threshold emission current density of the tip cathode for a delay time range of 10−9–10−7 s is presented.
Selective reactive ion etching of silicon nitride over silicon using CHF3 with N2 addition
Authors: Li Y. X. , French P. J. , Wolffenbuttel R. F.
Published: July 2002

In this article the effects of process parameters of CHF3+N2 plasma etching chemistry (rf power 50–70 W, pressure 22.5–52.5 mTorr, and N2 content 0%–95%) and mask materials (photoresist, aluminum, and silicon nitride) on the etching selectivity of silicon nitride over polysilicon are investigated. It was found that the selectivity increased with the N2 content in the range of 0%–85% and then decreased, leading to the maximum selectivity (16) at 7.5 sccm CHF3+42.5 sccm N2 (85% N2) at 60 W and 37.5 mTorr. The selectivity increased linearly with power and decreased with pressure. The higher the Si/N ratio of the nitride, the faster the nitride is etched. No influence of the residual stress level on the etch rate of the nitride was observed. The selectivity with resist masks was found to be higher than with either aluminum or nitride masks. Removal of N atoms is suggested to be one of the major rate-limiting factors in the nitride etching. It is argued that the addition of N2 in CHF3 dilutes the polymer-forming radicals and generates abundant N atoms, which diffuse to the substrate and combine with the N atoms adsorbed there due to etching. Both of these effects enhance nitride etch rate.
Surface topography and composition of InP(100) after various sulfur passivation treatments
Authors: Gao L. J. , Anderson G. W. , Esposto F. , Norton P. R. , Mason B. F. , Lu Z-H. , Graham M. J.
Published: July 2002

InP(100) surfaces were S passivated in S2Cl2, (NH4)2S and sulfide-containing Br2 solutions. After S2Cl2 treatments, observations using atomic force microscopy indicated that the sample surface was rougher than the as-received sample. Some residual oxide was also identified by Auger electron spectroscopy and x-ray photoelectron spectroscopy analysis. Treatment of InP(100) in (NH4)2S and Br2/MeOH solutions containing trace amounts of S2Cl2 and (NH4)2S significantly reduced the surface roughness of the as-received sample. These treated surfaces were also found to be free of oxide and S passivated. These solutions therefore effectively removed the native oxide leaving substrates approaching atomic flatness and subsequently passivated surfaces with sulfur from the solution.
Molecular-beam epitaxy growth and characterization of high quality GaAsSb
Authors: Chen H. C. , Rane A. B. , Zhang D. X. , Murry S. J. , Pei S. S. , Tao Y. K. , Pearah P. J. , Cheng K. Y.
Published: July 2002

We have grown bulk GaAsSb layers lattice matched to InP by molecular-beam epitaxy. From the studies of scanning electron microscopy, x-ray diffraction, and photoluminescence characterizations, these films exhibit mirror-like surface morphology and good crystallographic quality, and show promising optical characteristic. The 300 K and 77 K photoluminescence spectra showed strong emission intensities. The measured 10 K linewidth was 8.6 meV for films grown at 510 °C with a V/III ratio of 4. The Sb flux is only 3.6% of the As flux, confirming that the Sb incorporation rate limits the alloy composition of this ternary compound. No discrepancy was observed between the photoluminescence peak energies and calculated values, suggesting negligible radiative recombination via deep level traps.
Focused ion beam lithography of multiperiod gratings for a wavelength-division-multiplexed transmitter laser array
Authors: Templeton I. M. , Fallahi M. , Erickson L. E. , Chatenoud F. , Koteles E. S. , Champion H. G. , He J. J. , Barber R.
Published: July 2002

Wavelength-division multiplexing with closely spaced multiple wavelengths is of great interest for high-capacity data transmission. One major and very critical requirement of such a system is the fabrication of a laser array with very small wavelength separations (∼2 nm). In this paper, the design, fabrication, and performance of an integrated eight-channel system is described. Focused ion beam lithography, with the beam deflection sensitivity modified from its calibrated value, is used to write the critical stepped-period distributed-Bragg-reflector gratings required to provide the tightly controlled multiple laser frequencies. The outputs of the lasers are combined via curved waveguides into a single optical output.
Cross-linked polymers for nanofabrication of high-resolution zone plates in nickel and germanium
Authors: Schneider G. , Schliebe T. , Aschoff H.
Published: July 2002

A high resolution cross-linked PMMA resist has been synthesized and optimized for the generation of zone plate patterns down to 19 nm linewidth with e-beam lithography. This resist shows an increased resolution compared to PMMA for generating periodic structures with a line to space ratio of 1:1. Furthermore, we developed a cross-linked copolymer based on styrene and divinylbenzene, which is used in a new trilevel reactive ion etching (RIE) process. In this process a resist pattern of low aspect ratio can be transferred into a copolymer galvanoform with high aspect ratios for the electrodeposition of nickel. The copolymer has also been used as a highly selective etching mask for zone plate pattern transfer into germanium by RIE.
Recent insights into the physical modeling of the spreading resistance point contact
Authors: Clarysse T. , De Wolf P. , Bender H. , Vandervorst W.
Published: July 2002

The generation of accurate electrically active dopant profiles from raw spreading resistance probe (SRP) data requires a realistic physical description of the high-pressure point contact used. Comparisons between SRP and secondary ion mass spectrometry for junction isolated structures have previously indicated a need to introduce, into the one-dimensional Poisson calculations, rather high permittivity and band gap narrowing values close to the contact. To clarify the situation, a systematic survey of the literature has been made regarding the mechanical and electrical aspects of pressure contacts, including finite element calculations of the internal stress distributions and the characteristics of the high-pressure phases of silicon. Furthermore correlation has been sought with current–voltage curves of the SRP point contact, nano-SRP low weight measurements, and atomic force microscopy and transmission electron microscopy analysis of SRP probe imprints. The emerging physical contact model is one dominated under the high-pressure contact by a series of 20–50-nm-deep plastically deformed metallic β-tin Ohmic microcontacts embedded in an elastically deformed narrow band gap and high permittivity region several micrometers deep. On junction isolated structures the higher permittivity results in an enhanced reverse carrier spilling effect causing an apparent on-bevel junction shift larger than predicted by zero-field simulations.
Secondary electrons imaging of metal–semiconductor field-effect transistor operation
Authors: Mil’shtein S. , Kharas D. , Lee C. , Ersland P.
Published: July 2002

Quantitative measurements of an electrical field and impurity profiles in metal–semiconductor field-effect transistor (MESFET) are obtained by using the scanning electron microscopy–dark voltage contrast (SEM–DVC) technique. The measurements require the taking of an image of a MESFET with all electrodes grounded and an image of the same transistor under dc bias, the subtraction of one image from the other, and the calibration of the contrast in accordance with the voltages at the drain and gate electrodes. Digital image processing allows us to measure the field profile along the channel of a transistor and to reconstruct the doping profile. Two types of GaAs MESFET with recessed gates were measured: one with a 1-μm-long gate and another with a 0.5-μm-long gate. In the field-effect transistor (FET) with the longer gate, we observed that failure to pinch-off is related to doping irregularities in the channel. The submicron MESFET was used to study the dynamic behavior of the field-effect transistor. While changing the gate voltage, the response of the MESFET was videotaped, in an effort to observe the appearance of hot electron areas in the channel. The new quantitative SEM–DVC technique was established in studies of Zener diodes, photodetectors, solar cells, and FETs. The dynamic behavior of these devices was also videotaped.
Large-area achromatic interferometric lithography for 100 nm period gratings and grids
Authors: Savas T. A. , Schattenburg M. L. , Carter J. M. , Smith Henry I.
Published: July 2002

Achromatic interferometric lithography is the preferred approach for producing large-area, spatially coherent 100 nm period gratings and grids. We report on improvements to processes which have enabled exposure areas of ≊10 cm2. In addition, we report on the fabrication of 100 nm period free-standing gold gratings.
Fabrication of metal–oxide–semiconductor devices with extreme ultraviolet lithography
Authors: Nguyen K. B. , Cardinale G. F. , Tichenor D. A. , Kubiak G. D. , Berger K. , Ray-Chaudhuri A. K. , Perras Y. , Haney S. J. , Nissen R. , Krenz K. , Stulen R. H. , Fujioka H. , Hu C. , Bokor J. , Tennant D. M. , Fetter L. A.
Published: July 2002

This article reports results from the successful fabrication of metal–oxide–semiconductor (MOS) devices with extreme ultraviolet lithography. n-type MOS transistors with gate lengths of 0.1 μm were fabricated and demonstrated good device characteristics. The alignment strategy, mask layout, mask fabrication, and device characteristics will be reported.
High emittance electron gun for projection lithography
Authors: DeVore W. , Berger S. D.
Published: July 2002

The source requirements for a high-throughput projection electron-beam stepper are radically different than those for more typical focused beam systems. The SCALPEL®, proof-of-concept stepper requires a uniform, 1 mm2 parallel beam at the mask plane with a convergence angle of 0.5 mrad and a beam current on the order of 10 μA. These requirements translate to an axial brightness of ∼1000 A/cm2 sr which is many orders of magnitude less than a typical direct-write electron-beam system. Another characteristic of a radiation source is emittance, the product of beam size, and angular extent. Unlike axial brightness, this property is not conserved throughout the optical column but is reduced by the presence of apertures. The required emittance of the SCALPEL system is ∼700 μm mrad at the mask and wafer plane. For comparison, a typical direct-write system might have an emittance of ∼1 μm mrad at the wafer plane. In principle, the gun emittance requirement can be met with any combination of source size and angular extent. In practice, limitations imposed by spherical aberration in the illumination lenses mean that designs for projection systems need to maximize the source size. In this article we present data from a gun designed to meet the requirements of the SCALPEL® proof-of-concept system. This gun has been built and tested at 100 kV. The tests were carried out on a test stand that examines the beam far-field intensity distribution by means of a yttrium aluminum garnet (YAG) scintillation crystal. Angular intensity uniformity is measured directly by examining the YAG with a calibrated video camera/frame grabber/486PC system. Source size is determined by looking at the penumbral beam rise from the gun aperture edge in the same system. Results to date show the gun producing a virtual source size of >50 μm diameter and a uniform beam of angular extent >12 mrad, which corresponds to an emittance >600 μm mrad. The gun is normally run with temperature-limited emission from the 〈100〉 lanthanum hexaboride cathode, and it achieves a beam current stability of a few percent per hour. Beam currents of 1–50 μA and larger can be set by changing cathode temperature. Because of the low brightness required by the stepper, normal cathode temperature is about 1250 K.
Energy spread in liquid metal ion sources at low currents
Authors: Beckman J. C. , Chang T. H. P. , Wagner A. , Pease R. F. W.
Published: July 2002

In previous work, attempts to lower the energy spread in liquid metal ion sources (LMIS) by resorting to low current operation have rarely been successful. We have found the energy spread of gallium LMIS to be ≊4.5 eV full width at half-maximum for emission currents from 0.45 μA down to 13 nA. Our experimental results suggest that this occurs because emission <0.45 μA is formed by pulses of height 0.45 μA and an appropriate duty cycle. Several observations support this hypothesis: (1) For sources that had a minimum current, below which they could not be made to operate, the minimum current was always 0.45 μA at room temperature, regardless of apex radius or surface roughness. (2) Emission ≤0.45 μA from blunt sources at room temperature always showed pulses of height 0.45 μA, and a clear transition to dc at 0.45 μA. The pulse height and transition current rose with source temperature. (3) Emission ≤0.45 μA from sharp sources always showed pulsing from the lowest currents up to the current at which the amplifier bandwidth of 1 MHz was exceeded. (4) The angular intensity of emission on axis was in constant proportion to emission current up to 0.45 μA, and in declining proportion at higher currents.
Biosensor based on force microscope technology
Authors: Baselt David R. , Lee Gil U , Colton Richard J.
Published: July 2002

We are developing a sensor capable of detecting biological species such as cells, proteins, toxins, and DNA at concentrations as low as 10−18 M. The force amplified biological sensor will take advantage of the high sensitivity of force microscope cantilevers to detect the presence of as little as one superparamagnetic particle bound to a cantilever by a sandwich immunoassay technique. The device, which will ultimately be small enough for hand-held use, will perform an assay in about 10 min. Lock-in detection and use of a reference cantilever will provide a high degree of vibration immunity. An array of ten or more cantilevers will provide greater sensitivity and the capability to detect multiple species simultaneously. The force amplified biological sensor also offers the potential of distinguishing and studying chemical species via its ability to measure binding forces.
Scattering of electromagnetic waves by silicon-nitride tips
Authors: Bouju X. , Dereux A. , Vigneron J. P. , Girard C.
Published: July 2002

Recently, the use of an atomic force microscope silicon-nitride tip as a scanning near-field optical microscope probe to collect the optical near field close to a surface, has been successfully demonstrated. However, several questions about such a setup are still unanswered: the influences of the surface topography and the polarization of light on the imaging process are not clearly understood; the scattering cross sections of the reflected and transmitted light are not accurately estimated. With the aim of clarifying these questions, in this article we propose numerical simulations performed on a two-dimensional model of a SiN tip within the framework of the Green’s function technique. The treatment provides precise calculations of the near and far fields by exploiting an iterative numerical scheme based on the parallel use of the Lippman–Schwinger and Dyson’s equations. A remarkable result demonstrates that a branch of the SiN tip acts as an optical waveguide. Consequently, a significant amount of light is scattered in directions where scanning near-field optical microscope setups using SiN tips do not detect. A modification of the experimental configuration leading to the detection of this signal is suggested.
Surface roughness-induced artifacts in secondary ion mass spectrometry depth profiling and a simple technique to smooth the surface
Authors: Herner S. B. , Gila B. P. , Jones K. S. , Gossmann H.-J. , Poate J. M. , Luftman H. S.
Published: July 2002

We report on secondary ion mass spectrometry (SIMS) depth profile artifacts induced by surface roughness. The formation of a TiSi2 film at 800 °C on a boron doping superlattice (DSL) of Si results in a rough (22.0 nm root mean square) interface between the film and Si DSL. After chemically etching off the TiSi2 film, SIMS information is collected while sputtering through the surface of the Si DSL. The resulting depth profiles are irreproducible due to the initial surface roughness. By chemo-mechanically polishing the Si prior to SIMS analysis, we smooth the surface and the resulting depth profiles are then consistent and easily explained by current diffusion theory.
Field emission characteristics of the scanning tunneling microscope for nanolithography
Authors: Mayer T. M. , Adams D. P. , Marder B. M.
Published: July 2002

We present a systematic study of the performance of scanning tunneling microscope (STM)-based, low energy electron beam lithography, using simulations of field emission from STM tips, emphasizing realistic conditions of tip geometry and operation. We calculate the potentials and electric field for a hemispherical model emitter in an axially symmetric system. Emission current density at the tip is calculated using the Fowler–Nordheim equation, and current density at the sample is obtained by calculating trajectories of emitted electrons. We characterize the beam diameter at the sample as a function of emitter radius, tip–sample bias, emission current, resist thickness, and tip work function. The beam diameter is primarily affected by the tip–sample gap, increasing at larger gaps, characteristic of high bias and large tip curvature. For optimal tip radius the beam diameter increases linearly with bias from approximately 2 nm at 5 V to 25 nm at 50 V. Beam diameter is nearly independent of emission current over the range 0.05–50 nA. Dielectric resist films cause an increase in beam diameter due to increased tip–substrate gap. Beam diameter is very sensitive to tip work function, increasing dramatically for low work function tips. Tips comprised of asperities on flat surfaces produce significantly smaller beams compared to ‘‘standard’’ tips of the same emitter radius. However, for low bias (<15 V) beam diameter becomes insensitive to tip geometry. We compare these simulations to selected experimental results to evaluate the limitations to performance and assess the feasibility of routine sub-10 nm structure fabrication using STM-based low energy electron beam lithography.
Interfacial chemical bonds, reactions, and band alignment in ZnSe/GaAs(001) heterojunctions
Authors: Bratina G. , Ozzello T. , Franciosi A.
Published: July 2002

ZnSe/GaAs(001) interfaces were fabricated through molecular beam epitaxy by predosing the GaAs(001)2×4 surface with ordered monolayers of Se or Zn, prior to ZnSe growth in stoichiometric growth conditions. We performed the predosing at room temperature (RT) and achieved ZnSe epitaxial overgrowth at RT to minimize desorption of the adsorbed species and minimize interdiffusion. In situ synchrotron radiation photoemission studies indicate that Se-predosing results in valence band offsets as low as 0.40±0.05 eV, and that Zn-predosing yields valence band offsets as high as 1.01±0.05 eV.
Electron emission observations from as-grown and vacuum-coated chemical vapor deposited diamond
Authors: Lamouri A. , Wang Yaxin , Mearini G. T. , Krainsky I. L. , Dayton J. A. , Mueller W.
Published: July 2002

Field emission has been observed from chemical vapor deposited diamond grown on Mo and Si substrates. Emission was observed at fields as low as 20 kV/cm. The samples were tested in the as-grown form, and after coating with thin films of Au, CsI, and Ni. The emission current was typically maximum at the onset of the applied field, but was unstable, and decreased rapidly with time from the as-grown films. Thin Au layers, ∼15 nm thick, vacuum deposited onto the diamond samples significantly improved the stability of the emission current at values approximately equal to those from uncoated samples at the onset of the applied field. Thin layers of CsI, ∼5 nm thick, were also observed to improve the stability of the emission current but at values less than those from the uncoated samples at the onset of the applied field. While Au and CsI improved the stability of the emission, Ni was observed to have no effect.
Field emission measurements with μm resolution on chemical-vapor-deposited polycrystalline diamond films
Authors: Pupeter N. , Göhl A. , Habermann T. , Mahner E. , Müller G. , Piel H. , Niedermann Ph. , Hänni W.
Published: July 2002

The distribution of field emitting sites on polycrystalline diamond films at electrical surface fields has been investigated between 2.5 and 150 MV/m by means of a field emission scanning microscope with μm resolution. For the first time field emission scans were performed on broad-area (≊cm2) diamond cathodes with in situ scanning electron microscope analysis of the localized sites. The 2–3-μm-thick diamond films were chemical-vapor deposited on Mo substrates by the hot-filament technique. Undoped and p-type boron-doped films with low content of sp2-bonded carbons were studied. The highest emitter density of ∼2000/cm2 at 100 MV/m was detected on undoped diamond surfaces. A preliminary study of localized emitters indicated both sporadic particles of foreign materials at the emitting sites as well as intrinsic emission from diamond. In addition, the Fowler–Nordheim parameters β and S, the elemental composition, and the current stability of localized emitters were measured.
Combined scanning force, lateral force, and scanning surface potential microscopy on phase-separated Langmuir–Blodgett films
Authors: Jacobi S. , Chi L. F. , Fuchs H.
Published: July 2002

Phase-separated Langmuir–Blodgett films composed of one- and two-component amphiphiles are studied by scanning probe microscopy. Information obtained from various methods, such as scanning force microscopy, lateral force microscopy, and scanning surface potential microscopy, allow one to understand the nucleation, the initial growth of the condensed phase, and the miscibility of differing components in such quasi 2D systems.
Increasing the value of atomic force microscopy process metrology using a high-accuracy scanner, tip characterization, and morphological image analysis
Authors: Schneir J. , Villarrubia J. S. , McWaid T. H. , Tsai V. W. , Dixson R.
Published: July 2002

Atomic force microscopes are being used increasingly for process metrology. As a case study, the measurement by atomic force microscope of a soda lime glass optical disk patterned using optical lithography and reactive plasma etching is examined. The atomic force microscope used for this measurement has a highly accurate scanner system. The X, Y, and Z axes are calibrated using laser interferometry. To determine the shape of the tip used a commercially available tip calibration artifact was imaged both before and after the measurement. The image was corrected for the tip shape using mathematical morphology. The value of the atomic force microscope measurement is defined to be the impacts of the metrology on the product or process. It is shown that the value of atomic force microscopy process metrology on an optical disk is increased by using an accurate scanner, tip characterization, and morphological image analysis; however, the cost per measurement is increased as well. In general, the characteristics of the metrology required depends on the specific manufacturing process being supported.
Thermal stability and degradation mechanism of WSiN/InGaP Schottky diodes
Authors: Shiojima Kenji , Nishimura Kazumi , Hyuga Fumiaki
Published: July 2002

This article shows that the thermal stability of an InGaP Schottky contact can be improved by the refractory metal WSiN. Both the electrical characteristics and interfacial reactions were estimated by the I–V (current–voltage method), scanning electron microscopy, atomic force microscopy, and Auger electron spectroscopy. The WSiN/InGaP shows excellent I–V characteristics, and the Schottky barrier height is 0.85 eV after annealing at 400 °C. Over 500 °C, an interfacial reaction occurs and the I–V characteristic becomes leaky. We present an interfacial reaction model that shows In atoms condense and an eutectic alloy with W is formed.
Scanning force microscopy with two optical levers for detection of deformations of the cantilever
Authors: Kawakatsu Hideki , Saito Takashi
Published: July 2002

A scanning force microscope equipped with two optical levers was implemented to detect the deformations of the cantilever with multidegree of freedom. By measuring the deflection and torsion at two different points on the cantilever, enough information was obtained to distinguish bending from buckling and thus detect the relative displacement of the tip end point to the base of the cantilever in the x, y, and z directions. Movement of the tip end point when scanning mica in the repulsive mode was monitored and plotted at regular time intervals. The plot revealed stick points reflecting the lattice structure as well as the trajectory of the tip. The sample was rotated with 30° increments to verify the operation of the proposed detection system.
Strain-imaging observation of a Pb(Zr,Ti)O3 thin film
Authors: Takata Keiji
Published: July 2002

In this article I describe strain-imaging observation of a lead–zirconate–titanate film using a tunneling acoustic microscope. Strain Imaging is based on microscopically detecting fine strains generated in samples by any modulation. In piezoelectric films, the piezoelectric properties are measured with high resolution by detecting strains generated by the tip voltage. The strains are detected either as a surface displacement of the sample by the feedback loop, which keeps the tip-to-sample spacing constant, or as a vibration generated by an alternate current tip voltage by means of the acoustic transducer in the tunneling acoustic microscope. Microscopic fluctuations of properties and flexible domain structures were observed in a 70-nm-thick Pb(Zr0.5Ti0.5)O3 film grown by reactive evaporation.
Shallow ripples with giant wavelengths observed by atomic force microscopy: Real effects and the report of a new artifact
Authors: Dai Zhenxi , Yoo Minsun , de Lozanne Alex
Published: July 2002

The (210) surface of ammonium perchlorate has been studied with an atomic force microscope. Unexpected surface ripples with shallow amplitudes (typically less than 3 nm) and giant wavelengths (typically between 0.5 and 1.3 μm) have been discovered. The dominant type shows a wave vector along the [001] direction, and a second type forms a pattern in which two wave vectors make an angle of ∼60° with each other. The amplitude and wavelength of the ripples are clearly correlated. Their size depends on the local surface structure, but their direction is usually keyed to the main crystalline directions. Unfortunately we have also discovered a new artifact that can produce similar images. We discuss the evidence we have gathered thus far to support the existence of the ripples in addition to that of the artifact.
Surface decontamination of patterned GaAs substrates for molecular beam epitaxy regrowth using a hydrogen radical source
Authors: Burke T. M. , Quierin M. A. , Grimshaw M. P. , Ritchie D. A. , Pepper M. , Burroughes J. H.
Published: July 2002

To investigate the efficiency of hydrogen radical surface cleaning of patterned GaAs substrates, resonant tunneling devices have been fabricated in which the regrowth interface lies between the collector and the double barrier structure. Secondary-ion-mass spectroscopy data collected at the patterned substrate/regrown layer interface show a significant reduction of contaminant species after radical cleaning at ∼450 °C for 2 h. The current–voltage characteristics of the resonant tunneling device further indicate a significant improvement in the quality of the regrowth interface in comparison to that achieved by standard thermal decontamination.
Dry etch damage in GaAs metal-semiconductor field-effect transistors exposed to inductively coupled plasma and electron cyclotron resonance Ar plasmas
Authors: Ren F. , Lee J. W. , Abernathy C. R. , Pearton S. J. , Constantine C. , Barratt C. , Shul R. J.
Published: July 2002

The effects of Ar plasma exposure on transconductance, channel sheet resistance, output resistance, and gate contact ideality factor of GaAs metal-semiconductor field-effect transistors (MESFETs) were investigated using two different high-density plasma sources, namely inductively coupled plasma and electron resonance plasma. Ion-induced damage is found to be reduced at moderate source powers (∼200 W) because of the reduction in cathode dc self-bias and hence ion energy, but at higher source powers the increase in ion flux produces significant deterioration of the device performance. Careful attention must be paid to both ion flux and ion energy in order to minimize ion-induced damage. Due to their relatively low channel doping levels, MESFETs are found to be more sensitive to plasma damage than devices with very heavily doped component layers such as heterojunction bipolar transistors.
Novel lithography and signal processing with water vapor ions
Authors: Koops H. W. P. , Dobisz E. , Urban J.
Published: July 2002

A novel model is presented for the operation of field emission sources in air. Under this condition the cathode–anode distance is less than the mean free path for the particles emitted in air. Such conditions are encountered in scanning tunneling microscope lithography in air and in novel integrated microtriode tube devices designed to operate in air. In air, the presence of a high electric field gradient, produced at the tip, will cause the polar water molecules coating the surface to align with the field and move to the high field region. As a result, a Taylor cone of water, like that as it is observed with liquid metal ion sources, will form. The high electric field gradient at the Taylor cone, enhanced by the high dielectric constant, will produce a very finely focused beam of ions. We examine the case of water ion formation. With a positive tip bias, hydronium ions will form at electric fields of 1 V/nm. This is a factor of 4 smaller than that required to produce the field emission with electrons. The electric field distribution and the hydronium ion trajectories from a metal tip with a high permittivity material cone are calculated. The spot size of the ion beam on the substrate was 2.9 nm. A model for lithography, based on water ions, is presented. The model is applied to the design of a microtriode device for signal processing. The three-dimensional fabrication of such a device by e-beam induced chemical vapor deposition is demonstrated.
Plasma reactive ion etching of 193 nm attenuated phase shift mask materials
Authors: Smith B. W. , Fonseca C. , Zavyalova L. , Alam Z. , Bourov A.
Published: July 2002

This article gives details on plasma etch process development for potential attenuated phase shift masking materials for use at 193 nm. Masking films investigated include materials based on aluminum nitride, zirconium nitride, molybdenum–silicon oxide, tantalum–silicon nitride, and tantalum–silicon oxide. A variety of halogenated etch plasmas were investigated, including fluorine-based chemistries (CF4 and SF6) and chlorine-based chemistries (Cl2, CCl4) combined with oxygen, argon, and hydrogen. Thin films of TaN, MoSiO, SixNy, and TaO that allow for sufficient volatility in fluorine plasma and processes using SF6 were chosen for optimization. Fluorides of aluminum and zirconium exhibit very low vapor pressure so Cl2+Ar mixtures were chosen for study. Al and Zr chlorides can be made volatile but ion assistance is generally needed to produce sufficiently high etch rates. Because of this, selectivity to resist is generally poor. Of all the materials evaluated, attenuated phase shift mask films of TaN/Si3N4 etched with SF6 allow the largest etch selectivity to both fused silica and resist.
New complimentary metal–oxide semiconductor technology with self-aligned Schottky source/drain and low-resistance T gates
Authors: Rishton S. A. , Ismail K. , Chu J. O. , Chan K. K. , Lee K. Y.
Published: July 2002

A new experimental complimentary metal–oxide semiconductor (CMOS) technology is presented, fabricated with Schottky source and drain and a T-shaped gate. The process results in a significant reduction in the number of steps required to fabricate CMOS, and no longer relies on implantation of the source and drain. The gate resistance and the source/drain contact resistance are very low compared to conventional designs. Performance of 0.25 and 0.15 μm channel length devices has been measured and the technology is readily scalable to sub-0.1 μm dimensions.
Fabrication of 30 nm gate length electrically variable shallow-junction metal–oxide–semiconductor field-effect transistors using a calixarene resist
Authors: Sakamoto T. , Kawaura H. , Baba T. , Fujita J. , Ochiai Y.
Published: July 2002

We have fabricated electrically variable shallow-junction metal–oxide–semiconductor field-effect transistors (EJ-MOSFETs) with an ultrafine gate for the first time. The gate length was reduced to 32 nm by using electron-beam lithography with a calixarene resist, which has an under 10 nm resolution with a sharp pattern edge. Moreover, normal transistor operation of 32 nm gate-length EJ-MOSFETs was confirmed.
Comparative study of gated single crystal silicon and polysilicon field emitters
Authors: Huq S. E. , Grayer G. H. , Prewett P. D.
Published: July 2002

Both single crystal silicon and polysilicon are attractive emitter materials for displays using cold field emission. Although single crystal silicon has been under investigation for some time, by contrast, interest in polysilicon is more recent. Using state of the art fabrication techniques including high resolution electron beam lithography and plasma dry etch both single crystal silicon and polysilicon have been processed to fabricate sharp and uniform gated emitter arrays. We report in this article a comparative study of material aspects, processing, and emission properties of the two materials.
“Safe” solvent resist process for sub-quarter micron T-gates
Authors: Via D. , Bozada C. , Cerny C. , DeSalvo G. , Dettmer R. , Ebel J. , Gillespie J. , Jenkins T. , Nakano K. , Pettiford C. , Quach T. , Sewell J.
Published: July 2002

With the advent of the “green” revolution, the semiconductor industry must develop alternative processes that utilize environmentally friendly products. As a first step toward this end we have demonstrated an electron beam patterned sub-quarter micron T-gate process using safe resists manufactured by Microlithography Chemical Corp. (MCC). Instead of the more conventional chlorobenzene based poly methyl methacrylate (PMMA) and 2-ethoxyethanol copolymer solutions, new anisole based PMMA and an ethyl lactate based copolymer are used. In addition to replacing the non-environmentally friendly resists, we sought to increase gate yield by improving the shape of the resist profile. Focused ion beam (FIB) cross-sectional analysis of 0.2 μm T-gates fabricated using our conventional process showed metal discontinuity at the stem-to-cap transition. This was attributed to a sharp transition in the resist from the bottom layer of PMMA to the copolymer. With the safe resists we sought to grade the transition between the stem and cap to improve metal continuity. Multiple techniques were used to evaluate and characterize the safe resist process. FIB cross sectioning provided a rapid and less destructive method for resist profile inspection. In addition, metal deposition was examined prior to liftoff to view evaporation buildup. Scanning electron microscopy and atomic force microscopy were used to give comparative measures of gate length. A safe resist process for sub-quarter micron T-gate fabrication is described.